namespace MrGameEng.Genetics;

/// <summary>
/// Shared, deterministic allele sampling used by both <see cref="Genome.Generate"/> (gene defaults)
/// and <see cref="GenomeTemplate"/> (per-individual base overrides). Centralizes the numeric
/// spread+clamp and the weighted discrete pick so the two paths stay consistent.
/// </summary>
internal static class GeneSampling
{
    /// <summary>A numeric allele drawn as <c>baseValue ± spread·|baseValue|</c>, clamped to the gene's range.</summary>
    public static float Numeric(GeneDef gene, float baseValue, float spread, Random random)
    {
        var value = baseValue + (random.NextSingle() * 2f - 1f) * spread * MathF.Abs(baseValue);
        return Math.Clamp(value, gene.Min, gene.Max);
    }

    /// <summary>
    /// A discrete variant index in <c>[0, Variants)</c>, picked from <paramref name="weights"/> when
    /// they match the variant count, otherwise the gene's own weights, otherwise uniformly.
    /// </summary>
    public static float Variant(GeneDef gene, float[]? weights, Random random)
    {
        var variants = Math.Max(1, gene.Variants);
        var w =
            weights is { Length: > 0 } && weights.Length == variants
                ? weights
                : gene.VariantWeights;
        if (w.Length != variants)
        {
            return random.Next(variants);
        }

        var total = 0f;
        foreach (var value in w)
        {
            total += MathF.Max(0f, value);
        }

        if (total <= 0f)
        {
            return random.Next(variants);
        }

        var roll = random.NextSingle() * total;
        for (var i = 0; i < variants; i++)
        {
            roll -= MathF.Max(0f, w[i]);
            if (roll < 0f)
            {
                return i;
            }
        }

        return variants - 1;
    }
}