Implement DataPrefix module

lib/data/data-prefix.coffee

@@ -0,0 +1,15 @@
+fsUtils = require('../fs-utils/fs-utils')
+
+prefix = null
+
+exports.get = ->
+	return prefix
+
+exports.set = (newPrefix) ->
+	if not fsUtils.isValidPath(newPrefix)
+		throw new Error('Invalid path')
+
+	prefix = newPrefix
+
+exports.clear = ->
+	prefix = null

lib/data/data-prefix.spec.coffee

@@ -0,0 +1,55 @@
+expect = require('chai').expect
+_ = require('lodash')
+dataPrefix = require('./data-prefix')
+
+PREFIXES =
+	main: '~/.resin'
+	new: '~/.resin-new'
+	invalid: { path: '~/.resin' }
+
+describe 'DataPrefix', ->
+
+	describe 'given no prefix', ->
+
+		beforeEach ->
+			dataPrefix.clear()
+
+		describe '#get()', ->
+
+			it 'should return nothing', ->
+				expect(dataPrefix.get()).to.not.exist
+
+		describe '#set()', ->
+
+			it 'should be able to set a prefix', ->
+				expect(dataPrefix.get()).to.not.exist
+				dataPrefix.set(PREFIXES.main)
+				expect(dataPrefix.get()).to.equal(PREFIXES.main)
+
+			it 'should throw an error if passing an invalid path', ->
+				setInvalidPrefix = _.partial(dataPrefix.set, PREFIXES.invalid)
+				expect(setInvalidPrefix).to.throw(Error)
+
+	describe 'given a prefix', ->
+
+		beforeEach ->
+			dataPrefix.set(PREFIXES.main)
+
+		describe '#get()', ->
+
+			it 'should return the saved prefix', ->
+				expect(dataPrefix.get()).to.equal(PREFIXES.main)
+
+		describe '#set()', ->
+
+			it 'should be able to override the prefix', ->
+				expect(dataPrefix.get()).to.equal(PREFIXES.main)
+				dataPrefix.set(PREFIXES.new)
+				expect(dataPrefix.get()).to.equal(PREFIXES.new)
+
+		describe '#clear()', ->
+
+			it 'should clear the prefix', ->
+				expect(dataPrefix.get()).to.equal(PREFIXES.main)
+				dataPrefix.clear()
+				expect(dataPrefix.get()).to.not.exist