use std::collections::BTreeMap;
use std::sync::LazyLock;

use anyhow::{Result, anyhow};
use nostr_sdk::prelude::*;
use serde::{Deserialize, Serialize};

use crate::control::{
    ChannelMetadata, CommunityGenesis, CommunityMetadata, ControlFold, ROOT_EPOCH,
};
use crate::derive::control_signer_group_key;
use crate::edition::{EntityHead, Floors, ParsedEdition, vsk};
use crate::stream::OpenedStream;
use crate::{ChannelId, CommunityId, Epoch};

static LOCAL_KEYS: LazyLock<Keys> = LazyLock::new(Keys::generate);

const CHANNEL_TAG: SingleLetterTag = SingleLetterTag::LOWERCASE_C;
const MARK_TAG: SingleLetterTag = SingleLetterTag::LOWERCASE_T;
const MARK_VALUE: &str = "concord";
const WRAP_TAG: &str = "e";
const KIND_TAG: &str = "k";
const STATE_PREFIX: &str = "concord/";

pub async fn cache_rumor(
    database: &dyn NostrDatabase,
    channel: &ChannelId,
    opened: &OpenedStream,
) -> Result<()> {
    let tags = vec![
        Tag::identifier(opened.rumor_id),
        Tag::custom(KIND_TAG, [opened.rumor.kind.to_string()]),
        Tag::custom(WRAP_TAG, [opened.wrapper_id.to_string()]),
        Tag::custom(MARK_TAG.as_str(), [MARK_VALUE]),
        Tag::custom(CHANNEL_TAG.as_str(), [channel.to_hex()]),
        Tag::public_key(opened.author),
    ];
    let at = Timestamp::from_secs(opened.at_ms / 1000);
    let event = EventBuilder::new(Kind::ApplicationSpecificData, opened.rumor.as_json())
        .tags(tags)
        .custom_created_at(at)
        .finalize_async(&*LOCAL_KEYS)
        .await?;

    database.save_event(&event).await?;

    Ok(())
}

pub async fn query_rumors(
    database: &dyn NostrDatabase,
    channel: &ChannelId,
    until: Option<Timestamp>,
    limit: usize,
) -> Result<Vec<UnsignedEvent>> {
    let mut filter = Filter::new()
        .kind(Kind::ApplicationSpecificData)
        .custom_tag(MARK_TAG, MARK_VALUE)
        .custom_tag(CHANNEL_TAG, channel.to_hex());

    if let Some(until) = until {
        filter = filter.until(until);
    }

    let mut newest: BTreeMap<String, Event> = BTreeMap::new();
    for event in database.query(filter).await? {
        let Some(rumor_id) = event.tags.identifier() else {
            continue;
        };

        match newest.get(&rumor_id) {
            Some(existing) if existing.created_at >= event.created_at => {}
            _ => {
                newest.insert(rumor_id, event);
            }
        }
    }

    let mut events: Vec<Event> = newest.into_values().collect();
    events.sort_by_key(|event| std::cmp::Reverse(event.created_at));
    events.truncate(limit);

    let mut rumors = Vec::with_capacity(events.len());
    for event in events {
        let rumor = UnsignedEvent::from_json(event.content)
            .map_err(|error| anyhow!("cached rumor is not a valid event: {error}"))?;
        rumors.push(rumor);
    }

    Ok(rumors)
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ChannelKeyRef {
    pub id: ChannelId,
    pub name: String,
    pub private: bool,
    pub epoch: Epoch,
}

/// One local document per community, keyed by `concord/<community_id>`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct CommunityState {
    pub id: CommunityId,
    pub owner: PublicKey,
    pub owner_salt: [u8; 32],
    pub community_root: [u8; 32],
    pub root_epoch: Epoch,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub control_root: Option<[u8; 32]>,
    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
    pub control_pks: BTreeMap<u64, PublicKey>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub channels: Vec<ChannelKeyRef>,
    pub relays: Vec<RelayUrl>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub heads: Vec<EntityHead>,
    pub added_at_ms: u64,
}

impl CommunityState {
    pub fn from_genesis(
        genesis: &CommunityGenesis,
        editions: &[ParsedEdition],
        added_at_ms: u64,
    ) -> Result<Self> {
        let mut channels = Vec::new();
        let mut heads = Vec::with_capacity(editions.len());
        let mut relays = Vec::new();

        for edition in editions {
            heads.push(EntityHead {
                entity: edition.entity,
                version: edition.version,
                self_hash: edition.self_hash,
                rumor_id: edition.rumor_id,
            });

            match edition.subkind.as_str() {
                vsk::COMMUNITY_METADATA => {
                    let metadata: CommunityMetadata = serde_json::from_str(&edition.content)?;
                    relays.extend(
                        metadata
                            .relays
                            .iter()
                            .filter_map(|relay| RelayUrl::parse(relay).ok()),
                    );
                }
                vsk::CHANNEL_METADATA => {
                    let metadata: ChannelMetadata = serde_json::from_str(&edition.content)?;
                    channels.push(ChannelKeyRef {
                        id: ChannelId::from_bytes(edition.entity),
                        name: metadata.name,
                        private: metadata.private,
                        epoch: ROOT_EPOCH,
                    });
                }
                _ => {}
            }
        }

        let control_pks = BTreeMap::from([(
            ROOT_EPOCH.0,
            control_signer_group_key(
                &genesis.control_root,
                &genesis.identity.community_id,
                ROOT_EPOCH,
            )?
            .pk(),
        )]);

