using System;
using Goo.Animation;

namespace Goo.FpsUI;

// Secondary bar under health: drains while sprinting and regenerates otherwise. Engine-free.
public sealed class StaminaModel
{
    public float MaxStamina = 100f;                  // full-bar value
    public float DrainRate  = 0.55f;                 // fraction of max stamina drained per second while sprinting
    public float Stamina { get; private set; } = 100f;   // current value

    bool        _sprinting;
    SpringFloat _shown = new( 1f, 18f, 0.85f );      // displayed fill
    DecayFloat  _flash = new( 0f, 0.12f );           // blip when it empties

    public float ShownFraction => Math.Clamp( _shown.Current, 0f, 1f ); // animated fill 0..1
    public float Flash         => Math.Clamp( _flash.Current, 0f, 1f ); // 1 on empty, decays
    public bool  Sprinting     => _sprinting;

    public void Reset()
    {
        Stamina = MaxStamina;
        _shown = new SpringFloat( 1f, 18f, 0.85f );
        _flash = new DecayFloat( 0f, 0.12f );
    }

    public void SetSprinting( bool on ) => _sprinting = on;          // call from game code each frame
    public void SetStamina( float v ) => Stamina = Math.Clamp( v, 0f, MaxStamina ); // set directly (custom)

    public bool Tick( float dt )
    {
        // Drain whenever the sprint key is held (pinned at 0 once gassed), regenerate only when not sprinting.
        // Regenerating at 0 while still held would bounce stamina above 0 each frame and flip the sprint gate
        // on and off, letting a gassed player keep sprinting. Holding sprint must keep it at 0.
        float prev = Stamina;
        Stamina = _sprinting
            ? MathF.Max( 0f, Stamina - MaxStamina * DrainRate * dt )
            : MathF.Min( MaxStamina, Stamina + MaxStamina * 0.30f * dt );
        if ( prev > 0f && Stamina <= 0f ) _flash.Current = 1f;  // gassed-out blip
        _shown.Target = MaxStamina > 0f ? Stamina / MaxStamina : 0f;
        _flash.Target = 0f;
        bool moving = _shown.Tick( dt ) | _flash.Tick( dt );
        return moving || _sprinting;
    }
}