--[[
mpv-gallery-view | https://github.com/occivink/mpv-gallery-view

This mpv script implements a worker for generating gallery thumbnails.
It is meant to be used by other scripts.
Multiple copies of this script can be loaded by mpv.

File placement: inside scripts directory
Settings: script-opts/gallery_worker.conf
]]

local utils = require("mp.utils")
local msg = require("mp.msg")

local jobs_queue = {} -- queue of thumbnail jobs
local failed = {} -- list of failed output paths, to avoid redoing them
local script_id = mp.get_script_name() .. utils.getpid()

local opts = {
	ytdl_exclude = "",
};
(require("mp.options")).read_options(opts, "gallery_worker")

local ytdl = {
	path = "youtube-dl",
	searched = false,
	blacklisted = {}, -- Add patterns of URLs you want blacklisted from youtube-dl,
	-- see gallery_worker.conf or ytdl_hook-exclude in the mpv manpage for more info
}

function append_table(lhs, rhs)
	for i = 1, #rhs do
		lhs[#lhs + 1] = rhs[i]
	end
	return lhs
end

local function file_exists(path)
	local info = utils.file_info(path)
	return info ~= nil and info.is_file
end

local video_extensions = { "mkv", "webm", "mp4", "avi", "wmv" }

function is_video(input_path)
	local extension = string.match(input_path, "%.([^.]+)$")
	if extension then
		extension = string.lower(extension)
		for _, ext in ipairs(video_extensions) do
			if extension == ext then
				return true
			end
		end
	end
	return false
end

function is_blacklisted(url)
	if opts.ytdl_exclude == "" then
		return false
	end
	if #ytdl.blacklisted == 0 then
		local joined = opts.ytdl_exclude
		while joined:match("%|?[^|]+") do
			local _, e, substring = joined:find("%|?([^|]+)")
			table.insert(ytdl.blacklisted, substring)
			joined = joined:sub(e + 1)
		end
	end
	if #ytdl.blacklisted > 0 then
		url = url:match("https?://(.+)")
		for _, exclude in ipairs(ytdl.blacklisted) do
			if url:match(exclude) then
				msg.verbose("URL matches excluded substring. Skipping.")
				return true
			end
		end
	end
	return false
end

function ytdl_thumbnail_url(input_path)
	local function exec(args)
		local ret = utils.subprocess({ args = args, cancellable = false })
		return ret.status, ret.stdout, ret
	end
	local function first_non_nil(x, ...)
		if x ~= nil then
			return x
		end
		return first_non_nil(...)
	end

	-- if input_path is youtube, generate our own URL
	youtube_id1 = string.match(input_path, "https?://youtu%.be/([%a%d%-_]+).*")
	youtube_id2 = string.match(input_path, "https?://w?w?w?%.?youtube%.com/v/([%a%d%-_]+).*")
	youtube_id3 = string.match(input_path, "https?://w?w?w?%.?youtube%.com/watch%?v=([%a%d%-_]+).*")
	youtube_id4 = string.match(input_path, "https?://w?w?w?%.?youtube%.com/embed/([%a%d%-_]+).*")
	youtube_id = youtube_id1 or youtube_id2 or youtube_id3 or youtube_id4

	if youtube_id then
		-- the hqdefault.jpg thumbnail should always exist, since it's used on the search result page
		return "https://i.ytimg.com/vi/" .. youtube_id .. "/hqdefault.jpg"
	end

	--otherwise proceed with the slower `youtube-dl -J` method
	if not ytdl.searched then --search for youtude-dl in mpv's config directory
		local exesuf = (package.config:sub(1, 1) == "\\") and ".exe" or ""
		local ytdl_mcd = mp.find_config_file("youtube-dl")
		if not (ytdl_mcd == nil) then
			msg.error("found youtube-dl at: " .. ytdl_mcd)
			ytdl.path = ytdl_mcd
		end
		ytdl.searched = true
	end
	local command = { ytdl.path, "--no-warnings", "--no-playlist", "-J", input_path }
	local es, json, result = exec(command)

	if (es < 0) or (json == nil) or (json == "") then
		msg.error("fetching thumbnail url with youtube-dl failed for" .. input_path)
		return input_path
	end
	local json, err = utils.parse_json(json)
	if json == nil then
		msg.error("failed to parse json for youtube-dl thumbnail: " .. err)
		return input_path
	end

	if (json.thumbnail == nil) or (json.thumbnail == "") then
		msg.error("no thumbnail url from youtube-dl.")
		return input_path
	end
	return json.thumbnail
end

function thumbnail_command(input_path, width, height, take_thumbnail_at, output_path, accurate, with_mpv)
	local vf = string.format(
		"%s,%s",
		string.format("scale=iw*min(1\\,min(%d/iw\\,%d/ih)):-2", width, height),
		string.format("pad=%d:%d:(%d-iw)/2:(%d-ih)/2:color=0x00000000", width, height, width, height)
	)
	local out = {}
	local add = function(table)
		out = append_table(out, table)
	end

	if input_path:find("^https?://") and not is_blacklisted(input_path) then
		-- returns the original input_path on failure
		input_path = ytdl_thumbnail_url(input_path)
	end

