module Intcode

using OffsetArrays

export parseInput, Program, runProgram, doOperation, onHalt, onStop

const parseInput(i) = split(i, ",") |>
    lines -> map(x -> parse(Int, x), lines) |>
    x -> OffsetArray(x, -1)

mutable struct Program
    memory :: OffsetArrays.OffsetArray{Int64,1,Array{Int64,1}}
    address :: Int
    input :: Array{Int, 1}
    output :: Array{Int, 1}
    relativeBase :: Int
    halted :: Bool
    paused :: Bool
    stopOnOutput :: Bool
    onStop :: Function
    onHalt :: Function
    doOperation :: Function
end

function parseOpcode(opcode::Int)
    if opcode <= 10 || opcode == 99
        return (opcode, (0, 0, 0))
    end

    digs = digits(opcode; pad = 5)

    if [digs[1], digs[2]] == [9,9]
        return (99, (digs[3], digs[4], digs[5]))
    end

    return (digs[1], (digs[3], digs[4], digs[5]))
end

function accessMemory(program::Program, address::Int, output=false)
    diff = address-length(program.memory)+1

    if diff <= 0
        return program.memory[address]
    else
        resize!(parent(program.memory), length(program.memory)+(diff))
        return 0
    end
end

function applyMode(program::Program, mode::Int, value::Int, output=false)
    if mode == 0
        return !output ? accessMemory(program, value) : value
    elseif mode == 1
        return value
    elseif mode == 2
        return !output ? accessMemory(program, value+program.relativeBase) : value+program.relativeBase
    end
end

function parseInstructions(program::Program, opcode::Int, modes::Tuple{Int, Int, Int})
    if opcode == 99
        return (0, 0, 0)
    elseif opcode == 3
        return (0, 0, applyMode(program, modes[1], program.memory[program.address+1], true))
    elseif opcode in [4, 9]
        return (applyMode(program, modes[1], program.memory[program.address+1], false), 0, 0)
    else
        return map(((i, mode),) -> applyMode(program, mode, program.memory[program.address+i], i == 3), enumerate(modes))
    end
end

const operations  = Dict(
    1 => (program, input, output) -> begin
        program.memory[output] = input[1] + input[2]
        program.address += 4
    end,
    2 => (program, input, output) -> begin
        program.memory[output] = input[1] * input[2]
        program.address += 4
    end,
    3 => (program, input, output) -> begin
        program.memory[output] = popfirst!(program.input)
        program.address += 2
    end,
    4 => (program, input, output) -> begin
        push!(program.output, input[1])
        program.address += 2

        if program.stopOnOutput
            program.paused == true
        end
    end,
    5 => (program, input, output) -> begin
        program.address = input[1] != 0 ? input[2] : program.address + 3
    end,
    6 => (program, input, output) -> begin
        program.address = input[1] == 0 ? input[2] : program.address + 3
    end,
    7 => (program, input, output) -> begin
        program.memory[output] = input[1] < input[2] ? 1 : 0
        program.address += 4
    end,
    8 => (program, input, output) -> begin
        program.memory[output] = input[1] == input[2] ? 1 : 0
        program.address += 4
    end,
    9 => (program, input, output) -> begin
        program.relativeBase += input[1]
        program.address += 2
    end,
    99 => (program, input, output) -> program.halted = true
)

function doOperation(program::Program)
    memoryValue = accessMemory(program, program.address)
    opcode, modes = parseOpcode(memoryValue)

    instructions = parseInstructions(program, opcode, modes)
    input = instructions[1:2]
    outputAddress = instructions[end]

    accessMemory(program, outputAddress)

    #println("#", program.address, " " ,opcode, " ", modes, " ", memoryValue, " ", (instructions[1], instructions[2])  , " ", isnothing(outputAddress) ? 0 : outputAddress)

    operations[opcode](program, input, outputAddress)
end

const runProgram(program::Program) = begin
    while !program.halted
        program.doOperation(program)
    end

    program.onHalt(program)
end

const onStop(program::Program) = println(program.output[end])
const onHalt(program::Program) = println(program.output[end])

end