package app

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"os"
	"strings"

	"github.com/stig/goaichat/internal/chat"
	"github.com/stig/goaichat/internal/config"
	"github.com/stig/goaichat/internal/openai"
)

// App encapsulates the Goaichat application runtime wiring.
type App struct {
	logger *slog.Logger
	config *config.Config
	openAI *openai.Client
	chat   *chat.Service
	input  io.Reader
	output io.Writer
}

// New constructs a new App instance.
func New(logger *slog.Logger, cfg *config.Config, opts ...Option) *App {
	app := &App{
		logger: logger,
		config: cfg,
		input:  os.Stdin,
		output: os.Stdout,
	}

	for _, opt := range opts {
		opt(app)
	}

	if app.input == nil {
		app.input = os.Stdin
	}
	if app.output == nil {
		app.output = os.Stdout
	}

	return app
}

// Option configures an App instance.
type Option func(*App)

// WithIO overrides the input/output streams, primarily for testing.
func WithIO(in io.Reader, out io.Writer) Option {
	return func(a *App) {
		a.input = in
		a.output = out
	}
}

// Run starts the application lifecycle.
func (a *App) Run(ctx context.Context) error {
	if a == nil {
		return errors.New("app is nil")
	}
	if ctx == nil {
		return errors.New("context is nil")
	}

	if err := a.initOpenAIClient(); err != nil {
		return err
	}
	if err := a.initChatService(); err != nil {
		return err
	}

	a.logger.InfoContext(ctx, "starting goaichat", "model", a.config.Model.Name, "api_url", a.config.API.URL)

	if err := a.runCLILoop(ctx); err != nil {
		return err
	}

	a.logger.InfoContext(ctx, "goaichat shutdown complete")

	return nil
}

func (a *App) initOpenAIClient() error {
	if a.openAI != nil {
		return nil
	}

	client, err := openai.NewClient(
		a.config.API.Key,
		openai.WithBaseURL(a.config.API.URL),
	)
	if err != nil {
		return err
	}

	a.openAI = client
	return nil
}

func (a *App) initChatService() error {
	if a.chat != nil {
		return nil
	}

	service, err := chat.NewService(a.logger.With("component", "chat"), a.config.Model, a.openAI)
	if err != nil {
		return err
	}

	a.chat = service
	return nil
}

func (a *App) runCLILoop(ctx context.Context) error {
	scanner := bufio.NewScanner(a.input)

	if _, err := fmt.Fprintln(a.output, "Type your message. Use /exit to quit, /reset to clear history."); err != nil {
		return err
	}

	for {
		if _, err := fmt.Fprint(a.output, "> "); err != nil {
			return err
		}

		if !scanner.Scan() {
			if err := scanner.Err(); err != nil {
				return err
			}
			return nil
		}

		input := scanner.Text()

		handled, exit, err := a.handleCommand(ctx, input)
		if err != nil {
			if _, writeErr := fmt.Fprintf(a.output, "Command error: %v\n", err); writeErr != nil {
				return writeErr
			}
			continue
		}
		if handled {
			if exit {
				return nil
			}
			continue
		}

		reply, err := a.chat.Send(ctx, input)
		if err != nil {
			if _, writeErr := fmt.Fprintf(a.output, "Error: %v\n", err); writeErr != nil {
				return writeErr
			}
			continue
		}

		if _, err := fmt.Fprintf(a.output, "AI: %s\n", reply); err != nil {
			return err
		}
	}
}

func (a *App) handleCommand(ctx context.Context, input string) (handled bool, exit bool, err error) {
	_ = ctx
	trimmed := strings.TrimSpace(input)
	if trimmed == "" {
		return true, false, errors.New("no input provided")
	}
	if !strings.HasPrefix(trimmed, "/") {
		return false, false, nil
	}

	switch trimmed {
	case "/exit":
		return true, true, nil
	case "/reset":
		a.chat.Reset()
		_, err := fmt.Fprintln(a.output, "History cleared.")
		return true, false, err
	case "/help":
		_, err := fmt.Fprintln(a.output, "Commands: /exit, /reset, /help (more coming soon)")
		return true, false, err
	default:
		_, err := fmt.Fprintf(a.output, "Unknown command %q. Try /help.\n", trimmed)
		return true, false, err
	}
}