import { Injectable } from '@nestjs/common';
import {
  PermissionAction,
  PermissionViewer,
  PondRole,
  canSeePond,
  hasPondRole,
  resolvePageCapability,
} from '@dorfteich/shared';
import { Prisma, User } from '@prisma/client';

import { toGrant } from '../grants/grant-mappers';
import { PrismaService } from '../prisma/prisma.service';
import { PondPermissionCache, PondPermissionContext } from './pond-permission-cache';

/** The role a permission decorator can require at pond level. `reader` means
 * "may see the pond at all" — any allow grant, at any scope (shared
 * `canSeePond`); `editor`/`pond_admin` are pond-wide roles. */
export type RequiredPondRole = 'reader' | PondRole;

/** What page filtering needs to know about one page; `labelIds` may be
 * preloaded by the caller (one grouped query otherwise). */
export interface FilterablePage {
  id: string;
  labelIds?: string[];
}

/**
 * The API-side entry point for every permission question (issue #52). Pure
 * resolution lives in `@dorfteich/shared` (permissions.md is normative); this
 * service loads the inputs — grants and label hierarchy per pond (cached, see
 * {@link PondPermissionCache}) and the page's labels (fresh) — and delegates.
 * Nothing outside this module may answer an access question itself.
 */
@Injectable()
export class PermissionService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly cache: PondPermissionCache,
  ) {}

  static viewerOf(user: User | null | undefined): PermissionViewer {
    return { userId: user?.id ?? null, isSiteAdmin: user?.isSiteAdmin ?? false };
  }

  /** The pond's grants and label hierarchy, from cache or two indexed queries. */
  async pondContext(pondId: string): Promise<PondPermissionContext> {
    const cached = this.cache.get(pondId);
    if (cached) return cached;
    const [grantRows, labels] = await Promise.all([
      this.prisma.roleGrant.findMany({ where: { pondId } }),
      this.prisma.label.findMany({ where: { pondId }, select: { id: true, parentId: true } }),
    ]);
    const context: PondPermissionContext = {
      grants: grantRows.map(toGrant),
      labelParents: Object.fromEntries(labels.map((l) => [l.id, l.parentId])),
    };
    this.cache.set(pondId, context);
    return context;
  }

  /** May the user see that the pond exists (metadata, shell)? */
  async canSeePond(user: User | null, pondId: string): Promise<boolean> {
    const { grants } = await this.pondContext(pondId);
    return canSeePond(PermissionService.viewerOf(user), grants);
  }

  /** Does the user hold `role` pond-wide? (`reader` = may see the pond.) */
  async hasPondRole(user: User | null, pondId: string, role: RequiredPondRole): Promise<boolean> {
    if (role === 'reader') return this.canSeePond(user, pondId);
    const { grants } = await this.pondContext(pondId);
    return hasPondRole(role, PermissionService.viewerOf(user), grants);
  }

  /**
   * May the user perform `action` on one live page? (Trash views go through
   * {@link canAccessTrashedPage}.) The page's own labels are loaded fresh.
   */
  async canAccessPage(
    user: User | null,
    page: { id: string; pondId: string },
    action: PermissionAction,
  ): Promise<boolean> {
    const allowed = await this.filterPages(user, page.pondId, [{ id: page.id }], action);
    return allowed.has(page.id);
  }

  /** May the user see/restore/purge the page in trash views (= write capability,
   * ADR 0013)? The trashed flag itself is the caller's routing decision. */
  async canAccessTrashedPage(
    user: User | null,
    page: { id: string; pondId: string },
  ): Promise<boolean> {
    return this.canAccessPage(user, page, 'write');
  }

  /**
   * Resolve `action` for many pages of one pond at once — the page-list,
   * search, backlink, and trash filters. Returns the ids the user may access.
   * Pages without preloaded `labelIds` get them in one grouped query.
   */
  async filterPages(
    user: User | null,
    pondId: string,
    pages: FilterablePage[],
    action: PermissionAction,
  ): Promise<Set<string>> {
    if (pages.length === 0) return new Set();
    const viewer = PermissionService.viewerOf(user);
    if (viewer.isSiteAdmin) return new Set(pages.map((p) => p.id));

    const { grants, labelParents } = await this.pondContext(pondId);
    const missing = pages.filter((p) => p.labelIds === undefined).map((p) => p.id);
    const labelsByPage = new Map<string, string[]>();
    if (missing.length > 0) {
      const rows = await this.prisma.pageLabel.findMany({
        where: { pageId: { in: missing } },
        select: { pageId: true, labelId: true },
      });
      for (const row of rows) {
        const list = labelsByPage.get(row.pageId) ?? [];
        list.push(row.labelId);
        labelsByPage.set(row.pageId, list);
      }
    }

    const allowed = new Set<string>();
    for (const page of pages) {
      const pageLabelIds = page.labelIds ?? labelsByPage.get(page.id) ?? [];
      const ok = resolvePageCapability(action, {
        viewer,
        grants,
        pageId: page.id,
        pageLabelIds,
        labelParents,
      });
      if (ok) allowed.add(page.id);
    }
    return allowed;
  }

  /**
   * The ponds the user may see, or `null` for "all" (Site Admin). Visibility
   * is `canSeePond`: any matching allow grant, which this single indexed
   * query expresses exactly (deny grants never *create* visibility).
   */
  async visiblePondIds(user: User): Promise<string[] | null> {
    if (user.isSiteAdmin) return null;
    const rows = await this.prisma.roleGrant.findMany({
      where: {
        effect: 'ALLOW',
        OR: [
          { subjectType: 'USER', subjectId: user.id },
          { subjectType: 'AUTHENTICATED' },
          { subjectType: 'PUBLIC' },
        ],
      },
      select: { pondId: true },
      distinct: ['pondId'],
    });
    return rows.map((row) => row.pondId);
  }

  /** Prisma `where` fragment restricting pond queries to visible rows. */
  async visiblePondsWhere(user: User): Promise<Prisma.PondWhereInput> {
    const ids = await this.visiblePondIds(user);
    return ids === null ? {} : { id: { in: ids } };
  }
}