using System.Text.RegularExpressions;

namespace Application.Features.Api.Feed.Shared;

public static partial class FeedContent
{
    [GeneratedRegex(@"<[^>]+>", RegexOptions.Compiled)]
    private static partial Regex HtmlTagRegex();

    [GeneratedRegex(@"\s+", RegexOptions.Compiled)]
    private static partial Regex WhitespaceRegex();

    public static string Excerpt(string? html, int maxLength)
    {
        if (string.IsNullOrWhiteSpace(html))
        {
            return string.Empty;
        }

        var stripped = HtmlTagRegex().Replace(html, " ");
        var normalized = WhitespaceRegex().Replace(stripped, " ").Trim();

        if (normalized.Length <= maxLength)
        {
            return normalized;
        }

        return string.Concat(normalized.AsSpan(0, maxLength), "…");
    }

    [GeneratedRegex(@"#([\p{L}\p{N}_가-힣]+)", RegexOptions.Compiled)]
    public static partial Regex HashtagRegex();

    [GeneratedRegex(@"@([A-Za-z0-9]{3,20})", RegexOptions.Compiled)]
    public static partial Regex MentionRegex();

    public static List<string> ExtractHashtags(string? text, int maxTags = 10)
    {
        if (string.IsNullOrWhiteSpace(text))
        {
            return [];
        }

        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        var result = new List<string>();

        foreach (Match m in HashtagRegex().Matches(text))
        {
            var tag = m.Groups[1].Value;
            if (seen.Add(tag))
            {
                result.Add(tag);
                if (result.Count >= maxTags)
                {
                    break;
                }
            }
        }

        return result;
    }

    public static List<string> ExtractMentions(string? text, int maxMentions = 20)
    {
        if (string.IsNullOrWhiteSpace(text))
        {
            return [];
        }

        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        var result = new List<string>();

        foreach (Match m in MentionRegex().Matches(text))
        {
            var sid = m.Groups[1].Value;
            if (seen.Add(sid))
            {
                result.Add(sid);
                if (result.Count >= maxMentions)
                {
                    break;
                }
            }
        }

        return result;
    }
}