AudioSystem/Assets/Scripts/OCES/Audio/HandWritten/ChannelFader.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace OCES.Audio
{
    /// <summary>
    /// 与Transition无关的音量/生命周期管理逻辑
    /// </summary>
    public class ChannelFader
    {
        readonly MusicContainerPlayer m_player;
        readonly MonoBehaviour m_coroutineHost;
        
        public ContainerPlayHandle CurrentHandle { get; private set; }
        public uint CurrentContainerId { get; private set; }
        public float CurrentVolume { get; private set; }

        public ChannelFader(MusicContainerPlayer player, MonoBehaviour coroutineHost)
        {
            this.m_player = player;
            this.m_coroutineHost = coroutineHost;
        }
        
        void StartNew(uint containerId, float startVolume)
        {
            CurrentContainerId = containerId;
            CurrentVolume      = startVolume;
            CurrentHandle      = this.m_player.Play(containerId);
        }

        public void StopCurrent()
        {
            StopHandle(CurrentHandle);
            CurrentHandle      = null;
            CurrentContainerId = 0;
        }

        void StopHandle(ContainerPlayHandle handle)
        {
            if (handle == null) return;
            this.m_player.Stop(handle);
        }
        
        /// <summary>
        /// 淡出分支：fire-and-forget，由调用方 StartCoroutine
        /// </summary>
        internal IEnumerator FadeOutBranch(ContainerPlayHandle outgoingHandle, float outgoingVolume, float fadeOutOffset, float fadeOutTime)
        {
            if (outgoingHandle == null) yield break;
 
            if (fadeOutOffset > 0f)
            {
                Debug.Log($"Waiting for {fadeOutOffset} to fade out.");
                yield return new WaitForSeconds(fadeOutOffset);
            }
 
            if (fadeOutTime > 0f )
                yield return this.m_coroutineHost.StartCoroutine(
                    FadeOut(outgoingHandle, outgoingVolume, fadeOutTime));
            else
                StopHandle(outgoingHandle);
        }

        /// <summary>
        /// 淡入分支：等待 FadeInOffset 后启动新音乐并淡入。
        /// 主协程 yield return 此分支，以便 DoTransition 在新音乐就绪后才结束。
        /// </summary>
        internal IEnumerator FadeInBranch(uint newContainerId, float fadeInOffset, float fadeInTime, Action onContainerStarted = null)
        {
            if (fadeInOffset > 0f)
            {
                Debug.Log($"Waiting {fadeInOffset} to fade in.");
                yield return new WaitForSeconds(fadeInOffset);
            }
 
            if (newContainerId == 0)
            {
                CurrentHandle      = null;
                CurrentContainerId = 0;
                yield break;
            }
 
            float startVolume = fadeInTime > 0f ? 0f : 1f;
            StartNew(newContainerId, startVolume);
 
            if (fadeInTime > 0f )
            {
                yield return this.m_coroutineHost.StartCoroutine(
                    FadeIn(CurrentHandle, fadeInTime));
            }
        }
        
        IEnumerator FadeOut(ContainerPlayHandle handle, float fromVolume, float duration)
        {
            Debug.Log($"Fading out in {duration} seconds.");
            if (handle == null || handle.Cancelled) yield break;

            float elapsed = 0f;
            List<AudioSource> sources = new();
            handle.CollectActiveSources(sources);

            while (elapsed < duration)
            {
                if (handle.Cancelled) break;
                elapsed += Time.deltaTime;
                float t = Mathf.Clamp01(elapsed / duration);
                float vol = Mathf.Lerp(fromVolume, 0f, t);
                foreach (AudioSource src in sources)
                    if (src) src.volume = vol;
                yield return null;
            }

            StopHandle(handle);
        }

        IEnumerator FadeIn(ContainerPlayHandle handle, float duration)
        {
            Debug.Log($"Fading In {duration} seconds.");
            if (handle == null || handle.Cancelled) yield break;

            float elapsed = 0f;
            List<AudioSource> sources = new();

            while (elapsed < duration)
            {
                if (handle.Cancelled) yield break;
                elapsed += Time.deltaTime;
                float t = Mathf.Clamp01(elapsed / duration);

                // 每帧重新收集（Blend 模式下新 source 可能中途加入）
                sources.Clear();
                handle.CollectActiveSources(sources);
                foreach (AudioSource src in sources)
                    if (src) src.volume = Mathf.Lerp(0f, 1f, t);
                yield return null;
            }

            // 确保最终音量准确
            sources.Clear();
            handle.CollectActiveSources(sources);
            foreach (AudioSource src in sources)
                if (src) src.volume = 1f;

            CurrentVolume = 1f;
        }
        

    }
}