local Cgi = {}

-- Return a urlencoded copy of Str. For example,
--   "Here & there + 97% of other places"
-- is encoded as
--   "Here%20%26%20there%20%2B%2097%25%20of%20other%20places"

function Cgi.Encode(Str)
  return string.gsub(Str, '%W', function(Str)
    return string.format('%%%02X', string.byte(Str)) end )
end

-- Returns a urldecoded copy of Str. This function reverses the effects of
-- Cgi.Encode.

function Cgi.Decode(Str)
  Str = string.gsub(Str, '%+', ' ')
  Str = string.gsub(Str, '%%(%x%x)', function(Str)
    return string.char(tonumber(Str, 16)) end )
  return Str
end

-- Returns an escaped copy of Str in which the characters &<>" are escaped for
-- display in HTML documents.

function Cgi.Escape(Str)
  Str = string.gsub(Str or "", "%&", "&amp;")
  Str = string.gsub(Str, '%"', "&quot;")
  Str = string.gsub(Str, "%<", "&lt;")
  return string.gsub(Str, "%>", "&gt;")
end

-- This function returns an associative array with the parsed contents of the
-- urlencoded string Str. Multiple values with the same name are placed into an
-- indexed table with the name.

local function LclParse(Str)
  local Decode, Tbl = Cgi.Decode, {}
  for KeyStr, ValStr in string.gmatch(Str .. '&', '(.-)%=(.-)%&') do
    local Key = Decode(KeyStr)
    local Val = Decode(ValStr)
    local Sub = Tbl[Key]
    local SubCat = type(Sub)
    -- If there are multiple values with the same name, place them in an
    -- indexed table.
    if SubCat == "string" then -- replace string with table
      Tbl[Key] = { Sub, Val }
    elseif SubCat == "table" then -- insert into existing table
      table.insert(Sub, Val)
    else -- add as string field
      Tbl[Key] = Val
    end
  end
  return Tbl
end

-- Returns an associative array with both the GET and POST contents which
-- accompany an HTTP request. Multi-part form data, usually used with uploaded
-- files, is not currently supported.

function Cgi.Params()
  local PostLen, GetStr, PostStr, KeyList, Obj
  KeyList = {
    'PATH_INFO',
    'PATH_TRANSLATED',
    'REMOTE_HOST',
    'REMOTE_ADDR',
    'GATEWAY_INTERFACE',
    'SCRIPT_NAME',
    'REQUEST_METHOD',
    'HTTP_ACCEPT',
    'HTTP_ACCEPT_CHARSET',
    'HTTP_ACCEPT_ENCODING',
    'HTTP_ACCEPT_LANGUAGE',
    'HTTP_FROM',
    'HTTP_HOST',
    'HTTP_REFERER',
    'HTTP_USER_AGENT',
    'QUERY_STRING',
    'SERVER_SOFTWARE',
    'SERVER_NAME',
    'SERVER_PROTOCOL',
    'SERVER_PORT',
    'CONTENT_TYPE',
    'CONTENT_LENGTH',
    'AUTH_TYPE' }

  Obj = {}
  for J, KeyStr in ipairs(KeyList) do
    Obj[KeyStr] = os.getenv(KeyStr)
  end
  if not Obj.SERVER_SOFTWARE then -- Command line invocation
    Obj.QUERY_STRING = arg[1]
    PostStr = arg[2]
  elseif "application/x-www-form-urlencoded" == Obj.CONTENT_TYPE then
    -- Web server invocation with posted urlencoded content
    PostLen = tonumber(Obj.CONTENT_LENGTH)
    if PostLen and PostLen > 0 then
      PostStr = io.read(PostLen)
    end
  end
  PostStr = PostStr or ""
  Obj.Post = LclParse(PostStr)
  Obj.POST_STRING = PostStr
  GetStr = Obj.QUERY_STRING or ""
  Obj.Get = LclParse(GetStr)
  return Obj
end

return Cgi