Mixtape Application

mixtape_changes.json

{
  "playlists":
     [
      {
        "action": "add",
        "user_id": "7",
        "song_ids": [
          "3",
          "6"
        ]
      },
      {
        "action": "update",
        "id": "2",
        "song_id": "20"
      },
       {
         "action": "remove",
         "id": "1"
       }
     ]

}

mixtape_mixtape-app.py

import argparse
import json

class Mixtape:
    def __init__(self, mixtape, changes):
        self.mixtape = mixtape
        self.changes = changes
        self.playlists = {}
        self.playlist_idx = []
        self.songs = {}
        self.users = {}
        self.counter = 0

    def _parse_songs(self, songs):
        for song in songs:
            self.songs[song["id"]] = {
                "artist": song["artist"],
                "title": song["title"]
            }

    def _is_valid_song(self, songids):
        for songid in songids:
            if songid not in self.songs:
                return False
        return True

    def _is_valid_user(self, userid):
        if userid in self.users:
            return True
        return False

    def _parse_users(self, users):
        for user in users:
            self.users[user["id"]] = {
                "name": user["name"]
            }

    def _parse_playlists(self, playlists):
        for idx, playlist in enumerate(playlists):
            self.playlist_idx.append({
                                    "id": playlist["id"],
                                    "user_id": playlist["user_id"],
                                    "song_ids": playlist["song_ids"]
                                })
            self.counter += 1
            self.playlists[playlist["id"]] = len(self.playlist_idx) - 1

    def _is_valid_playlist(self, playlistid):
        if playlistid in self.playlists:
            return True
        return False

    def parse_mixtape(self):
        """ parse mixtape file """
        self._parse_songs(self.mixtape["songs"])
        self._parse_users(self.mixtape["users"])
        self._parse_playlists(self.mixtape["playlists"])

    def apply_changes(self):
        """ apply changes specified in changes.json to mixtape-data.json """
        self.parse_mixtape()
        for change in self.changes["playlists"]:
            if change["action"] == "add":
                self.add_playlist(change)
            elif change["action"] == "update":
                self.update_playlist(change)
            elif change["action"] == "remove":
                self.remove_playlist(change)

    def add_playlist(self, change):
        """ add a new playlist in O(1)"""
        if not change["song_ids"]:
            return
        if self._is_valid_song(change["song_ids"]) and self._is_valid_user(change["user_id"]):
            new_id = self.counter + 1
            self.playlist_idx.append({
                "id": new_id,
                "user_id": change["user_id"],
                "song_ids": change["song_ids"]
                })
            self.playlists[new_id] = len(self.playlist_idx) - 1

    def update_playlist(self, change):
        """ adds an existing song to an existing playlist in O(1)"""
        if self._is_valid_playlist(change["id"]) and self._is_valid_song([change["song_id"]]):
            playlist_idx = self.playlists[change["id"]]
            playlist_obj = self.playlist_idx[playlist_idx]
            playlist_obj.update({
                "song_ids": playlist_obj["song_ids"] + [change["song_id"]]
                })

    def remove_playlist(self, change):
        """ removes an existing playlist in O(1) """
        _id = change["id"]
        if self._is_valid_playlist(_id):
            remove_idx = self.playlists[_id]

            last_obj = self.playlist_idx[-1]
            self.playlist_idx[remove_idx], self.playlist_idx[-1] = self.playlist_idx[-1], self.playlist_idx[remove_idx]
            self.playlists[last_obj["id"]] = remove_idx

            del self.playlists[_id]
            self.playlist_idx.pop()

    def generate_output(self):
        """ writes output to output.json """
        mixtape = {"users": self.mixtape["users"],
                   "playlists": sorted(self.playlist_idx, key= lambda x: str(x["id"])),
                   "songs": self.mixtape["songs"]
                   }
        with open("output.json", 'w') as fd:
            json.dump(mixtape, fd, indent=4)

def main():
    # Parse arguments
    parser = argparse.ArgumentParser(description='mixtape application')
    parser.add_argument("mixtape", type=argparse.FileType("r"))
    parser.add_argument("changes", type=argparse.FileType("r"))
    args = parser.parse_args()
    handle_changes(args)

