chore: refactor the backend (#17)

Reviewed-on: #17

crates/signed_git/src/repo.rs

@@ -0,0 +1,488 @@
+use std::path::Path;
+
+use anyhow::{Context, Result, bail};
+
+use crate::history::open_with_cache;
+use crate::worktree::{force_checkout, worktree_dirty};
+
+/// The merge base of two revisions in the repository at `repo_path`,
+/// revisions may be branch names, remote-tracking refs or commit ids.
+///
+/// `Ok(None)` when the revisions share no common ancestor.
+///
+/// Unresolvable revisions are errors.
+pub fn merge_base(repo_path: &Path, a: &str, b: &str) -> Result<Option<String>> {
+    let repo = open_with_cache(repo_path)?;
+    let a = repo.rev_parse_single(a.as_bytes())?;
+    let b = repo.rev_parse_single(b.as_bytes())?;
+    match repo.merge_base(a, b) {
+        Ok(id) => Ok(Some(id.to_string())),
+        // No common ancestor, a valid outcome for a proposal.
+        Err(gix::repository::merge_base::Error::NotFound { .. }) => Ok(None),
+        Err(e) => Err(e.into()),
+    }
+}
+
+/// The commit HEAD points to in the repository at `repo_path`.
+///
+/// `None` when the repository has no commits yet, an unborn HEAD.
+pub fn head_commit_id(repo_path: &Path) -> Result<Option<String>> {
+    let Ok(repo) = gix::open(repo_path) else {
+        return Ok(None);
+    };
+
+    match repo.head_id() {
+        Ok(id) => Ok(Some(id.to_string())),
+        Err(_) => Ok(None),
+    }
+}
+
+/// The commits in `base..HEAD` of the repository at `repo_path`, oldest first.
+/// This is the order `git am` creates them.
+///
+/// `HEAD` alone when `base` is `None`.
+pub fn commits_since(repo_path: &Path, base: Option<&str>) -> Result<Vec<String>> {
+    let repo = match gix::open(repo_path) {
+        Ok(repo) => repo,
+        Err(_) if base.is_none() => return Ok(Vec::new()),
+        Err(e) => return Err(e.into()),
+    };
+
+    let head = match repo.head_id() {
+        Ok(head) => head,
+        Err(_) if base.is_none() => return Ok(Vec::new()),
+        Err(e) => return Err(e).context("repository has no commits"),
+    };
+
+    let Some(base) = base else {
+        // `HEAD` alone when no base is given.
+        return Ok(vec![head.to_string()]);
+    };
+
+    let base = repo.rev_parse_single(base.as_bytes())?;
+    let mut commits = Vec::new();
+
+    for info in repo
+        .rev_walk([head])
+        .sorting(gix::revision::walk::Sorting::ByCommitTime(
+            gix::traverse::commit::simple::CommitTimeOrder::NewestFirst,
+        ))
+        .with_hidden([base])
+        .all()?
+    {
+        commits.push(info?.id().to_string());
+    }
+
+    // Oldest first, like `git rev-list --reverse`, the order `git am` creates them.
+    commits.reverse();
+
+    Ok(commits)
+}
+
+/// The identity written to reflogs and commits created by this crate itself.
+///
+/// Like `git -c user.name=… -c user.email=…` per invocation: the repository works
+/// without a global git identity, and `gix` runs no hooks and never signs.
+pub(crate) fn repository_signature() -> (gix::actor::Signature, gix::date::parse::TimeBuf) {
+    let seconds = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|duration| duration.as_secs() as i64)
+        .unwrap_or_default();
+
+    let signature = gix::actor::Signature {
+        name: gix::bstr::BString::from("Signed"),
+        email: gix::bstr::BString::from("signed@localhost"),
+        time: gix::date::Time { seconds, offset: 0 },
+    };
+
+    (signature, gix::date::parse::TimeBuf::default())
+}
+
+/// Create a repository at `path` with an initial `main` branch.
+/// Write a `README.md` from `name` and `description`, then create the initial commit.
+///
+/// Returns the initial commit id.
+pub fn init_repository(path: &Path, name: &str, description: &str) -> Result<String> {
+    use gix::refs::transaction::{Change, LogChange, PreviousValue, RefEdit, RefLog};
+
+    std::fs::create_dir_all(path)
+        .with_context(|| format!("failed to create {}", path.display()))?;
+
+    let repo = gix::init(path)?;
+
+    let (signature, mut time_buf) = repository_signature();
+    let signature = signature.to_ref(&mut time_buf);
+
+    // The initial branch is `main`, regardless of `init.defaultBranch` in
+    // the user's git configuration: point the unborn HEAD there.
