use std::collections::hash_map::DefaultHasher;
use std::collections::{HashMap, HashSet};
use std::future::Future;
use std::hash::{Hash, Hasher};
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};

use anyhow::{Context as AnyhowContext, Error, anyhow, bail};
use bitcoin_hashes::sha1::Hash as Sha1Hash;
use gpui::{App, AppContext, Context, Entity, EventEmitter, Global, Task};
use nostr::event::IntoEventBuilder;
use nostr_connect::prelude::*;
use nostr_sdk::client::SyncSummary;
use nostr_sdk::prelude::*;
use signed_core::{Announcement, RepoAddr, build_state, filters, identifier_from_name, repo_addr};
use signed_nostr::{SignedAuthUrlHandler, UniversalSigner, Update};

use crate::git_store::GitStore;

/// Keyring entry for the user credential.
pub const USER_KEYRING: &str = "Signed Safe Storage";
/// Timeout for NIP-46 signer responses.
pub const NOSTR_CONNECT_TIMEOUT: u64 = 60;

/// Relays connected at startup, before any user-specific relay config is known.
pub const BOOTSTRAP_RELAYS: [&str; 4] = [
    "wss://relay.primal.net",
    "wss://relay.ditto.pub",
    "wss://index.ngit.dev",
    "wss://profiles.nostr1.com",
];

/// Relays used to index the user's NIP-65 relay list.
pub const INDEXER_RELAYS: [&str; 2] = ["wss://indexer.coracle.social", "wss://user.kindpag.es"];

/// How long an identical fetch or sync request is suppressed after it started.
const FETCH_DEDUP_WINDOW: Duration = Duration::from_secs(5 * 60);

#[derive(Debug, Clone)]
pub enum BackendEvent {
    /// User has no signer configured.
    SignerRequired,
    /// The stored identity is NIP-49 encrypted key.
    PassphraseRequired,
    /// The signer changed on login, logout or account switch.
    SignerChanged,
    /// A new event was received from a relay and stored in the database.
    NostrUpdate(Update),
    /// A negentropy sync completed.
    Synced,
    /// A negentropy sync is in flight.
    SyncProgress {
        /// Total events to process.
        total: u64,
        /// Events processed so far.
        current: u64,
    },
    /// An event built locally was signed, broadcast and stored.
    Published(Box<Event>),
    /// An error occurred.
    Error(String),
}

impl BackendEvent {
    pub fn error<T>(error: T) -> Self
    where
        T: Into<String>,
    {
        Self::Error(error.into())
    }
}

/// The global backend entity.
///
/// Owns the nostr client, the signer and the notification pump.
pub struct Backend {
    client: Client,
    signer: UniversalSigner,
    current_user: Option<PublicKey>,
    sync_progress: Option<(u64, u64)>,
    /// True when the stored credential is NIP-49 encrypted.
    passphrase_required: bool,
    /// Fingerprints of recently started fetches and syncs, a relay plus filter set.
    recent_fetches: HashMap<u64, Instant>,
    /// Repositories with a push in flight, mirror or checkout based.
    pushing_repos: Arc<Mutex<HashSet<RepoAddr>>>,
    tasks: Vec<Task<Result<(), Error>>>,
}

struct GlobalBackend(Entity<Backend>);

impl Global for GlobalBackend {}

/// Removes its repository from the in-flight push set when dropped.
///
/// A push task cancelled by its panel closing cannot leave the repository locked.
struct PushGuard {
    repos: Arc<Mutex<HashSet<RepoAddr>>>,
    addr: RepoAddr,
}

impl Drop for PushGuard {
    fn drop(&mut self) {
        if let Ok(mut repos) = self.repos.lock() {
            repos.remove(&self.addr);
        }
    }
}

impl EventEmitter<BackendEvent> for Backend {}

impl Backend {
    /// Retrieve the global backend.
    pub fn global(cx: &App) -> Entity<Self> {
        cx.global::<GlobalBackend>().0.clone()
    }

    pub(crate) fn set_global(entity: Entity<Self>, cx: &mut App) {
        cx.set_global(GlobalBackend(entity));
    }

    pub(crate) fn new(client: Client, signer: UniversalSigner, cx: &mut Context<Self>) -> Self {
        let pump_client = client.clone();

        let pump = cx.spawn(async move |this, cx| {
            let mut notifications = pump_client.notifications();

            while let Some(notification) = notifications.next().await {
                let ClientNotification::Event { event, .. } = notification else {
                    continue;
                };

                let update = Update::from_event(&event);

                if this
                    .update(cx, |_, cx| cx.emit(BackendEvent::NostrUpdate(update)))
                    .is_err()
                {
                    break;
                }
            }

            Ok(())
        });

        let mut this = Self {
            client,
            signer,
            current_user: None,
            sync_progress: None,
            passphrase_required: false,
            recent_fetches: HashMap::new(),
            pushing_repos: Arc::new(Mutex::new(HashSet::new())),
            tasks: vec![pump],
        };

        this.bootstrap(cx);
        this
    }

    /// Track a spawned task, pruning finished tasks first.
    ///
    /// Keeps the store's task list bounded by the number of in-flight tasks.
    fn push_task(&mut self, task: Task<Result<(), Error>>) {
        self.tasks.retain(|task| !task.is_ready());
        self.tasks.push(task);
    }

    /// Bootstrap the client.
    ///
    /// Restore the saved session, if any.
    fn bootstrap(&mut self, cx: &mut Context<Self>) {
        let client = self.client.clone();

        let task = cx.background_spawn(async move {
            for url in BOOTSTRAP_RELAYS {
                client.add_relay(url).await?;
            }
            for url in INDEXER_RELAYS {
                client
                    .add_relay(url)
                    .capabilities(RelayCapabilities::DISCOVERY)
                    .await?;
            }
            client.connect().await;
            Ok::<(), Error>(())
        });

        self.push_task(cx.spawn(async move |this, cx| {
            match task.await {
                Ok(()) => {
                    this.update(cx, |_this, cx| cx.notify())?;
                }
                Err(e) => {
                    this.update(cx, |_this, cx| cx.emit(BackendEvent::error(e.to_string())))?;
                }
            }
            Ok(())
        }));

        self.restore_session(cx);
    }

    /// Restore the saved session from the keyring.
    ///
    /// Emits [`BackendEvent::SignerRequired`] when no credential is stored.
    ///
    /// Emits [`BackendEvent::PassphraseRequired`] for a NIP-49 encrypted identity.
    pub fn restore_session(&mut self, cx: &mut Context<Self>) {
        if cfg!(target_arch = "wasm32") {
            cx.emit(BackendEvent::SignerRequired);
            return;
        }

        let user = cx.read_credentials(USER_KEYRING);

