package providers

import (
	"bufio"
	"encoding/json"
	"fmt"
	"io"
	"strings"

	"gophergate/internal/models"
)

// MessagesToOpenAIJSON converts unified messages to OpenAI-compatible JSON, including tools and images.
func MessagesToOpenAIJSON(messages []models.UnifiedMessage) ([]interface{}, error) {
	var result []interface{}
	for _, m := range messages {
		role := strings.ToLower(m.Role)
		if role == "model" {
			role = "assistant"
		}

		if role == "tool" || role == "function" {
			text := ""
			if len(m.Content) > 0 {
				text = m.Content[0].Text
			}
			msg := map[string]interface{}{
				"role":    "tool",
				"content": text,
			}
			id := "unknown"
			if m.ToolCallID != nil {
				id = *m.ToolCallID
			}
			msg["tool_call_id"] = id

			if m.Name != nil {
				msg["name"] = *m.Name
			}
			result = append(result, msg)
			continue
		}

		var parts []interface{}
		for _, p := range m.Content {
			if p.Type == "text" {
				parts = append(parts, map[string]interface{}{
					"type": "text",
					"text": p.Text,
				})
			} else if p.Image != nil {
				base64Data, mimeType, err := p.Image.ToBase64()
				if err != nil {
					return nil, fmt.Errorf("failed to convert image to base64: %w", err)
				}
				parts = append(parts, map[string]interface{}{
					"type": "image_url",
					"image_url": map[string]interface{}{
						"url": fmt.Sprintf("data:%s;base64,%s", mimeType, base64Data),
					},
				})
			}
		}

		var finalContent interface{}
		if len(parts) == 0 {
			finalContent = nil
		} else if len(parts) == 1 {
			if p, ok := parts[0].(map[string]interface{}); ok && p["type"] == "text" {
				finalContent = p["text"]
			} else {
				finalContent = parts
			}
		} else {
			finalContent = parts
		}

		msg := map[string]interface{}{
			"role":    role,
			"content": finalContent,
		}

		if m.ReasoningContent != nil {
			msg["reasoning_content"] = *m.ReasoningContent
		}

		if len(m.ToolCalls) > 0 {
			sanitizedCalls := make([]models.ToolCall, len(m.ToolCalls))
			copy(sanitizedCalls, m.ToolCalls)
			for i := range sanitizedCalls {
				if sanitizedCalls[i].Type == "" {
					sanitizedCalls[i].Type = "function"
				}
			}
			msg["tool_calls"] = sanitizedCalls
			msg["content"] = "" // OpenAI requirement: content must be string if tool_calls present
		}

		if m.Name != nil {
			msg["name"] = *m.Name
		}
		result = append(result, msg)
	}
	return result, nil
}

func BuildOpenAIBody(request *models.UnifiedRequest, messagesJSON []interface{}, stream bool) map[string]interface{} {
	body := map[string]interface{}{
		"model":    request.Model,
		"messages": messagesJSON,
		"stream":   stream,
	}

	if stream {
		body["stream_options"] = map[string]interface{}{
			"include_usage": true,
		}
	}

	if request.Temperature != nil {
		body["temperature"] = *request.Temperature
	}
	if request.MaxTokens != nil {
		body["max_tokens"] = *request.MaxTokens
	}
	if len(request.Tools) > 0 {
		body["tools"] = request.Tools
	}
	if request.ToolChoice != nil {
		var toolChoice interface{}
		if err := json.Unmarshal(request.ToolChoice, &toolChoice); err == nil {
			body["tool_choice"] = toolChoice
		}
	}

	return body
}

// BuildOpenAIResponsesBody builds the request body for the Responses API endpoint.
func BuildOpenAIResponsesBody(req *models.ResponsesRequest, stream bool) map[string]interface{} {
	body := map[string]interface{}{
		"model":  req.Model,
		"stream": stream,
	}

