package ai

import (
	"context"
	"fmt"
	"strings"
)

// stubProvider 离线占位实现:未配置真实模型时的兜底,内容为字符串模板。
type stubProvider struct{}

func (stubProvider) Name() string { return "stub" }

func (stubProvider) Complete(_ context.Context, req ChatReq) (ChatRes, error) {
	return chatStub(req), nil
}

func chatStub(req ChatReq) ChatRes {
	driver := req.Driver
	if driver == "" {
		driver = "mysql"
	}
	db := req.Database
	if db == "" {
		db = "your_db"
	}
	sql := strings.TrimSpace(req.SQL)
	prompt := strings.TrimSpace(req.Prompt)

	switch strings.ToLower(req.Action) {
	case "ask":
		if prompt == "" {
			prompt = "当前问题"
		}
		return ChatRes{Content: fmt.Sprintf("离线体验无法回答「%s」。请在设置 → 大模型配置 AI 供应商；如需试写 SQL，可切换为「生成 SQL」。", prompt)}
	case "generate":
		q := prompt
		if q == "" {
			q = "示例查询"
		}
		gen := fmt.Sprintf("-- 根据描述生成（%s / %s）\n-- 需求: %s\nSELECT *\nFROM `%s`.some_table\nWHERE 1=1\nLIMIT 100;", driver, db, q, db)
		return ChatRes{
			Content: fmt.Sprintf("已根据「%s」生成 SQL（stub，可替换为真实模型）。\n\n```sql\n%s\n```", q, gen),
			SQL:     gen,
		}
	case "explain":
		if sql == "" {
			sql = "SELECT 1"
		}
		return ChatRes{Content: fmt.Sprintf("## 解释 SQL\n\n```sql\n%s\n```\n\n- 这是一条在 **%s** 上执行的查询。\n- 建议检查 WHERE 条件是否走索引，避免 `SELECT *` 拉取过大结果集。\n- （stub 回复）", sql, driver)}
	case "optimize":
		opt := sql
		if opt == "" {
			opt = "SELECT id, name FROM users WHERE status = 1 LIMIT 100;"
		} else if strings.Contains(strings.ToUpper(opt), "SELECT *") {
			opt = strings.Replace(opt, "*", "id /* TODO: 显式列 */", 1)
		}
		opt = strings.TrimSpace(opt)
		if !strings.Contains(strings.ToUpper(opt), "LIMIT") {
			opt = opt + "\nLIMIT 100;"
		}
		return ChatRes{
			Content: fmt.Sprintf("## 优化建议\n\n1. 避免不必要的全表扫描\n2. 显式列出列名\n3. 加合理 LIMIT\n\n```sql\n%s\n```", opt),
			SQL:     opt,
		}
	case "fix":
		fixed := sql
		if fixed == "" {
			fixed = "SELECT 1 AS ok;"
		}
		msg := req.Error
		if msg == "" {
			msg = "未知错误"
		}
		return ChatRes{
			Content: fmt.Sprintf("## 修复错误\n\n原错误：`%s`\n\n尝试修正后的 SQL：\n\n```sql\n%s\n```\n\n（stub：请结合真实报错继续调整）", msg, fixed),
			SQL:     fixed,
		}
	case "dialect":
		out := sql
		if out == "" {
			out = "SELECT * FROM dual"
		}
		out = strings.ReplaceAll(out, "`", "\"")
		return ChatRes{
			Content: fmt.Sprintf("## 方言转换 → PostgreSQL 风格（示例）\n\n```sql\n%s\n```", out),
			SQL:     out,
		}
	case "sample":
		sample := fmt.Sprintf("SELECT id, name, created_at\nFROM `%s`.users\nORDER BY id DESC\nLIMIT 20;", db)
		return ChatRes{
			Content: fmt.Sprintf("## 样例 SQL（%s）\n\n```sql\n%s\n```", driver, sample),
			SQL:     sample,
		}
	default:
		return ChatRes{Content: "未知 AI 动作。可用：ask / generate / explain / optimize / fix / dialect / sample"}
	}
}