add local event filter functions.

filter.js

@@ -0,0 +1,26 @@
+export function matchFilter(filter, event) {
+  if (filter.id && event.id !== filter.id) return false
+  if (filter.kind && event.kind !== filter.kind) return false
+  if (filter.author && event.pubkey !== filter.author) return false
+  if (filter.authors && filter.author.indexOf(event.pubkey) === -1) return false
+  if (
+    filter['#e'] &&
+    event.tags.find(([t, v]) => t === 'e' && v === filter['#e']) === null
+  )
+    return false
+  if (
+    filter['#p'] &&
+    event.tags.find(([t, v]) => t === 'p' && v === filter['#p']) === null
+  )
+    return false
+  if (filter.since && event.created_at <= filter.since) return false
+
+  return true
+}
+
+export function matchFilters(filters, event) {
+  for (let i = 0; i < filters.length; i++) {
+    if (matchFilter(filters[i], event)) return true
+  }
+  return false
+}