import { documentHasRecurrence, parseProperty, recurrenceBase } from "@/worker/caldav/ical/core";
import { parseCalendarDocument } from "@/worker/caldav/ical/parse";
import { calendarOccurrences, occurrenceOverlaps } from "@/worker/caldav/ical/recurrence";
import type { CalendarOccurrence, CalendarTimeRange, RecurrenceBounds } from "@/worker/caldav/ical/types";

function formatUtcDate(ms: number): string {
  const date = new Date(ms);
  const pad = (value: number) => String(value).padStart(2, "0");
  return `${date.getUTCFullYear()}${pad(date.getUTCMonth() + 1)}${pad(date.getUTCDate())}`;
}

function formatUtcDateTime(ms: number): string {
  const date = new Date(ms);
  const pad = (value: number) => String(value).padStart(2, "0");
  return `${formatUtcDate(ms)}T${pad(date.getUTCHours())}${pad(date.getUTCMinutes())}${pad(date.getUTCSeconds())}Z`;
}

function datePropertyLine(name: string, ms: number, valueType: "date" | "date-time"): string {
  return valueType === "date" ? `${name};VALUE=DATE:${formatUtcDate(ms)}` : `${name}:${formatUtcDateTime(ms)}`;
}

function expandedComponent(occurrence: CalendarOccurrence, forceRecurrenceId: boolean): string[] {
  const excluded = new Set(["DTSTART", "DTEND", "DUE", "DURATION", "RRULE", "RDATE", "EXDATE", "RECURRENCE-ID"]);
  const preserved = occurrence.component.lines.filter((line) => {
    const prop = parseProperty(line);
    return prop && !excluded.has(prop.name);
  });
  const lines = [`BEGIN:${occurrence.component.componentType}`, ...preserved];
  const recurrenceValueType =
    occurrence.component.recurrenceId?.valueType ?? recurrenceBase(occurrence.component)?.valueType ?? "date-time";
  const startValueType =
    occurrence.component.dtstart?.valueType ?? recurrenceBase(occurrence.component)?.valueType ?? "date-time";
  if (forceRecurrenceId || !occurrence.isInitial || occurrence.component.recurrenceId) {
    lines.push(datePropertyLine("RECURRENCE-ID", occurrence.originalStartMs, recurrenceValueType));
  }
  lines.push(datePropertyLine("DTSTART", occurrence.startMs, startValueType));
  if (occurrence.component.componentType === "VEVENT") {
    if (occurrence.endMs !== occurrence.startMs)
      lines.push(datePropertyLine("DTEND", occurrence.endMs, startValueType));
  } else if (occurrence.component.componentType === "VTODO") {
    lines.push(datePropertyLine("DUE", occurrence.endMs, startValueType));
  }
  lines.push(`END:${occurrence.component.componentType}`);
  return lines;
}

export function expandCalendarData(body: string, range: CalendarTimeRange, bounds: RecurrenceBounds): string {
  const document = parseCalendarDocument(body);
  const lines = ["BEGIN:VCALENDAR", "VERSION:2.0", "PRODID:-//dab//CalDAV//EN"];
  const forceRecurrenceId = documentHasRecurrence(document.components) && document.overrides.length === 0;
  for (const occurrence of calendarOccurrences(document, bounds, range)) {
    if (occurrenceOverlaps(document, occurrence, range)) {
      lines.push(...expandedComponent(occurrence, forceRecurrenceId));
    }
  }
  lines.push("END:VCALENDAR", "");
  return lines.join("\r\n");
}