package account

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"time"

	"github.com/go-jet/jet/v2/postgres"
	"github.com/google/uuid"

	"scrabble/backend/internal/postgres/jet/backend/table"
)

// ErrIdentityTaken is returned when a platform identity being linked already
// belongs to another account; the caller turns it into a merge.
var ErrIdentityTaken = errors.New("account: identity already linked to another account")

// ErrLastIdentity is returned when removing an identity would leave the account with
// none, making it unreachable after logout. The admin email-erase refuses it.
var ErrLastIdentity = errors.New("account: cannot remove the last identity")

// RemoveIdentity deletes the account's identity of the given kind (and, for an email,
// any pending confirmations for it), freeing it for reuse. It refuses when that is the
// account's only identity (ErrLastIdentity) — which would leave the account
// unreachable — and returns ErrNotFound when the account has no identity of that kind.
// It backs the profile Unlink control and the admin "erase email" action.
func (s *Store) RemoveIdentity(ctx context.Context, accountID uuid.UUID, kind string) error {
	ids, err := s.Identities(ctx, accountID)
	if err != nil {
		return err
	}
	var toRetain []Identity
	others := 0
	for _, id := range ids {
		if id.Kind == kind {
			toRetain = append(toRetain, id)
		} else {
			others++
		}
	}
	if len(toRetain) == 0 {
		return ErrNotFound
	}
	if others == 0 {
		return ErrLastIdentity
	}
	return withTx(ctx, s.db, func(tx *sql.Tx) error {
		// Journal the detached credential before removing it, so the legal dossier
		// survives while the identity frees for reuse (see retention.go).
		for _, id := range toRetain {
			if err := retainIdentityTx(ctx, tx, accountID, id.Kind, id.ExternalID, id.Confirmed, id.CreatedAt, retainUnlink); err != nil {
				return err
			}
		}
		delID := table.Identities.DELETE().WHERE(
			table.Identities.AccountID.EQ(postgres.UUID(accountID)).
				AND(table.Identities.Kind.EQ(postgres.String(kind))),
		)
		if _, err := delID.ExecContext(ctx, tx); err != nil {
			return fmt.Errorf("account: delete %s identity %s: %w", kind, accountID, err)
		}
		if kind == KindEmail {
			delConf := table.EmailConfirmations.DELETE().WHERE(
				table.EmailConfirmations.AccountID.EQ(postgres.UUID(accountID)),
			)
			if _, err := delConf.ExecContext(ctx, tx); err != nil {
				return fmt.Errorf("account: delete email confirmations %s: %w", accountID, err)
			}
		}
		return nil
	})
}

// RemoveEmailIdentity erases the account's email identity. It backs the admin console's
// "erase email" action; the user-facing profile never unlinks email (it is changed).
func (s *Store) RemoveEmailIdentity(ctx context.Context, accountID uuid.UUID) error {
	return s.RemoveIdentity(ctx, accountID, KindEmail)
}

// RequestLinkCode issues and mails a confirm-code for email to accountID,
// replacing any prior pending code. Unlike RequestCode it never refuses up front
// (taken or already-confirmed): possession of the address is the authorization for
// a later link or merge, and the merge is only revealed once the code is verified,
// so a probe cannot learn whether an address is registered.
func (s *EmailService) RequestLinkCode(ctx context.Context, accountID uuid.UUID, email string) error {
	addr, err := normalizeEmail(email)
	if err != nil {
		return err
	}
	if !s.allowSend(addr) {
		return ErrTooManyRequests
	}
	return s.issueCode(ctx, accountID, addr, purposeLink, s.accountLocale(ctx, accountID))
}

