import type { IChunkSource } from "../types";

export class FileChunkSource implements IChunkSource {
  private readonly path: string;
  private readonly chunkSize: number;

  public constructor(path: string, chunkSize: number = 64 * 1024) {
    this.path = path;
    this.chunkSize = Math.max(1024, chunkSize);
  }

  public async *chunks(): AsyncIterable<string> {
    // Prefer Bun if available; fall back to Node streams to keep portability
    if (typeof Bun !== "undefined" && typeof Bun.file === "function") {
      const file = Bun.file(this.path);
      const reader = file.stream().getReader();
      try {
        while (true) {
          const { value, done } = await reader.read();
          if (done) break;
          if (value) yield Buffer.from(value).toString("utf8");
        }
      } finally {
        reader.releaseLock();
      }
      return;
    }

    // Node.js fallback
    const { createReadStream } = await import("node:fs");
    const stream = createReadStream(this.path, { encoding: "utf8", highWaterMark: this.chunkSize });
    for await (const chunk of stream) {
      yield chunk as string;
    }
  }
}