package formula

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

	domai "haixun-backend/internal/model/ai/domain/usecase"
	cfdom "haixun-backend/internal/model/content_formula/domain/usecase"
)

type GenerateInput struct {
	Topic         string
	Brief         string
	PersonaBlock  string
	ResearchNotes string
	Formula       cfdom.FormulaSummary
}

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

func BuildGenerateSystemPrompt() string {
	return strings.TrimSpace(`你是 Threads 文案寫手。依「爆款公式」與「人設」為指定主題寫一篇新貼文。

規則：
- 用台灣繁體中文，符合人設語氣。
- 套用公式結構，但內容必須圍繞使用者主題，不可抄襲範例貼文。
- 只回傳 JSON：text, hook, angle, rationale, structure_notes（繁體中文）。`)
}

func BuildGenerateUserPrompt(in GenerateInput) string {
	var b strings.Builder
	b.WriteString("【主題】\n")
	b.WriteString(strings.TrimSpace(in.Topic))
	if brief := strings.TrimSpace(in.Brief); brief != "" {
		b.WriteString("\n補充：")
		b.WriteString(brief)
	}
	b.WriteString("\n\n【人設】\n")
	b.WriteString(strings.TrimSpace(in.PersonaBlock))
	b.WriteString("\n\n【公式】\n")
	b.WriteString(strings.TrimSpace(in.Formula.Formula))
	if tpl := strings.TrimSpace(in.Formula.PostTemplate); tpl != "" {
		b.WriteString("\n\n【發文模板】\n")
		b.WriteString(tpl)
	}
	if hook := strings.TrimSpace(in.Formula.HookPattern); hook != "" {
		b.WriteString("\n\n【Hook 模式】\n")
		b.WriteString(hook)
	}
	if structure := strings.TrimSpace(in.Formula.Structure); structure != "" {
		b.WriteString("\n\n【結構節奏】\n")
		b.WriteString(structure)
	}
	if len(in.Formula.ReplicationTips) > 0 {
		b.WriteString("\n\n【複製技巧】\n")
		b.WriteString(strings.Join(in.Formula.ReplicationTips, "\n"))
	}
	if len(in.Formula.Avoid) > 0 {
		b.WriteString("\n\n【避免】\n")
		b.WriteString(strings.Join(in.Formula.Avoid, "\n"))
	}
	if notes := strings.TrimSpace(in.ResearchNotes); notes != "" {
		b.WriteString("\n\n【周邊知識參考】\n")
		b.WriteString(notes)
	}
	if src := strings.TrimSpace(in.Formula.SourcePostText); src != "" {
		b.WriteString("\n\n【參考原文（僅學結構，勿抄內容）】\n")
		b.WriteString(src)
	}
	b.WriteString("\n\n請產出一篇可直接發布的 Threads 貼文 JSON。")
	return b.String()
}

func GenerateDraft(ctx context.Context, ai domai.UseCase, req domai.GenerateRequest, in GenerateInput) (*GeneratedDraft, error) {
	temp := 0.75
	req.System = BuildGenerateSystemPrompt()
	req.Messages = []domai.Message{{Role: "user", Content: BuildGenerateUserPrompt(in)}}
	req.Temperature = &temp
	out, err := ai.GenerateText(ctx, req)
	if err != nil {
		return nil, err
	}
	return ParseGeneratedDraft(out.Text)
}

func ParseGeneratedDraft(raw string) (*GeneratedDraft, error) {
	raw = strings.TrimSpace(raw)
	start := strings.Index(raw, "{")
	end := strings.LastIndex(raw, "}")
	if start < 0 || end <= start {
		return nil, fmt.Errorf("generate output missing json object")
	}
	var draft GeneratedDraft
	if err := json.Unmarshal([]byte(raw[start:end+1]), &draft); err != nil {
		return nil, fmt.Errorf("parse generated draft: %w", err)
	}
	draft.Text = strings.TrimSpace(draft.Text)
	if draft.Text == "" {
		return nil, fmt.Errorf("generated draft missing text")
	}
	return &draft, nil
}