//! Git bridge (spec §23), export side: each state the current bookmark

//! passed through becomes a Git commit through `git fast-import`, with the

//! state's full tree and the previous state's commit as parent. A state

//! that added exactly one change carries that change's message, author,

//! and `Change-Id`/`Oxy-Hash` trailers; every commit carries `Oxy-State`.

//!

//! Marks make re-exports incremental: `.oxy/git/<target>/git-marks` is

//! git's own marks file and `oxy-marks` maps state refs to marks.

use super::*;

use std::process::{Command, Stdio};

#[derive(Debug, Clone, Default, PartialEq, Eq)]

pub struct GitImportReport {

    pub commits: usize,

    pub merges: usize,

    /// Gitlink entries imported as subrepo nodes with Git pins.

    pub submodules: usize,

    pub heads: usize,

}

/// A running `git cat-file --batch`, for reading many blobs cheaply.

struct CatFile {

    child: std::process::Child,

    stdin: std::process::ChildStdin,

    stdout: std::io::BufReader<std::process::ChildStdout>,

}

impl CatFile {

    fn start(git_dir: &Path) -> Result<CatFile> {

        let mut child = Command::new("git")

            .arg("-C")

            .arg(git_dir)

            .args(["cat-file", "--batch"])

            .stdin(Stdio::piped())

            .stdout(Stdio::piped())

            .stderr(Stdio::null())

            .spawn()

            .map_err(|e| RepoError::Msg(format!("running git cat-file: {e}")))?;

        let stdin = child.stdin.take().unwrap();

        let stdout = std::io::BufReader::new(child.stdout.take().unwrap());

        Ok(CatFile { child, stdin, stdout })

    }

    fn read(&mut self, sha: &str) -> Result<Vec<u8>> {

        use std::io::{BufRead, Read};

        writeln!(self.stdin, "{sha}")?;

        self.stdin.flush()?;

        let mut header = String::new();

        self.stdout.read_line(&mut header)?;

        let parts: Vec<&str> = header.trim_end().split(' ').collect();

        if parts.len() != 3 {

            return fail(format!("git cat-file: object {sha} not found"));

        }

        let size: usize = parts[2].parse().map_err(|_| RepoError::Msg("git cat-file: bad size".into()))?;

        let mut body = vec![0u8; size];

        self.stdout.read_exact(&mut body)?;

        let mut nl = [0u8; 1];

        self.stdout.read_exact(&mut nl)?;

        Ok(body)

    }

}

impl Drop for CatFile {

    fn drop(&mut self) {

        let _ = self.child.kill();

        let _ = self.child.wait();

    }

}

/// One commit as `git log` describes it.

struct GitCommit {

    sha: String,

    parents: Vec<String>,

    author_secs: u64,

    author: String,

    message: String,

}

fn list_commits(git_dir: &Path, branch: &str) -> Result<Vec<GitCommit>> {

    let out = Command::new("git")

        .arg("-C")

        .arg(git_dir)

        .args(["log", "--reverse", "--topo-order", "--format=%H%x00%P%x00%at%x00%an <%ae>%x00%B%x1e", branch])

        .output()

        .map_err(|e| RepoError::Msg(format!("running git log: {e}")))?;

    if !out.status.success() {

        return fail(format!("git log {branch} failed: {}", String::from_utf8_lossy(&out.stderr).trim()));

    }

    let text = String::from_utf8_lossy(&out.stdout);

    let mut commits = Vec::new();

    for record in text.split('\x1e') {

        let record = record.trim_start_matches('\n');

        if record.trim().is_empty() {

            continue;

        }

        let f: Vec<&str> = record.splitn(5, '\0').collect();

        if f.len() != 5 {

            return fail("unexpected git log record");

        }

        commits.push(GitCommit {

            sha: f[0].to_string(),

            parents: f[1].split_whitespace().map(str::to_string).collect(),

            author_secs: f[2].parse().unwrap_or(0),

            author: f[3].to_string(),

            message: f[4].trim_end().to_string(),

        });

    }

    Ok(commits)

}

/// `path → (mode, blob sha)` for a commit's tree.

fn list_tree(git_dir: &Path, sha: &str) -> Result<BTreeMap<String, (String, String)>> {

    let text = git(git_dir, &["ls-tree", "-r", "-z", sha])?;

    let mut out = BTreeMap::new();

    for entry in text.split('\0') {

        if entry.is_empty() {

            continue;

        }

        let Some((meta, path)) = entry.split_once('\t') else { continue };

        let m: Vec<&str> = meta.split(' ').collect();

        if m.len() == 3 {

            out.insert(path.to_string(), (m[0].to_string(), m[2].to_string()));

