package llm

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

type Client struct {
	baseURL string
	apiKey  string
	model   string
	http    *http.Client
}

type Message struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}

type ChatInput struct {
	System         string          `json:"system,omitempty"`
	User           string          `json:"user,omitempty"`
	Messages       []Message       `json:"messages,omitempty"`
	Temperature    *float64        `json:"temperature,omitempty"`
	MaxTokens      int             `json:"max_tokens,omitempty"`
	ResponseFormat json.RawMessage `json:"response_format,omitempty"`
}

type Usage struct {
	PromptTokens     int `json:"prompt_tokens"`
	CompletionTokens int `json:"completion_tokens"`
	TotalTokens      int `json:"total_tokens"`
}

type ChatResult struct {
	Content    string `json:"content"`
	Model      string `json:"model"`
	Usage      *Usage `json:"usage,omitempty"`
	DurationMS int64  `json:"duration_ms"`
}

type chatRequest struct {
	Model          string           `json:"model"`
	Messages       []Message        `json:"messages"`
	Temperature    float64          `json:"temperature"`
	MaxTokens      int              `json:"max_tokens,omitempty"`
	ResponseFormat *json.RawMessage `json:"response_format,omitempty"`
}

type chatResponse struct {
	Model   string `json:"model,omitempty"`
	Choices []struct {
		Message Message `json:"message"`
	} `json:"choices"`
	Usage *Usage `json:"usage,omitempty"`
	Error *struct {
		Message string `json:"message"`
	} `json:"error,omitempty"`
}

func New(baseURL, apiKey, model string, timeout time.Duration) *Client {
	return &Client{
		baseURL: strings.TrimRight(strings.TrimSpace(baseURL), "/"),
		apiKey:  apiKey,
		model:   model,
		http:    &http.Client{Timeout: timeout},
	}
}

func (c *Client) Chat(ctx context.Context, in ChatInput) (*ChatResult, error) {
	if c == nil || c.baseURL == "" {
		return nil, fmt.Errorf("llm not configured")
	}
	messages := normalizeMessages(in)
	if len(messages) == 0 {
		return nil, fmt.Errorf("messages are required")
	}
	temp := 0.1
	if in.Temperature != nil {
		temp = *in.Temperature
	}
	reqBody := chatRequest{
		Model:       c.model,
		Messages:    messages,
		Temperature: temp,
		MaxTokens:   in.MaxTokens,
	}
	if len(in.ResponseFormat) > 0 {
		reqBody.ResponseFormat = &in.ResponseFormat
	}
	body, err := json.Marshal(reqBody)
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/v1/chat/completions", bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	if c.apiKey != "" {
		req.Header.Set("Authorization", "Bearer "+c.apiKey)
	}

	start := time.Now()
	resp, err := c.http.Do(req)
	duration := time.Since(start)
	if err != nil {
		return nil, fmt.Errorf("llm do: %w", err)
	}
	defer resp.Body.Close()

	raw, err := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
	if err != nil {
		return nil, fmt.Errorf("llm read: %w", err)
	}
	if resp.StatusCode >= 300 {
		return nil, fmt.Errorf("llm HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(raw)))
	}
	var out chatResponse
	if err := json.Unmarshal(raw, &out); err != nil {
		return nil, fmt.Errorf("llm decode: %w", err)
	}
	if out.Error != nil {
		return nil, fmt.Errorf("llm error: %s", out.Error.Message)
	}
	if len(out.Choices) == 0 {
		return nil, fmt.Errorf("llm: empty choices")
	}
	modelName := out.Model
	if modelName == "" {
		modelName = c.model
	}
	return &ChatResult{
		Content:    out.Choices[0].Message.Content,
		Model:      modelName,
		Usage:      out.Usage,
		DurationMS: duration.Milliseconds(),
	}, nil
}

func normalizeMessages(in ChatInput) []Message {
	if len(in.Messages) > 0 {
		return in.Messages
	}
	var out []Message
	if strings.TrimSpace(in.System) != "" {
		out = append(out, Message{Role: "system", Content: in.System})
	}
	if strings.TrimSpace(in.User) != "" {
		out = append(out, Message{Role: "user", Content: in.User})
	}
	return out
}