namespace Theriapolis.Core.Rules.Stats;

/// <summary>
/// Standard d20 XP-to-level table. Phase 5 awards XP and persists it but
/// does not act on level-up — <see cref="LevelForXp"/> is exposed for the
/// HUD to display "next level in N XP" without requiring a level-up
/// flow yet.
/// </summary>
public static class XpTable
{
    /// <summary>XP threshold for each level 1..20. <c>Threshold[1] = 0</c> by convention.</summary>
    public static readonly int[] Threshold = new[]
    {
        0,        // index 0 unused
        0,        // level 1
        300,      // level 2
        900,
        2_700,
        6_500,
        14_000,
        23_000,
        34_000,
        48_000,
        64_000,
        85_000,
        100_000,
        120_000,
        140_000,
        165_000,
        195_000,
        225_000,
        265_000,
        305_000,
        355_000,  // level 20
    };

    public static int LevelForXp(int xp)
    {
        if (xp < 0) throw new ArgumentOutOfRangeException(nameof(xp));
        for (int lv = 20; lv >= 1; lv--)
            if (xp >= Threshold[lv]) return lv;
        return 1;
    }

    public static int XpRequiredForNextLevel(int currentLevel)
    {
        if (currentLevel < 1 || currentLevel > 20)
            throw new ArgumentOutOfRangeException(nameof(currentLevel));
        if (currentLevel == 20) return int.MaxValue;
        return Threshold[currentLevel + 1];
    }
}