#!/usr/bin/env lua

--[[
Challenge 103

TASK #2 › What’s playing?
Submitted by: Albert Croft
Working from home, you decided that on occasion you wanted some background
noise while working. You threw together a network streamer to continuously
loop through the files and launched it in a tmux (or screen) session, giving
it a directory tree of files to play. During the day, you connected an audio
player to the stream, listening through the workday, closing it when done.

For weeks you connect to the stream daily, slowly noticing a gradual drift of
the media. After several weeks, you take vacation. When you return, you are
pleasantly surprised to find the streamer still running. Before connecting,
however, if you consider the puzzle of determining which track is playing.

After looking at a few modules to read info regarding the media, a quick bit
of coding gave you a file list. The file list is in a simple CSV format, each
line containing two fields: the first the number of milliseconds in length,
the latter the media’s title (this example is of several episodes available
from the MercuryTheatre.info):

    1709363,"Les Miserables Episode 1: The Bishop (broadcast date: 1937-07-23)"
    1723781,"Les Miserables Episode 2: Javert (broadcast date: 1937-07-30)"
    1723781,"Les Miserables Episode 3: The Trial (broadcast date: 1937-08-06)"
    1678356,"Les Miserables Episode 4: Cosette (broadcast date: 1937-08-13)"
    1646043,"Les Miserables Episode 5: The Grave (broadcast date: 1937-08-20)"
    1714640,"Les Miserables Episode 6: The Barricade (broadcast date: 1937-08-27)"
    1714640,"Les Miserables Episode 7: Conclusion (broadcast date: 1937-09-03)"
For this script, you can assume to be provided the following information:

    * the value of $^T ($BASETIME) of the streamer script,
    * the value of time(), and
    * a CSV file containing the media to play consisting of the length in
milliseconds and an identifier for the media (title, filename, or other).
Write a program to output which file is currently playing. For purposes of
this script, you may assume gapless playback, and format the output as you
see fit.

Optional: Also display the current position in the media as a time-like value.

Example:

Input: 3 command line parameters: start time, current time, file name

    # Streamer start time: Tue Nov 23 12:22:03 2020
    1606134123

    # Current time:        Mon Mar  1 09:34:36 2021
    1614591276

    # filelist.csv

Output:

    "Les Miserables Episode 1: The Bishop (broadcast date: 1937-07-23)"
    00:17:33
--]]

start_secs    = tonumber(arg[1])
current_secs  = tonumber(arg[2])
playlist_file = arg[3]

-- read playlist
playlist = {}
playlist_total_secs = 0
for line in io.lines(playlist_file) do
    local ms, title = line:match('%s*(.-),%s*"(.-)"')
    local secs = math.floor(tonumber(ms)/1000+0.5)
    table.insert(playlist, { secs, title })
    playlist_total_secs = playlist_total_secs + secs
end

-- compute location
total_secs = current_secs - start_secs
playlist_secs = total_secs % playlist_total_secs

-- find current track
for k, v in pairs(playlist) do
    local secs, title = v[1], v[2]
    if playlist_secs < secs then            -- playing this title
        io.write(title, "\n")

        local hh = math.floor(playlist_secs / 3600)
        playlist_secs = playlist_secs % 3600
        local mm = math.floor(playlist_secs / 60)
        playlist_secs = playlist_secs % 60
        local ss = playlist_secs

        io.write(string.format("%02d:%02d:%02d", hh, mm, ss), "\n")
        break
    else
        playlist_secs = playlist_secs - secs
    end
end