FIX: fix double validation (#314)

The old float validation had several bugs. It will recognize strings
like "a1.2" and "3.4b" as valid doubles, but will not recognize integers
like "1234" as doubles. Also, since an empty string is not falsy in Ruby,
it will recognize "Inf" as -Infinity.

This commit fixes these issues

lib/discourse_data_explorer/parameter.rb

@@ -153,16 +153,16 @@ def cast_to_ruby(string)
           invalid_format string, e.message
         end
       when :double
-        if string =~ /-?\d*(\.\d+)/
+        if string.strip =~ /^-?\d*\.?\d+$/
           value = Float(string)
         elsif string =~ /^(-?)Inf(inity)?$/i
-          if $1
+          if $1.present?
             value = -Float::INFINITY
           else
             value = Float::INFINITY
           end
         elsif string =~ /^(-?)NaN$/i
-          if $1
+          if $1.present?
             value = -Float::NAN
           else
             value = Float::NAN

spec/lib/parameter_spec.rb

@@ -16,6 +16,26 @@ def param(identifier, type, default, nullable)
       )
     end
 
+    describe "double type" do
+      let!(:double_param) { param("double", :double, nil, false) }
+
+      it "raises an error if not a double" do
+        expect { double_param.cast_to_ruby("abcd") }.to raise_error(
+          ::DiscourseDataExplorer::ValidationError,
+        )
+      end
+
+      it "returns the float number if it can be a valid double" do
+        expect(double_param.cast_to_ruby("3.14")).to eq(3.14)
+        expect(double_param.cast_to_ruby(".314")).to eq(0.314)
+        expect(double_param.cast_to_ruby("1")).to eq(1.0)
+        expect(double_param.cast_to_ruby("Inf")).to eq(Float::INFINITY)
+        expect(double_param.cast_to_ruby("-Infinity")).to eq(-Float::INFINITY)
+        expect(double_param.cast_to_ruby("-NaN").nan?).to eq(true)
+        expect(double_param.cast_to_ruby("NaN").nan?).to eq(true)
+      end
+    end
+
     describe "post_id type" do
       fab!(:post)