// ── Timer Engine ───────────────────────────────────────────────
// Core timer types, state machine, and lifecycle management

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

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

export type TimerType = 'alarm' | 'countdown' | 'pomodoro' | 'event';

export type TimerState =
  | 'idle'
  | 'active'
  | 'warning'
  | 'firing'
  | 'snoozed'
  | 'dismissed'
  | 'completed'
  | 'paused';

export interface Timer {
  id: string;
  type: TimerType;
  label: string;
  description?: string;
  urgency: UrgencyLevel;
  state: TimerState;

  // Time fields
  targetTime: number; // epoch ms — when the timer fires
  duration: number | null; // ms — for countdowns/pomodoro
  createdAt: number;
  startedAt: number | null;
  pausedAt: number | null;
  firedAt: number | null;
  dismissedAt: number | null;
  completedAt: number | null;

  // Elapsed tracking for pause/resume
  elapsedBeforePause: number; // ms accumulated before last pause

  // Cascade
  cascade: CascadeConfig;
  warnings: CascadeWarning[];

  // Pomodoro-specific
  pomodoroConfig?: PomodoroConfig;
  pomodoroState?: PomodoroState;

  // Snooze
  snoozeCount: number;
  snoozedUntil: number | null;

  // Metadata
  category?: string;
  tags?: string[];
  linkedTimerId?: string | null;
  recurringTimerId?: string | null;
}

export interface PomodoroConfig {
  workMinutes: number;
  breakMinutes: number;
  longBreakMinutes: number;
  rounds: number;
}

export interface PomodoroState {
  currentRound: number;
  isBreak: boolean;
  isLongBreak: boolean;
  completedRounds: number;
}

export const DEFAULT_POMODORO_CONFIG: PomodoroConfig = {
  workMinutes: 25,
  breakMinutes: 5,
  longBreakMinutes: 15,
  rounds: 4,
};

// ── Factory Functions ──────────────────────────────────────────

export interface CreateAlarmParams {
  label: string;
  targetTime: number;
  urgency?: UrgencyLevel;
  cascade?: CascadeConfig;
  category?: string;
  description?: string;
}

export function createAlarm(params: CreateAlarmParams): Timer {
  const cascade = params.cascade ?? { preset: 'standard', intervals: [] };
  const intervals = getCascadeIntervals(cascade);
  const now = Date.now();

  return {
    id: uuidv4(),
    type: 'alarm',
    label: params.label,
    description: params.description,
    urgency: params.urgency ?? 'standard',
    state: 'active',
    targetTime: params.targetTime,
    duration: params.targetTime - now,
    createdAt: now,
    startedAt: now,
    pausedAt: null,
    firedAt: null,
    dismissedAt: null,
    completedAt: null,
    elapsedBeforePause: 0,
    cascade,
    warnings: calculateCascadeWarnings(params.targetTime, intervals, now),
    snoozeCount: 0,
    snoozedUntil: null,
    category: params.category,
  };
}

export interface CreateCountdownParams {
  label: string;
  durationMs: number;
  urgency?: UrgencyLevel;
  cascade?: CascadeConfig;
  category?: string;
  description?: string;
}

export function createCountdown(params: CreateCountdownParams): Timer {
  const now = Date.now();
  const targetTime = now + params.durationMs;
  const cascade = params.cascade ?? { preset: 'standard', intervals: [] };
  const intervals = getCascadeIntervals(cascade);

  return {
    id: uuidv4(),
    type: 'countdown',
    label: params.label,
    description: params.description,
    urgency: params.urgency ?? 'standard',
    state: 'active',
    targetTime,
    duration: params.durationMs,
    createdAt: now,
    startedAt: now,
    pausedAt: null,
    firedAt: null,
    dismissedAt: null,
    completedAt: null,
    elapsedBeforePause: 0,
    cascade,
    warnings: calculateCascadeWarnings(targetTime, intervals, now),
    snoozeCount: 0,
    snoozedUntil: null,
    category: params.category,
  };
}

