Initial commit

.gitignore

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+node_modules

example.js

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+"use strict";
+
+const Promise = require("bluebird");
+
+const pipe = require("@promistream/pipe");
+const fromIterable = require("@promistream/from-iterable");
+const rangeNumbers = require("@promistream/range-numbers");
+const combineSequentialStreaming = require("./");
+const collect = require("@promistream/collect");
+
+return Promise.try(() => {
+	return pipe([
+		fromIterable([
+			rangeNumbers(0, 3),
+			rangeNumbers(3, 5),
+			rangeNumbers(5, 10),
+		]),
+		combineSequentialStreaming(),
+		collect()
+	]).read();
+}).then((result) => {
+	console.log(result); // [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
+});

index.js

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+"use strict";
+
+const Promise = require("bluebird");
+
+const pipe = require("@promistream/pipe");
+const sequentialize = require("@promistream/sequentialize");
+const isEndOfStream = require("@promistream/is-end-of-stream");
+const propagateAbort = require("@promistream/propagate-abort");
+
+module.exports = function combineSequentialStreaming() {
+	let currentStream;
+
+	function tryLoadNextStream(source) {
+		if (currentStream == null) {
+			return Promise.try(() => {
+				return source.read();
+			}).then((stream) => {
+				// FIXME: Validate that it's actually a promistream
+				currentStream = stream;
+				return tryLoadNextStream(source);
+			});
+		}
+	}
+
+	function tryRead(source) {
+		return Promise.try(() => {
+			return tryLoadNextStream(source);
+		}).then(() => {
+			return Promise.try(() => {
+				return currentStream.read();
+			}).catch(isEndOfStream, () => {
+				currentStream = null;
+
+				// The next read attempt will load in a new stream
+				return tryRead(source);
+			});
+		});
+	}
+
+	return pipe([
+		{
+			_promistreamVersion: 0,
+			description: `sequential combiner stream`,
+			abort: propagateAbort, // Once aborted, need to abort any substreams that come in afterwards
+			peek: function peek(source) {
+				return Promise.try(() => {
+					return tryLoadNextStream(source);
+				}).then(() => {
+					// FIXME: This won't be completely accurate - if the current stream produces multiple peek=true for EndOfStream markers, then only one of them will actually be read out before the stream is switched out - need to have some code to drain remaining peeks before swapping out the stream, so as to remain spec-compliant
+					return currentStream.peek();
+				});
+			},
+			read: function produceValue_combineSequentialStreaming(source) {
+				// FIXME: Define how this interacts with aborts - does an abort in a single source stream also propagate to an abort for the parent pipeline, including any following substreams?
+				return tryRead(source);
+			}
+		},
+		// FIXME: Make parallelism-capable
+		sequentialize()
+	]);
+};

package.json

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+{
+  "name": "@promistream/combine-sequential-streaming",
+  "version": "0.1.0",
+  "main": "index.js",
+  "keywords": [
+    "promistream"
+  ],
+  "repository": "http://git.cryto.net/promistream/combine-sequential-streaming.git",
+  "author": "Sven Slootweg <admin@cryto.net>",
+  "license": "WTFPL OR CC0-1.0",
+  "devDependencies": {
+    "@joepie91/eslint-config": "^1.1.0",
+    "@promistream/collect": "^0.1.1",
+    "@promistream/range-numbers": "^0.1.2",
+    "eslint": "^6.8.0"
+  },
+  "dependencies": {
+    "@promistream/pipe": "^0.1.6",
+    "@promistream/from-iterable": "^0.1.0",
+    "@promistream/is-end-of-stream": "^0.1.1",
+    "@promistream/propagate-abort": "^0.1.7",
+    "@promistream/sequentialize": "^0.1.0",
+    "bluebird": "^3.7.2"
+  }
+}