Implement all features and tests

Author: bartveneman

.travis.yml

@@ -0,0 +1,7 @@
+language: node_js
+node_js:
+  - '6'
+  - '7'
+  - '8'
+  - '9'
+  - '10'

diff.js

@@ -0,0 +1,41 @@
+const diffNumbers = require('./src/diff-numbers.js')
+const diffLists = require('./src/diff-lists.js')
+
+function diffStats(statsA, statsB) {
+	// This assumes that the statsB is newer than statsA
+	return Object.entries(statsB).reduce((diff, [key, value]) => {
+		return diff.set(key, diffStat(statsA[key], value))
+	}, new Map())
+}
+
+function diffStat(statA, statB) {
+	if (typeof statB === 'undefined') {
+		statB = statA
+		statA = undefined
+	}
+
+	if (typeof statA === 'undefined') {
+		statA = null
+	}
+
+	// Abort if the types are not compatible
+	// A must have the same type as B, or A must be null
+	if (typeof statA !== typeof statB && statA !== null) {
+		throw new Error(
+			`Stat types do not match. ${typeof statA} is not compatible to compare with ${typeof statB}`
+		)
+	}
+
+	if (!Number.isNaN(statB) && Number.isFinite(statB)) {
+		return diffNumbers(statA, statB)
+	}
+
+	if (Array.isArray(statB)) {
+		statA = statA === null ? [] : statA
+		return diffLists(statA, statB)
+	}
+
+	return null
+}
+
+module.exports = diffStats