package web

import (
	"context"
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strings"

	"git.arnef.de/arnef/nidus/internal/web/templates"
)

// maxUploadMemory bounds how much of a multipart upload is buffered in
// memory before spilling to a temp file on disk (see multipart.Reader).
const maxUploadMemory = 32 << 20 // 32 MiB

// filesRoot returns the on-disk directory a user's web file browser is
// rooted at. This is intentionally the same directory the WebDAV handler
// (internal/webdav) serves at /files/, so the web UI is just another view
// onto the same files.
func (s *Server) filesRoot(username string) string {
	return filepath.Join(s.cfg.Storage.DataDir, username, "files")
}

// sanitizeRelPath cleans a slash-separated relative path (as received from
// a URL or an uploaded file's name) and rejects any attempt to escape the
// root via ".." segments. The returned path never has a leading slash.
func sanitizeRelPath(p string) (string, error) {
	p = strings.ReplaceAll(p, "\\", "/")
	clean := path.Clean("/" + p)
	clean = strings.TrimPrefix(clean, "/")
	if clean == "." || clean == "" {
		return "", nil
	}
	for _, seg := range strings.Split(clean, "/") {
		if seg == ".." || seg == "" {
			return "", fmt.Errorf("invalid path %q", p)
		}
	}
	return clean, nil
}

// isWithinRoot reports whether p is root itself or a descendant of it,
// guarding against path traversal escaping the user's own file storage.
func isWithinRoot(root, p string) bool {
	rp, err := filepath.Abs(root)
	if err != nil {
		return false
	}
	pp, err := filepath.Abs(p)
	if err != nil {
		return false
	}
	rel, err := filepath.Rel(rp, pp)
	if err != nil {
		return false
	}
	return rel == "." || (!strings.HasPrefix(rel, "..") && rel != "..")
}

// handleFiles serves the /files/{path...} route mounted under /web/: GET
// lists a directory (or downloads a file), POST uploads one or more files
// (optionally nested in folders, via each multipart file's name carrying
// a relative path) into the current directory.
func (s *Server) handleFiles(w http.ResponseWriter, r *http.Request) {
	username := userFromContext(r.Context())
	root := s.filesRoot(username)
	if err := os.MkdirAll(root, 0o755); err != nil {
		s.logger.Error("creating user files dir", "user", username, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	relPath, err := sanitizeRelPath(r.PathValue("path"))
	if err != nil {
		http.Error(w, "invalid path", http.StatusBadRequest)
		return
	}
	fullPath := filepath.Join(root, filepath.FromSlash(relPath))
	if !isWithinRoot(root, fullPath) {
		http.Error(w, "invalid path", http.StatusBadRequest)
		return
	}

	switch r.Method {
	case http.MethodGet:
		s.handleFilesGet(w, r, username, relPath, fullPath)
	case http.MethodPost:
		if r.URL.Query().Has("mkdir") {
			s.handleFilesMkdir(w, r, root, fullPath)
			return
		}
		s.handleFilesUpload(w, r, root, fullPath)
	case http.MethodDelete:
		s.handleFilesDelete(w, r, root, relPath, fullPath)
	default:
		w.Header().Set("Allow", "GET, POST, DELETE")
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

// handleFilesDelete removes the file or folder (recursively) at fullPath,
// mounted at DELETE /files/{path}. The root itself (relPath == "") can
// never be deleted this way.
func (s *Server) handleFilesDelete(w http.ResponseWriter, r *http.Request, root, relPath, fullPath string) {
	if relPath == "" {
		http.Error(w, "cannot delete the root folder", http.StatusBadRequest)
		return
	}
	if _, err := os.Lstat(fullPath); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			http.NotFound(w, r)
			return
		}
		s.logger.Error("stat path to delete", "path", fullPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	if err := os.RemoveAll(fullPath); err != nil {
		s.logger.Error("deleting path", "path", fullPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
	fmt.Fprintf(w, "deleted %q", filepath.Base(fullPath))
}

// handleFilesMkdir creates a new subdirectory named by the "name" form
// field directly inside fullPath (the current directory), mounted at
// POST /files/{path}?mkdir=1.
func (s *Server) handleFilesMkdir(w http.ResponseWriter, r *http.Request, root, fullPath string) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "invalid form", http.StatusBadRequest)
		return
	}
	name := strings.TrimSpace(r.PostForm.Get("name"))
	if !resourceNameRe.MatchString(name) {
		http.Error(w, "name must be 1-64 letters, digits, dots, '-' or '_'", http.StatusBadRequest)
		return
	}

	destPath := filepath.Join(fullPath, name)
	if !isWithinRoot(root, destPath) {
		http.Error(w, "invalid path", http.StatusBadRequest)
		return
	}

	if _, err := os.Stat(destPath); err == nil {
		http.Error(w, "a file or folder with that name already exists", http.StatusConflict)
		return
	} else if !errors.Is(err, os.ErrNotExist) {
		s.logger.Error("stat new folder", "path", destPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	if err := os.Mkdir(destPath, 0o755); err != nil {
		s.logger.Error("creating folder", "path", destPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
	fmt.Fprintf(w, "created folder %q", name)
}

