package store

import (
	"context"
	"database/sql"
	"fmt"
)

// Vote toggles or sets a user's vote on a question (value must be 1 or -1).
func Vote(ctx context.Context, db *sql.DB, userID, questionID string, value int) error {
	if value != 1 && value != -1 {
		return fmt.Errorf("invalid vote")
	}
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer tx.Rollback()
	var current sql.NullInt64
	err = tx.QueryRowContext(ctx, `SELECT value FROM votes WHERE user_id = $1 AND question_id = $2`, userID, questionID).Scan(&current)
	if err != nil && err != sql.ErrNoRows {
		return err
	}
	if err == nil && current.Valid && int(current.Int64) == value {
		_, err = tx.ExecContext(ctx, `DELETE FROM votes WHERE user_id = $1 AND question_id = $2`, userID, questionID)
	} else {
		_, err = tx.ExecContext(ctx, `INSERT INTO votes (user_id, question_id, value) VALUES ($1, $2, $3)
ON CONFLICT (user_id, question_id) DO UPDATE SET value = excluded.value`, userID, questionID, value)
	}
	if err != nil {
		return err
	}
	return tx.Commit()
}