// Package user exposes methods for representing users in a database.
package user

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"time"

	"golang.org/x/crypto/scrypt"

	"micromdm.io/v2/pkg/id"
)

// User is a MicroMDM user.
type User struct {
	ID               string
	Username         string
	Email            string
	Password         []byte
	Salt             []byte
	ConfirmationHash *string
	CreatedAt        time.Time
	UpdatedAt        time.Time
}

func columns() []string {
	return []string{
		"id",
		"username",
		"email",
		"password",
		"salt",
		"confirmation_hash",
		"created_at",
		"updated_at",
	}
}

// IsConfirmed returns true after the user confirms registration to the site.
// The user creation process always creates a confirmation token,
// which is deleted when the user accepts, by following the URL in email.
// Confirmation methods other than email should be possible to implement.
func (u *User) IsConfirmed() bool { return u.ConfirmationHash == nil }

// ValidatePassword compares the plaintext password with a stored password hash.
func (u *User) ValidatePassword(plaintext string) error {
	derived, err := scrypt.Key([]byte(plaintext), u.Salt, scryptCost, 8, 1, 32)
	if err != nil {
		return err
	}

	if 1 != subtle.ConstantTimeCompare(u.Password, derived) {
		return errors.New("password does not match")
	}

	return nil
}

func (u *User) setPassword(plaintext string) error {
	salt, err := random(32, base64.StdEncoding)
	if err != nil {
		return err
	}

	derived, err := scrypt.Key([]byte(plaintext), salt, scryptCost, 8, 1, 32)
	if err != nil {
		return err
	}

	u.Salt = salt
	u.Password = derived
	return nil
}

func random(keySize int, enc *base64.Encoding) ([]byte, error) {
	key := make([]byte, keySize)
	_, err := rand.Read(key)
	if err != nil {
		return nil, err
	}
	buf := make([]byte, enc.EncodedLen(len(key)))
	enc.Encode(buf, key)
	return buf, nil
}

// DB

func create(username, email, password string) (*User, error) {
	val := Error{invalid: make(map[string]string)}

	if username == "" {
		val.invalid["username"] = constraints["chk_username_not_empty"]["username"]
	}

	if email == "" {
		val.invalid["email"] = constraints["chk_email_not_empty"]["email"]
	}

	if password == "" {
		val.invalid["password"] = constraints["chk_password_not_empty"]["password"]
	}

	if len(val.invalid) > 0 {
		return nil, val
	}

	u := &User{
		ID:       id.New(),
		Username: username,
		Email:    email,
	}

	confirmationHash, err := random(32, base64.RawURLEncoding)
	if err != nil {
		return nil, fmt.Errorf("create confirmation_hash (email %s): %w", email, err)
	}
	cs := string(confirmationHash)
	u.ConfirmationHash = &cs

	if err := u.setPassword(password); err != nil {
		return nil, fmt.Errorf("set password for user (email %s): %w", email, err)
	}

	return u, nil
}

type Error struct {
	invalid map[string]string

	// missingEmail gets set when the user tries to log in without a real email.
	// This causes the frontend to respond with an "Invalid email or password" message.
	// Might want to change this implementation later, just needed something quick.
	missingEmail string
	missingHash  string
}

func (err Error) Invalid() map[string]string {
	switch {
	case err.missingHash != "":
		return map[string]string{
			"confirmation_hash": "Confirmation token unknown or already used.",
		}
	case err.missingEmail != "":
		return map[string]string{
			"email":    "Invalid email or password.",
			"password": "Invalid email or password.",
		}
	default:
		return err.invalid
	}
}

func (err Error) Error() string {
	switch {
	case err.missingEmail != "":
		return fmt.Sprintf("user with email %q not found", err.missingEmail)
	case err.missingHash != "":
		return fmt.Sprintf("user confirmation hash %q", err.missingHash)
	}

	switch len(err.invalid) {
	case 0:
		return "user validation failed"
	case 1:
		var key, value string
		for k, v := range err.invalid {
			key = k
			value = v
			break
		}
		return fmt.Sprintf("user validation failed: %s - %s", key, value)
	default:
		var key, value string
		for k, v := range err.invalid {
			key = k
			value = v
			break
		}
		return fmt.Sprintf("user validation failed: %s - %s and %d other errors", key, value, len(err.invalid)-1)
	}
}

var (
	constraints = map[string]map[string]string{
		"chk_email_not_empty":    map[string]string{"email": "You must provide an email address."},
		"chk_username_not_empty": map[string]string{"username": "You must provide a username."},
		"chk_password_not_empty": map[string]string{"password": "You must provide a password."},
	}

	constraintsUnique = map[string]map[string]string{
		"users.username": map[string]string{"username": "This username already exists."},
		"users.email":    map[string]string{"email": "This email already exists."},
	}
)