local input  = arg[1]
local output = arg[2]

local f = assert(io.open(input, "r"))
local s = f:read("*a")
f:close()

local delim = ","
local out, row = {}, {}
local i, n = 1, #s

local function csv_escape(cell)
  local needs_quotes =
    cell:find(delim, 1, true) or cell:find('"', 1, true) or
    cell:find("\\ ", 1, true) or cell:find("[\r\n]", 1, true)
  if needs_quotes then
    cell = cell:gsub('"','""')
    return '"' .. cell .. '"'
  end
  return cell
end

local function push_cell(cell) row[#row+1] = cell end
local function end_row() out[#out+1] = row; row = {} end

while i <= n do
  local c = s:sub(i,i)

  if c == '"' then
    i = i + 1
    local buf = {}
    while i <= n do
      c = s:sub(i,i)
      if c == '"' then
        local nextc = s:sub(i+1,i+1)
        if nextc == '"' then
          buf[#buf+1] = '"'
          i = i + 2
        else
          i = i + 1
          break
        end
      else
        buf[#buf+1] = c
        i = i + 1
      end
    end
    local cell = table.concat(buf)
    cell = cell:gsub("\r\n","\\\\{}")
    cell = cell:gsub("\n","\\\\{}")
    cell = cell:gsub("\r","\\\\{}")
    push_cell(cell)

    local c2 = s:sub(i,i)
    if c2 == delim then i = i + 1
    elseif c2 == "\n" then i = i + 1; end_row()
    elseif c2 == "\r" then
      if s:sub(i+1,i+1) == "\n" then i = i + 2 else i = i + 1 end
      end_row()
    end
  else
    local buf = {}
    while i <= n do
      c = s:sub(i,i)
      if c == delim or c == "\n" or c == "\r" then break end
      buf[#buf+1] = c
      i = i + 1
    end
    local cell = table.concat(buf)
    cell = cell:gsub("\r\n","\\\\{}")
    cell = cell:gsub("\n","\\\\{}")
    cell = cell:gsub("\r","\\\\{}")
    push_cell(cell)

    if i <= n and s:sub(i,i) == delim then i = i + 1
    elseif i <= n and s:sub(i,i) == "\n" then i = i + 1; end_row()
    elseif i <= n and s:sub(i,i) == "\r" then
      if s:sub(i+1,i+1) == "\n" then i = i + 2 else i = i + 1 end
      end_row()
    end
  end
end

if #row > 0 then end_row() end

local fo = assert(io.open(output, "w"))
for r = 1, #out do
  local cells = out[r]
  for k = 1, #cells do
    if k > 1 then fo:write(delim) end
    fo:write(csv_escape(cells[k] or ""))
  end
  if r < #out then fo:write("\n") end
end
fo:close()