build: Migrate to flat project structure

This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.

1 files changed, 101 insertions, 0 deletions

diff --git a/opendc-harness/src/main/kotlin/org/opendc/harness/internal/DslDiscovery.kt b/opendc-harness/src/main/kotlin/org/opendc/harness/internal/DslDiscovery.kt
new file mode 100644
index 00000000..eb6303d6
--- /dev/null
+++ b/opendc-harness/src/main/kotlin/org/opendc/harness/internal/DslDiscovery.kt
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2021 AtLarge Research
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.opendc.harness.internal
+
+import io.github.classgraph.ClassGraph
+import io.github.classgraph.ScanResult
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.asFlow
+import org.opendc.harness.api.ExperimentDefinition
+import org.opendc.harness.dsl.Experiment
+import org.opendc.harness.engine.discovery.Discovery
+import org.opendc.harness.engine.discovery.DiscoveryFilter
+import org.opendc.harness.engine.discovery.DiscoveryRequest
+import org.opendc.harness.engine.discovery.DiscoverySelector
+
+/**
+ * A [Discovery] implementation that discovers [Experiment] instances on the classpath.
+ */
+internal class DslDiscovery : Discovery {
+    /*
+     * Lazily memoize the results of the classpath scan.
+     */
+    private val scanResult by lazy { scan() }
+
+    override fun discover(request: DiscoveryRequest): Flow<ExperimentDefinition> {
+        return findExperiments()
+            .map { cls ->
+                val exp = cls.constructors[0].newInstance() as Experiment
+                exp.toDefinition()
+            }
+            .filter(select(request.selectors))
+            .filter(filter(request.filters))
+            .asFlow()
+    }
+
+    /**
+     * Find the classes on the classpath implementing the [Experiment] class.
+     */
+    private fun findExperiments(): Sequence<Class<out Experiment>> {
+        return scanResult
+            .getSubclasses(Experiment::class.java.name)
+            .filter { !(it.isAbstract || it.isInterface) }
+            .map { it.loadClass() }
+            .filterIsInstance<Class<out Experiment>>()
+            .asSequence()
+    }
+
+    /**
+     * Create a predicate for filtering the experiments based on the specified [filters].
+     */
+    private fun filter(filters: List<DiscoveryFilter>): (ExperimentDefinition) -> Boolean = { def ->
+        filters.isEmpty() || filters.all { it.test(def) }
+    }
+
+    /**
+     * Create a predicate for selecting the experiments based on the specified [selectors].
+     */
+    private fun select(selectors: List<DiscoverySelector>): (ExperimentDefinition) -> Boolean = { def ->
+        selectors.isEmpty() || selectors.any { it.test(def) }
+    }
+
+    /**
+     * Scan the classpath using [ClassGraph].
+     */
+    private fun scan(): ScanResult {
+        return ClassGraph()
+            .enableClassInfo()
+            .enableExternalClasses()
+            .ignoreClassVisibility()
+            .rejectPackages(
+                "java.*",
+                "javax.*",
+                "sun.*",
+                "com.sun.*",
+                "kotlin.*",
+                "androidx.*",
+                "org.jetbrains.kotlin.*",
+                "org.junit.*"
+            ).scan()
+    }
+}