// ============================================================================
// Caesar cipher — shift letters using an alphabet lookup
// ============================================================================
//
// Builds the shifted output by finding each character's position in the
// lowercase alphabet with index_of, rotating by the shift, and indexing back
// in. Non-letters pass through unchanged. Decrypt = encrypt with (26 - shift).
//
// Run: soma run caesar.cell --signal encrypt "hello" 3

cell Caesar {
    face {
        signal encrypt(text: String, shift: Int) -> String
        signal decrypt(text: String, shift: Int) -> String
    }

    on encrypt(text: String, shift: Int) {
        let alpha = "abcdefghijklmnopqrstuvwxyz"
        let k = ((shift % 26) + 26) % 26
        let low = lowercase(text)
        let out = ""
        for i in range(0, len(low)) {
            let c = low[i]
            let pos = index_of(alpha, c)
            if pos >= 0 {
                out = out + alpha[(pos + k) % 26]
            } else {
                out = out + c
            }
        }
        return out
    }

    on decrypt(text: String, shift: Int) {
        return encrypt(text, 26 - (shift % 26))
    }
}

cell test CaesarTest {
    rules {
        assert encrypt("hello", 3) == "khoor"
        assert encrypt("xyz", 5) == "cde"
        assert decrypt("khoor", 3) == "hello"
        assert encrypt("abc 123", 1) == "bcd 123"
        assert encrypt("hello", 0) == "hello"
        assert decrypt(encrypt("attack at dawn", 13), 13) == "attack at dawn"
    }
}