        Ok(Self {
            id: genesis.identity.community_id,
            owner: genesis.identity.owner,
            owner_salt: genesis.identity.owner_salt,
            community_root: genesis.community_root,
            root_epoch: ROOT_EPOCH,
            control_root: Some(genesis.control_root),
            control_pks,
            channels,
            relays,
            heads,
            added_at_ms,
        })
    }

    pub fn identifier(&self) -> String {
        state_identifier(&self.id)
    }

    pub fn floors(&self) -> Floors {
        self.heads
            .iter()
            .map(|head| (head.entity, head.clone()))
            .collect()
    }

    pub fn apply_fold(&mut self, fold: &ControlFold) {
        self.heads = fold.floors.values().cloned().collect();

        if let Some(community) = &fold.community {
            self.relays = community
                .relays
                .iter()
                .filter_map(|relay| RelayUrl::parse(relay).ok())
                .collect();
        }

        for (id, metadata) in &fold.channels {
            if metadata.deleted.unwrap_or(false) {
                self.channels.retain(|channel| channel.id != *id);
                continue;
            }

            match self.channels.iter_mut().find(|channel| channel.id == *id) {
                Some(channel) => {
                    channel.name = metadata.name.clone();

                    if !metadata.private {
                        channel.private = false;
                    }
                }
                None if !metadata.private => self.channels.push(ChannelKeyRef {
                    id: *id,
                    name: metadata.name.clone(),
                    private: false,
                    epoch: self.root_epoch,
                }),
                None => {}
            }
        }
    }
}

fn state_identifier(id: &CommunityId) -> String {
    format!("{STATE_PREFIX}{}", id.to_hex())
}

pub async fn save_state<D>(database: &D, state: &CommunityState) -> Result<()>
where
    D: NostrDatabase,
{
    let event = EventBuilder::new(Kind::ApplicationSpecificData, serde_json::to_string(state)?)
        .tags([Tag::identifier(state.identifier())])
        .finalize_async(&*LOCAL_KEYS)
        .await?;

    database.save_event(&event).await?;

    Ok(())
}

pub async fn load_state<D>(database: &D, id: &CommunityId) -> Result<Option<CommunityState>>
where
    D: NostrDatabase,
{
    let filter = Filter::new()
        .kind(Kind::ApplicationSpecificData)
        .identifier(state_identifier(id))
        .limit(1);

    match database.query(filter).await?.into_iter().next() {
        Some(event) => Ok(Some(serde_json::from_str(&event.content)?)),
        None => Ok(None),
    }
}

#[cfg(test)]
mod tests {
    use nostr_memory::MemoryDatabase;

    use super::*;
    use crate::Epoch;
    use crate::derive::channel_group_key;
    use crate::stream::{
        KIND_WRAP, SealForm, build_rumor_ms, build_seal, channel_binding_tags, open_wrap, wrap_seal,
    };

    const SECRET: [u8; 32] = [0x07u8; 32];

    #[test]
    fn rumors_read_back_after_a_restart() {
        let database = MemoryDatabase::unbounded();
        let channel = ChannelId::from_bytes([0xabu8; 32]);
        let author = Keys::generate();

        smol::block_on(async {
            let group = channel_group_key(&SECRET, &channel, Epoch(0)).expect("derives");

            for (content, at_ms) in [("first", 1_000_000u64), ("second", 2_000_000)] {
                let rumor = build_rumor_ms(
                    9,
                    author.public_key(),
                    content,
                    channel_binding_tags(&channel, Epoch(0)),
                    at_ms,
                );
                let seal = build_seal(&rumor, SealForm::Encrypted, &group, &author).expect("seals");
                let (wrap, _) = wrap_seal(
                    &seal,
                    &group,
                    KIND_WRAP,
                    Timestamp::from_secs(at_ms / 1000),
                    &[],
                )
                .expect("wraps");

                let opened = open_wrap(&wrap, &group).expect("opens");
                cache_rumor(&database, &channel, &opened)
                    .await
                    .expect("caches");
            }

            // The group key is gone; only the local cache stands in for it.
            let rumors = query_rumors(&database, &channel, None, 10)
                .await
                .expect("queries");
            assert_eq!(rumors.len(), 2, "both messages come back");
            assert_eq!(rumors[0].content, "second", "newest first");
            assert_eq!(rumors[1].content, "first");

            // A page boundary in message time, not in cache time.
            let until = Timestamp::from_secs(1_500);
            let page = query_rumors(&database, &channel, Some(until), 10)
                .await
                .expect("queries");
            assert_eq!(page.len(), 1);
            assert_eq!(page[0].content, "first");

            let capped = query_rumors(&database, &channel, None, 1)
                .await
                .expect("queries");
            assert_eq!(capped.len(), 1);
            assert_eq!(capped[0].content, "second");
        });
    }
}