brainfuck.swift

import Foundation

let valids = [">", "<", "+", "-", ".", ",", "[", "]"] as Set<Character>
var ip = 0
var dp = 0
var data = [UInt8](count: 30_000, repeatedValue: 0)

let input = Process.arguments

if input.count != 2 {
    fatalError("Need one input file")
}

let infile = String(contentsOfFile: input[1], encoding: NSUTF8StringEncoding, error: nil) ?? ""
var program = ""

// remove invalid chars
for c in infile {
    if valids.contains(c) {
        program += String(c)
    }
}

let numChars = count(program)

if numChars == 0 {
    fatalError("Error reading file")
}

func increaseInstructionPointer() {
    ++ip
}

func executeInstruction(ins:Character) {
    switch ins {
    case ">":
        ++dp
        increaseInstructionPointer()
    case "<":
        --dp
        increaseInstructionPointer()
    case "+":
        data[dp] = data[dp] &+ 1
        increaseInstructionPointer()
    case "-":
        data[dp] = data[dp] &- 1
        increaseInstructionPointer()
    case ".":
        // println(data[dp])
        print(Character(UnicodeScalar(data[dp])))
        increaseInstructionPointer()
    case ",":
        handleIn()
        increaseInstructionPointer()
    case "[":
        handleOpenBracket()
    case "]":
        handleClosedBracket()
    default:
        fatalError("What")
    }
}

func handleIn() {
    let input = NSFileHandle.fileHandleWithStandardInput()
    let bytes = input.availableData.bytes
    let buf = unsafeBitCast(UnsafeBufferPointer(start: bytes, count: 1),
        UnsafeBufferPointer<UInt8>.self)
    
    data[dp] = buf[0]
}

func handleOpenBracket() {
    if data[dp] == 0 {
        var i = 1
        
        while i > 0 {
            let ins = program[advance(program.startIndex, ++ip)]
            
            if ins == "[" {
                ++i
            } else if ins == "]" {
                --i
            }
        }
    } else {
        increaseInstructionPointer()
    }
}

func handleClosedBracket() {
    if data[dp] != 0 {
        var i = 1
        
        while i > 0 {
            let ins = program[advance(program.startIndex, --ip)]
            
            if ins == "[" {
                --i
            } else if ins == "]" {
                ++i
            }
        }
    } else {
        increaseInstructionPointer()
    }
}

func printState() {
    println("Instruction Pointer: \(ip)")
    println("Data Pointer \(dp)")
    println("Data in Cell: \(data[dp])")
    println()
}

func tick() {
    let ins = program[advance(program.startIndex, ip)]
    
    if valids.contains(ins) {
        //println("Current instruction: \(ins)")
        //printState()
        executeInstruction(ins)
    } else {
        increaseInstructionPointer()
    }
}

while ip != numChars {
    tick()
}