Add helpful functions for interacting with db manually (modrinth#3602)

Brought over from modrinth/labrinth#862

Author: triphora

apps/labrinth/migrations/20240115052708_base62-helper-functions.sql

@@ -0,0 +1,40 @@
+CREATE OR REPLACE FUNCTION from_base62(input VARCHAR)
+RETURNS BIGINT AS $$
+DECLARE
+    base INT := 62;
+    chars VARCHAR := '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
+    result BIGINT := 0;
+    i INT;
+    char VARCHAR;
+    index INT;
+BEGIN
+    FOR i IN 1..LENGTH(input) LOOP
+        char := SUBSTRING(input FROM i FOR 1);
+        index := POSITION(char IN chars) - 1;
+        IF index < 0 THEN
+            RAISE EXCEPTION 'Error: Invalid character in input string';
+        END IF;
+        result := result * base + index;
+    END LOOP;
+
+    RETURN result;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION to_base62(input BIGINT)
+RETURNS VARCHAR AS $$
+DECLARE
+    base INT := 62;
+    chars VARCHAR := '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
+    result VARCHAR := '';
+    remainder INT;
+BEGIN
+    WHILE input > 0 LOOP
+        remainder := input % base;
+        result := SUBSTRING(chars FROM remainder + 1 FOR 1) || result;
+        input := input / base;
+    END LOOP;
+
+    RETURN result;
+END;
+$$ LANGUAGE plpgsql;