-- Prosody IM

-- 

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

local file = nil;

local last = nil;

local function read(expected)

	local ch;

	if last then

		ch = last; last = nil;

	else ch = file:read(1); end

	if expected and ch ~= expected then error("expected: "..expected.."; got: "..(ch or "nil")); end

	return ch;

end

local function pushback(ch)

	if last then error(); end

	last = ch;

end

local function peek()

	if not last then last = read(); end

	return last;

end

local _A, _a, _Z, _z, _0, _9, __, _at, _space = string.byte("AaZz09@_ ", 1, 9);

local function isLowerAlpha(ch)

	ch = string.byte(ch) or 0;

	return (ch >= _a and ch <= _z);

end

local function isNumeric(ch)

	ch = string.byte(ch) or 0;

	return (ch >= _0 and ch <= _9);

end

local function isAtom(ch)

	ch = string.byte(ch) or 0;

	return (ch >= _A and ch <= _Z) or (ch >= _a and ch <= _z) or (ch >= _0 and ch <= _9) or ch == __ or ch == _at;

end

local function isSpace(ch)

	ch = string.byte(ch) or "x";

	return ch <= _space;

end

local escapes = {["\\b"]="\b", ["\\d"]="\d", ["\\e"]="\e", ["\\f"]="\f", ["\\n"]="\n", ["\\r"]="\r", ["\\s"]="\s", ["\\t"]="\t", ["\\v"]="\v", ["\\\""]="\"", ["\\'"]="'", ["\\\\"]="\\"};

local function readString()

	read("\""); -- skip quote

	local slash = nil;

	local str = "";

	while true do

		local ch = read();

		if slash then

			slash = slash..ch;

			if not escapes[slash] then error("Unknown escape sequence: "..slash); end

			str = str..escapes[slash];

			slash = nil;

		elseif ch == "\"" then

			break;

		elseif ch == "\\" then

			slash = ch;

		else

			str = str..ch;

		end

	end

	return str;

end

local function readAtom1()

	local var = read();

	while isAtom(peek()) do

		var = var..read();

	end

	return var;

end

local function readAtom2()

	local str = read("'");

	local slash = nil;

	while true do

		local ch = read();

		str = str..ch;

		if ch == "'" and not slash then break; end

	end

	return str;

end

local function readNumber()

	local num = read();

	while isNumeric(peek()) do

		num = num..read();

	end

	return tonumber(num);

end

local readItem = nil;

local function readTuple()

	local t = {};

	local s = ""; -- string representation

	read(); -- read {, or [, or <

	while true do

		local item = readItem();

		if not item then break; end

		if type(item) ~= type(0) or item > 255 then

			s = nil;

		elseif s then

			s = s..string.char(item);

		end

		table.insert(t, item);

	end

	read(); -- read }, or ], or >

	if s and s ~= "" then

		return s

	else

		return t

	end;

end

local function readBinary()

	read("<"); -- read <

	local t = readTuple();

	read(">") -- read >

	local ch = peek();

	if type(t) == type("") then

		-- binary is a list of integers

		return t;

	elseif type(t) == type({}) then

		if t[1] then

			-- binary contains string

			return t[1];

		else

			-- binary is empty

			return "";

		end;

	else

		error();

	end

end

readItem = function()

	local ch = peek();

	if ch == nil then return nil end

	if ch == "{" or ch == "[" then

		return readTuple();

	elseif isLowerAlpha(ch) then

		return readAtom1();

	elseif ch == "'" then

		return readAtom2();

	elseif isNumeric(ch) then

		return readNumber();

	elseif ch == "\"" then

		return readString();

	elseif ch == "<" then

		return readBinary();

	elseif isSpace(ch) or ch == "," or ch == "|" then

		read();

		return readItem();

	else

		--print("Unknown char: "..ch);

		return nil;

	end

end

local function readChunk()

	local x = readItem();

	if x then read("."); end

	return x;

end

local function readFile(filename)

	file = io.open(filename);

	if not file then error("File not found: "..filename); os.exit(0); end

	return function()

		local x = readChunk();

		if not x and peek() then error("Invalid char: "..peek()); end

		return x;

	end;

end

module "erlparse"

function parseFile(file)

	return readFile(file);

end

return _M;