+    let head = gix::refs::FullName::try_from("HEAD")
+        .map_err(|e| anyhow::anyhow!("invalid ref name: {e}"))?;
+
+    repo.edit_references_as(
+        [RefEdit {
+            change: Change::Update {
+                log: LogChange {
+                    mode: RefLog::AndReference,
+                    force_create_reflog: false,
+                    message: "checkout: moving to main".into(),
+                },
+                expected: PreviousValue::Any,
+                new: gix::refs::Target::Symbolic(
+                    gix::refs::FullName::try_from("refs/heads/main")
+                        .map_err(|e| anyhow::anyhow!("invalid ref name: {e}"))?,
+                ),
+            },
+            name: head,
+            deref: false,
+        }],
+        Some(signature),
+    )?;
+
+    let readme = if description.trim().is_empty() {
+        format!("# {name}\n")
+    } else {
+        format!("# {name}\n\n{description}\n")
+    };
+
+    std::fs::write(path.join("README.md"), &readme).context("failed to write README.md")?;
+
+    let blob = repo.write_object(gix::objs::Blob {
+        data: readme.into_bytes(),
+    })?;
+
+    let tree = repo.write_object(gix::objs::Tree {
+        entries: vec![gix::objs::tree::Entry {
+            mode: gix::objs::tree::EntryKind::Blob.into(),
+            filename: gix::bstr::BString::from("README.md"),
+            oid: blob.into(),
+        }],
+    })?;
+
+    let commit = repo.commit_as(
+        signature,
+        signature,
+        "HEAD",
+        "Initial commit",
+        tree,
+        Vec::<gix::ObjectId>::new(),
+    )?;
+
+    // Populate the index so the fresh repository is clean,
+    // as `git add` and`git commit` would leave it.
+    let mut index = repo.index_from_tree(&tree)?;
+    index.write(gix::index::write::Options::default())?;
+
+    let commit = commit.to_string();
+    if commit.len() != 40 {
+        bail!("unexpected initial commit id: {commit}");
+    }
+
+    Ok(commit)
+}
+
+/// The earliest unique commit of the repository at `repo_path`.
+/// Used as the NIP-34 announcement's `euc` marker.
+///
+/// `None` for a repository without commits.
+pub fn root_commit(repo_path: &Path) -> Result<Option<String>> {
+    let Ok(repo) = gix::open(repo_path) else {
+        return Ok(None);
+    };
+
+    let Ok(head) = repo.head_id() else {
+        // An unborn HEAD with no commits yet has no root commit.
+        return Ok(None);
+    };
+
+    for info in repo
+        .rev_walk([head])
+        .sorting(gix::revision::walk::Sorting::ByCommitTime(
+            gix::traverse::commit::simple::CommitTimeOrder::NewestFirst,
+        ))
+        .all()?
+    {
+        let info = info?;
+        if info.parent_ids().next().is_none() {
+            let id = info.id().to_string();
+            return Ok((id.len() == 40).then_some(id));
+        }
+    }
+
+    Ok(None)
+}
+
+/// Full ref names under `prefix`, sorted lexicographically, like `git for-each-ref`.
+/// `prefix` is a ref namespace like `refs/fork/<owner>/<id>`.
+///
+/// Returns an empty list when nothing matches.
+pub fn refs_with_prefix(repo_path: &Path, prefix: &str) -> Result<Vec<String>> {
+    let pattern = prefix.trim_end_matches('/');
+    let repo = gix::open(repo_path)?;
+    let mut names = Vec::new();
+
+    for reference in repo.references()?.all()? {
+        let reference = reference.map_err(|error| anyhow::anyhow!("{error}"))?;
+        let name = String::from_utf8_lossy(reference.name().as_bstr()).into_owned();
+
+        // Match the pattern itself and everything beneath it, like `git for-each-ref`.
+        let under_pattern = name
+            .strip_prefix(pattern)
+            .is_some_and(|rest| rest.is_empty() || rest.starts_with('/'));
+
+        if under_pattern {
+            names.push(name);
+        }
+    }
+
+    // Sort lexicographically, like `git for-each-ref`.
