"""The AI queue's budget rule, from the reference implementation (Cairn's ai.py, 2026-10-13).

It reads the meter's state file: {"at": iso, "buckets": [{"id", "used", "exact", "resets"}, ...]}, one bucket per
limit, e.g. "claude-week", "claude-session", "codex-week". budget() says, per plan, how much the queue may spend now.
"""
import datetime as dt, math, time


def meter_state():
    raise NotImplementedError("return your meter's state dict")


METER = None   # the folder holding readings.tsv, if any estimated bucket is kept

PLANS = {   # plan -> (weekly bucket, 5-hour bucket or None, meter --read bucket for an estimated week, or None)
    "claude": ("claude-week", "claude-session", "claude_week"),
    "codex": ("codex-week", "codex-session", None),
    "gemini": ("gemini-week", "gemini-session", None),
    "grok": ("grok-week", None, "grok"),
}


MARGIN_ESTIMATED = 5.0               # Claude's and Grok's percentages are estimates: keep this far under the line


SESSION_GATE = 50.0                  # never start on a plan whose 5-hour window is past this


STALE_S = 30 * 60                    # an older meter reading is no reading


EVENING = (21, 3)                    # the daily spend runs from 21:00 to 03:00 …


BEFORE_RESET_S = 2 * 3600            # … and in the last two hours before a plan's own weekly reset, at any hour


def last_reading(bucket):
    """when the newest human reading of this --read bucket was taken, as an epoch, or None"""
    try:
        rows = (METER / "readings.tsv").read_text().splitlines()[1:]
    except OSError:
        return None
    best = None
    for r in rows:
        c = r.split("\t")
        if len(c) > 1 and c[1] == bucket:
            try:            # a row hand-typed in another format is skipped, not fatal
                best = max(best or 0, dt.datetime.fromisoformat(c[0].strip()).timestamp())
            except ValueError:
                pass
    return best


def budget(state=None, at=None):
    """one dict per plan: used, line, room, and whether the queue may spend it now (ok, why)."""
    state = state if state is not None else meter_state()
    t = at if at is not None else time.time()
    by = {b["id"]: b for b in (state or {}).get("buckets", [])}
    fresh = False
    if state and state.get("at"):
        try:
            fresh = t - dt.datetime.fromisoformat(state["at"]).timestamp() <= STALE_S
        except ValueError:
            pass
    hour = dt.datetime.fromtimestamp(t).hour
    evening = hour >= EVENING[0] or hour < EVENING[1]
    out = {}
    for plan, (wk, sess, read) in PLANS.items():
        b, s = by.get(wk), by.get(sess) if sess else None
        row = {"plan": plan, "used": None, "line": None, "room": 0.0, "day": None, "resets": None,
               "session": s.get("used") if s else None, "exact": bool(b and b.get("exact")), "ok": False, "why": ""}
        out[plan] = row
        if not fresh:
            row["why"] = "the meter reading is stale"
            continue
        if not b or b.get("used") is None:
            row["why"] = "no reading for this plan"
            continue
        row["used"] = b["used"]
        if not b.get("resets"):
            row["why"] = "no weekly reset time"
            continue
        reset = dt.datetime.fromisoformat(b["resets"]).timestamp()
        start = reset - 7 * 86400
        row["resets"] = b["resets"]
        row["day"] = day = max(1, min(7, math.ceil((t - start) / 86400)))
        margin = 0.0 if b.get("exact") else MARGIN_ESTIMATED
        row["line"] = line = min(DAILY * day, CEILING)
        row["room"] = room = round(max(0.0, line - margin - b["used"]), 1)
        if read and not b.get("exact") and (last_reading(read) or 0) < start:
            row["why"] = "no human reading since this week began (its percentage is an estimate)"
        elif s and s.get("used") is not None and s["used"] > SESSION_GATE:
            row["why"] = f"its 5-hour window is {s['used']:.0f} % used"
        elif room <= 0:
            row["why"] = "at or over tonight's line"
        elif not (evening or reset - t <= BEFORE_RESET_S):
            row["why"] = "spends after 21:00, or in the 2 h before its reset"
        else:
            row["ok"] = True
    return out