#!/usr/bin/env python3
"""
agents-sync — PreToolUse(Bash) hook.

Before any Bash command runs, walks the project tree and enforces one
filesystem invariant in every directory:

  AGENTS.md is the real file; CLAUDE.md is a symlink pointing at it.

Per directory:
  - AGENTS.md real, no CLAUDE.md ........ create symlink CLAUDE.md -> AGENTS.md
  - CLAUDE.md real, no AGENTS.md ........ rename to AGENTS.md, symlink back
  - CLAUDE.md symlink -> AGENTS.md ...... already canonical, nothing to do
  - CLAUDE.md symlink elsewhere ......... re-point at AGENTS.md
  - AGENTS.md symlink -> real CLAUDE.md . reversed layout: swap to canonical
  - both real, identical content ........ replace CLAUDE.md with the symlink
  - both real, different content ........ DON'T touch; report the conflict

The hook never blocks the tool call and never deletes content: every branch
either performs a lossless fix or reports. Fixes/conflicts are surfaced via
hookSpecificOutput.additionalContext; silence means the tree was already
canonical. Any unexpected error fails open (exit 0).
"""
import sys, os, json, filecmp

SKIP_DIRS = {"node_modules", "__pycache__", "venv", "vendor"}


def same_file(a, b):
    try:
        return os.path.realpath(a) == os.path.realpath(b)
    except OSError:
        return False


def fix_dir(d, root, fixes, conflicts):
    agents = os.path.join(d, "AGENTS.md")
    claude = os.path.join(d, "CLAUDE.md")
    a = os.path.lexists(agents)
    c = os.path.lexists(claude)
    if not a and not c:
        return

    rel = lambda p: os.path.relpath(p, root)
    a_link = a and os.path.islink(agents)
    c_link = c and os.path.islink(claude)

    if a and not c:
        if a_link and not os.path.exists(agents):
            conflicts.append("%s: broken symlink and no CLAUDE.md" % rel(agents))
            return
        os.symlink("AGENTS.md", claude)
        fixes.append("%s: created symlink -> AGENTS.md" % rel(claude))
        return

    if c and not a:
        if c_link:
            conflicts.append("%s: symlink to missing target (%s)"
                             % (rel(claude), os.readlink(claude)))
            return
        os.rename(claude, agents)
        os.symlink("AGENTS.md", claude)
        fixes.append("%s: renamed to AGENTS.md, symlink left in place" % rel(claude))
        return

    # Both exist.
    if c_link:
        if same_file(claude, agents):
            return  # canonical
        old = os.readlink(claude)
        os.remove(claude)
        os.symlink("AGENTS.md", claude)
        fixes.append("%s: re-pointed symlink (%s -> AGENTS.md)" % (rel(claude), old))
        return

    if a_link:
        # Reversed layout: AGENTS.md is the symlink, CLAUDE.md the real file.
        if same_file(agents, claude):
            os.remove(agents)
            os.rename(claude, agents)
            os.symlink("AGENTS.md", claude)
            fixes.append("%s: swapped — AGENTS.md is now the real file" % rel(agents))
        else:
            conflicts.append("%s: symlink elsewhere while CLAUDE.md is a real file"
                             % rel(agents))
        return

    # Both are real files.
    try:
        identical = filecmp.cmp(agents, claude, shallow=False)
    except OSError:
        identical = False
    if identical:
        os.remove(claude)
        os.symlink("AGENTS.md", claude)
        fixes.append("%s: identical to AGENTS.md, replaced with symlink" % rel(claude))
    else:
        conflicts.append("%s: AGENTS.md and CLAUDE.md are different real files — "
                         "merge manually" % (rel(d) if rel(d) != "." else "<root>"))


def main():
    try:
        payload = json.load(sys.stdin)
    except Exception:
        payload = {}

    root = os.environ.get("CLAUDE_PROJECT_DIR") or payload.get("cwd") or os.getcwd()
    if not os.path.isdir(root):
        return

    fixes, conflicts = [], []
    for dirpath, dirnames, _ in os.walk(root):
        dirnames[:] = [n for n in dirnames
                       if n not in SKIP_DIRS and not n.startswith(".")]
        try:
            fix_dir(dirpath, root, fixes, conflicts)
        except OSError:
            pass  # unwritable dir etc. — skip, never block the command

    if fixes or conflicts:
        parts = []
        if fixes:
            parts.append("agents-sync fixed:\n  " + "\n  ".join(fixes))
        if conflicts:
            parts.append("agents-sync needs manual resolution:\n  "
                         + "\n  ".join(conflicts))
        print(json.dumps({
            "hookSpecificOutput": {
                "hookEventName": "PreToolUse",
                "additionalContext": "\n".join(parts),
            }
        }))


if __name__ == "__main__":
    try:
        main()
    except Exception:
        pass  # fail open — this hook must never break Bash
    sys.exit(0)