	// The input field can be a string or a structured array.
	// Try to preserve the original format.
	if req.Input != nil {
		// Try as string first
		var inputStr string
		if err := json.Unmarshal(req.Input, &inputStr); err == nil {
			body["input"] = inputStr
		} else {
			// Try as array of messages
			var inputArr []interface{}
			if err := json.Unmarshal(req.Input, &inputArr); err == nil {
				body["input"] = inputArr
			}
		}
	}

	if req.Instructions != "" {
		body["instructions"] = req.Instructions
	}
	if req.Temperature != nil {
		body["temperature"] = *req.Temperature
	}
	if req.MaxOutputTokens != nil {
		body["max_output_tokens"] = *req.MaxOutputTokens
	}
	if req.TopP != nil {
		body["top_p"] = *req.TopP
	}
	if req.Tools != nil {
		var tools interface{}
		if err := json.Unmarshal(req.Tools, &tools); err == nil {
			body["tools"] = tools
		}
	}
	if req.ToolChoice != nil {
		var toolChoice interface{}
		if err := json.Unmarshal(req.ToolChoice, &toolChoice); err == nil {
			body["tool_choice"] = toolChoice
		}
	}
	if req.Store != nil {
		body["store"] = *req.Store
	}

	if stream {
		body["stream_options"] = map[string]interface{}{
			"include_usage": true,
		}
	}

	return body
}

// ParseOpenAIResponsesResponse parses a raw JSON map into a ResponsesResponse.
func ParseOpenAIResponsesResponse(respJSON map[string]interface{}, model string) (*models.ResponsesResponse, error) {
	data, err := json.Marshal(respJSON)
	if err != nil {
		return nil, err
	}

	var resp models.ResponsesResponse
	if err := json.Unmarshal(data, &resp); err != nil {
		return nil, err
	}

	// Re-parse usage with the detailed tokens
	if usageData, ok := respJSON["usage"]; ok {
		var responsesUsage models.ResponsesUsage
		usageBytes, _ := json.Marshal(usageData)
		if err := json.Unmarshal(usageBytes, &responsesUsage); err == nil {
			resp.Usage = &responsesUsage
		}
	}

	return &resp, nil
}

// ParseOpenAIResponsesStreamChunk parses a single SSE line into a ResponsesStreamChunk.
// Returns the chunk, whether this is the [DONE] signal, and any error.
func ParseOpenAIResponsesStreamChunk(line string) (*models.ResponsesStreamChunk, bool, error) {
	if line == "" {
		return nil, false, nil
	}
	if !strings.HasPrefix(line, "data: ") {
		return nil, false, nil
	}

	data := strings.TrimPrefix(line, "data: ")
	if data == "[DONE]" {
		return nil, true, nil
	}

	var chunk models.ResponsesStreamChunk
	if err := json.Unmarshal([]byte(data), &chunk); err != nil {
		return nil, false, fmt.Errorf("failed to unmarshal responses stream chunk: %w", err)
	}

	return &chunk, false, nil
}

// StreamOpenAIResponses reads SSE chunks from the body and sends them to the channel.
func StreamOpenAIResponses(ctx io.ReadCloser, ch chan<- *models.ResponsesStreamChunk) error {
	defer ctx.Close()
	scanner := bufio.NewScanner(ctx)
	for scanner.Scan() {
		line := scanner.Text()
		chunk, done, err := ParseOpenAIResponsesStreamChunk(line)
		if err != nil {
			return err
		}
		if done {
			break
		}
		if chunk != nil {
			ch <- chunk
		}
	}
	return scanner.Err()
}

type openAIUsage struct {
	PromptTokens        uint32 `json:"prompt_tokens"`
	CompletionTokens    uint32 `json:"completion_tokens"`
	TotalTokens         uint32 `json:"total_tokens"`
	PromptTokensDetails *struct {
		CachedTokens uint32 `json:"cached_tokens"`
	} `json:"prompt_tokens_details"`
	CompletionTokensDetails *struct {
		ReasoningTokens uint32 `json:"reasoning_tokens"`
	} `json:"completion_tokens_details"`
}

func (u *openAIUsage) ToUnified() *models.Usage {
	usage := &models.Usage{
		PromptTokens:     u.PromptTokens,
		CompletionTokens: u.CompletionTokens,
		TotalTokens:      u.TotalTokens,
	}
	if u.PromptTokensDetails != nil && u.PromptTokensDetails.CachedTokens > 0 {
		usage.CacheReadTokens = &u.PromptTokensDetails.CachedTokens
	}
	if u.CompletionTokensDetails != nil && u.CompletionTokensDetails.ReasoningTokens > 0 {
		usage.ReasoningTokens = &u.CompletionTokensDetails.ReasoningTokens
	}
	return usage
}

func ParseOpenAIResponse(respJSON map[string]interface{}, model string) (*models.ChatCompletionResponse, error) {
	data, err := json.Marshal(respJSON)
	if err != nil {
		return nil, err
	}

	var resp models.ChatCompletionResponse
	if err := json.Unmarshal(data, &resp); err != nil {
		return nil, err
	}

