package storage

import (
	"context"
	"crypto/sha1"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"io/ioutil"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"strings"

	"github.com/emersion/go-ical"
	"github.com/emersion/go-vcard"
	"github.com/emersion/go-webdav"
	"github.com/emersion/go-webdav/caldav"
	"github.com/emersion/go-webdav/carddav"

	"git.sr.ht/~sircmpwn/tokidoki/debug"
)

type filesystemBackend struct {
	webdav.UserPrincipalBackend
	path          string
	caldavPrefix  string
	carddavPrefix string
}

var (
	validFilenameRegex = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_-]+(.[a-zA-Z]+)?$`)
)

func NewFilesystem(fsPath, caldavPrefix, carddavPrefix string, userPrincipalBackend webdav.UserPrincipalBackend) (caldav.Backend, carddav.Backend, error) {
	info, err := os.Stat(fsPath)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to create filesystem backend: %s", err.Error())
	}
	if !info.IsDir() {
		return nil, nil, fmt.Errorf("base path for filesystem backend must be a directory")
	}
	backend := &filesystemBackend{
		UserPrincipalBackend: userPrincipalBackend,
		path:                 fsPath,
		caldavPrefix:         caldavPrefix,
		carddavPrefix:        carddavPrefix,
	}
	return backend, backend, nil
}

func (b *filesystemBackend) AddressbookHomeSetPath(ctx context.Context) (string, error) {
	upPath, err := b.CurrentUserPrincipal(ctx)
	if err != nil {
		return "", err
	}

	return path.Join(upPath, b.carddavPrefix) + "/", nil
}

func (b *filesystemBackend) CalendarHomeSetPath(ctx context.Context) (string, error) {
	upPath, err := b.CurrentUserPrincipal(ctx)
	if err != nil {
		return "", err
	}

	return path.Join(upPath, b.caldavPrefix) + "/", nil
}

func ensureLocalDir(path string) error {
	if _, err := os.Stat(path); os.IsNotExist(err) {
		err = os.MkdirAll(path, 0755)
		if err != nil {
			return fmt.Errorf("error creating '%s': %s", path, err.Error())
		}
	}
	return nil
}

// don't use this directly, use localCalDAVPath or localCardDAVPath instead.
func (b *filesystemBackend) safeLocalPath(homeSetPath string, urlPath string) (string, error) {
	localPath := filepath.Join(b.path, homeSetPath, "default")
	if err := ensureLocalDir(localPath); err != nil {
		return "", err
	}

	if urlPath == "" {
		return localPath, nil
	}

	// We are mapping to local filesystem path, so be conservative about what to accept
	// TODO this changes once multiple addess books are supported
	dir, file := path.Split(urlPath)
	// only accept resources in default calendar/adress book for now
	if path.Clean(dir) != path.Join(homeSetPath, "default") {
		if strings.HasPrefix(dir, homeSetPath) {
			err := fmt.Errorf("invalid request path: %s (%s is not %s)", urlPath, dir, path.Join(homeSetPath, "default"))
			return "", webdav.NewHTTPError(400, err)
		} else {
			err := fmt.Errorf("Access to resource outside of home set: %s", urlPath)
			return "", webdav.NewHTTPError(403, err)
		}
	}
	// only accept simple file names for now
	if !validFilenameRegex.MatchString(file) {
		debug.Printf("%s does not match regex!\n", file)
		err := fmt.Errorf("invalid file name: %s", file)
		return "", webdav.NewHTTPError(400, err)
	}

