import { EBBINGHAUS_INTERVALS } from '../constants.js';
import { state } from '../core/state.js';
import { MAX_RECORDS, saveRecords, saveSchedule } from '../core/storage.js';

/**
 * Ebbinghaus scheduling and study-record helpers. Inputs are word IDs, dates,
 * and quiz outcomes; mutations update shared state and persist records:<libraryId>
 * and schedule:<libraryId> through the storage service.
 */
// ==================== Ebbinghaus Algorithm ====================
export function toLocalDateStr(d) {
  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
}

export function getToday() {
  return toLocalDateStr(new Date());
}

export function addDays(dateStr, days) {
  const [y, m, day] = dateStr.split('-').map(Number);
  const d = new Date(y, m - 1, day);
  d.setDate(d.getDate() + days);
  return toLocalDateStr(d);
}

export function getDueWords() {
  const today = getToday();
  const due = [];
  for (const [wordId, sch] of Object.entries(state.schedule)) {
    if (sch.nextReview <= today) {
      const word = state.words.find(w => w.id === Number(wordId));
      if (word) due.push({ ...word, schedule: sch });
    }
  }
  return due;
}

export function initWordSchedule(wordId, save = true) {
  if (state.schedule[wordId]) return true;

  state.schedule[wordId] = {
    stage: 0,
    nextReview: getToday(),
    correctCount: 0,
    incorrectCount: 0
  };
  if (!save || saveSchedule()) return true;

  delete state.schedule[wordId];
  return false;
}

export function trimRecords(records, maxRecords, keepPerWord) {
  if (records.length <= maxRecords) return records;

  const selected = new Set();
  const counts = new Map();

  // 第一轮尽可能为每个单词和记录类型保留最新一条，避免整个组合被裁掉
  for (let i = records.length - 1; i >= 0; i--) {
    const record = records[i];
    const key = `${record.wordId}:${record.type}`;
    if (counts.has(key)) continue;

    selected.add(i);
    counts.set(key, 1);
    if (selected.size === maxRecords) break;
  }

  // 第二轮按时间从新到旧填充剩余容量，每个组合优先保留 keepPerWord 条
  for (let i = records.length - 1; i >= 0 && selected.size < maxRecords; i--) {
    if (selected.has(i)) continue;

    const record = records[i];
    const key = `${record.wordId}:${record.type}`;
    const count = counts.get(key) || 0;
    if (count < keepPerWord) {
      selected.add(i);
      counts.set(key, count + 1);
    }
  }

  // 组合较少时前两轮可能未填满容量，继续保留其余最新记录，避免一次裁剪丢失大量历史
  for (let i = records.length - 1; i >= 0 && selected.size < maxRecords; i--) {
    selected.add(i);
  }

  return [...selected]
    .sort((a, b) => a - b)
    .map(index => records[index]);
}

export function recordAndUpdateSchedule(wordId, isCorrect, type, quizMode, options = {}) {
  const previousRecords = state.records;
  const previousSchedule = state.schedule;
  const nextRecords = previousRecords.slice();
  const previousWordSchedule = previousSchedule[wordId];
  const nextWordSchedule = previousWordSchedule ? { ...previousWordSchedule } : {
    stage: 0,
    nextReview: getToday(),
    correctCount: 0,
    incorrectCount: 0
  };

  nextRecords.push({
    wordId,
    date: getToday(),
    time: Date.now(),
    isCorrect,
    type,
    quizMode
  });

  let recordsToSave = nextRecords;
  if (options.removeIncorrectQuizRecords && isCorrect) {
    recordsToSave = nextRecords.filter(record => !(
      record.wordId === wordId
      && record.type === 'quiz'
      && !record.isCorrect
    ));
  }
  if (recordsToSave.length > MAX_RECORDS) {
    recordsToSave = trimRecords(recordsToSave, MAX_RECORDS, 10);
  }

  if (isCorrect) {
    nextWordSchedule.correctCount++;
    nextWordSchedule.stage = Math.min(nextWordSchedule.stage + 1, EBBINGHAUS_INTERVALS.length - 1);
  } else {
    nextWordSchedule.incorrectCount++;
    nextWordSchedule.stage = Math.max(0, nextWordSchedule.stage - 1);
  }
  nextWordSchedule.nextReview = addDays(getToday(), EBBINGHAUS_INTERVALS[nextWordSchedule.stage]);

  state.records = recordsToSave;
  state.schedule = { ...previousSchedule, [wordId]: nextWordSchedule };

  const recordsSaved = saveRecords();
  const scheduleSaved = saveSchedule();
  if (recordsSaved && scheduleSaved) return true;

  state.records = previousRecords;
  state.schedule = previousSchedule;
  saveRecords();
  saveSchedule();
  return false;
}