CREATE OR REPLACE FUNCTION migrate_exercise(target_exercise int, duplicated_exercise int)
    RETURNS VOID
    LANGUAGE plpgsql
AS
$$
DECLARE

BEGIN
    IF target_exercise = duplicated_exercise THEN
        RETURN;
    END IF;

    UPDATE submissions SET exercise_id = target_exercise WHERE exercise_id = duplicated_exercise;
    UPDATE request_for_comments SET exercise_id = target_exercise WHERE exercise_id = duplicated_exercise;

    WITH rename_candidates AS (
        SELECT target.name, target.id AS target_id, duplicated.id AS duplicated_id
        FROM files AS target
                 INNER JOIN files AS duplicated ON target.name = duplicated.name
        WHERE target.context_id = target_exercise
          AND target.context_type = 'Exercise'
          AND target.read_only = FALSE
          AND duplicated.context_id = duplicated_exercise
          AND duplicated.context_type = 'Exercise'
          AND duplicated.read_only = FALSE
    ),
         files_mapping AS (
             SELECT files.id, rename_candidates.target_id
             FROM files
                      INNER JOIN rename_candidates ON file_id = duplicated_id)
    UPDATE files
    SET file_id = files_mapping.target_id
    FROM files_mapping
    WHERE files.id = files_mapping.id;

    UPDATE events SET exercise_id = target_exercise where exercise_id = duplicated_exercise;
    UPDATE searches SET exercise_id = target_exercise where exercise_id = duplicated_exercise;
    UPDATE user_exercise_interventions SET exercise_id = target_exercise where exercise_id = duplicated_exercise;
    UPDATE user_proxy_exercise_exercises SET exercise_id = target_exercise where exercise_id = duplicated_exercise;

    DELETE FROM anomaly_notifications WHERE exercise_id = duplicated_exercise;
    DELETE FROM exercise_tags WHERE exercise_id = duplicated_exercise;
    DELETE FROM lti_parameters WHERE exercise_id = duplicated_exercise;
    DELETE FROM remote_evaluation_mappings WHERE exercise_id = duplicated_exercise;

    -- Preventing duplicated entries in exercise_collection_items
    -- An exercise should not be present twice in an exercise collection.
    DELETE
    FROM exercise_collection_items
    WHERE id IN (SELECT duplicated.id
                 FROM exercise_collection_items AS target,
                      exercise_collection_items AS duplicated
                 WHERE target.exercise_id = target_exercise
                   AND duplicated.exercise_id = duplicated_exercise
                   AND target.exercise_collection_id = duplicated.exercise_collection_id);
    UPDATE exercise_collection_items SET exercise_id = target_exercise where exercise_id = duplicated_exercise;

    -- Preventing duplicated entries in exercises_proxy_exercises
    -- The same proxy exercise should not have two entries for the same exercise it proxies.
    DELETE
    FROM exercises_proxy_exercises
    WHERE exercise_id = duplicated_exercise
      AND proxy_exercise_id IN (SELECT duplicated.proxy_exercise_id
                                FROM exercises_proxy_exercises AS target,
                                     exercises_proxy_exercises AS duplicated
                                WHERE target.exercise_id = target_exercise
                                  AND duplicated.exercise_id = duplicated_exercise
                                  AND target.proxy_exercise_id = duplicated.proxy_exercise_id);
    UPDATE exercises_proxy_exercises SET exercise_id = target_exercise where exercise_id = duplicated_exercise;

    -- Preventing duplicated entries in user_exercise_feedbacks
    -- An exercise should not have two feedbacks from the same user.
    DELETE
    FROM user_exercise_feedbacks
    WHERE id IN (SELECT target.id
                 FROM user_exercise_feedbacks AS target,
                      user_exercise_feedbacks AS duplicated
                 WHERE target.exercise_id = target_exercise
                   AND duplicated.exercise_id = duplicated_exercise
                   AND target.user_id = duplicated.user_id
                   AND target.user_type = duplicated.user_type);
    UPDATE user_exercise_feedbacks SET exercise_id = target_exercise where exercise_id = duplicated_exercise;

    DELETE FROM files WHERE context_id = duplicated_exercise and context_type = 'Exercise';
    DELETE FROM exercises WHERE id = duplicated_exercise;

END;
$$;

/* Execute migration
do $$
begin
	perform migrate_exercise(target_exercise := 237, duplicated_exercise := 695);
end
$$;
*/