package auth

import (
	"context"
	"errors"
	"strings"
	"time"

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

// DefaultPasswordResetTTL is the self-serve reset link lifetime.
const DefaultPasswordResetTTL = time.Hour

// PasswordResetIssue is returned once when a reset token is created (plaintext token for email only).
type PasswordResetIssue struct {
	UserID uuid.UUID
	Email  string
	Token  string
}

// IssuePasswordReset creates a durable hashed reset token for an active user with a deliverable email.
// Unknown, inactive, and synthetic @legacy.local addresses return ErrUserNotFound / ErrSyntheticEmail
// so callers can respond opaquely without enumeration.
func (s *Service) IssuePasswordReset(ctx context.Context, email string, ttl time.Duration) (PasswordResetIssue, error) {
	email = strings.ToLower(strings.TrimSpace(email))
	if email == "" {
		return PasswordResetIssue{}, ErrEmailRequired
	}
	if IsSyntheticLegacyEmail(email) {
		return PasswordResetIssue{}, ErrSyntheticEmail
	}
	if ttl <= 0 {
		ttl = DefaultPasswordResetTTL
	}

	var (
		userID   uuid.UUID
		isActive bool
	)
	err := s.Pool.QueryRow(ctx, `
		SELECT id, is_active
		FROM users
		WHERE lower(email) = $1`, email).Scan(&userID, &isActive)
	if errors.Is(err, pgx.ErrNoRows) {
		return PasswordResetIssue{}, ErrUserNotFound
	}
	if err != nil {
		return PasswordResetIssue{}, err
	}
	if !isActive {
		return PasswordResetIssue{}, ErrUserNotFound
	}

	token, err := RandomToken(24)
	if err != nil {
		return PasswordResetIssue{}, err
	}
	expiresAt := time.Now().UTC().Add(ttl)

	tx, err := s.Pool.Begin(ctx)
	if err != nil {
		return PasswordResetIssue{}, err
	}
	defer tx.Rollback(ctx)

	// Invalidate prior unused tokens so only the latest link works.
	if _, err := tx.Exec(ctx, `
		UPDATE password_reset_tokens
		SET expires_at = least(expires_at, now())
		WHERE user_id = $1 AND consumed_at IS NULL AND expires_at > now()`, userID); err != nil {
		return PasswordResetIssue{}, err
	}

	if _, err := tx.Exec(ctx, `
		INSERT INTO password_reset_tokens (user_id, token_hash, expires_at)
		VALUES ($1, $2, $3)`, userID, HashInviteToken(token), expiresAt); err != nil {
		return PasswordResetIssue{}, err
	}
	if err := tx.Commit(ctx); err != nil {
		return PasswordResetIssue{}, err
	}

	return PasswordResetIssue{UserID: userID, Email: email, Token: token}, nil
}

// ResetPasswordWithToken consumes a one-time reset token and sets a new password
// regardless of must_set_password (dedicated reset path — not SetPassword / ForceSetPassword).
func (s *Service) ResetPasswordWithToken(ctx context.Context, rawToken, password string) error {
	rawToken = strings.TrimSpace(rawToken)
	if rawToken == "" {
		return ErrTokenInvalid
	}
	passwordHash, err := HashPassword(password)
	if err != nil {
		return err
	}

	tx, err := s.Pool.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(ctx)

	var (
		tokenID    uuid.UUID
		userID     uuid.UUID
		expiresAt  time.Time
		consumedAt *time.Time
	)
	err = tx.QueryRow(ctx, `
		SELECT id, user_id, expires_at, consumed_at
		FROM password_reset_tokens
		WHERE token_hash = $1
		FOR UPDATE`, HashInviteToken(rawToken)).Scan(&tokenID, &userID, &expiresAt, &consumedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return ErrTokenInvalid
	}
	if err != nil {
		return err
	}
	if consumedAt != nil || !expiresAt.After(time.Now().UTC()) {
		return ErrTokenInvalid
	}

	var isActive bool
	err = tx.QueryRow(ctx, `SELECT is_active FROM users WHERE id = $1 FOR UPDATE`, userID).Scan(&isActive)
	if errors.Is(err, pgx.ErrNoRows) || (err == nil && !isActive) {
		return ErrTokenInvalid
	}
	if err != nil {
		return err
	}

	ct, err := tx.Exec(ctx, `
		UPDATE users
		SET password_hash = $2,
		    must_set_password = false,
		    session_version = session_version + 1,
		    updated_at = now()
		WHERE id = $1 AND is_active = true`, userID, passwordHash)
	if isUndefinedColumn(err) {
		// Pre-042 DBs: still reset password; session revoke requires session_version migration.
		ct, err = tx.Exec(ctx, `
			UPDATE users
			SET password_hash = $2, must_set_password = false, updated_at = now()
			WHERE id = $1 AND is_active = true`, userID, passwordHash)
	}
	if err != nil {
		return err
	}
	if ct.RowsAffected() == 0 {
		return ErrTokenInvalid
	}

	if _, err := tx.Exec(ctx, `
		UPDATE password_reset_tokens
		SET consumed_at = now()
		WHERE id = $1`, tokenID); err != nil {
		return err
	}
	// Expire any sibling unused tokens for this user.
	if _, err := tx.Exec(ctx, `
		UPDATE password_reset_tokens
		SET expires_at = least(expires_at, now())
		WHERE user_id = $1 AND id <> $2 AND consumed_at IS NULL AND expires_at > now()`,
		userID, tokenID); err != nil {
		return err
	}

	return tx.Commit(ctx)
}