using Microsoft.Xna.Framework;
using MrGameEng.Core;

namespace MrGameEng.Host;

/// <summary>
/// A scene transition that draws a full-screen overlay through a
/// <see cref="TransitionRenderer"/>. The timing state machine lives in
/// <see cref="SceneManager"/>; <see cref="GameHost"/> renders the overlay each draw while a
/// transition is active. Transitions are stateless and reusable.
/// </summary>
public abstract class OverlayTransition : Transition
{
    /// <summary>Creates a transition with explicit phase durations.</summary>
    protected OverlayTransition(float outDuration, float inDuration)
        : base(outDuration, inDuration) { }

    /// <summary>
    /// Draws the overlay. <paramref name="coverage"/> is 0 (scene fully visible) to
    /// 1 (scene fully covered); <paramref name="phase"/> tells which side of the switch this is.
    /// </summary>
    public abstract void Draw(TransitionRenderer renderer, float coverage, TransitionPhase phase);
}

/// <summary>Factories for the built-in visual scene transitions.</summary>
public static class Transitions
{
    /// <summary>Fade through a solid color (black by default). Total duration is split between out and in.</summary>
    public static Transition Fade(float duration = 0.6f, Color? color = null) =>
        new FadeTransition(duration / 2f, duration / 2f, color ?? Color.Black);

    /// <summary>A curtain wiping across the screen (black by default). Total duration is split between out and in.</summary>
    public static Transition Wipe(float duration = 0.6f, Color? color = null) =>
        new WipeTransition(duration / 2f, duration / 2f, color ?? Color.Black);

    private sealed class FadeTransition(float outDuration, float inDuration, Color color)
        : OverlayTransition(outDuration, inDuration)
    {
        public override void Draw(
            TransitionRenderer renderer,
            float coverage,
            TransitionPhase phase
        ) => renderer.Fill(0f, 0f, 1f, 1f, color, coverage);
    }

    private sealed class WipeTransition(float outDuration, float inDuration, Color color)
        : OverlayTransition(outDuration, inDuration)
    {
        public override void Draw(
            TransitionRenderer renderer,
            float coverage,
            TransitionPhase phase
        )
        {
            // Out: шторка растёт слева направо; In: уезжает дальше вправо.
            if (phase == TransitionPhase.Out)
            {
                renderer.Fill(0f, 0f, coverage, 1f, color);
            }
            else
            {
                renderer.Fill(1f - coverage, 0f, coverage, 1f, color);
            }
        }
    }
}