func (s *Server) handleFilesGet(w http.ResponseWriter, r *http.Request, username, relPath, fullPath string) {
	info, err := os.Stat(fullPath)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			http.NotFound(w, r)
			return
		}
		s.logger.Error("stat file", "path", fullPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	if !info.IsDir() {
		f, err := os.Open(fullPath)
		if err != nil {
			s.logger.Error("opening file", "path", fullPath, "error", err)
			http.Error(w, "internal error", http.StatusInternalServerError)
			return
		}
		defer f.Close()
		// Force a download only when explicitly requested (the "Download"
		// link/button); otherwise serve "inline" so the browser can render
		// natively-supported types (video, audio, images, PDF, text) right
		// in the tab instead of always saving to disk.
		disposition := "inline"
		if r.URL.Query().Has("download") {
			disposition = "attachment"
		}
		w.Header().Set("Content-Disposition", disposition+`; filename="`+filepath.Base(fullPath)+`"`)
		http.ServeContent(w, r, info.Name(), info.ModTime(), f)
		return
	}

	dirEntries, err := os.ReadDir(fullPath)
	if err != nil {
		s.logger.Error("reading dir", "path", fullPath, "error", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	// os.ReadDir already returns entries sorted by filename, so filtering
	// into two passes keeps each group (directories, then files)
	// alphabetically sorted while grouping directories first.
	var dirs, files []templates.FileEntry
	for _, de := range dirEntries {
		entryInfo, err := de.Info()
		if err != nil {
			continue
		}
		childRel := path.Join(relPath, de.Name())
		entry := templates.FileEntry{
			Name:    de.Name(),
			IsDir:   de.IsDir(),
			ModTime: entryInfo.ModTime().Format("2006-01-02 15:04"),
			RelPath: childRel,
		}
		if de.IsDir() {
			dirs = append(dirs, entry)
		} else {
			entry.Size = humanSize(entryInfo.Size())
			files = append(files, entry)
		}
	}
	entries := append(dirs, files...)

	var breadcrumbs []templates.Breadcrumb
	if relPath != "" {
		segs := strings.Split(relPath, "/")
		for i, seg := range segs {
			breadcrumbs = append(breadcrumbs, templates.Breadcrumb{
				Name: seg,
				Path: strings.Join(segs[:i+1], "/"),
			})
		}
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	_ = templates.FilesPage(username, breadcrumbs, entries, relPath).Render(context.Background(), w)
}

func (s *Server) handleFilesUpload(w http.ResponseWriter, r *http.Request, root, fullPath string) {
	info, err := os.Stat(fullPath)
	if err != nil || !info.IsDir() {
		http.Error(w, "upload target is not a directory", http.StatusBadRequest)
		return
	}

	if err := r.ParseMultipartForm(maxUploadMemory); err != nil {
		http.Error(w, "invalid upload", http.StatusBadRequest)
		return
	}
	if r.MultipartForm == nil {
		http.Error(w, "no files", http.StatusBadRequest)
		return
	}
	defer r.MultipartForm.RemoveAll()

	fileHeaders := r.MultipartForm.File["files"]
	if len(fileHeaders) == 0 {
		http.Error(w, "no files", http.StatusBadRequest)
		return
	}
	// The stdlib strips any directory components from fh.Filename (per RFC
	// 7578 §4.2), so folder uploads/drops send each file's relative path
	// separately in a parallel "paths" field (same order as "files") for
	// the server to recreate the directory structure.
	relPaths := r.MultipartForm.Value["paths"]

	for i, fh := range fileHeaders {
		relFile := fh.Filename
		if i < len(relPaths) && relPaths[i] != "" {
			relFile = relPaths[i]
		}
		relFile, err := sanitizeRelPath(relFile)
		if err != nil || relFile == "" {
			s.logger.Warn("skipping upload with invalid filename", "filename", fh.Filename)
			continue
		}
		destPath := filepath.Join(fullPath, filepath.FromSlash(relFile))
		if !isWithinRoot(root, destPath) {
			s.logger.Warn("skipping upload escaping root", "filename", fh.Filename)
			continue
		}
		if err := s.saveUploadedFile(fh, destPath); err != nil {
			s.logger.Error("saving uploaded file", "path", destPath, "error", err)
			http.Error(w, "failed to save "+fh.Filename, http.StatusInternalServerError)
			return
		}
	}

	w.WriteHeader(http.StatusOK)
	fmt.Fprintf(w, "uploaded %d file(s)", len(fileHeaders))
}

func (s *Server) saveUploadedFile(fh *multipart.FileHeader, destPath string) error {
	if err := os.MkdirAll(filepath.Dir(destPath), 0o755); err != nil {
		return err
	}
	src, err := fh.Open()
	if err != nil {
		return err
	}
	defer src.Close()

	dst, err := os.Create(destPath)
	if err != nil {
		return err
	}
	defer dst.Close()

	_, err = io.Copy(dst, src)
	return err
}

func humanSize(size int64) string {
	const unit = 1024
	if size < unit {
		return fmt.Sprintf("%d B", size)
	}
	div, exp := int64(unit), 0
	for n := size / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %ciB", float64(size)/float64(div), "KMGTPE"[exp])
}