        self.push_task(cx.spawn(async move |this, cx| {
            let content = match user.await {
                Ok(Some((_username, secret))) => String::from_utf8(secret)?,
                _ => {
                    this.update(cx, |_, cx| cx.emit(BackendEvent::SignerRequired))?;
                    return Ok(());
                }
            };

            let result = async {
                if content.starts_with("nsec1") {
                    let keys = Keys::new(SecretKey::parse(&content)?);
                    this.update(cx, |this, cx| this.set_signer(keys, cx))?;
                } else if content.starts_with("bunker://") {
                    let (base, keys) = extract_master_key(&content);
                    let uri = NostrConnectUri::parse(base)?;
                    let mut signer = NostrConnect::new(
                        uri,
                        keys,
                        Duration::from_secs(NOSTR_CONNECT_TIMEOUT),
                        None,
                    )?;
                    signer.auth_url_handler(SignedAuthUrlHandler);
                    this.update(cx, |this, cx| this.set_signer(signer, cx))?;
                } else if content.starts_with("ncryptsec1") {
                    // Encrypted identity.
                    // A passphrase is required to decrypt it before the session can resume.
                    log::warn!("stored identity is ncryptsec-encrypted; waiting for passphrase");
                    this.update(cx, |this, cx| {
                        this.passphrase_required = true;
                        cx.emit(BackendEvent::PassphraseRequired);
                    })?;
                } else {
                    this.update(cx, |_, cx| cx.emit(BackendEvent::SignerRequired))?;
                }

                Ok::<_, Error>(())
            }
            .await;

            if let Err(e) = result {
                this.update(cx, |_, cx| {
                    cx.emit(BackendEvent::error(e.to_string()));
                    cx.emit(BackendEvent::SignerRequired);
                })?;
            }

            Ok(())
        }));
    }

    /// Decrypt the NIP-49 keyring credential with the given passphrase.
    pub fn restore_with_passphrase(
        &mut self,
        password: &str,
        cx: &mut Context<Self>,
    ) -> Task<Result<PublicKey, Error>> {
        let password = password.to_owned();
        let user = cx.read_credentials(USER_KEYRING);

        cx.spawn(async move |this, cx| {
            let content = user
                .await?
                .map(|(_username, secret)| String::from_utf8(secret))
                .transpose()?
                .ok_or_else(|| anyhow!("no stored credential; nothing to unlock"))?;

            if !content.starts_with("ncryptsec1") {
                return Err(anyhow!("stored credential is not passphrase-encrypted"));
            }

            let decrypt_task = cx.background_spawn(async move {
                let encrypted = EncryptedSecretKey::from_bech32(&content)?;
                let secret = encrypted.decrypt(&password)?;
                Ok::<_, Error>(Keys::new(secret))
            });

            let keys = decrypt_task.await?;
            let public_key = keys.public_key();

            this.update(cx, |this, cx| this.set_signer(keys, cx))?;

            Ok(public_key)
        })
    }

    /// Create a new identity.
    pub fn create_identity(
        &mut self,
        name: &str,
        password: &str,
        cx: &mut Context<Self>,
    ) -> Task<Result<PublicKey, Error>> {
        let name = name.trim().to_owned();
        let password = password.to_owned();

        if name.is_empty() || name.len() > 255 {
            return Task::ready(Err(anyhow!("Name must be 1-255 characters")));
        }
        if password.is_empty() {
            return Task::ready(Err(anyhow!("Passphrase must not be empty")));
        }

        cx.spawn(async move |this, cx| {
            let job = cx.background_spawn(async move {
                let keys = Keys::generate();
                let encrypted =
                    EncryptedSecretKey::new(keys.secret_key(), &password, 16, KeySecurity::Medium)?;
                let ncryptsec = encrypted.to_bech32()?;
                Ok::<_, Error>((keys, ncryptsec))
            });

            let (keys, ncryptsec) = job.await?;
            let public_key = keys.public_key();

            // Persist the encrypted credential.
            let write = cx.update(|cx| {
                cx.write_credentials(USER_KEYRING, &public_key.to_hex(), ncryptsec.as_bytes())
            });
            write.await?;

            this.update(cx, |this, cx| {
                // Become the new identity so later publishes are signed with the new keys.
                this.signer.swap_inner(keys);
                this.current_user = Some(public_key);
                this.bootstrap_user(public_key, cx);
                cx.emit(BackendEvent::SignerChanged);
                cx.notify();

                let relays: Vec<(RelayUrl, Option<RelayMetadata>)> = [
                    (
                        RelayUrl::parse("wss://relay.primal.net").unwrap(),
                        Some(RelayMetadata::Read),
                    ),
                    (
                        RelayUrl::parse("wss://relay.ditto.pub").unwrap(),
                        Some(RelayMetadata::Read),
                    ),
                    (
                        RelayUrl::parse("wss://relay.nostr.net").unwrap(),
                        Some(RelayMetadata::Write),
                    ),
                    (
                        RelayUrl::parse("wss://nos.lol").unwrap(),
                        Some(RelayMetadata::Write),
                    ),
                ]
                .to_vec();

                this.send_fire_and_forget(RelayList::new(relays).into_event_builder(), cx);

                let metadata = Metadata::new()
                    .name(&name)
                    .display_name(&name)
                    .into_event_builder();

                this.send_fire_and_forget(metadata, cx);

                let grasp_servers: Vec<RelayUrl> = ["wss://gitnostr.com", "wss://relay.ngit.dev"]
                    .into_iter()
                    .map(|url| RelayUrl::parse(url).expect("valid relay URL"))
                    .collect();

                this.send_fire_and_forget(
                    GitUserGraspList { grasp_servers }.into_event_builder(),
                    cx,
                );
            })?;

            Ok(public_key)
        })
    }

    /// Initialize a local clone with a `main` branch and a `README.md`.
    ///
    /// The task yields the announcement and the path of the working copy.
    pub fn create_repository(
        &mut self,
        name: &str,
        description: &str,
        folder: PathBuf,
        grasp_servers: Vec<RelayUrl>,
        cx: &mut Context<Self>,
    ) -> Task<Result<(Announcement, PathBuf), Error>> {
        let name = name.trim().to_owned();
        let description = description.trim().to_owned();

        if name.is_empty() {
            return Task::ready(Err(anyhow!("Repository name is required")));
        }

        if grasp_servers.is_empty() {
            return Task::ready(Err(anyhow!("Add at least one grasp server")));
        }

        if !folder.is_dir() {
            return Task::ready(Err(anyhow!("Choose a folder for the repository")));
        }

        let Some(public_key) = self.current_user else {
            return Task::ready(Err(anyhow!("Sign in to create a repository")));
        };

