merged TimelineStore and PersistentTimelineStore #41

LocoKit/Timelines/ItemsObserver.swift

@@ -0,0 +1,79 @@
+//
+//  ItemsObserver.swift
+//  LocoKit
+//
+//  Created by Matt Greenfield on 11/9/18.
+//
+
+import os.log
+import GRDB
+
+class ItemsObserver: TransactionObserver {
+
+    var store: TimelineStore
+    var changedRowIds: Set<Int64> = []
+
+    init(store: TimelineStore) {
+        self.store = store
+    }
+
+    // observe updates to next/prev item links
+    func observes(eventsOfKind eventKind: DatabaseEventKind) -> Bool {
+        switch eventKind {
+        case .update(let tableName, let columnNames):
+            guard tableName == "TimelineItem" else { return false }
+            let itemEdges: Set<String> = ["previousItemId", "nextItemId"]
+            return itemEdges.intersection(columnNames).count > 0
+        default: return false
+        }
+    }
+
+    func databaseDidChange(with event: DatabaseEvent) {
+        changedRowIds.insert(event.rowID)
+    }
+
+    func databaseDidCommit(_ db: Database) {
+        let rowIds: Set<Int64> = store.mutex.sync {
+            let rowIds = changedRowIds
+            changedRowIds = []
+            return rowIds
+        }
+
+        if rowIds.isEmpty { return }
+
+        /** maintain the timeline items linked list locally, for changes made outside the managed environment **/
+
+        do {
+            let marks = repeatElement("?", count: rowIds.count).joined(separator: ",")
+            let query = "SELECT itemId, previousItemId, nextItemId FROM TimelineItem WHERE rowId IN (\(marks))"
+            let rows = try Row.fetchCursor(db, query, arguments: StatementArguments(rowIds))
+
+            while let row = try rows.next() {
+                let previousItemIdString = row["previousItemId"] as String?
+                let nextItemIdString = row["nextItemId"] as String?
+
+                guard let uuidString = row["itemId"] as String?, let itemId = UUID(uuidString: uuidString) else { continue }
+                guard let item = store.object(for: itemId) as? TimelineItem else { continue }
+
+                if let uuidString = previousItemIdString, item.previousItemId?.uuidString != uuidString {
+                    item.previousItemId = UUID(uuidString: uuidString)
+
+                } else if previousItemIdString == nil && item.previousItemId != nil {
+                    item.previousItemId = nil
+                }
+
+                if let uuidString = nextItemIdString, item.nextItemId?.uuidString != uuidString {
+                    item.nextItemId = UUID(uuidString: uuidString)
+
+                } else if nextItemIdString == nil && item.nextItemId != nil {
+                    item.nextItemId = nil
+                }
+            }
+
+        } catch {
+            os_log("SQL Exception: %@", error.localizedDescription)
+        }
+    }
+
+    func databaseDidRollback(_ db: Database) {}
+}