+    names.sort();
+
+    Ok(names)
+}
+
+/// Delete every ref under `prefix` of the repository at `repo_path`.
+/// `prefix` is a ref namespace like `refs/fork/<owner>/<id>`.
+pub fn delete_refs_with_prefix(repo_path: &Path, prefix: &str) -> Result<()> {
+    use gix::refs::transaction::{Change, PreviousValue, RefEdit, RefLog};
+
+    let refs = refs_with_prefix(repo_path, prefix)?;
+    if refs.is_empty() {
+        return Ok(());
+    }
+
+    let repo = gix::open(repo_path)?;
+    let edits: Vec<RefEdit> = refs
+        .iter()
+        .map(|name| {
+            let full = gix::refs::FullName::try_from(name.as_str())
+                .map_err(|e| anyhow::anyhow!("invalid ref name {name}: {e}"))?;
+            Ok(RefEdit {
+                change: Change::Delete {
+                    expected: PreviousValue::Any,
+                    log: RefLog::AndReference,
+                },
+                name: full,
+                deref: false,
+            })
+        })
+        .collect::<Result<Vec<_>>>()?;
+
+    // Delete all refs with the given prefix.
+    repo.edit_references(edits)?;
+
+    Ok(())
+}
+
+/// Short name of the branch HEAD points to at `workdir`,
+/// `None` when detached or unreadable, like `git branch --show-current`.
+pub fn worktree_current_branch(workdir: &Path) -> Option<String> {
+    let repo = gix::open(workdir).ok()?;
+    let head = repo.head().ok()?;
+    let name = head.referent_name()?;
+    Some(String::from_utf8_lossy(name.shorten()).into_owned())
+}
+
+/// Whether the reference `name` exists in the repository at `workdir`.
+pub fn worktree_ref_exists(workdir: &Path, name: &str) -> bool {
+    let Ok(repo) = gix::open(workdir) else {
+        return false;
+    };
+    repo.find_reference(name).is_ok()
+}
+
+/// Fast-forward local branches that trail their remote-tracking counterpart.
+///
+/// Returns whether any branch moved.
+pub fn fast_forward_branches(workdir: &Path) -> Result<bool> {
+    let repo = gix::open(workdir)?;
+    let current = worktree_current_branch(workdir);
+    let heads = refs_with_prefix(workdir, "refs/heads")?;
+
+    let (signature, mut time_buf) = repository_signature();
+    let signature = signature.to_ref(&mut time_buf);
+
+    let mut moved = false;
+
+    for head in heads {
+        let Some(branch) = head.strip_prefix("refs/heads/") else {
+            continue;
+        };
+
+        let remote = format!("refs/remotes/origin/{branch}");
+        // No remote-tracking counterpart means the remote lacks this branch.
+        let Ok(mut remote_reference) = repo.find_reference(&remote) else {
+            continue;
+        };
+
+        let Ok(mut local_reference) = repo.find_reference(&head) else {
+            continue;
+        };
+
+        let Ok(remote_oid) = remote_reference.peel_to_id() else {
+            continue;
+        };
+
+        let Ok(local_oid) = local_reference.peel_to_id() else {
+            continue;
+        };
+
+        let remote_oid = remote_oid.detach();
+        let local_oid = local_oid.detach();
+
+        if local_oid == remote_oid {
+            continue;
+        }
+
+        // Only fast-forward.
+        // Local-only commits or diverged history must never be rewritten by a refresh.
+        let Ok(base) = repo.merge_base(local_oid, remote_oid) else {
+            continue;
+        };
+
+        if base != local_oid {
+            continue;
+        }
+
+        let full = gix::refs::FullName::try_from(head.as_str())
+            .map_err(|e| anyhow::anyhow!("invalid ref name: {e}"))?;
+
+        let edit = |new: gix::refs::Target| {
+            use gix::refs::transaction::{Change, LogChange, PreviousValue, RefEdit, RefLog};
+            RefEdit {
+                change: Change::Update {
+                    log: LogChange {
+                        mode: RefLog::AndReference,
+                        force_create_reflog: false,
+                        message: format!("merge {remote}: Fast-forward").into(),
+                    },
+                    expected: PreviousValue::ExistingMustMatch(gix::refs::Target::Object(
+                        local_oid,
+                    )),
+                    new,
+                },
+                name: full.clone(),
+                deref: false,
+            }
+        };
+
+        if current.as_deref() == Some(branch) {
+            // Merge so the checked-out worktree follows the branch.
