package webdav

import (
	"context"
	"encoding/xml"
	"io"
	"net/http"
	"os"
	"strconv"
	"strings"

	"github.com/emersion/go-webdav/internal"
)

// FileSystem is a WebDAV server backend.
type FileSystem interface {
	Open(ctx context.Context, name string) (io.ReadCloser, error)
	Stat(ctx context.Context, name string) (*FileInfo, error)
	ReadDir(ctx context.Context, name string, recursive bool) ([]FileInfo, error)
	Create(ctx context.Context, name string) (io.WriteCloser, error)
	RemoveAll(ctx context.Context, name string) error
	Mkdir(ctx context.Context, name string) error
	Copy(ctx context.Context, name, dest string, recursive, overwrite bool) (created bool, err error)
	MoveAll(ctx context.Context, name, dest string, overwrite bool) (created bool, err error)
}

// Handler handles WebDAV HTTP requests. It can be used to create a WebDAV
// server.
type Handler struct {
	FileSystem FileSystem
}

// ServeHTTP implements http.Handler.
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if h.FileSystem == nil {
		http.Error(w, "webdav: no filesystem available", http.StatusInternalServerError)
		return
	}

	b := backend{h.FileSystem}
	hh := internal.Handler{&b}
	hh.ServeHTTP(w, r)
}

// NewHTTPError creates a new error that is associated with an HTTP status code
// and optionally an error that lead to it. Backends can use this functions to
// return errors that convey some semantics (e.g. 404 not found, 403 access
// denied, etc) while also providing an (optional) arbitrary error context
// (intended for humans).
func NewHTTPError(statusCode int, cause error) error {
	return &internal.HTTPError{Code: statusCode, Err: cause}
}

type backend struct {
	FileSystem FileSystem
}

func (b *backend) Options(r *http.Request) (caps []string, allow []string, err error) {
	fi, err := b.FileSystem.Stat(r.Context(), r.URL.Path)
	if os.IsNotExist(err) {
		return nil, []string{http.MethodOptions, http.MethodPut, "MKCOL"}, nil
	} else if err != nil {
		return nil, nil, err
	}

	allow = []string{
		http.MethodOptions,
		http.MethodDelete,
		"PROPFIND",
		"COPY",
		"MOVE",
	}

	if !fi.IsDir {
		allow = append(allow, http.MethodHead, http.MethodGet, http.MethodPut)
	}

	return nil, allow, nil
}

func (b *backend) HeadGet(w http.ResponseWriter, r *http.Request) error {
	fi, err := b.FileSystem.Stat(r.Context(), r.URL.Path)
	if os.IsNotExist(err) {
		return &internal.HTTPError{Code: http.StatusNotFound, Err: err}
	} else if err != nil {
		return err
	}
	if fi.IsDir {
		return &internal.HTTPError{Code: http.StatusMethodNotAllowed}
	}

	f, err := b.FileSystem.Open(r.Context(), r.URL.Path)
	if err != nil {
		return err
	}
	defer f.Close()

	w.Header().Set("Content-Length", strconv.FormatInt(fi.Size, 10))
	if fi.MIMEType != "" {
		w.Header().Set("Content-Type", fi.MIMEType)
	}
	if !fi.ModTime.IsZero() {
		w.Header().Set("Last-Modified", fi.ModTime.UTC().Format(http.TimeFormat))
	}
	if fi.ETag != "" {
		w.Header().Set("ETag", internal.ETag(fi.ETag).String())
	}

	if rs, ok := f.(io.ReadSeeker); ok {
		// If it's an io.Seeker, use http.ServeContent which supports ranges
		http.ServeContent(w, r, r.URL.Path, fi.ModTime, rs)
	} else {
		if r.Method != http.MethodHead {
			io.Copy(w, f)
		}
	}
	return nil
}

func (b *backend) PropFind(r *http.Request, propfind *internal.PropFind, depth internal.Depth) (*internal.MultiStatus, error) {
	// TODO: use partial error Response on error

	fi, err := b.FileSystem.Stat(r.Context(), r.URL.Path)
	if os.IsNotExist(err) {
		return nil, &internal.HTTPError{Code: http.StatusNotFound, Err: err}
	} else if err != nil {
		return nil, err
	}

	var resps []internal.Response
	if depth != internal.DepthZero && fi.IsDir {
		children, err := b.FileSystem.ReadDir(r.Context(), r.URL.Path, depth == internal.DepthInfinity)
		if err != nil {
			return nil, err
		}

		resps = make([]internal.Response, len(children))
		for i, child := range children {
			resp, err := b.propFindFile(propfind, &child)
			if err != nil {
				return nil, err
			}
			resps[i] = *resp
		}
	} else {
		resp, err := b.propFindFile(propfind, fi)
		if err != nil {
			return nil, err
		}

		resps = []internal.Response{*resp}
	}

	return internal.NewMultiStatus(resps...), nil
}

func (b *backend) propFindFile(propfind *internal.PropFind, fi *FileInfo) (*internal.Response, error) {
	props := make(map[xml.Name]internal.PropFindFunc)

	props[internal.ResourceTypeName] = func(*internal.RawXMLValue) (interface{}, error) {
		var types []xml.Name
		if fi.IsDir {
			types = append(types, internal.CollectionName)
		}
		return internal.NewResourceType(types...), nil
	}

	if !fi.IsDir {
		props[internal.GetContentLengthName] = func(*internal.RawXMLValue) (interface{}, error) {
			return &internal.GetContentLength{Length: fi.Size}, nil
		}

		if !fi.ModTime.IsZero() {
			props[internal.GetLastModifiedName] = func(*internal.RawXMLValue) (interface{}, error) {
				return &internal.GetLastModified{LastModified: internal.Time(fi.ModTime)}, nil
			}
		}

