// Reading plan catalog — pure data + helpers. No React, no storage; progress
// tracking (and custom plan storage) lives in useReadingPlans.js.
import { bookOptions, CHAPTER_COUNTS, NT_BOOK_NUMBER } from './bibleUtils.jsx';

const BOOK_NAME_BY_ABBREV = Object.fromEntries(bookOptions.map((b) => [b.abbrev, b.name]));

export const ALL_BOOKS = bookOptions.map((b) => b.abbrev);
export const NT_BOOKS = ALL_BOOKS.filter((a) => NT_BOOK_NUMBER[a]);
export const OT_BOOKS = ALL_BOOKS.filter((a) => !NT_BOOK_NUMBER[a]);
export const GOSPELS = ['MAT', 'MRK', 'LUK', 'JHN'];
export const PENTATEUCH = ['GEN', 'EXO', 'LEV', 'NUM', 'DEU'];
export const WISDOM_BOOKS = ['JOB', 'PSA', 'PRO', 'ECC', 'SNG'];

// Flattens an ordered list of book abbreviations into one chapter-by-chapter list.
// `chapterRanges` (optional) is { [bookAbbrev]: { start, end } } — a custom plan's
// per-book override to read only part of a book instead of the whole thing.
function chaptersFor(bookAbbrevs, chapterRanges) {
  const list = [];
  for (const book of bookAbbrevs) {
    const total = CHAPTER_COUNTS[book] ?? 0;
    const range = chapterRanges?.[book];
    const start = Math.max(1, range?.start ?? 1);
    const end = Math.min(total, range?.end ?? total);
    for (let chapter = start; chapter <= end; chapter += 1) list.push({ book, chapter });
  }
  return list;
}

// Chapter count a book contributes to a plan, honoring a chapter-range override.
export function bookChapterCount(bookAbbrev, chapterRanges) {
  const total = CHAPTER_COUNTS[bookAbbrev] ?? 0;
  const range = chapterRanges?.[bookAbbrev];
  if (!range) return total;
  return Math.max(0, Math.min(total, range.end) - Math.max(1, range.start) + 1);
}

// Splits a flat chapter list into `days` nearly-equal, contiguous slices.
function distributeIntoDays(chapters, days) {
  const total = chapters.length;
  const schedule = [];
  for (let d = 0; d < days; d += 1) {
    const start = Math.round((d * total) / days);
    const end = Math.round(((d + 1) * total) / days);
    schedule.push(chapters.slice(start, end));
  }
  return schedule;
}

// Per-category color theme used for card accents/gradients when a plan has no cover image yet.
export const CATEGORY_THEME = {
  'Whole Bible': { gradient: 'from-indigo-500 to-violet-600', text: 'text-indigo-600', chip: 'bg-indigo-100 text-indigo-700' },
  'New Testament': { gradient: 'from-sky-500 to-blue-600', text: 'text-sky-600', chip: 'bg-sky-100 text-sky-700' },
  'Old Testament': { gradient: 'from-amber-500 to-orange-600', text: 'text-amber-600', chip: 'bg-amber-100 text-amber-700' },
  Topical: { gradient: 'from-emerald-500 to-teal-600', text: 'text-emerald-600', chip: 'bg-emerald-100 text-emerald-700' },
  'My Plans': { gradient: 'from-rose-500 to-pink-600', text: 'text-rose-600', chip: 'bg-rose-100 text-rose-700' },
};
const DEFAULT_THEME = { gradient: 'from-slate-500 to-slate-700', text: 'text-slate-600', chip: 'bg-slate-100 text-slate-700' };

export function themeForCategory(category) {
  return CATEGORY_THEME[category] ?? DEFAULT_THEME;
}

