local json = {
	_version = "0.1.0"
}

local function error(str)
	Application:error(str)
end

local encode = nil
local escape_char_map = {
	[""] = "\\f",
	[""] = "\\b",
	["\n"] = "\\n",
	["\t"] = "\\t",
	["\\"] = "\\\\",
	["\r"] = "\\r",
	["\""] = "\\\""
}
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(val)
	return "null"
end

local function encode_table(val, stack)
	local res = {}
	stack = stack or {}

	if stack[val] then
		error("circular reference")
	end

	stack[val] = true

	if val[1] ~= nil or next(val) == nil then
		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

		for i, v in ipairs(val) do
			table.insert(res, encode(v, stack))
		end

		stack[val] = nil

		return "[" .. table.concat(res, ",") .. "]"
	else
		for k, v in pairs(val) do
			if type(k) ~= "string" then
				error("invalid table: mixed or invalid key types")
			end

			table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
		end

		stack[val] = nil

		return "{" .. table.concat(res, ",") .. "}"
	end
end

local function encode_string(val)
	return "\"" .. val:gsub("[%z-\\\"]", escape_char) .. "\""
end

local function encode_number(val)
	if val ~= val or val <= -math.huge or math.huge <= val then
		error("unexpected number value '" .. tostring(val) .. "'")
	end

	return string.format("%.14g", val)
end

local type_func_map = {
	nil = encode_nil,
	table = encode_table,
	string = encode_string,
	number = encode_number,
	boolean = tostring,
	userdata = encode_nil,
	function = encode_nil
}

function encode(val, stack)
	local t = type(val)
	local f = type_func_map[t]

	if f then
		return f(val, stack)
	end

	error("unexpected type '" .. t .. "'")
end

function json.encode(val)
	return encode(val)
end

local parse = nil

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 = {
	false = false,
	true = true
}

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)
	local f = math.floor

	if n <= 127 then
		return string.char(n)
	elseif n <= 2047 then
		return string.char(f(n / 64) + 192, n % 64 + 128)
	elseif n <= 65535 then
		return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
	elseif n <= 1114111 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(3, 6), 16)
	local n2 = tonumber(s:sub(9, 12), 16)

	if n2 then
		return codepoint_to_utf8((n1 - 55296) * 1024 + n2 - 56320 + 65536)
	else
		return codepoint_to_utf8(n1)
	end
end

local function parse_string(str, i)
	local has_unicode_escape = false
	local has_surrogate_escape = false
	local has_escape = false
	local last = nil

	for j = i + 1, #str do
		local x = str:byte(j)

		if x < 32 then
			decode_error(str, j, "control character in string")
		end

		if last == 92 then
			if x == 117 then
				local hex = str:sub(j + 1, j + 5)

				if not hex:find("%x%x%x%x") then
					decode_error(str, j, "invalid unicode escape in string")
				end

				if hex:find("^[dD][89aAbB]") then
					has_surrogate_escape = true
				else
					has_unicode_escape = true
				end
			else
				local c = string.char(x)

				if not escape_chars[c] then
					decode_error(str, j, "invalid escape char '" .. c .. "' in string")
				end

				has_escape = true
			end

			last = nil
		elseif x == 34 then
			local s = str:sub(i + 1, j - 1)

			if has_surrogate_escape then
				s = s:gsub("\\u[dD][89aAbB]..\\u....", parse_unicode_escape)
			end

			if has_unicode_escape then
				s = s:gsub("\\u....", parse_unicode_escape)
			end

			if has_escape then
				s = s:gsub("\\.", escape_char_map_inv)
			end

			return s, j + 1
		else
			last = x
		end
	end

	decode_error(str, i, "expected closing quote for string")
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 true do
		local x = nil
		i = next_char(str, i, space_chars, true)

		if str:sub(i, i) == "]" then
			i = i + 1

			break
		end

		x, i = parse(str, i)
		res[n] = x
		n = n + 1
		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 true do
		local key, val = nil
		i = next_char(str, i, space_chars, true)

		if str:sub(i, i) == "}" then
			i = i + 1

			break
		end

		if str:sub(i, i) ~= "\"" then
			decode_error(str, i, "expected string for key")
		end

		key, i = parse(str, i)
		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)
		val, i = parse(str, i)
		res[key] = val
		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
}

function parse(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

	return parse(str, next_char(str, 1, space_chars, true))
end

return json
