local TMP_FOLDER = '/tmp/memebot/'

local internet  =  require 'internet'

--------------------------------------------------------------------------------

local function ensure_tmp_folder_exists ()
    os.execute(('mkdir --parents "%s"'):format(TMP_FOLDER))
end

local function video_length (video_filename)
    assert(type(video_filename) == 'string')
    local f    =  io.popen(('ffprobe -i "%s" -show_entries format=duration -v quiet -of csv="p=0"'):format(video_filename), 'r')
    local str  =  f:read '*all'
                  f:close()
    local len  =  tonumber(str)
    if type(len) ~= 'number' then
        error('Could not determine length of file "'..video_filename..'". ffprobe had this to say: '..str)
    end
    --
    return len
end

local function video_silences (video_filename, decibel, duration)
    assert(type(video_filename) == 'string')
    assert(type(decibel) == 'number')
    assert(type(duration) == 'number')
    --
    local log_filename  =  os.tmpname()
    os.execute(('ffmpeg -loglevel panic -y -i "%s" -af silencedetect=n=%sdB:d=%s -f null - 1> /dev/null 2> %s'):format(video_filename, decibel, duration, log_filename))
    local f = io.open(log_filename)
    local silences  =  {}
    for line in f:lines() do
        local silence_end, duration  =  line:gsub('\027%[.-;', ''):match '^%[silencedetect @ 0x%x+%]%s*silence_end:%s*([%d.]+)%s*|%s*silence_duration:%s*([%d.]+)$'
        if silence_end then
            local silence_end, duration  =  tonumber(silence_end), tonumber(duration)
            silences[#silences+1]  =  {
                start     =  silence_end - duration,
                stop      =  silence_end,
                duration  =  duration
            }
        end
    end
    f:close()
    return silences
end

local function video_silence_at_end (video_filename, ...)
    assert(type(video_filename) == 'string')
    --
    local silences  =  video_silences(video_filename, ...)
    local duration  =  video_length(video_filename)
    --
    for _, silence in ipairs(silences) do
        if math.abs(silence.stop - duration) < 0.1 then
            return silence
        end
    end
    --
    return nil
end

local function paste_audio_onto_video (video_filename, audio_filename, timestamp)
    timestamp = timestamp or 0
    assert(type(timestamp) == 'number')
    assert(type(video_filename) == 'string')
    assert(type(audio_filename) == 'string')
    print('Hah!', timestamp)

    -- Generate silence
    local silence_filename  =  TMP_FOLDER..'silence.mp3'
    os.execute(('ffmpeg -loglevel panic -y -f lavfi -i anullsrc=channel_layout=5.1:sample_rate=48000 -t %s %s &> /dev/null'):format(timestamp, silence_filename))

    -- Paste audio onto video
    local output_filename  =  TMP_FOLDER..'output.webm'
    local cmd  =  (('ffmpeg -loglevel panic -y -i "%s" -i "concat:%s|%s" -filter_complex "[0:a:0][1:a:0]amerge=inputs=2[a]" -map 0:v:0 -map "[a]" -c:v copy -c:a libvorbis -ac 2 -shortest %s &> /dev/null'):format(video_filename, silence_filename, audio_filename, output_filename))
    os.execute(cmd)

    return output_filename
end

--------------------------------------------------------------------------------

local CURB_YOUR_ENTHUSIASM_THEME_FILENAME  =  './sound/curb_your_enthusiasm_theme.mp3'
local DEFAULT_THEME_LENGTH  =  10

local function determine_timestamp_for_curb_your_video (video_filename)
    assert(type(video_filename) == 'string')
    --
    local silence_start
    local silence  =  video_silence_at_end(video_filename, -18, 1)
    local len      =  video_length(video_filename)
    local silence_end    =  len
    local silence_start  =  silence and silence.start or (len - 5)
    local silence_diff   =  silence_end - silence_start

    silence_end  =  math.max(len/2, silence_end - math.min(5, silence_diff))
    local silence_diff   =  silence_end - silence_start
    silence_start  =  math.max(len/2, silence_start + math.min(3, silence_diff))

    assert(len/2 <= silence_start and silence_start <= len)
    assert(len/2 <= silence_end   and silence_end   <= len)
    return (silence_start + silence_end) / 2
end

local function curb_your_video (video_url, timestamp)
    assert(type(video_url) == 'string')
    assert(type(timestamp) == 'number' or timestamp == nil)
    -- Download video
    ensure_tmp_folder_exists()
    local video_filename   =  internet.download_video(video_url)
    -- Figure out timestamp to start theme
    if timestamp == nil then
        timestamp  =  determine_timestamp_for_curb_your_video(video_filename)
        assert(type(timestamp) == 'number')
        assert(timestamp < video_length(video_filename))
    elseif timestamp < 0 then
        timestamp  =  video_length(video_filename)  +  timestamp
    end
    -- Paste audio
    print(timestamp)
    return paste_audio_onto_video(video_filename, CURB_YOUR_ENTHUSIASM_THEME_FILENAME, timestamp)
end

--------------------------------------------------------------------------------

return { your_video = curb_your_video }