package social

import (
	"context"
	"errors"
	"fmt"
	"time"

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

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

// Friendship statuses persisted in friendships.status.
const (
	friendPending  = "pending"
	friendAccepted = "accepted"
)

// SendFriendRequest records a pending friend request from requesterID to
// addresseeID. It refuses a self-request, a request blocked by either a per-user
// block or the addressee's block_friend_requests toggle, and a duplicate of an
// existing request or friendship in either direction.
func (svc *Service) SendFriendRequest(ctx context.Context, requesterID, addresseeID uuid.UUID) error {
	if requesterID == addresseeID {
		return ErrSelfRelation
	}
	blocked, err := svc.store.isBlocked(ctx, requesterID, addresseeID)
	if err != nil {
		return err
	}
	addressee, err := svc.accounts.GetByID(ctx, addresseeID)
	if err != nil {
		if errors.Is(err, account.ErrNotFound) {
			return account.ErrNotFound
		}
		return err
	}
	if blocked || addressee.BlockFriendRequests {
		return ErrRequestBlocked
	}
	exists, err := svc.store.friendshipExists(ctx, requesterID, addresseeID)
	if err != nil {
		return err
	}
	if exists {
		return ErrRequestExists
	}
	if err := svc.store.insertFriendRequest(ctx, requesterID, addresseeID); err != nil {
		if isUniqueViolation(err) {
			return ErrRequestExists
		}
		return err
	}
	return nil
}

// RespondFriendRequest lets addresseeID accept or decline the pending request
// from requesterID. Accepting flips it to a friendship; declining deletes it.
// Either way ErrRequestNotFound is returned when no pending request matches.
func (svc *Service) RespondFriendRequest(ctx context.Context, addresseeID, requesterID uuid.UUID, accept bool) error {
	var ok bool
	var err error
	if accept {
		ok, err = svc.store.acceptFriendRequest(ctx, requesterID, addresseeID, svc.now())
	} else {
		ok, err = svc.store.deletePendingRequest(ctx, requesterID, addresseeID)
	}
	if err != nil {
		return err
	}
	if !ok {
		return ErrRequestNotFound
	}
	return nil
}

// CancelFriendRequest withdraws requesterID's own pending request to addresseeID.
func (svc *Service) CancelFriendRequest(ctx context.Context, requesterID, addresseeID uuid.UUID) error {
	ok, err := svc.store.deletePendingRequest(ctx, requesterID, addresseeID)
	if err != nil {
		return err
	}
	if !ok {
		return ErrRequestNotFound
	}
	return nil
}

// Unfriend removes the friendship between the two accounts, in either direction.
// It is idempotent: removing a non-existent friendship is not an error.
func (svc *Service) Unfriend(ctx context.Context, accountID, otherID uuid.UUID) error {
	return svc.store.deleteFriendship(ctx, accountID, otherID)
}

// ListFriends returns the account IDs that are accepted friends of accountID.
func (svc *Service) ListFriends(ctx context.Context, accountID uuid.UUID) ([]uuid.UUID, error) {
	return svc.store.listFriends(ctx, accountID)
}

// ListIncomingRequests returns the account IDs that have a pending friend request
// awaiting accountID's response.
func (svc *Service) ListIncomingRequests(ctx context.Context, accountID uuid.UUID) ([]uuid.UUID, error) {
	return svc.store.listIncomingRequests(ctx, accountID)
}

// friendshipExists reports whether any friendship row (pending or accepted) exists
// between a and b in either direction.
func (s *Store) friendshipExists(ctx context.Context, a, b uuid.UUID) (bool, error) {
	stmt := postgres.SELECT(table.Friendships.Status).
		FROM(table.Friendships).
		WHERE(edgeEither(a, b)).
		LIMIT(1)
	var row model.Friendships
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return false, nil
		}
		return false, fmt.Errorf("social: friendship exists: %w", err)
	}
	return true, nil
}

// insertFriendRequest inserts a pending request from requester to addressee.
func (s *Store) insertFriendRequest(ctx context.Context, requester, addressee uuid.UUID) error {
	stmt := table.Friendships.INSERT(
		table.Friendships.RequesterID, table.Friendships.AddresseeID, table.Friendships.Status,
	).VALUES(requester, addressee, friendPending)
	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return fmt.Errorf("social: insert friend request: %w", err)
	}
	return nil
}

