feat(reader): Add implementation with tests

Author: Walker

.eslintignore

@@ -0,0 +1 @@
+coverage

.gitignore

@@ -6,3 +6,4 @@ tmp/**/*
 .idea/**/*
 *.iml
 *.log
+coverage

.travis.yml

@@ -2,7 +2,6 @@ language: node_js
 
 node_js:
   - "8"
-  - "6"
 
 script:
   - npm test

lib/reader.js

@@ -0,0 +1,75 @@
+const { Readable, PassThrough, Transform } = require('stream');
+const { stringify, parse } = require('JSONStream');
+const mergeStream = require('merge-stream');
+const { dedupe, sort, setOrder } = require('./util');
+const assert = require('assert');
+
+module.exports = class Reader extends Readable {
+    constructor(streams) {
+        super();
+
+        assert(
+            streams,
+            `Expected first argument to new Reader() to be a stream or array of streams. 
+            Instead got ${typeof stream}`
+        );
+
+        if (!Array.isArray(streams)) {
+            streams = [streams];
+        }
+
+        assert(
+            streams.length,
+            `Expected at least one stream to be provided to new Reader(). Got none.`
+        );
+
+        const merged = mergeStream();
+
+        let count = 0;
+        streams.forEach((readStream, index) => {
+            const tmpStream = new PassThrough({ objectMode: true });
+            merged.add(tmpStream);
+
+            readStream.on('file found', file => {
+                this.emit('file found', file);
+                readStream
+                    .pipe(parse('*'))
+                    .on('error', err => {
+                        this.emit('error', err);
+                    })
+                    .pipe(setOrder(index))
+                    .pipe(tmpStream);
+
+                count++;
+                if (count === streams.length) {
+                    this.emit('pipeline ready');
+                }
+            });
+
+            readStream.on('file not found', file => {
+                this.emit('file not found', file);
+                tmpStream.end();
+
+                count++;
+                if (count === streams.length) {
+                    this.emit('pipeline ready');
+                }
+            });
+        });
+
+        this.data = merged.pipe(dedupe()).pipe(sort());
+        this.data.pause();
+
+        this.data.on('data', chunk => {
+            this.push(chunk.content);
+        });
+
+        this.data.on('end', () => {
+            this.push(null);
+        });
+    }
+
+    _read(size) {
+        return this.data.resume();
+    }
+};

lib/util.js

@@ -0,0 +1,85 @@
+const { Transform } = require('stream');
+
+function compareByOrder(a, b) {
+    if (a.order === b.order) return 0;
+    return a.order > b.order ? 1 : -1;
+}
+
+class Dedupe extends Transform {
+    constructor() {
+        super({
+            objectMode: true
+        });
+
+        this.rows = new Map();
+    }
+
+    _transform(chunk, enc, callback) {
+        if (chunk && chunk.id) {
+            this.rows.set(chunk.id, chunk);
+        }
+
+        callback();
+    }
+
+    _flush(callback) {
+        Array.from(this.rows.values()).forEach(row => this.push(row));
+        callback();
+    }
+}
+
+class SetOrder extends Transform {
+    constructor(index) {
+        super({
+            objectMode: true
+        });
+
+        this.index = index;
+    }
+
+    _transform(chunk, enc, callback) {
+        chunk.order = this.index;
+        callback(null, chunk);
+    }
+}
+
+class Sort extends Transform {
+    constructor() {
+        super({
+            objectMode: true
+        });
+
+        this.rows = new Map();
+    }
+
+    _transform(chunk, enc, callback) {
+        if (
+            chunk &&
+            chunk.order !== null &&
+            typeof chunk.order !== 'undefined'
+        ) {
+            this.rows.set(chunk.order, chunk);
+        }
+        callback();
+    }
+
+    _flush(callback) {
+        Array.from(this.rows.values())
+            .sort(compareByOrder)
+            .forEach(row => this.push(row));
+        callback();
+    }
+}
+
+module.exports = {
+    dedupe() {
+        return new Dedupe();
+    },
+    setOrder(index) {
+        return new SetOrder(index);
+    },
+    sort() {
+        return new Sort();
+    },
+    compareByOrder
+};