move version rationalization to it's own class

scripts/Version.js

@@ -0,0 +1,56 @@
+var _ = require('lodash');
+var package = require('../package.json');
+var branches = package.config.supported_es_branches;
+var semver = require('semver');
+
+var maxMinorVersion = function (majorV) {
+  var versions = branches.map(function (v) { return v + '.0'; });
+  return new Version(semver.maxSatisfying(versions, '^' + majorV));
+};
+
+function Version(v) {
+  this.version = v;
+  this.major = semver.major(v);
+  this.minor = semver.minor(v);
+  this.patch = semver.patch(v);
+}
+
+Version.fromBranch = function (branch) {
+  var m;
+
+  // master === the highest version number
+  if (branch === 'master') return new Version('2.0.0');
+
+  // n.m -> n.m.0
+  if (m = branch.match(/^\d+\.\d+$/)) return new Version(branch + '.0');
+
+  // n.x -> n.(maxVersion + 1).0
+  if (m = branch.match(/^(\d+)\.x$/i)) return maxMinorVersion(m[1]).increment('minor');
+
+  throw new Error('unable to convert branch "' + branch + '" to semver');
+};
+
+Version.prototype.increment = function (which) {
+  return new Version(semver.inc(this.version, which));
+};
+
+Version.prototype.satisfies = function (range) {
+  return semver.satisfies(this.version, range);
+};
+
+// merge a list of option objects, each of which has a "version" key dictating
+// the range of versions those options should be included in. Options are merged
+// in the order of the array
+Version.prototype.mergeOpts = function (opts, defaults) {
+  var self = this;
+
+  return opts
+  .filter(function (rule) {
+    return self.satisfies(rule.version);
+  })
+  .reduce(function (overrides, rule) {
+    return _.merge(overrides, _.omit(rule, 'version'));
+  }, defaults ? _.clone(defaults) : {});
+};
+
+module.exports = Version;