refactor: Extract Signal Flow into odcsim

1 files changed, 90 insertions, 0 deletions

diff --git a/odcsim/odcsim-api/src/main/kotlin/com/atlarge/odcsim/signal/Signal.kt b/odcsim/odcsim-api/src/main/kotlin/com/atlarge/odcsim/signal/Signal.kt
new file mode 100644
index 00000000..da6298a3
--- /dev/null
+++ b/odcsim/odcsim-api/src/main/kotlin/com/atlarge/odcsim/signal/Signal.kt
@@ -0,0 +1,90 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2020 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 com.atlarge.odcsim.signal
+
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.InternalCoroutinesApi
+import kotlinx.coroutines.channels.BroadcastChannel
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.FlowCollector
+import kotlinx.coroutines.flow.asFlow
+
+/**
+ * A [Flow] that contains a single value that changes over time.
+ *
+ * This class exists to implement the DataFlow/StateFlow functionality that will be implemented in `kotlinx-coroutines`
+ * in the future, but is not available yet.
+ * See: https://github.com/Kotlin/kotlinx.coroutines/pull/1354
+ */
+public interface Signal<T> : Flow<T> {
+    /**
+     * The current value of this signal.
+     *
+     * Setting a value that is [equal][Any.equals] to the previous one does nothing.
+     */
+    public var value: T
+}
+
+/**
+ * Creates a [Signal] with a given initial [value].
+ */
+@Suppress("FunctionName")
+public fun <T> Signal(value: T): Signal<T> = SignalImpl(value)
+
+/**
+ * Internal implementation of the [Signal] interface.
+ */
+private class SignalImpl<T>(initialValue: T) : Signal<T> {
+    /**
+     * The [BroadcastChannel] to back this signal.
+     */
+    @OptIn(ExperimentalCoroutinesApi::class)
+    private val chan = BroadcastChannel<T>(Channel.CONFLATED)
+
+    /**
+     * The internal [Flow] backing this signal.
+     */
+    @OptIn(FlowPreview::class)
+    private val flow = chan.asFlow()
+
+    init {
+        @OptIn(ExperimentalCoroutinesApi::class)
+        chan.offer(initialValue)
+    }
+
+    @OptIn(ExperimentalCoroutinesApi::class)
+    public override var value: T = initialValue
+        set(value) {
+            if (field != value) {
+                chan.offer(value)
+                field = value
+            }
+        }
+
+    @InternalCoroutinesApi
+    override suspend fun collect(collector: FlowCollector<T>) = flow.collect(collector)
+}