import {
  BadRequestException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { Prisma } from '@prisma/client';
import { PrismaService } from '../prisma/prisma.service';
import type {
  CreateWebsiteBlogCategoryDto,
  CreateWebsiteBlogPostDto,
} from './dto/website-blog.dto';

@Injectable()
export class WebsiteBlogService {
  constructor(private readonly prisma: PrismaService) {}


  async listCategories() {
    const items = await this.prisma.websiteBlogCategory.findMany({
      orderBy: { name: 'asc' },
    });
    return { items };
  }

  async createCategory(dto: CreateWebsiteBlogCategoryDto) {
    const name = dto.name.trim();
    if (!name) {
      throw new BadRequestException('Enter a category name.');
    }

    const parentId = dto.parentId?.trim()
      ? this.parseId(dto.parentId.trim())
      : null;
    if (parentId) {
      const parent = await this.prisma.websiteBlogCategory.findUnique({
        where: { id: parentId },
      });
      if (!parent) {
        throw new NotFoundException('Parent category not found.');
      }
    }

    const existing = await this.prisma.websiteBlogCategory.findFirst({
      where: {
        parentId,
        name: { equals: name, mode: 'insensitive' },
      },
    });
    if (existing) {
      throw new BadRequestException('This category already exists here.');
    }

    try {
      return await this.prisma.websiteBlogCategory.create({
        data: {
          name,
          nameFa: dto.nameFa?.trim() || null,
          description: dto.description?.trim() || null,
          parentId: parentId ?? null,
        },
      });
    } catch (error) {
      if (
        error instanceof Prisma.PrismaClientKnownRequestError &&
        error.code === 'P2002'
      ) {
        throw new BadRequestException('This category already exists here.');
      }
      throw error;
    }
  }

  async updateCategory(id: string, dto: CreateWebsiteBlogCategoryDto) {
    const categoryId = this.parseId(id);
    const current = await this.prisma.websiteBlogCategory.findUnique({
      where: { id: categoryId },
    });
    if (!current) {
      throw new NotFoundException('Category not found.');
    }

    const name = dto.name.trim();
    if (!name) {
      throw new BadRequestException('Enter a category name.');
    }

    const parentId = dto.parentId?.trim()
      ? this.parseId(dto.parentId.trim())
      : null;
    if (parentId === categoryId) {
      throw new BadRequestException('A category cannot be its own parent.');
    }

    const rows = await this.prisma.websiteBlogCategory.findMany({
      select: { id: true, parentId: true },
    });
    if (parentId) {
      const descendants = this.descendantIds(categoryId, rows);
      if (descendants.has(parentId.toString())) {
        throw new BadRequestException(
          'Choose a parent outside this category.',
        );
      }
      const parent = rows.find((row) => row.id === parentId);
      if (!parent) {
        throw new NotFoundException('Parent category not found.');
      }
    }

    const existing = await this.prisma.websiteBlogCategory.findFirst({
      where: {
        parentId,
        name: { equals: name, mode: 'insensitive' },
        NOT: { id: categoryId },
      },
    });
    if (existing) {
      throw new BadRequestException('This category already exists here.');
    }

    return this.prisma.websiteBlogCategory.update({
      where: { id: categoryId },
      data: {
        name,
        nameFa: dto.nameFa?.trim() || null,
        description: dto.description?.trim() || null,
        parentId,
      },
    });
  }

  async deleteCategory(id: string) {
    const rootId = this.parseId(id);
    const rows = await this.prisma.websiteBlogCategory.findMany({
      select: { id: true, parentId: true },
    });
    if (!rows.some((row) => row.id === rootId)) {
      throw new NotFoundException('Category not found.');
    }

    const subtree = this.subtreePostOrder(rootId, rows);
    const posts = await this.prisma.websiteBlogPost.count({
      where: { categoryId: { in: subtree } },
    });
    if (posts > 0) {
      throw new BadRequestException(
        'Remove posts in this category before deleting it.',
      );
    }

