"""Process-safe transaction boundary for a local Git checkout.

This module is intentionally not wired into the claim loop yet.  It provides
the repository-local half of HARNESS-WP-0003-T02 while the Activity Core lease
boundary is still under owner review.
"""

from __future__ import annotations

import fcntl
import hashlib
import json
import os
import subprocess
import uuid
from dataclasses import dataclass
from datetime import datetime, timezone
from pathlib import Path
from types import TracebackType
from typing import Any, TextIO


class RepositoryTransactionError(RuntimeError):
    """Base error for repository transaction refusal or setup failure."""


class GitRepositoryError(RepositoryTransactionError):
    """The target cannot provide the required Git repository state."""


class RepositoryBusyError(RepositoryTransactionError):
    """Another process owns the canonical repository lock."""

    def __init__(self, repo_id: str, owner: dict[str, Any] | None = None) -> None:
        self.repo_id = repo_id
        self.owner = owner or {}
        owner_tx = self.owner.get("transaction_id")
        suffix = f" owner_transaction={owner_tx}" if owner_tx else ""
        super().__init__(f"repository is already locked: repo_id={repo_id}{suffix}")


class DirtyRepositoryError(RepositoryTransactionError):
    """An unattended transaction was refused because its baseline is dirty."""

    def __init__(self, baseline: "RepositoryBaseline") -> None:
        self.baseline = baseline
        super().__init__(
            "repository baseline is dirty: "
            f"repo_id={baseline.repo_id} entries={baseline.dirty_entries}"
        )


@dataclass(frozen=True)
class RepositoryBaseline:
    """Exact local facts captured while the canonical repository lock is held."""

    repo_root: Path
    git_common_dir: Path
    repo_id: str
    head: str
    branch: str | None
    clean: bool
    dirty_entries: int
    status_digest: str
    index_diff_digest: str
    worktree_diff_digest: str
    upstream_ref: str | None
    upstream_oid: str | None
    remote_refs: tuple[tuple[str, str], ...]

    @property
    def detached(self) -> bool:
        return self.branch is None

    def evidence(self) -> dict[str, Any]:
        """Return bounded, path-safe baseline evidence for run results."""
        remote_payload = "\n".join(f"{name} {oid}" for name, oid in self.remote_refs)
        return {
            "repo_id": self.repo_id,
            "repo_name": self.repo_root.name,
            "head": self.head,
            "branch": self.branch,
            "detached": self.detached,
            "clean": self.clean,
            "dirty_entries": self.dirty_entries,
            "status_digest": self.status_digest,
            "index_diff_digest": self.index_diff_digest,
            "worktree_diff_digest": self.worktree_diff_digest,
            "upstream_ref": self.upstream_ref,
            "upstream_oid": self.upstream_oid,
            "remote_ref_count": len(self.remote_refs),
            "remote_refs_digest": _digest(remote_payload),
        }


class RepositoryTransaction:
    """Hold one canonical Git repository lock and capture its baseline.

    Lock files live outside the checkout and are keyed by the resolved Git
    common directory.  This makes aliases and linked worktrees for one local
    repository contend on the same lock while unrelated repositories proceed
    independently.
    """

    def __init__(
        self,
        repo: Path,
        *,
        correlation_id: str = "",
        state_dir: Path | None = None,
        require_clean: bool = True,
    ) -> None:
        self.repo = Path(repo).expanduser().resolve()
        self.correlation_id = _bounded_text(correlation_id, 200)
        self.state_dir = Path(state_dir).expanduser().resolve() if state_dir else _state_dir()
        self.require_clean = require_clean
        self.transaction_id = uuid.uuid4().hex
        self.baseline: RepositoryBaseline | None = None
        self.lock_path: Path | None = None
        self._lock_file: TextIO | None = None