        }

    }

    Ok(out)

}

/// The ChangeId for a Git commit: its `Change-Id` trailer if it has a

/// 32-hex one, else BLAKE3-128 of the commit hash (spec §23).

fn change_id_for(sha: &str, message: &str) -> ChangeId {

    for line in message.lines().rev() {

        if let Some(v) = line.strip_prefix("Change-Id:") {

            if let Some(id) = ChangeId::from_hex(v.trim()) {

                return id;

            }

        }

    }

    let h = blake3::hash(sha.as_bytes());

    ChangeId(h.as_bytes()[..16].try_into().unwrap())

}

/// Git commits with a known Oxygen counterpart.

struct GitKnown {

    /// Imported commit → its change.

    imported: HashMap<String, ChangeHash>,

    /// Exported commit (or a fetched tip) → the bookmark state it equals.

    exported: HashMap<String, ObjectRef>,

}

#[derive(Debug, Clone, Default, PartialEq, Eq)]

pub struct GitExportReport {

    pub exported: usize,

    pub skipped: usize,

    /// Subrepo nodes with Oxygen pins, which Git cannot represent.

    pub skipped_subrepos: usize,

    pub branch: String,

    pub heads: usize,

}

fn git(dir: &Path, args: &[&str]) -> Result<String> {

    let out = Command::new("git").arg("-C").arg(dir).args(args).output().map_err(|e| RepoError::Msg(format!("running git: {e}")))?;

    if !out.status.success() {

        return fail(format!("git {} failed: {}", args.join(" "), String::from_utf8_lossy(&out.stderr).trim()));

    }

    Ok(String::from_utf8_lossy(&out.stdout).trim().to_string())

}

impl Repo {

    fn git_marks_dir(&self, git_dir: &Path) -> Result<PathBuf> {

        let canonical = git_dir.canonicalize().unwrap_or_else(|_| git_dir.to_path_buf());

        let key = hash_object(ObjectType::Chunk, canonical.to_string_lossy().as_bytes()).short(16);

        let dir = self.oxy.join("git").join(key);

        fs::create_dir_all(&dir)?;

        Ok(dir)

    }

    /// `state ref → Git commit sha` for bookmark states that equal a Git

    /// commit's tree (recorded by import and fetch).

    fn read_git_states(path: &Path) -> Result<BTreeMap<ObjectRef, String>> {

        let mut out = BTreeMap::new();

        if let Ok(text) = fs::read_to_string(path) {

            for line in text.lines() {

                if let Some((h, sha)) = line.split_once(' ') {

                    if let Some(h) = ObjectRef::from_hex(h) {

                        out.insert(h, sha.trim().to_string());

                    }

                }

            }

        }

        Ok(out)

    }

    fn record_git_state(&self, git_dir: &Path, state: &ObjectRef, sha: &str) -> Result<()> {

        let path = self.git_marks_dir(git_dir)?.join("git-states");

        let mut states = Self::read_git_states(&path)?;

        states.insert(*state, sha.to_string());

        let text: String = states.iter().map(|(h, s)| format!("{} {s}\n", h.to_hex())).collect();

        write_atomic(&path, text.as_bytes())

    }

    /// The bare mirror this repository keeps for the Git remote `url`.

    fn git_mirror(&self, url: &str) -> Result<PathBuf> {

        let key = hash_object(ObjectType::Chunk, url.as_bytes()).short(16);

        let dir = self.oxy.join("git").join(key).join("mirror.git");

        if !dir.join("HEAD").exists() {

            fs::create_dir_all(&dir)?;

            git(&dir, &["init", "--bare", "-q"])?;

        }

        Ok(dir)

    }

    /// Git commits already imported into the bookmark, by sha.

    fn imported_commits(&self) -> Result<HashMap<String, ChangeHash>> {

        let mut map = HashMap::new();

        for e in self.log()? {

            if e.is_working_copy {

                continue;

            }

            if let Some(sha) = e.change.message.lines().rev().find_map(|l| l.strip_prefix("Git-Commit: ")) {

                map.insert(sha.trim().to_string(), e.hash);

            }

        }

        Ok(map)

    }

    /// Bring the mirror's `branch` up to date with the Git remote `url`.

