add Film observability with trace id and metrics (#44)

* add Film observability with trace id and metrics

* test: provide meter registry in FilmServiceTest

src/main/kotlin/com/project/movienight/adapters/web/ApiExceptionHandler.kt

@@ -3,6 +3,8 @@ package com.project.movienight.adapters.web
 import com.project.movienight.domain.exception.BlockedValueException
 import com.project.movienight.domain.exception.DomainException
 import com.project.movienight.domain.exception.EntityNotFoundException
+import org.slf4j.LoggerFactory
+import org.slf4j.MDC
 import org.springframework.http.HttpStatus
 import org.springframework.web.bind.annotation.ExceptionHandler
 import org.springframework.web.bind.annotation.ResponseStatus
@@ -10,22 +12,60 @@ import org.springframework.web.bind.annotation.RestControllerAdvice
 
 @RestControllerAdvice
 class ApiExceptionHandler {
+    private val log = LoggerFactory.getLogger(javaClass)
+
     @ExceptionHandler(EntityNotFoundException::class)
     @ResponseStatus(HttpStatus.NOT_FOUND)
-    fun handleNotFound(exception: EntityNotFoundException): ErrorResponse =
-        ErrorResponse(message = exception.message ?: "Entity not found")
+    fun handleNotFound(exception: EntityNotFoundException): ErrorResponse {
+        val traceId = currentTraceId()
+        log.warn("Entity not found: traceId='{}', message='{}'", traceId, exception.message)
+
+        return ErrorResponse(
+            message = exception.message ?: "Entity not found",
+            traceId = traceId,
+        )
+    }
 
     @ExceptionHandler(BlockedValueException::class)
     @ResponseStatus(HttpStatus.BAD_REQUEST)
-    fun handleBlockedValue(exception: BlockedValueException): ErrorResponse =
-        ErrorResponse(message = exception.message ?: "Blocked value")
+    fun handleBlockedValue(exception: BlockedValueException): ErrorResponse {
+        val traceId = currentTraceId()
+        log.warn("Blocked value: traceId='{}', message='{}'", traceId, exception.message)
+
+        return ErrorResponse(
+            message = exception.message ?: "Blocked value",
+            traceId = traceId,
+        )
+    }
 
     @ExceptionHandler(DomainException::class)
     @ResponseStatus(HttpStatus.BAD_REQUEST)
-    fun handleDomainException(exception: DomainException): ErrorResponse =
-        ErrorResponse(message = exception.message ?: "Domain error")
+    fun handleDomainException(exception: DomainException): ErrorResponse {
+        val traceId = currentTraceId()
+        log.warn("Domain error: traceId='{}', message='{}'", traceId, exception.message)
+
+        return ErrorResponse(
+            message = exception.message ?: "Domain error",
+            traceId = traceId,
+        )
+    }
+
+    @ExceptionHandler(Exception::class)
+    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
+    fun handleUnexpectedException(exception: Exception): ErrorResponse {
+        val traceId = currentTraceId()
+        log.error("Unexpected error: traceId='{}'", traceId, exception)
+
+        return ErrorResponse(
+            message = "Internal server error",
+            traceId = traceId,
+        )
+    }
+
+    private fun currentTraceId(): String = MDC.get("traceId") ?: "unknown"
 }
 
 data class ErrorResponse(
     val message: String,
+    val traceId: String,
 )

src/main/kotlin/com/project/movienight/adapters/web/TraceIdFilter.kt

@@ -0,0 +1,27 @@
+package com.project.movienight.adapters.web
+
+import jakarta.servlet.FilterChain
+import jakarta.servlet.http.HttpServletRequest
+import jakarta.servlet.http.HttpServletResponse
+import org.slf4j.MDC
+import org.springframework.stereotype.Component
+import org.springframework.web.filter.OncePerRequestFilter
+import java.util.UUID
+
+@Component
+class TraceIdFilter : OncePerRequestFilter() {
+    override fun doFilterInternal(
+        request: HttpServletRequest,
+        response: HttpServletResponse,
+        filterChain: FilterChain,
+    ) {
+        val traceId = UUID.randomUUID().toString()
+        MDC.put("traceId", traceId)
+
+        try {
+            filterChain.doFilter(request, response)
+        } finally {
+            MDC.remove("traceId")
+        }
+    }
+}