//! 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,

    pub skipped_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())

}

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

pub struct GitExportReport {

    pub exported: usize,

    pub skipped: 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)

    }

    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> {

        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 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: bookmark.clone(), 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;

        let mut last_mark: Option<u64> = 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(m) = marks.get(&state_ref) {

                report.skipped += 1;

                last_mark = Some(*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<u64> = last_mark.into_iter().collect();

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

            marks.insert(state_ref, mark);

            last_mark = Some(mark);

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

            report.exported += 1;

        }

        match last_mark {

            Some(m) => stream.extend_from_slice(format!("reset refs/heads/{bookmark}\nfrom :{m}\n\ndone\n").as_bytes()),

            None => 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()));

        }

        let mut child = cmd.stdin(Stdio::piped()).stdout(Stdio::null()).stderr(Stdio::piped()).spawn().map_err(|e| RepoError::Msg(format!("running git fast-import: {e}")))?;

        child.stdin.take().unwrap().write_all(&stream)?;

        let out = child.wait_with_output()?;

        if !out.status.success() {

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

        }

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

        write_atomic(&oxy_marks_path, text.as_bytes())?;

        let _ = git(git_dir, &["update-ref", "-d", "refs/oxy/export"]);

        Ok(report)

    }

    /// Import branch `branch` of the Git repository at `git_dir` into this

    /// (empty) repository's bookmark (spec §23): one change per commit, its

    /// edits the difference between the union of its parents' states and its

    /// tree, so merge commits become resolutions. Submodules are skipped.

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

        if !self.bookmark_heads()?.is_empty() {

            return fail("git import needs an empty bookmark; import into a fresh repository");

        }

        let commits = list_commits(git_dir, branch)?;

        let mut cat = CatFile::start(git_dir)?;

        let mut report = GitImportReport::default();

        let mut change_of: HashMap<String, ChangeHash> = HashMap::new();

        // The state after the most recently imported commit, reused when the

        // next commit's first parent is that commit.

        let mut last: Option<(String, State)> = None;

        let mut blob_cache: HashMap<String, Vec<u8>> = HashMap::new();

        let mut cache_bytes: usize = 0;

        for gc in &commits {

            // Base: union of every parent's state.

            let mut base = match (&gc.parents.first(), &last) {

                (Some(p1), Some((sha, st))) if *p1 == sha => st.clone(),

                (Some(p1), _) => self.git_ancestor_state(git_dir, &[p1.as_str()], &change_of)?,

                (None, _) => State::new(),

            };

            if gc.parents.len() > 1 {

                report.merges += 1;

                let mut args: Vec<String> = gc.parents[1..].to_vec();

                args.push(format!("^{}", gc.parents[0]));

                let extra = git(git_dir, &["rev-list".to_string()].iter().map(String::as_str).chain(args.iter().map(String::as_str)).collect::<Vec<_>>())?;

                for sha in extra.lines() {

                    if let Some(h) = change_of.get(sha) {

                        base.add_unchecked(self.store.get_change(h)?);

                    }

                }

            }

            let base_snapshot = base.materialize();

            // The commit's tree as in-memory entries.

            let mut entries: BTreeMap<String, FsEntry> = BTreeMap::new();

            for (path, (mode, sha)) in list_tree(git_dir, &gc.sha)? {

                let (kind, exec) = match mode.as_str() {

                    "100644" | "100664" => (NodeKind::File, false),

                    "100755" => (NodeKind::File, true),

                    "120000" => (NodeKind::Symlink, false),

                    "160000" => {

                        report.skipped_submodules += 1;

                        continue;

                    }

                    _ => continue,

                };

                let content = match blob_cache.get(&sha) {

                    Some(c) => c.clone(),

                    None => {

                        let c = cat.read(&sha)?;

                        if cache_bytes + c.len() > 256 * 1024 * 1024 {

                            blob_cache.clear();

                            cache_bytes = 0;

                        }

                        cache_bytes += c.len();

                        blob_cache.insert(sha.clone(), c.clone());

                        c

                    }

                };

                entries.insert(path, FsEntry { kind, exec, content });

            }

            let built = self.build_from_entries(&base, &base_snapshot, HashMap::new(), &entries)?;

            let mut deps: BTreeSet<ChangeHash> = built.contributors.iter().copied().collect();

            let mut message = gc.message.clone();

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

                message.push('\n');

            }

            message.push_str(&format!("\nGit-Commit: {}\nGit-Author: {}\n", gc.sha, gc.author));

            let mut change = Change {

                change_id: change_id_for(&gc.sha, &gc.message),

                deps: vec![],

                author: ObjectRef::ZERO,

                hlc: Hlc { wall_ms: gc.author_secs * 1000, logical: 0 },

                message,

                tree_ops: built.tree_ops,

                edits: built.edits,

                kind: if built.resolves { ChangeKind::Resolution } else { ChangeKind::Normal },

            };

            deps.extend(referenced_changes(&change, &base));

            change.deps = deps.into_iter().collect();

            change.normalize();

            let hash = self.store.put_change(&change)?;

            base.add_unchecked(change);

            change_of.insert(gc.sha.clone(), hash);

            last = Some((gc.sha.clone(), base));

            report.commits += 1;

        }

        // The bookmark: heads of the tip's state; the working copy follows.

        let Some((_, tip_state)) = last else { return Ok(report) };

        let heads = tip_state.heads();

        report.heads = heads.len();

        let (op_ref, op) = self.head_op()?;

        let mut view = op.view.clone();

        view.bookmarks.insert(self.config.bookmark.clone(), self.store.put_state(&StateObject::new(heads.clone()))?);

        self.record_op(&[op_ref], &format!("oxy git import {} {branch}", git_dir.display()), view)?;

        self.checkout(&heads, true, "oxy git import (checkout)")?;

        Ok(report)

    }

    /// The state holding the changes of every Git ancestor of `shas`.

    fn git_ancestor_state(&self, git_dir: &Path, shas: &[&str], change_of: &HashMap<String, ChangeHash>) -> Result<State> {

        let mut args = vec!["rev-list"];

        args.extend(shas);

        let out = git(git_dir, &args)?;

        let mut st = State::new();

        for sha in out.lines() {

            if let Some(h) = change_of.get(sha) {

                st.add_unchecked(self.store.get_change(h)?);

            }

        }

        Ok(st)

    }