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

namespace AOC09
{
    class IntcodeComputer
    {
        public Dictionary<int,int> Program;
        public int instructionPointer = -2;
        public List<int> Inputs;
        public bool PhaseUsed = false;
        public int RelativeBase = 0;

        public IntcodeComputer(int[] program)
        {
            Program = new Dictionary<int, int>();
            var i = 0;
            foreach (var p in program)
            {
                Program.Add(i, p);
                i++;
            }
            Inputs = new List<int>();
        }

        public int Parse()
        {
            instructionPointer += 2;

            while (true)
            {
                var current = Program[instructionPointer];
                var currentS = current.ToString("D5");
                var opcode = current % 100;
                var modes = currentS.Substring(0, currentS.Length - 2).Select(d => int.Parse(d.ToString())).ToList();
                modes.Reverse();

                switch (opcode)
                {
                    case 1: // a * b at c
                        var a = GetParameter(0);
                        var b = GetParameter(1);
                        var c = GetValue(instructionPointer + 3);
                        SetValue(c, a + b);
                        instructionPointer += 4;
                        break;
                    case 2:
                        a = GetParameter(0);
                        b = GetParameter(1);
                        c = GetValue(instructionPointer + 3);
                        SetValue(c, a * b);
                        instructionPointer += 4;
                        break;
                    case 3:
                        SetValue(GetValue(instructionPointer + 1), Inputs[0]);
                            Inputs.RemoveAt(0);
                        instructionPointer += 2;
                        break;
                    case 4:
                        return GetParameter(0);
                    case 5:
                        if (GetParameter(0) != 0)
                        {
                            instructionPointer = GetParameter(1);
                        }
                        else
                        {
                            instructionPointer += 3;
                        }
                        break;
                    case 6:
                        if (GetParameter(0) == 0)
                        {
                            instructionPointer = GetParameter(1);
                        }
                        else
                        {
                            instructionPointer += 3;
                        }
                        break;
                    case 7:
                        SetValue(GetValue(instructionPointer + 3), GetParameter(0) < GetParameter(1) ? 1 : 0);
                        instructionPointer += 4;
                        break;
                    case 8:
                        SetValue(GetValue(instructionPointer + 3), GetParameter(0) == GetParameter(1) ? 1 : 0);
                        instructionPointer += 4;
                        break;
                    case 99:
                        return int.MaxValue;
                    case 9:
                        RelativeBase = GetParameter(0);
                        instructionPointer += 2;
                        break;
                    default:
                        instructionPointer++;
                        break;
                }

                //Gets a value from memory at the given index.
                int GetValue(int index)
                {
                    if (Program.ContainsKey(index)) { return Program[index]; }
                    return 0;
                }

                //Sets a value in memory at the given index.
                void SetValue(int index, int value)
                {
                    if (Program.ContainsKey(index)) { Program[index] = value; }
                    else { Program.Add(index, value); }
                }

                //Gets a value from memory based on the given parameter mode and parameter index.
                int GetParameter(int i)
                {
                    switch (modes[i])
                    {
                        case 0:
                            return GetValue(GetValue(instructionPointer + i + 1));
                        case 1:
                            return GetValue(instructionPointer + i + 1);
                        case 2:
                            return GetValue(GetValue(instructionPointer + i + 1) + RelativeBase);
                        default:
                            Console.WriteLine("ERROR: INVALID PARAMETER MODE. MUST BE 0,1,2");
                            return 0;
                    }
                }
            }
        }
    }
}