package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
)

// -----------------------------------------------------------------------------
// 路由处理器
// -----------------------------------------------------------------------------

type fileResponse struct {
	Filename   string    `json:"filename"`
	URL        string    `json:"url"`
	Size       int64     `json:"size"`
	UploadedAt time.Time `json:"uploaded_at"`
	ExpiresAt  time.Time `json:"expires_at"`
}

// validateFilename 从 URL/JSON 参数提取并校验 filename.
// 返回 (sanitized, true) 表示安全可访问, 否则返回 ("", false).
// 规则与 downloadHandler 原内联逻辑一致: filepath.Base + 拒绝 "" / "." / ".."
// + 拒绝含 "/" "\" NUL 的名字 (后者同时兜住 Windows 路径).
func validateFilename(raw string) (string, bool) {
	name := filepath.Base(raw)
	if name == "" || name == "." || name == ".." ||
		strings.ContainsAny(name, "/\\\x00") {
		return "", false
	}
	return name, true
}

func uploadHandler(c *gin.Context) {
	f, err := c.FormFile(fieldName)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "missing form field 'file'"})
		audit(c, "upload", gin.H{"file": "", "result": "missing_form_field"})
		return
	}
	// 早 reject: 防止 NUL 字节 + 超长文件名打爆 Stat/Save
	if strings.ContainsRune(f.Filename, 0) {
		c.JSON(http.StatusBadRequest, gin.H{"error": "filename contains null byte"})
		audit(c, "upload", gin.H{"file": f.Filename, "result": "null_byte"})
		return
	}
	// Linux/macOS 路径分量 NAME_MAX = 255 字节
	if len(f.Filename) > 200 {
		c.JSON(http.StatusBadRequest, gin.H{"error": "filename too long (max 200 bytes)"})
		audit(c, "upload", gin.H{"file": f.Filename, "result": "filename_too_long"})
		return
	}

	if err := os.MkdirAll(*uploadDir, 0o755); err != nil {
		log.Printf("[upload] mkdir failed: %v", err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
		audit(c, "upload", gin.H{"file": f.Filename, "result": "mkdir_failed"})
		return
	}

	// 配额检查 (单文件能塞下 + 不会超总配额)
	if *quota > 0 && f.Size > quotaRemaining() {
		used, cap_ := quotaSnapshot()
		c.JSON(http.StatusInsufficientStorage, gin.H{
			"error": fmt.Sprintf("quota exceeded: %s used / %s cap, file size %s",
				formatSize(used), formatSize(cap_), formatSize(f.Size)),
		})
		audit(c, "upload", gin.H{
			"file":   f.Filename,
			"size":   f.Size,
			"result": "quota_exceeded",
		})
		return
	}

	name := uniqueFilename(*uploadDir, f.Filename)
	dst := filepath.Join(*uploadDir, name)
	if err := c.SaveUploadedFile(f, dst); err != nil {
		log.Printf("[upload] save failed: %v", err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
		audit(c, "upload", gin.H{"file": f.Filename, "result": "save_failed"})
		return
	}

	// 实际写入的字节数可能与 f.Size 略有差异 (SaveUploadedFile 内部处理), 用 stat 拿真实值
	var written int64 = f.Size
	if info, statErr := os.Stat(dst); statErr == nil {
		written = info.Size()
	}
	// 原子预留配额, 兜住并发下 pre-save 检查放行的多个请求
	if !quotaReserve(written) {
		_ = os.Remove(dst)
		used, cap_ := quotaSnapshot()
		c.JSON(http.StatusInsufficientStorage, gin.H{
			"error": fmt.Sprintf("quota exceeded: %s used / %s cap, file size %s",
				formatSize(used), formatSize(cap_), formatSize(written)),
		})
		audit(c, "upload", gin.H{
			"file":   name,
			"size":   written,
			"result": "quota_exceeded",
		})
		return
	}

	now := time.Now()
	_ = os.Chtimes(dst, now, now)

	c.JSON(http.StatusOK, fileResponse{
		Filename:   name,
		URL:        "/download/" + name,
		Size:       f.Size,
		UploadedAt: now,
		ExpiresAt:  now.Add(*fileTTL),
	})
	audit(c, "upload", gin.H{
		"file":   name, // 落盘后的名字 (可能加了 (1) 后缀)
		"orig":   f.Filename,
		"size":   f.Size,
		"result": "ok",
	})
}

// uniqueFilename 把 original 清洗后, 在 dir 中找一个不存在的名字.
// 规则: 原名 → 原名 (1) → 原名 (2) → ...
// 例:  report.pdf       -> report.pdf
//
//	report.pdf (1)   -> report.pdf (1)
//	.gitignore       -> .gitignore
//	.gitignore (1)   -> .gitignore (1)
func uniqueFilename(dir, original string) string {
	// 1. 剥离路径组件, 防穿越
	base := filepath.Base(original)
	if base == "" || base == "." || base == ".." {
		base = "file"
	}