	// dir (= homeSetPath) is already included in path, so only file here
	return filepath.Join(localPath, file), nil
}

func (b *filesystemBackend) localCalDAVPath(ctx context.Context, urlPath string) (string, error) {
	homeSetPath, err := b.CalendarHomeSetPath(ctx)
	if err != nil {
		return "", err
	}

	return b.safeLocalPath(homeSetPath, urlPath)
}

func (b *filesystemBackend) localCardDAVPath(ctx context.Context, urlPath string) (string, error) {
	homeSetPath, err := b.AddressbookHomeSetPath(ctx)
	if err != nil {
		return "", err
	}

	return b.safeLocalPath(homeSetPath, urlPath)
}

func etagForFile(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	h := sha1.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	csum := h.Sum(nil)

	return base64.StdEncoding.EncodeToString(csum[:]), nil
}

func vcardPropFilter(card vcard.Card, props []string) vcard.Card {
	if card == nil {
		return nil
	}

	if len(props) == 0 {
		return card
	}

	result := make(vcard.Card)
	result["VERSION"] = card["VERSION"]
	for _, prop := range props {
		value, ok := card[prop]
		if ok {
			result[prop] = value
		}
	}

	return result
}

func vcardFromFile(path string, propFilter []string) (vcard.Card, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	dec := vcard.NewDecoder(f)
	card, err := dec.Decode()
	if err != nil {
		return nil, err
	}

	return vcardPropFilter(card, propFilter), nil
}

func calendarFromFile(path string, propFilter []string) (*ical.Calendar, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	dec := ical.NewDecoder(f)
	cal, err := dec.Decode()
	if err != nil {
		return nil, err
	}

	return cal, nil
	// TODO implement
	//return icalPropFilter(cal, propFilter), nil
}

func createDefaultAddressBook(path, localPath string) error {
	// TODO what should the default address book look like?
	defaultAB := carddav.AddressBook{
		Path:                 path,
		Name:                 "My contacts",
		Description:          "Default address book",
		MaxResourceSize:      1024,
		SupportedAddressData: nil,
	}
	blob, err := json.MarshalIndent(defaultAB, "", "  ")
	if err != nil {
		return fmt.Errorf("error creating default address book: %s", err.Error())
	}
	err = os.WriteFile(localPath, blob, 0644)
	if err != nil {
		return fmt.Errorf("error writing default address book: %s", err.Error())
	}
	return nil
}

func (b *filesystemBackend) AddressBook(ctx context.Context) (*carddav.AddressBook, error) {
	debug.Printf("filesystem.AddressBook()")
	localPath, err := b.localCardDAVPath(ctx, "")
	if err != nil {
		return nil, err
	}
	localPath = filepath.Join(localPath, "addressbook.json")

	debug.Printf("loading addressbook from %s", localPath)

	data, readErr := ioutil.ReadFile(localPath)
	if os.IsNotExist(readErr) {
		urlPath, err := b.AddressbookHomeSetPath(ctx)
		if err != nil {
			return nil, err
		}
		urlPath = path.Join(urlPath, "default") + "/"
		debug.Printf("creating default addressbook (URL:path): %s:%s", urlPath, localPath)
		err = createDefaultAddressBook(urlPath, localPath)
		if err != nil {
			return nil, err
		}
		data, readErr = ioutil.ReadFile(localPath)
	}
	if readErr != nil {
		return nil, fmt.Errorf("error opening address book: %s", readErr.Error())
	}
	var addressBook carddav.AddressBook
	err = json.Unmarshal(data, &addressBook)
	if err != nil {
		return nil, fmt.Errorf("error reading address book: %s", err.Error())
	}

	return &addressBook, nil
}

func (b *filesystemBackend) GetAddressObject(ctx context.Context, objPath string, req *carddav.AddressDataRequest) (*carddav.AddressObject, error) {
	debug.Printf("filesystem.GetAddressObject(%s, %v)", objPath, req)
	localPath, err := b.localCardDAVPath(ctx, objPath)
	if err != nil {
		return nil, err
	}

	info, err := os.Stat(localPath)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil, webdav.NewHTTPError(404, err)
		}
		return nil, err
	}

	var propFilter []string
	if req != nil && !req.AllProp {
		propFilter = req.Props
	}

	card, err := vcardFromFile(localPath, propFilter)
	if err != nil {
		return nil, err
	}

	etag, err := etagForFile(localPath)
	if err != nil {
		return nil, err
	}

	obj := carddav.AddressObject{
		Path:          objPath,
		ModTime:       info.ModTime(),
		ContentLength: info.Size(),
		ETag:          etag,
		Card:          card,
	}
	return &obj, nil
}

