Calculator: Support chaining and repeating operations

The calculator now supports chaining (hitting "1+2+3=" shows "6"
instead of "5") and repeating ("2+2===" shows "8") operations. :^)

5 files changed, 126 insertions, 72 deletions

diff --git a/Userland/Applications/Calculator/Calculator.cpp b/Userland/Applications/Calculator/Calculator.cpp
index 451aa5ea01..9e68d1882a 100644
--- a/Userland/Applications/Calculator/Calculator.cpp
+++ b/Userland/Applications/Calculator/Calculator.cpp
@@ -10,9 +10,13 @@
 #include <AK/Math.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 
-Crypto::BigFraction Calculator::begin_operation(Operation operation, Crypto::BigFraction argument)
+Optional<Crypto::BigFraction> Calculator::operation_with_literal_argument(Operation operation, Crypto::BigFraction argument)
 {
-    Crypto::BigFraction res {};
+    // If a previous operation is still in progress, finish it
+    // Makes hitting "1+2+3=" equivalent to hitting "1+2=+3="
+    if (m_binary_operation_in_progress != Operation::None) {
+        argument = finish_binary_operation(m_binary_operation_saved_left_side, m_binary_operation_in_progress, argument);
+    }
 
     switch (operation) {
     case Operation::None:
@@ -22,78 +26,117 @@ Crypto::BigFraction Calculator::begin_operation(Operation operation, Crypto::Big
     case Operation::Subtract:
     case Operation::Multiply:
     case Operation::Divide:
-        m_saved_argument = argument;
-        m_operation_in_progress = operation;
-        return argument;
+        m_binary_operation_saved_left_side = argument;
+        m_binary_operation_in_progress = operation;
+        m_current_value = argument;
+        break;
 
     case Operation::Sqrt:
         if (argument < Crypto::BigFraction {}) {
             m_has_error = true;
-            return argument;
+            m_current_value = argument;
+            break;
         }
-        res = argument.sqrt();
+        m_current_value = argument.sqrt();
         clear_operation();
         break;
     case Operation::Inverse:
         if (argument == Crypto::BigFraction {}) {
             m_has_error = true;
-            return argument;
+            m_current_value = argument;
+            break;
         }
-        res = argument.invert();
+        m_current_value = argument.invert();
         clear_operation();
         break;
     case Operation::Percent:
-        res = argument * Crypto::BigFraction { 1, 100 };
+        m_current_value = argument * Crypto::BigFraction { 1, 100 };
         break;
     case Operation::ToggleSign:
-        res = -argument;
+        m_current_value = -argument;
         break;
 
     case Operation::MemClear:
         m_mem.set_to_0();
-        res = argument;
+        m_current_value = argument;
         break;
     case Operation::MemRecall:
-        res = m_mem;
+        m_current_value = m_mem;
         break;
     case Operation::MemSave:
         m_mem = argument;
-        res = argument;
+        m_current_value = argument;
         break;
     case Operation::MemAdd:
         m_mem = m_mem + argument; // avoids the need for operator+=()
-        res = m_mem;
+        m_current_value = m_mem;
+        break;
+    case Operation::Equals:
+        m_current_value = argument;
         break;
     }
 
-    return res;
+    return m_current_value;
+}
+
+static bool operation_is_binary(Calculator::Operation operation)
+{
+    switch (operation) {
+
+    case Calculator::Operation::Add:
+    case Calculator::Operation::Subtract:
+    case Calculator::Operation::Multiply:
+    case Calculator::Operation::Divide:
+        return true;
+
+    default:
+        return false;
+    }
 }
 
-Crypto::BigFraction Calculator::finish_operation(Crypto::BigFraction argument)
+Optional<Crypto::BigFraction> Calculator::operation_without_argument(Operation operation)
+{
+    bool in_binary_operation = m_binary_operation_in_progress != Operation::None;
+    bool entering_new_binary_operation = operation_is_binary(operation);
+    bool previous_operation_was_binary = operation_is_binary(m_previous_operation);
+
+    if (in_binary_operation && entering_new_binary_operation) {
+        m_binary_operation_in_progress = operation;
+        return {};
+    }
+    if (!in_binary_operation && previous_operation_was_binary && operation == Operation::Equals) {
+        m_current_value = finish_binary_operation(m_current_value, m_previous_operation, m_previous_binary_operation_right_side);
+        return m_current_value;
+    }
+    return operation_with_literal_argument(operation, m_current_value);
+}
+
+Crypto::BigFraction Calculator::finish_binary_operation(Crypto::BigFraction const& left_side, Operation operation, Crypto::BigFraction const& right_side)
 {
     Crypto::BigFraction res {};
 
