namespace GeometriCS
{
    /// <summary>
    /// Common utilities throughout the library.
    /// </summary>
    public static class Utils
    {
        /// <summary>
        /// Default precision for double equality comparison.
        /// </summary>
        private const double DOUBLEPRECISION = 1E-5;

        /// <summary>
        /// Is this number in the range <lower; higher> (inclusive).
        /// </summary>
        /// <param name="num">Number to compare</param>
        /// <param name="lower">Lower end of the range.</param>
        /// <param name="higher">Higher end of the range.</param>
        /// <returns><c>true</c>if number is in the range <lower; higher>, <c>false</c> if it is outside.</returns>
        public static bool IsInRange(this double num, double lower, double higher)
        {
            return num >= lower && num <= higher;
        }

        /// <summary>
        /// Tests whether the difference between two doubles is within a given limit.
        /// </summary>
        /// <param name="a">First value to test.</param>
        /// <param name="b">Second value to test.</param>
        /// <param name="prec">Maximum allowed difference.</param>
        /// <returns>Do the values almost equal each other.</returns>
        public static bool DoubleEquals(double a, double b, double prec = DOUBLEPRECISION) => Math.Abs(a - b) <= prec;

        /// <summary>
        /// Returns the coefficients of a line defined by equation Ax + By + C = 0, 
        /// given two points that lie on the line.
        /// </summary>
        /// <param name="pt1">First point on the line.</param>
        /// <param name="pt2">Second point on the line.</param>
        /// <returns>Touple (Coeff_A, Coeff_B, Coeff_C).</returns>
        public static (double A, double B, double C) Line2CoefficientsFromTwoPoints(Vector2d pt1, Vector2d pt2) 
        {
            double coeff_A = pt2.Y - pt1.Y;
            double coeff_B = pt1.X - pt2.X;
            double coeff_C = (pt1.Y * (pt2.X - pt1.X)) -
                             (pt1.X * (pt2.Y - pt1.Y));
            return (coeff_A, coeff_B, coeff_C);
        }
    }
}