--
-- json.lua
--
-- Copyright (c) 2020 rxi (v0.1.2) edit by DarhangeR (v0.1.4)
--
-- Permission is hereby granted, free of charge, to any person obtaining a copy of
-- this software and associated documentation files (the "Software"), to deal in
-- the Software without restriction, including without limitation the rights to
-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-- of the Software, and to permit persons to whom the Software is furnished to do
-- so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in all
-- copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-- SOFTWARE.
--

local pairs, string_format, error, rawget, next, string_char, type, ipairs, table_concat, tostring, select, tonumber = pairs, string.format, error, rawget, next, string.char, type, ipairs, table.concat, tostring, select, tonumber
local json = { _version = "0.1.4" };

-------------------------------------------------------------------------------
-- Encode
-------------------------------------------------------------------------------

local encode

local escape_char_map = {
  [ "\\" ] = "\\",
  [ "\"" ] = "\"",
  [ "\b" ] = "b",
  [ "\f" ] = "f",
  [ "\n" ] = "n",
  [ "\r" ] = "r",
  [ "\t" ] = "t",
};

local escape_char_map_inv = { [ "/" ] = "/" }
for k, v in pairs(escape_char_map) do
	escape_char_map_inv[v] = k;
end;

local function escape_char(c)
	return "\\" .. (escape_char_map[c] or string_format("u%04x", c:byte()));
end;

local function encode_nil(rope)
	rope[#rope + 1] = "null"
end;

local function encode_table(rope, val, stack)
	-- Circular reference?
	if stack[val] then error("circular reference") end
		stack[val] = true
	if rawget(val, 1) ~= nil or next(val) == nil then
		-- Treat as array -- check keys are valid and it is not sparse
		local n = 0;
		for k in pairs(val) do
			if type(k) ~= "number" then
				error("invalid table: mixed or invalid key types")
			end
			n = n + 1
		end
		if n ~= #val then
			error("invalid table: sparse array")
		end
		-- Encode
		rope[#rope + 1] = "["
		for i, v in ipairs(val) do
		if i > 1 then
			rope[#rope + 1] = ","
		end
			encode(rope, v, stack)
		end
		rope[#rope + 1] = "]"
	else
		-- Treat as an object
		rope[#rope + 1] = "{"
		local first = true;
		for k, v in pairs(val) do
			if type(k) ~= "string" then
				error("invalid table: mixed or invalid key types")
			end
			if not first then
				rope[#rope + 1] = ","
			end
			encode(rope, k, stack)
			rope[#rope + 1] = ":"
			encode(rope, v, stack)
			first = false
		end
		rope[#rope + 1] = "}"
	end
	stack[val] = nil
end;

local function encode_string(rope, val)
	rope[#rope + 1] = '"'
	rope[#rope + 1] = val:gsub('[%z\1-\31\\"]', escape_char)
	rope[#rope + 1] = '"'
end;

local function encode_number(rope, val)
	-- Check for NaN, -inf and inf
	if val ~= val or val <= -math.huge or val >= math.huge then
		error("unexpected number value '" .. tostring(val) .. "'")
	end
	-- See www.cs.berkeley.edu/~wkahan/ieee754status/IEEE754.PDF
	-- 17 digits suffice to losslessly represent 64-bit IEEE754 floats
	rope[#rope + 1] = ("%.17g"):format(val)
end;

local function encode_boolean(rope, val)
	rope[#rope + 1] = val and "true" or "false"
end;

local type_func_map = {
  [ "nil"     ] = encode_nil,
  [ "table"   ] = encode_table,
  [ "string"  ] = encode_string,
  [ "number"  ] = encode_number,
  [ "boolean" ] = encode_boolean,
};

function encode(rope, val, stack)
	local t = type(val)
	local encoder = type_func_map[t]
	if encoder then
		return encoder(rope, val, stack)
	end
	error("unexpected type '" .. t .. "'")
end;

function json.encode(val)
	local rope = {}
	encode(rope, val, {})
	return table_concat(rope);
end;

-------------------------------------------------------------------------------
-- Decode
-------------------------------------------------------------------------------

local parse

local function create_set(...)
	local res = {};
	for i = 1, select("#", ...) do
		res[ select(i, ...) ] = true
	end
	return res;
end

local space_chars   = create_set(" ", "\t", "\r", "\n");
local delim_chars   = create_set(" ", "\t", "\r", "\n", "]", "}", ",");
local escape_chars  = create_set("\\", "/", '"', "b", "f", "n", "r", "t", "u");
local literals      = create_set("true", "false", "null");

local literal_map = {
  [ "true"  ] = true,
  [ "false" ] = false,
  [ "null"  ] = nil,
};

local function next_char(str, idx, set, negate)
	for i = idx, #str do
		if set[str:sub(i, i)] ~= negate then
			return i
		end
	end
	return #str + 1;
end;

local function decode_error(str, idx, msg)
	local line_count = 1
	local col_count = 1
	for i = 1, idx - 1 do
		col_count = col_count + 1
		if str:sub(i, i) == "\n" then
			line_count = line_count + 1
			col_count = 1
		end
	end
	error(string_format("%s at line %d col %d", msg, line_count, col_count))
end;

