Add MergedProperties

paperweight-lib/src/main/kotlin/io/papermc/paperweight/util/MergedProperties.kt

@@ -0,0 +1,63 @@
+/*
+ * paperweight is a Gradle plugin for the PaperMC project.
+ *
+ * Copyright (c) 2023 Kyle Wood (DenWav)
+ *                    Contributors
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 only, no later versions.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
+ * USA
+ */
+
+package io.papermc.paperweight.util
+
+import java.util.Properties
+import kotlin.io.path.*
+import kotlin.reflect.KProperty
+import org.gradle.api.Project
+
+class MergedProperties(private val properties: List<Properties>) {
+    // val someProperty by mergedProperties
+    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
+        return get(property.name)
+    }
+
+    // mergedProperties["someProperty"] | mergedProperties.get("someProperty")
+    operator fun get(propertyName: String): String {
+        for (props in properties) {
+            if (props.containsKey(propertyName)) {
+                return props.getProperty(propertyName)
+            }
+        }
+        error("No value for property '$propertyName'")
+    }
+
+    companion object {
+        fun fromAllProjects(project: Project, relativePath: String): MergedProperties {
+            // give our project priority
+            val projects = listOf(project) + project.rootProject.allprojects
+            val properties = projects.asSequence()
+                .distinct()
+                .map { it.layout.projectDirectory.file(relativePath).path }
+                .filter { it.exists() }
+                .map {
+                    Properties().apply {
+                        load(it.bufferedReader())
+                    }
+                }
+                .toList()
+            return MergedProperties(properties)
+        }
+    }
+}