InputCommon: Extract ControlReference from ControllerInterface

Better separation of concerns. Relegates `ControllerInterface` to
enumerating input controls, and the new `ControlReference` deals with
combining inputs and configuration expression parsing.

Source/Core/InputCommon/ControlReference/ControlReference.h

@@ -0,0 +1,79 @@
+// Copyright 2016 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "InputCommon/ControlReference/ExpressionParser.h"
+#include "InputCommon/ControllerInterface/Device.h"
+
+// ControlReference
+//
+// These are what you create to actually use the inputs, InputReference or OutputReference.
+//
+// After being bound to devices and controls with UpdateReference,
+// each one can link to multiple devices and controls
+// when you change a ControlReference's expression,
+// you must use UpdateReference on it to rebind controls
+//
+
+class ControlReference
+{
+public:
+  static bool InputGateOn();
+
+  virtual ControlState State(const ControlState state = 0) = 0;
+  virtual ciface::Core::Device::Control* Detect(const unsigned int ms,
+                                                ciface::Core::Device* const device) = 0;
+
+  void UpdateReference(ciface::Core::DeviceContainer& devices,
+                       const ciface::Core::DeviceQualifier& default_device);
+
+  ControlState range;
+  std::string expression;
+  const bool is_input;
+  ciface::ExpressionParser::ExpressionParseStatus parse_error;
+
+  virtual ~ControlReference() { delete parsed_expression; }
+  int BoundCount()
+  {
+    if (parsed_expression)
+      return parsed_expression->num_controls;
+    else
+      return 0;
+  }
+
+protected:
+  ControlReference(const bool _is_input) : range(1), is_input(_is_input), parsed_expression(nullptr)
+  {
+  }
+  ciface::ExpressionParser::Expression* parsed_expression;
+};
+
+//
+// InputReference
+//
+// Control reference for inputs
+//
+class InputReference : public ControlReference
+{
+public:
+  InputReference() : ControlReference(true) {}
+  ControlState State(const ControlState state) override;
+  ciface::Core::Device::Control* Detect(const unsigned int ms,
+                                        ciface::Core::Device* const device) override;
+};
+
+//
+// OutputReference
+//
+// Control reference for outputs
+//
+class OutputReference : public ControlReference
+{
+public:
+  OutputReference() : ControlReference(false) {}
+  ControlState State(const ControlState state) override;
+  ciface::Core::Device::Control* Detect(const unsigned int ms,
+                                        ciface::Core::Device* const device) override;
+};