using UnityEngine;

/// <summary>
///   Audio source that fades between clips instead of playing them immediately.
/// </summary>
[RequireComponent(typeof(AudioSource))]
public class FadingAudioSource : MonoBehaviour {
	#region Fields

	/// <summary>
	///   Volume to end the previous clip at.
	/// </summary>
	public float FadeOutThreshold = 0.05f;

	/// <summary>
	///   Volume change per second when fading.
	/// </summary>
	public float FadeSpeed = 1f;

	/// <summary>
	///   Actual audio source.
	/// </summary>
	private AudioSource audioSource;

	/// <summary>
	///   Whether the audio source is currently fading, in or out.
	/// </summary>
	private FadeState fadeState = FadeState.None;

	/// <summary>
	///   Next clip to fade to.
	/// </summary>
	private AudioClip nextClip;

	/// <summary>
	///   Whether to loop the next clip.
	/// </summary>
	private bool nextClipLoop;

	/// <summary>
	///   Target volume to fade the next clip to.
	/// </summary>
	private float nextClipVolume;

	#endregion

	#region Enums

	public enum FadeState {
		None,

		FadingOut,

		FadingIn
	}

	#endregion

	#region Public Properties

	/// <summary>
	///   Current clip of the audio source.
	/// </summary>
	public AudioClip Clip {
		get {
			return this.audioSource.clip;
		}
	}

	/// <summary>
	///   Whether the audio source is currently playing a clip.
	/// </summary>
	public bool IsPlaying {
		get {
			return this.audioSource.isPlaying;
		}
	}

	/// <summary>
	///   Whether the audio source is looping the current clip.
	/// </summary>
	public bool Loop {
		get {
			return this.audioSource.loop;
		}
	}

	/// <summary>
	///   Current volume of the audio source.
	/// </summary>
	public float Volume {
		get {
			return this.audioSource.volume;
		}
	}

	#endregion

	#region Public Methods and Operators

	/// <summary>
	///   If the audio source is enabled and playing, fades out the current clip and fades in the specified one, after.
	///   If the audio source is enabled and not playing, fades in the specified clip immediately.
	///   If the audio source is not enalbed, fades in the specified clip as soon as it gets enabled.
	/// </summary>
	/// <param name="clip">Clip to fade in.</param>
	/// <param name="volume">Volume to fade to.</param>
	/// <param name="loop">Whether to loop the new clip, or not.</param>
	public void Fade(AudioClip clip, float volume, bool loop) {
		if (clip == null || clip == this.audioSource.clip) {
			return;
		}

		this.nextClip = clip;
		this.nextClipVolume = volume;
		this.nextClipLoop = loop;

		if (this.audioSource.enabled) {
			if (this.IsPlaying) {
				this.fadeState = FadeState.FadingOut;
			} else {
				this.FadeToNextClip();
			}
		} else {
			this.FadeToNextClip();
		}
	}

	/// <summary>
	///   Continues fading in the current audio clip.
	/// </summary>
	public void Play() {
		this.fadeState = FadeState.FadingIn;
		this.audioSource.Play();
	}

	/// <summary>
	///   Stop playing the current audio clip immediately.
	/// </summary>
	public void Stop() {
		this.audioSource.Stop();
		this.fadeState = FadeState.None;
	}

	#endregion

	#region Methods

	private void Awake() {
		this.audioSource = GetComponent<AudioSource>();
		this.audioSource.volume = 0f;
	}

	private void FadeToNextClip() {
		this.audioSource.clip = this.nextClip;
		this.audioSource.loop = this.nextClipLoop;

		this.fadeState = FadeState.FadingIn;

		if (this.audioSource.enabled) {
			this.audioSource.Play();
		}
	}

	private void OnDisable() {
		this.audioSource.enabled = false;
		this.Stop();
	}

	private void OnEnable() {
		this.audioSource.enabled = true;
		this.Play();
	}

	private void Update() {
		if (!this.audioSource.enabled) {
			return;
		}

		if (this.fadeState == FadeState.FadingOut) {
			if (this.audioSource.volume > this.FadeOutThreshold) {
				// Fade out current clip.
				this.audioSource.volume -= this.FadeSpeed * Time.deltaTime;
			} else {
				// Start fading in next clip.
				this.FadeToNextClip();
			}
		} else if (this.fadeState == FadeState.FadingIn) {
			if (this.audioSource.volume < this.nextClipVolume) {
				// Fade in next clip.
				this.audioSource.volume += this.FadeSpeed * Time.deltaTime;
			} else {
				// Stop fading in.
				this.fadeState = FadeState.None;
			}
		}
	}

	#endregion
}