// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package webdav provides a WebDAV server implementation.
package webdav

import (
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path"
	"strings"
)

type Handler struct {
	// Prefix is the URL path prefix to strip from WebDAV resource paths.
	Prefix string
	// FileSystem is the virtual file system.
	FileSystem FileSystem
	// Logger is an optional error logger. If non-nil, it will be called
	// for all HTTP requests.
	Logger func(*http.Request, error)
}

func (h *Handler) stripPrefix(p string) (string, int, error) {
	if h.Prefix == "" {
		return p, http.StatusOK, nil
	}
	if r := strings.TrimPrefix(p, h.Prefix); len(r) < len(p) {
		return r, http.StatusOK, nil
	}
	return p, http.StatusNotFound, errPrefixMismatch
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	status, err := http.StatusBadRequest, errUnsupportedMethod
	if h.FileSystem == nil {
		status, err = http.StatusInternalServerError, errNoFileSystem
	} else {
		switch r.Method {
		case "OPTIONS":
			status, err = h.handleOptions(w, r)
		case "GET", "HEAD", "POST":
			status, err = h.handleGetHeadPost(w, r)
		case "DELETE":
			status, err = h.handleDelete(w, r)
		case "PUT":
			status, err = h.handlePut(w, r)
		case "MKCOL":
			status, err = h.handleMkcol(w, r)
		case "COPY", "MOVE":
			status, err = h.handleCopyMove(w, r)
		case "PROPFIND":
			status, err = h.handlePropfind(w, r)
		}
	}

	if status != 0 {
		w.WriteHeader(status)
		if status != http.StatusNoContent {
			w.Write([]byte(http.StatusText(status)))
		}
	}
	if h.Logger != nil {
		h.Logger(r, err)
	}
}

func (h *Handler) handleOptions(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}
	ctx := r.Context()
	allow := "OPTIONS, PUT, MKCOL"
	if fi, err := h.FileSystem.Stat(ctx, reqPath); err == nil {
		if fi.IsDir() {
			allow = "OPTIONS, DELETE, COPY, MOVE, PROPFIND"
		} else {
			allow = "OPTIONS, GET, HEAD, POST, DELETE, COPY, MOVE, PROPFIND, PUT"
		}
	}
	w.Header().Set("Allow", allow)
	// http://www.webdav.org/specs/rfc4918.html#dav.compliance.classes
	w.Header().Set("DAV", "1, 2")
	// http://msdn.microsoft.com/en-au/library/cc250217.aspx
	w.Header().Set("MS-Author-Via", "DAV")
	return 0, nil
}

func (h *Handler) handleGetHeadPost(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}
	ctx := r.Context()
	f, err := h.FileSystem.OpenFile(ctx, reqPath, os.O_RDONLY, 0)
	if err != nil {
		return http.StatusNotFound, err
	}
	defer f.Close()
	fi, err := f.Stat()
	if err != nil {
		return http.StatusNotFound, err
	}
	if fi.IsDir() {
		return http.StatusMethodNotAllowed, nil
	}
	etag, err := findETag(ctx, h.FileSystem, reqPath, fi)
	if err != nil {
		return http.StatusInternalServerError, err
	}
	w.Header().Set("ETag", etag)
	// Let ServeContent determine the Content-Type header.
	http.ServeContent(w, r, reqPath, fi.ModTime(), f)
	return 0, nil
}

func (h *Handler) handleDelete(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}

	ctx := r.Context()

	// TODO: return MultiStatus where appropriate.

