workaround for message is too big for the index (#50)

src/VahterBanBot/DB.fs

@@ -9,6 +9,7 @@ open Dapper
 open VahterBanBot.Utils
 
 let private connString = getEnv "DATABASE_URL"
+let private truncateTextLimit = getEnvOr "DATABASE_TRUNCATE_TEXT_LIMIT" "3000" |> int
 
 let upsertUser (user: DbUser): Task<DbUser> =
     task {
@@ -184,7 +185,7 @@ WITH less_than_n_messages AS (SELECT u.id, COUNT(DISTINCT m.text) < @criticalMsg
                        WHERE NOT EXISTS(SELECT 1 FROM false_positive_users fpu WHERE fpu.user_id = b.banned_user_id)
                          AND NOT EXISTS(SELECT 1
                                         FROM false_positive_messages fpm
-                                        WHERE fpm.text = b.message_text)
+                                        WHERE b.message_text LIKE fpm.text || '%')
                          AND b.message_text IS NOT NULL
                          AND b.banned_at >= @criticalDate),
      spam_or_ham AS (SELECT x.text,
@@ -246,6 +247,11 @@ WHERE banned_user_id = @userId
 let markMessageAsFalsePositive (message: DbMessage): Task =
     task {
         use conn = new NpgsqlConnection(connString)
+
+        // we need to truncate the text to work around the fact that
+        // text is being indexed and btree index has a limit of 2704 bytes
+        // https://dba.stackexchange.com/questions/25138/index-max-row-size-error/25139
+        let message = { message with text = message.text.Substring(0, Math.Min(truncateTextLimit, message.text.Length)) }
 
         //language=postgresql
         let sql =
@@ -336,7 +342,7 @@ WITH stats AS (SELECT m.message_id,
                                   ON m.message_id = bbb.message_id AND m.chat_id = bbb.banned_in_chat_id
                         LEFT JOIN public.false_negative_messages fnm
                                   ON m.message_id = fnm.message_id AND m.chat_id = fnm.chat_id
-                        LEFT JOIN false_positive_messages fpm ON m.text = fpm.text
+                        LEFT JOIN false_positive_messages fpm ON m.text LIKE fpm.text || '%'
                WHERE m.user_id = @userId
                ORDER BY m.created_at DESC
                LIMIT @n),