local function codepoint_to_utf8(n)
	-- http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=iws-appendixa
	local f = math.floor;
	if n <= 0x7f then
		return string_char(n)
elseif n <= 0x7ff then
		return string_char(f(n / 64) + 192, n % 64 + 128)
elseif n <= 0xffff then
		return string_char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
elseif n <= 0x10ffff then
		return string_char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128,
        f(n % 4096 / 64) + 128, n % 64 + 128)
	end
	error( string_format("invalid unicode codepoint '%x'", n) )
end;

local function parse_unicode_escape(s)
	local n1 = tonumber(s:sub(1, 4), 16);
	local n2 = tonumber(s:sub(7, 10), 16);
	-- Surrogate pair?
	if n2 then
		return codepoint_to_utf8((n1 - 0xd800) * 0x400 + (n2 - 0xdc00) + 0x10000);
	else
		return codepoint_to_utf8(n1);
	end
end;

local function parse_string(str, i)
	local res = {};
	local j = i + 1;
	local k = j;

	while j <= #str do
		local x = str:byte(j);
		if x < 32 then
			decode_error(str, j, "control character in string")
    elseif x == 92 then -- `\`: Escape
			res[#res + 1] = str:sub(k, j - 1)
			j = j + 1
			local c = str:sub(j, j)
			if c == "u" then
				local hex = str:match("^[dD][89aAbB]%x%x\\u%x%x%x%x", j + 1)
				or str:match("^%x%x%x%x", j + 1)
				or decode_error(str, j - 1, "invalid unicode escape in string")
				res[#res + 1] = parse_unicode_escape(hex)
				j = j + #hex
			else
				if not escape_chars[c] then
					decode_error(str, j - 1, "invalid escape char '" .. c .. "' in string")
				end
				res[#res + 1] = escape_char_map_inv[c]
			end
			k = j + 1
	elseif x == 34 then -- `"`: End of string
			res[#res + 1] = str:sub(k, j - 1)
			return table_concat(res), j + 1
		end
		j = j + 1
	end
	decode_error(str, i, "expected closing quote for string")
	return table_concat(res);
end;

local function parse_number(str, i)
	local x = next_char(str, i, delim_chars);
	local s = str:sub(i, x - 1);
	local n = tonumber(s);
	if not n then
		decode_error(str, i, "invalid number '" .. s .. "'")
	end
	return n, x;
end;

local function parse_literal(str, i)
	local x = next_char(str, i, delim_chars)
	local word = str:sub(i, x - 1)
	if not literals[word] then
		decode_error(str, i, "invalid literal '" .. word .. "'")
	end
	return literal_map[word], x;
end;

local function parse_array(str, i)
	local res = {};
	local n = 1;
	i = i + 1
	while 1 do
		local x;
		i = next_char(str, i, space_chars, true)
		-- Empty / end of array?
		if str:sub(i, i) == "]" then
			i = i + 1
			break;
		end
		-- Read token
		x, i = parse(str, i)
		res[n] = x
		n = n + 1
		-- Next token
		i = next_char(str, i, space_chars, true)
		local chr = str:sub(i, i);
		i = i + 1
		if chr == "]" then 
			break; 
		end
		if chr ~= "," then 
			decode_error(str, i, "expected ']' or ','") 
		end
	end
	return res, i;
end;

local function parse_object(str, i)
	local res = {};
	i = i + 1
	while 1 do
		local key, val;
		i = next_char(str, i, space_chars, true)
		-- Empty / end of object?
		if str:sub(i, i) == "}" then
			i = i + 1
			break;
		end
		-- Read key
		if str:sub(i, i) ~= '"' then
			decode_error(str, i, "expected string for key")
		end
		key, i = parse(str, i)
		-- Read ':' delimiter
		i = next_char(str, i, space_chars, true)
		if str:sub(i, i) ~= ":" then
			decode_error(str, i, "expected ':' after key")
		end
		i = next_char(str, i + 1, space_chars, true)
		-- Read value
		val, i = parse(str, i)
		-- Set
		res[key] = val
		-- Next token
		i = next_char(str, i, space_chars, true)
		local chr = str:sub(i, i)
		i = i + 1
		if chr == "}" then 
			break; 
		end
		if chr ~= "," then 
			decode_error(str, i, "expected '}' or ','") end
		end
	return res, i;
end;

local char_func_map = {
	[ '"' ] = parse_string,
	[ "0" ] = parse_number,
	[ "1" ] = parse_number,
	[ "2" ] = parse_number,
	[ "3" ] = parse_number,
	[ "4" ] = parse_number,
	[ "5" ] = parse_number,
	[ "6" ] = parse_number,
	[ "7" ] = parse_number,
	[ "8" ] = parse_number,
	[ "9" ] = parse_number,
	[ "-" ] = parse_number,
	[ "t" ] = parse_literal,
	[ "f" ] = parse_literal,
	[ "n" ] = parse_literal,
	[ "[" ] = parse_array,
	[ "{" ] = parse_object,
};

parse = function(str, idx)
	local chr = str:sub(idx, idx);
	local f = char_func_map[chr];
	if f then
		return f(str, idx);
	end
	decode_error(str, idx, "unexpected character '" .. chr .. "'");
end;

function json.decode(str)
	if type(str) ~= "string" then
		error("expected argument of type string, got " .. type(str));
	end
	local res, idx = parse(str, next_char(str, 1, space_chars, true))
	idx = next_char(str, idx, space_chars, true)
	if idx <= #str then
		decode_error(str, idx, "trailing garbage")
	end
	return res;
end;

return json;