"""FCST-03 - the hours the feed has not published yet, and what may not rest on them.

specs.md 8.3: unknown hours use yesterday's profile and are flagged
`provisional: true`, and no irreversible action may be taken on a provisional
price. This module owns the fill and the gate; the widening arithmetic is in
price.py. The flag is never passed through: a carried point is built only by
`_carried()` (no flag parameter), a published point is passed by identity, and
`_audit()` raises on a mismatch. The fill keys on the Brussels wall-clock hour,
and a sub-hourly feed is never decimated. An hour with neither a published
price nor a yesterday value is left out, never filled (`at()` raises `Absence`,
11.4 applies). `begin_phase()` is the price-justified entry point only; the
calendar path is untouched. All of it:
DECISIONS/FCST-03-the-hours-not-yet-published.md."""

import logging
from dataclasses import dataclass
from datetime import datetime, timedelta, timezone
from enum import Enum

from . import messages
from .maintenance import CHARGE_TIMEOUT_MIN, DRAIN_TIMEOUT_MIN
from .price import PricePoint, PriceRead, _Outcome, brussels

_LOG = logging.getLogger("goodwe.price.forecast")


class Provenance(Enum):
    """Where a point in a filled series came from. INTERNAL: the wire format carries
    only the boolean. It gives `_audit()` and the log names for the two cases."""
    PUBLISHED = "published"    # the provider printed this hour. Flag: the
                               # feed's own - a real-time print may be
                               # published AND provisional (§9.2).
    CARRIED = "carried"        # yesterday's same-wall-clock hour (§8.3).
                               # Flag: ALWAYS True, by construction.


# The fill

def _utc_hour(instant: datetime) -> datetime:
    u = instant.astimezone(timezone.utc)
    return u.replace(minute=0, second=0, microsecond=0)


def _published_by_hour(read: PriceRead) -> dict:
    """UTC hour -> the provider's OWN points that start inside it, in order. A tuple
    per hour, not a point: a dict of `{hour: p}` silently keeps the last one and
    decimates a quarter-hourly feed."""
    out: dict = {}
    read.match(
        series=lambda r: [out.setdefault(_utc_hour(p.start), []).append(p)
                          for p in r.points],
        no_data=lambda _r: [])
    return {u: tuple(ps) for u, ps in out.items()}


def _carried(start_utc: datetime, eur_per_kwh: float) -> PricePoint:
    """A point filled from yesterday's profile. 8.3: ALWAYS provisional. There is no
    `provisional` parameter: the flag is a literal, nothing to pass or copy."""
    return PricePoint(start=brussels(start_utc),
                      eur_per_kwh=round(float(eur_per_kwh), 6),
                      provisional=True)


def _audit(points, published) -> None:
    """Post-condition: every flag matches the point's TRUE provenance (AC1).

    `published` maps a UTC hour to the TUPLE of points the provider produced for it.
    PUBLISHED: the point must be one of `published[u]` by identity, emitted once,
    flag whatever the feed said (never forced to False). CARRIED: the hour must not
    be in `published`, the flag exactly True, no second point in that hour.

    Provenance, NOT completeness: it accepts a decimated or empty output, because
    `published` is unwindowed while the fill emits [since, until). The point count
    and identity checks in the tests guard that. Raises, never repairs.
    DECISIONS/FCST-03-the-hours-not-yet-published.md."""
    carried_hours = set()
    emitted = set()
    for p in points:
        u = _utc_hour(p.start)
        src = published.get(u)
        if src is None:
            if u in carried_hours:
                raise ValueError(
                    f"the filled series repeats the carried hour "
                    f"{u.isoformat()}; a duplicated hour is how a DST day gets "
                    f"mispriced")
            carried_hours.add(u)
            if p.provisional is not True:
                raise ValueError(
                    f"{u.isoformat()} is {Provenance.CARRIED.value} and is "
                    f"flagged provisional={p.provisional!r}. §8.3: an hour "
                    f"filled from yesterday's profile is provisional whether "
                    f"or not the number turns out to be right - the flag is a "
                    f"claim about PROVENANCE, not about accuracy.")
        else:
            if not any(p is q for q in src):
                raise ValueError(
                    f"{u.isoformat()} is {Provenance.PUBLISHED.value} but the "
                    f"series carries a COPY of that point rather than the "
                    f"point itself. A copy is where the provisional flag gets "
                    f"lost; published points pass through by identity.")
            if id(p) in emitted:
                raise ValueError(
                    f"the filled series emits the published point at "
                    f"{p.start.isoformat()} TWICE. The provider's own points "
                    f"are strictly increasing (`_validate_raw`), so a repeat "
                    f"is never a second print - it is a duplicated hour, which "
                    f"is how a DST day gets mispriced")
            emitted.add(id(p))


def fill_from_yesterday(read: PriceRead, *, yesterday: PriceRead,
                        since: datetime, until: datetime,
                        stamp: datetime) -> PriceRead:
    """8.3: fill the hours the feed has not published with yesterday's profile.

