#!/usr/bin/env python3
"""ClaudeForge: convert a CLAUDE.md tree into an AGENTS.md for Codex / Gemini users.

Three modes:

* ``--symlink`` (default on macOS/Linux): create ``AGENTS.md`` as a symlink to
  ``CLAUDE.md``. Single source of truth forever. Windows falls back to
  ``--copy`` with a warning printed to stderr.
* ``--copy``: byte-copy ``CLAUDE.md`` → ``AGENTS.md``. Snapshot, not live-linked.
* ``--inline-chain``: walk every ``@path/.../CLAUDE.md`` import recursively and
  produce a single flat ``AGENTS.md`` with every chained file inlined under a
  header that names its relative path. The right choice for Codex / Gemini
  because those tools don't auto-resolve Claude's ``@`` imports.

An existing ``AGENTS.md`` is backed up to ``AGENTS.md.backup.<UTC-timestamp>``
before overwrite, unless ``--force`` is passed.

Exit codes: ``0`` success, ``1`` user error (missing source, unsafe overwrite,
unknown mode), ``2`` filesystem error (permission denied, symlink unsupported).
"""
from __future__ import annotations

import argparse
import datetime as _dt
import os
import re
import shutil
import sys
from pathlib import Path

CHAIN_IMPORT = re.compile(r"^\s*@([^\s]+)\s*$")
BACKLINK_LINE = re.compile(
    r"^\s*>\s*(Parent context:|Chained import:).*$", re.IGNORECASE
)


def _ts() -> str:
    # Microsecond precision so two backups in the same second don't collide
    # (the smoke test for the inline-chain workflow re-backs-up within ms).
    return _dt.datetime.utcnow().strftime("%Y%m%d_%H%M%S_%f")


def _backup(dest: Path) -> Path | None:
    if not dest.exists() and not dest.is_symlink():
        return None
    backup = dest.with_name(f"{dest.name}.backup.{_ts()}")
    # ``shutil.move`` preserves symlinks-as-symlinks across same-filesystem.
    shutil.move(str(dest), str(backup))
    return backup


def _resolve_imports(root: Path, seen: set[Path]) -> list[tuple[Path, str]]:
    """Depth-first walk of ``@path`` chain imports rooted at ``root``.

    Returns a list of ``(relative_path, content)`` tuples in encounter order.
    Cycles are short-circuited (a file is read at most once).
    """
    root = root.resolve()
    if root in seen:
        return []
    if not root.exists():
        return []
    seen.add(root)

    lines = root.read_text(encoding="utf-8").splitlines()
    cleaned: list[str] = []
    children: list[tuple[Path, str]] = []
    parent_dir = root.parent

    for line in lines:
        m = CHAIN_IMPORT.match(line)
        if m:
            target = (parent_dir / m.group(1)).resolve()
            if target.suffix == "" and target.is_dir():
                target = target / "CLAUDE.md"
            children.extend(_resolve_imports(target, seen))
            # Drop the @-import line from the inlined parent body.
            continue
        if BACKLINK_LINE.match(line):
            # Backlinks like "> Parent context: see the root [CLAUDE.md]..."
            # are Claude-specific scaffolding. Drop in inline-chain output.
            continue
        cleaned.append(line)

    rel = str(root.relative_to(Path.cwd().resolve())) if root.is_relative_to(
        Path.cwd().resolve()
    ) else root.name
    return [(rel, "\n".join(cleaned).strip() + "\n")] + children


def _do_symlink(src: Path, dest: Path) -> int:
    if os.name == "nt":
        print(
            "claude-to-agents: symlinks on Windows require admin / dev mode; "
            "falling back to --copy",
            file=sys.stderr,
        )
        return _do_copy(src, dest)
    try:
        dest.symlink_to(src.name)
    except OSError as exc:
        print(f"claude-to-agents: symlink failed ({exc}); use --copy or --inline-chain", file=sys.stderr)
        return 2
    return 0


def _do_copy(src: Path, dest: Path) -> int:
    shutil.copyfile(src, dest)
    return 0


def _do_inline_chain(src: Path, dest: Path) -> int:
    chain = _resolve_imports(src, set())
    if not chain:
        print(f"claude-to-agents: source {src} not found", file=sys.stderr)
        return 1
    out: list[str] = [
        "<!-- Generated by ClaudeForge /claude-to-agents --inline-chain -->",
        "<!-- Source: CLAUDE.md (this file flattens the @path chain for tools that don't auto-import). -->",
        "",
    ]
    for rel, body in chain:
        out.append(f"<!-- inlined from {rel} -->")
        out.append("")
        out.append(body.strip())
        out.append("")
    dest.write_text("\n".join(out).rstrip() + "\n", encoding="utf-8")
    return 0


def main(argv: list[str] | None = None) -> int:
    parser = argparse.ArgumentParser(prog="claude-to-agents", description=__doc__.split("\n\n")[0])
    parser.add_argument("--source", default="CLAUDE.md")
    parser.add_argument("--output", default="AGENTS.md")
    parser.add_argument(
        "--mode",
        choices=("symlink", "copy", "inline-chain"),
        default="symlink",
    )
    parser.add_argument("--force", action="store_true", help="overwrite without backup")
    args = parser.parse_args(argv)

    src = Path(args.source)
    dest = Path(args.output)
    if not src.exists():
        print(f"claude-to-agents: source {src} not found", file=sys.stderr)
        return 1

    if (dest.exists() or dest.is_symlink()) and not args.force:
        backup = _backup(dest)
        if backup is not None:
            print(f"claude-to-agents: backed up existing {dest} -> {backup}", file=sys.stderr)
    elif args.force and (dest.exists() or dest.is_symlink()):
        dest.unlink()

    handlers = {
        "symlink": _do_symlink,
        "copy": _do_copy,
        "inline-chain": _do_inline_chain,
    }
    rc = handlers[args.mode](src, dest)
    if rc == 0:
        kind = "symlink" if args.mode == "symlink" and dest.is_symlink() else "file"
        print(f"claude-to-agents: wrote {dest} ({args.mode}, {kind})", file=sys.stderr)
    return rc


if __name__ == "__main__":
    sys.exit(main())