export interface CreateEventParams {
  label: string;
  targetTime: number; // epoch ms — the future event date
  urgency?: UrgencyLevel;
  cascade?: CascadeConfig;
  category?: string;
  description?: string;
  milestones?: number[]; // days before event to warn (e.g. [30, 7, 1])
}

export const DEFAULT_EVENT_MILESTONES = [30, 7, 3, 1]; // days before

export function createEvent(params: CreateEventParams): Timer {
  const now = Date.now();
  const milestones = params.milestones ?? DEFAULT_EVENT_MILESTONES;
  // Convert milestone days to cascade warning minutes
  const milestoneMinutes = milestones
    .map((days) => days * 24 * 60)
    .filter((mins) => mins * 60_000 < (params.targetTime - now)); // only include if before now

  const cascade = params.cascade ?? { preset: 'custom', intervals: [] };

  return {
    id: uuidv4(),
    type: 'event',
    label: params.label,
    description: params.description,
    urgency: params.urgency ?? 'gentle',
    state: 'active',
    targetTime: params.targetTime,
    duration: params.targetTime - now,
    createdAt: now,
    startedAt: now,
    pausedAt: null,
    firedAt: null,
    dismissedAt: null,
    completedAt: null,
    elapsedBeforePause: 0,
    cascade,
    warnings: calculateCascadeWarnings(params.targetTime, milestoneMinutes, now),
    snoozeCount: 0,
    snoozedUntil: null,
    category: params.category,
  };
}

export interface CreatePomodoroParams {
  label?: string;
  config?: Partial<PomodoroConfig>;
  urgency?: UrgencyLevel;
}

export function createPomodoro(params: CreatePomodoroParams = {}): Timer {
  const now = Date.now();
  const config = { ...DEFAULT_POMODORO_CONFIG, ...params.config };
  const durationMs = config.workMinutes * 60 * 1000;
  const targetTime = now + durationMs;

  return {
    id: uuidv4(),
    type: 'pomodoro',
    label: params.label ?? 'Focus Session',
    urgency: params.urgency ?? 'standard',
    state: 'active',
    targetTime,
    duration: durationMs,
    createdAt: now,
    startedAt: now,
    pausedAt: null,
    firedAt: null,
    dismissedAt: null,
    completedAt: null,
    elapsedBeforePause: 0,
    cascade: { preset: 'minimal', intervals: [] },
    warnings: calculateCascadeWarnings(targetTime, [1], now),
    pomodoroConfig: config,
    pomodoroState: {
      currentRound: 1,
      isBreak: false,
      isLongBreak: false,
      completedRounds: 0,
    },
    snoozeCount: 0,
    snoozedUntil: null,
  };
}

// ── State Transitions ──────────────────────────────────────────

export function pauseTimer(timer: Timer): Timer {
  if (timer.state !== 'active' && timer.state !== 'warning') return timer;
  const now = Date.now();
  const elapsed = timer.elapsedBeforePause + (now - (timer.startedAt ?? now));
  return {
    ...timer,
    state: 'paused',
    pausedAt: now,
    elapsedBeforePause: elapsed,
  };
}

export function resumeTimer(timer: Timer): Timer {
  if (timer.state !== 'paused') return timer;
  const now = Date.now();
  const remainingMs = (timer.duration ?? 0) - timer.elapsedBeforePause;
  const newTargetTime = now + remainingMs;

  const intervals = getCascadeIntervals(timer.cascade);
  return {
    ...timer,
    state: 'active',
    startedAt: now,
    pausedAt: null,
    targetTime: newTargetTime,
    warnings: calculateCascadeWarnings(newTargetTime, intervals, now),
  };
}

export function fireTimer(timer: Timer): Timer {
  if (timer.state === 'dismissed' || timer.state === 'completed') return timer;
  return {
    ...timer,
    state: 'firing',
    firedAt: Date.now(),
  };
}