		if fi.MIMEType != "" {
			props[internal.GetContentTypeName] = func(*internal.RawXMLValue) (interface{}, error) {
				return &internal.GetContentType{Type: fi.MIMEType}, nil
			}
		}

		if fi.ETag != "" {
			props[internal.GetETagName] = func(*internal.RawXMLValue) (interface{}, error) {
				return &internal.GetETag{ETag: internal.ETag(fi.ETag)}, nil
			}
		}
	}

	return internal.NewPropFindResponse(fi.Path, propfind, props)
}

func (b *backend) PropPatch(r *http.Request, update *internal.PropertyUpdate) (*internal.Response, error) {
	// TODO: return a failed Response instead
	return nil, internal.HTTPErrorf(http.StatusForbidden, "webdav: PROPPATCH is unsupported")
}

func (b *backend) Put(r *http.Request) (*internal.Href, error) {
	wc, err := b.FileSystem.Create(r.Context(), r.URL.Path)
	if err != nil {
		return nil, err
	}
	defer wc.Close()

	if _, err := io.Copy(wc, r.Body); err != nil {
		return nil, err
	}

	return nil, wc.Close()
}

func (b *backend) Delete(r *http.Request) error {
	err := b.FileSystem.RemoveAll(r.Context(), r.URL.Path)
	if os.IsNotExist(err) {
		return &internal.HTTPError{Code: http.StatusNotFound, Err: err}
	}
	return err
}

func (b *backend) Mkcol(r *http.Request) error {
	if r.Header.Get("Content-Type") != "" {
		return internal.HTTPErrorf(http.StatusUnsupportedMediaType, "webdav: request body not supported in MKCOL request")
	}
	err := b.FileSystem.Mkdir(r.Context(), r.URL.Path)
	if os.IsNotExist(err) {
		return &internal.HTTPError{Code: http.StatusConflict, Err: err}
	}
	return err
}

func (b *backend) Copy(r *http.Request, dest *internal.Href, recursive, overwrite bool) (created bool, err error) {
	created, err = b.FileSystem.Copy(r.Context(), r.URL.Path, dest.Path, recursive, overwrite)
	if os.IsExist(err) {
		return false, &internal.HTTPError{http.StatusPreconditionFailed, err}
	}
	return created, err
}

func (b *backend) Move(r *http.Request, dest *internal.Href, overwrite bool) (created bool, err error) {
	created, err = b.FileSystem.MoveAll(r.Context(), r.URL.Path, dest.Path, overwrite)
	if os.IsExist(err) {
		return false, &internal.HTTPError{http.StatusPreconditionFailed, err}
	}
	return created, err
}

// BackendSuppliedHomeSet represents either a CalDAV calendar-home-set or a
// CardDAV addressbook-home-set. It should only be created via
// caldav.NewCalendarHomeSet or carddav.NewAddressbookHomeSet. Only to
// be used server-side, for listing a user's home sets as determined by the
// (external) backend.
type BackendSuppliedHomeSet interface {
	GetXMLName() xml.Name
}

// UserPrincipalBackend can determine the current user's principal URL for a
// given request context.
type UserPrincipalBackend interface {
	CurrentUserPrincipal(ctx context.Context) (string, error)
}

// Capability indicates the features that a server supports.
type Capability string

// ServePrincipalOptions holds options for ServePrincipal.
type ServePrincipalOptions struct {
	CurrentUserPrincipalPath string
	HomeSets                 []BackendSuppliedHomeSet
	Capabilities             []Capability
}

// ServePrincipal replies to requests for a principal URL.
func ServePrincipal(w http.ResponseWriter, r *http.Request, options *ServePrincipalOptions) {
	switch r.Method {
	case http.MethodOptions:
		caps := []string{"1", "3"}
		for _, c := range options.Capabilities {
			caps = append(caps, string(c))
		}
		allow := []string{http.MethodOptions, "PROPFIND", "REPORT", "DELETE", "MKCOL"}
		w.Header().Add("DAV", strings.Join(caps, ", "))
		w.Header().Add("Allow", strings.Join(allow, ", "))
		w.WriteHeader(http.StatusNoContent)
	case "PROPFIND":
		if err := servePrincipalPropfind(w, r, options); err != nil {
			internal.ServeError(w, err)
		}
	default:
		http.Error(w, "unsupported method", http.StatusMethodNotAllowed)
	}
}

func servePrincipalPropfind(w http.ResponseWriter, r *http.Request, options *ServePrincipalOptions) error {
	var propfind internal.PropFind
	if err := internal.DecodeXMLRequest(r, &propfind); err != nil {
		return err
	}
	props := map[xml.Name]internal.PropFindFunc{
		internal.ResourceTypeName: func(*internal.RawXMLValue) (interface{}, error) {
			return internal.NewResourceType(principalName), nil
		},
		internal.CurrentUserPrincipalName: func(*internal.RawXMLValue) (interface{}, error) {
			return &internal.CurrentUserPrincipal{Href: internal.Href{Path: options.CurrentUserPrincipalPath}}, nil
		},
	}

	// TODO: handle Depth and more properties

	for _, homeSet := range options.HomeSets {
		hs := homeSet // capture variable for closure
		props[homeSet.GetXMLName()] = func(*internal.RawXMLValue) (interface{}, error) {
			return hs, nil
		}
	}

	resp, err := internal.NewPropFindResponse(r.URL.Path, &propfind, props)
	if err != nil {
		return err
	}

	ms := internal.NewMultiStatus(*resp)
	return internal.ServeMultiStatus(w, ms)
}