package handler

import (
	"crypto/rand"
	"encoding/hex"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// saveUploadFile 保存上传文件（工艺图纸PDF / 巡检照片），返回生成的文件名
func saveUploadFile(r *http.Request, field, dir string) (string, error) {
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return "", err
	}
	file, header, err := r.FormFile(field)
	if err != nil {
		return "", err
	}
	defer file.Close()

	ext := strings.ToLower(filepath.Ext(header.Filename))
	if ext == "" {
		ext = ".bin"
	}
	name := time.Now().Format("20060102150405") + "_" + randHex(6) + ext
	dst, err := os.Create(filepath.Join(dir, name))
	if err != nil {
		return "", err
	}
	defer dst.Close()
	if _, err := io.Copy(dst, file); err != nil {
		return "", err
	}
	return name, nil
}

func randHex(n int) string {
	b := make([]byte, n)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)[:n*2]
}

// serveUploadFile 下发上传目录中的文件（限制为单段文件名，防路径穿越）
func serveUploadFile(w http.ResponseWriter, r *http.Request, dir, name string) {
	name = strings.TrimSpace(filepath.Base(name))
	if name == "" || name == "." || name == ".." || strings.Contains(name, "..") {
		http.Error(w, "非法文件名", http.StatusBadRequest)
		return
	}
	f, err := os.Open(filepath.Join(dir, name))
	if err != nil {
		http.Error(w, "文件不存在", http.StatusNotFound)
		return
	}
	defer f.Close()
	ct := "application/octet-stream"
	switch {
	case strings.HasSuffix(strings.ToLower(name), ".pdf"):
		ct = "application/pdf"
	case strings.HasSuffix(strings.ToLower(name), ".jpg"), strings.HasSuffix(strings.ToLower(name), ".jpeg"):
		ct = "image/jpeg"
	case strings.HasSuffix(strings.ToLower(name), ".png"):
		ct = "image/png"
	}
	w.Header().Set("Content-Type", ct)
	http.ServeContent(w, r, name, time.Time{}, f)
}