        // The repository identifier is derived from the name.
        let repo_id = identifier_from_name(&name);

        if repo_id.is_empty() || repo_id.len() > 100 {
            return Task::ready(Err(anyhow!(
                "Repository name must produce an identifier of 1-100 characters"
            )));
        }

        if !repo_id.chars().any(|c| c.is_ascii_alphanumeric()) {
            return Task::ready(Err(anyhow!(
                "Repository name must contain at least one alphanumeric character"
            )));
        }

        let addr = repo_addr(public_key, repo_id.clone());
        let cache = GitStore::global(cx).cache().clone();
        let path = cache.repo_path(&addr);
        let owner = public_key.to_bech32().unwrap();
        let servers = grasp_servers.clone();

        cx.spawn(async move |this, cx| {
            // Initialize the local clone and create the user's working copy from it.
            let work = cx.background_spawn({
                let path = path.clone();
                let folder = folder.clone();
                let name = name.clone();
                let description = description.clone();
                let owner = owner.clone();
                let repo_id = repo_id.clone();
                let servers = servers.clone();

                async move {
                    let parent = path
                        .parent()
                        .ok_or_else(|| anyhow!("invalid repository path"))?;
                    std::fs::create_dir_all(parent)?;
                    let commit = signed_git::init_repository(&path, &name, &description)?;

                    // Point `origin` at the first grasp server.
                    // Later fetches and pushes have a target, like ngit.
                    if let Some(base) = servers.first().and_then(grasp_base_url) {
                        let url = format!("{base}/{owner}/{repo_id}.git");
                        signed_git::ensure_origin(&path, &url).ok();
                    }

                    // A working copy at `<folder>/<name>`, like the header's Clone action.
                    // Cloned from the mirror above so it shares the announced history.
                    // `origin` is set to the first grasp server, not the mirror path.
                    let destination = {
                        let dir_name = signed_git::sanitize_path_component(&name);
                        let dir_name = if dir_name.is_empty() {
                            "repository".to_owned()
                        } else {
                            dir_name
                        };
                        folder.join(dir_name)
                    };

                    let mirror_url = Url::from_file_path(&path)
                        .map_err(|_| anyhow!("invalid mirror path"))?
                        .to_string();

                    signed_git::clone_repo(&[mirror_url], &destination).with_context(|| {
                        format!(
                            "failed to create the working copy at {}",
                            destination.display()
                        )
                    })?;

                    if let Some(base) = servers.first().and_then(grasp_base_url) {
                        let url = format!("{base}/{owner}/{repo_id}.git");
                        signed_git::set_origin(&destination, &url)?;
                    }

                    Ok::<_, Error>((commit, destination))
                }
            });

            let (commit, checkout_path) = work.await?;
            let commit_sha = Sha1Hash::from_str(&commit).map_err(|_| anyhow!("invalid id"))?;

            // The nostr client queues events until each relay is connected.
            this.update(cx, |this, cx| {
                let urls: Vec<String> = servers.iter().map(ToString::to_string).collect();
                this.add_relays(urls, cx);
            })?;

            // The state event is the push authorization. It must be accepted before the push below.
            let announcement = GitRepositoryAnnouncement {
                id: repo_id.clone(),
                name: Some(name.clone()),
                description: (!description.is_empty()).then_some(description.clone()),
                web: Vec::new(),
                clone: servers
                    .iter()
                    .filter_map(|relay| grasp_clone_url(relay, &owner, &repo_id))
                    .collect(),
                relays: servers.clone(),
                euc: Some(commit_sha),
                maintainers: Vec::new(),
            };

            let event = this
                .update(cx, |this, cx| {
                    this.send(announcement.into_event_builder(), cx)
                })?
                .await?;

            let state_event = match this
                .update(cx, |this, cx| {
                    let builder = build_state(
                        &repo_id,
                        &[("refs/heads/main".to_owned(), commit)],
                        Some("main"),
                    );
                    this.send(builder, cx)
                })?
                .await
            {
                Ok(state_event) => state_event,
                Err(e) => {
                    this.update(cx, |this, cx| {
                        this.retract_events(std::slice::from_ref(&event), cx);
                    })
                    .ok();

                    return Err(e.context(
                        "The repository was announced, but its state could not be published. \
                         The announcement has been retracted",
                    ));
                }
            };

            // Push to every grasp server. Creation fails only when no server accepted it.
            let push = cx.background_spawn({
                let path = path.clone();
                let owner = owner.clone();
                let repo_id = repo_id.clone();
                let servers = servers.clone();
                push_to_grasp_servers(path, owner, repo_id, servers, signed_git::push_main)
            });

            if let Err(e) = push.await {
                // The events are already published. Retract them so the repository is not left announced without content.
                this.update(cx, |this, cx| {
                    this.retract_events(&[event.clone(), state_event.clone()], cx);
                })
                .ok();

                return Err(e.context(
                    "The repository was announced, but the push to every grasp server failed. \
                     The announcement has been retracted",
                ));
            }

            let announcement = Announcement::from_event(&event)
                .ok_or_else(|| anyhow!("failed to parse announcement"))?;

            Ok((announcement, checkout_path))
        })
    }

    /// Publish an existing local repository to NIP-34.
    pub fn publish_local_repo(
        &mut self,
        path: PathBuf,
        name: &str,
        description: &str,
        grasp_servers: Vec<RelayUrl>,
        cx: &mut Context<Self>,
    ) -> Task<Result<Announcement, Error>> {
        let name = name.trim().to_owned();
        let description = description.trim().to_owned();

        if name.is_empty() {
            return Task::ready(Err(anyhow!("Repository name is required")));
        }

        if grasp_servers.is_empty() {
            return Task::ready(Err(anyhow!("Add at least one grasp server")));
        }

        let Some(public_key) = self.current_user else {
            return Task::ready(Err(anyhow!("Sign in to publish a repository")));
        };

        // The identifier derives from the name, as in [`Self::create_repository`].
        let repo_id = identifier_from_name(&name);

        if repo_id.is_empty() || repo_id.len() > 100 {
            return Task::ready(Err(anyhow!(
                "Repository name must produce an identifier of 1-100 characters"
            )));
        }

        if !repo_id.chars().any(|c| c.is_ascii_alphanumeric()) {
            return Task::ready(Err(anyhow!(
                "Repository name must contain at least one alphanumeric character"
            )));
        }

        let owner = public_key.to_bech32().unwrap();
        let servers = grasp_servers.clone();

        cx.spawn(async move |this, cx| {
            let work = cx.background_spawn({
                let path = path.clone();
                async move {
                    let state = signed_git::worktree_ref_state(&path)?;
                    let euc = signed_git::root_commit(&path)?;
                    Ok::<_, Error>((state, euc))
                }
            });
            let (state, euc) = work.await?;

