implemented 09-system-metrics.md: added system metrics: introduced system monitoring with a metrics collector, REST API endpoint, Thymeleaf UI rendering, and lifecycle management

src/main/kotlin/de/hoennig/gittally/server/ServerMetricsLifecycle.kt

@@ -0,0 +1,28 @@
+package de.hoennig.gittally.server
+
+import de.hoennig.gittally.metrics.SystemMetricsCollector
+import jakarta.annotation.PreDestroy
+import org.springframework.boot.context.event.ApplicationReadyEvent
+import org.springframework.context.annotation.Profile
+import org.springframework.context.event.EventListener
+import org.springframework.stereotype.Component
+
+/**
+ * Starts the system-metrics sampling loop once the server context is ready and
+ * stops it on shutdown. Only in the `server` profile, like [ServerWatcherLifecycle].
+ */
+@Component
+@Profile("server")
+class ServerMetricsLifecycle(
+    private val collector: SystemMetricsCollector,
+) {
+    @EventListener(ApplicationReadyEvent::class)
+    fun onApplicationReady() {
+        collector.start()
+    }
+
+    @PreDestroy
+    fun onShutdown() {
+        collector.stop()
+    }
+}

src/main/kotlin/de/hoennig/gittally/server/SystemApiController.kt

@@ -0,0 +1,18 @@
+package de.hoennig.gittally.server
+
+import de.hoennig.gittally.metrics.SystemMetrics
+import de.hoennig.gittally.metrics.SystemMetricsCollector
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.RestController
+
+@RestController
+class SystemApiController(
+    private val collector: SystemMetricsCollector,
+) {
+    /**
+     * The current system snapshot plus min/max/avg aggregates (the legacy
+     * `system.json`). Unavailable metrics are null, never an error.
+     */
+    @GetMapping("/api/system")
+    fun system(): SystemMetrics = collector.snapshot()
+}

src/main/kotlin/de/hoennig/gittally/server/UiController.kt

@@ -5,6 +5,7 @@ import de.hoennig.gittally.build.BuildExecutor
 import de.hoennig.gittally.build.BuildResultRepository
 import de.hoennig.gittally.build.BuildStatus
 import de.hoennig.gittally.config.ConfigLoader
+import de.hoennig.gittally.metrics.SystemMetricsCollector
 import org.springframework.beans.factory.ObjectProvider
 import org.springframework.boot.info.BuildProperties
 import org.springframework.http.HttpStatus
@@ -32,6 +33,7 @@ class UiController(
     private val artifactStore: ArtifactStore,
     private val controlTokens: ControlTokenService,
     private val configLoader: ConfigLoader,
+    private val metricsCollector: SystemMetricsCollector,
     private val buildProperties: ObjectProvider<BuildProperties>,
 ) {
     var workingDir: Path = Paths.get(".")
@@ -80,6 +82,13 @@ class UiController(
         return "current"
     }
 
+    @GetMapping("/system")
+    fun system(model: Model): String {
+        baseModel(model, view = "system", pageTitle = "System Metrics")
+        model.addAttribute("metrics", SystemMetricsView.from(metricsCollector.snapshot()))
+        return "system"
+    }
+
     /** Artifact index rendered from the artifact store — legacy pre-generated this page as static HTML. */
     @GetMapping("/builds/{artifactKey}")
     fun artifactIndex(

src/main/kotlin/de/hoennig/gittally/server/UiViews.kt

@@ -2,12 +2,15 @@ package de.hoennig.gittally.server
 
 import de.hoennig.gittally.build.BuildResult
 import de.hoennig.gittally.config.GiteaConfig
+import de.hoennig.gittally.metrics.MetricAggregate
+import de.hoennig.gittally.metrics.SystemMetrics
 import java.net.URLEncoder
 import java.nio.charset.StandardCharsets
 import java.time.Duration
 import java.time.Instant
 import java.time.ZoneId
 import java.time.format.DateTimeFormatter
+import java.util.Locale
 