// ConfirmLink verifies code for (accountID, email) and reports the address's
// current owner. When the address is free it binds a confirmed email identity to
// accountID and returns (accountID, true, nil). When accountID already owns it,
// it returns (accountID, true, nil) unchanged. When another account owns it, it
// returns (owner, false, nil) without consuming the code, so the explicit merge
// step can re-verify the same live code. It returns the usual confirm-code errors
// (ErrNoPendingCode, ErrCodeExpired, ErrTooManyAttempts, ErrCodeMismatch).
func (s *EmailService) ConfirmLink(ctx context.Context, accountID uuid.UUID, email, code string) (uuid.UUID, bool, error) {
	addr, err := normalizeEmail(email)
	if err != nil {
		return uuid.Nil, false, err
	}
	conf, err := s.verifyPendingCode(ctx, accountID, addr, code)
	if err != nil {
		return uuid.Nil, false, err
	}
	owner, ok, err := s.store.confirmedEmailAccount(ctx, addr)
	if err != nil {
		return uuid.Nil, false, err
	}
	if ok {
		if owner == accountID {
			return accountID, true, nil
		}
		return owner, false, nil
	}
	if err := s.store.confirmEmailIdentity(ctx, conf.id, accountID, addr, s.now()); err != nil {
		return uuid.Nil, false, err
	}
	return accountID, true, nil
}

// RequestChangeCode issues and mails a confirm-code to newEmail for an authenticated
// email change on accountID, replacing any prior pending code. Like RequestLinkCode it
// never refuses up front on "taken" (anti-enumeration): possession of newEmail is the
// authorization, and a conflict with another account is revealed only at confirm — as a
// non-disclosing refusal, never a merge.
func (s *EmailService) RequestChangeCode(ctx context.Context, accountID uuid.UUID, newEmail string) error {
	addr, err := normalizeEmail(newEmail)
	if err != nil {
		return err
	}
	if !s.allowSend(addr) {
		return ErrTooManyRequests
	}
	return s.issueCode(ctx, accountID, addr, purposeChange, s.accountLocale(ctx, accountID))
}

// ConfirmChange verifies code for (accountID, newEmail) and atomically replaces the
// account's confirmed email with newEmail, freeing the old address. When newEmail is
// already confirmed by another account it refuses with ErrEmailTaken (surfaced to the
// user as a non-disclosing "check the address or contact support"), never merging; when
// the account already owns newEmail it is an idempotent no-op. It returns the usual
// confirm-code errors (ErrNoPendingCode, ErrCodeExpired, ErrTooManyAttempts,
// ErrCodeMismatch) and the updated account on success.
func (s *EmailService) ConfirmChange(ctx context.Context, accountID uuid.UUID, newEmail, code string) (Account, error) {
	addr, err := normalizeEmail(newEmail)
	if err != nil {
		return Account{}, err
	}
	conf, err := s.verifyPendingCode(ctx, accountID, addr, code)
	if err != nil {
		return Account{}, err
	}
	owner, ok, err := s.store.confirmedEmailAccount(ctx, addr)
	if err != nil {
		return Account{}, err
	}
	if ok && owner != accountID {
		return Account{}, ErrEmailTaken
	}
	if ok && owner == accountID {
		if err := s.store.consumeConfirmation(ctx, conf.id, s.now()); err != nil {
			return Account{}, err
		}
		return s.store.GetByID(ctx, accountID)
	}
	if err := s.store.replaceEmailIdentity(ctx, conf.id, accountID, addr, s.now()); err != nil {
		return Account{}, err
	}
	return s.store.GetByID(ctx, accountID)
}

// HasEmail reports whether accountID owns a confirmed email. The account-deletion step-up
// mails a confirm-code when it does, and falls back to a typed phrase otherwise.
func (s *EmailService) HasEmail(ctx context.Context, accountID uuid.UUID) (bool, error) {
	_, ok, err := s.store.confirmedEmailOf(ctx, accountID)
	return ok, err
}

// RequestDeleteCode mails an account-deletion confirm-code to the account's own confirmed
// email (no deeplink — deletion is confirmed in the app). It returns ErrNoEmail when the
// account holds no email, ErrTooManyRequests when throttled.
func (s *EmailService) RequestDeleteCode(ctx context.Context, accountID uuid.UUID) error {
	addr, ok, err := s.store.confirmedEmailOf(ctx, accountID)
	if err != nil {
		return err
	}
	if !ok {
		return ErrNoEmail
	}
	if !s.allowSend(addr) {
		return ErrTooManyRequests
	}
	return s.issueCode(ctx, accountID, addr, purposeDelete, s.accountLocale(ctx, accountID))
}

