Continue work on hot-reload functionality

src/hot_reload/hot_reload.odin

@@ -0,0 +1,138 @@
+package hot_reload
+
+import "core:dynlib"
+import "core:fmt"
+import "core:os"
+
+when ODIN_OS == .Windows {
+	LIB_EXT :: ".dll"
+} else when ODIN_OS == .Darwin {
+	LIB_EXT :: ".dylib"
+} else {
+	LIB_EXT :: ".so"
+}
+
+GAME_LIB_DIR :: "build/"
+GAME_LIB_PATH :: GAME_LIB_DIR + "game" + LIB_EXT
+
+// -----------------------------------------
+
+Hot_Reload :: struct {
+	loaded_libs: [dynamic]Game_API,
+}
+
+Hot_Reload_Error :: enum u8 {
+	None                 = 0,
+	Load_Game_Lib_Failed = 1,
+	Unimplemented        = 127,
+	Okay                 = None,
+}
+
+Error :: union #shared_nil {
+	Hot_Reload_Error,
+}
+
+Game_API :: struct {
+	lib:          dynlib.Library,
+	init:         proc(),
+	update:       proc(),
+	render:       proc(),
+	destroy:      proc(),
+	should_close: proc() -> bool,
+	api_version:  int, // iteration of the game lib
+}
+
+// -----------------------------------------
+
+hot_reload_init :: proc() -> (state: Hot_Reload, error: Error) {
+	api: Game_API
+	api.api_version = -1
+
+	api_ok := load_game_lib(&api)
+	if !api_ok {
+		fmt.println("Failed to load Game API")
+		return {}, .Load_Game_Lib_Failed
+	}
+
+	state.loaded_libs = make([dynamic]Game_API)
+	append(&state.loaded_libs, api)
+
+	return state, nil
+}
+
+hot_reload_destroy :: proc(state: ^Hot_Reload) {
+	for &api in state.loaded_libs {
+		unload_game_lib(&api)
+	}
+
+	delete(state.loaded_libs)
+}
+
+// -----------------------------------------
+
+active_lib :: proc(hr: ^Hot_Reload) -> ^Game_API {
+	return &hr.loaded_libs[len(hr.loaded_libs) - 1]
+}
+
+should_close :: proc(hr: ^Hot_Reload) -> bool {
+	api := active_lib(hr)
+	if api.lib == nil do return true
+	return api.should_close()
+}
+
+copy_lib :: proc(to: string) -> bool {
+	copy_err := os.copy_file(to, GAME_LIB_PATH)
+	if copy_err != nil {
+		fmt.printfln(
+			"error: Failed to copy " + GAME_LIB_PATH + " to {0}: %v",
+			to,
+			copy_err,
+		)
+		return false
+	}
+
+	return true
+}
+
+// Load game lib symbols
+load_game_lib :: proc(api: ^Game_API) -> bool {
+	// Load next iteration
+	api.api_version += 1
+
+	lib_name := fmt.tprintf(
+		GAME_LIB_DIR + "game_{0}" + LIB_EXT,
+		api.api_version,
+	)
+	copy_lib(lib_name) or_return
+
+	// Match the names of the fields in Game_API to symbols in the game DLL
+	_, ok := dynlib.initialize_symbols(api, GAME_LIB_PATH, "", "lib")
+	if !ok {
+		fmt.printfln("Failed initializing symbols: {0}", dynlib.last_error())
+	}
+
+	return ok
+}
+
+// Unload game lib, used during full restarts
+unload_game_lib :: proc(api: ^Game_API) {
+	if api.lib != nil {
+		if !dynlib.unload_library(api.lib) {
+			fmt.eprintfln(
+				"error: Failed unloading lib: {0}",
+				dynlib.last_error(),
+			)
+		}
+	}
+
+	if os.remove(
+		   fmt.tprintf(GAME_LIB_DIR + "game_{0}" + LIB_EXT, api.api_version),
+	   ) !=
+	   nil {
+		fmt.printfln(
+			"error: Failed to remove {0}game_{1}" + LIB_EXT + " copy",
+			GAME_LIB_DIR,
+			api.api_version,
+		)
+	}
+}