using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using BizHawk.Common;

namespace BizHawk.Emulation.Computers.Commodore64.MOS
{
	sealed public partial class Sid
	{
		sealed class Envelope
		{
			const int stateAttack = 0;
			const int stateDecay = 1;
			const int stateRelease = 2;

			int attack;
			int decay;
			bool delay;
			int envCounter;
			int expCounter;
			int expPeriod;
			bool freeze;
			int lfsr;
			bool gate;
			int rate;
			int release;
			int state;
			int sustain;

			static int[] adsrTable = new int[]
			{
				0x7F00, 0x0006, 0x003C, 0x0330,
				0x20C0, 0x6755, 0x3800, 0x500E,
				0x1212, 0x0222, 0x1848, 0x59B8,
				0x3840, 0x77E2, 0x7625, 0x0A93
			};

			static int[] expCounterTable = new int[]
			{
				0xFF, 0x5D, 0x36, 0x1A, 0x0E, 0x06, 0x00
			};

			static int[] expPeriodTable = new int[]
			{
				0x01, 0x02, 0x04, 0x08, 0x10, 0x1E, 0x01
			};

			static int[] sustainTable = new int[]
			{
				0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
				0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF
			};

			public Envelope()
			{
				HardReset();
			}

			public void ExecutePhase2()
			{

				{
					if (!delay)
					{
						envCounter--;
						delay = true;
						UpdateExpCounter();
					}

					if (lfsr != rate)
					{
						int feedback = ((lfsr >> 14) ^ (lfsr >> 13)) & 0x1;
						lfsr = ((lfsr << 1) & 0x7FFF) | feedback;
						return;
					}
					lfsr = 0x7FFF;

					if (state == stateAttack || ++expCounter == expPeriod)
					{
						expCounter = 0;
						if (freeze)
							return;

						switch (state)
						{
							case stateAttack:
								envCounter++;
								if (envCounter == 0xFF)
								{
									state = stateDecay;
									rate = adsrTable[decay];
								}
								break;
							case stateDecay:
								if (envCounter == sustainTable[sustain])
								{
									return;
								}
								if (expPeriod != 1)
								{
									delay = false;
									return;
								}
								envCounter--;
								break;
							case stateRelease:
								if (expPeriod != 1)
								{
									delay = false;
									return;
								}
								envCounter--;
								break;
						}
						envCounter &= 0xFF;
						UpdateExpCounter();
					}
				}
			}

			public void HardReset()
			{
				attack = 0;
				decay = 0;
				delay = true;
				envCounter = 0;
				expCounter = 0;
				expPeriod = expPeriodTable[0];
				freeze = false;
				gate = false;
				lfsr = 0x7FFF;
				rate = adsrTable[release];
				release = 0;
				state = stateRelease;
				sustain = 0;
			}

			private void UpdateExpCounter()
			{

				{
					for (int i = 0; i < 7; i++)
					{
						if (envCounter == expCounterTable[i])
							expPeriod = expPeriodTable[i];
					}
					if (envCounter == 0)
						freeze = true;
				}
			}

			// ------------------------------------

			public int Attack
			{
				get
				{
					return attack;
				}
				set
				{
					attack = (value & 0xF);
					if (state == stateAttack)
						rate = adsrTable[attack];
				}
			}

			public int Decay
			{
				get
				{
					return decay;
				}
				set
				{
					decay = (value & 0xF);
					if (state == stateDecay)
						rate = adsrTable[decay];
				}
			}

			public bool Gate
			{
				get
				{
					return gate;
				}
				set
				{
					bool nextGate = value;
					if (nextGate && !gate)
					{
						state = stateAttack;
						rate = adsrTable[attack];
						delay = true;
						freeze = false;
					}
					else if (!nextGate && gate)
					{
						state = stateRelease;
						rate = adsrTable[release];
					}
					gate = nextGate;
				}
			}

			public int Level
			{
				get
				{
					return envCounter;
				}
			}

			public int Release
			{
				get
				{
					return release;
				}
				set
				{
					release = (value & 0xF);
					if (state == stateRelease)
						rate = adsrTable[release];
				}
			}

			public int Sustain
			{
				get
				{
					return sustain;
				}
				set
				{
					sustain = (value & 0xF);
				}
			}

			// ------------------------------------

			public void SyncState(Serializer ser)
			{
				SaveState.SyncObject(ser, this);
			}

			// ------------------------------------
		}
	}
}