module:set_global();

local async = require "util.async";

local datetime = require "util.datetime";

local record map_store<K,V>

	-- TODO move to somewhere sensible

	get : function (map_store<K,V>, string, K) : V

	set : function (map_store<K,V>, string, K, V)

end

local enum frequency

	"hourly"

	"daily"

	"weekly"

end

local record task_spec

	id : string -- unique id

	name : string -- name or short description

	when : frequency

	last : integer

	run : function (task_spec, integer)

	save : function (task_spec, integer)

end

local record task_event

	source : module

	item : task_spec

end

local periods : { frequency : integer } = { hourly = 3600, daily = 86400, weekly = 7*86400 }

local active_hosts : { string : boolean } = {  }

function module.add_host(host_module : moduleapi)

	local last_run_times = host_module:open_store("cron", "map") as map_store<string,integer>;

	active_hosts[host_module.host] = true;

	local function save_task(task : task_spec, started_at : integer)

		last_run_times:set(nil, task.id, started_at);

	end

	local function task_added(event : task_event) : boolean

		local task = event.item;

		if task.name == nil then

			task.name = task.when;

		end

		if task.id == nil then

			task.id = event.source.name .. "/" .. task.name:gsub("%W", "_"):lower();

		end

		if task.last == nil then

			task.last = last_run_times:get(nil, task.id);

		end

		task.save = save_task;

		module:log("debug", "%s task %s added, last run %s", task.when, task.id,

			task.last and datetime.datetime(task.last) or "never");

		if task.last == nil then

			-- initialize new tasks so e.g. daily tasks run at ~midnight UTC for now

			local now = os.time();

			task.last = now - now % periods[task.when];

		end

		return true;

	end

	local function task_removed(event : task_event) : boolean

		local task = event.item;

		host_module:log("debug", "Task %s removed", task.id);

		return true;

	end

	host_module:handle_items("task", task_added, task_removed, true);

	function host_module.unload()

		active_hosts[host_module.host]=nil;

	end

end

local function should_run(when : frequency, last : integer) : boolean

	return not last or last + periods[when]*0.995 <= os.time();

end

local function run_task(task : task_spec)

	local started_at = os.time();

	task:run(started_at);

	task.last = started_at;

	task:save(started_at);

end

module:add_timer(1, function() : integer

	module:log("info", "Running periodic tasks");

	local delay = 3600;

	for host in pairs(active_hosts) do

		module:log("debug", "Running periodic tasks for host %s", host);

		for _, task in ipairs(module:context(host):get_host_items("task") as { task_spec } ) do

			module:log("debug", "Considering %s task %s (%s)", task.when, task.id, task.run);

			if should_run(task.when, task.last) then task_runner:run(task); end

		end

	end

	module:log("debug", "Wait %ds", delay);

	return delay;

end);

-- TODO measure load, pick a good time to do stuff