using System;
using Core.Interfaces;

namespace Core.Memory
{
    public class MemoryBus : IMemory
    {
        // 8 Banks of 16KB RAM (Banks 0 through 7)
        private readonly byte[][] _ramBanks = new byte[8][];

        // 5 Banks of 16KB ROM (0-3 for the +2A, and 4 for the pure 48K)
        private readonly byte[][] _romBanks = new byte[5][];

        // --- Hardware State ---
        private int _currentRomBank = 4; // Defaults to 48K ROM
        private int _currentRamBankSlot3 = 0;
        private byte _port7FFD = 0;
        private byte _port1FFD = 0;
        private bool _pagingDisabled = false;

        public MemoryBus()
        {
            // Initialize the physical silicon chips!
            for (int i = 0; i < 8; i++) _ramBanks[i] = new byte[0x4000];
            for (int i = 0; i < 5; i++) _romBanks[i] = new byte[0x4000];
        }

        // Called when the machine is turned on or reset
        public void ResetPaging(MachineModel model)
        {
            _pagingDisabled = false;
            _port7FFD = 0;
            _port1FFD = 0;
            _currentRamBankSlot3 = 0;

            if (model == MachineModel.Spectrum48K)
            {
                _currentRomBank = 4; // Lock to the pure 48.rom
            }
            else
            {
                _currentRomBank = 0; // Boot into the +3 DOS menu!
            }
        }

        // Called by the IO Bus when the CPU writes to a paging port
        public void HandlePaging(ushort port, byte value)
        {
            if (_pagingDisabled || _currentRomBank == 4) return; // Ignore if locked or in 48K mode

            if (port == 0x7FFD)
            {
                _port7FFD = value;
                _currentRamBankSlot3 = value & 0x07; // Bottom 3 bits select the RAM bank
                if ((value & 0x20) != 0) _pagingDisabled = true; // Bit 5 permanently disables paging
            }
            else if (port == 0x1FFD)
            {
                _port1FFD = value;
            }

            // Calculate which of the 4 Amstrad ROMs is active based on the ports
            int romLow = (_port7FFD >> 4) & 0x01;
            int romHigh = (_port1FFD >> 2) & 0x01;
            _currentRomBank = (romHigh << 1) | romLow;
        }

        public byte Read(ushort address)
        {
            int slot = address >> 14; // Divide by 16384 to find Slot 0, 1, 2, or 3
            int offset = address & 0x3FFF; // Find the exact byte inside that 16KB slot

            switch (slot)
            {
                case 0: return _romBanks[_currentRomBank][offset];      // 0x0000 - 0x3FFF (ROM)
                case 1: return _ramBanks[5][offset];                    // 0x4000 - 0x7FFF (Always RAM 5)
                case 2: return _ramBanks[2][offset];                    // 0x8000 - 0xBFFF (Always RAM 2)
                case 3: return _ramBanks[_currentRamBankSlot3][offset]; // 0xC000 - 0xFFFF (Switchable RAM)
                default: return 0xFF;
            }
        }

        public void Write(ushort address, byte value)
        {
            if (address < 0x4000) return; // Cannot write to ROM

            int slot = address >> 14;
            int offset = address & 0x3FFF;

            switch (slot)
            {
                case 1: _ramBanks[5][offset] = value; break;
                case 2: _ramBanks[2][offset] = value; break;
                case 3: _ramBanks[_currentRamBankSlot3][offset] = value; break;
            }
        }

        public void LoadRom(byte[] romData, int bankIndex)
        {
            Array.Copy(romData, 0, _romBanks[bankIndex], 0, Math.Min(romData.Length, 0x4000));
        }

        public void CleanRAMData()
        {
            for (int bank = 0; bank < 8; bank++)
            {
                for (int i = 0; i < 0x4000; i++) _ramBanks[bank][i] = 0x00;
            }
        }

        public void CrapRAMData()
        {
            Random random = new Random();
            for (int bank = 0; bank < 8; bank++)
            {
                for (int i = 0; i < 0x4000; i++) _ramBanks[bank][i] = (byte)random.Next(0x00, 0xFF);
            }
        }
    }
}