-- Prosody IM

-- Copyright (C) 2008-2010 Matthew Wild

-- Copyright (C) 2008-2010 Waqas Hussain

--

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

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

--

local string_byte, string_char = string.byte, string.char;

local t_concat, t_insert = table.concat, table.insert;

local type, tonumber, tostring = type, tonumber, tostring;

local file = nil;

local last = nil;

local line = 1;

local function read(expected)

	local ch;

	if last then

		ch = last; last = nil;

	else

		ch = file:read(1);

		if ch == "\n" then line = line + 1; end

	end

	if expected and ch ~= expected then error("expected: "..expected.."; got: "..(ch or "nil").." on line "..line); 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, _minus = string_byte("AaZz09@_ -", 1, 10);

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) or ch == _minus;

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"]="\127", ["\\e"]="\27", ["\\f"]="\f", ["\\n"]="\n", ["\\r"]="\r", ["\\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+1] = escapes[slash];

			slash = nil;

		elseif ch == "\"" then

			break;

		elseif ch == "\\" then

			slash = ch;

		else

			str[#str+1] = ch;

		end

	end

	return t_concat(str);

end

local function readAtom1()

	local var = { read() };

	while isAtom(peek()) do

		var[#var+1] = read();

	end

	return t_concat(var);

end

local function readAtom2()

	local str = { read("'") };

	local slash = nil;

	while true do

		local ch = read();

		str[#str+1] = ch;

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

	end

	return t_concat(str);

end

local function readNumber()

	local num = { read() };

	while isNumeric(peek()) do

		num[#num+1] = read();

	end

	if peek() == "." then

		num[#num+1] = read();

		while isNumeric(peek()) do

			num[#num+1] = read();

		end

	end

	return tonumber(t_concat(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) ~= "number" or item > 255 then

			s = nil;

		elseif s then

			s[#s+1] = string_char(item);

		end

		t_insert(t, item);

	end

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

	if s and #s > 0  then

		return t_concat(s)

	else

		return t

	end;

end

local function readBinary()

	read("<"); -- read <

	-- Discard PIDs

	if isNumeric(peek()) then

		while peek() ~= ">" do read(); end

		read(">");

		return {};

	end

	local t = readTuple();

	read(">") -- read >

	local ch = peek();

	if type(t) == "string" then

		-- binary is a list of integers

		return t;

	elseif type(t) == "table" 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

local _M = {};

function _M.parseFile(file)

	return readFile(file);

end

return _M;