Add option 'units', it is a map of unit labels to values (in seconds)…

…, e.g. { 's': 1, 'm': 60, 'h': 3600 }

Modify ETA estimation to return the least granular unit for which the eta is >= 1, based on supplied values
Add replacement token ':unit', returns the label associated with the unit value
ProgressBar.defaultUnits holds the h/m/s arrangement; it is not actually used by default to preserve compatibility

Example usage: new ProgressBar(':eta:unit', { units: ProgressBar.defaultUnits });
Example output: '12.3m' -> '38.5s' (changes from minutes to seconds over time)

Addresses visionmedia#63

lib/node-progress.js

@@ -55,6 +55,7 @@ function ProgressBar(fmt, options) {
   this.fmt = fmt;
   this.curr = 0;
   this.total = options.total;
+  this.units = ProgressBar.mkUnits(options.units || { 's': 1 });
   this.width = options.width || this.total;
   this.clear = options.clear
   this.chars = {
@@ -67,6 +68,35 @@ function ProgressBar(fmt, options) {
   this.lastDraw = '';
 }
 
+/**
+ * The default unit bindings for enhanced ETA
+ */
+ProgressBar.defaultUnits = {
+  'h': 3600,
+  'm': 60,
+  's': 1
+};
+
+/**
+ * Converts object mappings into something more useful for calculating ETA with
+ *
+ * @param {object} obj Map of suffixes to unit values
+ */
+ProgressBar.mkUnits = function (obj) {
+  var arr = Object.keys(obj)
+    .map(function (key) {
+      return { label: key, value: obj[key] };
+    })
+    .sort(function (a, b) {
+      return a.value - b.value;
+    });
+
+  var values = arr.map(function (unit) { return unit.value; }),
+    labels = arr.map(function (unit) { return unit.label; });
+
+  return { labels: labels, values: values };
+};
+
 /**
  * "tick" the progress bar with optional `len` and optional `tokens`.
  *
@@ -86,7 +116,7 @@ ProgressBar.prototype.tick = function(len, tokens){
   // start time for eta
   if (0 == this.curr) this.start = new Date;
 
-  this.curr += len
+  this.curr += len;
 
   // schedule render
   if (!this.renderThrottleTimeout) {
@@ -125,15 +155,15 @@ ProgressBar.prototype.render = function (tokens) {
   var percent = ratio * 100;
   var incomplete, complete, completeLength;
   var elapsed = new Date - this.start;
-  var eta = (percent == 100) ? 0 : elapsed * (this.total / this.curr - 1);
+  var eta = this.estimate(elapsed, percent);
 
   /* populate the bar template with percentages and timestamps */
   var str = this.fmt
     .replace(':current', this.curr)
     .replace(':total', this.total)
     .replace(':elapsed', isNaN(elapsed) ? '0.0' : (elapsed / 1000).toFixed(1))
-    .replace(':eta', (isNaN(eta) || !isFinite(eta)) ? '0.0' : (eta / 1000)
-      .toFixed(1))
+    .replace(':eta', eta.value)
+    .replace(':unit', eta.suffix)
     .replace(':percent', percent.toFixed(0) + '%');
 
   /* compute the available space (non-zero) for the bar */
@@ -159,6 +189,44 @@ ProgressBar.prototype.render = function (tokens) {
   }
 };
 
+/**
+ * Estimate the remaining time and return it in the largest unit possible
+ *
+ * @param {number} elapsed
+ * @param {number} percent
+ * @api private
+ */
+ProgressBar.prototype.estimate = function (elapsed, percent) {
+  var eta = (percent == 100) ? 0 : elapsed * (this.total / this.curr - 1);
+  eta /= 1000;
+
+  var values = this.units.values;
+  var labels = this.units.labels;
+  var i = values.length - 1;
+  var suffix = labels[i];
+
+  if (isNaN(eta) || !isFinite(eta)) {
+    return {
+      eta: '0.0',
+      suffix: suffix
+    };
+  }
+
+  while (i > 0 && eta < values[i]) {
+    i--;
+  }
+  suffix = labels[i];
+
+  while (i > 0) {
+    eta /= values[i--];
+  }
+
+  return {
+    value: eta.toFixed(1),
+    suffix: suffix
+  };
+};
+
 /**
  * "update" the progress bar to represent an exact percentage.
  * The ratio (between 0 and 1) specified will be multiplied by `total` and