def handle_changes(args):
    # Read mixtape and change file
    with open(args.mixtape.name, 'r') as fd:
        mixtape = json.load(fd)
    with open(args.changes.name, 'r') as fd:
        changes = json.load(fd)
    m = Mixtape(mixtape, changes)
    m.apply_changes()
    m.generate_output()


if __name__ == '__main__':
    main()

mixtape_mixtape-data.json

{
  "users" : [
    {
      "id" : "1",
      "name" : "Albin Jaye"
    },
    {
      "id" : "2",
      "name" : "Dipika Crescentia"
    },
    {
      "id" : "3",
      "name" : "Ankit Sacnite"
    },
    {
      "id" : "4",
      "name" : "Galenos Neville"
    },
    {
      "id" : "5",
      "name" : "Loviise Nagib"
    },
    {
      "id" : "6",
      "name" : "Ryo Daiki"
    },
    {
      "id" : "7",
      "name" : "Seyyit Nedim"
    }
  ],
  "playlists" : [
    {
      "id" : "1",
      "user_id" : "2",
      "song_ids" : [
        "8",
        "32"
      ]
    },
    {
      "id" : "2",
      "user_id" : "3",
      "song_ids" : [
        "6",
        "8",
        "11"
      ]
    },
    {
      "id" : "3",
      "user_id" : "7",
      "song_ids" : [
        "7",
        "12",
        "13",
        "16",
        "2"
      ]
    }
  ],
  "songs": [
    {
      "id" : "1",
      "artist": "Camila Cabello",
      "title": "Never Be the Same"
    },
    {
      "id" : "2",
      "artist": "Zedd",
      "title": "The Middle"
    },
    {
      "id" : "3",
      "artist": "The Weeknd",
      "title": "Pray For Me"
    },
    {
      "id" : "4",
      "artist": "Drake",
      "title": "God's Plan"
    },
    {
      "id" : "5",
      "artist": "Bebe Rexha",
      "title": "Meant to Be"
    },
    {
      "id" : "6",
      "artist": "Imagine Dragons",
      "title": "Whatever It Takes"
    },
    {
      "id" : "7",
      "artist": "Maroon 5",
      "title": "Wait"
    },
    {
      "id" : "8",
      "artist": "Bazzi",
      "title": "Mine"
    },
    {
      "id" : "9",
      "artist": "Marshmello",
      "title": "FRIENDS"
    },
    {
      "id" : "10",
      "artist": "Dua Lipa",
      "title": "New Rules"
    },
    {
      "id" : "11",
      "artist": "Shawn Mendes",
      "title": "In My Blood"
    },
    {
      "id" : "12",
      "artist": "Post Malone",
      "title": "Psycho"
    },
    {
      "id" : "13",
      "artist": "Ariana Grande",
      "title": "No Tears Left To Cry"
    },
    {
      "id" : "14",
      "artist": "Bruno Mars",
      "title": "Finesse"
    },
    {
      "id" : "15",
      "artist": "Kendrick Lamar",
      "title": "All The Stars"
    },
    {
      "id" : "16",
      "artist": "G-Eazy",
      "title": "Him & I"
    },
    {
      "id" : "17",
      "artist": "Lauv",
      "title": "I Like Me Better"
    },
    {
      "id" : "18",
      "artist": "NF",
      "title": "Let You Down"
    },
    {
      "id" : "19",
      "artist": "Dua Lipa",
      "title": "IDGAF"
    },
    {
      "id" : "20",
      "artist": "Taylor Swift",
      "title": "Delicate"
    },
    {
      "id" : "21",
      "artist": "Calvin Harris",
      "title": "One Kiss"
    },
    {
      "id" : "22",
      "artist": "Ed Sheeran",
      "title": "Perfect"
    },
    {
      "id" : "23",
      "artist": "Meghan Trainor",
      "title": "No Excuses"
    },
    {
      "id" : "24",
      "artist": "Niall Horan",
      "title": "On The Loose"
    },
    {
      "id" : "25",
      "artist": "Halsey",
      "title": "Alone"
    },
    {
      "id" : "26",
      "artist": "Charlie Puth",
      "title": "Done For Me"
    },
    {
      "id" : "27",
      "artist": "Foster The People",
      "title": "Sit Next to Me"
    },
    {
      "id" : "28",
      "artist": "Max",
      "title": "Lights Down Low"
    },
    {
      "id" : "29",
      "artist": "Alice Merton",
      "title": "No Roots"
    },
    {
      "id" : "30",
      "artist": "5 Seconds Of Summer",
      "title": "Want You Back"
    },
    {
      "id" : "31",
      "artist": "Camila Cabello",
      "title": "Havana"
    },
    {
      "id" : "32",
      "artist": "Logic",
      "title": "Everyday"
    },
    {
      "id" : "33",
      "artist": "Drake",
      "title": "Nice For What"
    },
    {
      "id" : "34",
      "artist": "Halsey",
      "title": "Bad At Love"
    },
    {
      "id" : "35",
      "artist": "ZAYN",
      "title": "Let Me"
    },
    {
      "id" : "36",
      "artist": "Khalid",
      "title": "Love Lies"
    },
    {
      "id" : "37",
      "artist": "Post Malone",
      "title": "rockstar"
    },
    {
      "id" : "38",
      "artist": "Rudimental",
      "title": "These Days"
    },
    {
      "id" : "39",
      "artist": "Liam Payne",
      "title": "Familiar"
    },
    {
      "id" : "40",
      "artist": "Imagine Dragons",
      "title": "Thunder"
    }
  ]
}