func (b *filesystemBackend) loadAllContacts(ctx context.Context, propFilter []string) ([]carddav.AddressObject, error) {
	var result []carddav.AddressObject

	localPath, err := b.localCardDAVPath(ctx, "")
	if err != nil {
		return result, err
	}

	homeSetPath, err := b.AddressbookHomeSetPath(ctx)
	if err != nil {
		return result, err
	}

	err = filepath.Walk(localPath, func(filename string, info os.FileInfo, err error) error {
		if !info.Mode().IsRegular() || filepath.Ext(filename) != ".vcf" {
			return nil
		}

		card, err := vcardFromFile(filename, propFilter)
		if err != nil {
			return err
		}

		etag, err := etagForFile(filename)
		if err != nil {
			return err
		}

		obj := carddav.AddressObject{
			Path:          path.Join(homeSetPath, "default", filepath.Base(filename)),
			ModTime:       info.ModTime(),
			ContentLength: info.Size(),
			ETag:          etag,
			Card:          card,
		}
		result = append(result, obj)
		return nil
	})

	debug.Printf("filesystem.loadAllContacts() returning %d results from %s", len(result), localPath)
	return result, err
}

func (b *filesystemBackend) loadAllCalendars(ctx context.Context, propFilter []string) ([]caldav.CalendarObject, error) {
	var result []caldav.CalendarObject

	localPath, err := b.localCalDAVPath(ctx, "")
	if err != nil {
		return result, err
	}

	homeSetPath, err := b.CalendarHomeSetPath(ctx)
	if err != nil {
		return result, err
	}

	err = filepath.Walk(localPath, func(filename string, info os.FileInfo, err error) error {
		// Skip address book meta data files
		if !info.Mode().IsRegular() || filepath.Ext(filename) != ".ics" {
			return nil
		}

		cal, err := calendarFromFile(filename, propFilter)
		if err != nil {
			fmt.Printf("load calendar error for %s: %v\n", filename, err)
			return err
		}

		etag, err := etagForFile(filename)
		if err != nil {
			return err
		}

		obj := caldav.CalendarObject{
			Path:          path.Join(homeSetPath, "default", filepath.Base(filename)),
			ModTime:       info.ModTime(),
			ContentLength: info.Size(),
			ETag:          etag,
			Data:          cal,
		}
		result = append(result, obj)
		return nil
	})

	debug.Printf("filesystem.loadAllCalendars() returning %d results from %s", len(result), localPath)
	return result, err
}

func (b *filesystemBackend) ListAddressObjects(ctx context.Context, req *carddav.AddressDataRequest) ([]carddav.AddressObject, error) {
	debug.Printf("filesystem.ListAddressObjects(%v)", req)
	var propFilter []string
	if req != nil && !req.AllProp {
		propFilter = req.Props
	}

	return b.loadAllContacts(ctx, propFilter)
}

func (b *filesystemBackend) QueryAddressObjects(ctx context.Context, query *carddav.AddressBookQuery) ([]carddav.AddressObject, error) {
	debug.Printf("filesystem.QueryAddressObjects(%v)", query)
	var propFilter []string
	if query != nil && !query.DataRequest.AllProp {
		propFilter = query.DataRequest.Props
	}

	result, err := b.loadAllContacts(ctx, propFilter)
	if err != nil {
		return result, err
	}

	return carddav.Filter(query, result)
}

func (b *filesystemBackend) PutAddressObject(ctx context.Context, objPath string, card vcard.Card, opts *carddav.PutAddressObjectOptions) (loc string, err error) {
	debug.Printf("filesystem.PutAddressObject(%v, %v, %v)", objPath, card, opts)

