#!/usr/bin/env python3
"""Canonical Atlas project and Git-ref policy for distributed execution."""

from __future__ import annotations

import json
import os
import re
import stat
import subprocess
from pathlib import Path
from typing import Any


DATA_ROOT = Path(os.environ.get("HERMES_HOME", "/opt/data"))
PROJECT_ROOT = DATA_ROOT / "workspace/projects"
BOARD_ROOT = DATA_ROOT / "kanban/boards"
ATLAS_REPO = re.compile(
    r"https://scm\.bstein\.dev/titan/(?P<repo>[A-Za-z0-9][A-Za-z0-9_.-]{0,99})\.git\Z"
)
SAFE_PREFIXES = frozenset(
    {"feature", "fix", "chore", "docs", "test", "refactor", "wt", "review", "hermes", "handoff"}
)
IDENTIFIER = re.compile(r"[A-Za-z0-9][A-Za-z0-9_.-]{0,127}\Z")
GIT = "/usr/bin/git"
MAX_BOARD_BYTES = 64 * 1024
REPOSITORY_ALIASES = {"titan-iac": "atlas-iac"}


class ProjectPolicyError(ValueError):
    """Canonical project metadata or a requested ref failed closed."""


def _task_value(task: Any, name: str, default: Any = None) -> Any:
    return getattr(task, name, default)


def _run_git(workdir: Path, *arguments: str) -> str:
    completed = subprocess.run(
        [GIT, "-C", str(workdir), *arguments],
        check=False,
        stdin=subprocess.DEVNULL,
        capture_output=True,
        text=True,
        timeout=30,
        env={
            "HOME": "/nonexistent",
            "PATH": "/usr/bin:/bin",
            "GIT_CONFIG_NOSYSTEM": "1",
            "GIT_TERMINAL_PROMPT": "0",
        },
    )
    if completed.returncode:
        raise ProjectPolicyError("canonical project Git metadata is unavailable")
    return completed.stdout.strip()


def validate_branch(value: object, *, feature: bool) -> str:
    """Validate a complete local branch name with Git and a reviewed namespace."""
    if not isinstance(value, str) or not value or len(value) > 200:
        raise ProjectPolicyError("branch name exceeds the safe limit")
    if not value.isascii() or value.startswith("-"):
        raise ProjectPolicyError("branch name must be canonical ASCII")
    prefix = value.split("/", 1)[0]
    if feature and ("/" not in value or prefix not in SAFE_PREFIXES):
        raise ProjectPolicyError("task branch is outside the reviewed namespace")
    completed = subprocess.run(
        [GIT, "check-ref-format", f"refs/heads/{value}"],
        check=False,
        stdin=subprocess.DEVNULL,
        stdout=subprocess.DEVNULL,
        stderr=subprocess.DEVNULL,
        timeout=10,
        env={"PATH": "/usr/bin:/bin", "GIT_CONFIG_NOSYSTEM": "1"},
    )
    if completed.returncode:
        raise ProjectPolicyError("branch name is not a valid Git ref")
    return value


def _read_board(board: str) -> dict[str, Any]:
    if not IDENTIFIER.fullmatch(board):
        raise ProjectPolicyError("board slug is invalid")
    path = BOARD_ROOT / board / "board.json"
    descriptor = os.open(path, os.O_RDONLY | getattr(os, "O_NOFOLLOW", 0))
    try:
        info = os.fstat(descriptor)
        if not stat.S_ISREG(info.st_mode) or not 0 < info.st_size <= MAX_BOARD_BYTES:
            raise ProjectPolicyError("board registry entry is not a bounded regular file")
        raw = os.read(descriptor, MAX_BOARD_BYTES + 1)
    finally:
        os.close(descriptor)
    try:
        value = json.loads(raw)
    except (UnicodeError, json.JSONDecodeError) as error:
        raise ProjectPolicyError("board registry entry is malformed") from error
    if not isinstance(value, dict) or value.get("slug") != board or value.get("archived") is True:
        raise ProjectPolicyError("board registry identity is unavailable or archived")
    return value


def resolve_project(board: str) -> tuple[str, str, Path]:
    """Resolve repo and base exclusively from the canonical board registry.

    A board may be created before its primary checkout.  In that case the
    Atlas repository naming contract and ``main`` are the registry defaults;
    once a checkout exists, its credential-free origin and remote HEAD must
    agree with that identity.  This keeps a missing checkout from silently
    routing work to some other project's repository.
    """
    entry = _read_board(board)
    raw_workdir = entry.get("default_workdir")
    if not isinstance(raw_workdir, str) or not Path(raw_workdir).is_absolute():
        raise ProjectPolicyError("board default_workdir is missing")
    workdir = Path(raw_workdir).resolve(strict=False)
    project_root = PROJECT_ROOT.resolve(strict=True)
    try:
        workdir.relative_to(project_root)
    except ValueError as error:
        raise ProjectPolicyError("board workdir is outside the Atlas project registry") from error
    repository = REPOSITORY_ALIASES.get(board, board)
    remote = f"https://scm.bstein.dev/titan/{repository}.git"
    if not ATLAS_REPO.fullmatch(remote):
        raise ProjectPolicyError("board repository identity is invalid")
    if not workdir.exists():
        return remote, "main", workdir
    if not workdir.is_dir():
        raise ProjectPolicyError("board checkout is not a directory")
    checkout_remote = _run_git(workdir, "remote", "get-url", "origin")
    if "@" in checkout_remote or checkout_remote != remote:
        raise ProjectPolicyError("board origin disagrees with the Atlas registry")
    try:
        base = _run_git(workdir, "symbolic-ref", "--short", "refs/remotes/origin/HEAD")
        if not base.startswith("origin/"):
            raise ProjectPolicyError("origin HEAD is not canonical")
        base = base.removeprefix("origin/")
    except ProjectPolicyError:
        base = "main"
    return remote, validate_branch(base, feature=False), workdir


def resolve_assignment(board: str, task: Any) -> tuple[str, str, str]:
    """Resolve the exact repo/base and safe task branch for one board task."""
    repo, base, _workdir = resolve_project(board)
    task_id = str(_task_value(task, "id", "") or "")
    if not IDENTIFIER.fullmatch(task_id):
        raise ProjectPolicyError("task identity is invalid")
    branch = str(_task_value(task, "branch_name", "") or f"wt/{task_id}")
    return repo, validate_branch(branch, feature=True), base


def distributed_workspace_eligible(task: Any) -> bool:
    """Only pathless tasks migrate; an existing worktree stays with its local owner."""
    return not str(_task_value(task, "workspace_path", "") or "").strip()