#!/usr/bin/env python3
"""Issue #5 Phase 2a — lib_py/loop core and shadow watcher.

Written in the order the plan fixes: characterize the current writers BEFORE
routing them through a CAS boundary, so the refactor has an oracle rather than a
promise. Phase 1 proved the value of that ordering; it also proved that a fake
which cannot express a failure hides it, so every double here models the real
contract (herdr's exit/stream split, the registry lock, the record on disk).

Sections
  1. X-01..X-04  current writer behaviour (must hold before and after P2A-01).
  2. engine      the single CAS transition boundary and its lock discipline.
  3. watcher     herdr agent wait wrapping, stream split, reconnect backoff.
  4. policy      decisions checked against the phase-0 scenario contracts.
  5. shadow      the runner that cannot write, proven by hashing the registry.
"""
from __future__ import annotations

import hashlib
import json
import os
import subprocess
import sys
import time
from pathlib import Path

import pytest

REPO_ROOT = Path(__file__).resolve().parent.parent
SKILLS = REPO_ROOT / ".agents" / "skills"
WATCHER_FIXTURES = REPO_ROOT / "tests" / "fixtures" / "issue_5" / "watcher"

CAS_MODES = ("0", "1")  # MAM_ENGINE_CAS: legacy unconditional merge / CAS engine


# ==============================================================================
# Helpers
# ==============================================================================

def _reg(tmp_path) -> str:
    d = tmp_path / ".mam" / "jobs"
    d.mkdir(parents=True, exist_ok=True)
    return str(d)


def _make_job(registry_dir, **over):
    from lib_py.delegation import registry
    job_id = registry.register_job(over.pop("prompt", "p"), registry_dir=registry_dir, **over)
    return job_id


def _load(registry_dir, job_id):
    from lib_py.delegation import mqtt_common
    return mqtt_common.load_job(job_id, registry_dir)


def _dir_fingerprint(path: Path) -> dict:
    """File name -> sha256 for every file under path. Detects any byte change."""
    out = {}
    for p in sorted(Path(path).rglob("*")):
        if p.is_file():
            out[str(p.relative_to(path))] = hashlib.sha256(p.read_bytes()).hexdigest()
    return out


@pytest.fixture(autouse=True)
def _cas_on(monkeypatch):
    """Default every test to the CAS engine unless it says otherwise."""
    monkeypatch.setenv("MAM_ENGINE_CAS", "1")


# ==============================================================================
# 1. X-01..X-04 — the writers as they behave today
# ==============================================================================

@pytest.mark.parametrize("mode", CAS_MODES)
def test_x01_update_job_status_merges_arbitrary_fields(mam_sandbox, tmp_path, monkeypatch, mode):
    """X-01: update_job_status merges whatever it is given, in both modes.

    Its signature, return value and side effects are load-bearing: phase 1's
    G-1..G-4 assert through it, so routing it through the engine must not change
    what a caller observes."""
    monkeypatch.setenv("MAM_ENGINE_CAS", mode)
    monkeypatch.chdir(mam_sandbox)
    from lib_py.delegation import mqtt_common

    reg = _reg(tmp_path)
    job_id = _make_job(reg)
    out = mqtt_common.update_job_status(job_id, reg, status="running", iteration=4)
    assert out["status"] == "running"
    assert out["iteration"] == 4
    assert out["updated_at"], "updated_at must always be refreshed"
    assert _load(reg, job_id)["status"] == "running"


@pytest.mark.parametrize("mode", CAS_MODES)
def test_x02_pick_pending_claims_only_pending_and_only_once(mam_sandbox, tmp_path, monkeypatch, mode):
    """X-02: the claim path's real contract.

    pick_pending is not broken today: it filters on pending under the lock, so
    pending->running is already a correct swap. It is a *duplicate* of the
    chokepoint, not a hole in it. Routing it through the engine must preserve
    exactly this behaviour."""
    monkeypatch.setenv("MAM_ENGINE_CAS", mode)
    monkeypatch.chdir(mam_sandbox)
    from lib_py.delegation import registry

    reg = _reg(tmp_path)
    job_id = _make_job(reg, agent_session="herdr:s1")
    assert registry.pick_pending("herdr:s1", reg) == job_id
    assert _load(reg, job_id)["status"] == "running"
    # already claimed -> no second winner
    assert registry.pick_pending("herdr:s1", reg) is None
    # a different session never sees another session's work
    other = _make_job(reg, agent_session="herdr:s2")
    assert registry.pick_pending("herdr:s1", reg) is None
    assert registry.pick_pending("herdr:s2", reg) == other


@pytest.mark.parametrize("mode", CAS_MODES)
def test_x03_status_write_mirrors_into_the_audit_log(mam_sandbox, tmp_path, monkeypatch, mode):
    """X-03: a status change is mirrored to the audit log, in both modes.

    P2A-01 moves that mirror out of the lock; it must not lose it."""
    monkeypatch.setenv("MAM_ENGINE_CAS", mode)
    monkeypatch.chdir(mam_sandbox)
    from lib_py.delegation import mqtt_common

    reg = _reg(tmp_path)
    job_id = _make_job(reg)
    mqtt_common.update_job_status(job_id, reg, status="completed")

    logged = mqtt_common.read_logged_status(job_id, mqtt_common.get_logs_dir())
    assert logged and logged.get("status") == "completed"
    events = list(mqtt_common.iter_logged_events(job_id, mqtt_common.get_logs_dir()))
    changes = [e for e in events if e.get("event") == "status_changed"]
    assert changes, "a status change must appear in the audit log"
    assert changes[-1]["to"] == "completed"


@pytest.mark.parametrize("mode", CAS_MODES)
def test_x04_next_seq_and_register_are_unaffected(mam_sandbox, tmp_path, monkeypatch, mode):
    """X-04: the non-status writers keep their behaviour under either mode."""
    monkeypatch.setenv("MAM_ENGINE_CAS", mode)
    monkeypatch.chdir(mam_sandbox)
    from lib_py.delegation import mqtt_common

    reg = _reg(tmp_path)
    job_id = _make_job(reg)
    assert _load(reg, job_id)["status"] == "pending"
    assert mqtt_common.next_seq(job_id, reg) == 1
    assert mqtt_common.next_seq(job_id, reg) == 2
    assert _load(reg, job_id)["last_seq"] == 2
    assert _load(reg, job_id)["status"] == "pending", "next_seq must not touch status"