+            // Only proceed on a clean worktree, like `git merge --ff-only`.
+            if worktree_dirty(workdir) {
+                continue;
+            }
+
+            let tree = repo.find_object(remote_oid)?.peel_to_tree()?.id;
+
+            // Check out the remote tree, discarding local changes.
+            force_checkout(&repo, &tree)?;
+
+            // Update the branch reference to point to the remote tree.
+            repo.edit_references_as(
+                [edit(gix::refs::Target::Object(remote_oid))],
+                Some(signature),
+            )?;
+
+            moved = true;
+        } else {
+            // Update the branch reference to point to the remote tree.
+            repo.edit_references_as(
+                [edit(gix::refs::Target::Object(remote_oid))],
+                Some(signature),
+            )?;
+
+            moved = true;
+        }
+    }
+
+    Ok(moved)
+}
+
+/// Short names of local branches, `refs/heads/*`, of `repo`, sorted alphabetically.
+pub fn repo_branches(repo: &gix::Repository) -> Result<Vec<String>> {
+    let mut names = Vec::new();
+    for reference in repo.references()?.local_branches()? {
+        let reference = reference.map_err(|error| anyhow::anyhow!("{error}"))?;
+        names.push(String::from_utf8_lossy(reference.name().shorten()).into_owned());
+    }
+    names.sort();
+    Ok(names)
+}
+
+/// Short names of tags, `refs/tags/*`, of `repo`, sorted alphabetically.
+pub fn repo_tags(repo: &gix::Repository) -> Result<Vec<String>> {
+    let mut names = Vec::new();
+    for reference in repo.references()?.tags()? {
+        let reference = reference.map_err(|error| anyhow::anyhow!("{error}"))?;
+        names.push(String::from_utf8_lossy(reference.name().shorten()).into_owned());
+    }
+    names.sort();
+    Ok(names)
+}
+
+/// Short names of local branches, `refs/heads/*`, sorted alphabetically.
+pub fn worktree_branches(workdir: &Path) -> Result<Vec<String>> {
+    repo_branches(&gix::open(workdir)?)
+}
+
+/// Short name of the branch HEAD points to, or `None` when detached.
+///
+/// Detached after checking out a tag or a commit directly.
+pub fn current_branch(repo: &gix::Repository) -> Result<Option<String>> {
+    let head = repo.head()?;
+    let Some(name) = head.referent_name() else {
+        return Ok(None);
+    };
+    Ok(Some(String::from_utf8_lossy(name.shorten()).into_owned()))
+}
+
+/// Branch, tag and HEAD refs of a repository.
+///
+/// Ready for a NIP-34 kind-30618 repository state announcement.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RepoRefState {
+    /// `(full refname, commit id)` pairs for heads and tags, sorted.
+    pub refs: Vec<(String, String)>,
+    /// Short branch name HEAD points to, or `None` when detached.
+    pub head: Option<String>,
+}
+
+/// Collect the refs of `repo`.
+///
+/// Local branches and tags become `(refname, commit-id)` pairs.
+/// Also reports the branch HEAD points to.
+pub fn repo_ref_state(repo: &gix::Repository) -> Result<RepoRefState> {
+    let mut refs = Vec::new();
+
+    for reference in repo.references()?.local_branches()? {
+        let reference = reference.map_err(|error| anyhow::anyhow!("{error}"))?;
+        refs.push((
+            String::from_utf8_lossy(reference.name().as_bstr()).into_owned(),
+            reference.id().to_string(),
+        ));
+    }
+
+    for reference in repo.references()?.tags()? {
+        let reference = reference.map_err(|error| anyhow::anyhow!("{error}"))?;
+        refs.push((
+            String::from_utf8_lossy(reference.name().as_bstr()).into_owned(),
+            reference.id().to_string(),
+        ));
+    }
+    refs.sort();
+
+    let head = match repo.head() {
+        Ok(head) => head
+            .referent_name()
+            .filter(|name| name.as_bstr().starts_with(b"refs/heads/"))
+            .map(|name| String::from_utf8_lossy(name.shorten()).into_owned()),
+        Err(_) => None,
+    };
+
+    Ok(RepoRefState { refs, head })
+}
+
+/// [`repo_ref_state`] for the repository at `workdir`.
+pub fn worktree_ref_state(workdir: &Path) -> Result<RepoRefState> {
+    repo_ref_state(&gix::open(workdir)?)
+}