import {
  ConflictException,
  Injectable,
  NotFoundException,
  OnModuleInit,
} from "@nestjs/common";
import { InjectRepository } from "@nestjs/typeorm";
import { Repository } from "typeorm";
import {
  PaginatedResult,
  PaginationQueryDto,
} from "../common/dto/pagination.dto";
import { CreateSnippetDto } from "./dto/create-snippet.dto";
import { SnippetExportDto } from "./dto/snippet-export.dto";
import { UpdateSnippetDto } from "./dto/update-snippet.dto";
import { SnippetEntity } from "./snippet.entity";

export type SnippetOrderBy =
  | "id"
  | "alias"
  | "title"
  | "createdAt"
  | "updatedAt";

@Injectable()
export class SnippetService implements OnModuleInit {
  constructor(
    @InjectRepository(SnippetEntity)
    private readonly repo: Repository<SnippetEntity>,
  ) {}

  async onModuleInit(): Promise<void> {
    // Best-effort backfill for existing DBs that still have legacy `name` values.
    try {
      await this.repo.query(
        "UPDATE snippets SET alias = name WHERE (alias IS NULL OR alias = '') AND name IS NOT NULL",
      );
    } catch {
      // Ignore when legacy `name` column does not exist.
    }
    try {
      await this.repo.query(
        "UPDATE snippets SET title = COALESCE(alias, name, '') WHERE title IS NULL OR title = ''",
      );
    } catch {
      await this.repo.query(
        "UPDATE snippets SET title = COALESCE(alias, '') WHERE title IS NULL OR title = ''",
      );
    }
  }

  async create(dto: CreateSnippetDto): Promise<SnippetEntity> {
    const existing = await this.repo.findOneBy({ alias: dto.alias });
    if (existing) {
      throw new ConflictException(
        `Snippet alias "${dto.alias}" already exists`,
      );
    }
    return this.repo.save(
      this.repo.create({
        alias: dto.alias,
        title: dto.title,
        description: dto.description ?? null,
        code: dto.code,
      }),
    );
  }

  async findAll(
    query: PaginationQueryDto<SnippetOrderBy> = {},
  ): Promise<PaginatedResult<SnippetEntity>> {
    const page = query.page ?? 1;
    const limit = query.limit ?? 50;
    const orderBy = query.orderBy ?? "id";
    const orderDir = query.orderDir ?? "ASC";
    const [data, total] = await this.repo.findAndCount({
      order: { [orderBy]: orderDir },
      skip: (page - 1) * limit,
      take: limit,
    });
    return { data, total, page, limit };
  }

  async findOne(id: string): Promise<SnippetEntity> {
    const snippet = await this.repo.findOneBy({ id });
    if (!snippet) throw new NotFoundException(`Snippet ${id} not found`);
    return snippet;
  }

  async update(id: string, dto: UpdateSnippetDto): Promise<SnippetEntity> {
    const snippet = await this.findOne(id);
    if (dto.alias && dto.alias !== snippet.alias) {
      const conflict = await this.repo.findOneBy({ alias: dto.alias });
      if (conflict)
        throw new ConflictException(
          `Snippet alias "${dto.alias}" already exists`,
        );
    }
    Object.assign(snippet, dto);
    return this.repo.save(snippet);
  }

  async remove(id: string): Promise<void> {
    await this.findOne(id);
    await this.repo.delete(id);
  }

  /** Returns an alias→code map for all snippets (used by the executor). */
  async buildSnippetMap(): Promise<Record<string, string>> {
    const { data } = await this.findAll({ limit: 1000 });
    return Object.fromEntries(data.map((s) => [s.alias, s.code]));
  }

  exportSnippet(snippet: SnippetEntity): SnippetExportDto {
    return {
      kind: "snippet",
      id: snippet.id,
      alias: snippet.alias,
      title: snippet.title,
      description: snippet.description,
      code: snippet.code,
    };
  }

  async importSnippet(dto: SnippetExportDto): Promise<SnippetEntity> {
    const alias = dto.alias ?? dto.name;
    if (!alias) {
      throw new ConflictException("Snippet alias is required");
    }
    const title = dto.title ?? alias;

    if (dto.id) {
      const existing = await this.repo.findOneBy({ id: dto.id });
      if (existing) {
        Object.assign(existing, {
          alias,
          title,
          description: dto.description ?? null,
          code: dto.code,
        });
        return this.repo.save(existing);
      }
      return this.repo.save(
        this.repo.create({
          id: dto.id,
          alias,
          title,
          description: dto.description ?? null,
          code: dto.code,
        }),
      );
    }
    return this.repo.save(
      this.repo.create({
        alias,
        title,
        description: dto.description ?? null,
        code: dto.code,
      }),
    );
  }
}