/**
 * The page builder's edits as pure functions on GalleryState (#608).
 *
 * Each takes a state and returns a new one; PageBuilder wraps them in
 * setGallery() and adds what is not the state's business: confirming a
 * removal and marking the form dirty. Out here they have tests
 * (app/admin/__tests__/gallery-ops.test.ts).
 *
 * An index that does not exist leaves the state as it is.
 */

import { arrayMove } from '@dnd-kit/sortable';
import type { GalleryState } from './galleryYaml';
import type { AlbumEntry, PickerTarget, Section, Subpage } from './types';

/**
 * Where a list of albums lives: the standalone list, a subpage's own list, or
 * a section of a subpage. PickerTarget and ActiveEditAlbumAddress both carry
 * this shape.
 */
type AlbumListAddress = Pick<PickerTarget, 'type' | 'subpageIndex' | 'sectionIndex'>;

function mapSubpage(g: GalleryState, index: number, fn: (sp: Subpage) => Subpage): GalleryState {
  if (!g.subpages[index]) return g;
  return { ...g, subpages: g.subpages.map((sp, i) => (i === index ? fn(sp) : sp)) };
}

function mapSection(
  g: GalleryState,
  subpageIndex: number,
  sectionIndex: number,
  fn: (sec: Section) => Section,
): GalleryState {
  if (!g.subpages[subpageIndex]?.sections?.[sectionIndex]) return g;
  return mapSubpage(g, subpageIndex, (sp) => ({
    ...sp,
    sections: sp.sections!.map((sec, i) => (i === sectionIndex ? fn(sec) : sec)),
  }));
}

/** Replace the album list at an address. */
export function mapAlbums(
  g: GalleryState,
  at: AlbumListAddress,
  fn: (albums: AlbumEntry[]) => AlbumEntry[],
): GalleryState {
  if (at.type === 'standalone') return { ...g, albums: fn(g.albums) };
  if (at.subpageIndex == null) return g;
  if (at.type === 'subpage') {
    return mapSubpage(g, at.subpageIndex, (sp) => ({ ...sp, albums: fn(sp.albums) }));
  }
  if (at.sectionIndex == null) return g;
  return mapSection(g, at.subpageIndex, at.sectionIndex, (sec) => ({
    ...sec,
    albums: fn(sec.albums),
  }));
}

/** The album list at an address, or undefined when the address is stale. */
export function albumsAt(g: GalleryState, at: AlbumListAddress): AlbumEntry[] | undefined {
  if (at.type === 'standalone') return g.albums;
  const sp = at.subpageIndex == null ? undefined : g.subpages[at.subpageIndex];
  if (at.type === 'subpage') return sp?.albums;
  return at.sectionIndex == null ? undefined : sp?.sections?.[at.sectionIndex]?.albums;
}

// ── Albums ──────────────────────────────────────────────────────

export const addAlbum = (g: GalleryState, at: AlbumListAddress, entry: AlbumEntry) =>
  mapAlbums(g, at, (albums) => [...albums, entry]);

export const updateAlbum = (
  g: GalleryState,
  at: AlbumListAddress,
  albumIndex: number,
  updates: Partial<AlbumEntry>,
) =>
  mapAlbums(g, at, (albums) => albums.map((a, i) => (i === albumIndex ? { ...a, ...updates } : a)));

export const removeAlbum = (g: GalleryState, at: AlbumListAddress, albumIndex: number) =>
  mapAlbums(g, at, (albums) => albums.filter((_, i) => i !== albumIndex));

export const moveAlbum = (g: GalleryState, at: AlbumListAddress, from: number, to: number) =>
  mapAlbums(g, at, (albums) => arrayMove(albums, from, to));

// ── Hero ────────────────────────────────────────────────────────

export const addHero = (g: GalleryState, assetId: string): GalleryState => ({
  ...g,
  hero: [...g.hero, assetId],
});

export const removeHero = (g: GalleryState, index: number): GalleryState => ({
  ...g,
  hero: g.hero.filter((_, i) => i !== index),
});

export const moveHero = (g: GalleryState, from: number, to: number): GalleryState => ({
  ...g,
  hero: arrayMove(g.hero, from, to),
});

// ── Subpages and sections ───────────────────────────────────────

export const addSubpage = (g: GalleryState): GalleryState => ({
  ...g,
  subpages: [
    ...g.subpages,
    { name: `New Page ${g.subpages.length + 1}`, albums: [], sections: undefined },
  ],
});

export const removeSubpage = (g: GalleryState, index: number): GalleryState => ({
  ...g,
  subpages: g.subpages.filter((_, i) => i !== index),
});

export const updateSubpage = (g: GalleryState, index: number, updates: Partial<Subpage>) =>
  mapSubpage(g, index, (sp) => ({ ...sp, ...updates }));

export const moveSubpage = (g: GalleryState, from: number, to: number): GalleryState => ({
  ...g,
  subpages: arrayMove(g.subpages, from, to),
});

export const addSection = (g: GalleryState, subpageIndex: number) =>
  mapSubpage(g, subpageIndex, (sp) => ({
    ...sp,
    sections: [...(sp.sections || []), { title: 'New Section', albums: [] }],
  }));

export const removeSection = (g: GalleryState, subpageIndex: number, sectionIndex: number) =>
  mapSubpage(g, subpageIndex, (sp) => ({
    ...sp,
    sections: (sp.sections || []).filter((_, i) => i !== sectionIndex),
  }));

export const updateSection = (
  g: GalleryState,
  subpageIndex: number,
  sectionIndex: number,
  updates: Partial<Section>,
) => mapSection(g, subpageIndex, sectionIndex, (sec) => ({ ...sec, ...updates }));

// ── Reading ─────────────────────────────────────────────────────

/** The "03 — Collection" number the page renders: counted over enabled subpages only. */
export function enabledPosition(g: GalleryState, index: number): number | undefined {
  const sp = g.subpages[index];
  if (!sp || sp.enabled === false) return undefined;
  return g.subpages.slice(0, index).filter((s) => s.enabled !== false).length + 1;
}

/** Every album published anywhere, so the picker can mark the ones already in use. */
export function usedAlbumIds(g: GalleryState): Set<string> {
  const ids = new Set<string>();
  g.albums.forEach((a) => ids.add(a.id));
  g.subpages.forEach((sp) => {
    sp.albums.forEach((a) => ids.add(a.id));
    sp.sections?.forEach((sec) => sec.albums.forEach((a) => ids.add(a.id)));
  });
  return ids;
}

/**
 * Where the open subpage sheet goes after a drag, so the sheet stays on the
 * page it was showing.
 */
export function followMovedIndex(open: number | null, from: number, to: number): number | null {
  if (open === null) return null;
  if (open === from) return to;
  if (from < open && to >= open) return open - 1;
  if (from > open && to <= open) return open + 1;
  return open;
}