            // The nostr client queues events until each relay is connected.
            this.update(cx, |this, cx| {
                let urls: Vec<String> = servers.iter().map(ToString::to_string).collect();
                this.add_relays(urls, cx);
            })?;

            // The state event is the push authorization. It must be accepted before the push below.
            let announcement = GitRepositoryAnnouncement {
                id: repo_id.clone(),
                name: Some(name.clone()),
                description: (!description.is_empty()).then_some(description.clone()),
                web: Vec::new(),
                clone: servers
                    .iter()
                    .filter_map(|relay| grasp_clone_url(relay, &owner, &repo_id))
                    .collect(),
                relays: servers.clone(),
                euc: euc.and_then(|commit| Sha1Hash::from_str(&commit).ok()),
                maintainers: Vec::new(),
            };

            let event = this
                .update(cx, |this, cx| {
                    this.send(announcement.into_event_builder(), cx)
                })?
                .await?;

            let refs = state.refs.clone();
            let head = state.head.clone();
            let state_event = match this
                .update(cx, |this, cx| {
                    let builder = build_state(&repo_id, &refs, head.as_deref());
                    this.send(builder, cx)
                })?
                .await
            {
                Ok(state_event) => state_event,
                Err(e) => {
                    this.update(cx, |this, cx| {
                        this.retract_events(std::slice::from_ref(&event), cx);
                    })
                    .ok();

                    return Err(e.context(
                        "The repository was announced, but its state could not be published. \
                         The announcement has been retracted",
                    ));
                }
            };

            // Push every branch and tag to each grasp server. The push fails only when no server accepted it.
            //
            // An empty repository has nothing to push.
            if !refs.is_empty() {
                let push = cx.background_spawn({
                    let path = path.clone();
                    let owner = owner.clone();
                    let repo_id = repo_id.clone();
                    let servers = servers.clone();
                    push_to_grasp_servers(path, owner, repo_id, servers, signed_git::push_all)
                });
                if let Err(e) = push.await {
                    this.update(cx, |this, cx| {
                        this.retract_events(&[event.clone(), state_event.clone()], cx);
                    })
                    .ok();

                    return Err(e.context(
                        "The repository was announced, but the push to every grasp server failed. \
                         The announcement has been retracted",
                    ));
                }
            }

            // Point `origin` at the first grasp server so later pushes have a target.
            if let Some(base) = servers.first().and_then(grasp_base_url) {
                let url = format!("{base}/{owner}/{repo_id}.git");
                let path = path.clone();
                cx.background_spawn(async move {
                    signed_git::ensure_origin(&path, &url).ok();
                })
                .await;
            }

            Announcement::from_event(&event).ok_or_else(|| anyhow!("failed to parse announcement"))
        })
    }

    /// Re-push the repository's current refs to the grasp servers in its `relays` tag.
    pub fn push_repository(
        &mut self,
        announcement: Announcement,
        cx: &mut Context<Self>,
    ) -> Task<Result<(), Error>> {
        let cache = GitStore::global(cx).cache().clone();
        let path = cache.repo_path(&announcement.addr());
        self.push_repo_from(announcement, path, None, cx)
    }

    /// Push the refs of a local checkout to the grasp servers in its `relays` tag.
    /// The checkout is the working copy of the user's own repository.
    ///
    /// Publish a fresh state event, then push every branch and tag of the checkout.
    pub fn push_checkout(
        &mut self,
        announcement: Announcement,
        checkout: PathBuf,
        announced_head: Option<String>,
        cx: &mut Context<Self>,
    ) -> Task<Result<(), Error>> {
        self.push_repo_from(announcement, checkout, announced_head, cx)
    }

    /// Shared body of the mirror-based and checkout-based pushes.
    fn push_repo_from(
        &mut self,
        announcement: Announcement,
        path: PathBuf,
        announced_head: Option<String>,
        cx: &mut Context<Self>,
    ) -> Task<Result<(), Error>> {
        let addr = announcement.addr();
        let guard = {
            let mut pushing = self
                .pushing_repos
                .lock()
                .unwrap_or_else(|poisoned| poisoned.into_inner());
            if !pushing.insert(addr.clone()) {
                return Task::ready(Err(anyhow!(
                    "A push to this repository is already in progress"
                )));
            }
            PushGuard {
                repos: self.pushing_repos.clone(),
                addr: addr.clone(),
            }
        };

        let owner = announcement.owner.to_bech32().unwrap();
        let repo_id = announcement.id.clone();
        let relays = announcement.relays.clone();

        cx.spawn(async move |this, cx| {
            // Held for the whole task. Dropped on completion, on error and on cancellation alike.
            let _guard = guard;

            let mut state = {
                let work = cx.background_spawn({
                    let path = path.clone();
                    async move { signed_git::worktree_ref_state(&path) }
                });
                work.await?
            };

            // The state event announces the pushed refs.
            // Keep the announced default branch in `HEAD` when it is among the pushed refs.
            //
            // Otherwise `HEAD` stays the checkout's current branch.
            let heads: Vec<&str> = state
                .refs
                .iter()
                .filter_map(|(name, _)| name.strip_prefix("refs/heads/"))
                .collect();

            if let Some(head) = announced_head
                && heads.iter().any(|branch| *branch == head)
            {
                state.head = Some(head);
            }

            // Grasp servers authorize a push by the state they have seen.
            let refs = state.refs.clone();
            let head = state.head.clone();

            this.update(cx, |this, cx| {
                let builder = build_state(&repo_id, &refs, head.as_deref());
                this.send(builder, cx)
            })?
            .await?;

            if !refs.is_empty() {
                let push = cx.background_spawn({
                    let path = path.clone();
                    let owner = owner.clone();
                    let repo_id = repo_id.clone();
                    let relays = relays.clone();
                    async move {
                        push_to_grasp_servers(path, owner, repo_id, relays, signed_git::push_all)
                            .await
                    }
                });
                push.await?;
            }

            Ok(())
        })
    }

    /// Delete the repository from nostr.
    ///
    /// Only the repository owner may delete it.
    pub fn delete_repository(
        &mut self,
        addr: RepoAddr,
        cx: &mut Context<Self>,
    ) -> Task<Result<(), Error>> {
        let Some(public_key) = self.current_user else {
            return Task::ready(Err(anyhow!("Sign in to delete a repository")));
        };
        if public_key != addr.public_key {
            return Task::ready(Err(anyhow!("Only the repository owner can delete it")));
        }

        let client = self.client.clone();
        let addr = addr.clone();

        cx.spawn(async move |this, cx| {
            // Collect every event of the repository from the local database.
            let events = cx.background_spawn(async move {
                let db = client.database();
                let mut events = Vec::new();
                for filter in [
                    filters::announcement(&addr),
                    filters::state(&addr),
                    filters::activity(&addr),
                ] {
                    events.extend(db.query(filter).await?);
                }
                Ok::<_, Error>(events)
            });
            let events = events.await?;

            this.update(cx, |this, cx| {
                this.retract_events(&events, cx);
            })
            .ok();

