package viral

import (
	"encoding/json"
	"fmt"
	"regexp"
	"strings"

	"haixun-backend/internal/library/threadspost"
)

var codeFenceRE = regexp.MustCompile("(?s)```(?:json)?\\s*([\\s\\S]*?)```")

type ReplicateInput struct {
	TopicLabel        string
	TopicBrief        string
	Persona           string
	StyleProfile      string
	OriginalText      string
	AuthorName        string
	StructureAnalysis string
}

type ReplicateResult struct {
	Angle          string `json:"angle"`
	Hook           string `json:"hook"`
	Text           string `json:"text"`
	Rationale      string `json:"rationale"`
	StructureNotes string `json:"structureNotes"`
}

func BuildSystemPrompt() string {
	return strings.TrimSpace(`你是 Threads 爆款複製策略師。根據參考爆文，為使用者撰寫「同結構、同節奏、但完全原創」的貼文。

規則：
- 複製的是爆款公式（hook 手法、情緒節奏），不是抄襲原文
- 文筆必須像創作者本人，套用其 8D 風格策略
- text 主文 ≤ 500 字（Threads API 硬上限，含 #話題標籤）
- 爆款互動最佳 80～220 字：前 1～2 行強 hook，口語精簡；超過 300 字互動通常下降
- 只回傳一個 JSON 物件，欄位：angle, hook, text, rationale, structureNotes`)
}

func BuildUserPrompt(input ReplicateInput) string {
	var b strings.Builder
	b.WriteString("主題：")
	b.WriteString(strings.TrimSpace(input.TopicLabel))
	b.WriteString("\n")
	if brief := strings.TrimSpace(input.TopicBrief); brief != "" {
		b.WriteString("Brief：")
		b.WriteString(brief)
		b.WriteString("\n")
	}
	if persona := strings.TrimSpace(input.Persona); persona != "" {
		b.WriteString("\n人設與語氣：\n")
		b.WriteString(persona)
		b.WriteString("\n")
	}
	if style := strings.TrimSpace(input.StyleProfile); style != "" {
		b.WriteString("\n8D 風格策略：\n")
		b.WriteString(style)
		b.WriteString("\n")
	}
	author := strings.TrimSpace(input.AuthorName)
	if author == "" {
		author = "匿名"
	}
	if analysis := strings.TrimSpace(input.StructureAnalysis); analysis != "" {
		b.WriteString("\n爆款結構分析（仿寫時套用）：\n")
		b.WriteString(analysis)
		b.WriteString("\n")
	}
	b.WriteString("\n原文參考（@")
	b.WriteString(author)
	b.WriteString("，只學結構不抄內容）：\n")
	b.WriteString(strings.TrimSpace(input.OriginalText))
	b.WriteString("\n\n請產出一篇可發布的複製版貼文 JSON。")
	return b.String()
}

func ParseReplicateOutput(raw string) (ReplicateResult, error) {
	payload, err := extractJSONObject(raw)
	if err != nil {
		return ReplicateResult{}, err
	}
	var out ReplicateResult
	if err := json.Unmarshal(payload, &out); err != nil {
		return ReplicateResult{}, fmt.Errorf("parse viral replica json: %w", err)
	}
	out.Text = trimText(out.Text)
	if out.Text == "" {
		return ReplicateResult{}, fmt.Errorf("replica text missing")
	}
	out.Angle = strings.TrimSpace(out.Angle)
	out.Hook = strings.TrimSpace(out.Hook)
	out.Rationale = strings.TrimSpace(out.Rationale)
	out.StructureNotes = strings.TrimSpace(out.StructureNotes)
	return out, nil
}

func trimText(text string) string {
	text = strings.TrimSpace(text)
	runes := []rune(text)
	if len(runes) > threadspost.MaxPublishRunes {
		return string(runes[:threadspost.MaxPublishRunes])
	}
	return text
}

func extractJSONObject(raw string) ([]byte, error) {
	raw = strings.TrimSpace(raw)
	if m := codeFenceRE.FindStringSubmatch(raw); len(m) == 2 {
		raw = strings.TrimSpace(m[1])
	}
	start := strings.Index(raw, "{")
	end := strings.LastIndex(raw, "}")
	if start < 0 || end <= start {
		return nil, fmt.Errorf("replica output missing json object")
	}
	return []byte(raw[start : end+1]), nil
}