	// "godoc os RemoveAll" says that "If the path does not exist, RemoveAll
	// returns nil (no error)." WebDAV semantics are that it should return a
	// "404 Not Found". We therefore have to Stat before we RemoveAll.
	if _, err := h.FileSystem.Stat(ctx, reqPath); err != nil {
		if os.IsNotExist(err) {
			return http.StatusNotFound, err
		}
		return http.StatusMethodNotAllowed, err
	}
	if err := h.FileSystem.RemoveAll(ctx, reqPath); err != nil {
		return http.StatusMethodNotAllowed, err
	}
	return http.StatusNoContent, nil
}

func (h *Handler) handlePut(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}
	ctx := r.Context()

	f, err := h.FileSystem.OpenFile(ctx, reqPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
	if err != nil {
		return http.StatusNotFound, err
	}
	_, copyErr := io.Copy(f, r.Body)
	fi, statErr := f.Stat()
	closeErr := f.Close()
	// TODO(rost): Returning 405 Method Not Allowed might not be appropriate.
	if copyErr != nil {
		return http.StatusMethodNotAllowed, copyErr
	}
	if statErr != nil {
		return http.StatusMethodNotAllowed, statErr
	}
	if closeErr != nil {
		return http.StatusMethodNotAllowed, closeErr
	}
	etag, err := findETag(ctx, h.FileSystem, reqPath, fi)
	if err != nil {
		return http.StatusInternalServerError, err
	}
	w.Header().Set("ETag", etag)
	return http.StatusCreated, nil
}

func (h *Handler) handleMkcol(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}
	ctx := r.Context()

	if r.ContentLength > 0 {
		return http.StatusUnsupportedMediaType, nil
	}
	if err := h.FileSystem.Mkdir(ctx, reqPath, 0777); err != nil {
		if os.IsNotExist(err) {
			return http.StatusConflict, err
		}
		return http.StatusMethodNotAllowed, err
	}
	return http.StatusCreated, nil
}

func (h *Handler) handleCopyMove(w http.ResponseWriter, r *http.Request) (status int, err error) {
	hdr := r.Header.Get("Destination")
	if hdr == "" {
		return http.StatusBadRequest, errInvalidDestination
	}
	u, err := url.Parse(hdr)
	if err != nil {
		return http.StatusBadRequest, errInvalidDestination
	}
	if u.Host != "" && u.Host != r.Host {
		return http.StatusBadGateway, errInvalidDestination
	}

	src, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}

	dst, status, err := h.stripPrefix(u.Path)
	if err != nil {
		return status, err
	}

	if dst == "" {
		return http.StatusBadGateway, errInvalidDestination
	}
	if dst == src {
		return http.StatusForbidden, errDestinationEqualsSource
	}

	ctx := r.Context()

	if r.Method == "COPY" {
		// Section 9.8.3 says that "The COPY method on a collection without a Depth
		// header must act as if a Depth header with value "infinity" was included".
		depth := infiniteDepth
		if hdr := r.Header.Get("Depth"); hdr != "" {
			depth = parseDepth(hdr)
			if depth != 0 && depth != infiniteDepth {
				// Section 9.8.3 says that "A client may submit a Depth header on a
				// COPY on a collection with a value of "0" or "infinity"."
				return http.StatusBadRequest, errInvalidDepth
			}
		}
		return copyFiles(ctx, h.FileSystem, src, dst, r.Header.Get("Overwrite") != "F", depth, 0)
	}

	// Section 9.9.2 says that "The MOVE method on a collection must act as if
	// a "Depth: infinity" header was used on it. A client must not submit a
	// Depth header on a MOVE on a collection with any value but "infinity"."
	if hdr := r.Header.Get("Depth"); hdr != "" {
		if parseDepth(hdr) != infiniteDepth {
			return http.StatusBadRequest, errInvalidDepth
		}
	}
	return moveFiles(ctx, h.FileSystem, src, dst, r.Header.Get("Overwrite") == "T")
}

