!! String manipulation functions module

import math

def string_length(s) {
    return len(s);
}

def string_reverse(s) {
    let result = ``;
    let i = len(s);
    while (i > 0) {
        i = i - 1;
        result = result + substring(s, i, i + 1);
    }
    return result;
}

def string_startsWith(s, prefix) {
    if (len(prefix) > len(s)) {
        return 0;
    }
    return substring(s, 0, len(prefix)) == prefix ? 1 : 0;
}

def string_endsWith(s, suffix) {
    if (len(suffix) > len(s)) {
        return 0;
    }
    let start = len(s) - len(suffix);
    return substring(s, start, len(s)) == suffix ? 1 : 0;
}

def string_contains(s, substr) {
    if (len(substr) == 0) {
        return 1;
    }
    if (len(substr) > len(s)) {
        return 0;
    }
    let i = 0;
    while (i <= len(s) - len(substr)) {
        if (substring(s, i, i + len(substr)) == substr) {
            return 1;
        }
        i = i + 1;
    }
    return 0;
}

def string_replace(s, old, new) {
    if (len(old) == 0) {
        return s;
    }
    let result = ``;
    let i = 0;
    while (i < len(s)) {
        if (substring(s, i, i + len(old)) == old) {
            result = result + new;
            i = i + len(old);
        } else {
            result = result + substring(s, i, i + 1);
            i = i + 1;
        }
    }
    return result;
}

def string_toUpperCase(s) {
    return upper(s);
}

def string_toLowerCase(s) {
    return lower(s);
}

def string_trim(s) {
    let start = 0;
    while (start < len(s) && (substring(s, start, start + 1) == ` ` || substring(s, start, start + 1) == `\t` || substring(s, start, start + 1) == `\n` || substring(s, start, start + 1) == `\r`)) {
        start = start + 1;
    }
    let end = len(s) - 1;
    while (end >= start && (substring(s, end, end + 1) == ` ` || substring(s, end, end + 1) == `\t` || substring(s, end, end + 1) == `\n` || substring(s, end, end + 1) == `\r`)) {
        end = end - 1;
    }
    if (start > end) {
        return ``;
    }
    return substring(s, start, end + 1);
}

def string_split(s, delimiter) {
    // This is a placeholder for future implementation
    // In a real implementation, we would return an array
    return `split not implemented yet`;
}