#!/usr/bin/env python3
"""Prefect flow — periodically recompute S6 bucket sizing coefficients.

Cadence
───────
Controlled by env `S6_RECOMPUTE_INTERVAL_DAYS` (default 30). The flow is
idempotent: running it more often than the interval just produces a fresh
YAML and markdown report; nothing is auto-promoted.

Kill-switch
───────────
Set env `S6_RECOMPUTE_DISABLED=1` to skip — the flow logs and exits 0.

Wiring into supervisord/cron
────────────────────────────
Run this flow on the supervisord host. Recommended: daily timer that guards
internally on the last-run timestamp in `dolphin.s6_recompute_log`, or a
Prefect deployment with a cron schedule `0 3 * * *` and the interval env set.

This flow shells out to `prod/scripts/recompute_s6_coefficients.py` rather
than importing it so that the script remains independently runnable without
requiring Prefect — honours the plan's "recompute works whether or not
Prefect is installed" requirement.
"""

from __future__ import annotations

import os
import subprocess
import sys
from datetime import datetime, timedelta
from pathlib import Path

try:
    from prefect import flow, task, get_run_logger
except ImportError:  # pragma: no cover — allow import-only smoke tests
    def flow(fn=None, **_kw):
        if fn is None:
            return lambda f: f
        return fn
    def task(fn=None, **_kw):
        if fn is None:
            return lambda f: f
        return fn
    def get_run_logger():  # pragma: no cover
        import logging
        return logging.getLogger("s6_recompute_flow")


REPO_ROOT    = Path(__file__).resolve().parents[1]
RECOMPUTE_PY = REPO_ROOT / "prod" / "scripts" / "recompute_s6_coefficients.py"
TABLE_YML    = REPO_ROOT / "prod" / "configs" / "green_s6_table.yml"


@task
def check_interval_elapsed(interval_days: int) -> bool:
    """Return True if the YAML is missing OR older than the interval."""
    if not TABLE_YML.exists():
        return True
    try:
        import yaml
        doc = yaml.safe_load(TABLE_YML.read_text()) or {}
        ts_str = (doc.get("meta") or {}).get("generated_at", "")
        if not ts_str:
            return True
        ts = datetime.fromisoformat(ts_str.rstrip("Z"))
        return datetime.utcnow() - ts >= timedelta(days=interval_days)
    except Exception:
        # Any parsing trouble → safer to recompute
        return True


@task
def run_recompute(strategy: str, since: str, min_trades: int, source_branch: str) -> int:
    logger = get_run_logger()
    cmd = [
        sys.executable, str(RECOMPUTE_PY),
        "--strategy", strategy,
        "--since",    since,
        "--min-trades-per-bucket", str(min_trades),
        "--source-branch", source_branch,
    ]
    logger.info(f"[s6_recompute_flow] exec: {' '.join(cmd)}")
    rc = subprocess.call(cmd, cwd=str(REPO_ROOT))
    logger.info(f"[s6_recompute_flow] exit code: {rc}")
    return rc


@flow(name="s6-recompute")
def s6_recompute_flow(
    strategy: str = "blue",
    since: str = "2026-01-01",
    min_trades: int = 20,
    source_branch: str = "exp/green-s6-esof-aem-shadow-2026-04-21",
):
    logger = get_run_logger()

    if os.environ.get("S6_RECOMPUTE_DISABLED") == "1":
        logger.info("[s6_recompute_flow] disabled via S6_RECOMPUTE_DISABLED=1 — skipping")
        return 0

    try:
        interval_days = int(os.environ.get("S6_RECOMPUTE_INTERVAL_DAYS", "30"))
    except ValueError:
        interval_days = 30

    due = check_interval_elapsed(interval_days)
    if not due:
        logger.info(f"[s6_recompute_flow] interval not elapsed ({interval_days}d) — skipping")
        return 0

    return run_recompute(strategy, since, min_trades, source_branch)


if __name__ == "__main__":
    sys.exit(int(s6_recompute_flow() or 0))