func (h *Handler) handlePropfind(w http.ResponseWriter, r *http.Request) (status int, err error) {
	reqPath, status, err := h.stripPrefix(r.URL.Path)
	if err != nil {
		return status, err
	}
	ctx := r.Context()
	fi, err := h.FileSystem.Stat(ctx, reqPath)
	if err != nil {
		if os.IsNotExist(err) {
			return http.StatusNotFound, err
		}
		return http.StatusMethodNotAllowed, err
	}
	depth := infiniteDepth
	if hdr := r.Header.Get("Depth"); hdr != "" {
		depth = parseDepth(hdr)
		if depth == invalidDepth {
			return http.StatusBadRequest, errInvalidDepth
		}
	}
	pf, status, err := readPropfind(r.Body)
	if err != nil {
		return status, err
	}

	mw := multistatusWriter{w: w}

	walkFn := func(reqPath string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		var pstats []Propstat
		if pf.Propname != nil {
			pnames, err := propnames(ctx, h.FileSystem, reqPath)
			if err != nil {
				return err
			}
			pstat := Propstat{Status: http.StatusOK}
			for _, xmlname := range pnames {
				pstat.Props = append(pstat.Props, Property{XMLName: xmlname})
			}
			pstats = append(pstats, pstat)
		} else if pf.Allprop != nil {
			pstats, err = allprop(ctx, h.FileSystem, reqPath, pf.Prop)
		} else {
			pstats, err = props(ctx, h.FileSystem, reqPath, pf.Prop)
		}
		if err != nil {
			return err
		}
		href := path.Join(h.Prefix, reqPath)
		if href != "/" && info.IsDir() {
			href += "/"
		}
		return mw.write(makePropstatResponse(href, pstats))
	}

	walkErr := walkFS(ctx, h.FileSystem, depth, reqPath, fi, walkFn)
	closeErr := mw.close()
	if walkErr != nil {
		return http.StatusInternalServerError, walkErr
	}
	if closeErr != nil {
		return http.StatusInternalServerError, closeErr
	}
	return 0, nil
}

func makePropstatResponse(href string, pstats []Propstat) *response {
	resp := response{
		Href:     []string{(&url.URL{Path: href}).EscapedPath()},
		Propstat: make([]propstat, 0, len(pstats)),
	}
	for _, p := range pstats {
		var xmlErr *xmlError
		if p.XMLError != "" {
			xmlErr = &xmlError{InnerXML: []byte(p.XMLError)}
		}
		resp.Propstat = append(resp.Propstat, propstat{
			Status:              fmt.Sprintf("HTTP/1.1 %d %s", p.Status, http.StatusText(p.Status)),
			Prop:                p.Props,
			ResponseDescription: p.ResponseDescription,
			Error:               xmlErr,
		})
	}
	return &resp
}

const (
	infiniteDepth = -1
	invalidDepth  = -2
)

// parseDepth maps the strings "0", "1" and "infinity" to 0, 1 and
// infiniteDepth. Parsing any other string returns invalidDepth.
//
// Different WebDAV methods have further constraints on valid depths:
//	- PROPFIND has no further restrictions, as per section 9.1.
//	- COPY accepts only "0" or "infinity", as per section 9.8.3.
//	- MOVE accepts only "infinity", as per section 9.9.2.
// These constraints are enforced by the handleXxx methods.
func parseDepth(s string) int {
	switch s {
	case "0":
		return 0
	case "1":
		return 1
	case "infinity":
		// forbidden for security
		return invalidDepth
	}
	return invalidDepth
}

var (
	errDestinationEqualsSource = errors.New("webdav: destination equals source")
	errDirectoryNotEmpty       = errors.New("webdav: directory not empty")
	errInvalidDepth            = errors.New("webdav: invalid depth")
	errInvalidDestination      = errors.New("webdav: invalid destination")
	errInvalidPropfind         = errors.New("webdav: invalid propfind")
	errInvalidResponse         = errors.New("webdav: invalid response")
	errNoFileSystem            = errors.New("webdav: no file system")
	errNotADirectory           = errors.New("webdav: not a directory")
	errPrefixMismatch          = errors.New("webdav: prefix mismatch")
	errRecursionTooDeep        = errors.New("webdav: recursion too deep")
	errUnsupportedMethod       = errors.New("webdav: unsupported method")
)