using NUnit.Framework;
using ProjectM.Client;

namespace ProjectM.Tests
{
    /// <summary>
    /// Pure tests for <see cref="HudVisualMath"/> — the low-health screen vignette ramp + hurt-flash decay that
    /// drive the HUD damage overlay. Verifies the curve is 0 above the threshold, 1 at empty, monotonic between,
    /// and that the flash decays to zero without going negative.
    /// </summary>
    public class HudVisualMathTests
    {
        const float Eps = 1e-4f;

        [Test]
        public void Vignette_ZeroAtFullHealth_AndAtThreshold()
        {
            Assert.AreEqual(0f, HudVisualMath.VignetteIntensity(1f), Eps);
            Assert.AreEqual(0f, HudVisualMath.VignetteIntensity(HudVisualMath.LowHealthThreshold), Eps);
            Assert.AreEqual(0f, HudVisualMath.VignetteIntensity(0.9f), Eps);
        }

        [Test]
        public void Vignette_OneAtEmpty_HalfAtMidband()
        {
            Assert.AreEqual(1f, HudVisualMath.VignetteIntensity(0f), Eps);
            // Half of the [0, threshold] band → ~0.5 intensity.
            Assert.AreEqual(0.5f, HudVisualMath.VignetteIntensity(HudVisualMath.LowHealthThreshold * 0.5f), Eps);
        }

        [Test]
        public void Vignette_IsMonotonicDecreasingInHealth()
        {
            float prev = HudVisualMath.VignetteIntensity(0f);
            for (float f = 0.05f; f <= 0.4f; f += 0.05f)
            {
                float cur = HudVisualMath.VignetteIntensity(f);
                Assert.LessOrEqual(cur, prev + Eps, "intensity must not rise as health rises");
                prev = cur;
            }
        }

        [Test]
        public void VignetteOpacity_ScalesByMax()
        {
            Assert.AreEqual(HudVisualMath.MaxVignetteOpacity, HudVisualMath.VignetteOpacity(0f), Eps);
            Assert.AreEqual(0f, HudVisualMath.VignetteOpacity(1f), Eps);
        }

        [Test]
        public void Flash_DecaysToZero_NeverNegative()
        {
            Assert.AreEqual(0f, HudVisualMath.DecayFlash(HudVisualMath.HurtFlashKick, HudVisualMath.HurtFlashDuration), Eps);
            // Half the duration → roughly half the kick remains.
            Assert.AreEqual(HudVisualMath.HurtFlashKick * 0.5f,
                HudVisualMath.DecayFlash(HudVisualMath.HurtFlashKick, HudVisualMath.HurtFlashDuration * 0.5f), Eps);
            Assert.AreEqual(0f, HudVisualMath.DecayFlash(0.1f, 10f), Eps, "over-long dt clamps to 0, not negative");
        }

        [Test]
        public void CombinedOpacity_ClampsToOne()
        {
            Assert.AreEqual(1f, HudVisualMath.CombinedOpacity(0f, 1f), Eps);
            Assert.AreEqual(0f, HudVisualMath.CombinedOpacity(1f, 0f), Eps);
            float mid = HudVisualMath.CombinedOpacity(0.175f, 0.2f);
            Assert.Greater(mid, 0f);
            Assert.LessOrEqual(mid, 1f);
        }
    }
}