-- This script automatically loads playlist entries before and after the
-- the currently played file. It does so by scanning the directory a file is
-- located in when starting playback. It sorts the directory entries
-- alphabetically, and adds entries before and after the current file to
-- the internal playlist. (It stops if the it would add an already existing
-- playlist entry at the same position - this makes it "stable".)
-- Add at most 5000 * 2 files when starting a file (before + after).
MAXENTRIES = 5000

local options = require("mp.options")

o = {
	disabled = false,
}
options.read_options(o)

function Set(t)
	local set = {}
	for _, v in pairs(t) do
		set[v] = true
	end
	return set
end

EXTENSIONS = Set({
	"mkv",
	"avi",
	"mp4",
	"ogv",
	"webm",
	"rmvb",
	"flv",
	"wmv",
	"mpeg",
	"mpg",
	"m4v",
	"3gp",
	"mp3",
	"wav",
	"ogv",
	"flac",
	"m4a",
	"wma",
})

mputils = require("mp.utils")

function add_files_at(index, files)
	index = index - 1
	local oldcount = mp.get_property_number("playlist-count", 1)
	for i = 1, #files do
		mp.commandv("loadfile", files[i], "append")
		mp.commandv("playlist-move", oldcount + i - 1, index + i - 1)
	end
end

function get_extension(path)
	match = string.match(path, "%.([^%.]+)$")
	if match == nil then
		return "nomatch"
	else
		return match
	end
end

table.filter = function(t, iter)
	for i = #t, 1, -1 do
		if not iter(t[i]) then
			table.remove(t, i)
		end
	end
end

function find_and_add_entries()
	local path = mp.get_property("path", "")
	local dir, filename = mputils.split_path(path)
	if o.disabled or #dir == 0 then
		return
	end
	local pl_count = mp.get_property_number("playlist-count", 1)
	if
		(pl_count > 1 and autoload == nil)
		or (pl_count == 1 and EXTENSIONS[string.lower(get_extension(filename))] == nil)
	then
		return
	else
		autoload = true
	end

	local files = mputils.readdir(dir, "files")
	if files == nil then
		return
	end
	table.filter(files, function(v, k)
		if string.match(v, "^%.") then
			return false
		end
		local ext = get_extension(v)
		if ext == nil then
			return false
		end
		return EXTENSIONS[string.lower(ext)]
	end)
	table.sort(files, function(a, b)
		local len = string.len(a) - string.len(b)
		if len ~= 0 then -- case for ordering filename ending with such as X.Y.Z
			local ext = string.len(get_extension(a)) + 1
			a = string.sub(a, 1, -ext)
			b = string.sub(b, 1, -ext)
		end
		return string.lower(a) < string.lower(b)
	end)

	if dir == "." then
		dir = ""
	end

	local pl = mp.get_property_native("playlist", {})
	local pl_current = mp.get_property_number("playlist-pos", 0) + 1
	-- Find the current pl entry (dir+"/"+filename) in the sorted dir list
	local current
	for i = 1, #files do
		if files[i] == filename then
			current = i
			break
		end
	end
	if current == nil then
		return
	end

	local append = { [-1] = {}, [1] = {} }
	for direction = -1, 1, 2 do -- 2 iterations, with direction = -1 and +1
		for i = 1, MAXENTRIES do
			local file = files[current + i * direction]
			local pl_e = pl[pl_current + i * direction]
			if file == nil or file[1] == "." then
				break
			end

			local filepath = dir .. file
			if pl_e then
				-- If there's a playlist entry, and it's the same file, stop.
				if pl_e.filename == filepath then
					break
				end
			end

			if direction == -1 then
				if pl_current == 1 then -- never add additional entries in the middle
					mp.msg.info("Prepending " .. file)
					table.insert(append[-1], 1, filepath)
				end
			else
				mp.msg.info("Adding " .. file)
				table.insert(append[1], filepath)
			end
		end
	end

	add_files_at(pl_current + 1, append[1])
	add_files_at(pl_current, append[-1])
end

mp.register_event("start-file", find_and_add_entries)
