59 lines
1.5 KiB
Scala
59 lines
1.5 KiB
Scala
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package grib
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import cats.effect._
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import cats.effect.unsafe.implicits.global
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import fs2.io.file.{Files, Path}
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import java.nio.ByteBuffer
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// sbt "runMain grib.GribParser"
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object GribParser {
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def parseFile(path: Path): IO[List[Grib]] = {
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def loop(ptr: Long, acc: List[Grib]): IO[List[Grib]] = {
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for {
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fileSize <- Files[IO].size(path)
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result <- if (ptr >= fileSize) {
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IO.pure(acc.reverse)
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} else {
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for {
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grib <- parseGrib(path, ptr)
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nextResult <- loop(ptr + grib.length, grib :: acc)
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} yield nextResult
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}
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} yield result
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}
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loop(0L, List.empty)
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}
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def parseGrib(path: Path, ptr: Long): IO[Grib] = {
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for {
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bytes <- readBytes(path, ptr, 16)
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identifier = new String(bytes.take(4), "ASCII")
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discipline = bytes(6)
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version = bytes(7)
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length = ByteBuffer.wrap(bytes.slice(8, 16)).getLong
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_ <- IO.println(identifier, version, discipline, length)
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grib = Grib(version, discipline, length)
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} yield grib
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}
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def readBytes(path: Path, ptr: Long, len: Int): IO[Array[Byte]] = {
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Files[IO].readRange(path, 4096, ptr, ptr + len)
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.compile
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.to(Array)
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}
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def main(args: Array[String]): Unit = {
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val fileName = "data/HARMONIE_DINI_SF_2025-01-24T030000Z_2025-01-26T010000Z.grib"
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val path = Path(fileName)
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// Example of running the effect
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val program = for {
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_ <- parseFile(path)
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} yield ()
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program.unsafeRunSync()
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}
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}
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