"""UTC intervals and availability rules, independent of HTTP and storage."""

from datetime import date, datetime, time, timedelta
from zoneinfo import ZoneInfo


def make_slots(
    dates: list[str], start: str, end: str, minutes: int, zone: str
) -> list[int]:
    tz = ZoneInfo(zone)
    start_time = time.fromisoformat(start)
    end_time = time.min if end == "24:00" else time.fromisoformat(end)
    if any(t.second or t.microsecond or t.tzinfo for t in (start_time, end_time)):
        raise ValueError("Use local times with minute precision.")
    if end != "24:00" and end_time <= start_time:
        raise ValueError("The end must be after the start; use 24:00 for midnight.")
    slots = set()
    for day in sorted(set(dates)):
        first = datetime.combine(date.fromisoformat(day), start_time)
        last = datetime.combine(first.date(), end_time)
        if end == "24:00":
            last += timedelta(days=1)
        if (last - first).total_seconds() % (minutes * 60):
            raise ValueError("The daily range must contain whole slots.")
        current = first
        valid_minutes = set()
        while current < last:
            # Build valid UTC ranges first, then fit whole slots. This also handles
            # half-hour DST changes without producing overlapping hour-long slots.
            for fold in (0, 1):
                instant = int(current.replace(tzinfo=tz, fold=fold).timestamp())
                if datetime.fromtimestamp(instant, tz).replace(tzinfo=None) == current:
                    valid_minutes.add(instant)
            current += timedelta(minutes=1)
        step = minutes * 60
        for first_utc, last_utc in intervals(sorted(valid_minutes), 60):
            slots.update(range(first_utc, last_utc - step + 1, step))
    return sorted(slots)


def intervals(slots: list[int], seconds: int) -> list[tuple[int, int]]:
    result = []
    for slot in sorted(slots):
        if result and result[-1][1] == slot:
            result[-1] = (result[-1][0], slot + seconds)
        else:
            result.append((slot, slot + seconds))
    return result


def resize_slots(
    slots: list[int], old_minutes: int, new_minutes: int, zone: str = "UTC"
) -> list[int]:
    step = new_minutes * 60
    ranges = []
    tz = ZoneInfo(zone)
    for first, last in intervals(slots, old_minutes * 60):
        start_clock, end_clock = (
            datetime.fromtimestamp(first, tz),
            datetime.fromtimestamp(last, tz),
        )
        first -= (start_clock.minute % new_minutes) * 60
        last += (-end_clock.minute % new_minutes) * 60
        if ranges and first <= ranges[-1][1]:
            ranges[-1] = (ranges[-1][0], max(last, ranges[-1][1]))
        else:
            ranges.append((first, last))
    return [s for first, last in ranges for s in range(first, last - step + 1, step)]


def remap_votes(
    votes: dict[str, str], old_minutes: int, slots: list[int], new_minutes: int
) -> dict[str, str]:
    old = sorted(
        (int(start), int(start) + old_minutes * 60, value)
        for start, value in votes.items()
    )
    result = {}
    index = 0
    for start in slots:
        end = start + new_minutes * 60
        while index < len(old) and old[index][1] <= start:
            index += 1
        yes_seconds = 0
        overlaps = False
        for old_index in range(index, len(old)):
            a, b, value = old[old_index]
            if a >= end:
                break
            overlap = min(end, b) - max(start, a)
            if overlap > 0:
                overlaps = True
                if value == "yes":
                    yes_seconds += overlap
        if overlaps:
            result[str(start)] = "yes" if yes_seconds == end - start else "maybe"
    return result


def votes_lost(
    votes: dict[str, str], old_minutes: int, slots: list[int], minutes: int
) -> bool:
    ranges = intervals(slots, minutes * 60)
    return any(
        not any(a <= int(slot) and b >= int(slot) + old_minutes * 60 for a, b in ranges)
        for slot in votes
    )


def summaries(slots: list[int], minutes: int, people: list[dict]) -> dict:
    """Longest runs retain the exact participating set, not just its count."""
    result = {"yes": [], "inclusive": []}
    if not people:
        return result
    for mode, groups in result.items():
        runs = []
        for start in slots:
            ids = tuple(
                p["id"]
                for p in people
                if p["votes"].get(str(start))
                in (("yes",) if mode == "yes" else ("yes", "maybe"))
            )
            if runs and runs[-1]["end"] == start and runs[-1]["people"] == ids:
                runs[-1]["end"] += minutes * 60
            else:
                runs.append(
                    {"start": start, "end": start + minutes * 60, "people": ids}
                )
        for missing in range(min(3, len(people) // 4) + 1):
            eligible = [r for r in runs if len(r["people"]) >= len(people) - missing]
            longest = max((r["end"] - r["start"] for r in eligible), default=0)
            groups.append(
                {
                    "missing": missing,
                    "seconds": longest,
                    "stretches": [
                        r for r in eligible if r["end"] - r["start"] == longest
                    ],
                }
            )
    return result