// 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 (
	"encoding/json"
	"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 `json:"-"`
	PasswordHash string `json:"Password"`
	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 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 ErrUserExists = errors.New("user already exists")
var ErrUserNotFound = errors.New("user not found")
var ErrInvalidUsername = errors.New("invalid username")

func (u User) merge(updates User) (User, error) {
	merged := u

	if updates.Password != "" {
		pwHash, err := hashPassword(updates.Password)
		if err != nil {
			return u, fmt.Errorf("cannot hash password: %w", err)
		}
		merged.PasswordHash = pwHash
	}
	if updates.Role != "" {
		merged.Role = updates.Role
	}

	return merged, 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 {
		userBytes, err := json.Marshal(user)
		if err != nil {
			return fmt.Errorf("cannot marshal user: %w", err)
		}

		if _, exists, err := tx.Set(user.key(), string(userBytes), nil); err != nil {
			return err
		} else if exists {
			return ErrUserExists
		}

		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
	}
	if err := store.db.View(func(tx *buntdb.Tx) error {
		user.Username = username
		if val, err := tx.Get(user.key()); err != nil && err != buntdb.ErrNotFound {
			return err
		} else if err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else if err := json.Unmarshal([]byte(val), &user); err != nil {
			return fmt.Errorf("cannot unmarshal user: %w", err)
		}

		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 {
		var processingError error

		if err := tx.AscendKeys(userPrefix+"*", func(key, value string) bool {
			var user User

			if err := json.Unmarshal([]byte(value), &user); err != nil {
				processingError = err
				return false
			}

			// Just in case ...
			user.Username = strings.TrimPrefix(key, userPrefix)

			users = append(users, user)
			return true
		}); err != nil {
			return err
		}

		return processingError
	})

	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 {
		var existingUser User

		if val, err := tx.Get(user.key()); err != nil && err != buntdb.ErrNotFound {
			return err
		} else if err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else if err := json.Unmarshal([]byte(val), &existingUser); err != nil {
			return fmt.Errorf("cannot unmarshal user: %w", err)
		}

		mergedUser, err := existingUser.merge(user)
		if err != nil {
			return fmt.Errorf("cannot merge user: %w", err)
		}
		mergedUser.Username = user.Username

		userBytes, err := json.Marshal(mergedUser)
		if err != nil {
			return fmt.Errorf("cannot marshal user: %w", err)
		}

		_, _, err = tx.Set(mergedUser.key(), string(userBytes), nil)

		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}
		if _, err := tx.Delete(user.key()); err == buntdb.ErrNotFound {
			return ErrUserNotFound
		} else if err != nil {
			return err
		}
		return nil
	})
}

func hashPassword(password string) (string, error) {
	hash, err := bcrypt.GenerateFromPassword([]byte(password), 0)
	if err != nil {
		return "", err
	}
	return string(hash), nil
}