package auth

import (
	"context"
	"errors"
	"fmt"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

// User is the application-side view of a row in the users table.
type User struct {
	ID           uuid.UUID
	Email        string
	PasswordHash *string // nil for OIDC-only accounts
	OIDCSubject  *string
	OIDCIssuer   *string
	DisplayName  *string
}

// ErrUserNotFound is returned when no user matches the query.
var ErrUserNotFound = errors.New("user not found")

// UserStore wraps database access for the users table.
type UserStore struct {
	pool *pgxpool.Pool
}

// NewUserStore constructs a UserStore backed by the given pool.
func NewUserStore(pool *pgxpool.Pool) *UserStore {
	return &UserStore{pool: pool}
}

// CreateUser inserts a new user with a password hash (email/password accounts).
// It returns the created user. Email uniqueness violations surface as ErrEmailTaken.
var ErrEmailTaken = errors.New("email already registered")

func (s *UserStore) CreateUser(ctx context.Context, email, passwordHash, displayName string) (User, error) {
	const q = `
		INSERT INTO users (email, password_hash, display_name)
		VALUES ($1, $2, NULLIF($3, ''))
		RETURNING id, email, password_hash, oidc_subject, oidc_issuer, display_name`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, email, passwordHash, displayName).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if isUniqueViolation(err) {
			return User{}, fmt.Errorf("%w: %s", ErrEmailTaken, email)
		}
		return User{}, fmt.Errorf("create user: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}

// GetUserByEmail loads a user by its (case-sensitive) email address.
func (s *UserStore) GetUserByEmail(ctx context.Context, email string) (User, error) {
	const q = `
		SELECT id, email, password_hash, oidc_subject, oidc_issuer, display_name
		FROM users WHERE email = $1`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, email).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return User{}, ErrUserNotFound
		}
		return User{}, fmt.Errorf("get user by email: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}

// GetUserByID loads a user by its primary key.
func (s *UserStore) GetUserByID(ctx context.Context, id uuid.UUID) (User, error) {
	const q = `
		SELECT id, email, password_hash, oidc_subject, oidc_issuer, display_name
		FROM users WHERE id = $1`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, id).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return User{}, ErrUserNotFound
		}
		return User{}, fmt.Errorf("get user by id: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}

// GetByOIDCSubject loads a user by its (issuer, subject) pair. This is the key
// used to recognise a returning user across OIDC logins.
func (s *UserStore) GetByOIDCSubject(ctx context.Context, issuer, subject string) (User, error) {
	const q = `
		SELECT id, email, password_hash, oidc_subject, oidc_issuer, display_name
		FROM users WHERE oidc_issuer = $1 AND oidc_subject = $2`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, issuer, subject).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return User{}, ErrUserNotFound
		}
		return User{}, fmt.Errorf("get user by oidc subject: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}

// UpdateDisplayName sets the display_name of the user with the given id.
// An empty displayName clears the field (stores NULL).
func (s *UserStore) UpdateDisplayName(ctx context.Context, id uuid.UUID, displayName string) (User, error) {
	const q = `
		UPDATE users SET display_name = NULLIF($2, ''), updated_at = now()
		WHERE id = $1
		RETURNING id, email, password_hash, oidc_subject, oidc_issuer, display_name`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, id, displayName).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return User{}, ErrUserNotFound
		}
		return User{}, fmt.Errorf("update display name: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}

// CreateOIDCUser inserts a new user for an OIDC login. The user has no password
// (password_hash is NULL) and is identified by (issuer, subject). email may be
// empty if the IdP did not provide one; we store a synthesized placeholder so
// the NOT NULL + UNIQUE constraints hold and the account stays addressable.
func (s *UserStore) CreateOIDCUser(ctx context.Context, issuer, subject, email, displayName string) (User, error) {
	if email == "" {
		// Synthesize a stable, non-resolvable address for IdPs that don't return
		// an email (rare for Google, possible for generic providers).
		email = fmt.Sprintf("%s@oidc.local", subject)
	}
	const q = `
		INSERT INTO users (email, password_hash, oidc_subject, oidc_issuer, display_name)
		VALUES ($1, NULL, $2, $3, NULLIF($4, ''))
		RETURNING id, email, password_hash, oidc_subject, oidc_issuer, display_name`
	var u User
	var dn *string
	err := s.pool.QueryRow(ctx, q, email, subject, issuer, displayName).
		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
	if err != nil {
		if isUniqueViolation(err) {
			// Could be a duplicate email (owned by a password account) or a
			// race on the (issuer, subject) unique key. Surface a generic
			// conflict; the handler decides the HTTP code.
			return User{}, fmt.Errorf("%w: oidc account conflict", ErrEmailTaken)
		}
		return User{}, fmt.Errorf("create oidc user: %w", err)
	}
	u.DisplayName = dn
	return u, nil
}