"""Canonical period helpers shared by analytics report pages."""

from __future__ import annotations

from calendar import monthrange
from datetime import date, datetime


def parse_iso_date(value) -> date | None:
    if not value:
        return None
    if isinstance(value, datetime):
        return value.date()
    if isinstance(value, date):
        return value
    try:
        return datetime.strptime(str(value)[:10], "%Y-%m-%d").date()
    except (TypeError, ValueError):
        return None


def parse_month(value) -> date | None:
    if not value:
        return None
    if isinstance(value, datetime):
        return value.date().replace(day=1)
    if isinstance(value, date):
        return value.replace(day=1)
    try:
        return datetime.strptime(str(value)[:7], "%Y-%m").date()
    except (TypeError, ValueError):
        return None


def month_end(value) -> date | None:
    month_start = parse_month(value)
    if not month_start:
        return None
    return month_start.replace(day=monthrange(month_start.year, month_start.month)[1])


def make_analysis_period(start, end=None, *, mode="range", label=None) -> dict:
    start_date = parse_iso_date(start)
    end_date = parse_iso_date(end) if end else start_date
    if not start_date and end_date:
        start_date = end_date
    if not start_date or not end_date:
        return {
            "mode": mode,
            "label": label or "全部資料",
            "start_date": "",
            "end_date": "",
            "start_month": "",
            "end_month": "",
            "is_single_day": False,
            "is_single_month": False,
        }
    if start_date > end_date:
        start_date, end_date = end_date, start_date

    start_month = start_date.strftime("%Y-%m")
    end_month_value = end_date.strftime("%Y-%m")
    is_single_day = start_date == end_date
    is_single_month = start_month == end_month_value
    if not label:
        if is_single_day:
            label = start_date.strftime("%Y-%m-%d")
        elif is_single_month and start_date.day == 1 and end_date == month_end(start_date):
            label = start_date.strftime("%Y 年 %m 月")
        else:
            label = f"{start_date:%Y-%m-%d} 至 {end_date:%Y-%m-%d}"

    return {
        "mode": mode,
        "label": label,
        "start_date": start_date.isoformat(),
        "end_date": end_date.isoformat(),
        "start_month": start_month,
        "end_month": end_month_value,
        "is_single_day": is_single_day,
        "is_single_month": is_single_month,
    }


def make_month_period(value, *, mode="month") -> dict:
    start = parse_month(value)
    if not start:
        return make_analysis_period(None, mode=mode)
    return make_analysis_period(start, month_end(start), mode=mode)