namespace HSchool.Simulation;

/// <summary>
/// The speed buttons the player can pick, as an index on the wire. The table is duplicated in
/// <c>src/HSchool.Client/src/net/protocol.ts</c> — indexes, not multipliers, travel over the socket.
/// </summary>
public static class ClockSpeed
{
    /// <summary>×½, ×1, ×2, ×5, ×10.</summary>
    public static ReadOnlySpan<double> Multipliers => [0.5d, 1d, 2d, 5d, 10d];

    /// <summary>Index of ×1, the speed a school starts at.</summary>
    public const int DefaultIndex = 1;

    public static int Count => Multipliers.Length;

    public static bool IsValid(int index) => index >= 0 && index < Multipliers.Length;

    /// <summary>Multiplier for a validated index; out-of-range values fall back to ×1.</summary>
    public static double MultiplierAt(int index) => IsValid(index) ? Multipliers[index] : Multipliers[DefaultIndex];

    /// <summary>
    /// Calendar impulses between heavy-system ticks. ×5 and ×10 stride so walking and needs keep
    /// one game minute per heavy step instead of twenty tiny ones per second.
    /// </summary>
    public static int HeavySystemsStride(int speedIndex) => speedIndex switch
    {
        3 => 4,
        4 => 2,
        _ => 1,
    };

    /// <summary>
    /// Game minutes passed into presence, needs and learning on a heavy tick. High speeds use a
    /// fixed one-minute quantum; lower speeds pass the impulse's own advance.
    /// </summary>
    public static double HeavyGameMinutes(int speedIndex, double impulseMinutes) =>
        speedIndex is 3 or 4 ? 1d : impulseMinutes;
}