utils: merging two (reverse) sorted lists of events.

Author: fiatjaf

utils.test.ts

@@ -6,6 +6,7 @@ import {
   insertEventIntoDescendingList,
   binarySearch,
   normalizeURL,
+  mergeReverseSortedLists,
 } from './utils.ts'
 
 import type { Event } from './core.ts'
@@ -270,6 +271,94 @@ test('binary search', () => {
   expect(binarySearch(['a', 'b', 'd', 'e'], b => ('[' < b ? -1 : '[' === b ? 0 : 1))).toEqual([0, false])
 })
 
+describe('mergeReverseSortedLists', () => {
+  test('merge empty lists', () => {
+    const list1: Event[] = []
+    const list2: Event[] = []
+    expect(mergeReverseSortedLists(list1, list2)).toHaveLength(0)
+  })
+
+  test('merge list with empty list', () => {
+    const list1 = [buildEvent({ id: 'a', created_at: 30 }), buildEvent({ id: 'b', created_at: 20 })]
+    const list2: Event[] = []
+    const result = mergeReverseSortedLists(list1, list2)
+    expect(result).toHaveLength(2)
+    expect(result.map(e => e.id)).toEqual(['a', 'b'])
+  })
+
+  test('merge two simple lists', () => {
+    const list1 = [
+      buildEvent({ id: 'a', created_at: 30 }),
+      buildEvent({ id: 'b', created_at: 10 }),
+      buildEvent({ id: 'f', created_at: 3 }),
+      buildEvent({ id: 'g', created_at: 2 }),
+    ]
+    const list2 = [
+      buildEvent({ id: 'c', created_at: 25 }),
+      buildEvent({ id: 'd', created_at: 5 }),
+      buildEvent({ id: 'e', created_at: 1 }),
+    ]
+    const result = mergeReverseSortedLists(list1, list2)
+    expect(result.map(e => e.id)).toEqual(['a', 'c', 'b', 'd', 'f', 'g', 'e'])
+  })
+
+  test('merge lists with same timestamps', () => {
+    const list1 = [
+      buildEvent({ id: 'a', created_at: 30 }),
+      buildEvent({ id: 'b', created_at: 20 }),
+      buildEvent({ id: 'f', created_at: 10 }),
+    ]
+    const list2 = [
+      buildEvent({ id: 'c', created_at: 30 }),
+      buildEvent({ id: 'd', created_at: 20 }),
+      buildEvent({ id: 'e', created_at: 20 }),
+    ]
+    const result = mergeReverseSortedLists(list1, list2)
+    expect(result.map(e => e.id)).toEqual(['c', 'a', 'd', 'e', 'b', 'f'])
+  })
+
+  test('deduplicate events with same timestamp and id', () => {
+    const list1 = [
+      buildEvent({ id: 'a', created_at: 30 }),
+      buildEvent({ id: 'b', created_at: 20 }),
+      buildEvent({ id: 'b', created_at: 20 }),
+      buildEvent({ id: 'c', created_at: 20 }),
+      buildEvent({ id: 'd', created_at: 10 }),
+    ]
+    const list2 = [
+      buildEvent({ id: 'a', created_at: 30 }),
+      buildEvent({ id: 'c', created_at: 20 }),
+      buildEvent({ id: 'b', created_at: 20 }),
+      buildEvent({ id: 'd', created_at: 10 }),
+      buildEvent({ id: 'e', created_at: 10 }),
+      buildEvent({ id: 'd', created_at: 10 }),
+    ]
+    console.log('==================')
+    const result = mergeReverseSortedLists(list1, list2)
+    console.log(
+      'result:',
+      result.map(e => e.id),
+    )
+    expect(result.map(e => e.id)).toEqual(['a', 'c', 'b', 'd', 'e'])
+  })
+
+  test('merge when one list is completely before the other', () => {
+    const list1 = [buildEvent({ id: 'a', created_at: 50 }), buildEvent({ id: 'b', created_at: 40 })]
+    const list2 = [buildEvent({ id: 'c', created_at: 30 }), buildEvent({ id: 'd', created_at: 20 })]
+    const result = mergeReverseSortedLists(list1, list2)
+    expect(result).toHaveLength(4)
+    expect(result.map(e => e.id)).toEqual(['a', 'b', 'c', 'd'])
+  })
+
+  test('merge when one list is completely after the other', () => {
+    const list1 = [buildEvent({ id: 'a', created_at: 10 }), buildEvent({ id: 'b', created_at: 5 })]
+    const list2 = [buildEvent({ id: 'c', created_at: 30 }), buildEvent({ id: 'd', created_at: 20 })]
+    const result = mergeReverseSortedLists(list1, list2)
+    expect(result).toHaveLength(4)
+    expect(result.map(e => e.id)).toEqual(['c', 'd', 'a', 'b'])
+  })
+})
+
 describe('normalizeURL', () => {
   test('normalizes wss:// URLs', () => {
     expect(normalizeURL('wss://example.com')).toBe('wss://example.com/')

