def _inject_ctes_into_sql(sql, ctes):
    """
    `ctes` is a dict of CTEs in the form:

      {
        "cte_id_1": "__dbt__CTE__ephemeral as (select * from table)",
        "cte_id_2": "__dbt__CTE__events as (select id, type from events)"
      }

    Given `sql` like:

      "with internal_cte as (select * from sessions)
       select * from internal_cte"

    This will spit out:

      "with __dbt__CTE__ephemeral as (select * from table),
            __dbt__CTE__events as (select id, type from events),
            with internal_cte as (select * from sessions)
       select * from internal_cte"

    (Whitespace enhanced for readability.)
    """
    if len(ctes) == 0:
        return sql

    parsed_stmts = sqlparse.parse(sql)
    parsed = parsed_stmts[0]

    with_stmt = None
    for token in parsed.tokens:
        if token.is_keyword and token.normalized == 'WITH':
            with_stmt = token
            break

    if with_stmt is None:
        # no with stmt, add one, and inject CTEs right at the beginning
        first_token = parsed.token_first()
        with_stmt = sqlparse.sql.Token(sqlparse.tokens.Keyword, 'with')
        parsed.insert_before(first_token, with_stmt)
    else:
        # stmt exists, add a comma (which will come after injected CTEs)
        trailing_comma = sqlparse.sql.Token(sqlparse.tokens.Punctuation, ',')
        parsed.insert_after(with_stmt, trailing_comma)

    token = sqlparse.sql.Token(
        sqlparse.tokens.Keyword,
        ", ".join(c['sql'] for c in ctes)
    )
    parsed.insert_after(with_stmt, token)

    return dbt.compat.to_string(parsed)
`ctes` is a dict of CTEs in the form:

      {
        "cte_id_1": "__dbt__CTE__ephemeral as (select * from table)",
        "cte_id_2": "__dbt__CTE__events as (select id, type from events)"
      }

    Given `sql` like:

      "with internal_cte as (select * from sessions)
       select * from internal_cte"

    This will spit out:

      "with __dbt__CTE__ephemeral as (select * from table),
            __dbt__CTE__events as (select id, type from events),
            with internal_cte as (select * from sessions)
       select * from internal_cte"

    (Whitespace enhanced for readability.)