package backend

import (
	"fmt"
)

// NewWithName constructs a Backend for the given backend name.
// If name is empty, it falls back to the backends.conf default.
func NewWithName(name string) (Backend, error) {
	cfg := loadConfig()
	if name == "" {
		name = cfg.Default
	}
	if name == "" {
		return nil, fmt.Errorf("no backend specified: set 'backend' in backends.conf or pass backend= to the session")
	}
	return newBackendFromConfig(name, cfg)
}

func newBackend(which string) (Backend, error) {
	return newBackendFromConfig(which, loadConfig())
}

func newBackendFromConfig(which string, cfg configFile) (Backend, error) {
	bc := cfg.Backends[which]

	var b Backend
	var err error

	switch which {
	case "ollama":
		host := bc.Host
		b, err = NewOllama(host)

	case "openai":
		if bc.Key == "" {
			return nil, fmt.Errorf("openai: key required (backends.conf [openai] key=)")
		}
		b, err = NewOpenAI("openai", bc.URL, bc.Key)

	case "openrouter":
		url := bc.URL
		if url == "" {
			url = "https://openrouter.ai/api"
		}
		if bc.Key == "" {
			return nil, fmt.Errorf("openrouter: key required (backends.conf [openrouter] key=)")
		}
		b, err = NewOpenAI("openrouter", url, bc.Key)

	case "anthropic":
		if bc.Key == "" {
			return nil, fmt.Errorf("anthropic: key required (backends.conf [anthropic] key=)")
		}
		b, err = NewAnthropic(bc.Key)

	case "copilot":
		if bc.Key == "" {
			return nil, fmt.Errorf("copilot: key required (backends.conf [copilot] key=)")
		}
		b, err = NewCopilot(bc.Key)

	case "kiro", "codewhisperer":
		b, err = NewKiro(bc.Key)

	case "gemini":
		if bc.Key == "" {
			return nil, fmt.Errorf("gemini: key required (backends.conf [gemini] key=)")
		}
		b, err = NewGemini(bc.Key)

	default:
		return nil, fmt.Errorf("unknown backend %q (supported: ollama, openai, openrouter, anthropic, copilot, kiro, gemini)", which)
	}

	if err != nil {
		return nil, err
	}
	if bc.Model != "" {
		b.SetModel(bc.Model)
	}
	return b, nil
}

// Backends returns the list of supported backend names.
func Backends() []string {
	return []string{"ollama", "openai", "openrouter", "anthropic", "copilot", "kiro", "gemini"}
}