import { ConflictException, Injectable, NotFoundException } from '@nestjs/common';
import {
  CollabTokenResponse,
  CreatePageInput,
  PageListItemView,
  PageStateView,
  PageView,
  RepositionPageInput,
  SidebarSortMode,
  UpdatePageInput,
  pondSettingsSchema,
  slugify,
} from '@dorfteich/shared';
import { signCollabToken } from '@dorfteich/shared/token-crypto';
import { Page, Prisma, User } from '@prisma/client';
import { generateKeyBetween } from 'fractional-indexing';
import { PinoLogger } from 'nestjs-pino';

import { AppConfig } from '../config/app-config.service';
import { PermissionService } from '../permissions/permission.service';
import { PrismaService } from '../prisma/prisma.service';
import { SearchProvider } from '../search/search.provider';
import { evenlySpacedKeys, nextKeyOrRebalance } from './sort-key';
import { deriveContent, DerivedPageContent, emptyPageState } from './yjs-content';

/** `outline` is a plain JSON-serializable array; Prisma's Json input just needs the cast. */
function contentCacheData(
  content: DerivedPageContent,
): Prisma.PageContentCacheCreateWithoutPageInput {
  return {
    plainText: content.plainText,
    markdown: content.markdown,
    html: content.html,
    outline: content.outline as unknown as Prisma.InputJsonValue,
  };
}

/** Collaboration tokens are short-lived; the client re-fetches on reconnect
 * (realtime-collaboration.md). 60 s is the ceiling the story specifies. */
const COLLAB_TOKEN_TTL_SECONDS = 60;

@Injectable()
export class PagesService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly permissions: PermissionService,
    private readonly logger: PinoLogger,
    private readonly config: AppConfig,
    private readonly search: SearchProvider,
  ) {
    this.logger.setContext(PagesService.name);
  }

  viewOf(page: Page): PageView {
    return {
      id: page.id,
      pondId: page.pondId,
      title: page.title,
      slug: page.slug,
      sortKey: page.sortKey,
      createdAt: page.createdAt.toISOString(),
      updatedAt: page.updatedAt.toISOString(),
      deletedAt: page.deletedAt?.toISOString() ?? null,
    };
  }

  stateViewOf(page: Page): PageStateView {
    return { ...this.viewOf(page), state: Buffer.from(page.ydocState).toString('base64') };
  }

  /** Deterministic unique slug within one pond (mirrors PondsService). */
  private async generateUniqueSlugInPond(pondId: string, base: string): Promise<string> {
    const slug = slugify(base) || 'page';
    const taken = new Set(
      (
        await this.prisma.page.findMany({
          where: { pondId, OR: [{ slug }, { slug: { startsWith: `${slug}-` } }] },
          select: { slug: true },
        })
      ).map((row) => row.slug),
    );
    if (!taken.has(slug)) return slug;
    for (let n = 2; ; n += 1) {
      const candidate = `${slug}-${n}`;
      if (!taken.has(candidate)) return candidate;
    }
  }

  /** Loads a live page; permission is the guard's job since #52. */
  private async findLivePage(id: string): Promise<Page> {
    const page = await this.prisma.page.findFirst({ where: { id, deletedAt: null } });
    if (!page) throw new NotFoundException();
    return page;
  }

  private static readonly SORT_ORDER: Record<SidebarSortMode, Prisma.PageOrderByWithRelationInput> =
    {
      alpha: { title: 'asc' },
      created: { createdAt: 'asc' },
      // Manual reordering (drag-and-drop) arrives with #45; the fractional
      // `sortKey` already reflects creation order in the meantime.
      manual: { sortKey: 'asc' },
    };

  /** Sidebar page list, ordered per the pond's persisted sort mode (issue #26),
   * each with its assigned label ids for chips and filtering (issue #44).
   * Filtered to the pages the user may read (issue #52) — a label- or
   * page-scoped reader sees only their slice of the pond. */
  async list(user: User, pondId: string): Promise<PageListItemView[]> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
    if (!pond) throw new NotFoundException();
    const settings = pondSettingsSchema.parse(pond.settings ?? {});
    const pages = await this.prisma.page.findMany({
      where: { pondId, deletedAt: null },
      orderBy: PagesService.SORT_ORDER[settings.sidebarSort],
      include: { labels: { select: { labelId: true } } },
    });
    const readable = await this.permissions.filterPages(
      user,
      pondId,
      pages.map((page) => ({ id: page.id, labelIds: page.labels.map((l) => l.labelId) })),
      'read',
    );
    return pages
      .filter((page) => readable.has(page.id))
      .map((page) => ({
        ...this.viewOf(page),
        labelIds: page.labels.map((l) => l.labelId),
      }));
  }

  async create(user: User, pondId: string, input: CreatePageInput): Promise<PageView> {
    const page = await this.insertPage(user, pondId, input.title, emptyPageState());
    return this.viewOf(page);
  }

