File

+
−local known_traits = {};
+
−
+
−local function trait_added(event)
+
−	local trait = event.item;
+
−	local name = trait.name;
+
−	if known_traits[name] then return; end
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−
+
−	known_traits[name] = trait.probabilities;
+
−end
+
−
+
−local function trait_removed(event)
+
−	local trait = event.item;
+
−	known_traits[trait.name] = nil;
+
−end
+
−
+
−module:handle_items("account-trait", trait_added, trait_removed);
+
−
+
−local function bayes_probability(prior, prob_given_true, prob_given_false)
+
−	local numerator = prob_given_true * prior;
+
−	local denominator = numerator + prob_given_false * (1 - prior);
+
−	return numerator / denominator;
+
−end
+
−
+
−local function prob_is_bad(traits, prior)
+
−	prior = prior or 0.50;
+
−
+
−	for trait, state in pairs(traits) do
+
−		local probabilities = known_traits[trait];
+
−		if probabilities then
+
−			if state then
+
−				prior = bayes_probability(
+
−					prior,
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−					probabilities.prob_bad_true,
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−					probabilities.prob_bad_false
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−				);
+
−			else
+
−				prior = bayes_probability(
+
−					prior,
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−					1 - probabilities.prob_bad_true,
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−					1 - probabilities.prob_bad_false
+
−				);
+
−			end
+
−		end
+
−	end
+
−
+
−	return prior;
+
−end
+
−
+
−local function get_probability_bad(username, prior)
+
−	local user_traits = {};
+
−	module:fire_event("get-account-traits", { username = username, host = module.host, traits = user_traits });
+
−	local result = prob_is_bad(user_traits, prior);
+
−	return result;
+
−end
+
−
+
−return {
+
−	get_probability_bad = get_probability_bad;
+
−};