paginate

--Splits a string according to a pattern into a table
local function split(str, pattern)
  local t = { }
  local fpat = "(.-)" .. pattern
  local last_end = 1
  local s, e, cap = str:find(fpat, 1)
  while s do
    if s ~= 1 or cap ~= "" then
      table.insert(t,cap)
    end
    last_end = e+1
    s, e, cap = str:find(fpat, last_end)
  end
  if last_end <= #str then
    cap = str:sub(last_end)
    table.insert(t, cap)
  end
  return t
end

--[[ Main code ]]--

textStore = { }
--The number of characters on the present line, and the number of lines on the present page
local charCount, lineCount = 0, 0
--The maximum char and line count
local charMax, lineMax = 25, 21
--The command line arguments
local tArgs = {...}
--The wrapped peripheral
local printer = nil

--We locate the printer first
for k,v in pairs(rs.getSides()) do
    if peripheral.getType(v) == "printer" then
        printer = peripheral.wrap(v)
    end
end
if not printer then
    print("No printer attached!")
    return
end

--Catching missing arguments
if #tArgs == 0 then
    print("Usage: printpage <filename>")
    return
end

local filePath = shell.resolve(".").."/"..tArgs[1]

--Files use relative pathing, catching missing files
if not fs.exists(filePath) then
    print("File not found")
    return
end
--Catches trying to print entire directories
if fs.isDir(filePath) then
    print("Cannot print directory")
    return
end

--We rip the file open and cut it up here
local file = fs.open(filePath, "r")
textStore = split(file.readAll(), "\n")
file.close()

--Finishes the page, fires the new page down and keeps going
function finishPage()
    printer.endPage()
    lineCount = 0
    wordCount = 0

    rs.setOutput("bottom", true)
    sleep(0.1)
    rs.setOutput("bottom", false)

    printer.newPage()
    charMax, lineMax = printer.getPageSize()
end

--This will print the word with a basic write command but updates
--the char and line fields, and starts a new page if it needs to
function safePrint(word)
    printer.write(word)
    charCount = charCount + #word
    if charCount >= charMax then
        nextLine()
    end
end

--Moves to the next line, or the next page if need be
function nextLine()
    charCount = 0
    lineCount = lineCount + 1
    if lineCount >= lineMax then
        finishPage()
    else
        local _,oy = printer.getCursorPos()
        printer.setCursorPos(1,oy + 1)
    end
end

--The pagination script.
printer.newPage()
charMax, lineMax = printer.getPageSize()
for i=1,#textStore do
    local word = textStore[i]
    --We replace tab characters with spaces, for convenience
    string.gsub(word, "\t", " ")
    --We split by space for each subword
    local subwords = split(word, " ")
    for j=1,#subwords do
        local subword = subwords[j]

        --If the word goes over the line, we just print as much of it as we can
        --until it's short enough to fit on one line
        while #subword > charMax do
            safePrint(subword)
            subword = string.sub(subword, charMax - charCount)
        end

        --If the word is blocked by other stuff on the line, we just go to the next line
        if #subword + charCount > charMax then
            nextLine()
        end

        --We then print our word (or what's left of it)
        safePrint(subword)

        --Finally, if there's room a space character is added
        if charCount < charMax then
            safePrint(" ")
        end
        os.pullEvent("key")
    end
    nextLine()
end