package provider

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

	app "haixun-backend/internal/library/errors"
	"haixun-backend/internal/library/errors/code"
	"haixun-backend/internal/model/ai/domain/enum"
	domai "haixun-backend/internal/model/ai/domain/usecase"
)

type OpenAICompatible struct {
	id      enum.ProviderID
	baseURL string
	client  *http.Client
}

func NewOpenAICompatible(id enum.ProviderID, baseURL string) *OpenAICompatible {
	return &OpenAICompatible{
		id:      id,
		baseURL: strings.TrimRight(baseURL, "/"),
		client:  &http.Client{Timeout: 10 * time.Minute},
	}
}

func (p *OpenAICompatible) ID() enum.ProviderID {
	return p.id
}

func (p *OpenAICompatible) ListModels(ctx context.Context, credential domai.Credential) ([]string, error) {
	if strings.TrimSpace(credential.APIKey) == "" {
		return nil, app.For(code.AI).InputMissingRequired("missing AI provider token")
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, p.baseURL+"/models", nil)
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Authorization", "Bearer "+credential.APIKey)
	httpReq.Header.Set("Accept", "application/json")

	resp, err := p.client.Do(httpReq)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	data, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return nil, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, providerHTTPError("AI provider models request failed", resp.StatusCode, resp.Status)
	}

	var payload openAIModelsResponse
	if err := json.Unmarshal(data, &payload); err != nil {
		return nil, app.For(code.AI).SvcThirdParty("failed to parse AI provider models response")
	}

	models := make([]string, 0, len(payload.Data))
	for _, item := range payload.Data {
		id := strings.TrimSpace(item.ID)
		if id == "" {
			continue
		}
		models = append(models, id)
	}
	sort.Strings(models)
	return models, nil
}

func (p *OpenAICompatible) GenerateText(ctx context.Context, req domai.GenerateRequest) (*domai.GenerateResult, error) {
	if strings.TrimSpace(req.Credential.APIKey) == "" {
		return nil, app.For(code.AI).InputMissingRequired("missing AI provider token")
	}

	body := p.buildChatCompletionRequest(req, false)
	payload, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, p.baseURL+"/chat/completions", bytes.NewReader(payload))
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Authorization", "Bearer "+req.Credential.APIKey)
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("Accept", "application/json")

	resp, err := p.client.Do(httpReq)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	data, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return nil, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, providerHTTPError("AI provider request failed", resp.StatusCode, resp.Status)
	}

	var chatResp openAIChatResponse
	if err := json.Unmarshal(data, &chatResp); err != nil {
		return nil, app.For(code.AI).SvcThirdParty("failed to parse AI provider chat response")
	}
	if len(chatResp.Choices) == 0 {
		return nil, app.For(code.AI).SvcThirdParty("AI provider returned no choices")
	}

	choice := chatResp.Choices[0]
	return &domai.GenerateResult{
		Text:         extractAssistantText(choice.Message),
		FinishReason: choice.FinishReason,
	}, nil
}

func (p *OpenAICompatible) StreamText(ctx context.Context, req domai.GenerateRequest) (<-chan domai.StreamEvent, error) {
	if strings.TrimSpace(req.Credential.APIKey) == "" {
		return nil, app.For(code.AI).InputMissingRequired("missing AI provider token")
	}

	body := p.buildChatCompletionRequest(req, true)
	payload, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}

	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, p.baseURL+"/chat/completions", bytes.NewReader(payload))
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Authorization", "Bearer "+req.Credential.APIKey)
	httpReq.Header.Set("Content-Type", "application/json")
	httpReq.Header.Set("Accept", "text/event-stream")

	resp, err := p.client.Do(httpReq)
	if err != nil {
		return nil, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		defer resp.Body.Close()
		_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 4096))
		return nil, providerHTTPError("AI provider request failed", resp.StatusCode, resp.Status)
	}

	out := make(chan domai.StreamEvent)
	go func() {
		defer close(out)
		defer resp.Body.Close()
		parseOpenAIStream(resp.Body, out)
	}()
	return out, nil
}

type chatCompletionRequest struct {
	Model       string          `json:"model"`
	Messages    []chatMessage   `json:"messages"`
	Stream      bool            `json:"stream"`
	Temperature *float64        `json:"temperature,omitempty"`
	MaxTokens   *int            `json:"max_tokens,omitempty"`
	Thinking    *thinkingConfig `json:"thinking,omitempty"`
}

type thinkingConfig struct {
	Type string `json:"type,omitempty"`
}

type assistantMessage struct {
	Content          json.RawMessage `json:"content"`
	ReasoningContent string          `json:"reasoning_content"`
	Reasoning        string          `json:"reasoning"`
}

type openAIChatResponse struct {
	Choices []struct {
		Message      assistantMessage `json:"message"`
		FinishReason string           `json:"finish_reason"`
	} `json:"choices"`
}

