local M, assert, getenv = {}, assert, os.getenv

local function maybe(m)
	local ok, v = pcall(require, m)
	return ok and v
end
local lfs = maybe("lfs") -- LuaFileSystem; http://keplerproject.github.io/luafilesystem/
local zlib = maybe("zlib") -- lzlib; https://github.com/LuaDist/lzlib
local bit = maybe("bit") -- Lua BitOp; http://bitop.luajit.org
local socket = maybe("socket.http") -- LuaSocket; http://w3.impa.br/~diego/software/luasocket/home.html

local function shellEscape(s)
	return '"' .. s:gsub('"', '"\\\\""') .. '"'
end
local function readAndDeleteFile(path)
	local h, err = io.open(path, "rb")
	if h then
		local c = h:read("*a")
		h:close()
		h, err = c, nil
	end
	os.remove(path)
	return h, err
end

local dir_sep = package and package.config and package.config:sub(1,1) or "/"
do -- M.path(a, b, ...)
	M.path = function(a, b, ...)
		if a and b then
			return M.path(a .. (a:sub(-1) ~= dir_sep and dir_sep or "") .. b, ...)
		end
		return a
	end
end
M.url = function(a, b, ...)
	if a and b then
		return M.url(a .. ((a:sub(-1) == "/" or b:sub(1,1) == "/") and "" or "/") .. b, ...)
	end
	return a
end

M.commands =
	dir_sep == '/' and {toDevNull=' 2>/dev/null', ls='ls %s', mkdir='mkdir -p %s', gzip='gzip -dcq %s'} or
	dir_sep == '\\' and {toDevNull=' 2>NUL', ls='(for %%a in (%s) do @echo %%~fa)', mkdir='mkdir %s', gzip='gzip -dcq %s', TMP=os.getenv('TMP') or os.getenv('TEMP')}

M.tmpname = function()
	local tn = os.tmpname()
	return (M.commands and M.commands.TMP or "") .. tn
end

M.decompress = zlib and zlib.decompress or function(compressed)
	assert(type(compressed) == "string", 'Syntax: casc.platform.decompress("compressed")')
	assert(M.commands and M.commands.gzip and M.commands.toDevNull, 'unsupported platform')
	
	local f, f2 = M.tmpname(), M.tmpname()
	local h = io.open(f, "wb")
	h:write('\31\139\8\0\0\0\0\0')
	h:write(compressed)
	h:close()
	
	os.execute(M.commands.gzip:format(shellEscape(f)) .. " 1>" .. f2 .. " " .. M.commands.toDevNull)
	os.remove(f)
	
	return readAndDeleteFile(f2)
end

M.mkdir = lfs and lfs.mkdir or function(path)
	assert(type(path) == 'string', 'Syntax: casc.platform.mkdir("path")')
	assert(M.commands and M.commands.mkdir, 'unsupported platform')
	
	return os.execute(M.commands.mkdir:format(shellEscape(path)))
end

M.files = lfs and function(dir, glob)
	assert(type(dir) == "string" and type(glob) == 'string', 'Syntax: casc.platform.files("dir", "glob")')
	local pat = "^" .. glob:gsub("%.%-%+", "%%%0"):gsub("%*", ".*") .. "$"
	local t, ni = {}, 1
	for f in lfs.dir(dir) do
		if f ~= "." and f ~= ".." and f:match(pat) then
			t[ni], ni = M.path(dir, f), ni + 1
		end
	end
	return pairs(t)
end or function(dir, glob)
	assert(type(dir) == "string" and type(glob) == 'string', 'Syntax: casc.platform.files("dir", "glob")')
	assert(M.commands and M.commands.ls, 'unsupported platform')
	
	local dir, files = glob:match("^(.-)([^" .. dir_sep .. "]+)$")
	local t, ni, h = {}, 1, io.popen(M.commands.ls:format(shellEscape(dir) .. files), "r")
	for l in h:lines() do
		t[ni], ni = l, ni + 1
	end
	h:close()
	return pairs(t)
end

local floor = math.floor
M.rol = bit and bit.rol or function(n, b)
	local n, e2 = n % 2^32, 2^(32-b)
	return ((n % e2) * 2^b + floor(n/e2)) % 2^32
end

M.bxor = bit and bit.bxor or function(a, b)
   local out, m, lm = 0, 1
	for i=1,32 do
		m, lm = m+m, m
		local am, bm = a % m, b % m
		out, a, b = out + (am == bm and 0 or lm), a-am, b-bm
		if a == 0 or b == 0 then
			return (out + b + a) % 2^32
		end
	end
	return out
end

if socket then
	socket.USERAGENT, socket.TIMEOUT = "lcasc/1.1", 5
	local ltn12, RETRIES = require("ltn12"), 3
	M.http = function(url, h)
		for i=1,RETRIES do
			local sink = {}
			local ok, status, head = socket.request({url=url, sink=ltn12.sink.table(sink), headers=h})
			if ok then
				local cnt = table.concat(sink, "")
				return status >= 200 and status < 300 and cnt, status, head, cnt
			elseif i == RETRIES then
				error("HTTP request failed: " .. tostring(status) .. "\nURL: " .. tostring(url))
			end
		end
	end
else
	M.http = function(url, h)
		local c, of = "curl -s -S -A 'luacasc/1.1+curl'", M.tmpname()
		if type(h) == "table" then
			for k,v in pairs(h) do
				c = c .. ' -H ' .. shellEscape(k .. ": " .. v)
			end
		end
		c = c .. ' -o ' .. shellEscape(of)
		c = c .. ' ' .. shellEscape(url)
		if os.execute(c) == 0 then
			return readAndDeleteFile(of)
		end
		os.remove(of)
	end
end

return M