--[[
Copyright (c) 2011,2013 Robin Wellner

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, ipairs, tostring, type, concat, dump, floor, format = pairs, ipairs, tostring, type, table.concat, string.dump, math.floor, string.format

local function getchr(c)
	return "\\" .. c:byte()
end

local function make_safe(text)
	return ("%q"):format(text):gsub('\n', 'n'):gsub("[\128-\255]", getchr)
end

local oddvals = {[tostring(1/0)] = '1/0', [tostring(-1/0)] = '-1/0', [tostring(-(0/0))] = '-(0/0)', [tostring(0/0)] = '0/0'}
local function write(t, memo, rev_memo)
	local ty = type(t)
	if ty == 'number' then
		t = format("%.17g", t)
		return oddvals[t] or t
	elseif ty == 'boolean' or ty == 'nil' then
		return tostring(t)
	elseif ty == 'string' then
		return make_safe(t)
	elseif ty == 'table' or ty == 'function' then
		if not memo[t] then
			local index = #rev_memo + 1
			memo[t] = index
			rev_memo[index] = t
		end
		return '_[' .. memo[t] .. ']'
	else
		error("Trying to serialize unsupported type " .. ty)
	end
end

local kw = {['and'] = true, ['break'] = true, ['do'] = true, ['else'] = true,
	['elseif'] = true, ['end'] = true, ['false'] = true, ['for'] = true,
	['function'] = true, ['goto'] = true, ['if'] = true, ['in'] = true,
	['local'] = true, ['nil'] = true, ['not'] = true, ['or'] = true,
	['repeat'] = true, ['return'] = true, ['then'] = true, ['true'] = true,
	['until'] = true, ['while'] = true}
local function write_key_value_pair(k, v, memo, rev_memo, name)
	if type(k) == 'string' and k:match '^[_%a][_%w]*$' and not kw[k] then
		return (name and name .. '.' or '') .. k ..'=' .. write(v, memo, rev_memo)
	else
		return (name or '') .. '[' .. write(k, memo, rev_memo) .. ']=' .. write(v, memo, rev_memo)
	end
end

-- fun fact: this function is not perfect
-- it has a few false positives sometimes
-- but no false negatives, so that's good
local function is_cyclic(memo, sub, super)
	local m = memo[sub]
	local p = memo[super]
	return m and p and m < p
end

local function write_table_ex(t, memo, rev_memo, srefs, name)
	if type(t) == 'function' then
		return '_[' .. name .. ']=loadstring' .. make_safe(dump(t))
	end
	local m = {}
	local mi = 1
	for i = 1, #t do -- don't use ipairs here, we need the gaps
		local v = t[i]
		if v == t or is_cyclic(memo, v, t) then
			srefs[#srefs + 1] = {name, i, v}
			m[mi] = 'nil'
			mi = mi + 1
		else
			m[mi] = write(v, memo, rev_memo)
			mi = mi + 1
		end
	end
	for k,v in pairs(t) do
		if type(k) ~= 'number' or floor(k) ~= k or k < 1 or k > #t then
			if v == t or k == t or is_cyclic(memo, v, t) or is_cyclic(memo, k, t) then
				srefs[#srefs + 1] = {name, k, v}
			else
				m[mi] = write_key_value_pair(k, v, memo, rev_memo)
				mi = mi + 1
			end
		end
	end
	return '_[' .. name .. ']={' .. concat(m, ',') .. '}'
end

return function(t)
	local memo = {[t] = 0}
	local rev_memo = {[0] = t}
	local srefs = {}
	local result = {}

	-- phase 1: recursively descend the table structure
	local n = 0
	while rev_memo[n] do
		result[n + 1] = write_table_ex(rev_memo[n], memo, rev_memo, srefs, n)
		n = n + 1
	end

	-- phase 2: reverse order
	for i = 1, n*.5 do
		local j = n - i + 1
		result[i], result[j] = result[j], result[i]
	end

	-- phase 3: add all the tricky cyclic stuff
	for i, v in ipairs(srefs) do
		n = n + 1
		result[n] = write_key_value_pair(v[2], v[3], memo, rev_memo, '_[' .. v[1] .. ']')
	end

	-- phase 4: add something about returning the main table
	if result[n]:sub(1, 5) == '_[0]=' then
		result[n] = 'return ' .. result[n]:sub(6)
	else
		result[n + 1] = 'return _[0]'
	end

	-- phase 5: just concatenate everything
	result = concat(result, '\n')
	return n > 1 and 'local _={}\n' .. result or result
end