-    switch (m_operation_in_progress) {
-    case Operation::None:
-        return argument;
+    m_previous_binary_operation_right_side = right_side;
+
+    switch (operation) {
 
     case Operation::Add:
-        res = m_saved_argument + argument;
+        res = left_side + right_side;
         break;
     case Operation::Subtract:
-        res = m_saved_argument - argument;
+        res = left_side - right_side;
         break;
     case Operation::Multiply:
-        res = m_saved_argument * argument;
+        res = left_side * right_side;
         break;
     case Operation::Divide:
-        if (argument == Crypto::BigFraction {}) {
+        if (right_side == Crypto::BigFraction {}) {
             m_has_error = true;
-            return argument;
+        } else {
+            res = left_side / right_side;
         }
-        res = m_saved_argument / argument;
         break;
 
+    case Operation::None:
     case Operation::Sqrt:
     case Operation::Inverse:
     case Operation::Percent:
@@ -102,6 +145,7 @@ Crypto::BigFraction Calculator::finish_operation(Crypto::BigFraction argument)
     case Operation::MemRecall:
     case Operation::MemSave:
     case Operation::MemAdd:
+    case Operation::Equals:
         VERIFY_NOT_REACHED();
     }
 
@@ -111,7 +155,10 @@ Crypto::BigFraction Calculator::finish_operation(Crypto::BigFraction argument)
 
 void Calculator::clear_operation()
 {
-    m_operation_in_progress = Operation::None;
-    m_saved_argument.set_to_0();
+    if (m_binary_operation_in_progress != Operation::None) {
+        m_previous_operation = m_binary_operation_in_progress;
+        m_binary_operation_in_progress = Operation::None;
+    }
+    m_binary_operation_saved_left_side.set_to_0();
     clear_error();
 }
diff --git a/Userland/Applications/Calculator/Calculator.h b/Userland/Applications/Calculator/Calculator.h
index 5d995bf7e1..7d249a4539 100644
--- a/Userland/Applications/Calculator/Calculator.h
+++ b/Userland/Applications/Calculator/Calculator.h
@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <AK/Optional.h>
 #include <LibCrypto/BigFraction/BigFraction.h>
 
 // This type implements the regular calculator
@@ -36,11 +37,13 @@ public:
         MemClear,
         MemRecall,
         MemSave,
-        MemAdd
+        MemAdd,
+
+        Equals
     };
 
-    Crypto::BigFraction begin_operation(Operation, Crypto::BigFraction);
-    Crypto::BigFraction finish_operation(Crypto::BigFraction);
+    Optional<Crypto::BigFraction> operation_with_literal_argument(Operation, Crypto::BigFraction);
+    Optional<Crypto::BigFraction> operation_without_argument(Operation);
 
     bool has_error() const { return m_has_error; }
 
@@ -48,8 +51,16 @@ public:
     void clear_error() { m_has_error = false; }
 
 private:
-    Operation m_operation_in_progress { Operation::None };
-    Crypto::BigFraction m_saved_argument {};
     Crypto::BigFraction m_mem {};
+
+    Crypto::BigFraction m_current_value {};
+
+    Operation m_binary_operation_in_progress { Operation::None };
+    Crypto::BigFraction m_binary_operation_saved_left_side {};
+
+    Operation m_previous_operation { Operation::None };
+    Crypto::BigFraction m_previous_binary_operation_right_side {};
     bool m_has_error { false };
+
+    Crypto::BigFraction finish_binary_operation(Crypto::BigFraction const& left_side, Operation operation, Crypto::BigFraction const& right_side);
 };
diff --git a/Userland/Applications/Calculator/CalculatorWidget.cpp b/Userland/Applications/Calculator/CalculatorWidget.cpp
index c1129e5e07..a6615211a4 100644
--- a/Userland/Applications/Calculator/CalculatorWidget.cpp
+++ b/Userland/Applications/Calculator/CalculatorWidget.cpp
@@ -97,19 +97,22 @@ CalculatorWidget::CalculatorWidget()
     add_operation_button(*m_percent_button, Calculator::Operation::Percent);
 
     m_equals_button = *find_descendant_of_type_named<GUI::Button>("equal_button");
-    m_equals_button->on_click = [this](auto) {
-        Crypto::BigFraction argument = m_keypad.value();
-        Crypto::BigFraction res = m_calculator.finish_operation(move(argument));
-        m_keypad.set_value(move(res));
-        update_display();
-    };
+    add_operation_button(*m_equals_button, Calculator::Operation::Equals);
 }
 
