---------------------------------------------------------------------------
-- An abstract widget that handles a preset of concrete widget.
--
-- The `wibox.widget.template` widget is an abstraction layer that contains a
-- concrete widget definition. The template widget can be used to build widgets
-- that the user can customize at their will, thanks to the template mechanism.
--
-- @author Aire-One
-- @copyright 2021 Aire-One <aireone@aireone.xyz>
--
-- @classmod wibox.widget.template
-- @supermodule wibox.widget.base
---------------------------------------------------------------------------

local wbase = require("wibox.widget.base")
local gtable = require("gears.table")
local gtimer = require("gears.timer")

local default_update_callback = function()
    return nil
end

local default_template_widget = wbase.empty_widget()

local template = {
    mt = {},
    queued_updates = {}
}

function template:_do_update_now(args)
    self:update_callback(args)
    template.queued_updates[self] = false
end

--- Update the widget.
-- This function will call the `update_callback` function at the end of the
-- current GLib event loop. Updates are batched by event loop, it means that the
-- widget can only be update once by event loop. If the `template:update` method
-- is called multiple times during the same GLib event loop, only the first call
-- will be run.
-- All arguments are passed to the queued `update_callback` call.
-- @treturn boolean Returns `true` if the update_callback have been queued to be
--   run at the end of the event loop. Returns `false` if there is already an update
--   in the queue (in this case, this new update request is discared).
function template:update(args)
    local update_args = gtable.crush(gtable.clone(self.update_args, false), args or {})

    if not template.queued_updates[self] then
        gtimer.delayed_call(
            function()
                self:_do_update_now(update_args)
            end
        )
        template.queued_updates[self] = true

        return true
    end

    return false
end

--- Create a new `wibox.widget.template` instance.
-- @tparam[opt] table args
-- @tparam[opt] table|widget|function args.widget_template The template of widget to use.
-- @tparam[opt] function args.update_callback The callback function to update the widget.
-- @treturn wibox.widget.template The new instance.
function template.new(args)
    args = args or {}

    local widget_template =
        type(args.widget_template) == "function" and args.widget_template() or args.widget_template or
        default_template_widget

    local widget = wbase.make_widget_from_value(widget_template)

    widget.update_callback = args.update_callback or default_update_callback
    widget.update_args = args.update_args or {}

    gtable.crush(widget, template, true)

    return widget
end

function template.mt:__call(...) --luacheck: ignore unused variable self
    return template.new(...)
end

return setmetatable(template, template.mt)

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