From 9c009ac543defc9784c3da2a06cf7d146e0c7b81 Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Sat, 20 Jul 2024 13:55:09 -0500
Subject: [PATCH] getFilterLimit: handle parameterized replaceable events

---
 filter.test.ts | 10 ++++++++++
 filter.ts      | 17 +++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/filter.test.ts b/filter.test.ts
index d9d40e2..eb07079 100644
--- a/filter.test.ts
+++ b/filter.test.ts
@@ -215,6 +215,16 @@ describe('Filter', () => {
       expect(getFilterLimit({ kinds: [0, 3], authors: ['alex', 'fiatjaf'] })).toEqual(4)
     })
 
+    test('should handle parameterized replaceable events', () => {
+      expect(getFilterLimit({ kinds: [30078], authors: ['alex'] })).toEqual(Infinity)
+      expect(getFilterLimit({ kinds: [30078], authors: ['alex'], '#d': ['ditto'] })).toEqual(1)
+      expect(getFilterLimit({ kinds: [30078], authors: ['alex'], '#d': ['ditto', 'soapbox'] })).toEqual(2)
+      expect(getFilterLimit({ kinds: [30078], authors: ['alex', 'fiatjaf'], '#d': ['ditto', 'soapbox'] })).toEqual(4)
+      expect(
+        getFilterLimit({ kinds: [30000, 30078], authors: ['alex', 'fiatjaf'], '#d': ['ditto', 'soapbox'] }),
+      ).toEqual(8)
+    })
+
     test('should return Infinity for authors with regular kinds', () => {
       expect(getFilterLimit({ kinds: [1], authors: ['alex'] })).toEqual(Infinity)
     })
diff --git a/filter.ts b/filter.ts
index 5eab56d..00f00d9 100644
--- a/filter.ts
+++ b/filter.ts
@@ -1,5 +1,5 @@
 import { Event } from './core.ts'
-import { isReplaceableKind } from './kinds.ts'
+import { isParameterizedReplaceableKind, isReplaceableKind } from './kinds.ts'
 
 export type Filter = {
   ids?: string[]
@@ -72,7 +72,10 @@ export function mergeFilters(...filters: Filter[]): Filter {
   return result
 }
 
-/** Calculate the intrinsic limit of a filter. This function may return `Infinity`. */
+/**
+ * Calculate the intrinsic limit of a filter.
+ * This function returns a positive integer, or `Infinity` if there is no intrinsic limit.
+ */
 export function getFilterLimit(filter: Filter): number {
   if (filter.ids && !filter.ids.length) return 0
   if (filter.kinds && !filter.kinds.length) return 0
@@ -83,10 +86,20 @@ export function getFilterLimit(filter: Filter): number {
   }
 
   return Math.min(
+    // The `limit` property creates an artificial limit.
     Math.max(0, filter.limit ?? Infinity),
+
+    // There can only be one event per `id`.
     filter.ids?.length ?? Infinity,
+
+    // Replaceable events are limited by the number of authors and kinds.
     filter.authors?.length && filter.kinds?.every(kind => isReplaceableKind(kind))
       ? filter.authors.length * filter.kinds.length
       : Infinity,
+
+    // Parameterized replaceable events are limited by the number of authors, kinds, and "d" tags.
+    filter.authors?.length && filter.kinds?.every(kind => isParameterizedReplaceableKind(kind)) && filter['#d']?.length
+      ? filter.authors.length * filter.kinds.length * filter['#d'].length
+      : Infinity,
   )
 }