    for (const categoryId of subtree) {
      await this.prisma.websiteBlogCategory.delete({ where: { id: categoryId } });
    }
    return { ok: true };
  }

  async listPosts() {
    const posts = await this.prisma.websiteBlogPost.findMany({
      orderBy: { createdAt: 'desc' },
      include: { category: true },
    });
    return {
      total: posts.length,
      items: posts.map((post) => ({
        id: post.id,
        title: post.title,
        abstract: post.abstract,
        imageUrl: post.imageUrl,
        categoryId: post.categoryId,
        categoryName: post.category.name,
        tags: post.tags,
        createdAt: post.createdAt,
        updatedAt: post.updatedAt,
      })),
    };
  }

  async createPost(dto: CreateWebsiteBlogPostDto) {
    const categoryId = this.parseId(dto.categoryId);
    const category = await this.prisma.websiteBlogCategory.findUnique({
      where: { id: categoryId },
    });
    if (!category) {
      throw new NotFoundException('Category not found.');
    }

    const post = await this.prisma.websiteBlogPost.create({
      data: {
        title: dto.title.trim(),
        abstract: dto.abstract?.trim() || null,
        mainTextHtml: dto.mainTextHtml?.trim() || null,
        imageUrl: dto.imageUrl?.trim() || null,
        categoryId,
        tags: this.normalizeTags(dto.tags),
      },
      include: { category: true },
    });

    return {
      id: post.id,
      title: post.title,
      abstract: post.abstract,
      mainTextHtml: post.mainTextHtml,
      imageUrl: post.imageUrl,
      categoryId: post.categoryId,
      categoryName: post.category.name,
      tags: post.tags,
      createdAt: post.createdAt,
      updatedAt: post.updatedAt,
    };
  }

  async deletePost(id: string) {
    const postId = this.parseId(id);
    try {
      await this.prisma.websiteBlogPost.delete({ where: { id: postId } });
    } catch (error) {
      if (
        error instanceof Prisma.PrismaClientKnownRequestError &&
        error.code === 'P2025'
      ) {
        throw new NotFoundException('Blog post not found.');
      }
      throw error;
    }
    return { ok: true };
  }

  private descendantIds(
    rootId: bigint,
    rows: { id: bigint; parentId: bigint | null }[],
  ) {
    const childrenByParent = new Map<string, bigint[]>();
    for (const row of rows) {
      if (row.parentId == null) continue;
      const key = row.parentId.toString();
      const list = childrenByParent.get(key) ?? [];
      list.push(row.id);
      childrenByParent.set(key, list);
    }
    const result = new Set<string>();
    const queue = [...(childrenByParent.get(rootId.toString()) ?? [])];
    while (queue.length) {
      const current = queue.shift()!;
      const key = current.toString();
      if (result.has(key)) continue;
      result.add(key);
      queue.push(...(childrenByParent.get(key) ?? []));
    }
    return result;
  }

  private subtreePostOrder(
    rootId: bigint,
    rows: { id: bigint; parentId: bigint | null }[],
  ) {
    const childrenByParent = new Map<string, bigint[]>();
    for (const row of rows) {
      if (row.parentId == null) continue;
      const key = row.parentId.toString();
      const list = childrenByParent.get(key) ?? [];
      list.push(row.id);
      childrenByParent.set(key, list);
    }
    const order: bigint[] = [];
    const walk = (current: bigint) => {
      for (const child of childrenByParent.get(current.toString()) ?? []) {
        walk(child);
      }
      order.push(current);
    };
    walk(rootId);
    return order;
  }

  private parseId(value: string) {
    if (!/^\d+$/.test(value)) {
      throw new BadRequestException('Invalid id.');
    }
    return BigInt(value);
  }

  private normalizeTags(tags: string[] | undefined) {
    const seen = new Set<string>();
    const next: string[] = [];
    for (const tag of tags ?? []) {
      const trimmed = tag.trim();
      if (!trimmed) continue;
      const key = trimmed.toLowerCase();
      if (seen.has(key)) continue;
      seen.add(key);
      next.push(trimmed);
    }
    return next;
  }
}