    /// A remote without that branch yet leaves the mirror as it is.

    fn git_mirror_fetch(&self, mirror: &Path, url: &str, branch: &str) -> Result<()> {

        let spec = format!("+refs/heads/{branch}:refs/heads/{branch}");

        match git(mirror, &["fetch", "-q", url, &spec]) {

            Ok(_) => Ok(()),

            Err(e) => {

                let ls = git(mirror, &["ls-remote", "--heads", url, branch]).unwrap_or_default();

                if ls.trim().is_empty() { Ok(()) } else { Err(e) }

            }

        }

    }

    /// Fetch `branch` of the Git repository at `url` (a path or a Git URL)

    /// through a mirror and import the commits not yet in the bookmark

    /// (spec §23). Works on a repository that already has history: the

    /// new changes join the bookmark like a pull.

    pub fn git_fetch(&self, url: &str, branch: &str) -> Result<GitImportReport> {

        let mirror = self.git_mirror(url)?;

        self.git_mirror_fetch(&mirror, url, branch)?;

        if git(&mirror, &["rev-parse", "--verify", "-q", &format!("refs/heads/{branch}")]).is_err() {

            return fail(format!("{url} has no branch {branch:?}"));

        }

        self.import_git_commits(&mirror, branch, &format!("oxy git fetch {url} {branch}"))

    }

    /// Export the bookmark to `branch` of the Git repository at `url`

    /// through the mirror and push it. The remote's tip must already have

    /// been fetched (`git_fetch`), so the push fast-forwards.

    pub fn git_push(&self, url: &str, branch: &str) -> Result<GitExportReport> {

        let mirror = self.git_mirror(url)?;

        self.git_mirror_fetch(&mirror, url, branch)?;

        if let Ok(tip) = git(&mirror, &["rev-parse", "--verify", "-q", &format!("refs/heads/{branch}")]) {

            let known = self.git_known(&mirror)?;

            if !known.imported.contains_key(&tip) && !known.exported.contains_key(&tip) {

                return fail(format!("{url} {branch} has commits not yet fetched; run `oxy git fetch {url}` first"));

            }

        }

        let report = self.git_export_as(&mirror, branch)?;

        let spec = format!("refs/heads/{branch}:refs/heads/{branch}");

        git(&mirror, &["push", "-q", url, &spec])?;

        Ok(report)

    }

    fn read_oxy_marks(path: &Path) -> Result<BTreeMap<ObjectRef, u64>> {

        let mut out = BTreeMap::new();

        if let Ok(text) = fs::read_to_string(path) {

            for line in text.lines() {

                if let Some((h, m)) = line.split_once(' ') {

                    if let (Some(h), Ok(m)) = (ObjectRef::from_hex(h), m.parse()) {

                        out.insert(h, m);

                    }

                }

            }

        }

        Ok(out)

    }

    /// Export the current bookmark to the Git repository at `git_dir`,

    /// creating a bare one if nothing is there. Each state the bookmark

    /// passed through (per the operation log) becomes one commit whose tree

    /// is that state, so the Git branch is a linear history of full trees.

    pub fn git_export(&self, git_dir: &Path) -> Result<GitExportReport> {

        let bookmark = self.config.bookmark.clone();

        self.git_export_as(git_dir, &bookmark)

    }

    /// `git_export` to the Git branch `branch`. A state that came from a

    /// Git commit (`oxy git fetch`) is not re-exported: later states chain

    /// onto that commit, so a push back to the Git remote fast-forwards.

    pub fn git_export_as(&self, git_dir: &Path, branch: &str) -> Result<GitExportReport> {

        if !git_dir.join("HEAD").exists() && !git_dir.join(".git").exists() {

            fs::create_dir_all(git_dir)?;

            git(git_dir, &["init", "--bare", "-q"])?;

        }

        let marks_dir = self.git_marks_dir(git_dir)?;

        let git_marks = marks_dir.join("git-marks");

        let oxy_marks_path = marks_dir.join("oxy-marks");

        let mut marks = Self::read_oxy_marks(&oxy_marks_path)?;

        let git_states = Self::read_git_states(&marks_dir.join("git-states"))?;

        let mut next_mark = marks.values().copied().max().unwrap_or(0) + 1;

        let bookmark = self.config.bookmark.clone();

        let mut stream: Vec<u8> = Vec::new();

        let mut report = GitExportReport { branch: branch.to_string(), heads: self.bookmark_heads()?.len(), ..Default::default() };

        // States along the bookmark, oldest first, skipping unchanged and pruned ones.

        let mut ops = self.op_log()?;

        ops.reverse();

        let mut prev: Option<(ObjectRef, Vec<ChangeHash>)> = None;

        // The fast-import parent of the next commit: `:mark` or a commit sha.

