// ── Calendar .ics Import ──────────────────────────────────────
// Parse iCalendar (.ics) files and import events as timers

import type { Timer } from './timer-engine';
import type { UrgencyLevel } from './urgency';
import type { CascadeConfig } from './cascade';
import { v4 as uuidv4 } from 'uuid';
import { calculateCascadeWarnings, getCascadeIntervals } from './cascade';

// ── Types ─────────────────────────────────────────────────────

export interface IcsEvent {
  uid: string;
  summary: string;
  description?: string;
  dtstart: Date;
  dtend?: Date;
  location?: string;
  priority?: number; // 1-9, lower = higher priority
}

export interface ImportedEvent {
  event: IcsEvent;
  timer: Timer;
  conflicts: string[]; // IDs of existing timers that overlap
}

export interface CalendarImportResult {
  events: ImportedEvent[];
  errors: string[];
  totalParsed: number;
}

// ── .ics Parser ───────────────────────────────────────────────

/**
 * Parse an .ics file content into events.
 */
export function parseIcs(content: string): { events: IcsEvent[]; errors: string[] } {
  const events: IcsEvent[] = [];
  const errors: string[] = [];

  // Unfold lines (RFC 5545: continuation lines start with space/tab)
  const unfolded = content.replace(/\r\n[ \t]/g, '').replace(/\r\n/g, '\n').replace(/\r/g, '\n');
  const lines = unfolded.split('\n');

  let inEvent = false;
  let currentEvent: Partial<IcsEvent> = {};

  for (const line of lines) {
    const trimmed = line.trim();

    if (trimmed === 'BEGIN:VEVENT') {
      inEvent = true;
      currentEvent = {};
      continue;
    }

    if (trimmed === 'END:VEVENT') {
      inEvent = false;
      if (currentEvent.summary && currentEvent.dtstart) {
        events.push({
          uid: currentEvent.uid ?? uuidv4(),
          summary: currentEvent.summary,
          description: currentEvent.description,
          dtstart: currentEvent.dtstart,
          dtend: currentEvent.dtend,
          location: currentEvent.location,
          priority: currentEvent.priority,
        });
      } else {
        errors.push(`Event missing required fields (SUMMARY or DTSTART)`);
      }
      continue;
    }

    if (!inEvent) continue;

    // Parse property
    const colonIdx = trimmed.indexOf(':');
    if (colonIdx === -1) continue;

    const propPart = trimmed.slice(0, colonIdx);
    const value = trimmed.slice(colonIdx + 1);

    // Strip parameters (e.g., DTSTART;TZID=America/New_York:20260315T090000)
    const propName = propPart.split(';')[0].toUpperCase();

    switch (propName) {
      case 'UID':
        currentEvent.uid = value;
        break;
      case 'SUMMARY':
        currentEvent.summary = unescapeIcsText(value);
        break;
      case 'DESCRIPTION':
        currentEvent.description = unescapeIcsText(value);
        break;
      case 'LOCATION':
        currentEvent.location = unescapeIcsText(value);
        break;
      case 'DTSTART':
        currentEvent.dtstart = parseIcsDateTime(value);
        break;
      case 'DTEND':
        currentEvent.dtend = parseIcsDateTime(value);
        break;
      case 'PRIORITY':
        currentEvent.priority = parseInt(value, 10) || undefined;
        break;
    }
  }

  return { events, errors };
}

/**
 * Parse iCalendar date-time string.
 * Formats: 20260315T090000, 20260315T090000Z, 20260315
 */
function parseIcsDateTime(value: string): Date {
  const cleaned = value.trim();

  // Date only: YYYYMMDD
  if (cleaned.length === 8) {
    const y = parseInt(cleaned.slice(0, 4));
    const m = parseInt(cleaned.slice(4, 6)) - 1;
    const d = parseInt(cleaned.slice(6, 8));
    return new Date(y, m, d);
  }

  // DateTime: YYYYMMDDTHHMMSS or YYYYMMDDTHHMMSSZ
  const isUtc = cleaned.endsWith('Z');
  const dt = isUtc ? cleaned.slice(0, -1) : cleaned;
  const parts = dt.split('T');

  const y = parseInt(parts[0].slice(0, 4));
  const m = parseInt(parts[0].slice(4, 6)) - 1;
  const d = parseInt(parts[0].slice(6, 8));
  const h = parts[1] ? parseInt(parts[1].slice(0, 2)) : 0;
  const min = parts[1] ? parseInt(parts[1].slice(2, 4)) : 0;
  const s = parts[1] ? parseInt(parts[1].slice(4, 6)) : 0;

  if (isUtc) {
    return new Date(Date.UTC(y, m, d, h, min, s));
  }
  return new Date(y, m, d, h, min, s);
}

