// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { Buffer } from "jsr:/@std/io@^0.215.0/buffer";
import { writeAll } from "jsr:/@std/io@^0.215.0/write_all";
import { Reader } from "jsr:/@std/io@^0.215.0/types";

/**
 * Create a {@linkcode Reader} from an iterable of {@linkcode Uint8Array}s.
 *
 * ```ts
 * import { readerFromIterable } from "@std/streams/reader_from_iterable";
 * import { copy } from "@std/io/copy";
 *
 * const file = await Deno.open("build.txt", { write: true });
 * const reader = readerFromIterable((async function* () {
 *   while (true) {
 *     await new Promise((r) => setTimeout(r, 1000));
 *     const message = `data: ${JSON.stringify(Deno.build)}\n\n`;
 *     yield new TextEncoder().encode(message);
 *   }
 * })());
 * await copy(reader, file);
 * ```
 *
 * @deprecated (will be removed after 1.0.0) Use {@linkcode ReadableStream.from} instead.
 */
export function readerFromIterable(
  iterable: Iterable<Uint8Array> | AsyncIterable<Uint8Array>,
): Reader {
  const iterator: Iterator<Uint8Array> | AsyncIterator<Uint8Array> =
    (iterable as AsyncIterable<Uint8Array>)[Symbol.asyncIterator]?.() ??
      (iterable as Iterable<Uint8Array>)[Symbol.iterator]?.();
  const buffer = new Buffer();
  return {
    async read(p: Uint8Array): Promise<number | null> {
      if (buffer.length === 0) {
        const result = await iterator.next();
        if (result.done) {
          return null;
        } else {
          if (result.value.byteLength <= p.byteLength) {
            p.set(result.value);
            return result.value.byteLength;
          }
          p.set(result.value.subarray(0, p.byteLength));
          await writeAll(buffer, result.value.subarray(p.byteLength));
          return p.byteLength;
        }
      } else {
        const n = await buffer.read(p);
        if (n === null) {
          return this.read(p);
        }
        return n;
      }
    },
  };
}