            Ok(())
        })
    }

    /// Login with an `nsec1...` key or a `bunker://...` URI.
    pub fn login(&mut self, credential: &str, cx: &mut Context<Self>) {
        let credential = credential.trim();

        if credential.starts_with("nsec1") {
            self.login_with_nsec(credential, cx);
        } else if credential.starts_with("bunker://") {
            self.login_with_bunker(credential, cx);
        } else {
            cx.emit(BackendEvent::error(
                "Unsupported credential, expected nsec1... or bunker://...",
            ));
        }
    }

    /// Create a fresh identity and login with it.
    pub fn login_with_new_identity(&mut self, cx: &mut Context<Self>) {
        let nsec = Keys::generate()
            .secret_key()
            .to_bech32()
            .expect("infallible");
        self.login_with_nsec(&nsec, cx);
    }

    /// Login with an `nsec1...` secret key.
    pub fn login_with_nsec(&mut self, nsec: &str, cx: &mut Context<Self>) {
        let keys = match SecretKey::parse(nsec) {
            Ok(secret) => Keys::new(secret),
            Err(e) => {
                cx.emit(BackendEvent::error(e.to_string()));
                return;
            }
        };

        let nsec = nsec.trim().to_owned();
        let pubkey = keys.public_key().to_hex();
        let write = cx.write_credentials(USER_KEYRING, &pubkey, nsec.as_bytes());

        self.push_task(cx.spawn(async move |this, cx| {
            if let Err(e) = write.await {
                this.update(cx, |_, cx| cx.emit(BackendEvent::error(e.to_string())))?;
                return Ok(());
            }
            this.update(cx, |this, cx| this.set_signer(keys, cx))?;
            Ok(())
        }));
    }

    /// Login with a `bunker://...` URI, NIP-46.
    pub fn login_with_bunker(&mut self, uri: &str, cx: &mut Context<Self>) {
        let uri_string = uri.trim().to_owned();

        let connect_uri = match NostrConnectUri::parse(&uri_string) {
            Ok(uri) => uri,
            Err(e) => {
                cx.emit(BackendEvent::error(e.to_string()));
                return;
            }
        };

        let keys = Keys::generate();
        let credential = with_master_key(&uri_string, &keys);
        let write = cx.write_credentials(USER_KEYRING, "bunker", credential.as_bytes());

        self.push_task(cx.spawn(async move |this, cx| {
            let result = async {
                let mut signer = NostrConnect::new(
                    connect_uri,
                    keys,
                    Duration::from_secs(NOSTR_CONNECT_TIMEOUT),
                    None,
                )?;
                signer.auth_url_handler(SignedAuthUrlHandler);

                // Verify the signer before persisting the credential.
                signer.get_public_key_async().await?;
                write.await?;

                this.update(cx, |this, cx| this.set_signer(signer, cx))?;

                Ok::<_, Error>(())
            }
            .await;

            if let Err(e) = result {
                this.update(cx, |_, cx| cx.emit(BackendEvent::error(e.to_string())))?;
            }

            Ok(())
        }));
    }

    /// Remove the saved credential and reset to an anonymous session.
    pub fn logout(&mut self, cx: &mut Context<Self>) {
        let delete = cx.delete_credentials(USER_KEYRING);

        self.push_task(cx.spawn(async move |this, cx| {
            delete.await.ok();

            this.update(cx, |this, cx| {
                this.signer.swap_inner(Keys::generate());
                this.current_user = None;
                this.passphrase_required = false;
                cx.emit(BackendEvent::SignerChanged);
                cx.emit(BackendEvent::SignerRequired);
                cx.notify();
            })?;

            Ok(())
        }));
    }

    /// Fetch the user's grasp list and add the listed grasp servers as relays.
    fn bootstrap_user(&mut self, public_key: PublicKey, cx: &mut Context<Self>) {
        let client = self.client.clone();

        self.push_task(cx.spawn(async move |this, cx| {
            let result = async {
                let events: Vec<Event> = client
                    .fetch_events(filters::grasp_list(public_key))
                    .await?
                    .into_iter()
                    .collect();

                for url in latest_grasp_list_servers(events) {
                    client.add_relay(url.as_str()).await.ok();
                }
                client.connect().await;

                Ok::<_, Error>(())
            }
            .await;

            if let Err(e) = result {
                this.update(cx, |_, cx| cx.emit(BackendEvent::error(e.to_string())))?;
            }

            Ok(())
        }));
    }

    /// Get the nostr client.
    pub fn client(&self) -> Client {
        self.client.clone()
    }

    /// Get the current signer.
    pub fn signer(&self) -> UniversalSigner {
        self.signer.clone()
    }

    /// Get the current user's public key.
    pub fn current_user(&self) -> Option<PublicKey> {
        self.current_user
    }

    /// True when the stored credential is NIP-49 encrypted.
    pub fn passphrase_required(&self) -> bool {
        self.passphrase_required
    }

    /// Surface an error message through [`BackendEvent::Error`].
    pub fn emit_error(&mut self, message: impl Into<String>, cx: &mut Context<Self>) {
        cx.emit(BackendEvent::error(message));
    }

    /// Progress of the in-flight negentropy sync, if any.
    pub fn sync_progress(&self) -> Option<(u64, u64)> {
        self.sync_progress
    }

    /// Update the signer.
    pub fn set_signer<T>(&mut self, new_signer: T, cx: &mut Context<Self>)
    where
        T: AsyncGetPublicKey + AsyncSignEvent + AsyncNip44 + 'static,
        <T as AsyncGetPublicKey>::Error: std::error::Error + Send + Sync + 'static,
        <T as AsyncSignEvent>::Error: std::error::Error + Send + Sync + 'static,
        <T as AsyncNip44>::Error: std::error::Error + Send + Sync + 'static,
    {
        let task = cx.spawn(async move |this, cx| {
            match new_signer.get_public_key_async().await {
                Ok(public_key) => {
                    this.update(cx, |this, cx| {
                        this.signer.swap_inner(new_signer);
                        this.current_user = Some(public_key);
                        this.passphrase_required = false;
                        this.bootstrap_user(public_key, cx);
                        cx.emit(BackendEvent::SignerChanged);
                        cx.notify();
                    })?;
                }
                Err(e) => {
                    this.update(cx, |_this, cx| {
                        cx.emit(BackendEvent::error(e.to_string()));
                    })?;
                }
            }