/**
 * Unescape iCalendar text values.
 */
function unescapeIcsText(text: string): string {
  return text
    .replace(/\\n/g, '\n')
    .replace(/\\,/g, ',')
    .replace(/\\;/g, ';')
    .replace(/\\\\/g, '\\');
}

// ── Event → Timer Conversion ──────────────────────────────────

/**
 * Map iCalendar priority (1-9) to ChronoMind urgency level.
 * 1-2: critical, 3-4: important, 5: standard, 6-7: gentle, 8-9: passive
 */
export function mapPriorityToUrgency(priority?: number): UrgencyLevel {
  if (!priority || priority < 1 || priority > 9) return 'standard';
  if (priority <= 2) return 'critical';
  if (priority <= 4) return 'important';
  if (priority <= 5) return 'standard';
  if (priority <= 7) return 'gentle';
  return 'passive';
}

/**
 * Convert an IcsEvent to a Timer with auto-generated cascade.
 */
export function eventToTimer(event: IcsEvent, now: number = Date.now()): Timer {
  const urgency = mapPriorityToUrgency(event.priority);
  const targetTime = event.dtstart.getTime();

  // Auto-cascade based on urgency
  const cascadePresetMap: Record<UrgencyLevel, CascadeConfig> = {
    critical: { preset: 'aggressive', intervals: [] },
    important: { preset: 'standard', intervals: [] },
    standard: { preset: 'light', intervals: [] },
    gentle: { preset: 'minimal', intervals: [] },
    passive: { preset: 'none', intervals: [] },
  };

  const cascade = cascadePresetMap[urgency];
  const intervals = getCascadeIntervals(cascade);

  return {
    id: uuidv4(),
    type: 'alarm',
    label: event.summary,
    description: [event.description, event.location].filter(Boolean).join(' — '),
    urgency,
    state: targetTime > now ? 'active' : 'dismissed',
    targetTime,
    duration: event.dtend ? event.dtend.getTime() - targetTime : null,
    createdAt: now,
    startedAt: targetTime > now ? now : null,
    pausedAt: null,
    firedAt: targetTime <= now ? targetTime : null,
    dismissedAt: targetTime <= now ? now : null,
    completedAt: null,
    elapsedBeforePause: 0,
    cascade,
    warnings: calculateCascadeWarnings(targetTime, intervals, now),
    snoozeCount: 0,
    snoozedUntil: null,
  };
}

// ── Conflict Detection ────────────────────────────────────────

/**
 * Detect conflicts between an event and existing timers.
 * Conflict = existing timer fires within 15 minutes of event start.
 */
export function detectConflicts(
  event: IcsEvent,
  existingTimers: Timer[],
  conflictWindowMs: number = 15 * 60 * 1000
): string[] {
  const eventStart = event.dtstart.getTime();
  const eventEnd = event.dtend?.getTime() ?? eventStart + 60 * 60 * 1000;

  return existingTimers
    .filter((t) => {
      if (['dismissed', 'completed'].includes(t.state)) return false;
      const timerTime = t.targetTime;
      // Timer fires within event window or event starts within timer's range
      return (
        (timerTime >= eventStart - conflictWindowMs && timerTime <= eventEnd + conflictWindowMs)
      );
    })
    .map((t) => t.id);
}

// ── Full Import Pipeline ──────────────────────────────────────

/**
 * Parse .ics content and convert to importable timers with conflict detection.
 */
export function importCalendar(
  icsContent: string,
  existingTimers: Timer[],
  now: number = Date.now()
): CalendarImportResult {
  const { events: icsEvents, errors: parseErrors } = parseIcs(icsContent);

  const importedEvents: ImportedEvent[] = icsEvents.map((event) => {
    const timer = eventToTimer(event, now);
    const conflicts = detectConflicts(event, existingTimers);
    return { event, timer, conflicts };
  });

  return {
    events: importedEvents,
    errors: parseErrors,
    totalParsed: icsEvents.length,
  };
}