Sketch a scheduler for running periodic tasks

Periodic tasks are special in that they are usually kept around and
started based on a schedule. A new component checks periodic tasks and
submits them in the queue once they are due.

In order to avoid duplicate periodic jobs, the tracker of a job is
used to store the periodic job id. Each time a periodic task is due,
it is first checked if there is a job running (or queued) for this
task.

modules/common/src/main/scala/docspell/common/Hash.scala

@@ -0,0 +1,28 @@
+package docspell.common
+
+import scodec.bits.ByteVector
+import java.nio.charset.StandardCharsets
+
+final class Hash(bytes: ByteVector) {
+
+  private def digest(name: String): String =
+    bytes.digest(name).toHex.toLowerCase
+
+  def sha256: String =
+    digest("SHA-256")
+
+  def md5: String =
+    digest("MD5")
+
+  def add(str: String): Hash =
+    new Hash(bytes ++ ByteVector.view(str.getBytes(StandardCharsets.UTF_8)))
+
+  def add(id: Ident): Hash =
+    add(id.id)
+}
+
+object Hash {
+
+  def empty: Hash = new Hash(ByteVector.empty)
+
+}

modules/common/src/main/scala/docspell/common/Timestamp.scala

@@ -4,6 +4,8 @@ import java.time.{Instant, LocalDate, ZoneId}
 
 import cats.effect.Sync
 import io.circe.{Decoder, Encoder}
+import java.time.LocalDateTime
+import java.time.ZonedDateTime
 
 case class Timestamp(value: Instant) {
 
@@ -17,13 +19,20 @@ case class Timestamp(value: Instant) {
   def minusHours(n: Long): Timestamp =
     Timestamp(value.minusSeconds(n * 60 * 60))
 
-  def toDate: LocalDate =
-    value.atZone(ZoneId.of("UTC")).toLocalDate
+  def toUtcDate: LocalDate =
+    value.atZone(Timestamp.UTC).toLocalDate
+
+  def toUtcDateTime: LocalDateTime =
+    value.atZone(Timestamp.UTC).toLocalDateTime
+
+  def atZone(zone: ZoneId): ZonedDateTime =
+    value.atZone(zone)
 
   def asString: String = value.toString
 }
 
 object Timestamp {
+  val UTC = ZoneId.of("UTC")
 
   val Epoch = Timestamp(Instant.EPOCH)