feat: add help system command (#34)

README.md

@@ -42,13 +42,14 @@ export GEMINI_API_KEY=<your_api_key>
 The system chat message must begin with an exclamation mark and is used for internal operations.
 A short list of supported system commands:
 
-| Command | Description                                        |
-|---------|----------------------------------------------------|
-| !q      | Quit the application                               |
-| !p      | Select the system prompt for the chat <sup>1</sup> |
-| !i      | Toggle input mode (single-line <-> multi-line)     |
-| !m      | Select a model operation <sup>2</sup>              |
-| !h      | Select a history operation <sup>3</sup>            |
+| Command | Description                                                    |
+|---------|----------------------------------------------------------------|
+| !p      | Select the generative model system prompt <sup>1</sup>         |
+| !m      | Select from a list of generative model operations <sup>2</sup> |
+| !h      | Select from a list of chat history operations <sup>3</sup>     |
+| !i      | Toggle the input mode (single-line <-> multi-line)             |
+| !q      | Exit the application                                           |
+| !help   | Show system command instructions                               |
 
 <sup>1</sup> System instruction (also known as "system prompt") is a more forceful prompt to the model.
 The model will follow instructions more closely than with a standard prompt.

internal/chat/chat.go

@@ -39,8 +39,11 @@ func New(
 	}
 
 	systemIO := handler.NewIO(terminalIO, terminalIO.Prompt.Cli)
-	systemHandler := handler.NewSystemCommand(systemIO, session, configuration,
-		opts.GenerativeModel)
+	systemHandler, err := handler.NewSystemCommand(systemIO, session, configuration,
+		opts.GenerativeModel, opts.rendererOptions())
+	if err != nil {
+		return nil, err
+	}
 
 	return &Chat{
 		io:            terminalIO,

internal/cli/command.go

@@ -2,6 +2,7 @@ package cli
 
 const (
 	SystemCmdPrefix          = "!"
+	SystemCmdHelp            = "help"
 	SystemCmdQuit            = "q"
 	SystemCmdSelectPrompt    = "p"
 	SystemCmdSelectInputMode = "i"

internal/handler/help_command.go

@@ -0,0 +1,52 @@
+package handler
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/charmbracelet/glamour"
+	"github.com/reugn/gemini-cli/internal/cli"
+)
+
+// HelpCommand handles the help system command request.
+type HelpCommand struct {
+	*IO
+	renderer *glamour.TermRenderer
+}
+
+var _ MessageHandler = (*HelpCommand)(nil)
+
+// NewHelpCommand returns a new HelpCommand.
+func NewHelpCommand(io *IO, opts RendererOptions) (*HelpCommand, error) {
+	renderer, err := glamour.NewTermRenderer(
+		glamour.WithStylePath(opts.StylePath),
+		glamour.WithWordWrap(opts.WordWrap),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to instantiate terminal renderer: %w", err)
+	}
+
+	return &HelpCommand{
+		IO:       io,
+		renderer: renderer,
+	}, nil
+}
+
+// Handle processes the help system command.
+func (h *HelpCommand) Handle(_ string) (Response, bool) {
+	var b strings.Builder
+	b.WriteString("# System commands\n")
+	b.WriteString("Use a command prefixed with an exclamation mark (e.g., `!h`).\n")
+	fmt.Fprintf(&b, "* `%s` - Select the generative model system prompt.\n", cli.SystemCmdSelectPrompt)
+	fmt.Fprintf(&b, "* `%s` - Select from a list of generative model operations.\n", cli.SystemCmdModel)
+	fmt.Fprintf(&b, "* `%s` - Select from a list of chat history operations.\n", cli.SystemCmdHistory)
+	fmt.Fprintf(&b, "* `%s` - Toggle the input mode.\n", cli.SystemCmdSelectInputMode)
+	fmt.Fprintf(&b, "* `%s` - Exit the application.\n", cli.SystemCmdQuit)
+
+	rendered, err := h.renderer.Render(b.String())
+	if err != nil {
+		return newErrorResponse(fmt.Errorf("failed to format instructions: %w", err)), false
+	}
+
+	return dataResponse(rendered), false
+}

internal/handler/system_command.go

@@ -25,8 +25,14 @@ var _ MessageHandler = (*SystemCommand)(nil)
 
 // NewSystemCommand returns a new SystemCommand.
 func NewSystemCommand(io *IO, session *gemini.ChatSession, configuration *config.Configuration,
-	modelName string) *SystemCommand {
+	modelName string, rendererOptions RendererOptions) (*SystemCommand, error) {
+	helpCommandHandler, err := NewHelpCommand(io, rendererOptions)
+	if err != nil {
+		return nil, err
+	}
+
 	handlers := map[string]MessageHandler{
+		cli.SystemCmdHelp:            helpCommandHandler,
 		cli.SystemCmdQuit:            NewQuitCommand(io),
 		cli.SystemCmdSelectPrompt:    NewSystemPromptCommand(io, session, configuration.Data),
 		cli.SystemCmdSelectInputMode: NewInputModeCommand(io),
@@ -37,7 +43,7 @@ func NewSystemCommand(io *IO, session *gemini.ChatSession, configuration *config
 	return &SystemCommand{
 		IO:       io,
 		handlers: handlers,
-	}
+	}, nil
 }
 
 // Handle processes the chat system command.