package openai

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"image"
	_ "image/gif"
	"image/jpeg"
	_ "image/png"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	xdraw "golang.org/x/image/draw"
)

const moderationSystemPrompt = "你是中文社区的内容审核助手，负责对“帖子标题、正文、配图”做联合审核。目标是平衡社区安全与正常交流：必须拦截高风险违规内容，但不要误伤正常玩梗、二创、吐槽和轻度调侃。请只输出指定JSON。\n\n审核流程：\n1) 先判断是否命中硬性违规；\n2) 再判断语境（玩笑/自嘲/朋友间互动/作品讨论）；\n3) 做文图交叉判断（文本+图片合并理解）；\n4) 给出 approved 与简短 reason。\n\n硬性违规（命中任一项必须 approved=false）：\nA. 宣传对立与煽动撕裂：\n- 明确煽动群体对立、地域对立、性别对立、民族宗教对立，鼓动仇恨、排斥、报复。\nB. 严重人身攻击与网暴引导：\n- 持续性侮辱贬损、羞辱人格、号召围攻/骚扰/挂人/线下冲突。\nC. 开盒/人肉/隐私暴露：\n- 故意公开、拼接、索取他人可识别隐私信息（姓名+联系方式、身份证号、住址、学校单位、车牌、定位轨迹等）；\n- 图片/截图中出现可识别隐私信息并伴随曝光意图，也按违规处理。\nD. 其他高危违规：\n- 违法犯罪、暴力威胁、极端仇恨、色情低俗、诈骗引流、恶意广告等。\n\n放行规则（以下通常 approved=true）：\n- 正常玩梗、表情包、谐音梗、二次创作、无恶意的吐槽；\n- 非定向、轻度口语化吐槽（无明确攻击对象、无网暴号召、无隐私暴露）；\n- 对社会事件/作品的理性讨论、观点争论（即使语气尖锐，但未煽动对立或人身攻击）。\n\n边界判定：\n- 若只是“梗文化表达”且不指向现实伤害，优先通过；\n- 若存在明确伤害意图（煽动、围攻、曝光隐私），必须拒绝；\n- 对模糊内容不因个别粗口直接拒绝，需结合对象、意图、号召性和可执行性综合判断。\n\nreason 要求：\n- approved=false 时：中文10-30字，说明核心违规点；\n- approved=true 时：reason 为空字符串。\n\n输出格式（严格）：\n仅输出一行JSON对象，不要Markdown，不要额外解释：\n{\"approved\": true/false, \"reason\": \"...\"}"

const (
	defaultMaxImagesPerModerationRequest = 1
	maxModerationResultRetries           = 3
	maxChatCompletionRetries             = 3
	initialRetryBackoff                  = 500 * time.Millisecond
	maxDownloadImageBytes                = 10 * 1024 * 1024
	maxModerationImageSide               = 1280
	compressedJPEGQuality                = 72
	maxCompressedPayloadBytes            = 1536 * 1024
)

type Client interface {
	IsEnabled() bool
	Config() Config
	ModeratePost(ctx context.Context, title, content string, images []string) (bool, string, error)
	ModerateComment(ctx context.Context, content string, images []string) (bool, string, error)
}

type clientImpl struct {
	cfg        Config
	httpClient *http.Client
}

func NewClient(cfg Config) Client {
	timeout := cfg.RequestTimeoutSeconds
	if timeout <= 0 {
		timeout = 30
	}
	return &clientImpl{
		cfg: cfg,
		httpClient: &http.Client{
			Timeout: time.Duration(timeout) * time.Second,
		},
	}
}

func (c *clientImpl) IsEnabled() bool {
	return c.cfg.Enabled && c.cfg.APIKey != "" && c.cfg.BaseURL != ""
}

func (c *clientImpl) Config() Config {
	return c.cfg
}

func (c *clientImpl) ModeratePost(ctx context.Context, title, content string, images []string) (bool, string, error) {
	if !c.IsEnabled() {
		return true, "", nil
	}
	return c.moderateContentInBatches(ctx, fmt.Sprintf("帖子标题：%s\n帖子内容：%s", title, content), images)
}

func (c *clientImpl) ModerateComment(ctx context.Context, content string, images []string) (bool, string, error) {
	if !c.IsEnabled() {
		return true, "", nil
	}
	return c.moderateContentInBatches(ctx, fmt.Sprintf("评论内容：%s", content), images)
}

func (c *clientImpl) moderateContentInBatches(ctx context.Context, contentPrompt string, images []string) (bool, string, error) {
	cleanImages := normalizeImageURLs(images)
	optimizedImages := c.optimizeImagesForModeration(ctx, cleanImages)
	maxImagesPerRequest := c.maxImagesPerModerationRequest()
	totalBatches := 1
	if len(optimizedImages) > 0 {
		totalBatches = (len(optimizedImages) + maxImagesPerRequest - 1) / maxImagesPerRequest
	}