// Static catalog. `image` points at an optional cover photo the user can drop into
// public/plan-covers/ — see PIXABAY_SEARCH_LINKS below for where to find one. Cards
// fall back to a colorful gradient + icon when the file isn't there.
export const READING_PLANS = [
  {
    id: 'bible-year',
    title: 'Whole Bible in a Year',
    description: 'Read straight through Genesis to Revelation at a steady, sustainable pace.',
    category: 'Whole Bible',
    icon: '📖',
    image: '/plan-covers/bible-year.jpg',
    days: 365,
    books: ALL_BOOKS,
  },
  {
    id: 'bible-90',
    title: 'Whole Bible in 90 Days',
    description: 'An intensive read of the entire Bible, cover to cover.',
    category: 'Whole Bible',
    icon: '⏳',
    image: '/plan-covers/bible-90.jpg',
    days: 90,
    books: ALL_BOOKS,
  },
  {
    id: 'nt-90',
    title: 'New Testament in 90 Days',
    description: 'Matthew through Revelation in three months.',
    category: 'New Testament',
    icon: '✝️',
    image: '/plan-covers/nt-90.jpg',
    days: 90,
    books: NT_BOOKS,
  },
  {
    id: 'nt-30',
    title: 'New Testament in 30 Days',
    description: 'A fast-paced trip through the whole New Testament.',
    category: 'New Testament',
    icon: '⚡',
    image: '/plan-covers/nt-30.jpg',
    imageFocus: '50% 35%',
    days: 30,
    books: NT_BOOKS,
  },
  {
    id: 'gospels-30',
    title: 'The Gospels in 30 Days',
    description: 'Matthew, Mark, Luke, and John — the life of Jesus in a month.',
    category: 'Topical',
    icon: '🕊️',
    image: '/plan-covers/gospels-30.jpg',
    days: 30,
    books: GOSPELS,
  },
  {
    id: 'psalms-30',
    title: 'Psalms in 30 Days',
    description: 'Pray and read through all 150 Psalms in a month.',
    category: 'Topical',
    icon: '🎵',
    image: '/plan-covers/psalms-30.jpg',
    days: 30,
    books: ['PSA'],
  },
  {
    id: 'proverbs-31',
    title: 'Proverbs in 31 Days',
    description: 'One chapter a day — a natural fit for any month.',
    category: 'Topical',
    icon: '💡',
    image: '/plan-covers/proverbs-31.jpg',
    days: 31,
    books: ['PRO'],
  },
  {
    id: 'pentateuch-60',
    title: 'The Pentateuch in 60 Days',
    description: 'Genesis through Deuteronomy — the foundation of the Old Testament.',
    category: 'Old Testament',
    icon: '🏜️',
    image: '/plan-covers/pentateuch-60.jpg',
    days: 60,
    books: PENTATEUCH,
  },
  {
    id: 'wisdom-40',
    title: 'Wisdom Literature in 40 Days',
    description: 'Job, Psalms, Proverbs, Ecclesiastes, and Song of Songs.',
    category: 'Topical',
    icon: '🦉',
    image: '/plan-covers/wisdom-40.jpg',
    imageFocus: '50% 32%',
    days: 40,
    books: WISDOM_BOOKS,
  },
];

// Pixabay *search* pages (not specific photos — nothing here is a guessed asset URL)
// for each built-in plan, so a cover photo can be picked and dropped into
// public/plan-covers/<id>.jpg. Landscape, ~1200px wide, works best.
export const PIXABAY_SEARCH_LINKS = {
  'bible-year': 'https://pixabay.com/images/search/open%20bible/',
  'bible-90': 'https://pixabay.com/images/search/bible%20pages/',
  'nt-90': 'https://pixabay.com/images/search/cross%20sunrise/',
  'nt-30': 'https://pixabay.com/images/search/cross/',
  'gospels-30': 'https://pixabay.com/images/search/jesus/',
  'psalms-30': 'https://pixabay.com/images/search/harp/',
  'proverbs-31': 'https://pixabay.com/images/search/candle%20light/',
  'pentateuch-60': 'https://pixabay.com/images/search/desert%20mountain/',
  'wisdom-40': 'https://pixabay.com/images/search/owl%20book/',
};

const PLAN_BY_ID = Object.fromEntries(READING_PLANS.map((p) => [p.id, p]));
const scheduleCache = new Map();

export function getPlan(planId) {
  return PLAN_BY_ID[planId] ?? null;
}

// A plan can't have more days than it has chapters (the extra days would be empty, with
// nothing to read). Existing custom plans with too many days heal to one chapter a day.
export function clampPlanDays(books, chapterRanges, days) {
  const total = (books ?? []).reduce((sum, b) => sum + bookChapterCount(b, chapterRanges), 0);
  const wanted = Math.max(1, Math.round(Number(days) || 1));
  return total > 0 ? Math.min(wanted, total) : wanted;
}

export function normalizeCustomPlan(plan) {
  const days = clampPlanDays(plan.books, plan.chapterRanges, plan.days);
  return days === plan.days ? plan : { ...plan, days };
}

// Nearest day at or after `from` that has something to read, else the nearest one before it.
export function nearestReadingDay(schedule, from) {
  for (let i = Math.max(0, from); i < schedule.length; i += 1) if (schedule[i]?.length) return i;
  for (let i = Math.min(from, schedule.length) - 1; i >= 0; i -= 1) if (schedule[i]?.length) return i;
  return -1;
}