mixtape_output.json

{
    "users": [
        {
            "id": "1",
            "name": "Albin Jaye"
        },
        {
            "id": "2",
            "name": "Dipika Crescentia"
        },
        {
            "id": "3",
            "name": "Ankit Sacnite"
        },
        {
            "id": "4",
            "name": "Galenos Neville"
        },
        {
            "id": "5",
            "name": "Loviise Nagib"
        },
        {
            "id": "6",
            "name": "Ryo Daiki"
        },
        {
            "id": "7",
            "name": "Seyyit Nedim"
        }
    ],
    "playlists": [
        {
            "id": "2",
            "user_id": "3",
            "song_ids": [
                "6",
                "8",
                "11",
                "20"
            ]
        },
        {
            "id": "3",
            "user_id": "7",
            "song_ids": [
                "7",
                "12",
                "13",
                "16",
                "2"
            ]
        },
        {
            "id": 4,
            "user_id": "7",
            "song_ids": [
                "3",
                "6"
            ]
        }
    ],
    "songs": [
        {
            "id": "1",
            "artist": "Camila Cabello",
            "title": "Never Be the Same"
        },
        {
            "id": "2",
            "artist": "Zedd",
            "title": "The Middle"
        },
        {
            "id": "3",
            "artist": "The Weeknd",
            "title": "Pray For Me"
        },
        {
            "id": "4",
            "artist": "Drake",
            "title": "God's Plan"
        },
        {
            "id": "5",
            "artist": "Bebe Rexha",
            "title": "Meant to Be"
        },
        {
            "id": "6",
            "artist": "Imagine Dragons",
            "title": "Whatever It Takes"
        },
        {
            "id": "7",
            "artist": "Maroon 5",
            "title": "Wait"
        },
        {
            "id": "8",
            "artist": "Bazzi",
            "title": "Mine"
        },
        {
            "id": "9",
            "artist": "Marshmello",
            "title": "FRIENDS"
        },
        {
            "id": "10",
            "artist": "Dua Lipa",
            "title": "New Rules"
        },
        {
            "id": "11",
            "artist": "Shawn Mendes",
            "title": "In My Blood"
        },
        {
            "id": "12",
            "artist": "Post Malone",
            "title": "Psycho"
        },
        {
            "id": "13",
            "artist": "Ariana Grande",
            "title": "No Tears Left To Cry"
        },
        {
            "id": "14",
            "artist": "Bruno Mars",
            "title": "Finesse"
        },
        {
            "id": "15",
            "artist": "Kendrick Lamar",
            "title": "All The Stars"
        },
        {
            "id": "16",
            "artist": "G-Eazy",
            "title": "Him & I"
        },
        {
            "id": "17",
            "artist": "Lauv",
            "title": "I Like Me Better"
        },
        {
            "id": "18",
            "artist": "NF",
            "title": "Let You Down"
        },
        {
            "id": "19",
            "artist": "Dua Lipa",
            "title": "IDGAF"
        },
        {
            "id": "20",
            "artist": "Taylor Swift",
            "title": "Delicate"
        },
        {
            "id": "21",
            "artist": "Calvin Harris",
            "title": "One Kiss"
        },
        {
            "id": "22",
            "artist": "Ed Sheeran",
            "title": "Perfect"
        },
        {
            "id": "23",
            "artist": "Meghan Trainor",
            "title": "No Excuses"
        },
        {
            "id": "24",
            "artist": "Niall Horan",
            "title": "On The Loose"
        },
        {
            "id": "25",
            "artist": "Halsey",
            "title": "Alone"
        },
        {
            "id": "26",
            "artist": "Charlie Puth",
            "title": "Done For Me"
        },
        {
            "id": "27",
            "artist": "Foster The People",
            "title": "Sit Next to Me"
        },
        {
            "id": "28",
            "artist": "Max",
            "title": "Lights Down Low"
        },
        {
            "id": "29",
            "artist": "Alice Merton",
            "title": "No Roots"
        },
        {
            "id": "30",
            "artist": "5 Seconds Of Summer",
            "title": "Want You Back"
        },
        {
            "id": "31",
            "artist": "Camila Cabello",
            "title": "Havana"
        },
        {
            "id": "32",
            "artist": "Logic",
            "title": "Everyday"
        },
        {
            "id": "33",
            "artist": "Drake",
            "title": "Nice For What"
        },
        {
            "id": "34",
            "artist": "Halsey",
            "title": "Bad At Love"
        },
        {
            "id": "35",
            "artist": "ZAYN",
            "title": "Let Me"
        },
        {
            "id": "36",
            "artist": "Khalid",
            "title": "Love Lies"
        },
        {
            "id": "37",
            "artist": "Post Malone",
            "title": "rockstar"
        },
        {
            "id": "38",
            "artist": "Rudimental",
            "title": "These Days"
        },
        {
            "id": "39",
            "artist": "Liam Payne",
            "title": "Familiar"
        },
        {
            "id": "40",
            "artist": "Imagine Dragons",
            "title": "Thunder"
        }
    ]
}