func (p *OpenAICompatible) buildChatCompletionRequest(req domai.GenerateRequest, stream bool) chatCompletionRequest {
	return chatCompletionRequest{
		Model:       req.Model,
		Messages:    toChatMessages(req),
		Stream:      stream,
		Temperature: normalizeTemperature(p.id, req.Model, req.Temperature),
		MaxTokens:   normalizeMaxTokens(p.id, req.Model, req.MaxTokens),
		Thinking:    normalizeThinking(p.id, req.Model),
	}
}

func extractAssistantText(msg assistantMessage) string {
	if text := parseMessageContent(msg.Content); strings.TrimSpace(text) != "" {
		return text
	}
	if strings.TrimSpace(msg.ReasoningContent) != "" {
		return msg.ReasoningContent
	}
	return msg.Reasoning
}

func parseMessageContent(raw json.RawMessage) string {
	if len(raw) == 0 || string(raw) == "null" {
		return ""
	}

	var text string
	if err := json.Unmarshal(raw, &text); err == nil {
		return text
	}

	var parts []struct {
		Text string `json:"text"`
	}
	if err := json.Unmarshal(raw, &parts); err == nil {
		var b strings.Builder
		for _, part := range parts {
			if part.Text != "" {
				b.WriteString(part.Text)
			}
		}
		return b.String()
	}

	return ""
}

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

func toChatMessages(req domai.GenerateRequest) []chatMessage {
	messages := make([]chatMessage, 0, len(req.Messages)+1)
	if strings.TrimSpace(req.System) != "" {
		messages = append(messages, chatMessage{Role: "system", Content: req.System})
	}
	for _, msg := range req.Messages {
		messages = append(messages, chatMessage{Role: msg.Role, Content: msg.Content})
	}
	return messages
}

func normalizeTemperature(provider enum.ProviderID, model string, requested *float64) *float64 {
	if provider == enum.ProviderOpenCode && strings.HasPrefix(model, "kimi-") {
		v := 1.0
		return &v
	}
	return requested
}

func normalizeMaxTokens(provider enum.ProviderID, model string, requested *int) *int {
	if provider != enum.ProviderOpenCode || !strings.HasPrefix(model, "deepseek-") {
		return requested
	}

	// DeepSeek V4 thinking can consume the full budget before content appears.
	const minDeepSeekTokens = 2048
	if requested == nil || *requested < minDeepSeekTokens {
		v := minDeepSeekTokens
		return &v
	}
	return requested
}

func normalizeThinking(provider enum.ProviderID, model string) *thinkingConfig {
	// DeepSeek V4 on OpenCode Go defaults to thinking mode and may spend the entire
	// max_tokens budget on reasoning_content before emitting content.
	if provider == enum.ProviderOpenCode && strings.HasPrefix(model, "deepseek-") {
		return &thinkingConfig{Type: "disabled"}
	}
	return nil
}

func streamDeltaText(delta streamDelta) string {
	if delta.Content != "" {
		return delta.Content
	}
	if delta.Text != "" {
		return delta.Text
	}
	if delta.ReasoningContent != "" {
		return delta.ReasoningContent
	}
	return delta.Reasoning
}

func parseOpenAIStream(body io.Reader, out chan<- domai.StreamEvent) {
	scanner := bufio.NewScanner(body)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || !strings.HasPrefix(line, "data:") {
			continue
		}
		data := strings.TrimSpace(strings.TrimPrefix(line, "data:"))
		if data == "[DONE]" {
			out <- domai.StreamEvent{Type: "done"}
			return
		}
		var chunk openAIStreamChunk
		if err := json.Unmarshal([]byte(data), &chunk); err != nil {
			out <- domai.StreamEvent{Type: "error", Error: "failed to parse AI stream payload"}
			return
		}
		for _, choice := range chunk.Choices {
			if text := streamDeltaText(choice.Delta); text != "" {
				out <- domai.StreamEvent{Type: "delta", Text: text}
			}
			if choice.FinishReason != "" {
				out <- domai.StreamEvent{Type: "done", FinishReason: choice.FinishReason}
				return
			}
		}
	}
	if err := scanner.Err(); err != nil {
		out <- domai.StreamEvent{Type: "error", Error: err.Error()}
	}
}

type streamDelta struct {
	Content          string `json:"content"`
	Text             string `json:"text"`
	ReasoningContent string `json:"reasoning_content"`
	Reasoning        string `json:"reasoning"`
}

type openAIStreamChunk struct {
	Choices []struct {
		Delta        streamDelta `json:"delta"`
		FinishReason string      `json:"finish_reason"`
	} `json:"choices"`
}

type openAIModelsResponse struct {
	Data []struct {
		ID string `json:"id"`
	} `json:"data"`
}

func providerHTTPError(prefix string, statusCode int, statusLine string) error {
	return app.For(code.AI).SvcThirdParty(fmt.Sprintf("%s: HTTP %d %s", prefix, statusCode, statusLine))
}