-- Log statistics to Prometheus
--
-- Copyright (C) 2014 Daurnimator
-- Copyright (C) 2018 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
-- Copyright (C) 2021 Jonas Schäfer <jonas@zombofant.net>
--
-- This module is MIT/X11 licensed.

module:set_global();

local tostring = tostring;
local t_insert = table.insert;
local t_concat = table.concat;
local time_now = require "util.time".now;
local statsman = require "core.statsmanager";
local get_stats = statsman.get_stats;
local get_metric_registry = statsman.get_metric_registry;
local collect = statsman.collect;

local function escape(text)
	return text:gsub("\\", "\\\\"):gsub("\"", "\\\""):gsub("\n", "\\n");
end

local function escape_name(name)
	return name:gsub("/", "__"):gsub("[^A-Za-z0-9_]", "_"):gsub("^[^A-Za-z_]", "_%1");
end

local function get_timestamp()
	-- In milliseconds.
	return math.floor(time_now() * 1000);
end

local function repr_help(metric, docstring)
	docstring = docstring:gsub("\\", "\\\\"):gsub("\n", "\\n");
	return "# HELP "..escape_name(metric).." "..docstring.."\n";
end

local function repr_unit(metric, unit)
	if not unit then
		unit = ""
	else
		unit = unit:gsub("\\", "\\\\"):gsub("\n", "\\n");
	end
	return "# UNIT "..escape_name(metric).." "..unit.."\n";
end

-- local allowed_types = { counter = true, gauge = true, histogram = true, summary = true, untyped = true };
-- local allowed_types = { "counter", "gauge", "histogram", "summary", "untyped" };
local function repr_type(metric, type_)
	-- if not allowed_types:contains(type_) then
	-- 	return;
	-- end
	return "# TYPE "..escape_name(metric).." "..type_.."\n";
end

local function repr_label(key, value)
	return key.."=\""..escape(value).."\"";
end

local function repr_labels(labelkeys, labelvalues, extra_labels)
	local values = {}
	if labelkeys then
		for i, key in ipairs(labelkeys) do
			local value = labelvalues[i]
			t_insert(values, repr_label(escape_name(key), escape(value)));
		end
	end
	if extra_labels then
		for key, value in pairs(extra_labels) do
			t_insert(values, repr_label(escape_name(key), escape(value)));
		end
	end
	if #values == 0 then
		return "";
	end
	return "{"..t_concat(values, ",").."}";
end

local function repr_sample(metric, labelkeys, labelvalues, extra_labels, value)
	return escape_name(metric)..repr_labels(labelkeys, labelvalues, extra_labels).." "..string.format("%.17g", value).."\n";
end

local get_metrics;
if statsman.get_metric_registry then
	module:log("debug", "detected OpenMetrics statsmanager")
	-- Prosody 0.12+ with OpenMetrics
	function get_metrics(event)
		local response = event.response;
		response.headers.content_type = "application/openmetrics-text; version=0.0.4";

		if collect then
			-- Ensure to get up-to-date samples when running in manual mode
			collect()
		end

		local registry = get_metric_registry()
		if registry == nil then
			response.headers.content_type = "text/plain; charset=utf-8"
			response.status_code = 404
			return "No statistics provider configured\n"
		end
		local answer = {};
		for metric_family_name, metric_family in pairs(registry:get_metric_families()) do
			t_insert(answer, repr_help(metric_family_name, metric_family.description))
			t_insert(answer, repr_unit(metric_family_name, metric_family.unit))
			t_insert(answer, repr_type(metric_family_name, metric_family.type_))
			for labelset, metric in metric_family:iter_metrics() do
				for suffix, extra_labels, value in metric:iter_samples() do
					t_insert(answer, repr_sample(metric_family_name..suffix, metric_family.label_keys, labelset, extra_labels, value))
				end
			end
		end
		t_insert(answer, "# EOF\n")
		return t_concat(answer, "");
	end
else
	module:log("debug", "detected pre-OpenMetrics statsmanager")
	-- Pre-OpenMetrics

	local allowed_extras = { min = true, max = true, average = true };
	local function insert_extras(data, key, name, timestamp, extra)
		if not extra then
			return false;
		end
		local has_extra = false;
		for extra_name in pairs(allowed_extras) do
			if extra[extra_name] then
				local field = {
					value = extra[extra_name],
					labels = {
						["type"] = name,
						field = extra_name,
					},
					typ = "gauge";
					timestamp = timestamp,
				};
				t_insert(data[key], field);
				has_extra = true;
			end
		end
		return has_extra;
	end

	local function parse_stats()
		local timestamp = tostring(get_timestamp());
		local data = {};
		local stats, changed_only, extras = get_stats();
		for stat, value in pairs(stats) do
			-- module:log("debug", "changed_stats[%q] = %s", stat, tostring(value));
			local extra = extras[stat];
			local host, sect, name, typ = stat:match("^/([^/]+)/([^/]+)/(.+):(%a+)$");
			if host == nil then
				sect, name, typ = stat:match("^([^.]+)%.(.+):(%a+)$");
			elseif host == "*" then
				host = nil;
			end
			if sect:find("^mod_measure_.") then
				sect = sect:sub(13);
			elseif sect:find("^mod_statistics_.") then
				sect = sect:sub(16);
			end

			local key = escape_name("prosody_"..sect);
			local field = {
				value = value,
				labels = { ["type"] = name},
				-- TODO: Use the other types where it makes sense.
				typ = (typ == "rate" and "counter" or "gauge"),
				timestamp = timestamp,
			};
			if host then
				field.labels.host = host;
			end
			if data[key] == nil then
				data[key] = {};
			end
			if not insert_extras(data, key, name, timestamp, extra) then
				t_insert(data[key], field);
			end
		end
		return data;
	end

	function get_metrics(event)
		local response = event.response;
		response.headers.content_type = "text/plain; version=0.0.4";
		if statsman.collect then
			statsman.collect()
		end

		local answer = {};
		for key, fields in pairs(parse_stats()) do
			t_insert(answer, repr_help(key, ""));
			t_insert(answer, repr_type(key, fields[1].typ));
			for _, field in pairs(fields) do
				t_insert(answer, repr_sample(key, nil, nil, field.labels, field.value, field.timestamp));
			end
		end
		return t_concat(answer, "");
	end
end

function module.add_host(module)
	module:depends "http";
	module:provides("http", {
		default_path = "metrics";
		route = {
			GET = get_metrics;
		};
	});
end