	// 图片超过单批上限时分批审核，任一批次拒绝即整体拒绝
	for i := 0; i < totalBatches; i++ {
		start := i * maxImagesPerRequest
		end := start + maxImagesPerRequest
		if end > len(optimizedImages) {
			end = len(optimizedImages)
		}

		batchImages := []string{}
		if len(optimizedImages) > 0 {
			batchImages = optimizedImages[start:end]
		}

		approved, reason, err := c.moderateSingleBatch(ctx, contentPrompt, batchImages, i+1, totalBatches)
		if err != nil {
			return false, "", err
		}
		if !approved {
			if strings.TrimSpace(reason) != "" && totalBatches > 1 {
				reason = fmt.Sprintf("第%d/%d批图片未通过：%s", i+1, totalBatches, reason)
			}
			return false, reason, nil
		}
	}

	return true, "", nil
}

func (c *clientImpl) moderateSingleBatch(
	ctx context.Context,
	contentPrompt string,
	images []string,
	batchNo, totalBatches int,
) (bool, string, error) {
	userPrompt := fmt.Sprintf(
		"%s\n图片批次：%d/%d（本次仅提供当前批次图片）",
		contentPrompt,
		batchNo,
		totalBatches,
	)

	var lastErr error
	for attempt := 0; attempt < maxModerationResultRetries; attempt++ {
		replyText, err := c.chatCompletion(ctx, c.cfg.ModerationModel, moderationSystemPrompt, userPrompt, images, 0.1, 220)
		if err != nil {
			lastErr = err
		} else {
			parsed := struct {
				Approved bool   `json:"approved"`
				Reason   string `json:"reason"`
			}{}
			if err := json.Unmarshal([]byte(extractJSONObject(replyText)), &parsed); err != nil {
				lastErr = fmt.Errorf("failed to parse moderation result: %w", err)
			} else {
				return parsed.Approved, parsed.Reason, nil
			}
		}

		if attempt == maxModerationResultRetries-1 {
			break
		}
		if sleepErr := sleepWithBackoff(ctx, attempt); sleepErr != nil {
			return false, "", sleepErr
		}
	}

	return false, "", fmt.Errorf(
		"moderation batch %d/%d failed after %d attempts: %w",
		batchNo,
		totalBatches,
		maxModerationResultRetries,
		lastErr,
	)
}

type chatCompletionsRequest struct {
	Model       string        `json:"model"`
	Messages    []chatMessage `json:"messages"`
	Temperature float64       `json:"temperature,omitempty"`
	MaxTokens   int           `json:"max_tokens,omitempty"`
}

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

type contentPart struct {
	Type     string        `json:"type"`
	Text     string        `json:"text,omitempty"`
	ImageURL *imageURLPart `json:"image_url,omitempty"`
}

type imageURLPart struct {
	URL string `json:"url"`
}

type chatCompletionsResponse struct {
	Choices []struct {
		Message struct {
			Content string `json:"content"`
		} `json:"message"`
	} `json:"choices"`
}

func (c *clientImpl) chatCompletion(
	ctx context.Context,
	model string,
	systemPrompt string,
	userPrompt string,
	images []string,
	temperature float64,
	maxTokens int,
) (string, error) {
	if model == "" {
		return "", fmt.Errorf("model is empty")
	}

	cleanImages := normalizeImageURLs(images)

	userParts := []contentPart{
		{Type: "text", Text: userPrompt},
	}
	for _, image := range cleanImages {
		userParts = append(userParts, contentPart{
			Type:     "image_url",
			ImageURL: &imageURLPart{URL: image},
		})
	}

	reqBody := chatCompletionsRequest{
		Model: model,
		Messages: []chatMessage{
			{Role: "system", Content: systemPrompt},
			{Role: "user", Content: userParts},
		},
		Temperature: temperature,
		MaxTokens:   maxTokens,
	}

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

	baseURL := strings.TrimRight(c.cfg.BaseURL, "/")
	endpoint := baseURL + "/v1/chat/completions"
	if strings.HasSuffix(baseURL, "/v1") {
		endpoint = baseURL + "/chat/completions"
	}

	var lastErr error
	for attempt := 0; attempt < maxChatCompletionRetries; attempt++ {
		body, statusCode, err := c.doChatCompletionRequest(ctx, endpoint, data)
		if err != nil {
			lastErr = err
		} else if statusCode >= 400 {
			lastErr = fmt.Errorf("openai error status=%d body=%s", statusCode, string(body))
			if !isRetryableStatusCode(statusCode) {
				return "", lastErr
			}
		} else {
			var parsed chatCompletionsResponse
			if err := json.Unmarshal(body, &parsed); err != nil {
				return "", fmt.Errorf("decode response: %w", err)
			}
			if len(parsed.Choices) == 0 {
				return "", fmt.Errorf("empty response choices")
			}
			return parsed.Choices[0].Message.Content, nil
		}

		if attempt == maxChatCompletionRetries-1 {
			break
		}
		if sleepErr := sleepWithBackoff(ctx, attempt); sleepErr != nil {
			return "", sleepErr
		}
	}

	return "", lastErr
}

func (c *clientImpl) doChatCompletionRequest(ctx context.Context, endpoint string, data []byte) ([]byte, int, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(data))
	if err != nil {
		return nil, 0, fmt.Errorf("create request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.cfg.APIKey)

