// Copyright (c) 2020, Andreas Schneider
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the name of the <organization> nor the
//       names of its contributors may be used to endorse or promote products
//       derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package main

import (
	"errors"
	"fmt"
	"strings"

	uuid "github.com/satori/go.uuid"
	"github.com/tidwall/buntdb"
	"golang.org/x/crypto/bcrypt"
)

type UserStore interface {
	AddUser(user User) (err error)
	GetUser(username string) (user User, err error)
	GetUsers() ([]User, error)
	Update(user User) error
	RemoveUser(username string) (err error)
}

type ShareStore interface {
}

var _ UserStore = &DBStore{}

type GlobalRole string

const (
	GlobalRoleUser  GlobalRole = "user"
	GlobalRoleAdmin GlobalRole = "admin"
)

type ShareRole string

const (
	ShareRoleReader ShareRole = "reader"
	ShareRoleWriter ShareRole = "writer"
	ShareRoleAdmin  ShareRole = "admin"
)

type User struct {
	Username string
	Password string
	Role     GlobalRole
}

type Share struct {
	UUID      uuid.UUID
	Directory string
	Users     []ShareUser
}

type ShareUser struct {
	Username string
	Role     ShareRole
	Logins   []Login
}

type Login struct {
	Loginname string
	Password  string
}

const usersPrefix = "users:"

type DBStore struct {
	db *buntdb.DB
}

func (u User) key() string {
	return usersPrefix + u.Username
}

func (u User) prefix() string {
	return fmt.Sprintf("user:%s", u.Username)
}

func (u User) roleKey() string {
	return u.prefix() + ":role"
}

func (u User) passwordKey() string {
	return u.prefix() + ":password"
}

func NewDBStore(filename string) (*DBStore, error) {
	db, err := buntdb.Open(filename)
	if err != nil {
		return nil, err
	}

	return &DBStore{db}, nil
}

func (store *DBStore) Close() error {
	if err := store.db.Shrink(); err != nil {
		return err
	}
	return store.db.Close()
}

var ErrExists = errors.New("key already exists")
var ErrUserNotFound = errors.New("user not found")
var ErrInvalidUsername = errors.New("invalid username")

func (store *DBStore) setUserValues(tx *buntdb.Tx, user User) (exists bool, err error) {
	pwString, err := buildPassword(user.Username, user.Password)
	if err != nil {
		return false, fmt.Errorf("cannot hash password: %w", err)
	}

	if _, replaced, err := tx.Set(user.roleKey(), string(user.Role), nil); err != nil {
		return false, err
	} else if replaced {
		exists = true
	}
	if _, replaced, err := tx.Set(user.passwordKey(), pwString, nil); err != nil {
		return false, err
	} else if replaced {
		exists = true
	}

	return exists, nil
}

func (store *DBStore) AddUser(user User) (err error) {
	if strings.Contains(user.Username, ":") {
		return ErrInvalidUsername
	}
	if err = store.db.Update(func(tx *buntdb.Tx) error {
		if _, exists, err := tx.Set(user.key(), "", nil); err != nil {
			return err
		} else if exists {
			return ErrExists
		}

		if exists, err := store.setUserValues(tx, user); err != nil {
			return err
		} else if exists {
			return ErrExists
		}
		return nil
	}); err != nil {
		return err
	}
	return nil
}

func (store *DBStore) GetUser(username string) (user User, err error) {
	if strings.Contains(username, ":") {
		return user, ErrInvalidUsername
	}
	user.Username = username
	if err := store.db.View(func(tx *buntdb.Tx) error {
		if val, err := tx.Get(user.roleKey()); err != nil && err != buntdb.ErrNotFound {
			return err
		} else if err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else {
			user.Role = GlobalRole(val)
		}
		if val, err := tx.Get(user.passwordKey()); err != nil && err != buntdb.ErrNotFound {
			return err
		} else if err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else {
			user.Password = val
		}
		return nil
	}); err != nil {
		return user, err
	}
	return user, nil
}

func (store *DBStore) GetUsers() (users []User, err error) {
	err = store.db.View(func(tx *buntdb.Tx) error {
		if err := tx.AscendKeys(usersPrefix+"*", func(key, value string) bool {
			var user User
			user.Username = strings.TrimPrefix(key, usersPrefix)
			users = append(users, user)
			return true
		}); err != nil {
			return err
		}

		for i := range users {
			if roleString, err := tx.Get(users[i].roleKey()); err != nil {
				return err
			} else {
				users[i].Role = GlobalRole(roleString)
			}
		}

		return nil
	})

	return users, err
}

func (store *DBStore) Update(user User) error {
	if strings.Contains(user.Username, ":") {
		return ErrInvalidUsername
	}
	return store.db.Update(func(tx *buntdb.Tx) error {
		_, err := store.setUserValues(tx, user)
		return err
	})
}

func (store *DBStore) RemoveUser(username string) (err error) {
	if strings.Contains(username, ":") {
		return ErrInvalidUsername
	}
	return store.db.Update(func(tx *buntdb.Tx) error {
		user := User{Username: username}

		// Delete the main key first. This is a good indicator if the user generally exists.
		if _, err := tx.Delete(user.key()); err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else if err != nil {
			return err
		}

		// Now get all attributes and delete them as well. One by one.
		var keys []string
		if err := tx.AscendKeys(user.prefix()+":*", func(key, value string) bool {
			keys = append(keys, key)
			return true
		}); err != nil {
			return fmt.Errorf("cannot iterate keys: %w", err)
		}
		for _, key := range keys {
			if _, err := tx.Delete(key); err != nil {
				return fmt.Errorf("cannot remove key: %w", err)
			}
		}
		return nil
	})
}

func buildPassword(username string, password string) (string, error) {
	hash, err := bcrypt.GenerateFromPassword([]byte(password), 0)
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%s:%s", username, hash), nil
}