  /**
   * Create a page from a prepared Yjs state (issue #63 import): the imported
   * document is already a full Yjs state whose fragment the editor binds to, so
   * an opening client sees the converted content immediately. Same invariants
   * as {@link create} — unique slug, appended sort key, derived content cache,
   * phantom-link resolution, search indexing. Returns the persisted row so the
   * caller (the import worker) can link the document's media to it.
   */
  async createWithState(
    user: User,
    pondId: string,
    title: string,
    state: Uint8Array<ArrayBuffer>,
  ): Promise<Page> {
    return this.insertPage(user, pondId, title, state);
  }

  private async insertPage(
    user: User,
    pondId: string,
    title: string,
    state: Uint8Array<ArrayBuffer>,
  ): Promise<Page> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
    if (!pond) throw new NotFoundException();

    const slug = await this.generateUniqueSlugInPond(pond.id, title);
    const last = await this.prisma.page.findFirst({
      where: { pondId: pond.id },
      orderBy: { sortKey: 'desc' },
      select: { sortKey: true },
    });
    const sortKey = generateKeyBetween(last?.sortKey ?? null, null);
    const content = deriveContent(state);

    const page = await this.prisma.page.create({
      data: {
        pondId: pond.id,
        title,
        slug,
        sortKey,
        ydocState: state,
        createdBy: user.id,
        contentCache: { create: contentCacheData(content) },
      },
    });
    // A new page may satisfy phantom wikilinks that referenced its slug (#47).
    await this.resolvePhantomLinks(pond.id, slug, page.id);
    // Index the page so a title-only match is findable immediately (#49).
    await this.search.indexPage(page.id);
    this.logger.info({ pageId: page.id, pondId: pond.id, userId: user.id }, 'audit: page created');
    return page;
  }

  /**
   * Point phantom `page_links` (unresolved, `to_page_id` null) whose
   * `target_slug` matches `slug` within the pond at `pageId` (issue #47).
   * Called when a page is created or renamed to a slug that pages already link
   * to. Backlinks store the target's id, so once resolved a later target rename
   * keeps them connected.
   */
  private async resolvePhantomLinks(pondId: string, slug: string, pageId: string): Promise<void> {
    await this.prisma.$executeRaw`
      UPDATE page_links SET to_page_id = ${pageId}
      WHERE to_page_id IS NULL AND target_slug = ${slug}
        AND from_page_id IN (SELECT id FROM pages WHERE pond_id = ${pondId})`;
  }

  async getState(_user: User, id: string): Promise<PageStateView> {
    const page = await this.findLivePage(id);
    return this.stateViewOf(page);
  }

  /**
   * Mint a collaboration token for a page (issue #34). The permission check
   * runs in the api — the guard requires read access, and the collab server
   * never sees session cookies (ADR 0003). `mode` is `rw` for who may write
   * the page per the real grant resolution (issue #52) and `ro` otherwise.
   *
   * `user` is `null` for an anonymous visitor on a public page (issue #53): the
   * guard has already granted read access via a `public` grant, so they receive
   * an `ro` token with a `null` subject.
   */
  async issueCollabToken(user: User | null, id: string): Promise<CollabTokenResponse> {
    const page = await this.findLivePage(id);

    const canWrite = await this.permissions.canAccessPage(user, page, 'write');
    const mode = canWrite ? 'rw' : 'ro';
    const userId = user?.id ?? null;
    const token = signCollabToken(
      { userId, pageId: page.id, mode },
      this.config.env.COLLAB_TOKEN_SECRET,
      COLLAB_TOKEN_TTL_SECONDS,
    );
    // Debug level, and deliberately without the token value (issue #34).
    this.logger.debug({ pageId: page.id, userId, mode }, 'issued collab token');
    return { token, mode, expiresInSeconds: COLLAB_TOKEN_TTL_SECONDS };
  }

