Read forecast dates which are already downloaded

.gitignore

@@ -30,3 +30,4 @@ logs/
 .env-fly
 data/*
 !project/assembly.sbt
+!src/main/scala/data

src/main/scala/data/DataService.scala

@@ -0,0 +1,63 @@
+package data
+
+import cats.effect.IO
+import fs2.io.file.{Files, Path}
+import grib.{Grib, GribParser}
+
+import java.time.{ZoneId, ZonedDateTime}
+import java.time.format.DateTimeFormatter
+import scala.io.Source
+import scala.util.Try
+
+object DataService {
+  val FOLDER = "data"
+
+  def getFileList(): IO[List[String]] =
+    Files[IO]
+      .list(Path(FOLDER))
+      .map(_.toString)
+      .filter(_.endsWith(".grib"))
+      .map(_.replace(s"$FOLDER/", ""))
+      .compile
+      .toList
+
+  def getGribStucture(fileName: String): IO[List[Grib]] = {
+    val filePath = Path(s"$FOLDER/$fileName")
+
+    Files[IO].exists(filePath).flatMap {
+      case true => GribParser.parseFile(filePath)
+      case false => IO.raiseError(new Exception(s"File not found: $fileName"))
+    }
+  }
+
+  def getBinaryChunk(offset: Int, length: Int, fileName: String): IO[Array[Byte]] = {
+    IO {
+      val source = Source.fromFile(s"$FOLDER/$fileName", "ISO-8859-1")
+      try {
+        source.slice(offset, offset + length).map(_.toByte).toArray
+      } finally {
+        source.close()
+      }
+    }
+  }
+
+  def getForecasts(): IO[List[(ZonedDateTime, ZonedDateTime)]] = {
+    getFileList()
+      .map { fileNameList =>
+        fileNameList.flatMap(getTimeFromName)
+      }
+  }
+
+  private def getTimeFromName(filename: String): Option[(ZonedDateTime, ZonedDateTime)] = {
+    Try {
+      val formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HHmm'Z'").withZone(ZoneId.of("UTC"))
+      val start = filename.slice(9, 25) // gets "2025-02-05T1500Z"
+      val end = filename.slice(26, 42) // gets "2025-02-05T1800Z"
+      (
+        ZonedDateTime.parse(start, formatter),
+        ZonedDateTime.parse(end, formatter)
+      )
+    }.toOption
+  }
+
+}

src/main/scala/data/DataServiceTest.scala

@@ -0,0 +1,16 @@
+package data
+
+import cats.effect.IO
+import cats.effect.unsafe.implicits.global
+import io.circe.syntax.EncoderOps
+
+object DataServiceTest {
+  def main(args: Array[String]): Unit = {
+    val program = for {
+        forecasts <- DataService.getForecasts()
+        _ <- IO.println(forecasts.asJson)
+    } yield ()
+
+    program.unsafeRunSync()
+  }
+}