// Registers/updates/removes user-created plans in the lookup used by getPlan/getPlanSchedule.
// Called by useReadingPlans() whenever the custom-plans list changes.
export function registerCustomPlans(customPlans) {
  for (const key of Object.keys(PLAN_BY_ID)) {
    if (PLAN_BY_ID[key].custom && !customPlans.some((cp) => cp.id === key)) {
      delete PLAN_BY_ID[key];
      scheduleCache.delete(key);
    }
  }
  for (const cp of customPlans) {
    PLAN_BY_ID[cp.id] = { category: 'My Plans', icon: '✨', ...normalizeCustomPlan(cp), custom: true };
    scheduleCache.delete(cp.id);
  }
}

// Returns an array of `plan.days` entries, each an array of { book, chapter } refs.
export function getPlanSchedule(planId) {
  if (scheduleCache.has(planId)) return scheduleCache.get(planId);
  const plan = getPlan(planId);
  if (!plan) return [];
  const schedule = distributeIntoDays(chaptersFor(plan.books, plan.chapterRanges), plan.days);
  scheduleCache.set(planId, schedule);
  return schedule;
}

// Groups consecutive same-book chapters and renders "Genesis 1–3; Exodus 1" style text.
export function formatDayReadings(dayRefs) {
  if (!dayRefs || dayRefs.length === 0) return '';
  const groups = [];
  for (const ref of dayRefs) {
    const last = groups[groups.length - 1];
    if (last && last.book === ref.book && ref.chapter === last.end + 1) {
      last.end = ref.chapter;
    } else {
      groups.push({ book: ref.book, start: ref.chapter, end: ref.chapter });
    }
  }
  return groups
    .map((g) => {
      const name = BOOK_NAME_BY_ABBREV[g.book] ?? g.book;
      return g.start === g.end ? `${name} ${g.start}` : `${name} ${g.start}–${g.end}`;
    })
    .join('; ');
}

// The first chapter reference of a day's reading — where "Read" should jump to.
export function firstRefOfDay(dayRefs) {
  return dayRefs && dayRefs.length > 0 ? dayRefs[0] : null;
}

// Index (0-based) of the first day not yet marked complete, or null if the plan is finished.
export function nextUnreadDayIndex(plan, completedDays) {
  for (let i = 0; i < plan.days; i += 1) {
    if (!completedDays.includes(i)) return i;
  }
  return null;
}

// Index (0-based) of the day whose reading includes this exact book/chapter, or -1.
// Used by the reader to offer "mark today's plan reading done" inline.
export function findDayIndexForRef(schedule, bookAbbrev, chapter) {
  for (let i = 0; i < schedule.length; i += 1) {
    if (schedule[i].some((r) => r.book === bookAbbrev && r.chapter === chapter)) return i;
  }
  return -1;
}

// ---------------------------------------------------------------------------
// Streaks & pace — driven by a plain list of 'YYYY-MM-DD' local-date strings
// (one per calendar day something was marked read, across all plans).
// ---------------------------------------------------------------------------

export function localDateString(ts = Date.now()) {
  const d = new Date(ts);
  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
}

// { current, longest } consecutive-calendar-day streak. "current" stays alive
// through today even if today hasn't been logged yet (so it doesn't drop to 0
// the moment you wake up) but breaks once a full day is skipped.
export function computeStreak(activityDates) {
  if (!activityDates || activityDates.length === 0) return { current: 0, longest: 0 };
  const daySet = new Set(activityDates);
  const DAY_MS = 86400000;

  const sorted = Array.from(daySet).sort();
  let longest = 0;
  let run = 0;
  let prevTime = null;
  for (const ds of sorted) {
    const t = new Date(`${ds}T00:00:00`).getTime();
    run = prevTime != null && t - prevTime === DAY_MS ? run + 1 : 1;
    longest = Math.max(longest, run);
    prevTime = t;
  }

  let current = 0;
  const cursor = new Date();
  cursor.setHours(0, 0, 0, 0);
  if (!daySet.has(localDateString(cursor.getTime()))) cursor.setDate(cursor.getDate() - 1);
  while (daySet.has(localDateString(cursor.getTime()))) {
    current += 1;
    cursor.setDate(cursor.getDate() - 1);
  }
  return { current, longest };
}

// How many days a plan's pace has fallen behind, assuming one plan-day per
// calendar day since it was started. Purely informational — nothing enforces it.
export function daysBehindPace(plan, progress) {
  const elapsedDays = Math.floor((Date.now() - progress.startedAt) / 86400000);
  const expectedDayIndex = Math.min(plan.days - 1, Math.max(0, elapsedDays));
  return Math.max(0, expectedDayIndex - progress.completedDays.length);
}