  /** The trashed-page hint for editors (issue #31) moved into the guard. */
  async getStateBySlug(_user: User, pondId: string, slug: string): Promise<PageStateView> {
    const page = await this.prisma.page.findFirst({ where: { pondId, slug, deletedAt: null } });
    if (!page) throw new NotFoundException();
    return this.stateViewOf(page);
  }

  async update(_user: User, id: string, input: UpdatePageInput): Promise<PageView> {
    const page = await this.findLivePage(id);

    let slug = page.slug;
    if (input.slug !== undefined) {
      const normalized = slugify(input.slug) || page.slug;
      if (normalized !== page.slug) {
        const clash = await this.prisma.page.findFirst({
          where: { pondId: page.pondId, slug: normalized, id: { not: page.id } },
          select: { id: true },
        });
        if (clash) throw new ConflictException({ code: 'slug_taken' });
      }
      slug = normalized;
    }

    const updated = await this.prisma.page.update({
      where: { id: page.id },
      data: { title: input.title, slug },
    });
    // Renaming to a slug pages already link to resolves those phantom links (#47).
    if (slug !== page.slug) await this.resolvePhantomLinks(page.pondId, slug, page.id);
    // A changed title changes the (weighted) search entry (#49).
    if (input.title !== undefined && input.title !== page.title) {
      await this.search.indexPage(page.id);
    }
    return this.viewOf(updated);
  }

  /**
   * Reposition a page in the manual sidebar order (issue #45). Recomputes only
   * the moved page's `sort_key` to a value between its two new neighbours; when
   * that key would grow too long (or the client's neighbours are stale) the
   * whole pond is rebalanced to evenly-spaced keys with the page dropped at the
   * target slot. The order is server-authoritative, so every viewer sees the
   * same sequence. Requires write access; the sort mode does not have to be
   * `manual` (the key is stored regardless, just not applied in other modes).
   */
  async reposition(_user: User, id: string, input: RepositionPageInput): Promise<PageView> {
    const page = await this.findLivePage(id);
    const { afterId, beforeId } = input;
    if (afterId === id || beforeId === id) {
      throw new ConflictException({ code: 'bad_request' });
    }

    const [afterPage, beforePage] = await Promise.all([
      afterId
        ? this.prisma.page.findFirst({
            where: { id: afterId, pondId: page.pondId, deletedAt: null },
            select: { sortKey: true },
          })
        : null,
      beforeId
        ? this.prisma.page.findFirst({
            where: { id: beforeId, pondId: page.pondId, deletedAt: null },
            select: { sortKey: true },
          })
        : null,
    ]);
    if (afterId && !afterPage) throw new NotFoundException();
    if (beforeId && !beforePage) throw new NotFoundException();

    const key = nextKeyOrRebalance(afterPage?.sortKey ?? null, beforePage?.sortKey ?? null);
    if (key !== null) {
      const updated = await this.prisma.page.update({ where: { id }, data: { sortKey: key } });
      return this.viewOf(updated);
    }
    return this.rebalanceAndPlace(page.pondId, id, afterId, beforeId);
  }

  /**
   * Reassign evenly-spaced `sort_key`s to every page in the pond, with the
   * moved page inserted at the slot implied by `afterId`/`beforeId`. Runs in one
   * transaction so the order is never observed half-rebalanced.
   */
  private async rebalanceAndPlace(
    pondId: string,
    movedId: string,
    afterId: string | null,
    beforeId: string | null,
  ): Promise<PageView> {
    return this.prisma.$transaction(async (tx) => {
      const pages = await tx.page.findMany({
        where: { pondId, deletedAt: null },
        orderBy: { sortKey: 'asc' },
        select: { id: true },
      });
      const order = pages.map((p) => p.id).filter((pid) => pid !== movedId);
      let index = order.length;
      if (afterId) index = order.indexOf(afterId) + 1;
      else if (beforeId) index = Math.max(0, order.indexOf(beforeId));
      order.splice(index, 0, movedId);

      const keys = evenlySpacedKeys(order.length);
      await Promise.all(
        order.map((pid, i) => tx.page.update({ where: { id: pid }, data: { sortKey: keys[i]! } })),
      );
      this.logger.info({ pondId, movedId, pages: order.length }, 'audit: sort keys rebalanced');
      return this.viewOf(await tx.page.findUniqueOrThrow({ where: { id: movedId } }));
    });
  }

  /** Markdown export (issue #30) — serves the already-derived
   * `page_content_cache.markdown` (refreshed on every state save, #23)
   * rather than re-decoding the Yjs state, so export always matches what
   * the app itself considers the page's current Markdown representation. */
  async exportMarkdown(_user: User, id: string): Promise<{ slug: string; markdown: string }> {
    const page = await this.findLivePage(id);
    const cache = await this.prisma.pageContentCache.findUnique({ where: { pageId: page.id } });
    return { slug: page.slug, markdown: cache?.markdown ?? '' };
  }

  async softDelete(user: User, id: string): Promise<void> {
    const page = await this.findLivePage(id);
    await this.prisma.page.update({
      where: { id: page.id },
      data: { deletedAt: new Date(), deletedBy: user.id },
    });
    this.logger.info({ pageId: id, userId: user.id }, 'audit: page trashed');
  }
}