 /** Links into the Gitea web UI, like legacy `gitea_branch_web_url`; null when Gitea is not configured. */
 class GiteaWebLinks(
@@ -33,6 +36,8 @@ class GiteaWebLinks(
 object UiFormats {
     private val timestampFormat = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm").withZone(ZoneId.systemDefault())
 
+    private val timeOfDayFormat = DateTimeFormatter.ofPattern("HH:mm:ss").withZone(ZoneId.systemDefault())
+
     fun timestamp(instant: Instant): String = timestampFormat.format(instant)
 
     /** `m:ss`, or `h:mm:ss` from one hour — like the legacy `MM:SS` duration column. */
@@ -50,6 +55,16 @@ object UiFormats {
             "%d:%02d".format(minutes, rest)
         }
     }
+
+    /** Two-decimal metric value with a dot like JS `toFixed(2)`; `n/a` when the source is unavailable. */
+    fun metric(value: Double?): String =
+        if (value == null || !value.isFinite()) {
+            "n/a"
+        } else {
+            String.format(Locale.ROOT, "%.2f", value)
+        }
+
+    fun timeOfDay(instant: Instant): String = timeOfDayFormat.format(instant)
 }
 
 /** One row of the latest/history build tables. */
@@ -96,3 +111,60 @@ data class CurrentBuildView(
     val branchUrl: String?,
     val commitUrl: String?,
 )
+
+/**
+ * One row of the system-metrics table. The [key] matches the JSON field of
+ * `GET /api/system`, so `gittally.js` can update the cells in place.
+ */
+data class MetricRowView(
+    val key: String,
+    val label: String,
+    val current: String,
+    val min: String,
+    val max: String,
+    val avg: String,
+) {
+    companion object {
+        fun from(
+            key: String,
+            label: String,
+            aggregate: MetricAggregate?,
+        ) = MetricRowView(
+            key = key,
+            label = label,
+            current = UiFormats.metric(aggregate?.current),
+            min = UiFormats.metric(aggregate?.min),
+            max = UiFormats.metric(aggregate?.max),
+            avg = UiFormats.metric(aggregate?.avg),
+        )
+    }
+}
+
+/** The system view: the metric rows plus the totals/updated info line, like the legacy system page. */
+data class SystemMetricsView(
+    val rows: List<MetricRowView>,
+    val cpuCount: String,
+    val ramTotal: String,
+    val diskTotal: String,
+    val updated: String,
+) {
+    companion object {
+        fun from(metrics: SystemMetrics) =
+            SystemMetricsView(
+                rows =
+                    listOf(
+                        MetricRowView.from("cpuUsed", "CPU used (cores)", metrics.cpuUsed),
+                        MetricRowView.from("cpuIdle", "CPU idle (cores)", metrics.cpuIdle),
+                        MetricRowView.from("ramUsedGib", "RAM used (GiB)", metrics.ramUsedGib),
+                        MetricRowView.from("ramFreeGib", "RAM free (GiB)", metrics.ramFreeGib),
+                        MetricRowView.from("diskUsedGib", "Disk used (GiB)", metrics.diskUsedGib),
+                        MetricRowView.from("diskFreeGib", "Disk free (GiB)", metrics.diskFreeGib),
+                        MetricRowView.from("repoSizeGib", "Repo size (GiB)", metrics.repoSizeGib),
+                    ),
+                cpuCount = "${metrics.cpuCount} cores",
+                ramTotal = metrics.ramTotalGib?.let { "${UiFormats.metric(it)} GiB" } ?: "n/a",
+                diskTotal = metrics.diskTotalGib?.let { "${UiFormats.metric(it)} GiB" } ?: "n/a",
+                updated = metrics.timestamp?.let { UiFormats.timeOfDay(it) } ?: "n/a",
+            )
+    }
+}