    `yesterday` has no default. Returns a series (every published point, by
    identity, plus one `_carried()` point per remaining whole hour) or `no_data`,
    never an empty series. The window is whole hours at both ends. Idempotent and
    re-runnable (5.4): published hours win and the series is rebuilt."""
    for name, value in (("since", since), ("until", until), ("stamp", stamp)):
        if value.tzinfo is None or value.utcoffset() is None:
            raise ValueError(f"{name} must be tz-aware; a naive instant is "
                             f"ambiguous for one hour every October")

    published = _published_by_hour(read)

    # Yesterday's profile, keyed by BRUSSELS WALL-CLOCK HOUR. First point wins
    # when yesterday itself was a 25-hour day.
    by_local_hour = {}
    yesterday.match(
        series=lambda r: [by_local_hour.setdefault(brussels(p.start).hour, p)
                          for p in r.points],
        no_data=lambda _r: [])

    out = []
    u = _utc_hour(since)
    end = _utc_hour(until)
    while u < end:
        got = published.get(u)
        if got:
            out.extend(got)              # BY IDENTITY, and ALL of them. No copy,
        else:                            # and no decimation to one an hour.
            src = by_local_hour.get(brussels(u).hour)
            if src is not None:
                out.append(_carried(u, src.eur_per_kwh))
        u += timedelta(hours=1)

    if not out:
        reason = read.match(
            series=lambda r: (f"all {messages.count(len(r.points), 'published price')} "
                              f"fall outside {messages.when(brussels(since))} to "
                              f"{messages.when(brussels(until))}"),
            no_data=lambda r: r.reason)
        return PriceRead.no_data(
            f"no hours could be filled from yesterday's prices: {reason}. So "
            f"the fixed tariff is used, the plan is estimated and there is no "
            f"trading")

    _audit(out, published)
    carried = sum(1 for p in out if _utc_hour(p.start) not in published)
    if carried:
        # TARIFF-11: carried hours, total hours and published points are three
        # different quantities.
        total_h = len({_utc_hour(p.start) for p in out})
        _LOG.info("%d of %s use yesterday's prices, marked as estimated. "
                  "The feed published %s over the other %s.",
                  carried, messages.count(total_h, "hour"),
                  messages.count(len(out) - carried, "price"),
                  messages.count(total_h - carried, "hour"))

    product = read.match(series=lambda r: r.product,
                         no_data=lambda _r: yesterday.product)
    provider = read.match(series=lambda r: r.provider,
                          no_data=lambda r: yesterday.provider)
    return PriceRead.series(out, product, provider, stamp)


# AC2: irreversibility as a property of the ACTION, and the gate that reads it

@dataclass(frozen=True)
class Irreversible:
    """An action that cannot be undone once started. `commits_h` is the horizon it
    ties up: those hours must be firm before a price may justify it."""

    name: str            # the §10.2 reason code
    commits_h: float

    def __post_init__(self):
        if not self.name or not isinstance(self.name, str):
            raise ValueError("an irreversible action needs a reason code (§10.2)")
        if isinstance(self.commits_h, bool) or \
                not isinstance(self.commits_h, (int, float)) or \
                not self.commits_h > 0:
            raise ValueError(
                f"commits_h must be a positive number of hours, not "
                f"{self.commits_h!r}. An action that commits nothing is a "
                f"reversible one and does not belong here.")


