/// <summary>
/// A default parser that parser sites like: https://www.npr.org/podcasts/510208/car-talk/partials?start=1
/// </summary>
public class EpisodeDataParser : IEpisodeDataParser
{
    #region Regular expressions

    /// <summary>
    /// The regular expression to extract the episode number and the title from the
    /// newer format of title - for example: '#1825: Male Moron Syndrome', or 'Car Talk #1029: The Pep's Lincoln'
    /// </summary>
    private static readonly Regex EpisodeTitleWithNumberAndNameRegex = new Regex("^(Car Talk )?#(\\d+): (.*)$");

    #endregion

    #region IEpisodeDataParser implementation

    /// <summary>
    /// Parser the given html and finds all the episodes that are contained within it.
    /// </summary>
    /// <param name="html">The html file.</param>
    /// <returns>The list of all retrieved episodes.</returns>
    public List<EpisodeData> Parse(string html)
    {
        // Create html document
        var document = new HtmlDocument();
        document.LoadHtml(html);

        // Find all the episodes. Take the document node
        return document.DocumentNode
            // Get all inner divs
            .Descendants("div")
            // With the item-info class
            .Where(node => node.HasClass("item-info"))
            // Cast each element to an episode
            .Select(episodeNode =>
            {
                #region Parse date

                // From episode node
                var dateString = episodeNode
                    // Get the first 'time' element
                    .Descendants("time").First()
                    // And the datetime attribute value
                    .Attributes["datetime"].Value;

                // Parse the date
                var date = DateTime.ParseExact(dateString, "yyyy-MM-dd", CultureInfo.InvariantCulture);

                #endregion

                #region Parse title and number

                // Find the full title. From the episode node
                var fullTitle = episodeNode
                    // Get the first h2 element
                    .Descendants("h2").First()
                    // And its inner text
                    .InnerText.Trim();

                // Prepare variables to hold the result
                var title = (string)null;
                var number = (int?)null;

                // Try to match the title with the new format
                var newEpisodeMatch = EpisodeTitleWithNumberAndNameRegex.Match(fullTitle);

                // If it matches...
                if (newEpisodeMatch.Success)
                {
                    // Then the first group is the episode number
                    number = int.Parse(newEpisodeMatch.Groups[2].Value);

                    // And the second one is the title
                    title = newEpisodeMatch.Groups[3].Value;
                }
                // Otherwise...
                else
                {
                    // Log the title
                    Console.WriteLine($"Cannot parse this title: {fullTitle}");

                    // Assume that this is not a correct episode
                    return null;
                }

                #endregion

                #region Parse download link

                // From the episode node
                var link = episodeNode
                    // Take the first li elements
                    .Descendants("li").First()
                    // Take the first a element
                    .Descendants("a").First()
                    // And its href value
                    .Attributes["href"].Value.Trim();

                #endregion

                #region Parse teaser

                // From the episode node
                var teaser = episodeNode
                    // Take the first p elements
                    .Descendants("p").First()
                    // Take the last child (text)
                    .LastChild.InnerText.Trim();

                #endregion

                // Return the date
                return new EpisodeData
                {
                    Date = date,
                    Number = number,
                    Title = title,
                    DownloadLink = link,
                    Teaser = teaser
                };
            })
            // Take only non-nulls (i.e. sucessfully parsed)
            .Where(episode => episode != null)
            // Cast them to list
            .ToList();
    }

    #endregion
}