// VerifyDeleteCode verifies the account-deletion code against the account's own email and
// consumes it on success. It returns ErrNoEmail (no email), the usual confirm-code errors
// (ErrNoPendingCode, ErrCodeExpired, ErrTooManyAttempts, ErrCodeMismatch), or nil when the
// code is valid — the caller then performs the deletion.
func (s *EmailService) VerifyDeleteCode(ctx context.Context, accountID uuid.UUID, code string) error {
	addr, ok, err := s.store.confirmedEmailOf(ctx, accountID)
	if err != nil {
		return err
	}
	if !ok {
		return ErrNoEmail
	}
	conf, err := s.verifyPendingCode(ctx, accountID, addr, code)
	if err != nil {
		return err
	}
	return s.store.consumeConfirmation(ctx, conf.id, s.now())
}

// verifyPendingCode loads and checks the pending confirm-code for (accountID,
// addr), counting a wrong attempt. It returns the confirmation on success.
func (s *EmailService) verifyPendingCode(ctx context.Context, accountID uuid.UUID, addr, code string) (emailConfirmation, error) {
	conf, err := s.store.latestPendingConfirmation(ctx, accountID, addr)
	if err != nil {
		return emailConfirmation{}, err
	}
	if s.now().After(conf.expiresAt) {
		return emailConfirmation{}, ErrCodeExpired
	}
	if conf.attempts >= emailCodeMaxAttempts {
		return emailConfirmation{}, ErrTooManyAttempts
	}
	if hashCode(code) != conf.codeHash {
		if err := s.store.bumpConfirmationAttempts(ctx, conf.id); err != nil {
			return emailConfirmation{}, err
		}
		return emailConfirmation{}, ErrCodeMismatch
	}
	return conf, nil
}

// AccountIDByIdentity returns the account owning (kind, externalID) and true, or
// (uuid.Nil, false) when the identity is free. It backs the platform-identity link
// flow.
func (s *Store) AccountIDByIdentity(ctx context.Context, kind, externalID string) (uuid.UUID, bool, error) {
	acc, err := s.findByIdentity(ctx, kind, externalID)
	if errors.Is(err, ErrNotFound) {
		return uuid.Nil, false, nil
	}
	if err != nil {
		return uuid.Nil, false, err
	}
	return acc.ID, true, nil
}

// AttachIdentity links a new (kind, externalID) identity to an existing account.
// A unique-constraint violation means the identity was taken meanwhile, surfaced
// as ErrIdentityTaken. It is used to attach a platform identity (e.g. Telegram)
// to the current account during linking.
func (s *Store) AttachIdentity(ctx context.Context, accountID uuid.UUID, kind, externalID string, confirmed bool) error {
	id, err := uuid.NewV7()
	if err != nil {
		return fmt.Errorf("account: new identity id: %w", err)
	}
	ins := table.Identities.INSERT(
		table.Identities.IdentityID, table.Identities.AccountID, table.Identities.Kind,
		table.Identities.ExternalID, table.Identities.Confirmed,
	).VALUES(id, accountID, kind, externalID, confirmed)
	if _, err := ins.ExecContext(ctx, s.db); err != nil {
		if isUniqueViolation(err) {
			return ErrIdentityTaken
		}
		return fmt.Errorf("account: attach identity (%s, %s): %w", kind, externalID, err)
	}
	return nil
}

// ClearGuest removes the is_guest flag from accountID, promoting an ephemeral guest
// to a durable account once it gains its first identity. It is a no-op
// for an already-durable account.
func (s *Store) ClearGuest(ctx context.Context, accountID uuid.UUID) error {
	upd := table.Accounts.UPDATE(table.Accounts.IsGuest, table.Accounts.UpdatedAt).
		SET(postgres.Bool(false), postgres.TimestampzT(time.Now().UTC())).
		WHERE(
			table.Accounts.AccountID.EQ(postgres.UUID(accountID)).
				AND(table.Accounts.IsGuest.EQ(postgres.Bool(true))),
		)
	if _, err := upd.ExecContext(ctx, s.db); err != nil {
		return fmt.Errorf("account: clear guest %s: %w", accountID, err)
	}
	return nil
}