From 15f06a1d50c3a092272143a24b310fa11d7f65af Mon Sep 17 00:00:00 2001
From: Johann150 <johann.galle@protonmail.com>
Date: Sun, 24 Jul 2022 12:07:29 +0200
Subject: [PATCH] enable to fetch replies recursively

---
 .../1658656633972-note-replies-function.js    | 52 +++++++++++++++++++
 .../server/api/endpoints/notes/children.ts    | 31 ++++++-----
 2 files changed, 70 insertions(+), 13 deletions(-)
 create mode 100644 packages/backend/migration/1658656633972-note-replies-function.js

diff --git a/packages/backend/migration/1658656633972-note-replies-function.js b/packages/backend/migration/1658656633972-note-replies-function.js
new file mode 100644
index 0000000000..de2e28c6f2
--- /dev/null
+++ b/packages/backend/migration/1658656633972-note-replies-function.js
@@ -0,0 +1,52 @@
+export class noteRepliesFunction1658656633972 {
+	name = 'noteRepliesFunction1658656633972'
+
+	async up(queryRunner) {
+		await queryRunner.query(`
+			CREATE OR REPLACE FUNCTION note_replies(start_id varchar, max_depth integer, max_breadth integer) RETURNS TABLE (id VARCHAR) AS
+			$$
+				SELECT DISTINCT id FROM (
+					WITH RECURSIVE tree (id, ancestors, depth) AS (
+						SELECT start_id, '{}'::VARCHAR[], 0
+					UNION
+						SELECT
+							note.id,
+							CASE
+								WHEN note."replyId" = tree.id THEN tree.ancestors || note."replyId"
+								ELSE tree.ancestors || note."renoteId"
+							END,
+							depth + 1
+						FROM note, tree
+						WHERE (
+							note."replyId" = tree.id
+							OR
+							(
+								-- get renotes but not pure renotes
+								note."renoteId" = tree.id
+								AND
+								(
+									note.text IS NOT NULL
+									OR
+									CARDINALITY(note."fileIds") != 0
+									OR
+									note."hasPoll" = TRUE
+								)
+							)
+						) AND depth < max_depth
+					)
+					SELECT
+						id,
+						-- apply the limit per node
+						row_number() OVER (PARTITION BY ancestors[array_upper(ancestors, 1)]) AS nth_child
+					FROM tree
+					WHERE depth > 0
+				) AS recursive WHERE nth_child < max_breadth
+			$$
+			LANGUAGE SQL
+		`);
+	}
+
+	async down(queryRunner) {
+		await queryRunner.query(`DROP FUNCTION note_replies`);
+	}
+}
diff --git a/packages/backend/src/server/api/endpoints/notes/children.ts b/packages/backend/src/server/api/endpoints/notes/children.ts
index 4412972c33..feaf94dcfa 100644
--- a/packages/backend/src/server/api/endpoints/notes/children.ts
+++ b/packages/backend/src/server/api/endpoints/notes/children.ts
@@ -12,6 +12,8 @@ export const meta = {
 	requireCredential: false,
 	requireCredentialPrivateMode: true,
 
+	description: 'Get a list of children of a notes. Children includes replies as well as quote renotes that quote the respective post. A post will not be duplicated if it is a reply and a quote of a note in this thread. For depths larger than 1 the threading has to be computed by the client.',
+
 	res: {
 		type: 'array',
 		optional: false, nullable: false,
@@ -27,7 +29,20 @@ export const paramDef = {
 	type: 'object',
 	properties: {
 		noteId: { type: 'string', format: 'misskey:id' },
-		limit: { type: 'integer', minimum: 1, maximum: 100, default: 10 },
+		limit: {
+			description: 'The maximum number of replies/quotes to show per parent note, i.e. the maximum number of children each note may have.',
+			type: 'integer',
+			minimum: 1,
+			maximum: 100,
+			default: 10,
+		},
+		depth: {
+			description: 'The number of layers of replies to fetch at once. Defaults to 1 for backward compatibility.',
+			type: 'integer',
+			minimum: 1,
+			maximum: 100,
+			default: 1,
+		},
 		sinceId: { type: 'string', format: 'misskey:id' },
 		untilId: { type: 'string', format: 'misskey:id' },
 	},
@@ -37,17 +52,7 @@ export const paramDef = {
 // eslint-disable-next-line import/no-default-export
 export default define(meta, paramDef, async (ps, user) => {
 	const query = makePaginationQuery(Notes.createQueryBuilder('note'), ps.sinceId, ps.untilId)
-		.andWhere(new Brackets(qb => { qb
-			.where('note.replyId = :noteId', { noteId: ps.noteId })
-			.orWhere(new Brackets(qb => { qb
-				.where('note.renoteId = :noteId', { noteId: ps.noteId })
-				.andWhere(new Brackets(qb => { qb
-					.where('note.text IS NOT NULL')
-					.orWhere('note.fileIds != \'{}\'')
-					.orWhere('note.hasPoll = TRUE');
-				}));
-			}));
-		}))
+		.andWhere('note.id IN (SELECT id FROM note_replies(:noteId, :depth, :limit))', { noteId: ps.noteId, depth: ps.depth, limit: ps.limit })
 		.innerJoinAndSelect('note.user', 'user')
 		.leftJoinAndSelect('user.avatar', 'avatar')
 		.leftJoinAndSelect('user.banner', 'banner')
@@ -58,7 +63,7 @@ export default define(meta, paramDef, async (ps, user) => {
 		generateBlockedUserQuery(query, user);
 	}
 
-	const notes = await query.take(ps.limit).getMany();
+	const notes = await query.getMany();
 
 	return await Notes.packMany(notes, user, { detail: false });
 });