/*!
 * @file S3ExternalStorage.ts
 * @description This file contains the S3ExternalStorage class, which is used to store and retrieve page contents from S3.
 * @author Dean Heffernan
 * @copyright 2025 Squiz
 */

// External
import { DeleteObjectCommand, GetObjectCommand, PutObjectCommand, S3Client } from '@aws-sdk/client-s3';

/**
 * Represents the storage location of page contents in S3.
 */
export interface S3StorageLocation {
  type: 's3';
  key: string;
}

/**
 * The S3ExternalStorage class is used to store and retrieve page contents from S3.
 * @class S3ExternalStorage
 * @constructor
 * @param {string} bucket - The name of the S3 bucket to use for storing page contents.
 * @param {number} thresholdBytes - The threshold in bytes above which page contents will be stored externally.
 * @param {S3Client} s3Client - The S3 client to use for storing and retrieving page contents.
 * @returns {S3ExternalStorage} A new instance of the S3ExternalStorage class.
 */
export class S3ExternalStorage {
  /**
   * The config to use for storing and retrieving page contents.
   * @type {Config}
   */
  private readonly tenantId: string;
  /**
   * The name of the S3 bucket to use for storing page contents.
   * @type {string}
   */
  private readonly bucket: string;
  /**
   * The S3 client to use for storing and retrieving page contents.
   * @type {S3Client}
   */
  private readonly s3Client: S3Client;

  /**
   * Creates a new instance of the S3ExternalStorage class.
   * @constructor
   * @param {S3Client} s3Client - The S3 client to use for storing and retrieving page contents.
   * @returns {S3ExternalStorage} A new instance of the S3ExternalStorage class.
   */
  constructor(tenantId: string, s3Client: S3Client, bucket: string) {
    this.tenantId = tenantId;
    this.bucket = bucket;
    this.s3Client = s3Client;
  }

  /**
   * Saves a payload to S3.
   * @param {string} entityName - The name of the entity to save the payload for.
   * @param {string} referenceId - The reference ID of the payload.
   * @param {object} payload - The payload to save.
   * @returns {Promise<{ location: S3StorageLocation; size: number }>} A promise that resolves to the location and size of the saved payload.
   */
  public async save(
    entityName: string,
    referenceId: string,
    payload: object,
  ): Promise<{ location: S3StorageLocation; size: number }> {
    const body = JSON.stringify(payload);
    const key = `${this.tenantId}/${entityName}/${referenceId}.json`;
    await this.s3Client.send(
      new PutObjectCommand({
        Bucket: this.bucket,
        Key: key,
        Body: body,
        ContentType: 'application/json',
      }),
    );
    return {
      location: {
        type: 's3',
        key,
      },
      size: Buffer.byteLength(body, 'utf8'),
    };
  }

  /**
   * Loads a payload from S3.
   * @param location - The location of the payload to load.
   * @returns {Promise<Record<string, unknown>>} A promise that resolves to the loaded payload.
   */
  public async load(location: S3StorageLocation): Promise<Record<string, unknown>> {
    const response = await this.s3Client.send(
      new GetObjectCommand({
        Bucket: this.bucket,
        Key: location.key,
      }),
    );
    if (!response.Body) {
      throw new Error(`Failed to load externalised items from S3 object ${location.key}`);
    }
    const contents = await response.Body.transformToString();
    return JSON.parse(contents);
  }

  public async delete(location?: S3StorageLocation) {
    if (!location || !this.bucket) {
      return;
    }
    await this.s3Client.send(
      new DeleteObjectCommand({
        Bucket: this.bucket,
        Key: location.key,
      }),
    );
  }
}