IO Operators

src/io/IoHandler.kt

@@ -0,0 +1,10 @@
+package io
+
+interface IoHandler {
+    fun prompt(
+        message: String,
+        hint: () -> String = { "Please enter a valid input." }
+    ): String
+
+    fun say(message: String)
+}

src/io/Logger.kt

@@ -0,0 +1,24 @@
+package io
+
+object Logger {
+    enum class Level {
+        DEBUG, INFO, WARN, ERROR
+    }
+
+    val defaultLevel: Level = Level.WARN
+    var level: Level = defaultLevel
+
+    private val io: IoHandler = Terminal()
+
+    fun log(message: String, messageLevel: Level = defaultLevel) {
+        if (level <= messageLevel) {
+            val text = "$messageLevel: $message\n"
+            io.say(text)
+        }
+    }
+
+    fun debug(message: String) = log(message, Level.DEBUG)
+    fun info(message: String) = log(message, Level.INFO)
+    fun warn(message: String) = log(message, Level.WARN)
+    fun error(message: String) = log(message, Level.ERROR)
+}

src/io/Terminal.kt

@@ -0,0 +1,63 @@
+package io
+
+import java.io.BufferedReader
+import java.io.BufferedWriter
+import java.io.InputStream
+import java.io.OutputStream
+
+/**
+ * Handles input and output from a terminal.
+ */
+class Terminal(
+    inputStream: InputStream = System.`in`,
+    outputStream: OutputStream = System.`out`,
+    errorStream: OutputStream = System.err
+) : IoHandler {
+    val input: BufferedReader = inputStream.bufferedReader()
+    val output: BufferedWriter = outputStream.bufferedWriter()
+    val error: BufferedWriter = errorStream.bufferedWriter()
+
+    override fun prompt(
+        message: String,
+        hint: () -> String
+    ): String {
+        say("$message ")
+        var input: String = readLine()
+        while (input.isBlank()) {
+            say(hint(), error)
+            input = readLine()
+        }
+        return input
+    }
+
+    override fun say(message: String) {
+        output.write(message)
+        output.flush()
+    }
+
+    fun say(message: String, writer: BufferedWriter = output) {
+        writer.write(message)
+        writer.flush()
+    }
+
+    /**
+     * Reads a line from the input stream.
+     */
+    fun readLine(reader: BufferedReader = input): String {
+        val line = reader.readLine()
+        if (line == null) {
+            Logger.info("End of stream reached")
+            cleanup()
+        }
+        return line
+
+    }
+
+    fun cleanup() {
+        Logger.info("Closing terminal streams")
+        input.close()
+        output.close()
+        error.close()
+        System.exit(0)
+    }
+}