    @property
    def locked(self) -> bool:
        return self._lock_file is not None

    def __enter__(self) -> "RepositoryTransaction":
        if self.locked:
            raise RepositoryTransactionError("repository transaction is already entered")

        repo_root, common_dir, repo_id = _canonical_repository(self.repo)
        locks_dir = self.state_dir / "repository-locks"
        locks_dir.mkdir(parents=True, exist_ok=True)
        self.lock_path = locks_dir / f"{repo_id}.lock"
        lock_file = _open_private_lock(self.lock_path)
        try:
            fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
        except BlockingIOError as exc:
            owner = _read_lock_metadata(lock_file)
            lock_file.close()
            raise RepositoryBusyError(repo_id, owner) from exc

        self._lock_file = lock_file
        self._write_metadata(
            {
                "transaction_id": self.transaction_id,
                "repo_id": repo_id,
                "repo_name": repo_root.name,
                "pid": os.getpid(),
                "correlation_id": self.correlation_id,
                "acquired_at": _now(),
                "state": "capturing-baseline",
            }
        )
        try:
            baseline = _capture_baseline(repo_root, common_dir, repo_id)
            self.baseline = baseline
            self._write_metadata(
                {
                    "transaction_id": self.transaction_id,
                    "repo_id": repo_id,
                    "repo_name": repo_root.name,
                    "pid": os.getpid(),
                    "correlation_id": self.correlation_id,
                    "acquired_at": _now(),
                    "state": "active",
                    "baseline": baseline.evidence(),
                }
            )
            if self.require_clean and not baseline.clean:
                raise DirtyRepositoryError(baseline)
            return self
        except BaseException:
            self.release()
            raise

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        self.release()

    def release(self) -> None:
        """Release the OS lock without deleting checkout or lock-state data."""
        lock_file = self._lock_file
        if lock_file is None:
            return
        try:
            self._write_metadata(
                {
                    "transaction_id": self.transaction_id,
                    "repo_id": self.baseline.repo_id if self.baseline else None,
                    "repo_name": self.baseline.repo_root.name if self.baseline else self.repo.name,
                    "pid": os.getpid(),
                    "correlation_id": self.correlation_id,
                    "released_at": _now(),
                    "state": "released",
                }
            )
        finally:
            try:
                fcntl.flock(lock_file.fileno(), fcntl.LOCK_UN)
            finally:
                lock_file.close()
                self._lock_file = None

    def evidence(self) -> dict[str, Any]:
        """Return the bounded transaction and baseline result envelope."""
        if self.baseline is None:
            raise RepositoryTransactionError("repository baseline is not captured")
        return {
            "transaction_id": self.transaction_id,
            "correlation_id": self.correlation_id,
            "baseline": self.baseline.evidence(),
        }

    def _write_metadata(self, value: dict[str, Any]) -> None:
        if self._lock_file is None:
            return
        self._lock_file.seek(0)
        self._lock_file.truncate()
        json.dump(value, self._lock_file, sort_keys=True, separators=(",", ":"))
        self._lock_file.write("\n")
        self._lock_file.flush()
        os.fsync(self._lock_file.fileno())


def _state_dir() -> Path:
    explicit = os.environ.get("REIN_AHARNESS_STATE_DIR", "").strip()
    if explicit:
        return Path(explicit).expanduser().resolve()
    xdg = os.environ.get("XDG_STATE_HOME", "").strip()
    if xdg:
        return (Path(xdg).expanduser() / "rein-aharness").resolve()
    return (Path.home() / ".local" / "state" / "rein-aharness").resolve()


def _canonical_repository(repo: Path) -> tuple[Path, Path, str]:
    root_result = _run_git(repo, "rev-parse", "--show-toplevel")
    if root_result.returncode != 0:
        raise GitRepositoryError(f"not a Git working tree: {repo}")
    repo_root = Path(root_result.stdout.strip()).resolve()

    common_result = _run_git(repo_root, "rev-parse", "--git-common-dir")
    if common_result.returncode != 0 or not common_result.stdout.strip():
        raise GitRepositoryError(f"cannot resolve Git common directory: {repo_root}")
    raw_common = Path(common_result.stdout.strip())
    common_dir = (repo_root / raw_common).resolve() if not raw_common.is_absolute() else raw_common.resolve()
    repo_id = hashlib.sha256(str(common_dir).encode("utf-8")).hexdigest()[:32]
    return repo_root, common_dir, repo_id


