to playfair :keyword :message
local [matrix a b c d e f g h i j k l m n o p q r s t u v w x y z]
setkeyword jtoi lowercase :keyword
output encode (reduce "word :message)
end

;; Prepare the code array

to setkeyword :word
make "matrix reorder word :word (remove :word "abcdefghiklmnopqrstuvwxyz)
make "j :i
end

to remove :letters :string
if emptyp :string [output "]
if memberp first :string :letters [output remove :letters bf :string]
output word first :string remove :letters bf :string
end

to reorder :string
output reorder1 :string (mdarray [5 5]) 1 1
end

to reorder1 :string :array :row :column
if :row=6 [output :array]
if :column=6 [output reorder1 :string :array :row+1 1]
mdsetitem (list :row :column) :array first :string
make first :string (list :row :column)
output reorder1 (butfirst :string) :array :row :column+1
end

;; Encode the message

to encode :message
if emptyp :message [output "]
if emptyp butfirst :message [output paircode first :message "q]
if equalp (jtoi first :message) (jtoi first butfirst :message) ~
   [output word (paircode first :message "q) (encode butfirst :message)]
output word (paircode first :message first butfirst :message) ~
            (encode butfirst butfirst :message)
end

to paircode :one :two
local [row1 column1 row2 column2]
make "row1 first thing :one
make "column1 last thing :one
make "row2 first thing :two
make "column2 last thing :two
if :row1 = :row2 ~
   [output letters (list :row1 rotate (:column1+1)) ~
                   (list :row1 rotate (:column2+1))]
if :column1 = :column2 ~
   [output letters (list rotate (:row1+1) :column1)  ~
                   (list rotate (:row2+1) :column1)]
output letters (list :row1 :column2) (list :row2 :column1)
end

to rotate :index
output ifelse :index = 6 [1] [:index]
end

to letters :one :two
output word letter :one letter :two
end

to letter :rowcol
output itoj mditem :rowcol :matrix
end

;; I and J conversion

to jtoi :word
output map [ifelse equalp ? "j ["i] [?]] :word
end

to itoj :letter
if :letter = "i [if (random 3) = 0 [output "j]]
output :letter
end