feat(catalog): extend Catalog with dropTable

src/main/kotlin/kestrel/catalog/Catalog.kt

@@ -1,32 +1,61 @@
 package kestrel.catalog
 
 import kestrel.KestrelException
+import kestrel.sql.ast.NextValueExpression
+import kestrel.sql.ast.QueryStatement
+import kestrel.sql.ast.TriggerEvent
+import kestrel.sql.ast.TriggerTiming
+import kestrel.storage.Collation
 import kestrel.storage.Row
 import kestrel.storage.Table
+import kestrel.storage.Value
 
 class CatalogSnapshot(
     val tables: Map<String, Pair<TableSchema, List<Row>>>,
-    val indexDefinitions: List<IndexDefinition>
+    val indexDefinitions: List<IndexDefinition>,
+    val views: Map<String, ViewDefinition>,
+    val triggers: Map<String, TriggerDefinition>,
+    /**
+     * A reference copy of the map, not a deep copy of each [Sequence] - see [Sequence]'s own doc
+     * for why that is exactly what makes ROLLBACK undo CREATE/DROP/ALTER SEQUENCE while leaving a
+     * NEXTVAL advance in place.
+     */
+    val sequences: Map<String, Sequence>
 )
 
 class Catalog {
     private val tables = linkedMapOf<String, Table>()
     private val indexes = linkedMapOf<String, SortedIndex>()
+    private val views = linkedMapOf<String, ViewDefinition>()
+    private val triggers = linkedMapOf<String, TriggerDefinition>()
+    private val sequences = linkedMapOf<String, Sequence>()
 
     fun createTable(schema: TableSchema) {
         val key = schema.name.lowercase()
         if (tables.containsKey(key)) {
             throw KestrelException("table '${schema.name}' already exists")
         }
+        if (views.containsKey(key)) {
+            throw KestrelException("a view named '${schema.name}' already exists")
+        }
         tables[key] = Table(schema)
     }
 
-    fun dropTable(tableName: String) {
+    fun dropTable(tableName: String, cascade: Boolean = false) {
         val key = tableName.lowercase()
-        if (tables.remove(key) == null) {
+        if (!tables.containsKey(key)) {
+            if (views.containsKey(key)) {
+                throw KestrelException("'$tableName' is a view, use DROP VIEW")
+            }
             throw KestrelException("no such table: $tableName")
         }
+        dropDependentViews(tableName, cascade)
+        dropDependentForeignKeys(tableName, cascade)
+        tables.remove(key)
         indexes.entries.removeAll { it.value.definition.tableName.equals(tableName, ignoreCase = true) }
+        // A trigger without its table makes no sense to keep around - unlike a FOREIGN KEY
+        // reference, nothing else depends on it existing, so this always happens, CASCADE or not.
+        triggers.entries.removeAll { it.value.tableName.equals(tableName, ignoreCase = true) }
     }
 
     fun table(tableName: String): Table =