// Summary: LLM provider interfaces, request options, configuration, and factory to build a client from config.
package llm

import (
	"context"
	"errors"
	"strings"
)

// Message represents a chat-style prompt message.
type Message struct {
	Role    string
	Content string
}

// Client is a minimal LLM provider interface.
// Future providers (Ollama, etc.) should implement this.
type Client interface {
	// Chat sends chat messages and returns the assistant text.
	Chat(ctx context.Context, messages []Message, opts ...RequestOption) (string, error)
	// Name returns the provider's short name (e.g., "openai", "ollama").
	Name() string
	// DefaultModel returns the configured default model name.
	DefaultModel() string
}

// Streamer is an optional interface that providers may implement to support
// token-by-token streaming responses. Callers can type-assert to Streamer and
// fall back to Client.Chat when not implemented.
type Streamer interface {
	// ChatStream sends chat messages and invokes onDelta with incremental text
	// chunks as they are produced by the model. Implementations should call
	// onDelta with empty strings sparingly (prefer only non-empty chunks).
	ChatStream(ctx context.Context, messages []Message, onDelta func(string), opts ...RequestOption) error
}

// Options for a request. Providers may ignore unsupported fields.
type Options struct {
	Model       string
	Temperature float64
	MaxTokens   int
	Stop        []string
}

// RequestOption mutates Options.
type RequestOption func(*Options)

func WithModel(model string) RequestOption    { return func(o *Options) { o.Model = model } }
func WithTemperature(t float64) RequestOption { return func(o *Options) { o.Temperature = t } }
func WithMaxTokens(n int) RequestOption       { return func(o *Options) { o.MaxTokens = n } }
func WithStop(stop ...string) RequestOption {
	return func(o *Options) { o.Stop = append([]string{}, stop...) }
}

// Config defines provider configuration read from the Hexai config file.
type Config struct {
	Provider string
	// OpenAI options
	OpenAIBaseURL string
	OpenAIModel   string
	// Ollama options
	OllamaBaseURL string
	OllamaModel   string
	// Copilot options
	CopilotBaseURL string
	CopilotModel   string
}

// NewFromConfig creates an LLM client using only the supplied configuration.
// The OpenAI API key is supplied separately and may be read from the environment
// by the caller; other environment-based configuration is not used.
func NewFromConfig(cfg Config, openAIAPIKey, copilotAPIKey string) (Client, error) {
	p := strings.ToLower(strings.TrimSpace(cfg.Provider))
	if p == "" {
		p = "openai"
	}
	switch p {
	case "openai":
		if strings.TrimSpace(openAIAPIKey) == "" {
			return nil, errors.New("missing OPENAI_API_KEY for provider openai")
		}
		return newOpenAI(cfg.OpenAIBaseURL, cfg.OpenAIModel, openAIAPIKey), nil
	case "ollama":
		return newOllama(cfg.OllamaBaseURL, cfg.OllamaModel), nil
	case "copilot":
		if strings.TrimSpace(copilotAPIKey) == "" {
			return nil, errors.New("missing COPILOT_API_KEY for provider copilot")
		}
		return newCopilot(cfg.CopilotBaseURL, cfg.CopilotModel, copilotAPIKey), nil
	default:
		return nil, errors.New("unknown LLM provider: " + p)
	}
}