add tag dispatching example

Chapter17/fsm/app/src/main_fsm_state_pattern.cpp

@@ -135,7 +135,6 @@ const char* state_to_string(ble_state state) {
 }
 }
 
-
 int main()
 {
     hal::init();

Chapter17/fsm/app/src/main_fsm_state_pattern_tag_dispatch.cpp

@@ -0,0 +1,175 @@
+#include <cstdint>
+#include <cstdio>
+
+#include <functional>
+
+#include <stm32f072xb.h>
+
+#include <hal.hpp>
+#include <stm32f0xx_hal_uart.hpp>
+#include <uart_stm32.hpp>
+
+#include <retarget.hpp>
+
+#include "etl/vector.h"
+
+enum class ble_state {
+    idle,
+    advertising,
+    connected
+};
+
+struct ble_button_pressed{};
+struct connection_request{};
+struct timer_expired{};
+
+class state {
+public:
+    virtual ble_state handle_event(ble_button_pressed) {
+        return get_state_enum();
+    }
+    virtual ble_state handle_event(connection_request) {
+        return get_state_enum();
+    }
+    virtual ble_state handle_event(timer_expired) {
+        return get_state_enum();
+    }
+    virtual ble_state get_state_enum() = 0;
+};
+
+class idle : public state{
+public:
+    ble_state handle_event(ble_button_pressed bbp) override {
+        start_advertising();
+        return ble_state::advertising;
+    }
+
+    ble_state get_state_enum() {
+       return ble_state::idle; 
+    }
+private:
+    void start_advertising() {
+        printf("Action: start_advertising()\n");
+    }
+};
+
+class advertising : public state{
+public:
+    ble_state handle_event(connection_request cr) override {
+        return ble_state::connected;
+    }
+
+    ble_state handle_event(timer_expired te) override {
+        stop_advertising();
+        return ble_state::idle;
+    }
+
+    ble_state get_state_enum() {
+       return ble_state::advertising; 
+    }
+private:
+    void stop_advertising() {
+        printf("Action: stop_advertising()\n");
+    }
+};
+
+class connected : public state{
+public:
+    ble_state handle_event(ble_button_pressed) {
+        disconnect();
+        return ble_state::idle;
+    }
+
+    ble_state get_state_enum() {
+       return ble_state::connected; 
+    }
+private:
+    void disconnect() {
+        printf("Action: disconnect()\n");
+    }
+};
+
+class ble_fsm {
+public:
+    template<typename E>
+    void handle_event(E event) {
+        if(auto the_state = get_the_state(current_state_)) {
+            current_state_ = the_state->handle_event(event);
+        }
+    }
+
+    ble_state get_state() const {
+        return current_state_;
+    }
+
+    void add_state(state *the_state) {
+        states_.push_back(the_state);
+    }
+
+private:
+    etl::vector<state*, 3> states_;
+    ble_state current_state_ = ble_state::idle;
+
+    state* get_the_state(ble_state state_enum) {
+        const auto is_state_enum = [&] (state *the_state) {
+            return the_state->get_state_enum() == state_enum;
+        };
+        auto it = std::find_if(states_.begin(), states_.end(), is_state_enum);
+
+        if(it != states_.end()) {
+            return *it;
+        }
+        return nullptr;
+    }
+};
+
+namespace {
+const char* state_to_string(ble_state state) {
+    switch (state) {
+        case ble_state::idle:        return "idle";
+        case ble_state::advertising: return "advertising";
+        case ble_state::connected:   return "connected";
+        default:                     return "unknown";
+    }
+}
+}
+
+int main()
+{
+    hal::init();
+
+    hal::uart_stm32<hal::stm32::uart> uart(USART2);
+    uart.init();
+
+    retarget::set_stdio_uart(&uart);
+
+    ble_fsm my_ble_fsm;
+
+    idle idle_s;
+    advertising advertising_s;
+    connected connected_s;
+
+    my_ble_fsm.add_state(&idle_s);
+    my_ble_fsm.add_state(&advertising_s);
+    my_ble_fsm.add_state(&connected_s);
+
+    const auto print_current_state = [&]() {
+        printf("Current State: %s\n", state_to_string(my_ble_fsm.get_state()));
+    };
+
+    print_current_state();
+
+    my_ble_fsm.handle_event(ble_button_pressed{});
+    print_current_state();
+
+    my_ble_fsm.handle_event(connection_request{});
+    print_current_state();
+
+    my_ble_fsm.handle_event(ble_button_pressed{});
+    print_current_state();
+
+
+    while(true)
+    {
+    }
+}