/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

using System;
using System.Linq;
using CultMath;
using Xunit;
using static CultMath.math;
using float2 = CultMath.float2;

// Damage falloff (aetheria-release, damage-curve-fate-ruled): a weapon's damage is flat to its effective range, then one
// lerp to DamageAtMaxRange at its Range, and 0 outside [MinRange, Range]. The function, the catalog authored through it,
// and the fire-time freeze that reads it.
public sealed class RangeFalloffTests
{
    private static PerformanceStat Span(float min, float max) => new PerformanceStat { Min = min, Max = max };

    // [20, 60, 120], .25 at the end: flat to 60, then 1 -> .25 over 60 units.
    [Fact]
    public void TheFactorIsFlatToEffectiveThenOneLerp()
    {
        float F(float at) => WeaponData.RangeFactor(20f, 60f, 120f, .25f, at);
        Assert.Equal(0f, F(19.9f));
        Assert.Equal(0f, F(120.1f));
        Assert.Equal(1f, F(20f));
        Assert.Equal(1f, F(40f));
        Assert.Equal(1f, F(60f));
        Assert.Equal(.625f, F(90f), 5);
        Assert.Equal(.25f, F(120f), 5);
    }

    [Fact]
    public void AnUnauthoredOrDegenerateEffectiveRangeIsFlat()
    {
        var fresh = new InstantWeaponData { MinRange = Span(10, 10), Range = Span(100, 100) };
        Assert.True(float.IsPositiveInfinity(fresh.EffectiveRange.Min) && float.IsPositiveInfinity(fresh.EffectiveRange.Max));
        foreach (var at in new[] { 10f, 55f, 100f })
            Assert.Equal(1f, fresh.RatedRangeFactor(at));

        // Below the minimum range the effective range reads as the minimum: full damage only at it, then the lerp.
        Assert.Equal(1f, WeaponData.RangeFactor(20f, 5f, 120f, 0f, 20f));
        Assert.Equal(.5f, WeaponData.RangeFactor(20f, 5f, 120f, 0f, 70f), 5);
        // At or past the maximum range it is flat everywhere inside the gate.
        foreach (var at in new[] { 20f, 70f, 120f })
            Assert.Equal(1f, WeaponData.RangeFactor(20f, 120f, 120f, 0f, at));
        Assert.Equal(1f, WeaponData.RangeFactor(20f, 500f, 120f, 0f, 70f));
    }

    [Fact]
    public void ShippedWeaponsFallOffAsAuthored()
    {
        using var cache = RestoredHullsTests.OpenCatalog();
        var weapons = cache.GetAll<WeaponItemData>().SelectMany(i => i.Behaviors.OfType<WeaponData>().Select(w => (i.Name, w))).ToArray();
        Assert.Equal(27, weapons.Length);
        var falling = weapons.Where(x => !(x.w is LockWeaponData || x.w is GuidedWeaponData || x.w is MineLayerData)).ToArray();
        Assert.Equal(21, falling.Length);
        foreach (var (name, weapon) in falling)
        {
            Assert.True(weapon.EffectiveRange.Min == weapon.Range.Min * .5f && weapon.EffectiveRange.Max == weapon.Range.Max * .5f, $"{name}: effective range is half the range");
            Assert.Equal(weapon.Range.Terms.Select(t => (t.Source, t.Exponent, t.Role)), weapon.EffectiveRange.Terms.Select(t => (t.Source, t.Exponent, t.Role)));
            Assert.Equal(0f, weapon.DamageAtMaxRange);
        }
        foreach (var (name, weapon) in weapons.Except(falling))
            Assert.True(float.IsPositiveInfinity(weapon.EffectiveRange.Max) && float.IsPositiveInfinity(weapon.EffectiveRange.Min), $"{name}: no falloff");
        foreach (var (name, weapon) in weapons)
            for (var i = 0; i <= 64; i++)
                Assert.True(weapon.RatedRangeFactor(lerp(weapon.MinRange.Min, weapon.Range.Max, i / 64f)) <= 1f, $"{name}: factor above 1");
    }
}

public sealed partial class FireControlCut124Tests
{
    private ShotRecord FreezeAt(float targetRange, float effective = 50f, float weaponRange = 150f, float? damageOverride = null)
    {
        var e = Build(TestSettings(), SolidShape(5, 4), velocity: 0, damage: 100f, weaponRange: weaponRange, targetRange: targetRange,
            effectiveRange: effective, damageAtMaxRange: 0f);
        var shotId = FireControl.Fire(e.Weapon, e.WeaponItem, e.Shooter, damageOverride);
        Assert.NotEqual(0, shotId);
        return new ShotRecord { Damage = e.Zone.PendingShots.Single(s => s.ShotId == shotId).Damage };
    }

    private struct ShotRecord { public float Damage; }

    // The observation is where damage is decided at fire time: the shot right after Fire, before anything resolves.
    [Fact]
    public void FireFreezesDamageTimesTheFactorAtDeliveryRange()
    {
        Assert.Equal(50f, FreezeAt(100f).Damage, 3);   // halfway from 50 to 150
        Assert.Equal(100f, FreezeAt(40f).Damage, 3);   // inside the effective range
        Assert.Equal(0f, FreezeAt(150f).Damage, 3);    // at the maximum range
    }

    // A fused round with no target bursts at Range ("bomb fishing"), so it lands at the end multiplier.
    [Fact]
    public void AFusedRoundFishedToRangeLandsAtTheEndMultiplier()
    {
        var e = Build(TestSettings(), SolidShape(5, 4), velocity: 0, fuse: WeaponFuse.Proximity, blastRadius: 4f, damage: 100f,
            weaponRange: 150f, effectiveRange: 50f, damageAtMaxRange: .25f);
        e.Shooter.SetTarget(TargetRef.None);
        Aim(e, float2(0, 1));
        var shotId = FireControl.Fire(e.Weapon, e.WeaponItem, e.Shooter);
        Assert.NotEqual(0, shotId);
        Assert.Equal(25f, e.Zone.PendingShots.Single(s => s.ShotId == shotId).Damage, 3);
    }

    // A beam roll fires through damageOverride: the override is what the factor multiplies.
    [Fact]
    public void ABeamRollCarriesTheFactor() => Assert.Equal(5f, FreezeAt(100f, damageOverride: 10f).Damage, 3);
}