namespace BlueLaminate.Core.Tradeups;

/// <summary>
/// The exact float arithmetic of a CS2 tradeup. Kept pure and dependency-free so it
/// can be unit-tested in isolation and reused verbatim by any frontend.
/// <para>
/// The contract: each input float is normalised to its own skin's range FIRST, those
/// fractions are averaged, and the average is mapped onto the OUTPUT skin's range. The
/// output float depends only on the average input fraction — a single scalar — which
/// is what makes the search tractable (see the engine design notes).
/// </para>
/// </summary>
public static class TradeupMath
{
    /// <summary>
    /// Normalises an input float to the fraction of its own skin's wear range:
    /// <c>(value − min) / (max − min)</c>, clamped to [0,1]. A zero-width range
    /// (min == max) has no meaningful fraction and yields 0.
    /// </summary>
    public static decimal NormalizedFraction(decimal floatValue, decimal skinFloatMin, decimal skinFloatMax)
    {
        var span = skinFloatMax - skinFloatMin;
        if (span <= 0m)
        {
            return 0m;
        }

        var fraction = (floatValue - skinFloatMin) / span;
        return Math.Clamp(fraction, 0m, 1m);
    }

    /// <summary>
    /// Maps an average input fraction onto an output skin's wear range to get the exact
    /// float the tradeup would produce: <c>avgFraction × (max − min) + min</c>.
    /// </summary>
    public static decimal OutputFloat(decimal averageFraction, decimal outputFloatMin, decimal outputFloatMax)
        => averageFraction * (outputFloatMax - outputFloatMin) + outputFloatMin;
}