feat: add iCal export for reservations

src/main/java/com/slotline/ical/ICalController.java

@@ -0,0 +1,47 @@
+package com.slotline.ical;
+
+import com.slotline.security.AuthenticatedUser;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.tags.Tag;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@Tag(name = "iCal export")
+public class ICalController {
+
+    private static final MediaType calendarType = MediaType.parseMediaType("text/calendar;charset=UTF-8");
+
+    private final ICalService icalService;
+
+    public ICalController(ICalService icalService) {
+        this.icalService = icalService;
+    }
+
+    @GetMapping("/api/resources/{resourceId}/calendar.ics")
+    @Operation(summary = "iCal (.ics) feed of active reservations for a resource")
+    public ResponseEntity<String> forResource(@AuthenticationPrincipal AuthenticatedUser actor,
+                                              @PathVariable Long resourceId) {
+        String body = icalService.forResource(actor.organizationId(), resourceId);
+        return calendar(body, "resource-" + resourceId + ".ics");
+    }
+
+    @GetMapping("/api/reservations/calendar.ics")
+    @Operation(summary = "iCal (.ics) feed of the caller's active reservations")
+    public ResponseEntity<String> forCaller(@AuthenticationPrincipal AuthenticatedUser actor) {
+        String body = icalService.forUser(actor.id());
+        return calendar(body, "my-reservations.ics");
+    }
+
+    private ResponseEntity<String> calendar(String body, String filename) {
+        return ResponseEntity.ok()
+                .contentType(calendarType)
+                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + filename + "\"")
+                .body(body);
+    }
+}

src/main/java/com/slotline/ical/ICalService.java

@@ -0,0 +1,73 @@
+package com.slotline.ical;
+
+import com.slotline.reservation.Reservation;
+import com.slotline.reservation.ReservationRepository;
+import com.slotline.reservation.ReservationStatus;
+import com.slotline.resource.Resource;
+import com.slotline.resource.ResourceService;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.util.List;
+
+@Service
+public class ICalService {
+
+    private static final DateTimeFormatter icalTimestamp =
+            DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmss'Z'").withZone(ZoneOffset.UTC);
+    private static final String lineBreak = "\r\n";
+
+    private final ReservationRepository reservations;
+    private final ResourceService resources;
+
+    public ICalService(ReservationRepository reservations, ResourceService resources) {
+        this.reservations = reservations;
+        this.resources = resources;
+    }
+
+    @Transactional(readOnly = true)
+    public String forResource(Long organizationId, Long resourceId) {
+        Resource resource = resources.require(organizationId, resourceId);
+        List<Reservation> active = reservations
+                .findByResourceIdAndStatusOrderByStartTimeAsc(resource.getId(), ReservationStatus.ACTIVE);
+        return render("resource-" + resource.getId(), active);
+    }
+
+    @Transactional(readOnly = true)
+    public String forUser(Long userId) {
+        List<Reservation> active =
+                reservations.findByUserIdAndStatusOrderByStartTimeAsc(userId, ReservationStatus.ACTIVE);
+        return render("user-" + userId, active);
+    }
+
+    private String render(String feedName, List<Reservation> active) {
+        StringBuilder calendar = new StringBuilder();
+        calendar.append("BEGIN:VCALENDAR").append(lineBreak);
+        calendar.append("VERSION:2.0").append(lineBreak);
+        calendar.append("PRODID:-//slotline//reservation feed//EN").append(lineBreak);
+        calendar.append("CALSCALE:GREGORIAN").append(lineBreak);
+        calendar.append("X-WR-CALNAME:slotline ").append(feedName).append(lineBreak);
+        String stamp = icalTimestamp.format(Instant.now());
+        for (Reservation reservation : active) {
+            calendar.append("BEGIN:VEVENT").append(lineBreak);
+            calendar.append("UID:reservation-").append(reservation.getId()).append("@slotline").append(lineBreak);
+            calendar.append("DTSTAMP:").append(stamp).append(lineBreak);
+            calendar.append("DTSTART:").append(icalTimestamp.format(reservation.getStartTime())).append(lineBreak);
+            calendar.append("DTEND:").append(icalTimestamp.format(reservation.getEndTime())).append(lineBreak);
+            calendar.append("SUMMARY:").append(escape(reservation.getResource().getName())).append(lineBreak);
+            calendar.append("END:VEVENT").append(lineBreak);
+        }
+        calendar.append("END:VCALENDAR").append(lineBreak);
+        return calendar.toString();
+    }
+
+    private String escape(String text) {
+        return text.replace("\\", "\\\\")
+                .replace(";", "\\;")
+                .replace(",", "\\,")
+                .replace("\n", "\\n");
+    }
+}