	// 2. 拆分 stem 和 ext, 处理 .gitignore 这类隐藏文件
	ext := filepath.Ext(base)
	stem := strings.TrimSuffix(base, ext)
	if stem == "" {
		// 整个名字都是扩展名 (如 .gitignore), 把整个当 stem
		ext = ""
		stem = base
	}

	// 3. 依次尝试 base, base (1), base (2), ...
	// 用 O_CREATE|O_EXCL 原子占位, 解决 TOCTOU 竞态 (20 路并发同名上传必须各自拿到不同名字)
	// 占位的 0 字节 placeholder 会在 SaveUploadedFile 时被覆盖
	for i := range 10000 {
		var candidate string
		if i == 0 {
			candidate = base
		} else {
			candidate = fmt.Sprintf("%s (%d)%s", stem, i, ext)
		}
		p := filepath.Join(dir, candidate)
		f, err := os.OpenFile(p, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
		if err == nil {
			f.Close()
			return candidate
		}
		if !os.IsExist(err) {
			// 非 "已存在" 错误 (权限/磁盘满等), 兜底用时间戳
			log.Printf("[uniqueFilename] open err=%v, fallback to ts", err)
			return fmt.Sprintf("%s (%d)%s", stem, time.Now().UnixNano(), ext)
		}
	}
	return fmt.Sprintf("%s (%d)%s", stem, time.Now().UnixNano(), ext)
}

func downloadHandler(c *gin.Context) {
	raw := c.Param("filename")
	name, ok := validateFilename(raw)
	if !ok {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid filename"})
		audit(c, "download", gin.H{"file": raw, "result": "invalid_filename"})
		return
	}
	p := filepath.Join(*uploadDir, name)

	info, err := os.Stat(p)
	if os.IsNotExist(err) {
		c.JSON(http.StatusNotFound, gin.H{"error": "file not found or expired"})
		audit(c, "download", gin.H{"file": name, "result": "not_found"})
		return
	}
	if err != nil {
		log.Printf("[download] stat failed: %v", err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
		audit(c, "download", gin.H{"file": name, "result": "stat_failed"})
		return
	}
	if info.IsDir() {
		c.JSON(http.StatusBadRequest, gin.H{"error": "not a file"})
		audit(c, "download", gin.H{"file": name, "result": "is_dir"})
		return
	}

	// 强制下载 + 防 XSS (浏览器不会按扩展名/Content-Type 渲染)
	c.Header("Content-Disposition", `attachment; filename="`+name+`"`)
	c.Header("X-Content-Type-Options", "nosniff")

	// 下载即续期
	now := time.Now()
	_ = os.Chtimes(p, now, now)

	c.File(p)
	audit(c, "download", gin.H{
		"file":   name,
		"size":   info.Size(),
		"result": "ok",
	})
}

type fileInfo struct {
	Filename  string    `json:"filename"`
	URL       string    `json:"url"`
	Size      int64     `json:"size"`
	ModTime   time.Time `json:"mod_time"`
	ExpiresAt time.Time `json:"expires_at"`
}

func listHandler(c *gin.Context) {
	entries, err := os.ReadDir(*uploadDir)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}
	files := make([]fileInfo, 0, len(entries))
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}
		files = append(files, fileInfo{
			Filename:  e.Name(),
			URL:       "/download/" + e.Name(),
			Size:      info.Size(),
			ModTime:   info.ModTime(),
			ExpiresAt: info.ModTime().Add(*fileTTL),
		})
	}
	c.JSON(http.StatusOK, gin.H{
		"count": len(files),
		"now":   time.Now(),
		"ttl":   fileTTL.String(),
		"quota": func() gin.H {
			used, cap_ := quotaSnapshot()
			return gin.H{
				"used":     used,
				"cap":      cap_,
				"used_str": formatSize(used),
				"cap_str":  formatSize(cap_),
			}
		}(),
		"files": files,
	})
}

func deleteHandler(c *gin.Context) {
	raw := c.Param("filename")
	name, ok := validateFilename(raw)
	if !ok {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid filename"})
		audit(c, "delete", gin.H{"file": raw, "result": "invalid_filename"})
		return
	}
	p := filepath.Join(*uploadDir, name)

	info, err := os.Stat(p)
	if os.IsNotExist(err) {
		c.JSON(http.StatusNotFound, gin.H{"error": "file not found or already deleted"})
		audit(c, "delete", gin.H{"file": name, "result": "not_found"})
		return
	}
	if err != nil {
		log.Printf("[delete] stat failed: %v", err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
		audit(c, "delete", gin.H{"file": name, "result": "stat_failed"})
		return
	}
	if info.IsDir() {
		c.JSON(http.StatusBadRequest, gin.H{"error": "not a file"})
		audit(c, "delete", gin.H{"file": name, "result": "is_dir"})
		return
	}

	if err := os.Remove(p); err != nil {
		log.Printf("[delete] remove failed: %v", err)
		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
		audit(c, "delete", gin.H{"file": name, "result": "remove_failed"})
		return
	}
	quotaSub(info.Size())
	c.JSON(http.StatusOK, gin.H{"deleted": name})
	audit(c, "delete", gin.H{"file": name, "size": info.Size(), "result": "ok"})
}