get posix data from zoneinfo files

Signed-off-by: Peter Siegmund <developer@mars3142.org>

src/main/java/dev/mars3142/fhq/timezone_service/timezone/service/TimeZoneService.java

@@ -0,0 +1,5 @@
+package dev.mars3142.fhq.timezone_service.timezone.service;
+
+public interface TimeZoneService {
+  String getPosixTimeZone(String timezone);
+}

src/main/java/dev/mars3142/fhq/timezone_service/timezone/service/impl/TimeZoneServiceImpl.java

@@ -0,0 +1,24 @@
+package dev.mars3142.fhq.timezone_service.timezone.service.impl;
+
+import dev.mars3142.fhq.timezone_service.timezone.service.TimeZoneService;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import lombok.val;
+import org.springframework.stereotype.Service;
+
+@Service
+public class TimeZoneServiceImpl implements TimeZoneService {
+
+  @Override
+  public String getPosixTimeZone(String timezone) {
+    val filename = Path.of("/usr/share/zoneinfo/" + timezone);
+    try {
+      val bytes = Files.readAllBytes(filename);
+      val content = new String(bytes).split("\n");
+      return content[content.length - 1];
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}

src/main/java/dev/mars3142/fhq/timezone_service/timezone/web/controllers/TimeZoneController.java

@@ -2,6 +2,9 @@ package dev.mars3142.fhq.timezone_service.timezone.web.controllers;
 
 import dev.mars3142.fhq.timezone_service.timezone.domain.model.request.TimeZoneRequest;
 import dev.mars3142.fhq.timezone_service.timezone.domain.model.response.TimeZoneResponse;
+import dev.mars3142.fhq.timezone_service.timezone.service.TimeZoneService;
+import lombok.RequiredArgsConstructor;
+import lombok.val;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -9,10 +12,14 @@ import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 @RequestMapping("v1/timezone")
+@RequiredArgsConstructor
 public class TimeZoneController {
 
+  private final TimeZoneService timeZoneService;
+
   @PostMapping()
   public TimeZoneResponse getTimeZone(@RequestBody TimeZoneRequest request) {
-    return new TimeZoneResponse(request.timezone());
+    val timezone = timeZoneService.getPosixTimeZone(request.timezone());
+    return new TimeZoneResponse(timezone);
   }
 }