Copy utils from cytube-common and remove dep

The `cytube-common` module was created as part of a now-defunct
experiment and since then has just remained a crufty container for a few
utils.  Moved the utils to the main repo and removed the dependency.

src/metrics/jsonfilemetricsreporter.js

@@ -0,0 +1,73 @@
+import fs from 'fs';
+
+/** MetricsReporter that records metrics as JSON objects in a file, one per line */
+class JSONFileMetricsReporter {
+    /**
+     * Create a new JSONFileMetricsReporter that writes to the given file path.
+     *
+     * @param {string} filename file path to write to
+     */
+    constructor(filename) {
+        this.writeStream = fs.createWriteStream(filename, { flags: 'a' });
+        this.metrics = {};
+        this.timers = {};
+    }
+
+    /**
+     * @see {@link module:cytube-common/metrics/metrics.incCounter}
+     */
+    incCounter(counter, value) {
+        if (!this.metrics.hasOwnProperty(counter)) {
+            this.metrics[counter] = 0;
+        }
+
+        this.metrics[counter] += value;
+    }
+
+    /**
+     * Add a time metric
+     *
+     * @param {string} timer name of the timer
+     * @param {number} ms milliseconds to record
+     */
+    addTime(timer, ms) {
+        if (!this.timers.hasOwnProperty(timer)) {
+            this.timers[timer] = {
+                totalTime: 0,
+                count: 0,
+                p100: 0
+            };
+        }
+
+        this.timers[timer].totalTime += ms;
+        this.timers[timer].count++;
+        if (ms > this.timers[timer].p100) {
+            this.timers[timer].p100 = ms;
+        }
+    }
+
+    /**
+     * @see {@link module:cytube-common/metrics/metrics.addProperty}
+     */
+    addProperty(property, value) {
+        this.metrics[property] = value;
+    }
+
+    report() {
+        for (const timer in this.timers) {
+            this.metrics[timer+':avg'] = this.timers[timer].totalTime / this.timers[timer].count;
+            this.metrics[timer+':count'] = this.timers[timer].count;
+            this.metrics[timer+':p100'] = this.timers[timer].p100;
+        }
+
+        const line = JSON.stringify(this.metrics) + '\n';
+        try {
+            this.writeStream.write(line);
+        } finally {
+            this.metrics = {};
+            this.timers = {};
+        }
+    }
+}
+
+export { JSONFileMetricsReporter };

src/metrics/metrics.js

@@ -0,0 +1,132 @@
+import os from 'os';
+
+/** @module cytube-common/metrics/metrics */
+
+const MEM_RSS = 'memory:rss';
+const LOAD_1MIN = 'load:1min';
+const TIMESTAMP = 'time';
+const logger = require('@calzoneman/jsli')('metrics');
+
+var delegate = null;
+var reportInterval = null;
+var reportHooks = [];
+let warnedNoReporter = false;
+
+function warnNoReporter() {
+    if (!warnedNoReporter) {
+        warnedNoReporter = true;
+        logger.warn('No metrics reporter configured.  Metrics will not be recorded.');
+    }
+}
+
+/**
+ * Increment a metrics counter by the specified amount.
+ *
+ * @param {string} counter name of the counter to increment
+ * @param {number} value optional value to increment by (default 1)
+ */
+export function incCounter(counter, amount = 1) {
+    if (delegate === null) {
+        warnNoReporter();
+    } else {
+        delegate.incCounter(counter, amount);
+    }
+}
+
+/**
+ * Start a timer.  Returns a handle to use to end the timer.
+ *
+ * @param {string} timer name
+ * @return {object} timer handle
+ */
+export function startTimer(timer) {
+    return {
+        timer: timer,
+        hrtime: process.hrtime()
+    };
+}
+
+/**
+ * Stop a timer and record the time (as an average)
+ *
+ * @param {object} handle timer handle to Stop
+ */
+export function stopTimer(handle) {
+    if (delegate === null) {
+        warnNoReporter();
+        return;
+    }
+    const [seconds, ns] = process.hrtime(handle.hrtime);
+    delegate.addTime(handle.timer, seconds*1e3 + ns/1e6);
+}
+
+/**
+ * Add a property to the current metrics period.
+ *
+ * @param {string} property property name to add
+ * @param {any} property value
+ */
+export function addProperty(property, value) {
+    if (delegate === null) {
+        warnNoReporter();
+    } else {
+        delegate.addProperty(property, value);
+    }
+}
+
+/**
+ * Set the metrics reporter to record to.
+ *
+ * @param {MetricsReporter} reporter reporter to record metrics to
+ */
+export function setReporter(reporter) {
+    delegate = reporter;
+}
+
+/**
+ * Set the interval at which to report metrics.
+ *
+ * @param {number} interval time in milliseconds between successive reports
+ */
+export function setReportInterval(interval) {
+    clearInterval(reportInterval);
+    if (!isNaN(interval) && interval >= 0) {
+        reportInterval = setInterval(reportLoop, interval);
+    }
+}
+
+/**
+ * Add a callback to add additional metrics before reporting.
+ *
+ * @param {function(metricsReporter)} hook callback to be invoked before reporting
+ */
+export function addReportHook(hook) {
+    reportHooks.push(hook);
+}
+
+/**
+ * Force metrics to be reported right now.
+ */
+export function flush() {
+    reportLoop();
+}
+
+function addDefaults() {
+    addProperty(MEM_RSS, process.memoryUsage().rss / 1048576);
+    addProperty(LOAD_1MIN, os.loadavg()[0]);
+    addProperty(TIMESTAMP, new Date());
+}
+
+function reportLoop() {
+    if (delegate !== null) {
+        try {
+            addDefaults();
+            reportHooks.forEach(hook => {
+                hook(delegate);
+            });
+            delegate.report();
+        } catch (error) {
+            logger.error(error.stack);
+        }
+    }
+}