// The reporting period every report destination shares. It lives in the URL so a report can be
// reloaded, bookmarked or printed with the same filters.

export type ReportPreset = 'this-month' | 'last-month' | 'last-30' | 'this-quarter' | 'this-year' | 'custom';
export type ReportComparison = 'none' | 'previous' | 'year';

export interface ReportFilters {
    preset: ReportPreset;
    start: string;
    end: string;
    location: string;
    compare: ReportComparison;
}

export const PRESET_LABELS: Array<[ReportPreset, string]> = [
    ['this-month', 'This month'],
    ['last-month', 'Last month'],
    ['last-30', 'Last 30 days'],
    ['this-quarter', 'This quarter'],
    ['this-year', 'This year'],
    ['custom', 'Custom'],
];

export const COMPARISON_LABELS: Array<[ReportComparison, string]> = [
    ['none', 'No comparison'],
    ['previous', 'Previous period'],
    ['year', 'Same period last year'],
];

export const ALL_LOCATIONS = 'all';

const EN_DASH = String.fromCharCode(0x2013);
const pad = (value: number) => String(value).padStart(2, '0');
const isoDate = (date: Date) => date.getFullYear() + '-' + pad(date.getMonth() + 1) + '-' + pad(date.getDate());
const DATE_PATTERN = /^\d{4}-\d{2}-\d{2}$/;

export function presetRange(preset: ReportPreset, today: Date = new Date()): { start: string; end: string } | null {
    const year = today.getFullYear();
    const month = today.getMonth();
    switch (preset) {
        case 'this-month':
            return { start: isoDate(new Date(year, month, 1)), end: isoDate(new Date(year, month + 1, 0)) };
        case 'last-month':
            return { start: isoDate(new Date(year, month - 1, 1)), end: isoDate(new Date(year, month, 0)) };
        case 'last-30':
            return { start: isoDate(new Date(year, month, today.getDate() - 29)), end: isoDate(today) };
        case 'this-quarter': {
            const first = month - (month % 3);
            return { start: isoDate(new Date(year, first, 1)), end: isoDate(new Date(year, first + 3, 0)) };
        }
        case 'this-year':
            return { start: isoDate(new Date(year, 0, 1)), end: isoDate(new Date(year, 11, 31)) };
        default:
            return null;
    }
}

const PRESETS = new Set(PRESET_LABELS.map(([value]) => value));
const COMPARISONS = new Set(COMPARISON_LABELS.map(([value]) => value));

export function filtersFromSearch(params: URLSearchParams, today: Date = new Date()): ReportFilters {
    const start = params.get('start') ?? '';
    const end = params.get('end') ?? '';
    const compareParam = params.get('compare') as ReportComparison | null;
    const compare = compareParam && COMPARISONS.has(compareParam) ? compareParam : 'previous';
    const location = params.get('location') || ALL_LOCATIONS;
    if (DATE_PATTERN.test(start) && DATE_PATTERN.test(end)) {
        const presetParam = params.get('period') as ReportPreset | null;
        const preset = presetParam && PRESETS.has(presetParam) ? presetParam : 'custom';
        return { preset, start, end, location, compare };
    }
    const range = presetRange('this-month', today)!;
    return { preset: 'this-month', ...range, location, compare };
}

export function searchFromFilters(filters: ReportFilters): string {
    const params = new URLSearchParams({ period: filters.preset, start: filters.start, end: filters.end });
    if (filters.location !== ALL_LOCATIONS) params.set('location', filters.location);
    params.set('compare', filters.compare);
    return params.toString();
}

/** What the server is asked for; the server validates the same fields again. */
export function reportQuery(filters: ReportFilters): string {
    const params = new URLSearchParams({ start: filters.start, end: filters.end, compare: filters.compare });
    if (filters.location !== ALL_LOCATIONS) params.set('location', filters.location);
    return params.toString();
}

const MONTHS = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
const parts = (value: string) => value.split('-').map(Number) as [number, number, number];

/** "Sep 1-30, 2026", "Aug 30-Sep 5, 2026" or "Dec 28, 2025-Jan 3, 2026", with an en dash. */
// A loaded report is current only for the exact request it answered: kind, dates, comparison and location.
export function reportRequestKey(report: string, filters: ReportFilters): string {
    return report + '?' + reportQuery(filters);
}

export function formatRange(start: string, end: string, withYear = true): string {
    const [startYear, startMonth, startDay] = parts(start);
    const [endYear, endMonth, endDay] = parts(end);
    const year = withYear ? ', ' + endYear : '';
    if (startYear !== endYear) {
        return MONTHS[startMonth - 1] + ' ' + startDay + ', ' + startYear + EN_DASH + MONTHS[endMonth - 1] + ' ' + endDay + ', ' + endYear;
    }
    if (startMonth === endMonth) {
        const days = startDay === endDay ? String(startDay) : startDay + EN_DASH + endDay;
        return MONTHS[startMonth - 1] + ' ' + days + year;
    }
    return MONTHS[startMonth - 1] + ' ' + startDay + EN_DASH + MONTHS[endMonth - 1] + ' ' + endDay + year;
}