// Copyright 2023 RisingWave Labs
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use risingwave_expr::function;

#[function("lower(varchar) -> varchar")]
pub fn lower(s: &str, writer: &mut impl std::fmt::Write) {
    for c in s.chars() {
        writer.write_char(c.to_ascii_lowercase()).unwrap();
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_lower() {
        let cases = [
            ("HELLO WORLD", "hello world"),
            ("hello RUST", "hello rust"),
            ("3 PINEAPPLES", "3 pineapples"),
        ];

        for (s, expected) in cases {
            let mut writer = String::new();
            lower(s, &mut writer);
            assert_eq!(writer, expected);
        }
    }
}