            Ok(())
        });
        self.push_task(task);
    }

    /// Add relays and connect to them.
    pub fn add_relays(&mut self, urls: Vec<String>, cx: &mut Context<Self>) {
        let client = self.client.clone();

        let task = cx.background_spawn(async move {
            for url in urls {
                client.add_relay(&url).await?;
            }
            client.connect().await;
            Ok::<(), Error>(())
        });

        self.push_task(cx.spawn(async move |this, cx| {
            match task.await {
                Ok(()) => {
                    this.update(cx, |_this, cx| cx.notify())?;
                }
                Err(e) => {
                    this.update(cx, |_this, cx| cx.emit(BackendEvent::error(e.to_string())))?;
                }
            }
            Ok(())
        }));
    }

    /// Whether an identical fetch started within [`FETCH_DEDUP_WINDOW`] is still recent.
    ///
    /// Records the fingerprint when returning `false`, pruning expired entries first.
    fn fetch_recently_started(&mut self, fingerprint: u64) -> bool {
        self.recent_fetches
            .retain(|_, started| started.elapsed() < FETCH_DEDUP_WINDOW);
        if self.recent_fetches.contains_key(&fingerprint) {
            return true;
        }
        self.recent_fetches.insert(fingerprint, Instant::now());
        false
    }

    /// Connect to a repository's announced relays, its NIP-34 `relays` tag.
    pub fn connect_repo_relays(
        &mut self,
        relays: Vec<RelayUrl>,
        filters: Vec<Filter>,
        cx: &mut Context<Self>,
    ) {
        let relay_strs: Vec<&str> = relays.iter().map(|url| url.as_str()).collect();
        let fingerprint = fetch_fingerprint(&relay_strs, &filters);
        if self.fetch_recently_started(fingerprint) {
            log::debug!("skipping duplicate repo relay fetch");
            return;
        }

        let client = self.client.clone();

        self.push_task(cx.spawn(async move |this, cx| {
            if let Err(e) = connect_repo_relays_only(&client, relays, filters).await {
                log::warn!("repo relay fetch failed: {e}");
                // Allow an immediate retry after a failure.
                this.update(cx, |this, _cx| {
                    this.recent_fetches.remove(&fingerprint);
                })
                .ok();
            }
            Ok(())
        }));
    }

    /// One-shot subscription on the bootstrap relays only.
    pub fn subscribe_bootstrap(&mut self, filters: Vec<Filter>, cx: &mut Context<Self>) {
        let client = self.client.clone();

        let task =
            cx.background_spawn(async move { subscribe_bootstrap_only(&client, filters).await });

        self.push_task(cx.spawn(async move |this, cx| {
            if let Err(e) = task.await {
                this.update(cx, |_this, cx| cx.emit(BackendEvent::error(e.to_string())))?;
            }
            Ok(())
        }));
    }

    /// Negentropy-sync the given filter against the bootstrap relays.
    pub fn sync_bootstrap(&mut self, filter: Filter, cx: &mut Context<Self>) {
        let fingerprint = fetch_fingerprint(&BOOTSTRAP_RELAYS, std::slice::from_ref(&filter));
        if self.fetch_recently_started(fingerprint) {
            log::debug!("skipping duplicate bootstrap sync");
            return;
        }

        let client = self.client.clone();

        self.sync_progress = Some((0, 0));
        cx.notify();

        let (tx, mut rx) = SyncProgress::channel();

        self.push_task(cx.spawn(async move |this, cx| {
            let mut last_percent: u64 = 0;

            while rx.changed().await.is_ok() {
                let progress = *rx.borrow_and_update();
                let percent = (progress.percentage() * 100.0) as u64;

                if progress.current > 0 && percent != last_percent {
                    last_percent = percent;

                    let alive = this.update(cx, |this, cx| {
                        this.sync_progress = Some((progress.total, progress.current));
                        cx.emit(BackendEvent::SyncProgress {
                            total: progress.total,
                            current: progress.current,
                        });
                        cx.notify();
                    });

                    if alive.is_err() {
                        break;
                    }
                }
            }

            Ok(())
        }));

        let task = cx.background_spawn(async move {
            let opts = SyncOptions::default().progress(tx);
            sync_bootstrap_only(&client, filter, opts).await
        });

        self.push_task(cx.spawn(async move |this, cx| {
            match task.await {
                Ok(summary) => {
                    log::debug!(
                        "sync done: {} received, {} sent",
                        summary.received.len(),
                        summary.sent.len()
                    );
                    this.update(cx, |this, cx| {
                        this.sync_progress = None;
                        cx.emit(BackendEvent::Synced);
                        cx.notify();
                    })?;
                }
                Err(e) => {
                    this.update(cx, |this, cx| {
                        this.sync_progress = None;
                        // Allow an immediate retry after a failure.
                        this.recent_fetches.remove(&fingerprint);
                        cx.emit(BackendEvent::error(e.to_string()))
                    })?;
                }
            }
            Ok(())
        }));
    }

    /// Sign, broadcast and locally store an event.
    pub fn send(
        &mut self,
        builder: EventBuilder,
        cx: &mut Context<Self>,
    ) -> Task<Result<Event, Error>> {
        let client = self.client.clone();
        let signer = self.signer.clone();

        self.publish_task(cx, async move {
            // Sign with the current signer, broadcast and save locally.
            // The event is immediately visible to database queries.
            let event = builder.finalize_async(&signer).await?;
            broadcast_event(&client, &event).await
        })
    }

    /// Broadcast and locally store an already-signed event.
    pub fn publish_event(
        &mut self,
        event: Event,
        cx: &mut Context<Self>,
    ) -> Task<Result<Event, Error>> {
        let client = self.client.clone();
        self.publish_task(cx, async move { broadcast_event(&client, &event).await })
    }

    /// Run `work` in the background, then emit its outcome as a [`BackendEvent`].
    fn publish_task(
        &mut self,
        cx: &mut Context<Self>,
        work: impl Future<Output = Result<Event, Error>> + 'static + Send,
    ) -> Task<Result<Event, Error>> {
        cx.spawn(async move |this, cx| {
            let result = cx.background_spawn(work).await;

            match &result {
                Ok(event) => {
                    this.update(cx, |_this, cx| {
                        cx.emit(BackendEvent::Published(Box::new(event.clone())));
                    })
                    .ok();
                }
                Err(e) => {
                    this.update(cx, |_this, cx| {
                        cx.emit(BackendEvent::error(e.to_string()));
                    })
                    .ok();
                }
            }

            result
        })
    }

    /// Sign, broadcast and store an event without awaiting the result.
    fn send_fire_and_forget(&mut self, builder: EventBuilder, cx: &mut Context<Self>) {
        let task = self.send(builder, cx);

        self.push_task(cx.spawn(async move |this, cx| {
            if let Err(e) = task.await {
                this.update(cx, |_this, cx| {
                    cx.emit(BackendEvent::error(e.to_string()));
                })
                .ok();
            }
            Ok(())
        }));
    }

