Reverse playlist order button

[tomasklaen]

Discussed in #986

^{Originally posted by Dkzn September 11, 2024}
I think this would be very useful for youtube playlists for example.

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Once I implement menu buttons.

[MiKoto-Railgun]

So much time has passed, do you still have this plan?

[tomasklaen]

Yes, but I don't have much time to donate atm. Currently I mostly just fix bugs, and implement features that are either very easy to add (couple minutes of work), or something that I personally want or is bugging me. And this is something that I personally don't need, and will require bunch of work.

[Sneakpeakcss]

So much time has passed, do you still have this plan?

I tried making one when the button API was added, but i had an issue with proper state detection. The only reliable method i found was observing playlist, which is a bit questionable, especially for large playlists with thousands of entries.

reversePlaylist.lua

local utils = require "mp.utils"

function takePlaylistSnapshot()
    local playlist = mp.get_property_native("playlist")
    local playlist_id_total = 0
    for i = 1, #playlist do
        playlist_id_total = playlist_id_total + playlist[i].id
    end
    return playlist_id_total
end

function toggleButtonState(init)
    if not init then button_state = not button_state end
    mp.commandv("script-message-to", "uosc", "set-button", "reverse-playlist-button", utils.format_json({
        icon = "cached",
        active = button_state,
        tooltip = "Reverse Playlist",
        command = { "script-message-to", mp.get_script_name(), "reversePlaylist" },
    }))
    if not init and not button_state then
        previous_playlist_snapshot = nil
        current_snapshot = nil
        mp.unobserve_property(buttonState)
    end
end

function buttonState()
    if debounce then return end
    debounce = mp.add_timeout(0.1, function()
        if button_state then
            current_snapshot = takePlaylistSnapshot()
            if previous_playlist_snapshot == nil then
                previous_playlist_snapshot = current_snapshot
            elseif current_snapshot ~= previous_playlist_snapshot then
                toggleButtonState()
                previous_playlist_snapshot = current_snapshot
            end
        end
        debounce = nil
    end)
end

function reversePlaylist(keybind)
    local current_pos = mp.get_property_number("playlist-pos-1")
    local entries_num = mp.get_property_number("playlist-count")
    if entries_num == 0 and button_state then
        toggleButtonState()
        return
    elseif entries_num == 0 then
        mp.osd_message("Playlist is empty")
        return
    end
    -- Unobserve before reversing to avoid slowdown on big playlists
    mp.unobserve_property(buttonState)
    -- idle-active
    if current_pos == -1 and entries_num > 0 then
        current_pos = 1
    end
    for i = current_pos + 1, entries_num do
        mp.commandv("playlist-move", i - 1, current_pos - 1)
    end
    for i = current_pos - 1, 1, -1 do
        mp.commandv("playlist-move", i - 1, entries_num)
    end
    toggleButtonState()
    if button_state and not keybind then
        mp.observe_property("playlist", "none", buttonState)
    end
end

-- Init uosc button
toggleButtonState(true)
mp.register_script_message("reversePlaylist", reversePlaylist)

controls=button:reverse-playlist-button

It does work, but the observer also triggers on file change, which is not exactly preferable when you're manually jumping between files multiple times per second.