#!/usr/bin/env python3
"""doorpost_check.py — the Doorpost read BEFORE the image is built.

VavPipeline.Doorpost bakes @expected_hash over the category-grade spec
files (@spec_files in vav_pipeline/lib/vav_pipeline/doorpost.ex). An
image whose spec files do not hash to its pin logs
DOORPOST_DRIFT_AT_STARTUP, answers 503 on readiness, and takes the gate
dark with it — tablet 54, 2026-10-15: two spec edits shipped without a
pin move and every Claude Code session behind the gate was cut off.

This script computes the same hash the same way, with no Elixir:
  for each path in @spec_files, in listed order: sha256(contents)
  join "path\\thash" with "\\n"; sha256 of that.
and compares it with the pin. Exit 0 on a match, 1 on drift (the
message names each drifted file against a base revision), 2 on a
missing file or an unreadable module.

  scripts/doorpost_check.py                 # the working tree, as the image is built from
  scripts/doorpost_check.py --rev <rev>     # a git revision instead of the working tree
  scripts/doorpost_check.py --base <rev>    # on drift, diff the manifest against <rev> (default origin/main)
  scripts/doorpost_check.py --print         # print the hash only (what the pin should be)

Devarim 4:2 — nothing added, nothing taken: the pin moves by a commit
that moves it, never by a build that ignores it.
"""
import argparse, hashlib, os, re, subprocess, sys

ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
MODULE = "vav_pipeline/lib/vav_pipeline/doorpost.ex"


def read(rev, path):
    """Bytes of `path` at `rev`, or from the working tree when rev is None. None if missing."""
    if rev is None:
        full = os.path.join(ROOT, path)
        try:
            with open(full, "rb") as f:
                return f.read()
        except FileNotFoundError:
            return None
    r = subprocess.run(["git", "-C", ROOT, "show", f"{rev}:{path}"], capture_output=True)
    return r.stdout if r.returncode == 0 else None


def spec_files_and_pin(rev):
    src = read(rev, MODULE)
    if src is None:
        sys.exit(f"doorpost_check: cannot read {MODULE}" + (f" at {rev}" if rev else ""))
    src = src.decode()
    block = src.split("@spec_files [", 1)[1].split("]", 1)[0]
    files = re.findall(r'"([^"]+)"', block)
    pin = re.search(r'@expected_hash\s+"([0-9a-f]{64})"', src)
    if not files or not pin:
        sys.exit(f"doorpost_check: could not parse @spec_files/@expected_hash from {MODULE}")
    return files, pin.group(1)


def manifest(rev, files):
    out = {}
    for p in files:
        data = read(rev, p)
        out[p] = None if data is None else hashlib.sha256(data).hexdigest()
    return out


def identity(man):
    return hashlib.sha256("\n".join(f"{p}\t{h}" for p, h in man.items()).encode()).hexdigest()


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("--rev", help="git revision to check instead of the working tree")
    ap.add_argument("--base", default="origin/main", help="revision to name drifted files against")
    ap.add_argument("--print", action="store_true", help="print the computed hash only")
    a = ap.parse_args()

    files, pin = spec_files_and_pin(a.rev)
    man = manifest(a.rev, files)
    missing = [p for p, h in man.items() if h is None]
    if missing:
        print("doorpost_check: MISSING spec file(s): " + ", ".join(missing), file=sys.stderr)
        sys.exit(2)
    computed = identity(man)
    if a.print:
        print(computed)
        return
    where = a.rev or "working tree"
    if computed == pin:
        print(f"doorpost: {where} hashes to its pin {pin[:8]}… ({len(files)} files) — the Doorpost will verify")
        return
    print(f"doorpost: DRIFT in {where} — computed {computed}, pinned {pin}", file=sys.stderr)
    base_files, _ = spec_files_and_pin(a.base)
    base_man = manifest(a.base, base_files)
    for p in files:
        if base_man.get(p) != man[p]:
            print(f"  changed since {a.base}: {p}", file=sys.stderr)
    for p in files:
        if p not in base_man:
            print(f"  added to @spec_files since {a.base}: {p}", file=sys.stderr)
    print(f"  Move @expected_hash in {MODULE} to {computed} in the same commit as the spec change,", file=sys.stderr)
    print(f"  then run: mix test test/doorpost_test.exs. Refusing to build an image that would drift at startup.", file=sys.stderr)
    sys.exit(1)


if __name__ == "__main__":
    main()