	// Manually fix usage because ChatCompletionResponse uses the unified Usage struct
	// but the provider might have returned more details.
	if usageData, ok := respJSON["usage"]; ok {
		var oUsage openAIUsage
		usageBytes, _ := json.Marshal(usageData)
		if err := json.Unmarshal(usageBytes, &oUsage); err == nil {
			resp.Usage = oUsage.ToUnified()
		}
	}

	return &resp, nil
}

// Streaming support

func ParseOpenAIStreamChunk(line string) (*models.ChatCompletionStreamResponse, bool, error) {
	if line == "" {
		return nil, false, nil
	}
	if !strings.HasPrefix(line, "data: ") {
		return nil, false, nil
	}

	data := strings.TrimPrefix(line, "data: ")
	if data == "[DONE]" {
		return nil, true, nil
	}

	var chunk models.ChatCompletionStreamResponse
	if err := json.Unmarshal([]byte(data), &chunk); err != nil {
		return nil, false, fmt.Errorf("failed to unmarshal stream chunk: %w", err)
	}

	// Handle specialized usage in stream chunks
	var rawChunk struct {
		Usage *openAIUsage `json:"usage"`
	}
	if err := json.Unmarshal([]byte(data), &rawChunk); err == nil && rawChunk.Usage != nil {
		chunk.Usage = rawChunk.Usage.ToUnified()
	}

	return &chunk, false, nil
}

func StreamOpenAI(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamResponse) error {
	defer ctx.Close()
	scanner := bufio.NewScanner(ctx)
	for scanner.Scan() {
		line := scanner.Text()
		chunk, done, err := ParseOpenAIStreamChunk(line)
		if err != nil {
			return err
		}
		if done {
			break
		}
		if chunk != nil {
			ch <- chunk
		}
	}
	return scanner.Err()
}

// geminiStreamChunk is the shared data structure for parsing Gemini streaming responses.
type geminiStreamChunk struct {
	Candidates []struct {
		Content struct {
			Parts []struct {
				Text    string `json:"text,omitempty"`
				Thought string `json:"thought,omitempty"`
			} `json:"parts"`
		} `json:"content"`
		FinishReason string `json:"finishReason"`
	} `json:"candidates"`
	UsageMetadata struct {
		PromptTokenCount        uint32 `json:"promptTokenCount"`
		CandidatesTokenCount    uint32 `json:"candidatesTokenCount"`
		TotalTokenCount         uint32 `json:"totalTokenCount"`
		CachedContentTokenCount uint32 `json:"cachedContentTokenCount"`
	} `json:"usageMetadata"`
}

// emitGeminiChunk builds a ChatCompletionStreamResponse from a parsed geminiStreamChunk
// and sends it to the channel. Returns true if anything was emitted.
func emitGeminiChunk(ch chan<- *models.ChatCompletionStreamResponse, chunk *geminiStreamChunk, model string) bool {
	if len(chunk.Candidates) == 0 && chunk.UsageMetadata.TotalTokenCount == 0 {
		return false
	}

	content := ""
	var reasoning *string
	var finishReason *string
	if len(chunk.Candidates) > 0 {
		for _, p := range chunk.Candidates[0].Content.Parts {
			if p.Text != "" {
				content += p.Text
			}
			if p.Thought != "" {
				if reasoning == nil {
					reasoning = new(string)
				}
				*reasoning += p.Thought
			}
		}
		fr := strings.ToLower(chunk.Candidates[0].FinishReason)
		finishReason = &fr
	}

	ch <- &models.ChatCompletionStreamResponse{
		ID:      "gemini-stream",
		Object:  "chat.completion.chunk",
		Created: 0,
		Model:   model,
		Choices: []models.ChatStreamChoice{
			{
				Index: 0,
				Delta: models.ChatStreamDelta{
					Content:          &content,
					ReasoningContent: reasoning,
				},
				FinishReason: finishReason,
			},
		},
		Usage: &models.Usage{
			PromptTokens:     chunk.UsageMetadata.PromptTokenCount,
			CompletionTokens: chunk.UsageMetadata.CandidatesTokenCount,
			TotalTokens:      chunk.UsageMetadata.TotalTokenCount,
			CacheReadTokens:  uint32Ptr(chunk.UsageMetadata.CachedContentTokenCount),
		},
	}
	return true
}

