Limit all dates asking to 3 months range

src/main/scala/db/DBService.scala

@@ -81,6 +81,20 @@ class DBService(log: Logger[IO]) extends DataServiceTrait {
     } yield dates.sorted
   }
 
+  def getDatesByMonths(monthList: List[LocalDate]): IO[List[LocalDate]] = {
+    val dateFormatter = DateTimeFormatter.ofPattern("yyyyMMdd")
+    val monthFormatter = DateTimeFormatter.ofPattern("yyyyMM")
+    val monthStrList = monthList.map(_.format(monthFormatter))
+    for {
+      fileNames <- readFileNames(dataPath)
+      datesStr <- IO(fileNames.map(_.take(8)).distinct) // take yyyyMMdd
+      filteredDatesStr = datesStr.filter(date => monthStrList.contains(date.take(6)))
+      dates <- filteredDatesStr.traverse { str =>
+        IO(LocalDate.parse(str, dateFormatter)).option
+      }.map(_.flatten)
+    } yield dates.sorted
+  }
+
   def getDateFileNames(date: LocalDate): IO[List[String]] = {
     val formatter: DateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd")
     val dateStr: String = date.format(formatter)

src/main/scala/db/DataService.scala

@@ -63,6 +63,8 @@ class DataService private(
 
   def getDates: IO[List[LocalDate]] = dbService.getDates
 
+  def getDatesByMonths(monthList: List[LocalDate]): IO[List[LocalDate]] = dbService.getDatesByMonths(monthList)
+
   def getDateFileNames(date: LocalDate): IO[List[String]] = dbService.getDateFileNames(date)
 
   // TODO implement getting full data from state

src/main/scala/server/Server.scala

@@ -6,7 +6,7 @@ import com.comcast.ip4s.IpLiteralSyntax
 import db.DataService
 import fetch.FetchService
 import parse.{Aggregate, Parser, WeatherData}
-import server.ValidateRoutes.{AggKey, CityList, DateTimeRange, Granularity, ValidDate}
+import server.ValidateRoutes.{AggKey, CityList, DateTimeRange, Granularity, ValidDate, ValidateMonths}
 import io.circe.{Json, Printer}
 import org.http4s._
 import org.http4s.dsl.io._
@@ -89,6 +89,12 @@ class Server(dataService: DataService, fetch: FetchService, log: Logger[IO]) {
         Ok(dates.asJson.pretty)
       )
 
+    // http://0.0.0.0:8080/api/show/months/202304,202305,202306
+    case GET -> Root / "show" / "months" / ValidateMonths(monthList) =>
+      dataService.getDatesByMonths(monthList).flatMap(dates =>
+        Ok(dates.asJson.pretty)
+      )
+
     // http://0.0.0.0:8080/api/show/date/20230423
     case GET -> Root / "show" / "date" / ValidDate(date) =>
       dataService.getDateFileNames(date).flatMap(fileNames =>

src/main/scala/server/ValidateRoutes.scala

@@ -27,6 +27,21 @@ object ValidateRoutes {
     }
   }
 
+  object ValidateMonths {
+    def unapply(str: String): Option[List[LocalDate]] = {
+      val formatter = DateTimeFormatter.ofPattern("yyyyMMdd")
+      val monthList = str
+        .split(",")
+        .toList
+        .flatMap(str => Try(LocalDate.parse(str + "01", formatter)).toOption)
+
+      monthList match {
+        case Nil => None
+        case list => Some(list)
+      }
+    }
+  }
+
   object CityList {
     def unapply(str: String): Option[List[String]] = {
       str.split(",").toList match {

src/test/scala/db/DBServiceSpec.scala

@@ -34,6 +34,27 @@ class DBServiceSpec extends AnyFunSuite with Matchers {
     lines.length shouldBe 2142
   }
 
+  test("getDatesByMonths should return filtered dates") {
+    val monthFormatter = DateTimeFormatter.ofPattern("yyyyMMdd")
+    val monthList = List(
+      LocalDate.parse("20230401", monthFormatter),
+      LocalDate.parse("20230501", monthFormatter),
+      LocalDate.parse("20230601", monthFormatter),
+    )
+    val dbService = DBService.of.unsafeRunSync()
+    val dates = dbService.getDatesByMonths(monthList).unsafeRunSync()
+
+    dates should not be empty
+
+    val exportFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd")
+    val validPrefixes = Set("2023-04", "2023-05", "2023-06")
+    val invalidDates = dates
+      .map(_.format(exportFormatter))
+      .filterNot(date => validPrefixes.exists(prefix => date.startsWith(prefix)))
+
+    invalidDates shouldBe empty
+  }
+
   test("DBService.save should return correct result") {
     val dbService = DBService.of.unsafeRunSync()
     val fileName = "testFile.txt"