package storage

import (
	"context"
	"crypto/sha1"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"

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

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

type filesystemBackend struct {
	path string
}

var (
	nilBackend         carddav.Backend = (*filesystemBackend)(nil)
	validFilenameRegex                 = regexp.MustCompile(`^/[A-Za-z0-9][A-Za-z0-9_-]+(.[a-zA-Z]+)?$`)
)

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

func (b *filesystemBackend) pathForContext(ctx context.Context) (string, error) {
	authCtx, ok := auth.FromContext(ctx)
	if !ok {
		panic("Invalid data in auth context!")
	}
	if authCtx == nil {
		return "", fmt.Errorf("unauthenticated requests are not supported")
	}

	userDir := base64.RawStdEncoding.EncodeToString([]byte(authCtx.UserName))
	path := filepath.Join(b.path, userDir)

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

func (b *filesystemBackend) safePath(ctx context.Context, path string) (string, error) {
	basePath, err := b.pathForContext(ctx)
	if err != nil {
		return "", err
	}
	// We are mapping to local filesystem path, so be conservative about what to accept
	// TODO this changes once multiple addess books are supported
	if !validFilenameRegex.MatchString(path) {
		return "", fmt.Errorf("invalid request path")
	}
	return filepath.Join(basePath, path), nil
}

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 createDefaultAddressBook(path string) error {
	// TODO what should the default address book look like?
	defaultAB := carddav.AddressBook{
		Path:                 "/default",
		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(path, 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) {
	path, err := b.pathForContext(ctx)
	if err != nil {
		return nil, err
	}
	path = filepath.Join(path, "_default_ab.json")

	data, err := ioutil.ReadFile(path)
	if os.IsNotExist(err) {
		err = createDefaultAddressBook(path)
		if err != nil {
			return nil, err
		}
		data, err = ioutil.ReadFile(path)
	}
	if err != nil {
		return nil, fmt.Errorf("error opening address book: %s", err.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, path string, req *carddav.AddressDataRequest) (*carddav.AddressObject, error) {
	localPath, err := b.safePath(ctx, path)
	if err != nil {
		return nil, err
	}

	info, err := os.Stat(localPath)
	if err != nil {
		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:    path,
		ModTime: info.ModTime(),
		ETag:    etag,
		Card:    card,
	}
	return &obj, nil
}

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

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

	err = filepath.Walk(path, func(filename string, info os.FileInfo, err error) error {
		// Skip address book meta data files
		if !info.Mode().IsRegular() || filepath.Ext(filename) == ".json" {
			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:    "/" + filepath.Base(filename),
			ModTime: info.ModTime(),
			ETag:    etag,
			Card:    card,
		}
		result = append(result, obj)
		return nil
	})

	return result, err
}

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

	return b.loadAll(ctx, propFilter)
}

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

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

	return carddav.Filter(query, result)
}

func (b *filesystemBackend) hasUIDConflict(ctx context.Context, uid, path string) (bool, error) {
	all, err := b.loadAll(ctx, nil)
	if err != nil {
		return false, err
	}
	for _, contact := range all {
		if contact.Path != path && contact.Card.Value(vcard.FieldUID) == uid {
			return true, nil
		}
	}

	return false, nil
}

func (b *filesystemBackend) PutAddressObject(ctx context.Context, path string, card vcard.Card) (loc string, err error) {
	localPath, err := b.safePath(ctx, path)
	if err != nil {
		return "", err
	}

	conflict, err := b.hasUIDConflict(ctx, card.Value(vcard.FieldUID), path)
	if err != nil {
		return "", err
	}
	if conflict {
		return "", carddav.NewPreconditionError(carddav.PreconditionNoUIDConflict)
	}

	f, err := os.Create(localPath)
	if err != nil {
		return "", err
	}
	defer f.Close()

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

	return path, nil
}

func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string) error {
	localPath, err := b.safePath(ctx, path)
	if err != nil {
		return err
	}
	err = os.Remove(localPath)
	if err != nil {
		return err
	}
	return nil
}