Text Justification

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[!] VersionNotice: The below code pertains to an older Lua version, Lua 4. It does not run as is under Lua 5.

-- easy queue implementation ------------------------------------------



function q_create()

    local q = {}

    q.first = 0

    q.last = 0

    return q

end



function q_insert(q, s)

    q[q.last] = s

    q.last = q.last + 1

end



function q_empty(q)

    return q.first >= q.last

end



function q_remove(q)

    if q_empty(q) then

        return nil

    end

    local s = q[q.first]

    q[q.first] = nil

    q.first = q.first+1

    return s

end



function q_card(q)

    return q.last - q.first

end



function q_length(q, f)

    local l, i = 0, q.first

    while i < q.last do

        l = l + strlen(q[i])

        i = i + 1

    end

    return l

end



-- line creation routines ------------------------------------------



-- justifies one line to fit into MAX columns 

function justify(q)

    local blanks = MAX - q_length(q)

    local skips = q_card(q) - 1

    local line = q_remove(q)

    local quotient = floor(blanks/skips)

    local reminder = blanks/skips - quotient

    local error = 0

    while skips > 0 do

        error = error + reminder

        if error >= 0.5 then

            error = error - 1

            line = line .. strrep(" ", quotient+1)

        else

            line = line .. strrep(" ", quotient)

        end

        line = line .. q_remove(q)

        skips = skips - 1

    end

    return line or ""

end



-- join all words with one space between them

function catenate(q)

    local line = q_remove(q)

    while not q_empty(q) do

        line = line .. " " .. q_remove(q)

    end

    return line or ""

end



-- main program -----------------------------------------------------

DEFMAX = 72

-- tries to get MAX from command-line

if not arg or getn(arg) < 1 then

    MAX = DEFMAX

else

    MAX = tonumber(arg[1])

    if not MAX or MAX < 0 then

        MAX = DEFMAX

    end

end



-- collects all text from stdin

text = q_create()

line = read()

while line do

    _, n = gsub(line, "(%S+)", function (s) q_insert(%text, s) end)

    if n == 0 then

        q_insert(text, "\n")

    end

    line = read()

end



-- justify paragraphs

line = q_create()

word = q_remove(text)

size = 0

while word do

    if word == "\n" then

        if not q_empty(line) then

            write(catenate(line), "\n\n")

        else

            write("\n")

        end

        size = 0

    elseif size + strlen(word) > MAX then

        write(justify(line), "\n")

        size = 0

    end

    if word ~= "\n" then

        q_insert(line, word)

        size = size + strlen(word) + 1

    end

    word = q_remove(text)

end

write(catenate(line), "\n")