Add event id validation

tools/validate_data.ps1

@@ -1408,6 +1408,35 @@ function Check-Post-Battle-Choices($Choices, [string]$ScenarioId) {
     }
 }
 
+function Check-Event-Ids($Events, [string]$ScenarioId) {
+    $eventIds = New-Object System.Collections.Generic.HashSet[string]
+    if ($null -eq $Events) {
+        return ,$eventIds
+    }
+    if (-not ($Events -is [System.Array])) {
+        Fail "Scenario $ScenarioId events must be an array."
+    }
+    foreach ($event in @($Events)) {
+        if ($event -is [string] -or $event -is [System.Array]) {
+            Fail "Scenario $ScenarioId has malformed event."
+        }
+        if (-not (Has-Prop $event "id")) {
+            Fail "Scenario $ScenarioId event has empty id."
+        }
+        $eventId = [string](Get-Prop $event "id" "")
+        if ([string]::IsNullOrWhiteSpace($eventId)) {
+            Fail "Scenario $ScenarioId event has empty id."
+        }
+        if (-not ($eventId -match "^[a-z0-9_]+$")) {
+            Fail "Scenario $ScenarioId event has unstable id: $eventId"
+        }
+        if (-not $eventIds.Add($eventId)) {
+            Fail "Scenario $ScenarioId has duplicate event id: $eventId"
+        }
+    }
+    return ,$eventIds
+}
+
 function Check-Required-Flags($RequiredFlags, [string]$ScenarioId, [string]$Context) {
     if ($null -eq $RequiredFlags) {
         return
@@ -1602,12 +1631,7 @@ foreach ($scenario in $campaign.scenarios) {
         }
     }
 
-    $eventIds = New-Object System.Collections.Generic.HashSet[string]
-    foreach ($event in (Get-Prop $scenarioData "events" @())) {
-        if (Has-Prop $event "id") {
-            $eventIds.Add([string]$event.id) | Out-Null
-        }
-    }
+    $eventIds = Check-Event-Ids (Get-Prop $scenarioData "events" $null) $scenarioId
     $knownUnitIds = Collect-Scenario-Unit-Ids $scenarioData
 
     if (Has-Prop $scenarioData "conditions") {