function log(msg)
    ngx.log(ngx.STDERR, tostring(msg))
end

local ctx = {}

function ctx:setWantedScripts(graph)
    self._wanted_scripts = graph
end

function ctx:loadFromConfig(conf)
    ctx:setWantedScripts(conf.wantedScripts)
    ctx:loadChain()
end

function ctx:loadChain()
    self.compiled_chain = {}
    for module_name, module_config in pairs(self._wanted_scripts) do
        local module = require('scripts.' .. module_name)
        local module_state = module.init(module_config)
        -- TODO is it possible to make module_config readonly?
        table.insert(self.compiled_chain, {module, module_config, module_state})
    end
end

function ctx:onRequest()
    local request_uri = ngx.var.uri

    -- find out which modules to call based on their regexes
    local callbacks_to_call = {}
    for _, filter in ipairs(self.compiled_chain) do
        local module, module_config, state = unpack(filter)

        for callback_regex, callback_function in pairs(module.callbacks) do
            local match, error = ngx.re.match(request_uri, callback_regex)
            if match then
                table.insert(callbacks_to_call, {module, callback_function, module_config, state})
            end
        end
    end

    for _, tuple in ipairs(callbacks_to_call) do
        local module, callback_function, config, state = unpack(tuple)
        local status_code, body = callback_function(config, state)
        if status_code ~= nil then
            log('filtered by module ' .. module.name)
            ngx.status = status_code
            ngx.say(body or "request denied")
            ngx.exit(status_code)
        end
    end
end

return ctx