// SPDX-License-Identifier: AGPL-3.0-or-later

package store

import (
	"crypto/rand"
	"crypto/subtle"
	"database/sql"
	"encoding/base64"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"golang.org/x/crypto/argon2"

	"kode.naiv.no/olemd/favoritter/internal/model"
)

// Argon2id parameters. Defaults match OWASP recommendations.
var (
	Argon2Memory      uint32 = 65536 // 64 MB
	Argon2Time        uint32 = 3
	Argon2Parallelism uint8  = 2
	Argon2KeyLength   uint32 = 32
	Argon2SaltLength          = 16
)

var (
	ErrUserNotFound   = errors.New("user not found")
	ErrUserExists     = errors.New("username already taken")
	ErrUserDisabled   = errors.New("user account is disabled")
	ErrInvalidCredentials = errors.New("invalid username or password")
)

type UserStore struct {
	db *sql.DB
}

func NewUserStore(db *sql.DB) *UserStore {
	return &UserStore{db: db}
}

// Create creates a new user with the given username and plaintext password.
func (s *UserStore) Create(username, password, role string) (*model.User, error) {
	hash, err := hashPassword(password)
	if err != nil {
		return nil, fmt.Errorf("hash password: %w", err)
	}

	result, err := s.db.Exec(
		`INSERT INTO users (username, password_hash, role) VALUES (?, ?, ?)`,
		username, hash, role,
	)
	if err != nil {
		if strings.Contains(err.Error(), "UNIQUE constraint failed") {
			return nil, ErrUserExists
		}
		return nil, fmt.Errorf("insert user: %w", err)
	}

	id, _ := result.LastInsertId()
	return s.GetByID(id)
}

// CreateWithReset creates a new user that must reset their password on first login.
func (s *UserStore) CreateWithReset(username, tempPassword, role string) (*model.User, error) {
	hash, err := hashPassword(tempPassword)
	if err != nil {
		return nil, fmt.Errorf("hash password: %w", err)
	}

	result, err := s.db.Exec(
		`INSERT INTO users (username, password_hash, role, must_reset_password) VALUES (?, ?, ?, 1)`,
		username, hash, role,
	)
	if err != nil {
		if strings.Contains(err.Error(), "UNIQUE constraint failed") {
			return nil, ErrUserExists
		}
		return nil, fmt.Errorf("insert user: %w", err)
	}

	id, _ := result.LastInsertId()
	return s.GetByID(id)
}

// Authenticate verifies credentials and returns the user if valid.
func (s *UserStore) Authenticate(username, password string) (*model.User, error) {
	user, err := s.GetByUsername(username)
	if err != nil {
		if errors.Is(err, ErrUserNotFound) {
			// Still do a dummy hash comparison to prevent timing attacks.
			dummyHash(password)
			return nil, ErrInvalidCredentials
		}
		return nil, err
	}

	if user.Disabled {
		return nil, ErrUserDisabled
	}

	if !verifyPassword(password, user.PasswordHash) {
		return nil, ErrInvalidCredentials
	}

	return user, nil
}

// GetByID retrieves a user by their ID.
func (s *UserStore) GetByID(id int64) (*model.User, error) {
	return scanUserFrom(s.db.QueryRow(
		`SELECT id, username, display_name, bio, avatar_path, password_hash,
			role, profile_visibility, default_fave_privacy,
			must_reset_password, disabled, created_at, updated_at
		FROM users WHERE id = ?`, id,
	))
}

// GetByUsername retrieves a user by their username (case-insensitive).
func (s *UserStore) GetByUsername(username string) (*model.User, error) {
	return scanUserFrom(s.db.QueryRow(
		`SELECT id, username, display_name, bio, avatar_path, password_hash,
			role, profile_visibility, default_fave_privacy,
			must_reset_password, disabled, created_at, updated_at
		FROM users WHERE username = ?`, username,
	))
}

// UpdatePassword changes a user's password and clears the must_reset_password flag.
func (s *UserStore) UpdatePassword(userID int64, newPassword string) error {
	hash, err := hashPassword(newPassword)
	if err != nil {
		return fmt.Errorf("hash password: %w", err)
	}

	_, err = s.db.Exec(
		`UPDATE users SET password_hash = ?, must_reset_password = 0,
			updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		WHERE id = ?`,
		hash, userID,
	)
	return err
}

// UpdateProfile updates a user's profile fields.
func (s *UserStore) UpdateProfile(userID int64, displayName, bio, profileVisibility, defaultFavePrivacy string) error {
	_, err := s.db.Exec(
		`UPDATE users SET display_name = ?, bio = ?, profile_visibility = ?,
			default_fave_privacy = ?,
			updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		WHERE id = ?`,
		displayName, bio, profileVisibility, defaultFavePrivacy, userID,
	)
	return err
}