// acceptFriendRequest flips a pending request to accepted and reports whether a
// row matched.
func (s *Store) acceptFriendRequest(ctx context.Context, requester, addressee uuid.UUID, now time.Time) (bool, error) {
	stmt := table.Friendships.
		UPDATE(table.Friendships.Status, table.Friendships.RespondedAt).
		SET(postgres.String(friendAccepted), postgres.TimestampzT(now)).
		WHERE(
			table.Friendships.RequesterID.EQ(postgres.UUID(requester)).
				AND(table.Friendships.AddresseeID.EQ(postgres.UUID(addressee))).
				AND(table.Friendships.Status.EQ(postgres.String(friendPending))),
		)
	return execAffected(ctx, s.db, stmt, "social: accept friend request")
}

// deletePendingRequest removes a pending request and reports whether a row matched.
func (s *Store) deletePendingRequest(ctx context.Context, requester, addressee uuid.UUID) (bool, error) {
	stmt := table.Friendships.DELETE().WHERE(
		table.Friendships.RequesterID.EQ(postgres.UUID(requester)).
			AND(table.Friendships.AddresseeID.EQ(postgres.UUID(addressee))).
			AND(table.Friendships.Status.EQ(postgres.String(friendPending))),
	)
	return execAffected(ctx, s.db, stmt, "social: delete friend request")
}

// deleteFriendship removes an accepted friendship in either direction.
func (s *Store) deleteFriendship(ctx context.Context, a, b uuid.UUID) error {
	stmt := table.Friendships.DELETE().WHERE(
		edgeEither(a, b).AND(table.Friendships.Status.EQ(postgres.String(friendAccepted))),
	)
	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return fmt.Errorf("social: delete friendship: %w", err)
	}
	return nil
}

// listFriends returns the other side of every accepted edge touching accountID.
func (s *Store) listFriends(ctx context.Context, accountID uuid.UUID) ([]uuid.UUID, error) {
	stmt := postgres.SELECT(table.Friendships.RequesterID, table.Friendships.AddresseeID).
		FROM(table.Friendships).
		WHERE(
			table.Friendships.Status.EQ(postgres.String(friendAccepted)).
				AND(table.Friendships.RequesterID.EQ(postgres.UUID(accountID)).
					OR(table.Friendships.AddresseeID.EQ(postgres.UUID(accountID)))),
		)
	var rows []model.Friendships
	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("social: list friends: %w", err)
	}
	out := make([]uuid.UUID, 0, len(rows))
	for _, r := range rows {
		if r.RequesterID == accountID {
			out = append(out, r.AddresseeID)
		} else {
			out = append(out, r.RequesterID)
		}
	}
	return out, nil
}

// listIncomingRequests returns the requesters of every pending request to accountID.
func (s *Store) listIncomingRequests(ctx context.Context, accountID uuid.UUID) ([]uuid.UUID, error) {
	stmt := postgres.SELECT(table.Friendships.RequesterID).
		FROM(table.Friendships).
		WHERE(
			table.Friendships.AddresseeID.EQ(postgres.UUID(accountID)).
				AND(table.Friendships.Status.EQ(postgres.String(friendPending))),
		)
	var rows []model.Friendships
	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("social: list incoming requests: %w", err)
	}
	out := make([]uuid.UUID, 0, len(rows))
	for _, r := range rows {
		out = append(out, r.RequesterID)
	}
	return out, nil
}

// edgeEither matches a friendship row between a and b in either direction.
func edgeEither(a, b uuid.UUID) postgres.BoolExpression {
	return table.Friendships.RequesterID.EQ(postgres.UUID(a)).AND(table.Friendships.AddresseeID.EQ(postgres.UUID(b))).
		OR(table.Friendships.RequesterID.EQ(postgres.UUID(b)).AND(table.Friendships.AddresseeID.EQ(postgres.UUID(a))))
}

// execAffected runs a mutating statement and reports whether it changed a row.
func execAffected(ctx context.Context, db qrm.Executable, stmt postgres.Statement, what string) (bool, error) {
	res, err := stmt.ExecContext(ctx, db)
	if err != nil {
		return false, fmt.Errorf("%s: %w", what, err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return false, fmt.Errorf("%s rows: %w", what, err)
	}
	return n > 0, nil
}