import { assertEquals } from "jsr:@std/assert@1/equals";
import {
  readAll,
  readAllSync,
  type Reader,
  type ReaderSync,
} from "jsr:@std/[email protected]";

class SlowBuffer implements Reader, ReaderSync {
  #remaining: Uint8Array;

  constructor(bytes: Uint8Array) {
    this.#remaining = bytes;
  }

  // deno-lint-ignore require-await -- implementing `Reader` interface
  async read(p: Uint8Array): Promise<number | null> {
    return this.readSync(p);
  }

  readSync(p: Uint8Array): number | null {
    if (p.length === 0) {
      throw new TypeError("p is empty");
    }
    const remaining = this.#remaining;
    if (remaining.length === 0) {
      // no more bytes to read; signal end-of-stream
      return null;
    }
    // read one byte at a time
    this.#remaining = remaining.subarray(1);
    p[0] = remaining[0];
    return 1;
  }
}

Deno.test("readAll() with SlowBuffer", async () => {
  const testBytes = crypto.getRandomValues(new Uint8Array(20));
  const reader = new SlowBuffer(testBytes);
  const actualBytes = await readAll(reader);
  assertEquals(actualBytes, testBytes);
});

Deno.test("readAllSync() with SlowBuffer", () => {
  const testBytes = crypto.getRandomValues(new Uint8Array(20));
  const reader = new SlowBuffer(testBytes);
  const actualBytes = readAllSync(reader);
  assertEquals(actualBytes, testBytes);
});