def _capture_baseline(repo_root: Path, common_dir: Path, repo_id: str) -> RepositoryBaseline:
    head = _git(repo_root, "rev-parse", "--verify", "HEAD")
    branch_result = _run_git(repo_root, "symbolic-ref", "--quiet", "--short", "HEAD")
    if branch_result.returncode not in (0, 1):
        raise GitRepositoryError(
            f"cannot resolve branch state: {branch_result.stderr.strip()[:200]}"
        )
    branch = branch_result.stdout.strip() or None

    status = _git(repo_root, "status", "--porcelain=v2", "--untracked-files=all")
    status_lines = tuple(line for line in status.splitlines() if line)
    index_diff = _git(repo_root, "diff", "--cached", "--binary", "--no-ext-diff")
    worktree_diff = _git(repo_root, "diff", "--binary", "--no-ext-diff")

    remote_lines = _git(
        repo_root,
        "for-each-ref",
        "--format=%(refname) %(objectname)",
        "refs/remotes",
    )
    remote_refs: list[tuple[str, str]] = []
    for line in remote_lines.splitlines():
        name, separator, oid = line.partition(" ")
        if separator and name and oid:
            remote_refs.append((name, oid))

    upstream_result = _run_git(
        repo_root,
        "rev-parse",
        "--abbrev-ref",
        "--symbolic-full-name",
        "@{upstream}",
    )
    upstream_ref = upstream_result.stdout.strip() if upstream_result.returncode == 0 else None
    upstream_oid = _git(repo_root, "rev-parse", upstream_ref) if upstream_ref else None

    return RepositoryBaseline(
        repo_root=repo_root,
        git_common_dir=common_dir,
        repo_id=repo_id,
        head=head,
        branch=branch,
        clean=not status_lines,
        dirty_entries=len(status_lines),
        status_digest=_digest(status),
        index_diff_digest=_digest(index_diff),
        worktree_diff_digest=_digest(worktree_diff),
        upstream_ref=upstream_ref,
        upstream_oid=upstream_oid,
        remote_refs=tuple(remote_refs),
    )


def _run_git(repo: Path, *args: str) -> subprocess.CompletedProcess[str]:
    try:
        return subprocess.run(
            ["git", "-C", str(repo), *args],
            capture_output=True,
            text=True,
            timeout=60,
            check=False,
        )
    except (OSError, subprocess.TimeoutExpired) as exc:
        raise GitRepositoryError(f"git {' '.join(args)} failed: {exc}") from exc


def _git(repo: Path, *args: str) -> str:
    result = _run_git(repo, *args)
    if result.returncode != 0:
        reason = (result.stderr or result.stdout or "unknown Git error").strip()[:300]
        raise GitRepositoryError(f"git {' '.join(args)} failed: {reason}")
    return result.stdout.strip()


def _read_lock_metadata(lock_file: TextIO) -> dict[str, Any] | None:
    try:
        lock_file.seek(0)
        raw = lock_file.read(4096)
        value = json.loads(raw) if raw.strip() else None
    except (OSError, ValueError):
        return None
    return value if isinstance(value, dict) else None


def _open_private_lock(path: Path) -> TextIO:
    fd = os.open(path, os.O_RDWR | os.O_CREAT, 0o600)
    try:
        os.fchmod(fd, 0o600)
        return os.fdopen(fd, "r+", encoding="utf-8")
    except BaseException:
        os.close(fd)
        raise


def _digest(value: str) -> str:
    return hashlib.sha256(value.encode("utf-8", errors="replace")).hexdigest()


def _bounded_text(value: str, limit: int) -> str:
    cleaned = " ".join(str(value).split())
    return cleaned[:limit]


def _now() -> str:
    return datetime.now(timezone.utc).isoformat()