local URL = require('url')
local qs = require('querystring')

-- helper to find elements by its values
local function _indexOf (target, field)
	if type(target) == 'string' then
		return target:find(field, 1, true)
	end

	for index, value in pairs(target) do
		if value == field then return index end
	end

	return nil
end

-- list of supported methods to override
local function _supportMethod (method)
	local methods = {
		'get',
		'post',
		'put',
		'head',
		'delete',
		'options',
		'trace',
		'copy',
		'lock',
		'mkcol',
		'move',
		'propfind',
		'proppatch',
		'unlock',
		'report',
		'mkactivity',
		'checkout',
		'merge',
		'm-search',
		'notify',
		'subscribe',
		'unsubscribe',
		'patch'
	}

	return _indexOf(methods, method) ~= nil
end

-- create a getter for a given string
local function _createGetter (key)
	return function (req, res)
		if _indexOf(key:upper(), 'X-') == 1 then
			return req.headers[key:lower()] or ''
		else
			local parsedURL = URL.parse(req.url)

			if parsedURL.query and parsedURL.query ~= '' then
				local query = qs.parse(parsedURL.query)
				return query[key]
			end

			return ''
		end
	end
end

-- provides faux http method support
-- pass optional key param to use when checking for a method override, defaults to '_method'
local function methodOverride (key)
	key = key or 'X-HTTP-Method-Override'

	return function (req, res, nxt)
		req.originalMethod = req.originalMethod or req.method

		local get = _createGetter(key)
		local method = get(req, res)

		if _supportMethod(method:lower()) then
			req.method = method:upper()
		end

		nxt()
	end
end

return methodOverride