# Derived from the phase machine's own bounds, not typed here, so the gate
# cannot drift from it.
MAINTENANCE_DRAIN = Irreversible("MAINTENANCE_DRAIN", DRAIN_TIMEOUT_MIN / 60.0)
MAINTENANCE_CHARGE = Irreversible("MAINTENANCE_CHARGE", CHARGE_TIMEOUT_MIN / 60.0)


class Gate(_Outcome):
    """May an irreversible action proceed on the price evidence available?
    `permitted` carries `.action` and `.hours` (the firm points checked); `blocked`
    carries `.reason` only. No `__bool__`; both `match()` arms are required."""

    def match(self, *, permitted, blocked):
        return {"permitted": permitted, "blocked": blocked}[self.kind](self)

    @staticmethod
    def permit(action, hours):
        return _Permitted(action, hours)

    @staticmethod
    def block(reason):
        if not reason or not isinstance(reason, str):
            raise ValueError(
                "Gate.block() takes a reason a human can act on. §6 requires "
                "every decision to explain itself, and 'the maintenance cycle "
                "did not start' with no reason is indistinguishable from a bug.")
        return _Blocked(reason)


class _Permitted(Gate):
    kind = "permitted"

    def __init__(self, action, hours):
        if not isinstance(action, Irreversible):
            raise TypeError(f"action must be an Irreversible, not {action!r}")
        pts = tuple(hours)
        if not pts:
            raise ValueError(
                "a permission granted over ZERO checked hours is a permission "
                "granted on no evidence - the shape this whole file exists to "
                "refuse. Block instead.")
        if any(p.provisional for p in pts):
            raise ValueError(
                "a permitted gate cannot carry a provisional hour: §8.3 is the "
                "one rule this type has.")
        self.action = action
        self.hours = pts
        self.words = (f"allowed on {messages.count(len(pts), 'published price')} "
                      f"from {messages.when(brussels(pts[0].start))}")


class _Blocked(Gate):
    kind = "blocked"

    def __init__(self, reason):
        self.reason = reason
        self.words = f"blocked - {reason}"


def committed_hours(now: datetime, action: Irreversible) -> tuple:
    """The whole hours `action` started at `now` would run through (the gate and its caller must agree)."""
    if not isinstance(action, Irreversible):
        raise TypeError(f"action must be an Irreversible, not {action!r}")
    if now.tzinfo is None or now.utcoffset() is None:
        raise ValueError("now must be tz-aware")
    out = []
    u = _utc_hour(now)
    end = now.astimezone(timezone.utc) + timedelta(hours=action.commits_h)
    while u < end:
        out.append(u)
        u += timedelta(hours=1)
    return tuple(out)


def price_permits(read: PriceRead, now: datetime,
                  action: Irreversible) -> Gate:
    """8.3's rule as a value: may this irreversible action rest on this price?
    Blocks on no data (11.4), an hour with no price, or a provisional hour, and
    names the offending hour."""
    hours = committed_hours(now, action)
    return read.match(
        series=lambda r: _walk(r, hours, action),
        no_data=lambda r: Gate.block(
            f"{action.name} needs a price and there is none: {r.reason}. A "
            f"missing price is not a cheap one"))


def _walk(series, hours, action) -> Gate:
    pts = []
    for u in hours:
        if not series.covers(u):
            return Gate.block(
                f"{action.name} needs prices for {action.commits_h:g} hours "
                f"from {messages.when(brussels(hours[0]))}, and no price "
                f"covers {messages.when(brussels(u))}. An hour with no price "
                f"is not a free one")
        p = series.at(u)
        if p.provisional:
            return Gate.block(
                f"{action.name} needs prices for {action.commits_h:g} hours "
                f"from {messages.when(brussels(hours[0]))}, and the price for "
                f"{messages.when(brussels(u))} is only estimated. It can start "
                f"once the day-ahead prices are published, around 14:00 to "
                f"16:00")
        pts.append(p)
    return Gate.permit(action, pts)


def begin_phase(maint, now: datetime, read: PriceRead,
                action: Irreversible) -> Gate:
    """Start a maintenance phase BECAUSE OF A PRICE, or refuse and say why. The
    price-justified entry point, not the calendar one: a site with no provider must
    keep starting its monthly cycle as today (12). The blocking arm has no path to
    `maint.force_start(now)`."""
    gate = price_permits(read, now, action)
    return gate.match(permitted=lambda g: _go(maint, now, g),
                      blocked=lambda g: _no(g))


def _go(maint, now, gate) -> Gate:
    maint.force_start(now)
    _LOG.info("%s: %s", gate.action.name, gate.words)
    return gate


def _no(gate) -> Gate:
    _LOG.warning("An action that cannot be undone does not start: %s.",
                 gate.reason)
    return gate