1 files changed, 110 insertions, 0 deletions
diff --git a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/util/CompositeTableReader.kt b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/util/CompositeTableReader.kt
new file mode 100644
index 00000000..dafc0798
--- /dev/null
+++ b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/util/CompositeTableReader.kt
@@ -0,0 +1,110 @@
+/*
+ * 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.trace.util
+
+import org.opendc.trace.TableColumn
+import org.opendc.trace.TableReader
+
+/**
+ * A helper class to chain multiple [TableReader]s.
+ */
+public abstract class CompositeTableReader : TableReader {
+    /**
+     * A flag to indicate that the reader has starting, meaning the user called [nextRow] at least once
+     * (and in turn [nextReader]).
+     */
+    private var hasStarted = false
+
+    /**
+     * The active [TableReader] instance.
+     */
+    private var delegate: TableReader? = null
+
+    /**
+     * Obtain the next [TableReader] instance to read from or `null` if there are no more readers to read from.
+     */
+    protected abstract fun nextReader(): TableReader?
+
+    override fun nextRow(): Boolean {
+        if (!hasStarted) {
+            assert(delegate == null) { "Duplicate initialization" }
+            delegate = nextReader()
+            hasStarted = true
+        }
+
+        var delegate = delegate
+
+        while (delegate != null) {
+            if (delegate.nextRow()) {
+                break
+            }
+
+            delegate.close()
+            delegate = nextReader()
+            this.delegate = delegate
+        }
+
+        return delegate != null
+    }
+
+    override fun resolve(column: TableColumn<*>): Int {
+        val delegate = delegate
+        return delegate?.resolve(column) ?: -1
+    }
+
+    override fun isNull(index: Int): Boolean {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.isNull(index)
+    }
+
+    override fun get(index: Int): Any? {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.get(index)
+    }
+
+    override fun getBoolean(index: Int): Boolean {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.getBoolean(index)
+    }
+
+    override fun getInt(index: Int): Int {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.getInt(index)
+    }
+
+    override fun getLong(index: Int): Long {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.getLong(index)
+    }
+
+    override fun getDouble(index: Int): Double {
+        val delegate = checkNotNull(delegate) { "Invalid reader state" }
+        return delegate.getDouble(index)
+    }
+
+    override fun close() {
+        delegate?.close()
+    }
+
+    override fun toString(): String = "CompositeTableReader"
+}