Generate msgSend wrappers for swift, written in swift

msgSendGen.swift

#!/usr/bin/env swift

import Foundation

extension Int {
    var tabs: String {
        return Array(count: self, repeatedValue: "    ").joinWithSeparator("")
    }
}

func printUsage() {
    print("Usage: msgSendgen [numberOfArgs]")
}


guard Process.argc == 2 else {
    printUsage()
    exit(1)
}

guard let numberOfArgs = Int(Process.arguments[1]) where numberOfArgs >= 0 else {
    printUsage()
    exit(1)
}

func invokationFor(object: String, _ name: String, _ args: String, _ n: Int) -> String {
    let args = ([object, "Selector(\(name))"] + (n > 0 ? ((0...(n-1)).map { "\(args)[\($0)]" }) : [])).joinWithSeparator(", ")
    return "unsafeBitCast(objc_msgSend, Method\(n).self)(\(args))"
}

let initialDecls = [
    "@_silgen_name(\"objc_msgSend\") func objc_msgSend_(_: AnyObject?, _: Selector) -> AnyObject?",
    "let objc_msgSend = objc_msgSend_ as @convention(c) (AnyObject?, Selector) -> AnyObject?"
]
let structDecl = [
    "struct Runtime {", 
]
let typealiases = (0...numberOfArgs).map { (index: Int) -> String in
    let prefix = "    typealias Method\(index) = @convention(c) ("
    let args = ["AnyObject?", "Selector"] + Array(count: index, repeatedValue: "AnyObject?")
    let suffix = ") -> AnyObject?"
    return prefix + args.joinWithSeparator(", ") + suffix
}
let middleStruct = [
    "    weak private(set) var object: AnyObject?", 
    "", 
    "    init(_ cls: AnyClass) { self.object = cls }",
    "    init(_ object: AnyObject) { self.object = object }",
    "",
    "    func call(name: String, args: [AnyObject?]) -> AnyObject? {",
    "        switch args.count {",
]
let cases = ((0...numberOfArgs).map { "\(2.tabs)case \($0): return " + invokationFor("object", "name", "args", $0) })
let endStruct = [
    "        default: return nil",
    "        }",
    "    }",
    "}",
]
let firstHalf = initialDecls + [""] + structDecl + typealiases
let secondHalf = middleStruct + cases + endStruct

print((firstHalf + secondHalf).joinWithSeparator("\n"))

// vi:syntax=swift:softtabstop=4:tabstop=4:shiftwidth=4