package app

import (
	"context"
	"fmt"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/geo-platform/tenant-api/internal/shared/auth"
	"github.com/geo-platform/tenant-api/internal/shared/llm"
	"github.com/geo-platform/tenant-api/internal/shared/response"
)

const (
	maxOptimizeInstructionChars   = 800
	maxOptimizeMarkdownContextLen = 6000
	minOptimizeSelectedTextRunes  = 2
	optimizeSelectionTimeout      = 90 * time.Second
)

type ArticleSelectionOptimizeRequest struct {
	Title           string `json:"title"`
	MarkdownContent string `json:"markdown_content"`
	SelectedText    string `json:"selected_text"`
	Instruction     string `json:"instruction"`
}

type ArticleSelectionOptimizeResult struct {
	Content string `json:"content"`
	Model   string `json:"model"`
}

type ArticleSelectionOptimizeService struct {
	pool                *pgxpool.Pool
	llm                 llm.Client
	defaultMaxOutTokens int64
}

func NewArticleSelectionOptimizeService(
	pool *pgxpool.Pool,
	llmClient llm.Client,
	defaultMaxOutTokens int64,
) *ArticleSelectionOptimizeService {
	return &ArticleSelectionOptimizeService{
		pool:                pool,
		llm:                 llmClient,
		defaultMaxOutTokens: defaultMaxOutTokens,
	}
}

func (s *ArticleSelectionOptimizeService) ValidateRequest(
	ctx context.Context,
	articleID int64,
	req ArticleSelectionOptimizeRequest,
) error {
	if err := s.validateLLM(); err != nil {
		return err
	}
	if err := validateOptimizeSelectionPayload(req); err != nil {
		return err
	}

	actor := auth.MustActor(ctx)
	return s.ensureArticleEditable(ctx, articleID, actor.TenantID)
}

func (s *ArticleSelectionOptimizeService) OptimizeSelection(
	ctx context.Context,
	req ArticleSelectionOptimizeRequest,
	onDelta func(string),
) (*ArticleSelectionOptimizeResult, error) {
	result, err := s.llm.Generate(
		ctx,
		llm.GenerateRequest{
			Prompt:          buildOptimizeSelectionPrompt(req),
			Timeout:         optimizeSelectionTimeout,
			MaxOutputTokens: s.resolveMaxOutputTokens(req.SelectedText),
		},
		onDelta,
	)
	if err != nil {
		return nil, response.ErrInternal(50019, "article_selection_optimize_failed", err.Error())
	}

	content := strings.TrimSpace(result.Content)
	if content == "" {
		return nil, response.ErrInternal(50019, "article_selection_optimize_failed", "optimized content is empty")
	}

	return &ArticleSelectionOptimizeResult{
		Content: content,
		Model:   result.Model,
	}, nil
}

func (s *ArticleSelectionOptimizeService) validateLLM() error {
	if err := s.llm.Validate(); err != nil {
		return response.ErrServiceUnavailable(50304, "llm_unavailable", "llm provider is not configured")
	}
	return nil
}

func (s *ArticleSelectionOptimizeService) ensureArticleEditable(
	ctx context.Context,
	articleID int64,
	tenantID int64,
) error {
	var generateStatus string
	err := s.pool.QueryRow(
		ctx,
		`SELECT generate_status
		FROM articles
		WHERE id = $1 AND tenant_id = $2 AND deleted_at IS NULL`,
		articleID,
		tenantID,
	).Scan(&generateStatus)
	if err != nil {
		if err == pgx.ErrNoRows {
			return response.ErrNotFound(40411, "article_not_found", "article not found")
		}
		return response.ErrInternal(50020, "article_lookup_failed", "failed to query article state")
	}

	if generateStatus != "completed" {
		return response.ErrConflict(40913, "article_not_optimizable", "only completed articles can be optimized")
	}

	return nil
}

func (s *ArticleSelectionOptimizeService) resolveMaxOutputTokens(selectedText string) int64 {
	limit := s.defaultMaxOutTokens
	if limit <= 0 {
		limit = 1200
	}

	estimated := int64(utf8.RuneCountInString(strings.TrimSpace(selectedText))*4 + 240)
	if estimated < 256 {
		estimated = 256
	}
	if estimated > limit {
		return limit
	}
	return estimated
}

func validateOptimizeSelectionPayload(req ArticleSelectionOptimizeRequest) error {
	selectedText := strings.TrimSpace(req.SelectedText)
	if utf8.RuneCountInString(selectedText) < minOptimizeSelectedTextRunes {
		return response.ErrBadRequest(40019, "selected_text_required", "selected_text is required")
	}

	instruction := strings.TrimSpace(req.Instruction)
	if instruction == "" {
		return response.ErrBadRequest(40020, "optimize_instruction_required", "instruction is required")
	}

	if len([]rune(instruction)) > maxOptimizeInstructionChars {
		return response.ErrBadRequest(
			40021,
			"optimize_instruction_too_long",
			fmt.Sprintf("instruction cannot exceed %d characters", maxOptimizeInstructionChars),
		)
	}

	return nil
}

func buildOptimizeSelectionPrompt(req ArticleSelectionOptimizeRequest) string {
	title := sanitizeOptimizePromptSection(req.Title, 300)
	markdownContent := sanitizeOptimizePromptSection(req.MarkdownContent, maxOptimizeMarkdownContextLen)
	selectedText := sanitizeOptimizePromptSection(req.SelectedText, 2000)
	instruction := sanitizeOptimizePromptSection(req.Instruction, maxOptimizeInstructionChars)

	var builder strings.Builder
	builder.WriteString("你是一名资深中文内容编辑。请根据用户要求，优化一段文章选中文本。\n")
	builder.WriteString("请严格遵守以下规则：\n")
	builder.WriteString("1. 只输出优化后的正文内容，不要输出解释、标题、引号、前后缀说明或 Markdown 代码块。\n")
	builder.WriteString("2. 保持原文事实、结论、人物、时间、数字和专有名词准确，不得编造信息。\n")
	builder.WriteString("3. 优先遵循用户给出的优化要求，同时让表达与整篇文章风格保持自然一致。\n")
	builder.WriteString("4. 如果原文是一段话，默认输出一段话；除非用户明确要求改成其他结构。\n")
	builder.WriteString("5. 不要复述“以下是优化结果”等说明性文字。\n")

	if title != "" {
		builder.WriteString("\n文章标题：\n")
		builder.WriteString(title)
		builder.WriteString("\n")
	}

	if markdownContent != "" {
		builder.WriteString("\n文章草稿（用于参考语气和上下文，可能不是最终定稿）：\n")
		builder.WriteString(markdownContent)
		builder.WriteString("\n")
	}

	builder.WriteString("\n待优化原文：\n")
	builder.WriteString(selectedText)
	builder.WriteString("\n")

	builder.WriteString("\n用户的优化要求：\n")
	builder.WriteString(instruction)
	builder.WriteString("\n")

	builder.WriteString("\n现在请直接输出优化后的文本。")
	return builder.String()
}

func sanitizeOptimizePromptSection(value string, maxRunes int) string {
	normalized := strings.TrimSpace(value)
	if normalized == "" {
		return ""
	}

	normalized = strings.ReplaceAll(normalized, "\u0000", "")
	normalized = strings.ReplaceAll(normalized, "\r\n", "\n")
	normalized = strings.ReplaceAll(normalized, "\r", "\n")

	runes := []rune(normalized)
	if maxRunes > 0 && len(runes) > maxRunes {
		return strings.TrimSpace(string(runes[:maxRunes])) + "\n...[内容已截断]"
	}

	return normalized
}