Add source code for chapter 1

Author: mokagio

01-introduction/fizz_buzz.swift

@@ -0,0 +1,48 @@
+#!/usr/bin/env xcrun swift
+
+func fizzBuzz(_ number: Int) -> String {
+    let divisibleBy3 = number % 3 == 0
+    let divisibleBy5 = number % 5 == 0
+    switch (divisibleBy3, divisibleBy5) {
+        case (false, false): return "\(number)"
+        case (true, false): return "fizz"
+        case (false, true): return "buzz"
+        case (true, true): return "fizz buzz"
+    }
+}
+
+func test(value: String, matches expect: String) {
+    if value == expect {
+        print("PASSED")
+    } else {
+        print("FAILED")
+    }
+}
+
+func testFizzBuzz() {
+    test(value: fizzBuzz(1), matches: "1")
+    test(value: fizzBuzz(3), matches: "fizz")
+    test(value: fizzBuzz(5), matches: "buzz")
+    test(value: fizzBuzz(15), matches: "fizz buzz")
+}
+
+func main() {
+    let usage = "Usage: ./fizz_buzz.swift number"
+
+    guard CommandLine.argc > 1 else {
+        print(usage)
+        return
+    }
+
+    guard let number = Int(CommandLine.arguments[1]) else {
+        print(usage)
+        return
+    }
+
+    print(fizzBuzz(number))
+}
+
+// TODO: explain why we need to either run main or test? Alternatively, extract
+// the tests in a dedicated file?
+main()
+// testFizzBuzz()

01-introduction/hello_world.swift

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+#!/usr/bin/env xcrun swift
+
+func main() {
+    guard CommandLine.argc > 1 else {
+        print("Hello, World!")
+        return
+    }
+
+    print("Hello, \(CommandLine.arguments[1])!")
+}
+
+main()

01-introduction/test_fizz_buzz.swift

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+#!/usr/bin/env xcrun swift
+
+// There is currently (5 years later!) no way for a Swift script to import
+// another script.
+//
+// What follows is a bit of a hack where we test the fizz-buzz implementation
+// from fizz_buzz.swift by calling the script directly.
+//
+// I find this acceptable in the context of providing an harness for showing
+// how to write code that tests other code as part of the introduction of
+// Test-Driven Development in Swift (https://tddinswift.com). It definitely is
+// not a scalabe solution for testing Swift scripts, but, again, that's not
+// what the examples in the book introduction are about.
+
+import Foundation
+
+/// Run a shell command and capture its output
+func shell(_ command: String) -> String {
+    let task = Process()
+    let pipe = Pipe()
+
+    task.standardOutput = pipe
+    task.arguments = ["-c", command]
+    task.launchPath = "/bin/sh"
+    task.launch()
+
+    let data = pipe.fileHandleForReading.readDataToEndOfFile()
+    let output = String(data: data, encoding: .utf8)!
+
+    return output.trimmingCharacters(in: .whitespacesAndNewlines)
+}
+
+/// Call the fizz-buzz script with a given input and return the script's output.
+func fizzBuzz(_ number: Int) -> String {
+    return shell("./fizz_buzz.swift \(number)")
+}
+
+/// Check if two input `String`s are equal, printing "PASSED" if true and
+/// "FAILED" otherwise.
+func test(value: String, matches expect: String) {
+    if value == expect {
+        print("PASSED")
+    } else {
+        print("FAILED")
+    }
+}
+
+func testFizzBuzz() {
+    test(value: fizzBuzz(1), matches: "1")
+    test(value: fizzBuzz(3), matches: "fizz")
+    test(value: fizzBuzz(5), matches: "buzz")
+    test(value: fizzBuzz(15), matches: "fizz buzz")
+}
+
+testFizzBuzz()