# Playfair cipher

```ruby
func playfair(key, from = 'J', to = (from == 'J' ? 'I' : '')) {

    func canon(str) {
        str.gsub(/[^[:alpha:]]/, '').uc.gsub(from, to)
    }

    var m = canon(key + ('A'..'Z' -> join)).chars.uniq.slices(5)

    var :ENC = gather {
        m.each { |r|
            for i,j in (^r ~X ^r) {
                i == j && next
                take(Pair("#{r[i]}#{r[j]}", "#{r[(i+1)%5]}#{r[(j+1)%5]}"))
            }
        }

        ^5 -> each { |k|
            var c = m.map {|a| a[k] }
            for i,j in (^c ~X ^c) {
                i == j && next
                take(Pair("#{c[i]}#{c[j]}", "#{c[(i+1)%5]}#{c[(j+1)%5]}"))
            }
        }

        cartesian([^5, ^5, ^5, ^5], {|i1,j1,i2,j2|
            i1 == i2 && next
            j1 == j2 && next
            take(Pair("#{m[i1][j1]}#{m[i2][j2]}", "#{m[i1][j2]}#{m[i2][j1]}"))
        })
    }.map { (.key, .value) }...

    var DEC = ENC.flip

    func enc(red) {
        gather {
            var str = canon(red)
            while (var m = (str =~ /(.)(?(?=\1)|(.?))/g)) {
                take("#{m[0]}#{m[1] == '' ? 'X' : m[1]}")
            }
        }.map { ENC{_} }.join(' ')
    }

    func dec(black) {
        canon(black).split(2).map { DEC{_} }.join(' ')
    }

    return(enc, dec)
}

var (encode, decode) = playfair('Playfair example')

var orig = "Hide the gold in...the TREESTUMP!!!"
say " orig:\t#{orig}"

var black = encode(orig)
say "black:\t#{black}"

var red = decode(black)
say "  red:\t#{red}"
```

## Output:

```
 orig:  Hide the gold in...the TREESTUMP!!!
black:  BM OD ZB XD NA BE KU DM UI XM MO UV IF
  red:  HI DE TH EG OL DI NT HE TR EX ES TU MP
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://trizen.gitbook.io/sidef-lang/programming_tasks/p/playfair_cipher.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.