Add :scale shortcut to width/height of png and svg

Allows scaling while keeping the aspect ratio

Closes #91

spec/args/scale_box_spec.rb

@@ -0,0 +1,71 @@
+require 'spec_helper'
+require 'squib/args/scale_box'
+
+describe Squib::Args::ScaleBox do
+  subject(:box) { Squib::Args::ScaleBox.new({}) }
+
+  context 'unit conversion' do
+    it 'converts units on all args' do
+      args = {x: ['1in', '2in'], y: 300, width: '1in', height: '1in'}
+      box.load!(args, expand_by: 2)
+      expect(box).to have_attributes(
+        x: [300, 600],
+        y: [300, 300],
+        width: [300, 300],
+        height: [300, 300],
+      )
+    end
+  end
+
+  context 'validation' do
+    it 'replaces with deck width and height' do
+      args = {width: :deck, height: :deck}
+      deck = OpenStruct.new(width: 123, height: 456)
+      box = Squib::Args::Box.new(deck)
+      box.load!(args, expand_by: 1)
+      expect(box).to have_attributes(width: [123], height: [456])
+    end
+
+    it 'allows :native' do
+      args = {width: :native, height: :native}
+      box.load!(args, expand_by: 1)
+      expect(box).to have_attributes(width: [:native], height: [:native])
+    end
+
+    it 'allows native to be a string' do
+      args = {width: 'native'}
+      box.load!(args, expand_by: 1)
+      expect(box).to have_attributes(width: [:native], height: [:native])
+    end
+
+    it 'allows :scale on width if height has to_f' do
+      args = {width: :scale, height: 75}
+      box.load!(args, expand_by: 1)
+      expect(box).to have_attributes(width: [:scale], height: [75])
+    end
+
+    it 'allows :scale on width if height has to_f' do
+      args = {width: 75, height: :scale}
+      box.load!(args, expand_by: 1)
+      expect(box).to have_attributes(width: [75], height: [:scale])
+    end
+
+    it 'disallows both :scale' do
+      args = {width: :scale, height: :scale}
+      expect { box.load!(args, expand_by: 1) }.to raise_error('if width is :scale, height must be a number')
+    end
+
+    it 'disallows non-to_f on width' do
+      args = {width: :foo}
+      expect { box.load!(args, expand_by: 1) }.to raise_error('width must be a number, :scale, :native, or :deck')
+    end
+
+    it 'disallows non-to_f on height' do
+      args = {height: :foo}
+      expect { box.load!(args, expand_by: 1) }.to raise_error('height must be a number, :scale, :native, or :deck')
+    end
+
+  end
+
+
+end