using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Windows.Forms;
using System.Xml;
using System.Text;

namespace ToeCracker {
    /// <summary>
    /// Methods to look up a word in the thesaurus and parse the results.
    /// </summary>
    public static class Thesaurus {
        private const string RESULT_HEADER = "<div class=\"results\">";
        private const string RESULT_FOOTER = "</div>";

        /// <summary>
        /// A dictionary mapping English word group keys with translated values.
        /// Some keys might be missing, in which case they should be displayed as they are;
        /// you might want to open an issue to request those translations to be added.
        /// </summary>
        public static Dictionary<string, string> Translations {
            get {
                Dictionary<string, string> tr = new Dictionary<string, string>();
                tr["adjective"] = Properties.Resources.Adjective;
                tr["adverb"] = Properties.Resources.Verb;
                tr["noun"] = Properties.Resources.Noun;
                tr["sounds kind of like"] = Properties.Resources.SoundsLike;
                tr["rhymes with"] = Properties.Resources.RhymesWith;
                tr["verb"] = Properties.Resources.Verb;
                return tr;
            }
        }

        private static Uri BuildURI(string query) {
            return new Uri(String.Format(Properties.Settings.Default.BaseURL, query), UriKind.Absolute);
        }

        /// <summary>
        /// Look up a word in the thesaurus and return the results.
        /// </summary>
        /// <param name="query">Word to look for.</param>
        /// <returns>A dictionary holding an array of words for each word group.</returns>
        public static Dictionary<string, string[]> Search(string query) {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(BuildURI(query));
            request.UserAgent = String.Format("{0}/{1}", Application.ProductName, Application.ProductVersion);
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            if ((int)response.StatusCode < 200 || (int)response.StatusCode > 299)
                throw new WebException(String.Format("Unexpected HTTP status code {0}", response.StatusCode));

            XmlDocument doc = new XmlDocument();

            using (Stream stream = response.GetResponseStream()) {
                /*
                 * The HTML response is not XHTML, so we cannot parse it as XML at first.
                 * However, the search results (including a "Not found" error) are in a div tag
                 * whose contents can be parsed using an XML parser.
                 * We will look for the beginning of this <div> tag in the stream, read until the </div>,
                 * then parse it as XML.
                 */
                using (StreamReader reader = new StreamReader(stream)) {
                    StringBuilder sb = new StringBuilder(RESULT_HEADER);
                    string line;
                    while ((line = reader.ReadLine()) != null) {
                        if (line.Contains(RESULT_HEADER))
                            break;
                    }
                    if (line == null)
                        throw new XmlException("Result block not found.");

                    while ((line = reader.ReadLine()) != null) {
                        sb.AppendLine(line);
                        if (line.Contains(RESULT_FOOTER))
                            break;
                    }
                    if (line == null)
                        throw new XmlException("End of result block not found.");

                    doc.LoadXml(sb.ToString());
                }
            }

            /*
             * We can now iterate on the nodes inside of the <div>. We can expect three types of tags:
             * - <h2>, which contains the word we just searched and that we can ignore
             * - <h3>, the beginning of a new word group
             * - <ul>, listing words inside a new group.
             * We will ignore any other tags to stay flexible.
             */
            Dictionary<string, string[]> results = new Dictionary<string, string[]>();
            string groupName = null;
            List<string> words = new List<string>();

            foreach (XmlNode node in doc.ChildNodes[0].ChildNodes) {
                if (node.NodeType != XmlNodeType.Element)
                    continue;
                // Beginning of a new word group
                if (node.Name.ToLowerInvariant() == "h3") {
                    if (groupName != null && words.Count > 0) {
                        // End the current group, store it in the dictionary.
                        if (results.ContainsKey(groupName)) {
                            // Group names should only be unique, but we will tolerate duplicate group names by concatenating the word lists
                            List<string> newWords = new List<string>(results[groupName]);
                            newWords.AddRange(words);
                            results[groupName] = newWords.ToArray();
                        } else {
                            results[groupName] = words.ToArray();
                        }
                        words.Clear();
                    }
                    groupName = node.InnerText;
                } else if (node.Name.ToLowerInvariant() == "ul") {
                    if (groupName == null)
                        throw new XmlException("Unexpected word list with no group name.");
                    foreach (XmlNode listItem in node.ChildNodes) {
                        if (listItem.NodeType == XmlNodeType.Element && listItem.Name == "li")
                            words.Add(listItem.InnerText);
                    }
                }
            }

            // Once we have finished iterating, there might be one remaining group to add to the dictionary.
            if (groupName != null && words.Count > 0) {
                if (results.ContainsKey(groupName)) {
                    // Group names should only be unique, but we will tolerate duplicate group names by concatenating the word lists
                    List<string> newWords = new List<string>(results[groupName]);
                    newWords.AddRange(words);
                    results[groupName] = newWords.ToArray();
                } else {
                    results[groupName] = words.ToArray();
                }
            }

            return results;
        }
    }
}