// ============================================================================
// Run-length encoding — compress repeated characters
// ============================================================================
//
// "aaabbc" -> "a3b2c1". Decoding walks the encoded string reading a letter
// followed by its digit-run count. Demonstrates per-char scanning, run
// counting, and reconstructing a string by repetition.
//
// Run: soma run run_length.cell --signal encode "aaabbbcccd"

cell RunLength {
    face {
        signal encode(s: String) -> String
        signal decode(s: String) -> String
    }

    on encode(s: String) {
        if len(s) == 0 { return "" }
        let out = ""
        let prev = s[0]
        let count = 1
        for i in range(1, len(s)) {
            let c = s[i]
            if c == prev {
                count = count + 1
            } else {
                out = out + prev + to_string(count)
                prev = c
                count = 1
            }
        }
        return out + prev + to_string(count)
    }

    on decode(s: String) {
        let out = ""
        let i = 0
        let n = len(s)
        while i < n {
            let ch = s[i]
            i = i + 1
            // read the digit run that follows
            let num = ""
            while i < n && s[i] >= "0" && s[i] <= "9" {
                num = num + s[i]
                i = i + 1
            }
            let reps = to_int(num)
            for j in range(0, reps) {
                out = out + ch
            }
        }
        return out
    }
}

cell test RunLengthTest {
    rules {
        assert encode("aaabbbcccd") == "a3b3c3d1"
        assert encode("") == ""
        assert encode("x") == "x1"
        assert decode("a3b3c3d1") == "aaabbbcccd"
        assert decode(encode("wwwwwwwwwwaa")) == "wwwwwwwwwwaa"
    }
}