Hackathon: Post Reminders (#20555)

This PR adds the post reminder backend work.

We add a new API endpoint via which a user can set a reminder for a post. An ephemeral message will be sent down the line to let the user know about the action. And then after the time is over, the system admin bot will send a DM message to the user about the reminder post.

db/migrations/migrations.list

@@ -180,6 +180,8 @@ db/migrations/mysql/000089_add-channelid-to-reaction.down.sql
 db/migrations/mysql/000089_add-channelid-to-reaction.up.sql
 db/migrations/mysql/000090_create_enums.down.sql
 db/migrations/mysql/000090_create_enums.up.sql
+db/migrations/mysql/000091_create_post_reminder.down.sql
+db/migrations/mysql/000091_create_post_reminder.up.sql
 db/migrations/postgres/000001_create_teams.down.sql
 db/migrations/postgres/000001_create_teams.up.sql
 db/migrations/postgres/000002_create_team_members.down.sql
@@ -360,3 +362,5 @@ db/migrations/postgres/000089_add-channelid-to-reaction.down.sql
 db/migrations/postgres/000089_add-channelid-to-reaction.up.sql
 db/migrations/postgres/000090_create_enums.down.sql
 db/migrations/postgres/000090_create_enums.up.sql
+db/migrations/postgres/000091_create_post_reminder.down.sql
+db/migrations/postgres/000091_create_post_reminder.up.sql

db/migrations/mysql/000091_create_post_reminder.down.sql

@@ -0,0 +1,16 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'PostReminders'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_postreminders_targettime'
+    ) > 0,
+    'DROP INDEX idx_postreminders_targettime ON PostReminders;',
+    'SELECT 1'
+));
+
+PREPARE removeIndexIfExists FROM @preparedStatement;
+EXECUTE removeIndexIfExists;
+DEALLOCATE PREPARE removeIndexIfExists;
+
+DROP TABLE IF EXISTS PostReminders;

db/migrations/mysql/000091_create_post_reminder.up.sql

@@ -0,0 +1,21 @@
+CREATE TABLE IF NOT EXISTS PostReminders (
+    PostId varchar(26) NOT NULL,
+    UserId varchar(26) NOT NULL,
+    TargetTime bigint,
+    PRIMARY KEY (PostId, UserId)
+);
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'PostReminders'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_postreminders_targettime'
+    ) > 0,
+    'SELECT 1',
+    'CREATE INDEX idx_postreminders_targettime ON PostReminders(TargetTime);'
+));
+
+PREPARE createIndexIfNotExists FROM @preparedStatement;
+EXECUTE createIndexIfNotExists;
+DEALLOCATE PREPARE createIndexIfNotExists;

db/migrations/postgres/000091_create_post_reminder.down.sql

@@ -0,0 +1,3 @@
+DROP INDEX IF EXISTS idx_postreminders_targettime;
+
+DROP TABLE IF EXISTS postreminders;

db/migrations/postgres/000091_create_post_reminder.up.sql

@@ -0,0 +1,8 @@
+CREATE TABLE IF NOT EXISTS postreminders (
+    postid varchar(26) NOT NULL,
+    userid varchar(26) NOT NULL,
+    targettime bigint,
+    PRIMARY KEY (postid, userid)
+);
+
+CREATE INDEX IF NOT EXISTS idx_postreminders_targettime ON postreminders(targettime);