// ============================================================================
// Palindrome check — punctuation- and case-insensitive
// ============================================================================
//
// Strips everything but letters/digits, lowercases, then compares the cleaned
// string against its reverse. Demonstrates per-character filtering with s[i]
// and a descending range to build the reverse.
//
// Run: soma run palindrome.cell --signal is_palindrome "A man, a plan, a canal: Panama"

cell Palindrome {
    face {
        signal is_palindrome(s: String) -> Bool
        signal reverse_str(s: String) -> String
    }

    // Keep only alphanumeric characters, lowercased.
    on _clean(s: String) {
        let low = lowercase(s)
        let out = ""
        for i in range(0, len(low)) {
            let c = low[i]
            if (c >= "a" && c <= "z") || (c >= "0" && c <= "9") {
                out = out + c
            }
        }
        return out
    }

    on reverse_str(s: String) {
        let out = ""
        for i in range(len(s) - 1, -1, -1) {
            out = out + s[i]
        }
        return out
    }

    on is_palindrome(s: String) {
        let c = _clean(s)
        return c == reverse_str(c)
    }
}

cell test PalindromeTest {
    rules {
        assert is_palindrome("racecar")
        assert is_palindrome("A man, a plan, a canal: Panama")
        assert is_palindrome("Was it a car or a cat I saw?")
        assert !is_palindrome("hello")
        assert reverse_str("abc") == "cba"
        assert is_palindrome("12321")
    }
}