// Copyright (c) The Avalonia Project. All rights reserved.
// Licensed under the MIT license. See licence.md file in the project root for full license information.

using System;
using System.Runtime.InteropServices;

namespace Avalonia.Utilities
{
    /// <summary>
    /// Provides math utilities not provided in System.Math.
    /// </summary>
    public static class MathUtilities
    {
        /// <summary>
        /// AreClose - Returns whether or not two doubles are "close".  That is, whether or 
        /// not they are within epsilon of each other.
        /// </summary> 
        /// <param name="value1"> The first double to compare. </param>
        /// <param name="value2"> The second double to compare. </param>
        public static bool AreClose(double value1, double value2)
        {
            //in case they are Infinities (then epsilon check does not work)
            if (value1 == value2) return true;
            double eps = (Math.Abs(value1) + Math.Abs(value2) + 10.0) * double.Epsilon;
            double delta = value1 - value2;
            return (-eps < delta) && (eps > delta);
        }

        /// <summary>
        /// LessThan - Returns whether or not the first double is less than the second double.
        /// That is, whether or not the first is strictly less than *and* not within epsilon of
        /// the other number.
        /// </summary>
        /// <param name="value1"> The first double to compare. </param>
        /// <param name="value2"> The second double to compare. </param>
        public static bool LessThan(double value1, double value2)
        {
            return (value1 < value2) && !AreClose(value1, value2);
        }

        /// <summary>
        /// GreaterThan - Returns whether or not the first double is greater than the second double.
        /// That is, whether or not the first is strictly greater than *and* not within epsilon of
        /// the other number.
        /// </summary>
        /// <param name="value1"> The first double to compare. </param>
        /// <param name="value2"> The second double to compare. </param>
        public static bool GreaterThan(double value1, double value2)
        {
            return (value1 > value2) && !AreClose(value1, value2);
        }

        /// <summary>
        /// LessThanOrClose - Returns whether or not the first double is less than or close to
        /// the second double.  That is, whether or not the first is strictly less than or within
        /// epsilon of the other number.
        /// </summary>
        /// <param name="value1"> The first double to compare. </param>
        /// <param name="value2"> The second double to compare. </param>
        public static bool LessThanOrClose(double value1, double value2)
        {
            return (value1 < value2) || AreClose(value1, value2);
        }

        /// <summary>
        /// GreaterThanOrClose - Returns whether or not the first double is greater than or close to
        /// the second double.  That is, whether or not the first is strictly greater than or within
        /// epsilon of the other number.
        /// </summary>
        /// <param name="value1"> The first double to compare. </param>
        /// <param name="value2"> The second double to compare. </param>
        public static bool GreaterThanOrClose(double value1, double value2)
        {
            return (value1 > value2) || AreClose(value1, value2);
        }

        /// <summary>
        /// IsOne - Returns whether or not the double is "close" to 1.  Same as AreClose(double, 1),
        /// but this is faster.
        /// </summary>
        /// <param name="value"> The double to compare to 1. </param>
        public static bool IsOne(double value)
        {
            return Math.Abs(value - 1.0) < 10.0 * double.Epsilon;
        }

        /// <summary>
        /// IsZero - Returns whether or not the double is "close" to 0.  Same as AreClose(double, 0),
        /// but this is faster.
        /// </summary>
        /// <param name="value"> The double to compare to 0. </param>
        public static bool IsZero(double value)
        {
            return Math.Abs(value) < 10.0 * double.Epsilon;
        }

        /// <summary>
        /// Clamps a value between a minimum and maximum value.
        /// </summary>
        /// <param name="val">The value.</param>
        /// <param name="min">The minimum value.</param>
        /// <param name="max">The maximum value.</param>
        /// <returns>The clamped value.</returns>
        public static double Clamp(double val, double min, double max)
        {
            if (val < min)
            {
                return min;
            }
            else if (val > max)
            {
                return max;
            }
            else
            {
                return val;
            }
        }

        /// <summary>
        /// Calculates the value to be used for layout rounding at high DPI.
        /// </summary>
        /// <param name="value">Input value to be rounded.</param>
        /// <param name="dpiScale">Ratio of screen's DPI to layout DPI</param>
        /// <returns>Adjusted value that will produce layout rounding on screen at high dpi.</returns>
        /// <remarks>This is a layout helper method. It takes DPI into account and also does not return
        /// the rounded value if it is unacceptable for layout, e.g. Infinity or NaN. It's a helper associated with
        /// UseLayoutRounding  property and should not be used as a general rounding utility.</remarks>
        public static double RoundLayoutValue(double value, double dpiScale)
        {
            double newValue;

            // If DPI == 1, don't use DPI-aware rounding.
            if (!MathUtilities.AreClose(dpiScale, 1.0))
            {
                newValue = Math.Round(value * dpiScale) / dpiScale;
                // If rounding produces a value unacceptable to layout (NaN, Infinity or MaxValue), use the original value.
                if (double.IsNaN(newValue) ||
                    double.IsInfinity(newValue) ||
                    MathUtilities.AreClose(newValue, double.MaxValue))
                {
                    newValue = value;
                }
            }
            else
            {
                newValue = Math.Round(value);
            }

            return newValue;
        }

        /// <summary>
        /// Clamps a value between a minimum and maximum value.
        /// </summary>
        /// <param name="val">The value.</param>
        /// <param name="min">The minimum value.</param>
        /// <param name="max">The maximum value.</param>
        /// <returns>The clamped value.</returns>
        public static int Clamp(int val, int min, int max)
        {
            if (min > max)
            {
                throw new ArgumentException($"{min} cannot be greater than {max}.");
            }

            if (val < min)
            {
                return min;
            }
            else if (val > max)
            {
                return max;
            }
            else
            {
                return val;
            }
        }
    }
}