-- cache for alredy resolved titles and
-- titles that could not be resolved (filenames)
-- filename => title
local title_cache = {}

-- poor man's mutex
-- filename => true / false
local title_resolving = {}

local playlist_startswith = 'https://www.youtube.com/playlist?list='

-- resolve title using youtube-dl
-- ... and abusig gnu coreutils for what could be done in lua
function resolve_title(filename)
    print("resolving")
    -- workaround about poor man's mutex
    -- ensures that the actual check won't happen twice
    if title_cache[filename] then
        return title_cache[filename]
    end

    -- title cannot be resolved using youtube-dl
    title_resolving[filename] = true
    if not string.match(filename, "^https?://") then
        title_cache[filename] = filename
        title_resolving[filename] = false
    end

    local res = io.popen('youtube-dl --flat-playlist -e '.. filename .. ' | head -n 1'):read("*all")
    if res and res ~= '' then
        title_cache[filename] = res
    else
        -- try resolving as playlist
        res = io.popen('youtube-dl --flat-playlist -s '.. filename ..' | tail -n 1 | ' ..
            "awk 'match($0, /playlist: (.+$)/) { print substr($0, RSTART + 10, RLENGTH - 10) }'"):read("*all")
        if res and res ~= '' then
            title_cache[filename] = '[playlist]: ' .. res
        else
            -- finally give up
            title_cache[filename] = filename
        end
    end

    title_resolving[filename] = false
end

function get_playlist()
    local pos = mp.get_property_number('playlist-pos', 0) + 1
    local count, limlist = limited_list('playlist', pos)
    if count == 0 then
        return 'Empty playlist.'
    end

    local message = string.format('Playlist [%d/%d]:\n', pos, count)
    for i, v in ipairs(limlist) do
        local title = v.title
        if not title then

            -- try printing title from the cache
            if title_cache[v.filename] then
                title = title_cache[v.filename]

            -- if not, check if it's resolving in the background
            elseif title_resolving[v.filename] then
                title = v.filename

            -- if not, try to resolve it if filename looks like a network stream
            elseif string.match(v.filename, "https?://") then
                -- doesn't work for whatever reason
                --mp.add_timeout(0.05, resolve_title(v.filename))
                resolve_title(v.filename)

                -- temporary title while a proper one is being resolved
                title = v.filename

            -- else assume a local file and use it's filename
            else
                local _
                _, title = utils.split_path(v.filename)
                title_cache[v.filename] = title
            end
        end
        message = string.format('%s %s %s\n', message,
            (v.current and '●' or '○'), title)
    end
    return message
end