"""Git worktree + branch management for batch isolation.

Each batch × track combination gets its own git worktree so that:
  - Track A and Track B never share filesystem state.
  - Build directories are fully independent.
  - Every successful file migration is committed immediately to its branch.
"""

from __future__ import annotations

import subprocess
from pathlib import Path


# ---------------------------------------------------------------------------
# Low-level helper
# ---------------------------------------------------------------------------

def _git(args: list[str], cwd: Path | None = None) -> tuple[int, str, str]:
    result = subprocess.run(
        ["git"] + args,
        capture_output=True,
        text=True,
        cwd=str(cwd) if cwd else None,
    )
    return result.returncode, result.stdout.strip(), result.stderr.strip()


# ---------------------------------------------------------------------------
# Branch / worktree lifecycle
# ---------------------------------------------------------------------------

def branch_name(batch_id: str, track_id: str) -> str:
    """Canonical branch name: ``migration/<batch_id>/<track_id>``."""
    return f"migration/{batch_id}/{track_id}"


def setup_worktree(
    batch_id: str,
    track_id: str,
    repo_root: Path,
    workspace_root: Path,
) -> Path:
    """Ensure a git worktree exists for *batch_id* × *track_id*.

    Creates the branch (from HEAD) if it does not yet exist.
    Returns the worktree path.
    """
    branch = branch_name(batch_id, track_id)
    worktree_path = workspace_root / batch_id / track_id

    # Create the branch if needed.
    rc, _, _ = _git(["rev-parse", "--verify", branch], cwd=repo_root)
    if rc != 0:
        _git(["branch", branch], cwd=repo_root)

    # Remove stale worktree entry (if the directory was deleted manually).
    _git(["worktree", "prune"], cwd=repo_root)

    # Check whether the worktree is already registered.
    _, wt_list, _ = _git(["worktree", "list", "--porcelain"], cwd=repo_root)
    if str(worktree_path) in wt_list:
        return worktree_path

    worktree_path.parent.mkdir(parents=True, exist_ok=True)
    rc, out, err = _git(
        ["worktree", "add", str(worktree_path), branch],
        cwd=repo_root,
    )
    if rc != 0:
        raise RuntimeError(
            f"git worktree add failed for {worktree_path}: {err}"
        )
    return worktree_path


def teardown_worktree(
    batch_id: str,
    track_id: str,
    repo_root: Path,
    workspace_root: Path,
) -> None:
    """Remove the worktree (but keep the branch)."""
    worktree_path = workspace_root / batch_id / track_id
    _git(["worktree", "remove", "--force", str(worktree_path)], cwd=repo_root)
    _git(["worktree", "prune"], cwd=repo_root)


# ---------------------------------------------------------------------------
# Per-file commit helpers
# ---------------------------------------------------------------------------

def commit_migrated_file(
    file_path_in_worktree: Path,
    worktree_path: Path,
    track_id: str,
) -> None:
    """Stage and commit a single successfully migrated file."""
    _git(["add", str(file_path_in_worktree)], cwd=worktree_path)
    rel = file_path_in_worktree.relative_to(worktree_path)
    _git(
        ["commit", "-m", f"migrate({track_id}): {rel}"],
        cwd=worktree_path,
    )


def commit_generated_tests(
    tests_dir: Path,
    worktree_path: Path,
    track_id: str,
    test_prefix: str,
) -> None:
    """Stage and commit generated test files and their CMakeLists entry."""
    _git(["add", str(tests_dir)], cwd=worktree_path)
    _git(
        ["commit", "-m", f"test({track_id}): generated tests for {test_prefix}"],
        cwd=worktree_path,
    )


def commit_batch_summary(
    worktree_path: Path,
    track_id: str,
    batch_id: str,
) -> None:
    """Final commit for a batch (quarantine files, reports, etc.)."""
    _git(["add", "-A"], cwd=worktree_path)
    rc, _, _ = _git(
        ["diff", "--cached", "--quiet"], cwd=worktree_path
    )
    if rc != 0:   # there are staged changes
        _git(
            ["commit", "-m", f"batch({track_id}): finalise {batch_id}"],
            cwd=worktree_path,
        )