// StreamGemini handles Gemini streaming responses in two formats:
//  1. SSE format (newer models): each line is "data: {...}"
//  2. JSON array format (older models): response body is [ {...}, {...} ]
//
// Usage metadata is only present in the final chunk, which we accumulate
// and emit so the server can log it on stream end.
func StreamGemini(ctx io.ReadCloser, model string) (<-chan *models.ChatCompletionStreamResponse, error) {
	ch := make(chan *models.ChatCompletionStreamResponse)

	go func() {
		defer func() {
			_ = ctx.Close()
		}()
		defer close(ch)

		// Peek at the first byte to detect format
		peek := make([]byte, 6)
		n, _ := io.ReadAtLeast(ctx, peek, 1)
		if n == 0 {
			return
		}

		first := string(peek[:n])

		if first[0] == '[' {
			// JSON array format
			rest, _ := io.ReadAll(ctx)
			streamGeminiJSONArray(append([]byte(first), rest...), ch, model)
			return
		} else if strings.HasPrefix(first, "data:") || strings.HasPrefix(first, "data: ") {
			// SSE format — pre-pend the peeked bytes then run SSE scanner
			combined := io.MultiReader(
				strings.NewReader(string(peek[:n])),
				ctx,
			)
			streamGeminiSSE(combined, ch, model)
		} else {
			// Unknown format — might still be SSE starting after a peek char
			// Pre-pend peeked bytes and try SSE
			combined := io.MultiReader(
				strings.NewReader(string(peek[:n])),
				ctx,
			)
			streamGeminiSSE(combined, ch, model)
		}
	}()

	return ch, nil
}

// readAll reads remaining bytes from a reader (keeps the function signature simple
// for the JSON array fallback path).
func readAll(r io.Reader) []byte {
	b, _ := io.ReadAll(r)
	return b
}

func streamGeminiJSONArray(data []byte, ch chan<- *models.ChatCompletionStreamResponse, model string) {
	var chunks []geminiStreamChunk
	if err := json.Unmarshal(data, &chunks); err != nil {
		fmt.Printf("[Gemini-Stream] JSON array parse error: %v\n", err)
		return
	}
	// Track the last chunk with usage for the final emission
	var lastUsage *geminiStreamChunk
	for i := range chunks {
		if chunks[i].UsageMetadata.TotalTokenCount > 0 {
			lastUsage = &chunks[i]
		}
	}
	if lastUsage != nil {
		// Emit a synthetic final chunk with usage data
		if len(lastUsage.Candidates) == 0 && lastUsage.UsageMetadata.TotalTokenCount > 0 {
			emitGeminiChunk(ch, lastUsage, model)
		}
	}
	// Also emit each content-bearing chunk
	for i := range chunks {
		emitGeminiChunk(ch, &chunks[i], model)
	}
}

func streamGeminiSSE(r io.Reader, ch chan<- *models.ChatCompletionStreamResponse, model string) {
	scanner := bufio.NewScanner(r)
	// Track the last seen usage for emission at end of stream
	var lastUsage geminiStreamChunk

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" || !strings.HasPrefix(line, "data: ") {
			continue
		}

		data := strings.TrimPrefix(line, "data: ")
		if data == "[DONE]" {
			// Emit final usage if we have one
			if lastUsage.UsageMetadata.TotalTokenCount > 0 {
				emitGeminiChunk(ch, &lastUsage, model)
			}
			break
		}

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

		// Capture usage from any chunk (Gemini puts it in the final response)
		if chunk.UsageMetadata.TotalTokenCount > 0 {
			lastUsage = chunk
		}

		// Emit content chunks as they arrive
		if len(chunk.Candidates) > 0 {
			emitGeminiChunk(ch, &chunk, model)
		}
	}

	// If stream ended without [DONE] marker but we collected usage, emit it
	if lastUsage.UsageMetadata.TotalTokenCount > 0 {
		emitGeminiChunk(ch, &lastUsage, model)
	}

	if err := scanner.Err(); err != nil {
		fmt.Printf("[Gemini-Stream] SSE scan error: %v\n", err)
	}
}

// ensureEnglish injects a system message instructing the model to respond in
// English when no system prompt is already present. Some providers (e.g. DeepSeek)
// default to Chinese for certain prompts.
func ensureEnglish(req *models.UnifiedRequest) {
	if len(req.Messages) > 0 && req.Messages[0].Role == "system" {
		return // already has a system prompt, don't interfere
	}
	enMsg := models.UnifiedMessage{
		Role: "system",
		Content: []models.UnifiedContentPart{
			{Type: "text", Text: "You are a helpful assistant. Always respond in English."},
		},
	}
	req.Messages = append([]models.UnifiedMessage{enMsg}, req.Messages...)
}