export function snoozeTimer(timer: Timer, snoozeMinutes: number): Timer {
  if (timer.state !== 'firing') return timer;
  const now = Date.now();
  const snoozeUntil = now + snoozeMinutes * 60 * 1000;
  const intervals = getCascadeIntervals(timer.cascade);

  return {
    ...timer,
    state: 'snoozed',
    targetTime: snoozeUntil,
    snoozedUntil: snoozeUntil,
    snoozeCount: timer.snoozeCount + 1,
    warnings: calculateCascadeWarnings(snoozeUntil, intervals.filter(m => m <= snoozeMinutes), now),
  };
}

export function dismissTimer(timer: Timer): Timer {
  return {
    ...timer,
    state: 'dismissed',
    dismissedAt: Date.now(),
  };
}

export function completeTimer(timer: Timer): Timer {
  return {
    ...timer,
    state: 'completed',
    completedAt: Date.now(),
  };
}

// ── Pomodoro Transitions ───────────────────────────────────────

export function advancePomodoro(timer: Timer): Timer | null {
  if (timer.type !== 'pomodoro' || !timer.pomodoroConfig || !timer.pomodoroState) return null;

  const { pomodoroConfig: config, pomodoroState: state } = timer;
  const now = Date.now();

  if (state.isBreak || state.isLongBreak) {
    // Long break finished → all done
    if (state.isLongBreak) {
      return completeTimer(timer);
    }
    // Short break finished → start next work round
    const nextRound = state.currentRound + 1;
    if (nextRound > config.rounds) {
      return completeTimer(timer);
    }
    const durationMs = config.workMinutes * 60 * 1000;
    return {
      ...timer,
      state: 'active',
      targetTime: now + durationMs,
      duration: durationMs,
      startedAt: now,
      firedAt: null,
      elapsedBeforePause: 0,
      warnings: calculateCascadeWarnings(now + durationMs, [1], now),
      pomodoroState: {
        currentRound: nextRound,
        isBreak: false,
        isLongBreak: false,
        completedRounds: state.completedRounds,
      },
    };
  } else {
    // Work finished → start break
    const completedRounds = state.completedRounds + 1;
    const isLongBreak = completedRounds >= config.rounds;

    if (isLongBreak && completedRounds >= config.rounds) {
      // All rounds done, long break
      const durationMs = config.longBreakMinutes * 60 * 1000;
      return {
        ...timer,
        state: 'active',
        targetTime: now + durationMs,
        duration: durationMs,
        startedAt: now,
        firedAt: null,
        elapsedBeforePause: 0,
        warnings: [],
        pomodoroState: {
          currentRound: state.currentRound,
          isBreak: false,
          isLongBreak: true,
          completedRounds,
        },
      };
    }

    const durationMs = config.breakMinutes * 60 * 1000;
    return {
      ...timer,
      state: 'active',
      targetTime: now + durationMs,
      duration: durationMs,
      startedAt: now,
      firedAt: null,
      elapsedBeforePause: 0,
      warnings: [],
      pomodoroState: {
        currentRound: state.currentRound,
        isBreak: true,
        isLongBreak: false,
        completedRounds,
      },
    };
  }
}

// ── Utility ────────────────────────────────────────────────────

export function getRemainingMs(timer: Timer, now: number = Date.now()): number {
  if (timer.state === 'paused') {
    return (timer.duration ?? 0) - timer.elapsedBeforePause;
  }
  return Math.max(0, timer.targetTime - now);
}

export function isTimerActive(timer: Timer): boolean {
  return ['active', 'warning', 'snoozed'].includes(timer.state);
}

export function shouldTimerFire(timer: Timer, now: number = Date.now()): boolean {
  if (timer.state === 'snoozed' && timer.snoozedUntil && now >= timer.snoozedUntil) {
    return true;
  }
  if ((timer.state === 'active' || timer.state === 'warning') && now >= timer.targetTime) {
    return true;
  }
  return false;
}