from-node-stream/src/readable/index.js

"use strict";

const debug = require("debug")("promistream:from-node-stream:readable");

const attachHandlers = require("./attach-handlers");
const createPushBuffer = require("./push-buffer");
const destroyStream = require("../destroy-stream");
const assertErrorType = require("../assert-error-type");

module.exports = function wireUpReadableInterface(stream, { onEnd, onError } = {}) {
	let pushBuffer = createPushBuffer({
		onPause: function () {
			if (stream.pause != null) {
				debug("Pausing underlying stream");
				stream.pause();
				return true; // FIXME: Can we verify whether the pausing was successful, somehow? Eg. to deal with streams with `readable` event handlers attached.
			} else {
				return false;
			}
		},
		onResume: function () {
			if (stream.resume != null) {
				debug("Resuming underlying stream");
				stream.resume();
				return true;
			} else {
				throw new Error(`Stream was successfully paused but does not have a resume method. This should never happen!`);
			}
		}
	});

	// TODO: Verify that auto-detaching all event handlers upon end/error is actually the correct thing to do!
	attachHandlers({
		stream: stream,
		onData: (data) => {
			if (Buffer.isBuffer(data)) {
				debug(`Chunk emitted of length ${data.length}`);
			} else {
				debug(`Value emitted`);
			}

			pushBuffer.queueValue(data);
		},
		onError: (error) => {
			assertErrorType(error);
			pushBuffer.queueError(error);
			
			if (onError != null) {
				onError(error);
			}
		},
		onClose: () => {
			pushBuffer.markEnded();
			
			if (onEnd != null) {
				onEnd();
			}
		}
	});

	return {
		request: pushBuffer.queueRequest,
		consumeImmediateBuffer: pushBuffer.consumeImmediateBuffer,
		destroy: () => {
			return destroyStream(stream);
		}
	};
};