--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/mod_cron.lua	Sun Nov 21 15:50:36 2021 +0100
@@ -0,0 +1,59 @@
+module:set_global();
+
+local async = require("util.async");
+
+local periods = { hourly = 3600; daily = 86400 }
+
+local active_hosts = {}
+
+function module.add_host(host_module)
+
+	local last_run_times = host_module:open_store("cron", "map");
+	active_hosts[host_module.host] = true;
+
+	local function save_task(task, started_at) last_run_times:set(nil, task.id, started_at); end
+
+	local function task_added(event)
+		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 require("util.datetime").datetime(task.last) or "never");
+		return true
+	end
+
+	local function task_removed(event)
+		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, last) return not last or last + periods[when] <= os.time() end
+
+local function run_task(task)
+	local started_at = os.time();
+	task:run(started_at);
+	task:save(started_at);
+end
+
+local task_runner = async.runner(run_task);
+module:add_timer(1, function()
+	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")) 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);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/teal-src/plugins/mod_cron.tl	Sun Nov 21 15:50:36 2021 +0100
@@ -0,0 +1,98 @@
+module:set_global();
+
+local async = require "util.async";
+
+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"
+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 }
+
+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 require"util.datetime".datetime(task.last) or "never");
+		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] <= os.time();
+end
+
+local function run_task(task : task_spec)
+	local started_at = os.time();
+	task:run(started_at);
+	task:save(started_at);
+end
+
+local task_runner = async.runner(run_task);
+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