server: Add Blockhash model

server/app/com/xsn/explorer/models/Blockhash.scala

@@ -0,0 +1,31 @@
+package com.xsn.explorer.models
+
+import play.api.libs.json._
+
+class Blockhash private (val string: String) extends AnyVal
+
+object Blockhash {
+  private val pattern = "^[a-f0-9]{64}$".r.pattern
+
+  def from(string: String): Option[Blockhash] = {
+    val lowercaseString = string.toLowerCase
+
+    if (pattern.matcher(lowercaseString).matches()) {
+      Some(new Blockhash(lowercaseString))
+    } else {
+      None
+    }
+  }
+
+  implicit val reads: Reads[Blockhash] = Reads { json =>
+    json.validate[String].flatMap { string =>
+      from(string)
+          .map(JsSuccess.apply(_))
+          .getOrElse {
+            JsError.apply("Invalid blockhash")
+          }
+    }
+  }
+
+  implicit val writes: Writes[Blockhash] = Writes { obj => JsString(obj.string) }
+}