import { Injectable, NotFoundException } from '@nestjs/common';
import {
  collectSubtreeIds,
  extractTaskRows,
  type TaskOverviewPage,
  type TaskRow,
} from '@dorfteich/shared';
import { User } from '@prisma/client';

import { apiI18n } from '../i18n/api-i18n';
import { PermissionService } from '../permissions/permission.service';
import { PrismaService } from '../prisma/prisma.service';
import { escapeHtml } from '../public/html-shell';
import { docFromStateAndUpdates } from './yjs-content';

/**
 * The task overview's collection (issue #154): every task-list line of a page
 * and its live subtree, permission-filtered per source page — a page the
 * viewer may not read contributes nothing (same no-leak rule as the
 * transclusion expansion). Rows are extracted at read time from the stored
 * Yjs states; subtrees are small (depth ≤ 6), so no derived table is needed.
 */
@Injectable()
export class TasksService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly permissions: PermissionService,
  ) {}

  async collect(
    user: User | null,
    pondSlug: string,
    pageSlug: string,
  ): Promise<TaskOverviewPage[]> {
    const pond = await this.prisma.pond.findFirst({ where: { slug: pondSlug, deletedAt: null } });
    if (!pond) throw new NotFoundException();
    const root = await this.prisma.page.findFirst({
      where: { pondId: pond.id, slug: pageSlug, deletedAt: null },
      select: { id: true, pondId: true },
    });
    if (!root || !(await this.permissions.canAccessPage(user, root, 'read'))) {
      throw new NotFoundException();
    }
    return this.collectForPage(user, pond.id, root.id);
  }

  async collectForPage(
    user: User | null,
    pondId: string,
    rootPageId: string,
  ): Promise<TaskOverviewPage[]> {
    const tree = await this.prisma.page.findMany({
      where: { pondId, deletedAt: null },
      select: { id: true, parentId: true },
    });
    const subtree = collectSubtreeIds(tree, rootPageId);
    const pages = await this.prisma.page.findMany({
      where: { id: { in: [...subtree] } },
      select: {
        id: true,
        slug: true,
        title: true,
        ydocState: true,
        labels: { select: { labelId: true } },
      },
      orderBy: { title: 'asc' },
    });
    const readable = await this.permissions.filterPages(
      user,
      pondId,
      pages.map((page) => ({ id: page.id, labelIds: page.labels.map((l) => l.labelId) })),
      'read',
    );

    // The live document is the base state plus the update log (merged back
    // only at compaction) — apply both, or fresh edits would be invisible.
    const updateRows = await this.prisma.pageUpdate.findMany({
      where: { pageId: { in: [...subtree] } },
      orderBy: { seq: 'asc' },
      select: { pageId: true, update: true },
    });
    const updatesByPage = new Map<string, Uint8Array[]>();
    for (const row of updateRows) {
      const list = updatesByPage.get(row.pageId) ?? [];
      list.push(row.update);
      updatesByPage.set(row.pageId, list);
    }

    const result: TaskOverviewPage[] = [];
    // The root page leads; the readable descendants follow alphabetically.
    const ordered = [
      ...pages.filter((page) => page.id === rootPageId),
      ...pages.filter((page) => page.id !== rootPageId),
    ];
    const mentionIds = new Set<string>();
    const raw: { page: (typeof pages)[number]; rows: TaskRow[] }[] = [];
    for (const page of ordered) {
      if (!readable.has(page.id)) continue;
      let rows: TaskRow[] = [];
      try {
        rows = extractTaskRows(
          docFromStateAndUpdates(page.ydocState, updatesByPage.get(page.id) ?? []),
        );
      } catch {
        // An undecodable state contributes nothing rather than failing the view.
        rows = [];
      }
      if (rows.length === 0) continue;
      rows.forEach((row) => row.mentions.forEach((m) => m.userId && mentionIds.add(m.userId)));
      raw.push({ page, rows });
    }

    const users = mentionIds.size
      ? await this.prisma.user.findMany({
          where: { id: { in: [...mentionIds] } },
          select: { id: true, username: true, displayName: true },
        })
      : [];
    const userById = new Map(users.map((user_) => [user_.id, user_]));

    for (const { page, rows } of raw) {
      result.push({
        pageId: page.id,
        slug: page.slug,
        title: page.title,
        tasks: rows.map((row) => ({
          id: row.id,
          checked: row.checked,
          text: row.text,
          mentions: row.mentions
            .map((mention) => {
              const resolved = mention.userId ? userById.get(mention.userId) : undefined;
              return resolved
                ? {
                    id: resolved.id,
                    username: resolved.username,
                    displayName: resolved.displayName,
                  }
                : { id: '', username: mention.username, displayName: mention.username };
            })
            .filter((mention) => mention.username),
          startDate: row.startDate,
          dueDate: row.dueDate,
        })),
      });
    }
    return result;
  }

  /** Static table for the public view / exports (issue #154) — read-only. */
  async renderStaticTable(
    user: User | null,
    pondId: string,
    rootPageId: string,
    lang: 'de' | 'en',
  ): Promise<string> {
    const pages = await this.collectForPage(user, pondId, rootPageId);
    const t = (key: string): string => apiI18n.t(`tasks:${key}`, { lng: lang });
    const rows = pages.flatMap((page) =>
      page.tasks.map(
        (task) =>
          `<tr><td><input type="checkbox" disabled${task.checked ? ' checked' : ''}></td>` +
          `<td>${escapeHtml(task.text)}</td>` +
          `<td>${task.mentions.map((m) => `@${escapeHtml(m.displayName)}`).join(', ')}</td>` +
          `<td>${task.startDate ?? ''}</td><td>${task.dueDate ?? ''}</td>` +
          `<td><a class="wikilink" href="${escapeHtml(page.slug)}" data-wikilink="${escapeHtml(page.slug)}">${escapeHtml(page.title)}</a></td></tr>`,
      ),
    );
    if (rows.length === 0) {
      return `<div class="dt-task-overview-empty">${escapeHtml(t('empty'))}</div>`;
    }
    return (
      `<table class="dt-task-overview-table"><thead><tr>` +
      `<th><span class="visually-hidden">${escapeHtml(t('colDone'))}</span></th>` +
      `<th>${escapeHtml(t('colTask'))}</th><th>${escapeHtml(t('colMentions'))}</th>` +
      `<th>${escapeHtml(t('colStart'))}</th><th>${escapeHtml(t('colDue'))}</th>` +
      `<th>${escapeHtml(t('colPage'))}</th>` +
      `</tr></thead><tbody>${rows.join('')}</tbody></table>`
    );
  }
}