Add gradle task to download input

build.gradle.kts

@@ -1,3 +1,6 @@
+import java.net.URL
+import java.net.HttpURLConnection
+
 plugins {
     kotlin("jvm") version "1.7.22"
 }
@@ -17,3 +20,52 @@ tasks {
         gradleVersion = "7.6"
     }
 }
+
+tasks.register("downloadInput") {
+    doLast {
+        val day: String = findProperty("day") as? String ?: error("day is required")
+        val challengeUrl = "https://adventofcode.com/2022/day/$day"
+        val inputUrl = "$challengeUrl/input"
+        exec {
+            commandLine("xdg-open", challengeUrl)
+        }
+        var sessionCookie = System.getenv("AOC_SESSION")
+        if (sessionCookie.isNullOrBlank()) {
+            error("AOC_SESSION environment variable missing or empty")
+        }
+        if (!sessionCookie.startsWith("session=")) {
+            sessionCookie = "session=$sessionCookie"
+        }
+        val url = URL(inputUrl)
+        val connection = url.openConnection() as HttpURLConnection
+        connection.requestMethod = "GET"
+        connection.setRequestProperty("Cookie", sessionCookie)
+        val content = connection.inputStream.bufferedReader().readText()
+        val dayFileName = "Day${day.padStart(2, '0')}"
+        File("src", "${dayFileName}_test.txt").createNewFile()
+        File("src", "$dayFileName.txt").writeText(content)
+        val sourceFile = File("src", "$dayFileName.kt")
+        if (sourceFile.exists()) {
+            return@doLast
+        }
+        sourceFile.writeText("""
+            fun main() {
+                fun part1(input: List<String>): Int {
+                    return 0
+                }
+
+                fun part2(input: List<String>): Int {
+                    return 0
+                }
+
+                val testInput = readInput("${dayFileName}_test")
+                check(part1(testInput) == 0)
+                check(part2(testInput) == 0)
+
+                val input = readInput("$dayFileName")
+                println(part1(input))
+                println(part2(input))
+            }
+        """.trimIndent())
+    }
+}