#!/usr/bin/env python3
"""Preview or install maintained files; preserve unrelated files and back up edits."""
from __future__ import annotations

import argparse
from datetime import datetime, timezone
import hashlib
import json
import os
from pathlib import Path
import shutil
import tempfile
import uuid


ROOT = Path(__file__).resolve().parents[1]


def digest(data: bytes) -> str:
    return hashlib.sha256(data).hexdigest()


def plan(repo: Path, home: Path, include_prompt: bool = False) -> list:
    source = repo / "skills/codex-subagent-router"
    files = [(p, Path("skills/codex-subagent-router") / p.relative_to(source))
             for p in sorted(source.rglob("*")) if p.is_file()
             and "__pycache__" not in p.parts and p.suffix != ".pyc"]
    if not (source / "SKILL.md").is_file():
        raise ValueError("source SKILL.md missing")
    if include_prompt:
        files.append((repo / "prompts/AGENTS.md", Path("AGENTS.md")))
    changes = []
    for src, relative in files:
        if src.is_symlink():
            raise ValueError("refusing symlink source: " + str(relative))
        dest = home / relative
        for part in [dest, *dest.parents]:
            if part == home:
                break
            if part.is_symlink():
                raise ValueError("refusing symlink target: " + str(relative))
        if dest.exists() and not dest.is_file():
            raise ValueError("target is not a regular file: " + str(relative))
        before = dest.read_bytes() if dest.exists() else None
        after = src.read_bytes()
        if before != after:
            changes.append({"path": relative, "before": before, "after": after})
    return changes


def install(repo: Path, home: Path, include_prompt: bool = False, apply: bool = False) -> dict:
    home = home.expanduser().resolve()
    changes = plan(repo, home, include_prompt)
    result = {"changed_paths": [str(x["path"]) for x in changes], "applied": False, "backup": None}
    if not apply or not changes:
        return result
    # Check all baselines before any managed file is changed.
    for change in changes:
        dest = home / change["path"]
        current = dest.read_bytes() if dest.exists() else None
        if current != change["before"]:
            raise ValueError("target changed during planning: " + str(change["path"]))
    stamp = datetime.now(timezone.utc).strftime("%Y%m%dT%H%M%SZ") + "-" + uuid.uuid4().hex[:8]
    backup = home / "backups/codex-subagent-router" / stamp
    backup.mkdir(parents=True, exist_ok=False)
    manifest = []
    for change in changes:
        before = change["before"]
        if before is not None:
            saved = backup / change["path"]
            saved.parent.mkdir(parents=True, exist_ok=True)
            saved.write_bytes(before)
        manifest.append({"path": str(change["path"]), "existed": before is not None,
                         "before_sha256": digest(before) if before is not None else None,
                         "installed_sha256": digest(change["after"])})
    (backup / "manifest.json").write_text(json.dumps(manifest, indent=2) + "\n", encoding="utf-8")
    for change in changes:
        dest = home / change["path"]
        dest.parent.mkdir(parents=True, exist_ok=True)
        temporary = None
        try:
            with tempfile.NamedTemporaryFile(dir=dest.parent, delete=False) as stream:
                temporary = Path(stream.name)
                stream.write(change["after"])
            if dest.exists():
                shutil.copymode(dest, temporary)
            temporary.replace(dest)
        finally:
            if temporary is not None and temporary.exists():
                temporary.unlink()
    result.update(applied=True, backup=str(backup))
    return result


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--codex-home", type=Path,
                        default=Path(os.environ.get("CODEX_HOME") or "~/.codex"))
    parser.add_argument("--include-prompt", action="store_true", help="also replace the global AGENTS.md")
    parser.add_argument("--apply", action="store_true", help="write files; default is preview only")
    parser.add_argument("--check", action="store_true", help="exit 1 when maintained files differ")
    args = parser.parse_args()
    if args.apply and args.check:
        parser.error("--apply and --check are mutually exclusive")
    try:
        result = install(ROOT, args.codex_home, args.include_prompt, args.apply)
        print(json.dumps(result, ensure_ascii=False, indent=2))
        return 1 if args.check and result["changed_paths"] else 0
    except (OSError, ValueError) as error:
        print("Install failed: " + str(error))
        return 1


if __name__ == "__main__":
    raise SystemExit(main())