package app

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"path/filepath"
	"strings"

	"agentu/internal/agent"
	"agentu/internal/session"
	"agentu/internal/tools"
	"agentu/internal/tui"
	"agentu/pkg/config"
	"agentu/pkg/llm"
)

type cliOptions struct {
	configPath string
	yolo       bool
	plain      bool
	themeName  string
	resumeID   string
}

func Run() error {
	opts := parseCLIOptions()

	themeMode, err := tui.ParseThemeMode(opts.themeName)
	if err != nil {
		return err
	}

	cfg, err := loadConfig(opts.configPath)
	if err != nil {
		return err
	}

	providerName, providerConfig, provider := defaultProvider(cfg, http.DefaultClient)
	assistant := newAssistant(cfg, providerName, providerConfig, provider, opts.yolo, http.DefaultClient)
	modelManager, err := newSessionManager(cfg, assistant, http.DefaultClient)
	if err != nil {
		return err
	}

	if err := initializeSession(modelManager, opts.resumeID); err != nil {
		return err
	}

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
	defer stop()

	return runInterface(ctx, assistant, modelManager, providerConfig, cfg.Agent.WorkingDir, opts, themeMode)
}

func parseCLIOptions() cliOptions {
	configPath := flag.String("config", config.DefaultPath, "path to YAML config")
	yolo := flag.Bool("yolo", false, "also enable automatic file writes and shell execution")
	plain := flag.Bool("plain", false, "use the simple line-based REPL instead of the TUI")
	themeName := flag.String("theme", "light", "TUI theme: light or dark")
	resumeID := flag.String("resume", "", "resume a specific session by ID")
	flag.Parse()

	return cliOptions{
		configPath: *configPath,
		yolo:       *yolo,
		plain:      *plain,
		themeName:  *themeName,
		resumeID:   *resumeID,
	}
}

func loadConfig(configPath string) (*config.Config, error) {
	cfg, err := config.Load(configPath)
	if err == nil {
		return cfg, nil
	}
	if !errors.Is(err, os.ErrNotExist) {
		return nil, err
	}
	if bootstrapErr := bootstrapConfig(configPath); bootstrapErr != nil {
		return nil, bootstrapErr
	}
	return nil, fmt.Errorf("created default config at %s; edit it to set your API key and provider, then restart agentu", configPath)
}

func defaultProvider(cfg *config.Config, httpClient *http.Client) (string, config.ProviderConfig, llm.Provider) {
	providerName := cfg.DefaultProviderName()
	providerConfig := cfg.Providers[providerName]
	provider := llm.NewOpenAICompatibleClient(providerConfig.BaseURL, providerConfig.APIKey, httpClient)
	return providerName, providerConfig, provider
}

func newAssistant(cfg *config.Config, providerName string, providerConfig config.ProviderConfig, provider llm.Provider, yolo bool, httpClient *http.Client) *agent.Agent {
	return agent.New(agent.Options{
		Provider:         provider,
		ProviderName:     providerName,
		Model:            providerConfig.Model,
		Thinking:         providerConfig.Thinking,
		ThinkingParam:    providerConfig.ThinkingParam,
		ThinkingEnabled:  providerConfig.ThinkingConfigured,
		SystemPrompt:     systemPrompt(cfg, yolo),
		ToolRegistry:     newToolRegistry(cfg.Agent.WorkingDir, yolo, httpClient),
		ToolTimeout:      cfg.Agent.ToolTimeout,
		MaxContextTokens: maxContextTokens(cfg, providerConfig),
	})
}

func systemPrompt(cfg *config.Config, yolo bool) string {
	instructions := tools.AgentInstructions(cfg.Agent.WorkingDir, yolo)
	return strings.TrimSpace(cfg.Agent.SystemPrompt + "\n\n" + instructions)
}

func maxContextTokens(cfg *config.Config, providerConfig config.ProviderConfig) int {
	if cfg.Agent.MaxContextTokens != 0 {
		return cfg.Agent.MaxContextTokens
	}
	return providerConfig.ContextTokens
}

func newToolRegistry(workingDir string, yolo bool, httpClient *http.Client) *tools.Registry {
	var registry *tools.Registry
	if yolo {
		registry = tools.Builtins(workingDir)
	} else {
		registry = tools.ReadOnlyBuiltins(workingDir)
	}
	registry.Register(tools.NewBuiltinSearchTool(httpClient))
	registry.Register(tools.NewBuiltinFetchTool(httpClient))
	return registry
}

func newSessionManager(cfg *config.Config, assistant *agent.Agent, httpClient *http.Client) (*session.Manager, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return nil, fmt.Errorf("resolve home dir: %w", err)
	}
	sessionsDir := filepath.Join(home, ".agentu", "sessions")
	store, err := session.NewStore(sessionsDir)
	if err != nil {
		return nil, fmt.Errorf("init session store: %w", err)
	}
	return session.NewManager(cfg, assistant, httpClient, store)
}

func runInterface(ctx context.Context, assistant *agent.Agent, modelManager *session.Manager, providerConfig config.ProviderConfig, workingDir string, opts cliOptions, themeMode tui.ThemeMode) error {
	if opts.plain {
		return repl(ctx, assistant, modelManager)
	}

	err := tui.Run(ctx, assistant, tui.Options{
		ModelName:    providerConfig.Model,
		Yolo:         opts.yolo,
		ThemeMode:    themeMode,
		ModelManager: modelManager,
		WorkingDir:   workingDir,
	})
	printExitSession(modelManager)
	return err
}