	// Object always get saved as <UID>.vcf
	dirname, _ := path.Split(objPath)
	objPath = path.Join(dirname, card.Value(vcard.FieldUID)+".vcf")

	localPath, err := b.localCardDAVPath(ctx, objPath)
	if err != nil {
		return "", err
	}

	flags := os.O_RDWR | os.O_CREATE | os.O_TRUNC
	// TODO handle IfNoneMatch == ETag
	if opts.IfNoneMatch.IsWildcard() {
		// Make sure we're not overwriting an existing file
		flags |= os.O_EXCL
	} else if opts.IfMatch.IsWildcard() {
		// Make sure we _are_ overwriting an existing file
		flags &= ^os.O_CREATE
	} else if opts.IfMatch.IsSet() {
		// Make sure we overwrite the _right_ file
		etag, err := etagForFile(localPath)
		if err != nil {
			return "", webdav.NewHTTPError(http.StatusPreconditionFailed, err)
		}
		want, err := opts.IfMatch.ETag()
		if err != nil {
			return "", webdav.NewHTTPError(http.StatusBadRequest, err)
		}
		if want != etag {
			err = fmt.Errorf("If-Match does not match current ETag (%s/%s)", want, etag)
			return "", webdav.NewHTTPError(http.StatusPreconditionFailed, err)
		}
	}

	f, err := os.OpenFile(localPath, flags, 0666)
	if os.IsExist(err) {
		return "", carddav.NewPreconditionError(carddav.PreconditionNoUIDConflict)
	} else if err != nil {
		return "", err
	}
	defer f.Close()

	enc := vcard.NewEncoder(f)
	err = enc.Encode(card)
	if err != nil {
		return "", err
	}

	return objPath, nil
}

func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string) error {
	debug.Printf("filesystem.DeleteAddressObject(%s)", path)

	localPath, err := b.localCardDAVPath(ctx, path)
	if err != nil {
		return err
	}
	err = os.Remove(localPath)
	if err != nil {
		return err
	}
	return nil
}

func createDefaultCalendar(path, localPath string) error {
	// TODO what should the default calendar look like?
	defaultC := caldav.Calendar{
		Path:            path,
		Name:            "My calendar",
		Description:     "Default calendar",
		MaxResourceSize: 4096,
	}
	blob, err := json.MarshalIndent(defaultC, "", "  ")
	if err != nil {
		return fmt.Errorf("error creating default calendar: %s", err.Error())
	}
	err = os.WriteFile(localPath, blob, 0644)
	if err != nil {
		return fmt.Errorf("error writing default calendar: %s", err.Error())
	}
	return nil
}

func (b *filesystemBackend) Calendar(ctx context.Context) (*caldav.Calendar, error) {
	debug.Printf("filesystem.Calendar()")

	localPath, err := b.localCalDAVPath(ctx, "")
	if err != nil {
		return nil, err
	}
	localPath = filepath.Join(localPath, "calendar.json")

	debug.Printf("loading calendar from %s", localPath)

	data, readErr := ioutil.ReadFile(localPath)
	if os.IsNotExist(readErr) {
		urlPath, err := b.CalendarHomeSetPath(ctx)
		if err != nil {
			return nil, err
		}
		urlPath = path.Join(urlPath, "default") + "/"
		debug.Printf("creating default calendar (URL:path): %s:%s", urlPath, localPath)
		err = createDefaultCalendar(urlPath, localPath)
		if err != nil {
			return nil, err
		}
		data, readErr = ioutil.ReadFile(localPath)
	}
	if readErr != nil {
		return nil, fmt.Errorf("error opening calendar: %s", readErr.Error())
	}
	var calendar caldav.Calendar
	err = json.Unmarshal(data, &calendar)
	if err != nil {
		return nil, fmt.Errorf("error reading calendar: %s", err.Error())
	}

	return &calendar, nil
}

func (b *filesystemBackend) GetCalendarObject(ctx context.Context, objPath string, req *caldav.CalendarCompRequest) (*caldav.CalendarObject, error) {
	debug.Printf("filesystem.GetCalendarObject(%s, %v)", objPath, req)

	localPath, err := b.localCalDAVPath(ctx, objPath)
	if err != nil {
		return nil, err
	}

	info, err := os.Stat(localPath)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			debug.Printf("not found: %s", localPath)
			return nil, webdav.NewHTTPError(404, err)
		}
		return nil, err
	}