	if input_path:find("^archive://") or input_path:find("^edl://") then
		with_mpv = true
	end

	if not with_mpv then
		out = { "ffmpeg" }
		if is_video(input_path) then
			if string.sub(take_thumbnail_at, -1) == "%" then
				--if only fucking ffmpeg supported percent-style seeking
				local res = utils.subprocess({
					args = {
						"ffprobe",
						"-v",
						"error",
						"-show_entries",
						"format=duration",
						"-of",
						"default=noprint_wrappers=1:nokey=1",
						input_path,
					},
					cancellable = false,
				})
				if res.status == 0 then
					local duration = tonumber(string.match(res.stdout, "^%s*(.-)%s*$"))
					if duration then
						local percent = tonumber(string.sub(take_thumbnail_at, 1, -2))
						local start = tostring(duration * percent / 100)
						add({ "-ss", start })
					end
				end
			else
				add({ "-ss", take_thumbnail_at })
			end
		end
		if not accurate then
			add({ "-noaccurate_seek" })
		end
		add({
			"-i",
			input_path,
			"-vf",
			vf,
			"-map",
			"v:0",
			"-f",
			"rawvideo",
			"-pix_fmt",
			"bgra",
			"-c:v",
			"rawvideo",
			"-frames:v",
			"1",
			"-y",
			"-loglevel",
			"quiet",
			output_path,
		})
	else
		out = { "mpv", input_path }
		if take_thumbnail_at ~= "0" and is_video(input_path) then
			if not accurate then
				add({ "--hr-seek=no" })
			end
			add({ "--start=" .. take_thumbnail_at })
		end
		add({
			"--no-config",
			"--msg-level=all=no",
			"--vf=lavfi=[" .. vf .. ",format=bgra]",
			"--audio=no",
			"--sub=no",
			"--frames=1",
			"--image-display-duration=0",
			"--of=rawvideo",
			"--ovc=rawvideo",
			"--o=" .. output_path,
		})
	end
	return out
end

function generate_thumbnail(thumbnail_job)
	if file_exists(thumbnail_job.output_path) then
		return true
	end

	local dir, _ = utils.split_path(thumbnail_job.output_path)
	local tmp_output_path = utils.join_path(dir, script_id)

	local command = thumbnail_command(
		thumbnail_job.input_path,
		thumbnail_job.width,
		thumbnail_job.height,
		thumbnail_job.take_thumbnail_at,
		tmp_output_path,
		thumbnail_job.accurate,
		thumbnail_job.with_mpv
	)

	local res = utils.subprocess({ args = command, cancellable = false })
	--"atomically" generate the output to avoid loading half-generated thumbnails (results in crashes)
	if res.status == 0 then
		local info = utils.file_info(tmp_output_path)
		if not info or not info.is_file or info.size == 0 then
			return false
		end
		if os.rename(tmp_output_path, thumbnail_job.output_path) then
			return true
		end
	end
	return false
end

function handle_events(wait)
	e = mp.wait_event(wait)
	while e.event ~= "none" do
		if e.event == "shutdown" then
			return false
		elseif e.event == "client-message" then
			if e.args[1] == "push-thumbnail-front" or e.args[1] == "push-thumbnail-back" then
				local thumbnail_job = {
					requester = e.args[2],
					input_path = e.args[3],
					width = tonumber(e.args[4]),
					height = tonumber(e.args[5]),
					take_thumbnail_at = e.args[6],
					output_path = e.args[7],
					accurate = (e.args[8] == "true"),
					with_mpv = (e.args[9] == "true"),
				}
				if e.args[1] == "push-thumbnail-front" then
					jobs_queue[#jobs_queue + 1] = thumbnail_job
				else
					table.insert(jobs_queue, 1, thumbnail_job)
				end
			end
		end
		e = mp.wait_event(0)
	end
	return true
end

local registration_timeout = 2 -- seconds
local registration_period = 0.2

-- shitty custom event loop because I can't figure out a better way
-- works pretty well though
function mp_event_loop()
	local start_time = mp.get_time()
	local sleep_time = registration_period
	local last_broadcast_time = -registration_period
	local broadcast_func
	broadcast_func = function()
		local now = mp.get_time()
		if now >= start_time + registration_timeout then
			mp.commandv("script-message", "thumbnails-generator-broadcast", mp.get_script_name())
			sleep_time = 1e20
			broadcast_func = function() end
		elseif now >= last_broadcast_time + registration_period then
			mp.commandv("script-message", "thumbnails-generator-broadcast", mp.get_script_name())
			last_broadcast_time = now
		end
	end

	while true do
		if not handle_events(sleep_time) then
			return
		end
		broadcast_func()
		while #jobs_queue > 0 do
			local thumbnail_job = jobs_queue[#jobs_queue]
			if not failed[thumbnail_job.output_path] then
				if generate_thumbnail(thumbnail_job) then
					mp.commandv(
						"script-message-to",
						thumbnail_job.requester,
						"thumbnail-generated",
						thumbnail_job.output_path
					)
				else
					failed[thumbnail_job.output_path] = true
				end
			end
			jobs_queue[#jobs_queue] = nil
			if not handle_events(0) then
				return
			end
			broadcast_func()
		end
	end
end