using System.Globalization;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using HtmlAgilityPack;

namespace wp2ghost
{
    // =============================================================================
    // CommentBlockBuilder — WordPress-Kommentare als lesbaren Block ans Beitragsende hängen.
    // Ghost bietet keinen Weg, Kommentare zu importieren; so bleiben Name, Datum und Text
    // erhalten, ohne dass Mitglieder angelegt oder E-Mail-Adressen übertragen werden.
    // =============================================================================
    static class CommentBlockBuilder
    {
        // Kennzeichnet den Block im HTML (und ist die CSS-Klasse für das Theme)
        private const string BlockClass = "wp-comments";

        private static readonly CultureInfo German = CultureInfo.GetCultureInfo("de-AT");
        private static readonly HashSet<string> AllowedTags = new() { "a", "p", "br", "strong", "b", "em", "i", "blockquote", "code" };

        // Pingbacks ("[…] Auszug […]") und Fediverse-Reaktionen ("… gefiel dies!") sind keine Kommentare
        private static readonly Regex PingbackRegex = new(@"^\[(…|\.\.\.)\]", RegexOptions.Compiled);
        private static readonly Regex ReactionRegex = new(@"^(…|\.\.\.)\s*(gefiel dies|hat dies repostet)", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        public static bool IsRealComment(WpComment comment)
        {
            // Neuere Plugin-Version liefert den Typ mit
            if (!string.IsNullOrEmpty(comment.Type))
                return comment.Type == "comment";

            string text = WebUtility.HtmlDecode(comment.Content ?? "").Trim();
            return text.Length > 0 && !PingbackRegex.IsMatch(text) && !ReactionRegex.IsMatch(text);
        }

        public static int CountRealComments(IEnumerable<WpComment>? comments) => (comments ?? Enumerable.Empty<WpComment>()).Count(IsRealComment);

        /// <summary>Hängt den Kommentar-Block an (einmalig — ein vorhandener Block wird nicht verdoppelt).</summary>
        public static string Append(string html, IEnumerable<WpComment>? comments)
        {
            if (html.Contains($"class=\"{BlockClass}\"")) return html;
            string block = Build(comments);
            return block.Length > 0 ? html + "\n" + block : html;
        }

        public static string Build(IEnumerable<WpComment>? comments)
        {
            var real = (comments ?? Enumerable.Empty<WpComment>())
                .Where(IsRealComment)
                .OrderBy(c => ParseDate(c.Date) ?? DateTime.MaxValue)
                .ThenBy(c => c.Id)
                .ToList();
            if (real.Count == 0) return "";

            // Antworten unter ihren Kommentar hängen; fehlt der Bezug, steht der Kommentar auf oberster Ebene
            var ids = real.Select(c => c.Id).ToHashSet();
            var repliesByParent = real.Where(c => c.Parent > 0 && c.Parent != c.Id && ids.Contains(c.Parent)).ToLookup(c => c.Parent);
            var topLevel = real.Where(c => !(c.Parent > 0 && c.Parent != c.Id && ids.Contains(c.Parent)));

            var sb = new StringBuilder();
            // HTML-Karte: Ghost übernimmt den Inhalt unverändert
            sb.Append("<!--kg-card-begin: html-->\n");
            sb.Append($"<section class=\"{BlockClass}\">\n");
            sb.Append($"<h2 class=\"wp-comments__title\">Kommentare aus dem alten Blog ({real.Count})</h2>\n");
            AppendList(sb, topLevel, repliesByParent, isReplies: false, depth: 0);
            sb.Append("</section>\n");
            sb.Append("<!--kg-card-end: html-->");
            return sb.ToString();
        }

        private static void AppendList(StringBuilder sb, IEnumerable<WpComment> comments, ILookup<int, WpComment> repliesByParent, bool isReplies, int depth)
        {
            sb.Append(isReplies ? "<ol class=\"wp-comments__list wp-comments__replies\">\n" : "<ol class=\"wp-comments__list\">\n");
            foreach (var comment in comments)
            {
                string name = WebUtility.HtmlEncode(WebUtility.HtmlDecode(comment.AuthorName ?? "").Trim());
                if (name.Length == 0) name = "Anonym";
                var date = ParseDate(comment.Date);

                sb.Append($"<li class=\"wp-comment\" id=\"wp-comment-{comment.Id}\">\n");
                sb.Append($"<div class=\"wp-comment__meta\"><span class=\"wp-comment__author\">{name}</span>");
                if (date.HasValue)
                    sb.Append($" <time class=\"wp-comment__date\" datetime=\"{date.Value:yyyy-MM-dd}\">{date.Value.ToString("d. MMMM yyyy", German)}</time>");
                sb.Append("</div>\n");
                sb.Append($"<div class=\"wp-comment__text\">{SanitizeContent(comment.Content ?? "")}</div>\n");

                // Tiefe begrenzen, falls die Bezüge in WordPress einen Kreis bilden
                if (depth < 10 && repliesByParent[comment.Id].Any())
                    AppendList(sb, repliesByParent[comment.Id], repliesByParent, isReplies: true, depth + 1);
                sb.Append("</li>\n");
            }
            sb.Append("</ol>\n");
        }

        private static DateTime? ParseDate(string? date) =>
            DateTime.TryParse(date, CultureInfo.InvariantCulture, DateTimeStyles.None, out var parsed) ? parsed : null;

        /// <summary>
        /// Kommentartext ist fremde Eingabe: nur einfache Formatierung bleibt erhalten,
        /// alles andere (Skripte, Attribute, unbekannte Tags) wird entfernt.
        /// </summary>
        private static string SanitizeContent(string content)
        {
            var doc = new HtmlDocument();
            doc.LoadHtml(content);

            foreach (var node in doc.DocumentNode.Descendants().Where(n => n.NodeType == HtmlNodeType.Comment || n.Name is "script" or "style").ToList())
                node.Remove();

            foreach (var element in doc.DocumentNode.Descendants().Where(n => n.NodeType == HtmlNodeType.Element).ToList())
            {
                if (!AllowedTags.Contains(element.Name))
                {
                    // Tag entfernen, Inhalt behalten
                    foreach (var child in element.ChildNodes.ToList())
                        element.ParentNode!.InsertBefore(child, element);
                    element.Remove();
                    continue;
                }

                string href = element.Name == "a" ? HtmlEntity.DeEntitize(element.GetAttributeValue("href", "")).Trim() : "";
                element.Attributes.RemoveAll();
                if (element.Name != "a") continue;

                if (href.StartsWith("http://", StringComparison.OrdinalIgnoreCase) || href.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
                {
                    element.SetAttributeValue("href", href);
                    element.SetAttributeValue("rel", "nofollow noopener");
                }
            }

            string html = doc.DocumentNode.InnerHtml.Replace("\r\n", "\n").Trim();
            if (html.Contains("<p", StringComparison.OrdinalIgnoreCase)) return html;

            // Wie WordPress: Leerzeile = neuer Absatz, Zeilenumbruch = <br>
            var paragraphs = Regex.Split(html, @"\n\s*\n").Select(p => p.Trim()).Where(p => p.Length > 0);
            return string.Concat(paragraphs.Select(p => $"<p>{p.Replace("\n", "<br>")}</p>"));
        }
    }
}