Add initial API

library/build.gradle.kts

@@ -31,4 +31,20 @@ kotlin {
   androidNativeX64()
   mingwX64()
   watchosDeviceArm64()
+
+  sourceSets {
+    val commonMain by getting {
+      dependencies {
+        api("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3")
+      }
+    }
+  }
+}
+
+android {
+  compileSdk = 34
+  defaultConfig {
+    minSdk = 1
+  }
+  namespace = group.toString()
 }

library/src/commonMain/kotlin/com/tidal/networktime/NTPServer.kt

@@ -0,0 +1,41 @@
+package com.tidal.networktime
+
+import kotlin.time.Duration
+import kotlin.time.Duration.Companion.seconds
+
+sealed interface NTPServer {
+  val hostName: String
+  val responseTimeout: Duration
+  val dnsResolutionStrategy: DNSResolutionStrategy
+
+  sealed interface Unicast : NTPServer {
+    class Sequential(
+      override val hostName: String,
+      override val responseTimeout: Duration = 5.seconds,
+      override val dnsResolutionStrategy: DNSResolutionStrategy = DNSResolutionStrategy.ALL,
+      val outgoingRequestGap: Duration = OUTGOING_REQUEST_GAP_DEFAULT_SECONDS.seconds,
+    ) : Unicast
+
+    class Concurrent(
+      override val hostName: String,
+      override val responseTimeout: Duration = 5.seconds,
+      override val dnsResolutionStrategy: DNSResolutionStrategy = DNSResolutionStrategy.ALL,
+    ) : Unicast
+
+    companion object {
+      private const val OUTGOING_REQUEST_GAP_DEFAULT_SECONDS = 2
+    }
+  }
+
+  class Anycast(
+    override val hostName: String,
+    override val responseTimeout: Duration = 68.seconds,
+    override val dnsResolutionStrategy: DNSResolutionStrategy = DNSResolutionStrategy.ALL,
+  ) : NTPServer
+
+  enum class DNSResolutionStrategy {
+    IP_V4,
+    IP_V6,
+    ALL,
+  }
+}

library/src/commonMain/kotlin/com/tidal/networktime/SNTPClient.kt

@@ -0,0 +1,54 @@
+package com.tidal.networktime
+
+import kotlinx.coroutines.CoroutineScope
+import kotlin.time.Duration
+import kotlin.time.Duration.Companion.seconds
+
+/**
+ * Construct a new SNTP client that can be requested to periodically interact with the provided
+ * [ntpServers] to obtain information about their provided time.
+ *
+ * @param ntpServers Representation of supported NTP sources.
+ * @param coroutineScope The scope where synchronization will run on.
+ * @param ntpVersion The version number to write in packets.
+ * @param portSelectionStrategy The strategy for selecting a port to operate on.
+ * @param minimumSynchronizationInterval The minimum amount of time between performing time queries
+ * on all unicast sources. The actual value used may be larger than this on occasion based on
+ * changes to the difference between the time provided by [ntpServers] and [referenceClock] (if it
+ * ever changes), but will never be lower than this value.
+ * @param referenceClock A clock used to calculate timing differences with the information obtained
+ * from [ntpServers]. This clock will never be modified directly.
+ */
+class SNTPClient(
+  vararg val ntpServers: NTPServer,
+  val coroutineScope: CoroutineScope,
+  val ntpVersion: NTPVersion = NTPVersion.FOUR,
+  val portSelectionStrategy: PortSelectionStrategy = PortSelectionStrategy.RFC9109,
+  val minimumSynchronizationInterval: Duration = 64.seconds,
+  val referenceClock: () -> Long,
+) {
+
+  val time: Long?
+    get() = TODO("Getting the time")
+
+  fun startSynchronization(): Unit = TODO("Start or return")
+
+  fun stopSynchronization(): Unit = TODO("Stop or return")
+
+  enum class NTPVersion(val descriptor: Short) {
+    ZERO(0),
+    ONE(1),
+    TWO(2),
+    THREE(3),
+    FOUR(4),
+  }
+
+  sealed class PortSelectionStrategy(val pinnedPortNumber: Int?) {
+    data object RFC5905 : PortSelectionStrategy(123)
+
+    /**
+     * Make a new selection of a random available port every time a socket is opened.
+     */
+    data object RFC9109 : PortSelectionStrategy(null)
+  }
+}