using System.Net;
using System.Text.RegularExpressions;

namespace Journal.Core.Services.Entries;

public static class HtmlSanitizer
{
    public static string StripRichHtml(string content)
    {
        if (string.IsNullOrWhiteSpace(content))
            return content;
        if (!LooksLikeRichHtml(content))
            return content;

        var text = content.Replace("\r\n", "\n").Replace("\r", "\n");
        text = Regex.Replace(text, "<(script|style)\\b[^>]*>.*?</\\1>", "", RegexOptions.IgnoreCase | RegexOptions.Singleline);
        text = Regex.Replace(text, "<br\\s*/?>", "\n", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "</(p|div|h[1-6]|tr|table|ul|ol|blockquote)>", "\n", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "<li\\b[^>]*>", "\n- ", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "</li>", "\n", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "<(td|th)\\b[^>]*>", " | ", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "</(td|th)>", " ", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "<hr\\b[^>]*>", "\n---\n", RegexOptions.IgnoreCase);
        text = Regex.Replace(text, "<[^>]+>", "", RegexOptions.Singleline);
        text = WebUtility.HtmlDecode(text)
            .Replace('\u00a0', ' ')
            .Replace("\u200b", "", StringComparison.Ordinal);
        text = string.Join("\n", text.Split('\n').Select(line => line.TrimEnd()));
        text = Regex.Replace(text, "[ \\t]{2,}", " ");
        text = Regex.Replace(text, "\n{3,}", "\n\n").Trim();
        return string.IsNullOrEmpty(text) ? content : text;
    }

    public static bool LooksLikeRichHtml(string content)
    {
        var lowered = content.ToLowerInvariant();
        string[] markers =
        [
            "<p", "</p>", "<div", "<span", "<table", "<tr", "<td", "<li", "<ul", "<ol",
            "style=", "font-family:", "-webkit-text-stroke"
        ];
        if (markers.Any(marker => lowered.Contains(marker, StringComparison.Ordinal)))
            return true;
        return Regex.Matches(lowered, "</?[a-z][^>]*>").Count >= 8;
    }
}