// ── Linked Timers ─────────────────────────────────────────────
// "When timer A ends, start timer B" chain relationships

import type { Timer } from './timer-engine';

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

export interface TimerLink {
  fromId: string;  // timer that triggers
  toId: string;    // timer that starts
  delay: number;   // ms delay between from completing and to starting (0 = immediate)
}

export interface TimerChain {
  id: string;
  name: string;
  links: TimerLink[];
  timerIds: string[]; // ordered list of timer IDs in chain
}

// ── Chain Building ────────────────────────────────────────────

/**
 * Build a chain from an ordered list of timer IDs.
 * Each timer links to the next with the specified delay.
 */
export function buildChain(
  name: string,
  timerIds: string[],
  delayMs: number = 0
): TimerChain {
  const links: TimerLink[] = [];
  for (let i = 0; i < timerIds.length - 1; i++) {
    links.push({
      fromId: timerIds[i],
      toId: timerIds[i + 1],
      delay: delayMs,
    });
  }

  return {
    id: `chain-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`,
    name,
    links,
    timerIds,
  };
}

/**
 * Add a timer to the end of an existing chain.
 */
export function appendToChain(
  chain: TimerChain,
  timerId: string,
  delayMs: number = 0
): TimerChain {
  const lastId = chain.timerIds[chain.timerIds.length - 1];
  if (!lastId) return chain;

  return {
    ...chain,
    timerIds: [...chain.timerIds, timerId],
    links: [
      ...chain.links,
      { fromId: lastId, toId: timerId, delay: delayMs },
    ],
  };
}

/**
 * Remove a timer from a chain. Relinks neighbours if possible.
 */
export function removeFromChain(
  chain: TimerChain,
  timerId: string
): TimerChain {
  const idx = chain.timerIds.indexOf(timerId);
  if (idx === -1) return chain;

  const newTimerIds = chain.timerIds.filter((id) => id !== timerId);

  // Rebuild links from the new ordered list
  const newLinks: TimerLink[] = [];
  for (let i = 0; i < newTimerIds.length - 1; i++) {
    // Try to preserve original delay
    const existingLink = chain.links.find(
      (l) => l.fromId === newTimerIds[i] && l.toId === newTimerIds[i + 1]
    );
    newLinks.push({
      fromId: newTimerIds[i],
      toId: newTimerIds[i + 1],
      delay: existingLink?.delay ?? 0,
    });
  }

  return {
    ...chain,
    timerIds: newTimerIds,
    links: newLinks,
  };
}

// ── Chain Queries ─────────────────────────────────────────────

/**
 * Find the next timer to start when a timer completes/fires.
 */
export function getNextInChain(
  chains: TimerChain[],
  completedTimerId: string
): TimerLink | null {
  for (const chain of chains) {
    const link = chain.links.find((l) => l.fromId === completedTimerId);
    if (link) return link;
  }
  return null;
}

/**
 * Find the chain a timer belongs to.
 */
export function findChainForTimer(
  chains: TimerChain[],
  timerId: string
): TimerChain | null {
  return chains.find((c) => c.timerIds.includes(timerId)) ?? null;
}

/**
 * Get the position of a timer within its chain.
 * Returns null if timer is not in any chain.
 */
export function getChainPosition(
  chains: TimerChain[],
  timerId: string
): { chain: TimerChain; index: number; total: number } | null {
  const chain = findChainForTimer(chains, timerId);
  if (!chain) return null;
  const index = chain.timerIds.indexOf(timerId);
  return { chain, index, total: chain.timerIds.length };
}

/**
 * Get all timers in a chain with their labels, for visualization.
 */
export function getChainTimers(
  chain: TimerChain,
  allTimers: Timer[]
): (Timer | null)[] {
  return chain.timerIds.map((id) => allTimers.find((t) => t.id === id) ?? null);
}

/**
 * Check if cancelling a timer should prompt to cancel the whole chain.
 */
export function hasDownstreamTimers(
  chains: TimerChain[],
  timerId: string
): boolean {
  const chain = findChainForTimer(chains, timerId);
  if (!chain) return false;
  const idx = chain.timerIds.indexOf(timerId);
  return idx < chain.timerIds.length - 1;
}

/**
 * Get all downstream timer IDs (timers that follow this one in chain).
 */
export function getDownstreamTimerIds(
  chains: TimerChain[],
  timerId: string
): string[] {
  const chain = findChainForTimer(chains, timerId);
  if (!chain) return [];
  const idx = chain.timerIds.indexOf(timerId);
  if (idx === -1) return [];
  return chain.timerIds.slice(idx + 1);
}

// ── Built-in Chain Presets ────────────────────────────────────

export interface ChainPreset {
  name: string;
  steps: { label: string; durationMs: number }[];
}

export const CHAIN_PRESETS: ChainPreset[] = [
  {
    name: 'Pasta Timer',
    steps: [
      { label: 'Boil Water', durationMs: 10 * 60_000 },
      { label: 'Cook Pasta', durationMs: 12 * 60_000 },
      { label: 'Prepare Sauce', durationMs: 8 * 60_000 },
    ],
  },
  {
    name: 'Laundry',
    steps: [
      { label: 'Washer Cycle', durationMs: 45 * 60_000 },
      { label: 'Transfer to Dryer', durationMs: 5 * 60_000 },
      { label: 'Dryer Cycle', durationMs: 60 * 60_000 },
    ],
  },
  {
    name: 'Meeting Prep',
    steps: [
      { label: 'Review Notes', durationMs: 10 * 60_000 },
      { label: 'Get Ready', durationMs: 5 * 60_000 },
      { label: 'Travel / Join Call', durationMs: 5 * 60_000 },
    ],
  },
];