package llm

import (
	"fmt"
	"log/slog"
	"net/http"
	"time"
)

const (
	// chatCompletionsPath is the endpoint for chat completion requests.
	chatCompletionsPath = "/chat/completions"
	// chatTemplateEnableThinking is the chat-template argument that selects
	// whether a reasoning model emits reasoning tokens.
	chatTemplateEnableThinking = "enable_thinking"
	// defaultTimeout limits requests when Config.Timeout is zero.
	defaultTimeout = 5 * time.Minute
	// sseDone is the sentinel that terminates a chat completion stream.
	sseDone = "[DONE]"
)

// Config configures a Client.
type Config struct {
	// Key is sent as a bearer token. An empty key disables authentication.
	Key string `yaml:"key"`
	// Provider is returned unchanged by Client.Provider. It is not sent to the
	// inference endpoint.
	Provider string `yaml:"provider"`
	// Timeout limits each request, including reading a streaming response.
	// It defaults to five minutes when zero.
	Timeout time.Duration `yaml:"timeout"`
	// URL is the endpoint root. Client appends /chat/completions or /models.
	URL string `yaml:"url"`
}

// Validate reports whether Timeout is non-negative and URL is non-empty.
func (cfg Config) Validate() error {
	if cfg.Timeout < 0 {
		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
	}
	if cfg.URL == "" {
		return fmt.Errorf("missing URL")
	}
	return nil
}

// Client is an OpenAI-compatible inference client.
type Client struct {
	baseURL  string
	httpc    *http.Client
	key      string
	log      *slog.Logger
	provider string
	timeout  time.Duration
}

// NewClient creates a client from cfg.
func NewClient(cfg Config, log *slog.Logger) (*Client, error) {
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("invalid config: %w", err)
	}
	if log == nil {
		return nil, fmt.Errorf("missing logger")
	}

	timeout := cfg.Timeout
	if timeout == 0 {
		timeout = defaultTimeout
	}

	return &Client{
		baseURL:  cfg.URL,
		key:      cfg.Key,
		log:      log,
		provider: cfg.Provider,
		httpc:    &http.Client{},
		timeout:  timeout,
	}, nil
}

// Provider returns the application-defined provider name supplied in Config.
func (c *Client) Provider() string {
	return c.provider
}