[apps/calculation] create a class evaluate context

Change-Id: Ic2aa40a00dec0ff67aeeb63edcb1776c3825cfbe

apps/calculation/Makefile

@@ -2,6 +2,7 @@ app_objs += $(addprefix apps/calculation/,\
   app.o\
   calculation.o\
   calculation_store.o\
+  evaluate_context.o\
   selectable_table_view.o\
   history_view_cell.o\
   history_controller.o\

apps/calculation/evaluate_context.cpp

@@ -0,0 +1,27 @@
+#include "evaluate_context.h"
+#include <string.h>
+
+namespace Calculation {
+
+EvaluateContext::EvaluateContext(::Context * parentContext, CalculationStore * calculationStore) :
+  m_ansValue(Float(0.0f)),
+  m_calculationStore(calculationStore),
+  m_context(parentContext)
+{
+}
+
+Float * EvaluateContext::ansValue() {
+  Calculation * lastCalculation = m_calculationStore->calculationAtIndex(m_calculationStore->numberOfCalculations()-1);
+  m_ansValue = Float(lastCalculation->evaluation());
+  return &m_ansValue;
+}
+
+const Expression * EvaluateContext::expressionForSymbol(const Symbol * symbol) {
+  if (symbol->name() == Symbol::SpecialSymbols::Ans) {
+    return ansValue();
+  } else {
+    return m_context->expressionForSymbol(symbol);
+  }
+}
+
+}

apps/calculation/evaluate_context.h

@@ -0,0 +1,22 @@
+#ifndef CALCULATION_EVALUATECONTEXT_H
+#define CALCULATION_EVALUATECONTEXT_H
+
+#include <poincare.h>
+#include "calculation_store.h"
+
+namespace Calculation {
+
+class EvaluateContext : public ::Context {
+  public:
+    EvaluateContext(Context * parentContext, CalculationStore * calculationStore);
+    Float * ansValue();
+    const Expression * expressionForSymbol(const Symbol * symbol) override;
+  private:
+    Float m_ansValue;
+    CalculationStore * m_calculationStore;
+    ::Context * m_context;
+};
+
+}
+
+#endif