// <copyright file="Bus.cs" company="Adrian Conlon">
// Copyright (c) Adrian Conlon. All rights reserved.
// </copyright>

namespace EightBit
{
    using System;
    using System.Collections.Generic;
    using System.IO;

    public abstract class Bus : IMapper
    {
        private byte data;

        public event EventHandler<EventArgs> WritingByte;

        public event EventHandler<EventArgs> WrittenByte;

        public event EventHandler<EventArgs> ReadingByte;

        public event EventHandler<EventArgs> ReadByte;

        public byte Data { get => this.data; set => this.data = value; }

        public Register16 Address { get; } = new Register16();

        public abstract MemoryMapping Mapping(ushort absolute);

        public byte Peek() => this.Reference();

        public byte Peek(ushort absolute) => this.Reference(absolute);

        public byte Peek(Register16 absolute) => this.Peek(absolute.Word);

        public byte Peek(byte low, byte high) => this.Reference(low, high);

        public void Poke(byte value) => this.Reference() = value;

        public void Poke(ushort absolute, byte value) => this.Reference(absolute) = value;

        public void Poke(Register16 absolute, byte value) => this.Poke(absolute.Word, value);

        public void Poke(byte low, byte high, byte value) => this.Reference(low, high) = value;

        public byte Read()
        {
            this.OnReadingByte();
            var returned = this.Data = this.Reference();
            this.OnReadByte();
            return returned;
        }

        public byte Read(ushort absolute)
        {
            this.Address.Word = absolute;
            return this.Read();
        }

        public byte Read(Register16 absolute) => this.Read(absolute.Word);

        public byte Read(byte low, byte high)
        {
            this.Address.Low = low;
            this.Address.High = high;
            return this.Read();
        }

        public void Write()
        {
            this.OnWritingByte();
            this.Reference() = this.Data;
            this.OnWrittenByte();
        }

        public void Write(byte value)
        {
            this.Data = value;
            this.Write();
        }

        public void Write(ushort absolute, byte value)
        {
            this.Address.Word = absolute;
            this.Write(value);
        }

        public void Write(Register16 absolute, byte value) => this.Write(absolute.Word, value);

        public void Write(byte low, byte high, byte value)
        {
            this.Address.Low = low;
            this.Address.High = high;
            this.Write(value);
        }

        public virtual void RaisePOWER()
        {
        }

        public virtual void LowerPOWER()
        {
        }

        public abstract void Initialize();

        protected static Dictionary<ushort, List<byte>> ParseHexFile(string path)
        {
            var returned = new Dictionary<ushort, List<byte>>();

            using (var reader = File.OpenText(path))
            {
                var eof = false;
                while (!reader.EndOfStream && !eof)
                {
                    var line = reader.ReadLine();

                    var colon = line.Substring(0, 1);
                    if (colon != ":")
                    {
                        throw new System.InvalidOperationException("Invalid hex file: line does not begin with a colon");
                    }

                    var countString = line.Substring(1, 2);
                    var count = Convert.ToByte(countString, 16);

                    var addressString = line.Substring(3, 4);
                    var address = Convert.ToUInt16(addressString, 16);

                    var recordTypeString = line.Substring(7, 2);
                    var recordType = Convert.ToByte(recordTypeString, 16);

                    switch (recordType)
                    {
                        case 0x00:
                            {
                                var data = new List<byte>(count);
                                var requiredLength = 9 + 2 + (count * 2);
                                if (line.Length != requiredLength)
                                {
                                    throw new InvalidOperationException("Invalid hex file: line is not the required length");
                                }

                                for (var i = 0; i < count; ++i)
                                {
                                    var position = 9 + (i * 2);
                                    var datumString = line.Substring(position, 2);
                                    var datum = Convert.ToByte(datumString, 16);
                                    data.Add(datum);
                                }

                                returned[address] = data;
                            }

                            break;

                        case 0x01:
                            eof = true;
                            break;

                        default:
                            throw new InvalidOperationException("Unhandled hex file record.");
                    }
                }
            }

            return returned;
        }

        protected virtual void OnWritingByte() => this.WritingByte?.Invoke(this, EventArgs.Empty);

        protected virtual void OnWrittenByte() => this.WrittenByte?.Invoke(this, EventArgs.Empty);

        protected virtual void OnReadingByte() => this.ReadingByte?.Invoke(this, EventArgs.Empty);

        protected virtual void OnReadByte() => this.ReadByte?.Invoke(this, EventArgs.Empty);

        protected ref byte Reference(ushort absolute)
        {
            var mapped = this.Mapping(absolute);
            var offset = (ushort)((absolute - mapped.Begin) & mapped.Mask);
            if (mapped.Access == AccessLevel.ReadOnly)
            {
                this.Data = mapped.Memory.Peek(offset);
                return ref this.data;
            }

            return ref mapped.Memory.Reference(offset);
        }

        protected ref byte Reference(Register16 absolute) => ref this.Reference(absolute.Word);

        protected ref byte Reference() => ref this.Reference(this.Address);

        protected ref byte Reference(byte low, byte high) => ref this.Reference(new Register16(low, high).Word);

        protected void LoadHexFile(string path)
        {
            var chunks = ParseHexFile(path);
            foreach (var chunk in chunks)
            {
                var address = chunk.Key;
                var content = chunk.Value;
                var mapped = this.Mapping(address);
                var offset = address - mapped.Begin;
                mapped.Memory.Load(content.ToArray(), offset);
            }
        }
    }
}