 void CalculatorWidget::perform_operation(Calculator::Operation operation)
 {
-    Crypto::BigFraction argument = m_keypad.value();
-    Crypto::BigFraction res = m_calculator.begin_operation(operation, move(argument));
-    m_keypad.set_value(move(res));
+    Optional<Crypto::BigFraction> res;
+    if (m_keypad.in_typing_state()) {
+        Crypto::BigFraction argument = m_keypad.value();
+        res = m_calculator.operation_with_literal_argument(operation, move(argument));
+    } else {
+        res = m_calculator.operation_without_argument(operation);
+    }
+
+    if (res.has_value()) {
+        m_keypad.set_value(move(res.value()));
+    }
     update_display();
 }
 
@@ -156,7 +159,7 @@ void CalculatorWidget::update_display()
 void CalculatorWidget::keydown_event(GUI::KeyEvent& event)
 {
     if (event.key() == KeyCode::Key_Return || event.key() == KeyCode::Key_Equal) {
-        m_keypad.set_value(m_calculator.finish_operation(m_keypad.value()));
+        perform_operation(Calculator::Operation::Equals);
         mimic_pressed_button(m_equals_button);
     } else if (event.code_point() >= '0' && event.code_point() <= '9') {
         auto const digit = event.code_point() - '0';
@@ -184,35 +187,21 @@ void CalculatorWidget::keydown_event(GUI::KeyEvent& event)
     } else if (event.key() == KeyCode::Key_I) {
         perform_operation(Calculator::Operation::Inverse);
         mimic_pressed_button(m_inverse_button);
-    } else {
-        Calculator::Operation operation;
-
-        switch (event.code_point()) {
-        case '+':
-            operation = Calculator::Operation::Add;
-            mimic_pressed_button(m_add_button);
-            break;
-        case '-':
-            operation = Calculator::Operation::Subtract;
-            mimic_pressed_button(m_subtract_button);
-            break;
-        case '*':
-            operation = Calculator::Operation::Multiply;
-            mimic_pressed_button(m_multiply_button);
-            break;
-        case '/':
-            operation = Calculator::Operation::Divide;
-            mimic_pressed_button(m_divide_button);
-            break;
-        case '%':
-            operation = Calculator::Operation::Percent;
-            mimic_pressed_button(m_percent_button);
-            break;
-        default:
-            return;
-        }
-
-        m_keypad.set_value(m_calculator.begin_operation(operation, m_keypad.value()));
+    } else if (event.code_point() == '+') {
+        perform_operation(Calculator::Operation::Add);
+        mimic_pressed_button(m_add_button);
+    } else if (event.code_point() == '-') {
+        perform_operation(Calculator::Operation::Subtract);
+        mimic_pressed_button(m_subtract_button);
+    } else if (event.code_point() == '*') {
+        perform_operation(Calculator::Operation::Multiply);
+        mimic_pressed_button(m_multiply_button);
+    } else if (event.code_point() == '/') {
+        perform_operation(Calculator::Operation::Divide);
+        mimic_pressed_button(m_divide_button);
+    } else if (event.code_point() == '%') {
+        perform_operation(Calculator::Operation::Percent);
+        mimic_pressed_button(m_percent_button);
     }
 
     update_display();
diff --git a/Userland/Applications/Calculator/Keypad.cpp b/Userland/Applications/Calculator/Keypad.cpp
index c116c02580..66c911a771 100644
--- a/Userland/Applications/Calculator/Keypad.cpp
+++ b/Userland/Applications/Calculator/Keypad.cpp
@@ -135,6 +135,11 @@ DeprecatedString Keypad::to_deprecated_string() const
     return builder.to_deprecated_string();
 }
 
+bool Keypad::in_typing_state() const
+{
+    return m_state == State::TypingDecimal || m_state == State::TypingInteger;
+}
+
 void Keypad::set_rounding_length(unsigned rounding_threshold)
 {
     m_displayed_fraction_length = rounding_threshold;
diff --git a/Userland/Applications/Calculator/Keypad.h b/Userland/Applications/Calculator/Keypad.h
index 62a993a76d..af32de260f 100644
--- a/Userland/Applications/Calculator/Keypad.h
+++ b/Userland/Applications/Calculator/Keypad.h
@@ -35,6 +35,8 @@ public:
 
     DeprecatedString to_deprecated_string() const;
 
+    bool in_typing_state() const;
+
 private:
     // Internal representation of the current decimal value.
     // Those variables are only used when the user is entering a value.