--ANALYZE
local pairs = _G.pairs
local string = _G.string
local error = _G.error
local next = _G.next
local type = _G.type
local ipairs = _G.ipairs
local table = _G.table
local tostring = _G.tostring
local select = _G.select
local tonumber = _G.tonumber
local json = {}
-------------------------------------------------------------------------------
-- 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--[[#: string]])
	return escape_char_map[c] or string.format("\\u%04x", c:byte())
end

local function encode_nil(val--[[#: any]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	return "null"
end

local function encode_table(val--[[#: Table]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	local res = {}
	stack = stack or {}

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

	stack[val] = true

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

		stack[val] = nil
		return "[" .. table.concat(res, ",") .. "]"
	else
		-- Treat as an object
		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--[[#: string]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	return "\"" .. val:gsub("[%z\1-\31\"]", escape_char) .. "\""
end

local function encode_number(val--[[#: any]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	-- 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

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

json.null = {}

local function encode_null(val--[[#: nil]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	return "null"
end

local function encode_boolean(val--[[#: boolean]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	return 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,
}
encode = function(val--[[#: any]], stack--[[#: Map<|any, true|>]])--[[#: string]]
	if val == json.null then return encode_null(val, stack) end

	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--[[#: any]])
	return (encode(val, {}))
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--[[#: string]],
	idx--[[#: number]],
	set--[[#: Map<|string, true|>]],
	negate--[[#: nil | boolean]]
)--[[#: number]]
	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--[[#: string]], idx--[[#: number]], msg--[[#: string]])
	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--[[#: number]])--[[#: string]]
	-- 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--[[#: string]])--[[#: string]]
	local n1 = tonumber(s:sub(3, 6), 16)

	if not n1 then error("failed to parse unicode escape") end

	local n2 = tonumber(s:sub(9, 12), 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--[[#: string]], i--[[#: number]])--[[#: string,number]]
	local has_unicode_escape = false
	local has_surrogate_escape = false
	local has_escape = false
	local last--[[#: number | 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 -- "\\" (escape char)
			if x == 117 then -- "u" (unicode escape sequence)
				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 -- '"' (end of string)
			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--[[#: string]], i--[[#: number]])--[[#: (number, number)]]
	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--[[#: string]], i--[[#: number]])--[[#: (boolean | nil, number)]]
	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--[[#: string]], i--[[#: number]])--[[#: List<|any|>,number]] -- TODO: fix List<|any|>
	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--[[#: string]], i--[[#: number]])
		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--[[#: string]], i--[[#: number]])--[[#: Map<|string, any|>,number]]
	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)
		-- Union
		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--[[#: string]], idx--[[#: number]])--[[#: any,number]]
	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 .. "'")
	return nil, -1
end

function json.decode(str--[[#: string]])--[[#: Table]]
	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