	var propFilter []string
	if req != nil && !req.AllProps {
		propFilter = req.Props
	}

	calendar, err := calendarFromFile(localPath, propFilter)
	if err != nil {
		debug.Printf("error reading calendar: %v", err)
		return nil, err
	}

	etag, err := etagForFile(localPath)
	if err != nil {
		return nil, err
	}

	obj := caldav.CalendarObject{
		Path:          objPath,
		ModTime:       info.ModTime(),
		ContentLength: info.Size(),
		ETag:          etag,
		Data:          calendar,
	}
	return &obj, nil
	return nil, fmt.Errorf("not implemented")
}

func (b *filesystemBackend) ListCalendarObjects(ctx context.Context, req *caldav.CalendarCompRequest) ([]caldav.CalendarObject, error) {
	debug.Printf("filesystem.ListCalendarObjects(%v)", req)

	var propFilter []string
	if req != nil && !req.AllProps {
		propFilter = req.Props
	}

	return b.loadAllCalendars(ctx, propFilter)
}

func (b *filesystemBackend) QueryCalendarObjects(ctx context.Context, query *caldav.CalendarQuery) ([]caldav.CalendarObject, error) {
	debug.Printf("filesystem.QueryCalendarObjects(%v)", query)

	var propFilter []string
	if query != nil && !query.CompRequest.AllProps {
		propFilter = query.CompRequest.Props
	}

	result, err := b.loadAllCalendars(ctx, propFilter)
	if err != nil {
		return result, err
	}

	return caldav.Filter(query, result)
}

func (b *filesystemBackend) PutCalendarObject(ctx context.Context, objPath string, calendar *ical.Calendar, opts *caldav.PutCalendarObjectOptions) (loc string, err error) {
	debug.Printf("filesystem.PutCalendarObject(%s, %v, %v)", objPath, calendar, opts)

	_, uid, err := caldav.ValidateCalendarObject(calendar)
	if err != nil {
		return "", caldav.NewPreconditionError(caldav.PreconditionValidCalendarObjectResource)
	}

	// Object always get saved as <UID>.ics
	dirname, _ := path.Split(objPath)
	objPath = path.Join(dirname, uid+".ics")

	localPath, err := b.localCalDAVPath(ctx, objPath)
	if err != nil {
		return "", err
	}

	flags := os.O_RDWR | os.O_CREATE | os.O_TRUNC
	// TODO handle IfNoneMatch == ETag
	if opts.IfNoneMatch.IsWildcard() {
		// Make sure we're not overwriting an existing file
		flags |= os.O_EXCL
	} else if opts.IfMatch.IsWildcard() {
		// Make sure we _are_ overwriting an existing file
		flags &= ^os.O_CREATE
	} else if opts.IfMatch.IsSet() {
		// Make sure we overwrite the _right_ file
		etag, err := etagForFile(localPath)
		if err != nil {
			return "", webdav.NewHTTPError(http.StatusPreconditionFailed, err)
		}
		want, err := opts.IfMatch.ETag()
		if err != nil {
			return "", webdav.NewHTTPError(http.StatusBadRequest, err)
		}
		if want != etag {
			err = fmt.Errorf("If-Match does not match current ETag (%s/%s)", want, etag)
			return "", webdav.NewHTTPError(http.StatusPreconditionFailed, err)
		}
	}

	f, err := os.OpenFile(localPath, flags, 0666)
	if os.IsExist(err) {
		return "", caldav.NewPreconditionError(caldav.PreconditionNoUIDConflict)
	} else if err != nil {
		return "", err
	}
	defer f.Close()

	enc := ical.NewEncoder(f)
	err = enc.Encode(calendar)
	if err != nil {
		return "", err
	}

	return objPath, nil
}

func (b *filesystemBackend) DeleteCalendarObject(ctx context.Context, path string) error {
	debug.Printf("filesystem.DeleteCalendarObject(%s)", path)

	localPath, err := b.localCalDAVPath(ctx, path)
	if err != nil {
		return err
	}
	err = os.Remove(localPath)
	if err != nil {
		return err
	}
	return nil
}