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, 0, fmt.Errorf("request openai: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, 0, fmt.Errorf("read response: %w", err)
	}
	return body, resp.StatusCode, nil
}

func isRetryableStatusCode(statusCode int) bool {
	if statusCode == http.StatusTooManyRequests {
		return true
	}
	return statusCode >= 500 && statusCode <= 599
}

func sleepWithBackoff(ctx context.Context, attempt int) error {
	delay := initialRetryBackoff * time.Duration(1<<attempt)
	timer := time.NewTimer(delay)
	defer timer.Stop()

	select {
	case <-ctx.Done():
		return fmt.Errorf("request cancelled: %w", ctx.Err())
	case <-timer.C:
		return nil
	}
}

func normalizeImageURLs(images []string) []string {
	clean := make([]string, 0, len(images))
	for _, image := range images {
		trimmed := strings.TrimSpace(image)
		if trimmed == "" {
			continue
		}
		clean = append(clean, trimmed)
	}
	return clean
}

func extractJSONObject(raw string) string {
	text := strings.TrimSpace(raw)
	start := strings.Index(text, "{")
	end := strings.LastIndex(text, "}")
	if start >= 0 && end > start {
		return text[start : end+1]
	}
	return text
}

func (c *clientImpl) maxImagesPerModerationRequest() int {
	// 审核固定单图请求，降低单次payload体积，减少超时风险。
	if c.cfg.ModerationMaxImagesPerRequest <= 0 {
		return defaultMaxImagesPerModerationRequest
	}
	if c.cfg.ModerationMaxImagesPerRequest > 1 {
		return 1
	}
	return c.cfg.ModerationMaxImagesPerRequest
}

func (c *clientImpl) optimizeImagesForModeration(ctx context.Context, images []string) []string {
	if len(images) == 0 {
		return images
	}

	optimized := make([]string, 0, len(images))
	for _, imageURL := range images {
		optimized = append(optimized, c.tryCompressImageForModeration(ctx, imageURL))
	}
	return optimized
}

func (c *clientImpl) tryCompressImageForModeration(ctx context.Context, imageURL string) string {
	parsed, err := url.Parse(imageURL)
	if err != nil || (parsed.Scheme != "http" && parsed.Scheme != "https") {
		return imageURL
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, imageURL, nil)
	if err != nil {
		return imageURL
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return imageURL
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		return imageURL
	}
	if !strings.HasPrefix(strings.ToLower(resp.Header.Get("Content-Type")), "image/") {
		return imageURL
	}

	originBytes, err := io.ReadAll(io.LimitReader(resp.Body, maxDownloadImageBytes))
	if err != nil || len(originBytes) == 0 {
		return imageURL
	}

	srcImg, _, err := image.Decode(bytes.NewReader(originBytes))
	if err != nil {
		return imageURL
	}

	dstImg := resizeIfNeeded(srcImg, maxModerationImageSide)
	var buf bytes.Buffer
	if err := jpeg.Encode(&buf, dstImg, &jpeg.Options{Quality: compressedJPEGQuality}); err != nil {
		return imageURL
	}

	compressed := buf.Bytes()
	if len(compressed) == 0 || len(compressed) > maxCompressedPayloadBytes {
		return imageURL
	}
	// 压缩效果不明显时直接使用原图URL，避免增大请求体。
	if len(compressed) >= int(float64(len(originBytes))*0.95) {
		return imageURL
	}

	return "data:image/jpeg;base64," + base64.StdEncoding.EncodeToString(compressed)
}

func resizeIfNeeded(src image.Image, maxSide int) image.Image {
	bounds := src.Bounds()
	w := bounds.Dx()
	h := bounds.Dy()
	if w <= 0 || h <= 0 || max(w, h) <= maxSide {
		return src
	}

	newW, newH := w, h
	if w >= h {
		newW = maxSide
		newH = int(float64(h) * (float64(maxSide) / float64(w)))
	} else {
		newH = maxSide
		newW = int(float64(w) * (float64(maxSide) / float64(h)))
	}
	if newW < 1 {
		newW = 1
	}
	if newH < 1 {
		newH = 1
	}

	dst := image.NewRGBA(image.Rect(0, 0, newW, newH))
	xdraw.CatmullRom.Scale(dst, dst.Bounds(), src, bounds, xdraw.Over, nil)
	return dst
}