"""Parser for duty-schedule JSON format. No DB access."""

import json
from dataclasses import dataclass
from datetime import date, timedelta

# Символы, обозначающие день дежурства в ячейке duty (CSV с разделителем ;)
DUTY_MARKERS = frozenset({"б", "Б", "в", "Н", "О"})


@dataclass
class DutyScheduleResult:
    """Parsed duty schedule: start_date, end_date, and per-person duty dates."""

    start_date: date
    end_date: date
    entries: list[tuple[str, list[date]]]  # (full_name, list of duty dates)


class DutyScheduleParseError(Exception):
    """Invalid or missing fields in duty-schedule JSON."""

    pass


def parse_duty_schedule(raw_bytes: bytes) -> DutyScheduleResult:
    """Parse duty-schedule JSON. Returns start_date, end_date, and list of (full_name, duty_dates).

    - meta.start_date (YYYY-MM-DD) and schedule (array) required.
    - meta.weeks optional; number of days from max duty string length (split by ';').
    - For each schedule item: name (required), duty = CSV with ';'; index i = start_date + i days.
    - Cell value after strip in DUTY_MARKERS => duty day.
    """
    try:
        data = json.loads(raw_bytes.decode("utf-8"))
    except (json.JSONDecodeError, UnicodeDecodeError) as e:
        raise DutyScheduleParseError(f"Invalid JSON or encoding: {e}") from e

    meta = data.get("meta")
    if not meta or not isinstance(meta, dict):
        raise DutyScheduleParseError("Missing or invalid 'meta'")

    start_str = meta.get("start_date")
    if not start_str or not isinstance(start_str, str):
        raise DutyScheduleParseError("Missing or invalid meta.start_date")
    try:
        start_date = date.fromisoformat(start_str.strip())
    except ValueError as e:
        raise DutyScheduleParseError(f"Invalid meta.start_date: {start_str}") from e

    schedule = data.get("schedule")
    if not isinstance(schedule, list):
        raise DutyScheduleParseError("Missing or invalid 'schedule' (must be array)")

    max_days = 0
    entries: list[tuple[str, list[date]]] = []

    for row in schedule:
        if not isinstance(row, dict):
            raise DutyScheduleParseError("schedule item must be an object")
        name = row.get("name")
        if name is None or not isinstance(name, str):
            raise DutyScheduleParseError("schedule item must have 'name' (string)")
        full_name = name.strip()
        if not full_name:
            raise DutyScheduleParseError("schedule item 'name' cannot be empty")

        duty_str = row.get("duty")
        if duty_str is None:
            duty_str = ""
        if not isinstance(duty_str, str):
            raise DutyScheduleParseError("schedule item 'duty' must be string")

        cells = [c.strip() for c in duty_str.split(";")]
        max_days = max(max_days, len(cells))

        duty_dates: list[date] = []
        for i, cell in enumerate(cells):
            if cell in DUTY_MARKERS:
                d = start_date + timedelta(days=i)
                duty_dates.append(d)
        entries.append((full_name, duty_dates))

    if max_days == 0:
        end_date = start_date
    else:
        end_date = start_date + timedelta(days=max_days - 1)

    return DutyScheduleResult(start_date=start_date, end_date=end_date, entries=entries)