import type { readFile as ReadFileT } from "node:fs/promises";
import { Document } from "../../document.js";
import { getEnv } from "../../util/env.js";
import { BaseDocumentLoader } from "../base.js";

export class TextLoader extends BaseDocumentLoader {
  constructor(public filePathOrBlob: string | Blob) {
    super();
  }

  protected async parse(raw: string): Promise<string[]> {
    return [raw];
  }

  public async load(): Promise<Document[]> {
    let text: string;
    let metadata: Record<string, string>;
    if (typeof this.filePathOrBlob === "string") {
      const { readFile } = await TextLoader.imports();
      text = await readFile(this.filePathOrBlob, "utf8");
      metadata = { source: this.filePathOrBlob };
    } else {
      text = await this.filePathOrBlob.text();
      metadata = { source: "blob", blobType: this.filePathOrBlob.type };
    }
    const parsed = await this.parse(text);
    parsed.forEach((pageContent, i) => {
      if (typeof pageContent !== "string") {
        throw new Error(
          `Expected string, at position ${i} got ${typeof pageContent}`
        );
      }
    });
    return parsed.map(
      (pageContent, i) =>
        new Document({
          pageContent,
          metadata:
            parsed.length === 1
              ? metadata
              : {
                  ...metadata,
                  line: i + 1,
                },
        })
    );
  }

  static async imports(): Promise<{
    readFile: typeof ReadFileT;
  }> {
    try {
      const { readFile } = await import("node:fs/promises");
      return { readFile };
    } catch (e) {
      console.error(e);
      throw new Error(
        `Failed to load fs/promises. TextLoader available only on environment 'node'. It appears you are running environment '${getEnv()}'. See https://<link to docs> for alternatives.`
      );
    }
  }
}