    /// Publish NIP-09 deletions for `events`, best-effort.
    fn retract_events(&mut self, events: &[Event], cx: &mut Context<Self>) {
        if events.is_empty() {
            return;
        }

        let mut tags: Vec<Tag> = Vec::with_capacity(events.len() * 2);

        for event in events {
            tags.push(Tag::event(event.id));
            tags.push(Tag::parse(["k", &event.kind.to_string()]).expect("valid kind tag"));
        }

        let task = self.send(EventBuilder::new(Kind::EventDeletion, "").tags(tags), cx);

        self.push_task(cx.spawn(async move |_this, _cx| {
            if let Err(e) = task.await {
                log::warn!("failed to retract repository events: {e}");
            }
            Ok(())
        }));
    }
}

/// Broadcast an event and fail when no relay accepted it.
///
/// The client stores accepted events locally, visible to database queries.
async fn broadcast_event(client: &Client, event: &Event) -> Result<Event, Error> {
    let output = client.send_event(event).await?;

    if output.success.is_empty() && !output.failed.is_empty() {
        let reasons = output
            .failed
            .values()
            .cloned()
            .collect::<Vec<String>>()
            .join(", ");
        return Err(anyhow!("event not accepted by any relay: {reasons}"));
    }

    Ok(event.clone())
}

/// Fingerprint of a relay and filter set, for fetch dedup.
///
/// Relays and filters are sorted first, so the fingerprint is order-independent.
fn fetch_fingerprint(relays: &[&str], filters: &[Filter]) -> u64 {
    let mut relays: Vec<&str> = relays.to_vec();
    relays.sort_unstable();
    let mut filters: Vec<&Filter> = filters.iter().collect();
    filters.sort_unstable();

    let mut hasher = DefaultHasher::new();
    relays.hash(&mut hasher);
    filters.hash(&mut hasher);
    hasher.finish()
}

/// Add the given relays, connect and fetch the filters.
async fn connect_repo_relays_only(
    client: &Client,
    relays: Vec<RelayUrl>,
    filters: Vec<Filter>,
) -> Result<(), Error> {
    if relays.is_empty() {
        return Ok(());
    }

    let mut added = false;
    for url in &relays {
        added |= client.add_relay(url).await?;
    }

    // Connect only when the pool grew.
    if added {
        client.connect().await;
    }

    let opts = SubscribeAutoCloseOptions::default()
        .exit_policy(ReqExitPolicy::ExitOnEOSE)
        .timeout(Some(Duration::from_secs(10)));

    let target: HashMap<&str, Vec<Filter>> = relays
        .iter()
        .map(|url| (url.as_str(), filters.clone()))
        .collect();
    client.subscribe(target).close_on(opts).await?;

    // Sync the filters concurrently.
    let sync_opts = SyncOptions::default().initial_timeout(Duration::from_secs(5));
    let syncs = filters.into_iter().map(|filter| {
        let client = &client;
        let relays = &relays;
        let sync_opts = sync_opts.clone();
        async move {
            if let Err(e) = client
                .sync(filter)
                .with(relays.iter())
                .opts(sync_opts)
                .await
            {
                log::warn!("repo relay negentropy sync failed: {e}");
            }
        }
    });

    futures::future::join_all(syncs).await;

    Ok(())
}

/// Subscribe only on the bootstrap relays.
pub(crate) async fn subscribe_bootstrap_only(
    client: &Client,
    filters: Vec<Filter>,
) -> Result<(), Error> {
    let opts = SubscribeAutoCloseOptions::default()
        .exit_policy(ReqExitPolicy::ExitOnEOSE)
        .timeout(Some(Duration::from_secs(10)));

    let target: HashMap<&str, Vec<Filter>> = BOOTSTRAP_RELAYS
        .iter()
        .map(|relay| (*relay, filters.clone()))
        .collect();

    client.subscribe(target).close_on(opts).await?;

    Ok(())
}

/// Negentropy-sync the filter against the bootstrap relays only.
pub(crate) async fn sync_bootstrap_only(
    client: &Client,
    filter: Filter,
    opts: SyncOptions,
) -> Result<SyncSummary, Error> {
    let output = client
        .sync(filter)
        .with(BOOTSTRAP_RELAYS)
        .opts(opts)
        .await?;
    Ok(output.value)
}

/// Embed a NIP-46 session key into a bunker URI as `?master=<nsec>`.
fn with_master_key(uri: &str, keys: &Keys) -> String {
    let separator = if uri.contains('?') { '&' } else { '?' };
    let nsec = keys.secret_key().to_bech32().expect("infallible");
    format!("{uri}{separator}master={nsec}")
}

/// Base URL of a grasp server, `https://<host>`.
///
/// `ws://` grasp servers use `http://<host>`, like ngit.
pub(crate) fn grasp_base_url(relay: &RelayUrl) -> Option<String> {
    // `domain()` drops the port.
    let parsed = Url::parse(relay.as_str()).ok()?;
    let host = parsed.host_str()?;
    let port = parsed.port().map(|p| format!(":{p}")).unwrap_or_default();
    // `ws://` grasp servers, e.g. local dev relays, speak plain HTTP.
    let scheme = if relay.scheme().is_secure() {
        "https"
    } else {
        "http"
    };
    Some(format!("{scheme}://{host}{port}"))
}

/// GRASP clone URL of a repository on a grasp server.
fn grasp_clone_url(relay: &RelayUrl, owner: &str, repo_id: &str) -> Option<Url> {
    let base = grasp_base_url(relay)?;
    Url::parse(&format!("{base}/{owner}/{repo_id}.git")).ok()
}

/// GRASP-06 contributor namespace URL of a pull request tip.
pub(crate) fn grasp06_prs_url(base_url: &str, npub: &str, repo_id: &str) -> String {
    format!("{base_url}/prs/{npub}/{repo_id}.git")
}

/// Assemble the `clone` URLs of a pull request.
///
/// The author's GRASP-06 `/prs/` URLs come first.
pub(crate) fn pr_clone_urls(prs_urls: Vec<Url>, base_clone_urls: Vec<Url>) -> Vec<Url> {
    let mut seen = std::collections::HashSet::new();
    let mut urls = Vec::new();
    for url in prs_urls.into_iter().chain(base_clone_urls) {
        if seen.insert(url.to_string()) {
            urls.push(url);
        }
    }
    urls
}