        let mut last_parent: Option<String> = None;

        for (_, op) in &ops {

            let Some(state_ref) = op.view.bookmarks.get(&bookmark).copied() else { continue };

            if prev.as_ref().is_some_and(|(p, _)| *p == state_ref) {

                continue;

            }

            let Ok(state) = self.store.get_state(&state_ref) else { continue };

            if state.heads.is_empty() {

                prev = Some((state_ref, vec![]));

                continue;

            }

            if let Some(sha) = git_states.get(&state_ref) {

                report.skipped += 1;

                last_parent = Some(sha.clone());

                prev = Some((state_ref, state.heads.clone()));

                continue;

            }

            if let Some(m) = marks.get(&state_ref) {

                report.skipped += 1;

                last_parent = Some(format!(":{m}"));

                prev = Some((state_ref, state.heads.clone()));

                continue;

            }

            let prev_heads = prev.as_ref().map(|(_, h)| h.clone()).unwrap_or_default();

            let added = self.negotiate(&prev_heads, &state.heads).unwrap_or_default();

            let loaded = self.load_state(&state.heads)?;

            let snapshot = loaded.materialize();

            let (author, secs, mut message) = match added.as_slice() {

                [h] => {

                    let c = self.store.get_change(h)?;

                    let mut m = c.message.clone();

                    if !m.ends_with('\n') {

                        m.push('\n');

                    }

                    m.push_str(&format!("\nChange-Id: {}\nOxy-Hash: {}\n", c.change_id.to_hex(), h.to_hex()));

                    (self.git_author(&c), c.hlc.wall_ms / 1000, m)

                }

                [] => ("oxy <oxy@localhost>".to_string(), op.hlc.wall_ms / 1000, format!("oxy: {}\n\n", op.command)),

                many => {

                    let mut m = format!("oxy: {} ({} changes)\n\n", op.command, many.len());

                    for h in many {

                        let c = self.store.get_change(h)?;

                        m.push_str(&format!("- {} {}\n", c.change_id.short(8), c.message.lines().next().unwrap_or("")));

                    }

                    m.push_str(&format!("\nOxy-Changes: {}\n", many.iter().map(|h| h.to_hex()).collect::<Vec<_>>().join(" ")));

                    ("oxy <oxy@localhost>".to_string(), op.hlc.wall_ms / 1000, m)

                }

            };

            message.push_str(&format!("Oxy-State: {}\n", state_ref.to_hex()));

            if snapshot.is_conflicted() {

                message.push_str("Oxy-Conflicted: true\n");

            }

            let mark = next_mark;

            next_mark += 1;

            let parents: Vec<String> = last_parent.clone().into_iter().collect();

            self.write_commit(&mut stream, "refs/oxy/export", mark, &author, secs, &message, &parents, &snapshot)?;

            marks.insert(state_ref, mark);

            last_parent = Some(format!(":{mark}"));

            prev = Some((state_ref, state.heads.clone()));

            report.exported += 1;

        }

        if let Some(p) = &last_parent {

            stream.extend_from_slice(format!("reset refs/heads/{branch}\nfrom {p}\n\n").as_bytes());

        }

        // Tags: a tag whose state was exported as a bookmark state points at

        // that commit; otherwise its state gets a commit of its own.

        for t in self.tags()? {

            let target = match (git_states.get(&t.state), marks.get(&t.state)) {

                (Some(sha), _) => sha.clone(),

                (None, Some(m)) => format!(":{m}"),

                (None, None) => {

                    let loaded = self.load_state(&t.heads)?;

                    let snapshot = loaded.materialize();

                    let mark = next_mark;

                    next_mark += 1;

                    let message = format!("oxy: tag {}\n\n{}Oxy-State: {}\n", t.name, if t.message.is_empty() { String::new() } else { format!("{}\n\n", t.message) }, t.state.to_hex());

                    self.write_commit(&mut stream, "refs/oxy/export", mark, "oxy <oxy@localhost>", Hlc::now().wall_ms / 1000, &message, &[], &snapshot)?;

                    marks.insert(t.state, mark);

                    report.exported += 1;

                    format!(":{mark}")

                }

            };

            stream.extend_from_slice(format!("reset refs/tags/{}\nfrom {target}\n\n", t.name).as_bytes());

        }

        stream.extend_from_slice(b"done\n");

        let mut cmd = Command::new("git");

        // `--force`: the scratch ref may jump between unrelated states.

        cmd.arg("-C").arg(git_dir).args(["fast-import", "--quiet", "--done", "--force"]).arg(format!("--export-marks={}", git_marks.display()));

        if git_marks.exists() {

            cmd.arg(format!("--import-marks={}", git_marks.display()));