import { DeleteObjectCommand, PutObjectCommand, S3Client } from '@aws-sdk/client-s3';
import { Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

type UploadPublicFileInput = {
  key: string;
  body: Buffer;
  contentType?: string | null;
  fileName?: string | null;
};

@Injectable()
export class R2PublicFileService {
  private client?: S3Client;

  constructor(private readonly configService: ConfigService) {}

  isConfigured() {
    return Boolean(
      this.bucket
      && this.publicBaseUrl
      && this.accessKeyId
      && this.secretAccessKey,
    );
  }

  createLmsCourseFileKey(input: {
    courseId: string;
    week: number;
    kind: 'REFERENCE' | 'EXAMPLE_CODE';
    fileId: string;
    extension?: string;
  }) {
    const section = input.kind === 'EXAMPLE_CODE' ? 'example-codes' : 'references';
    return [
      this.publicPrefix,
      'lms',
      'courses',
      input.courseId,
      'weeks',
      String(input.week),
      section,
      `${input.fileId}${input.extension ?? ''}`,
    ].filter(Boolean).join('/');
  }

  async uploadPublicFile(input: UploadPublicFileInput) {
    if (!this.isConfigured()) return null;

    await this.getClient().send(new PutObjectCommand({
      Bucket: this.bucket,
      Key: input.key,
      Body: input.body,
      ContentLength: input.body.length,
      ContentType: input.contentType ?? 'application/octet-stream',
      ContentDisposition: input.fileName ? contentDispositionForFile(input.fileName) : undefined,
    }));

    return this.publicUrl(input.key);
  }

  async deletePublicFile(key: string) {
    if (!this.isConfigured() || !this.isPublicKey(key)) return;

    await this.getClient().send(new DeleteObjectCommand({
      Bucket: this.bucket,
      Key: key,
    }));
  }

  publicUrl(key: string) {
    if (!this.publicBaseUrl || !this.isPublicKey(key)) return null;
    return `${this.publicBaseUrl.replace(/\/$/, '')}/${encodeObjectKey(key)}`;
  }

  isPublicKey(value: string) {
    return value.startsWith(`${this.publicPrefix}/`);
  }

  private getClient() {
    if (this.client) return this.client;

    const endpoint = this.configService.get<string>('R2_ENDPOINT')
      || `https://${this.configService.get<string>('R2_ACCOUNT_ID')}.r2.cloudflarestorage.com`;

    this.client = new S3Client({
      region: this.configService.get<string>('R2_REGION', 'auto'),
      endpoint,
      credentials: {
        accessKeyId: this.accessKeyId,
        secretAccessKey: this.secretAccessKey,
      },
      forcePathStyle: this.configService.get<string>('R2_FORCE_PATH_STYLE', 'true') !== 'false',
    });

    return this.client;
  }

  private get bucket() {
    return this.configService.get<string>('R2_BUCKET')?.trim() ?? '';
  }

  private get publicBaseUrl() {
    return this.configService.get<string>('R2_PUBLIC_BASE_URL')?.trim() ?? '';
  }

  private get accessKeyId() {
    return this.configService.get<string>('R2_ACCESS_KEY_ID')?.trim() ?? '';
  }

  private get secretAccessKey() {
    return this.configService.get<string>('R2_SECRET_ACCESS_KEY')?.trim() ?? '';
  }

  private get publicPrefix() {
    return this.configService.get<string>('R2_PUBLIC_FILE_PREFIX', 'studio-files/public').replace(/^\/+|\/+$/g, '');
  }
}

function encodeObjectKey(key: string) {
  return key.split('/').map(encodeURIComponent).join('/');
}

function contentDispositionForFile(fileName: string) {
  const fallbackName = fileName.replace(/[\\\"\r\n]/g, '_');
  return `attachment; filename="${fallbackName}"; filename*=UTF-8''${encodeURIComponent(fileName)}`;
}