;;  Page properties.

(define PAGE_WIDTH 75)

;;  Paragraph properties.

(define INDENT "  ")
(define PARAGRAPH_POST "\n")
(define PAGE_MARGIN "   ")
(define PARAGRAPH_WIDTH PAGE_WIDTH)
(define QUOTE_WIDTH 65)
(define MARGIN PAGE_MARGIN)

;;  Variables

(define partext "")
(define section_number 1)
(define subsection_number 1)
(define subsubsection_number 1)

(define repeat-string
  (lambda (str n)
    (if (< n 1)
      ""
      (string-append str (repeat-string str (- n 1)))
    )
  )
)

(define title
  (lambda (text)
    (if (string? text)
      (if (string=? text "")
        ""
        (begin
          (display MARGIN)
          (display (repeat-string " " (quotient (- PARAGRAPH_WIDTH (string-length text)) 2)))
          (display text)
          (newline)
        )
      )
      (display "\n\n*** Error: No string in title. ***\n\n")
    )
  )
)

(define author title)
(define centre title)

(define hr
  (lambda ()
    (begin
      (display MARGIN)
      (display (repeat-string "_" (- PARAGRAPH_WIDTH 1)))
      (newline)
    )
  )
)

(define remove-newlines
  (lambda (text)
    (if (string=? text "")
      ""
      (if (eqv? (string-ref text 0) #\newline)
         (remove-newlines (substring text 1 (string-length text)))
         (string-append (string (string-ref text 0))
                        (remove-newlines
                          (substring text 1 (string-length text))))
      )
    )
  )
)

;; Get the position of the linebreak

(define get-linebreak
  (lambda (text)
    (if (string=? text "")
      0
      (if (> (string-length text) PARAGRAPH_WIDTH)
        (if (eqv? (string-ref text (+ 1 PARAGRAPH_WIDTH)) #\space)
          PARAGRAPH_WIDTH
          (get-linebreak (substring text 0 PARAGRAPH_WIDTH))
        )
        (if (or 
              (eqv? (string-ref text (- (string-length text) 1)) #\space)
              (eqv? (string-ref text (- (string-length text) 1)) #\-))
          (string-length text)
          (get-linebreak (substring text 0 (- (string-length text) 1)))
        )
      )
    )
  )
)

(define count-spaces
  (lambda (text)
    (if (string=? text "")
      0
      (if (eqv? (string-ref text 0) #\space)
        (+ 1 (count-spaces (substring text 1 (string-length text))))
        (count-spaces (substring text 1 (string-length text)))
      )
    )
  )
)

(define insert-spaces
  (lambda (text n)
    (if (or (< n 1) (string=? text ""))
      text
      (let
        (
          (addsp (quotient n (count-spaces text)))
          (extrasp (remainder n (count-spaces text)))
        )
        (if (eqv? (string-ref text 0) #\space)
          (if (> extrasp 0)
            (string-append
              (repeat-string " " (+ 2 addsp))
              (insert-spaces (substring text 1 (string-length text)) (- n (+ 1 addsp)))
            )
            (string-append
              (repeat-string " " (+ 1 addsp))
              (insert-spaces (substring text 1 (string-length text)) (- n addsp))
            )
          )
          (string-append
            (string (string-ref text 0))
            (insert-spaces (substring text 1 (string-length text)) n)
          )
        )
      )
    )
  )
)

(define grow-line
  (lambda (text)
    (if (eqv? (string-length text) PARAGRAPH_WIDTH)
      text
      (insert-spaces text (- PARAGRAPH_WIDTH (string-length text)))
    )
  )
)

(define display-lines
  (lambda (text)
    (if (> (string-length text) PARAGRAPH_WIDTH)
      (let ((linebreak (get-linebreak text)))
        (if (eqv? linebreak 0)
          (begin
            (display MARGIN)
            (display (substring text 0 (- PARAGRAPH_WIDTH 2)))
            (display "-")
            (newline)
            (display-lines (substring text (- PARAGRAPH_WIDTH 2) (string-length text)))
          )
          (begin
            (display MARGIN)
            (display (grow-line (substring text 0 (get-linebreak text))))
            (newline)
            (if (eqv? 
                  (string-ref (substring text linebreak (string-length text)) 0) 
                  #\space
                )
              (display-lines (substring text (+ 1 linebreak) (string-length text)))
              (display-lines (substring text linebreak (string-length text)))
            )
          )
        )
      )
      (begin
        (display MARGIN)
        (display text)
        (newline)
      )
    )
  )
)

(define firstparagraph
  (lambda (text)
    (if (string? text)
      (begin
        (set! PARAGRAPH_WIDTH PAGE_WIDTH)
        (set! MARGIN PAGE_MARGIN)
        (display-lines (string-append
                         (remove-newlines text)
                         PARAGRAPH_POST))
      )
      (display "\n*** Error: text in paragraph is not a string. ***\n\n")
    )
  )
)

(define quote
  (lambda (text)
    (if (string? text)
      (begin
        (set! PARAGRAPH_WIDTH QUOTE_WIDTH)
        (set! MARGIN 
              (repeat-string " "
                 (quotient (- PAGE_WIDTH QUOTE_WIDTH) 2)
              )
        )
        (display-lines (string-append
                         (remove-newlines text)
                         PARAGRAPH_POST))
      )
      (display "\n*** Error: text in quote is not a string. ***\n\n")
    )
  )
)

(define paragraph
  (lambda (text)
    (if (string? text)
      (begin
        (set! MARGIN PAGE_MARGIN)
        (set! partext (remove-newlines text))
        (if (> (string-length partext) PARAGRAPH_WIDTH)
          (begin
            (display MARGIN)
            (display INDENT)
            (set! PARAGRAPH_WIDTH (- PAGE_WIDTH (string-length INDENT)))
            (display (grow-line
              (substring partext 0 (get-linebreak partext)))
            )
            (newline)
            (set! partext
              (substring partext (get-linebreak partext)
                                 (string-length partext))
            )
            (set! PARAGRAPH_WIDTH PAGE_WIDTH)
            (display-lines
              (string-append partext PARAGRAPH_POST)
            )
          )
          (display (string-append MARGIN
                     INDENT partext "\n" 
                     PARAGRAPH_POST))
        )
      )
      (display "\n*** Error: text in paragraph is not a string. ***\n\n")
    )
  )
)

(define pre display)

(define section
  (lambda (text)
    (if (string? text)
      (begin
        (display
          (string-append
            MARGIN
            (number->string section_number)
            ". "
            text
            "\n\n"
          )
        )
        (set! section_number (+ 1 section_number))
        (set! subsection_number 1)
        (set! subsubsection_number 1)
      )
      (display "\n\n*** Error: text in section is not a string. ***\n\n")
    )
  )
)

(define subsection
  (lambda (text)
    (if (string? text)
      (begin
        (display
          (string-append
            MARGIN
            (number->string section_number)
            "."
            (number->string subsection_number)
            ". "
            text
            "\n\n"
          )
        )
        (set! subsection_number (+ 1 subsection_number))
        (set! subsubsection_number 1)
      )
      (display "\n\n*** Error: text in section is not a string. ***\n\n")
    )
  )
)

(define subsubsection
  (lambda (text)
    (if (string? text)
      (begin
        (display
          (string-append
            MARGIN
            (number->string section_number)
            "."
            (number->string section_number)
            "."
            (number->string section_number)
            ". "
            text
            "\n\n"
          )
        )
        (set! subsubsection_number (+ 1 subsection_number))
      )
      (display "\n\n*** Error: text in section is not a string. ***\n\n")
    )
  )
)