#!/usr/bin/env python3
"""Synchronize skill symlinks without taking ownership of unrelated entries."""
import argparse
from pathlib import Path
import os
import re
import sys


def lexical(path):
    return Path(os.path.abspath(path))


def link_target(path):
    return lexical(path.parent / os.readlink(path))


def inside(path, root):
    return path != root and root in path.parents


def main(argv=None):
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--dry-run', action='store_true', help='show changes without writing')
    parser.add_argument('--check', action='store_true', help='exit 1 if links differ; do not write')
    parser.add_argument('--global-dir', type=Path, default=Path(__file__).resolve().parents[1] / 'skills')
    parser.add_argument('--jev-dir', type=Path, default=Path.home() / 'Projects/work/JEV/.agents/skills')
    parser.add_argument('--target', action='append', type=Path, help='override target directories; repeatable')
    args = parser.parse_args(argv)
    sources = [lexical(args.global_dir), lexical(args.jev_dir)]
    targets = args.target if args.target is not None else [Path.home() / p for p in ('.agents/skills', '.codex/skills', '.claude/skills')]
    targets = [lexical(p) for p in targets]
    # Reject destinations inside catalogs (or containing them) before any mutation.
    for target in targets:
        resolved_target = target.resolve()
        if any(resolved_target == source.resolve() or
               inside(resolved_target, source.resolve()) or
               inside(source.resolve(), resolved_target) for source in sources):
            parser.error(f'target overlaps a source catalog: {target}')
    if not sources[0].is_dir():
        parser.error(f'global skill source unavailable: {sources[0]}')
    available = [p for p in sources if p.is_dir()]
    expected = {}
    errors = []
    for root in available:
        for child in sorted(root.iterdir()):
            if not child.is_dir():
                continue
            if not re.fullmatch(r'[a-z0-9]+(?:-[a-z0-9]+)*', child.name) or not (child / 'SKILL.md').is_file():
                errors.append(f'invalid skill directory: {child}')
                continue
            if child.name in expected:
                errors.append(f'colliding skill name: {child.name} ({expected[child.name]}, {child})')
            else:
                expected[child.name] = child
    if errors:
        print('\n'.join(errors), file=sys.stderr)
        return 2
    if len(available) != len(sources):
        print(f'WARN: JEV source unavailable; preserving its existing links: {sources[1]}', file=sys.stderr)
    changes = 0
    conflicts = 0
    readonly = args.check or args.dry_run
    for target in targets:
        if target.exists() and not target.is_dir():
            print(f'SKIP: target is not a directory: {target}', file=sys.stderr)
            conflicts += 1
            continue
        if not readonly:
            target.mkdir(parents=True, exist_ok=True)
        # Only prune links to sources that were successfully inventoried.
        for dest in sorted(target.iterdir()) if target.is_dir() else []:
            if dest.is_symlink() and any(inside(link_target(dest), root) for root in available) and dest.name not in expected:
                print(f'remove stale: {dest}')
                changes += 1
                if not readonly:
                    dest.unlink()
        for name, src in sorted(expected.items()):
            dest = target / name
            if dest.is_symlink():
                current = link_target(dest)
                if current == src:
                    continue
                if not any(inside(current, root) for root in available):
                    print(f'SKIP: unrelated symlink: {dest}', file=sys.stderr)
                    conflicts += 1
                    continue
            elif dest.exists():
                print(f'SKIP: unrelated entry: {dest}', file=sys.stderr)
                conflicts += 1
                continue
            print(f'link: {dest} -> {src}')
            changes += 1
            if not readonly:
                if dest.is_symlink():
                    dest.unlink()
                dest.symlink_to(src, target_is_directory=True)
    print(f'{"check" if args.check else "dry-run" if args.dry_run else "sync"}: {changes} changes, {conflicts} conflicts')
    return 1 if conflicts or (args.check and changes) else 0


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