packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="Newtonsoft.Json" version="4.5.10" targetFramework="net45" />
  <package id="taglib" version="2.1.0.0" targetFramework="net45" />
</packages>

Program.cs

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;
using System.Web;

namespace SpotifyImporter
{
    public class SongInfo
    {
        public string Artist { get; set; }
        public string Title { get; set; }
        public double Duration { get; set; }

        public override string ToString()
        {
            return Artist + " - " + Title;
        }
    }

    class Program
    {
        public static List<string> invalid = new List<string>();
        public static HashSet<SongInfo> songs = new HashSet<SongInfo>();

        static void Main(string[] args)
        {
            var lines = File.ReadAllLines("playlist.m3u");
            foreach (var line in lines)
            {
                if (line.StartsWith("#")) continue;
                if (String.IsNullOrWhiteSpace(line)) continue;

                if (File.Exists(line))
                {
                    using (var file = TagLib.File.Create(line))
                    {
                        var filename = Path.GetFileNameWithoutExtension(line);
                        var split = filename.Split('-');

                        var title = file.Tag.Title;
                        if (String.IsNullOrWhiteSpace(title))
                        {
                            title = null;
                            if (split.Length >= 2) title = split[1].Trim();
                            if (String.IsNullOrWhiteSpace(title))
                            {
                                invalid.Add(filename);
                                continue;
                            }
                        }

                        var artist = file.Tag.Performers.FirstOrDefault();
                        if (String.IsNullOrWhiteSpace(artist))
                        {
                            artist = file.Tag.AlbumArtists.FirstOrDefault();
                            if (String.IsNullOrWhiteSpace(artist))
                            {
                                artist = split[0].Trim();
                                if (String.IsNullOrWhiteSpace(artist))
                                {
                                    invalid.Add(filename);
                                    continue;
                                }
                            }
                        }

                        var song = new SongInfo
                        {
                            Artist = artist,
                            Title = title,
                            Duration = file.Properties.Duration.TotalSeconds
                        };
                        Console.WriteLine(song);
                        songs.Add(song);
                    }
                }
            }

            PrintInvalid("Could not determine metadata for:");

            Console.WriteLine();
            invalid.Clear();

            var output = new List<string>();
            foreach (var song in songs)
            {
                var response = Get<Response>("search", "track", song.Artist + " " + song.Title);
                var orderedTracks = response.Tracks.OrderBy(x => LevenshteinDistance.Compute(x.Artists.First().Name, song.Artist)).ThenBy(x => Math.Abs(x.Length - song.Duration));

                var bestMatch = orderedTracks.FirstOrDefault();
                if (bestMatch == null)
                {
                    invalid.Add(song.ToString());
                    continue;
                }

                output.Add(bestMatch.Href);
                System.Threading.Thread.Sleep(100); // limit API rate
            }

            PrintInvalid("Could not find tracks for:");
            File.WriteAllLines("notfound.txt", invalid);

            Console.WriteLine("Done! Generated output.txt");
            File.WriteAllLines("output.txt", output);

            Console.ReadLine();
        }

        public static void PrintInvalid(string msg)
        {
            if (invalid.Any())
            {
                Console.WriteLine();
                Console.WriteLine(msg);
                foreach (var file in invalid)
                {
                    Console.WriteLine("- " + file);
                }
            }
        }

        public class Response
        {
            public class ResponseInfo
            {
                [JsonProperty("num_results")]
                public int NumResults { get; set; }

                public int Limit { get; set; }
                public int Offset { get; set; }
                public int Page { get; set; }
            }

            public class ArtistInfo
            {
                public string Name { get; set; }
            }

            public class TrackInfo
            {
                public string Name { get; set; }
                public string Href { get; set; }
                public double Length { get; set; }
                public IEnumerable<ArtistInfo> Artists { get; set; }
            }

            public ResponseInfo Info { get; set; }
            public IEnumerable<TrackInfo> Tracks { get; set; }
        }

        static T Get<T>(string service, string method, string parameters = null) where T : class
        {
            var url = String.Format("http://ws.spotify.com/{0}/1/{1}", service, method);
            if (!String.IsNullOrWhiteSpace(parameters))
            {
                url += "?q=" + HttpUtility.UrlEncode(parameters);
            }

            string text = null;
            bool done = false;
            while (!done)
            {
                try
                {
                    Console.WriteLine("Requesting: " + url);

                    var request = (HttpWebRequest)HttpWebRequest.Create(url);
                    request.Accept = "application/json";

                    var response = (HttpWebResponse)request.GetResponse();

                    using (var sr = new StreamReader(response.GetResponseStream()))
                    {
                        text = sr.ReadToEnd();
                    }

                    done = true;
                }
                catch (WebException ex)
                {
                    Console.WriteLine("Exception: " + ex.Message);
                    Console.WriteLine("Retrying in 1 second...");
                    System.Threading.Thread.Sleep(1000);
                }
            }

            if (String.IsNullOrEmpty(text)) throw new InvalidOperationException();

            return JsonConvert.DeserializeObject<T>(text);
        }

        // http://www.dotnetperls.com/levenshtein
        static class LevenshteinDistance
        {
            /// <summary>
            /// Compute the distance between two strings.
            /// </summary>
            public static int Compute(string s, string t)
            {
                int n = s.Length;
                int m = t.Length;
                int[,] d = new int[n + 1, m + 1];

                // Step 1
                if (n == 0)
                {
                    return m;
                }

                if (m == 0)
                {
                    return n;
                }

                // Step 2
                for (int i = 0; i <= n; d[i, 0] = i++)
                {
                }

                for (int j = 0; j <= m; d[0, j] = j++)
                {
                }

                // Step 3
                for (int i = 1; i <= n; i++)
                {
                    //Step 4
                    for (int j = 1; j <= m; j++)
                    {
                        // Step 5
                        int cost = (t[j - 1] == s[i - 1]) ? 0 : 1;

                        // Step 6
                        d[i, j] = Math.Min(
                            Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1),
                            d[i - 1, j - 1] + cost);
                    }
                }
                // Step 7
                return d[n, m];
            }
        }

    }
}