From c0c63e5b2c00a7821e9e125e65fba9107650654f Mon Sep 17 00:00:00 2001
From: "Zed A. Shaw" <zed.shaw@gmail.com>
Date: Tue, 6 May 2025 01:05:28 -0400
Subject: [PATCH] Bring over the FSM and then use it to make the calculator
 demo better.

---
 demos/calc.cpp | 105 +++++++++++++++++++++++++++++++++++++------------
 fsm.hpp        |  28 +++++++++++++
 2 files changed, 107 insertions(+), 26 deletions(-)
 create mode 100644 fsm.hpp

diff --git a/demos/calc.cpp b/demos/calc.cpp
index 7e5b369..01c5ffc 100644
--- a/demos/calc.cpp
+++ b/demos/calc.cpp
@@ -6,6 +6,9 @@
 #include "constants.hpp"
 #include <fmt/xchar.h>
 
+#define FSM_DEBUG 1
+#include "fsm.hpp"
+
 constexpr const int WINDOW_WIDTH=300;
 constexpr const int WINDOW_HEIGHT=400;
 
@@ -17,22 +20,85 @@ const std::unordered_map<string, wstring> LABELS {
     {"btn5", L"5"}, {"btn6", L"6"}, {"btn7", L"7"},
     {"btn8", L"8"}, {"btn9", L"9"}, {"mult", L"*"},
     {"minus", L"-"}, {"plus", L"+"}, {"neg", L"!"},
-    {"dot", L"."}, {"eq", L"="}
+    {"div", L"/"}, {"eq", L"="}
     };
 
-struct Calculator {
+enum class Event {
+  NUMBER=0,
+  OP=1,
+  CLR=2,
+  NOT=3,
+  EQ=4
+};
+
+enum class State {
+  START=0,
+  CALCULATING=1,
+  CLEARED=3,
+  DISPLAYED=4
+};
+
+
+struct Calculator : DeadSimpleFSM<State, Event> {
+  wstring input;
+  double value = 0.0;
+
+  void event(Event ev, wchar_t op) {
+    switch($state) {
+      FSM_STATE(State, START, ev, op);
+      FSM_STATE(State, CALCULATING, ev, op);
+      FSM_STATE(State, CLEARED, ev, op);
+      FSM_STATE(State, DISPLAYED, ev, op);
+    }
+  }
+
+  void START(Event ev, wchar_t op) {
+    if(ev == Event::NUMBER) {
+      input += op;
+      state(State::CALCULATING);
+    }
+  }
+
+  void CALCULATING(Event ev, wchar_t op) {
+    if(ev == Event::NUMBER) {
+      input += op;
+    } else if(ev == Event::OP) {
+
+    } else if(ev == Event::NOT) {
+
+    } else if(ev == Event::EQ) {
+
+    } else if(ev == Event::CLR) {
+      input = L"";
+      state(State::CLEARED);
+    }
+  }
+
+  void CLEARED(Event ev, wchar_t op) {
+    if(ev == Event::NUMBER) {
+      input += op;
+      state(State::CALCULATING);
+    }
+  }
+
+  void DISPLAYED(Event ev, wchar_t op) {
+    fmt::println(L"ev={}, op={}", (int)ev, op);
+    state(State::CALCULATING);
+  }
+};
+
+struct CalculatorUI {
   guecs::UI $gui;
-  wstring $input;
-  double $value = 0.0;
+  Calculator $fsm;
 
-  Calculator() {
+  CalculatorUI() {
     $gui.position(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
     $gui.layout(
         "[*%(400)readout|_|_|_|clear]"
         "[btn7|btn8|btn9|mult]"
         "[btn4|btn5|btn6|minus]"
         "[btn1|btn2|btn3|plus]"
-        "[neg|btn0|dot|eq]");
+        "[neg|btn0|eq|div]");
   }
 
   void init() {
@@ -79,39 +145,26 @@ struct Calculator {
       case L'7':
       case L'8':
       case L'9':
-      case L'.':
-        if($input.size() <= 10) {
-          $input += op;
-        }
+        $fsm.event(Event::NUMBER, op);
         break;
       case L'*':
-        $value = $value * std::stof($input);
-        $input = L"";
-        break;
       case L'-':
-        $value = $value - std::stof($input);
-        $input = L"";
-        break;
       case L'+':
-        $value = $value + std::stof($input);
-        $input = L"";
-        break;
+      case L'/':
       case L'!':
-        $value = $value * -1.0;
-        $input = L"";
+        $fsm.event(Event::OP, op);
         break;
       case L'=':
-        $input = fmt::format(L"{}", $value);
-        $value = 0.0;
+        $fsm.event(Event::EQ, op);
         break;
       case L'C':
-        $input = L"";
+        $fsm.event(Event::CLR, op);
         break;
     }
 
     auto readout = $gui.entity("readout");
     auto& label = $gui.get<guecs::Textual>(readout);
-    label.update($input);
+    label.update($fsm.input);
   }
 };
 
@@ -126,7 +179,7 @@ int main() {
   window.setFramerateLimit(FRAME_LIMIT);
   window.setVerticalSyncEnabled(VSYNC);
 
-  Calculator calc;
+  CalculatorUI calc;
   calc.init();
 
   while(window.isOpen()) {
diff --git a/fsm.hpp b/fsm.hpp
new file mode 100644
index 0000000..8729dd8
--- /dev/null
+++ b/fsm.hpp
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <fmt/core.h>
+
+#ifndef FSM_DEBUG
+#define FSM_STATE(C, S, E, ...) case C::S: S(E, ##__VA_ARGS__); break
+#else
+#define FSM_STATE(C, S, E, ...) case C::S: fmt::println(">> " #C " " #S " event={}, state={}", int(E), int($state)); S(E, ##__VA_ARGS__); fmt::println("<< " #C " state={}", int($state)); break
+#endif
+
+template<typename S, typename E>
+class DeadSimpleFSM {
+protected:
+  // BUG: don't put this in your class because state() won't work
+ S $state = S::START;
+
+public:
+  template<typename... Types>
+  void event(E event, Types... args);
+
+  void state(S next_state) {
+    $state = next_state;
+  }
+
+  bool in_state(S state) {
+    return $state == state;
+  }
+};