mixtape_README.md

Mixtape Application

Python version 3.6

Description

Mixtape Application reads data from mixtape-data.json, loads it to memory.
Also reads changes.json, loads to memory and applies them to mixtape-data.json and produces output.json

Input File Formats:

mixtape-data.json - JSON
changes.json - JSON

Output File Format:

output.json - JSON

Usage:

Tested and Verified in Windows, expected to work in Linux, Mac

Takes two arguments mixtape-data.sjon, changes.json

python mixtape-app.py mixtape-data.json changes.json

Supported Operations:

1. Add a new playlist

    Create a dictionary object with song_ids, user_id, action: "add"
   

2. Add a new song to an existing playlist

    Create a dictionary object with playlist id, song_id, action: "update"
    Supports only one song update at a time, can be easily expanded to support multiple songs by changing the data type
   

3. Remove a playlist

    Create a dictionary object with id, action: "delete"
    Supports to remove only one playlist at a time, can be easily expanded to remove multiple playlists by changing the data type
   

Sample changes.json File:

{
  "playlists":
     [
      {
        "action": "add",
        "user_id": "7",
        "song_ids": [
          "3",
          "6"
        ]
      },
      {
        "action": "update",
        "id": "2",
        "song_id": "20"
      },
       {
         "action": "remove",
         "id": "1"
       }
     ]
}  

Time Complexity:

Now all the operations are done in O(1)

Scaling

As the files get larger, memory will be an issue and reading, writing to a file will not be efficient.

mixtape-data.json is the reference file, needs to be loaded somewhere first before applying changes.json one change at a time.

As there are relations between playlists, user, song, it would be efiicient to store it in a Relational DB like MySQL, 
distributed DB(if needed)

If changes.json gets larger, can be read in chunks and apply the changes iteratively to the mixtape-data.json file. 
Instaed of json, needs to be jsonl. changes.jsonl will have the json inputs in lines.

Assumptions

mixtape-data.json will always have some songs, users, playlists