/// The `g` tag servers of one kind-10317 grasp list event, in tag order.
fn grasp_list_servers(event: &Event) -> Vec<RelayUrl> {
    event
        .tags
        .iter()
        .filter(|tag| tag.kind() == "g")
        .filter_map(|tag| tag.content())
        .filter_map(|url| RelayUrl::parse(url).ok())
        .collect()
}

/// Grasp servers of the newest kind-10317 grasp list among `events`.
fn latest_grasp_list_servers(events: Vec<Event>) -> Vec<RelayUrl> {
    events
        .into_iter()
        .max_by_key(|event| event.created_at)
        .map(|event| grasp_list_servers(&event))
        .unwrap_or_default()
}

/// Resolve the user's published grasp servers from the local database.
pub async fn user_grasp_list_servers(
    client: Client,
    user: PublicKey,
) -> Result<Vec<RelayUrl>, Error> {
    let events: Vec<Event> = client
        .database()
        .query(filters::grasp_list(user))
        .await?
        .into_iter()
        .collect();
    Ok(latest_grasp_list_servers(events))
}

/// Push the repository at `path` to every grasp server.
async fn push_to_grasp_servers(
    path: PathBuf,
    owner: String,
    repo_id: String,
    servers: Vec<RelayUrl>,
    push: fn(&Path, &str, &str, &str) -> Result<(), Error>,
) -> Result<(), Error> {
    let mut failures = Vec::new();
    let mut pushed = 0;

    for relay in &servers {
        let Some(base_url) = grasp_base_url(relay) else {
            failures.push(format!("{relay}: no domain"));
            continue;
        };
        match push(&path, &base_url, &owner, &repo_id) {
            Ok(()) => pushed += 1,
            Err(e) => failures.push(format!("{relay}: {e}")),
        }
    }

    if pushed == 0 {
        bail!(
            "could not push the repository to any grasp server: {}",
            failures.join("; ")
        );
    }

    for failure in failures {
        log::warn!("grasp push failed: {failure}");
    }

    Ok(())
}

/// Split a stored bunker credential into the plain URI and the session key.
fn extract_master_key(credential: &str) -> (&str, Keys) {
    match credential.split_once("master=") {
        Some((base, nsec)) => {
            let keys = SecretKey::parse(nsec)
                .map(Keys::new)
                .unwrap_or_else(|_| Keys::generate());
            (base.trim_end_matches(['?', '&']), keys)
        }
        None => (credential, Keys::generate()),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn grasp_base_url_maps_schemes_like_ngit() {
        let wss = RelayUrl::parse("wss://relay.ngit.dev").expect("url");
        assert_eq!(
            grasp_base_url(&wss).as_deref(),
            Some("https://relay.ngit.dev")
        );

        let ws = RelayUrl::parse("ws://localhost:8080").expect("url");
        assert_eq!(
            grasp_base_url(&ws).as_deref(),
            Some("http://localhost:8080")
        );
    }

    #[test]
    fn grasp_clone_url_matches_ngit_format() {
        let relay = RelayUrl::parse("wss://gitnostr.com").expect("url");
        let url = grasp_clone_url(&relay, "npub1test", "my-repo").expect("url");
        assert_eq!(
            url.to_string(),
            "https://gitnostr.com/npub1test/my-repo.git"
        );
    }

    #[test]
    fn grasp06_prs_url_matches_ngit_format() {
        assert_eq!(
            grasp06_prs_url("https://relay.ngit.dev", "npub1author", "my-repo"),
            "https://relay.ngit.dev/prs/npub1author/my-repo.git"
        );
        // `ws://` grasp servers, local dev, keep their plain-HTTP base.
        assert_eq!(
            grasp06_prs_url("http://localhost:8080", "npub1author", "my-repo"),
            "http://localhost:8080/prs/npub1author/my-repo.git"
        );
    }

    #[test]
    fn pr_clone_urls_orders_author_first_and_deduplicates() {
        let prs = vec![
            Url::parse("https://a.example/prs/npub1me/repo.git").expect("url"),
            Url::parse("https://a.example/prs/npub1me/repo.git").expect("url"),
        ];
        let base = vec![
            Url::parse("https://a.example/npub1owner/repo.git").expect("url"),
            Url::parse("https://b.example/npub1owner/repo.git").expect("url"),
            Url::parse("https://b.example/npub1owner/repo.git").expect("url"),
        ];

        let urls = pr_clone_urls(prs, base);
        assert_eq!(
            urls.iter().map(ToString::to_string).collect::<Vec<_>>(),
            vec![
                "https://a.example/prs/npub1me/repo.git",
                "https://a.example/npub1owner/repo.git",
                "https://b.example/npub1owner/repo.git",
            ]
        );
    }

    fn grasp_list_event(servers: &[&str], created_at: u64) -> Event {
        let keys = Keys::generate();
        let tags: Vec<Tag> = servers
            .iter()
            .map(|url| Tag::parse(vec!["g", *url]).expect("valid tag"))
            .collect();
        EventBuilder::new(Kind::GitUserGraspList, "")
            .tags(tags)
            .custom_created_at(Timestamp::from(created_at))
            .finalize(&keys)
            .expect("signed event")
    }

    #[test]
    fn grasp_list_servers_reads_g_tags_in_order() {
        let event = grasp_list_event(
            &["wss://first.example", "wss://second.example", "not a url"],
            1000,
        );

        let servers = grasp_list_servers(&event);
        assert_eq!(
            servers.iter().map(ToString::to_string).collect::<Vec<_>>(),
            vec!["wss://first.example", "wss://second.example"]
        );
    }

    #[test]
    fn latest_grasp_list_servers_takes_the_newest_list_and_falls_back_empty() {
        let old = grasp_list_event(&["wss://old.example"], 1000);
        let fresh = grasp_list_event(&["wss://fresh.example", "wss://also.example"], 2000);

        // The newest list wins, its `g` order preserved.
        let servers = latest_grasp_list_servers(vec![old.clone(), fresh.clone()]);
        assert_eq!(
            servers.iter().map(ToString::to_string).collect::<Vec<_>>(),
            vec!["wss://fresh.example", "wss://also.example"]
        );

        // The order of the input events does not matter.
        let servers = latest_grasp_list_servers(vec![fresh, old]);
        assert_eq!(
            servers.iter().map(ToString::to_string).collect::<Vec<_>>(),
            vec!["wss://fresh.example", "wss://also.example"]
        );

        // No list at all, empty, so the caller falls back to the defaults.
        assert!(latest_grasp_list_servers(Vec::new()).is_empty());
    }
}