// SetMustResetPassword sets or clears the must_reset_password flag.
func (s *UserStore) SetMustResetPassword(userID int64, must bool) error {
	val := 0
	if must {
		val = 1
	}
	_, err := s.db.Exec(
		`UPDATE users SET must_reset_password = ?,
			updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		WHERE id = ?`,
		val, userID,
	)
	return err
}

// UpdateAvatar updates a user's avatar path.
func (s *UserStore) UpdateAvatar(userID int64, avatarPath string) error {
	_, err := s.db.Exec(
		`UPDATE users SET avatar_path = ?,
			updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		WHERE id = ?`,
		avatarPath, userID,
	)
	return err
}

// SetDisabled enables or disables a user account.
func (s *UserStore) SetDisabled(userID int64, disabled bool) error {
	val := 0
	if disabled {
		val = 1
	}
	_, err := s.db.Exec(
		`UPDATE users SET disabled = ?,
			updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		WHERE id = ?`,
		val, userID,
	)
	return err
}

// ListAll returns all users, ordered by username.
func (s *UserStore) ListAll() ([]*model.User, error) {
	rows, err := s.db.Query(
		`SELECT id, username, display_name, bio, avatar_path, password_hash,
			role, profile_visibility, default_fave_privacy,
			must_reset_password, disabled, created_at, updated_at
		FROM users ORDER BY username COLLATE NOCASE`,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var users []*model.User
	for rows.Next() {
		u, err := scanUserFrom(rows)
		if err != nil {
			return nil, err
		}
		users = append(users, u)
	}
	return users, rows.Err()
}

// Count returns the total number of users.
func (s *UserStore) Count() (int, error) {
	var n int
	err := s.db.QueryRow("SELECT COUNT(*) FROM users").Scan(&n)
	return n, err
}

// EnsureAdmin creates the initial admin user if no users exist yet.
// This is called on startup with the configured admin credentials.
func (s *UserStore) EnsureAdmin(username, password string) error {
	if username == "" || password == "" {
		// No admin credentials configured — only skip if users already exist.
		count, err := s.Count()
		if err != nil {
			return err
		}
		if count == 0 {
			slog.Warn("no admin credentials configured and no users exist — set FAVORITTER_ADMIN_USERNAME and FAVORITTER_ADMIN_PASSWORD")
		}
		return nil
	}

	// Check if this admin already exists.
	_, err := s.GetByUsername(username)
	if err == nil {
		return nil // Already exists.
	}
	if !errors.Is(err, ErrUserNotFound) {
		return err
	}

	_, err = s.Create(username, password, "admin")
	if err != nil {
		return fmt.Errorf("create admin user: %w", err)
	}

	slog.Info("created initial admin user", "username", username)
	return nil
}

// scanner is implemented by both *sql.Row and *sql.Rows.
type scanner interface {
	Scan(dest ...any) error
}

func scanUserFrom(s scanner) (*model.User, error) {
	u := &model.User{}
	var createdAt, updatedAt string
	err := s.Scan(
		&u.ID, &u.Username, &u.DisplayName, &u.Bio, &u.AvatarPath,
		&u.PasswordHash, &u.Role, &u.ProfileVisibility, &u.DefaultFavePrivacy,
		&u.MustResetPassword, &u.Disabled, &createdAt, &updatedAt,
	)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrUserNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("scan user: %w", err)
	}
	u.CreatedAt, _ = time.Parse(time.RFC3339, createdAt)
	u.UpdatedAt, _ = time.Parse(time.RFC3339, updatedAt)
	return u, nil
}

// Password hashing with Argon2id.
// Format: $argon2id$v=19$m=65536,t=3,p=2$<salt>$<hash>

func hashPassword(password string) (string, error) {
	salt := make([]byte, Argon2SaltLength)
	if _, err := rand.Read(salt); err != nil {
		return "", fmt.Errorf("generate salt: %w", err)
	}

	hash := argon2.IDKey([]byte(password), salt, Argon2Time, Argon2Memory, Argon2Parallelism, Argon2KeyLength)

	return fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version,
		Argon2Memory, Argon2Time, Argon2Parallelism,
		base64.RawStdEncoding.EncodeToString(salt),
		base64.RawStdEncoding.EncodeToString(hash),
	), nil
}

func verifyPassword(password, encodedHash string) bool {
	parts := strings.Split(encodedHash, "$")
	if len(parts) != 6 || parts[1] != "argon2id" {
		return false
	}

	var memory uint32
	var iterations uint32
	var parallelism uint8
	_, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &iterations, &parallelism)
	if err != nil {
		return false
	}

	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false
	}

	expectedHash, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false
	}

	hash := argon2.IDKey([]byte(password), salt, iterations, memory, parallelism, uint32(len(expectedHash)))

	return subtle.ConstantTimeCompare(hash, expectedHash) == 1
}

// dummyHash performs a hash operation to prevent timing-based username enumeration.
func dummyHash(password string) {
	salt := make([]byte, Argon2SaltLength)
	argon2.IDKey([]byte(password), salt, Argon2Time, Argon2Memory, Argon2Parallelism, Argon2KeyLength)
}