//! 字符串单词计数工具。
//!
//! 重构自 SYNSPEC `count_words.f`

/// 统计字符串中由空格分隔的单词数量。
///
/// # 参数
///
/// * `cadena` - 输入字符串
///
/// # 返回值
///
/// 字符串中的单词数量
///
/// # 算法
///
/// 遍历字符串，当遇到非空格字符且前一个字符是空格时，计数加一。
/// 如果第一个字符不是空格，则计数从 1 开始。
///
/// # 示例
///
/// ```
/// use spectrarust::math::count_words::count_words;
/// assert_eq!(count_words("hello world"), 2);
/// assert_eq!(count_words("  hello   world  "), 2);
/// assert_eq!(count_words(""), 0);
/// assert_eq!(count_words("   "), 0);
/// ```
pub fn count_words(cadena: &str) -> i32 {
    let chars: Vec<char> = cadena.chars().collect();
    let len = chars.len();

    if len == 0 {
        return 0;
    }

    let mut n: i32 = 0;
    let mut a = chars[0];

    // 如果第一个字符不是空格，计数从 1 开始
    if a != ' ' {
        n = 1;
    }

    // 遍历剩余字符
    for i in 1..len {
        let b = chars[i];
        // 如果当前字符不是空格且前一个字符是空格，增加计数
        if b != ' ' && a == ' ' {
            n += 1;
        }
        a = b;
    }

    n
}

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

    #[test]
    fn test_empty_string() {
        assert_eq!(count_words(""), 0);
    }

    #[test]
    fn test_only_spaces() {
        assert_eq!(count_words("   "), 0);
    }

    #[test]
    fn test_single_word() {
        assert_eq!(count_words("hello"), 1);
        assert_eq!(count_words("  hello"), 1);
        assert_eq!(count_words("hello  "), 1);
        assert_eq!(count_words("  hello  "), 1);
    }

    #[test]
    fn test_multiple_words() {
        assert_eq!(count_words("hello world"), 2);
        assert_eq!(count_words("hello world foo"), 3);
        assert_eq!(count_words("  hello   world  foo  "), 3);
    }

    #[test]
    fn test_fortran_style() {
        // Fortran character*1000 测试
        let long_str = "word1 word2 word3";
        assert_eq!(count_words(long_str), 3);
    }
}