package provider

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

// WenxinProvider implements AIProvider for Baidu Wenxin (ERNIE) models.
// Wenxin uses a unique API format that requires custom HTTP implementation.
type WenxinProvider struct {
	baseUrl string
	apiKey  string
}

func NewWenxinProvider(baseUrl, apiKey string) *WenxinProvider {
	if baseUrl == "" {
		baseUrl = "https://aip.baidubce.com/rpc/2.0/ai_custom/v1/wenxinworkshop/chat"
	}
	return &WenxinProvider{
		baseUrl: baseUrl,
		apiKey:  apiKey,
	}
}

func (p *WenxinProvider) Name() string {
	return "wenxin"
}

// wenxinMessage is Wenxin's message format
type wenxinMessage struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}

// wenxinRequest is the request body for Wenxin API
type wenxinRequest struct {
	Messages    []wenxinMessage `json:"messages"`
	Stream      bool            `json:"stream"`
	Temperature float64         `json:"temperature,omitempty"`
	MaxOutputTokens int         `json:"max_output_tokens,omitempty"`
}

// wenxinResponse is the non-streaming response from Wenxin API
type wenxinResponse struct {
	Id               string `json:"id"`
	Result           string `json:"result"`
	IsTruncated      bool   `json:"is_truncated"`
	NeedClearHistory bool   `json:"need_clear_history"`
	Usage            struct {
		PromptTokens     int `json:"prompt_tokens"`
		CompletionTokens int `json:"completion_tokens"`
		TotalTokens      int `json:"total_tokens"`
	} `json:"usage"`
	ErrorCode int    `json:"error_code"`
	ErrorMsg  string `json:"error_msg"`
}

// wenxinStreamResponse is a single SSE chunk from Wenxin API
type wenxinStreamResponse struct {
	Id               string `json:"id"`
	Result           string `json:"result"`
	IsEnd            bool   `json:"is_end"`
	IsTruncated      bool   `json:"is_truncated"`
	NeedClearHistory bool   `json:"need_clear_history"`
	Usage            struct {
		PromptTokens     int `json:"prompt_tokens"`
		CompletionTokens int `json:"completion_tokens"`
		TotalTokens      int `json:"total_tokens"`
	} `json:"usage"`
	ErrorCode int    `json:"error_code"`
	ErrorMsg  string `json:"error_msg"`
}

func (p *WenxinProvider) Chat(ctx context.Context, req *ChatRequest) (*ChatResponse, error) {
	wenxinReq := p.buildRequest(req, false)

	body, err := json.Marshal(wenxinReq)
	if err != nil {
		return nil, fmt.Errorf("wenxin marshal request: %w", err)
	}

	url := p.buildURL(req.Model)
	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("wenxin create request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("Authorization", "Bearer "+p.apiKey)

	resp, err := http.DefaultClient.Do(httpReq)
	if err != nil {
		return nil, fmt.Errorf("wenxin http request: %w", err)
	}
	defer resp.Body.Close()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("wenxin read response: %w", err)
	}

	var wenxinResp wenxinResponse
	if err := json.Unmarshal(respBody, &wenxinResp); err != nil {
		return nil, fmt.Errorf("wenxin unmarshal response: %w", err)
	}

	if wenxinResp.ErrorCode != 0 {
		return nil, fmt.Errorf("wenxin error %d: %s", wenxinResp.ErrorCode, wenxinResp.ErrorMsg)
	}

	return &ChatResponse{
		Content:      wenxinResp.Result,
		Model:        req.Model,
		InputTokens:  wenxinResp.Usage.PromptTokens,
		OutputTokens: wenxinResp.Usage.CompletionTokens,
		FinishReason: "stop",
	}, nil
}

func (p *WenxinProvider) ChatStream(ctx context.Context, req *ChatRequest) (<-chan *StreamChunk, error) {
	wenxinReq := p.buildRequest(req, true)

	body, err := json.Marshal(wenxinReq)
	if err != nil {
		return nil, fmt.Errorf("wenxin marshal request: %w", err)
	}

	url := p.buildURL(req.Model)
	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("wenxin create request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("Authorization", "Bearer "+p.apiKey)

	resp, err := http.DefaultClient.Do(httpReq)
	if err != nil {
		return nil, fmt.Errorf("wenxin http request: %w", err)
	}

	if resp.StatusCode != http.StatusOK {
		resp.Body.Close()
		return nil, fmt.Errorf("wenxin stream returned status %d", resp.StatusCode)
	}

	ch := make(chan *StreamChunk, 64)

	go func() {
		defer close(ch)
		defer resp.Body.Close()

		scanner := bufio.NewScanner(resp.Body)
		for scanner.Scan() {
			line := scanner.Text()
			if !strings.HasPrefix(line, "data: ") {
				continue
			}
			data := strings.TrimPrefix(line, "data: ")
			if data == "" {
				continue
			}

			var streamResp wenxinStreamResponse
			if err := json.Unmarshal([]byte(data), &streamResp); err != nil {
				continue
			}

			if streamResp.ErrorCode != 0 {
				select {
				case ch <- &StreamChunk{
					Content:      fmt.Sprintf("[wenxin error: %s]", streamResp.ErrorMsg),
					Done:         true,
					FinishReason: "error",
				}:
				case <-ctx.Done():
				}
				return
			}

			chunk := &StreamChunk{
				Content: streamResp.Result,
			}

			if streamResp.IsEnd {
				chunk.Done = true
				chunk.FinishReason = "stop"
				chunk.InputTokens = streamResp.Usage.PromptTokens
				chunk.OutputTokens = streamResp.Usage.CompletionTokens
			}

			select {
			case ch <- chunk:
			case <-ctx.Done():
				return
			}

			if streamResp.IsEnd {
				return
			}
		}

		// Ensure a final Done chunk
		select {
		case ch <- &StreamChunk{Done: true}:
		case <-ctx.Done():
		}
	}()

	return ch, nil
}

func (p *WenxinProvider) buildRequest(req *ChatRequest, stream bool) *wenxinRequest {
	messages := make([]wenxinMessage, 0, len(req.Messages))
	for _, m := range req.Messages {
		if m.Role == "system" {
			continue // Wenxin doesn't support system role in messages
		}
		messages = append(messages, wenxinMessage{
			Role:    m.Role,
			Content: m.Content,
		})
	}

	wenxinReq := &wenxinRequest{
		Messages: messages,
		Stream:   stream,
	}
	if req.Temperature > 0 {
		wenxinReq.Temperature = req.Temperature
	}
	if req.MaxTokens > 0 {
		wenxinReq.MaxOutputTokens = req.MaxTokens
	}
	return wenxinReq
}

func (p *WenxinProvider) buildURL(model string) string {
	// Wenxin uses model-specific endpoints
	// The baseUrl should include the full path for the model
	// e.g., https://aip.baidubce.com/rpc/2.0/ai_custom/v1/wenxinworkshop/chat/ernie-4.0-8k
	if strings.Contains(p.baseUrl, model) {
		return p.baseUrl
	}
	return strings.TrimRight(p.baseUrl, "/") + "/" + model
}