utils.ts

@@ -1,4 +1,4 @@
-import type { Event } from './core.ts'
+import type { NostrEvent } from './core.ts'
 
 export const utf8Decoder: TextDecoder = new TextDecoder('utf-8')
 export const utf8Encoder: TextEncoder = new TextEncoder()
@@ -22,7 +22,7 @@ export function normalizeURL(url: string): string {
   }
 }
 
-export function insertEventIntoDescendingList(sortedArray: Event[], event: Event): Event[] {
+export function insertEventIntoDescendingList(sortedArray: NostrEvent[], event: NostrEvent): NostrEvent[] {
   const [idx, found] = binarySearch(sortedArray, b => {
     if (event.id === b.id) return 0
     if (event.created_at === b.created_at) return -1
@@ -34,7 +34,7 @@ export function insertEventIntoDescendingList(sortedArray: Event[], event: Event
   return sortedArray
 }
 
-export function insertEventIntoAscendingList(sortedArray: Event[], event: Event): Event[] {
+export function insertEventIntoAscendingList(sortedArray: NostrEvent[], event: NostrEvent): NostrEvent[] {
   const [idx, found] = binarySearch(sortedArray, b => {
     if (event.id === b.id) return 0
     if (event.created_at === b.created_at) return -1
@@ -68,6 +68,62 @@ export function binarySearch<T>(arr: T[], compare: (b: T) => number): [number, b
   return [start, false]
 }
 
+export function mergeReverseSortedLists(list1: NostrEvent[], list2: NostrEvent[]): NostrEvent[] {
+  const result: NostrEvent[] = new Array(list1.length + list2.length)
+  result.length = 0
+  let i1 = 0
+  let i2 = 0
+  let sameTimestampIds: string[] = []
+
+  while (i1 < list1.length && i2 < list2.length) {
+    let next: NostrEvent
+    if (list1[i1]?.created_at > list2[i2]?.created_at) {
+      next = list1[i1]
+      i1++
+    } else {
+      next = list2[i2]
+      i2++
+    }
+
+    if (result.length > 0 && result[result.length - 1].created_at === next.created_at) {
+      if (sameTimestampIds.includes(next.id)) continue
+    } else {
+      sameTimestampIds.length = 0
+    }
+
+    result.push(next)
+    sameTimestampIds.push(next.id)
+  }
+
+  while (i1 < list1.length) {
+    const next = list1[i1]
+    i1++
+
+    if (result.length > 0 && result[result.length - 1].created_at === next.created_at) {
+      if (sameTimestampIds.includes(next.id)) continue
+    } else {
+      sameTimestampIds.length = 0
+    }
+    result.push(next)
+    sameTimestampIds.push(next.id)
+  }
+
+  while (i2 < list2.length) {
+    const next = list2[i2]
+    i2++
+
+    if (result.length > 0 && result[result.length - 1].created_at === next.created_at) {
+      if (sameTimestampIds.includes(next.id)) continue
+    } else {
+      sameTimestampIds.length = 0
+    }
+    result.push(next)
+    sameTimestampIds.push(next.id)
+  }
+
+  return result
+}
+
 export class QueueNode<V> {
   public value: V
   public next: QueueNode<V> | null = null