namespace Dpz.Core.Web.Models;

/// <summary>
/// Markdown 链接解析结果分类
/// </summary>
public enum CodeReadmeLinkKind
{
    /// <summary>
    /// 无需处理（空链接 / 同页锚点 / 查询串）
    /// </summary>
    Keep = 0,

    /// <summary>
    /// 外部链接（浏览器新窗口打开）
    /// </summary>
    External = 1,

    /// <summary>
    /// 仓库内路径（重写为代码浏览页地址）
    /// </summary>
    RepoPath = 2,
}

/// <summary>
/// Markdown 链接解析结果
/// </summary>
public sealed record CodeReadmeLinkResolution(
    CodeReadmeLinkKind Kind,
    string? RepoPath,
    string? Suffix
)
{
    public static CodeReadmeLinkResolution Keep { get; } = new(CodeReadmeLinkKind.Keep, null, null);

    public static CodeReadmeLinkResolution External { get; } =
        new(CodeReadmeLinkKind.External, null, null);

    public static CodeReadmeLinkResolution Repo(string repoPath, string? suffix) =>
        new(CodeReadmeLinkKind.RepoPath, repoPath, suffix);
}

/// <summary>
/// 代码浏览页 Markdown 链接解析：以文档所在目录为基准，
/// 将仓库相对路径折叠为库内绝对路径（渲染期零查库）
/// </summary>
public static class CodeReadmeLinkResolver
{
    private static readonly HashSet<string> ExternalSchemes = new(StringComparer.OrdinalIgnoreCase)
    {
        "http",
        "https",
        "ftp",
        "mailto",
        "tel",
        "data",
    };

    /// <summary>
    /// 解析一个链接 URL
    /// </summary>
    /// <param name="url">Markdown 链接原文（可为空）</param>
    /// <param name="basePaths">文档所在目录的路径分段（根目录为空集合）</param>
    /// <returns>链接分类与仓库内路径。</returns>
    public static CodeReadmeLinkResolution Resolve(
        string? url,
        IReadOnlyCollection<string> basePaths
    )
    {
        url = url?.Trim();
        if (string.IsNullOrEmpty(url))
        {
            return CodeReadmeLinkResolution.Keep;
        }

        var suffix = "";
        var suffixStart = url.IndexOfAny(['#', '?']);
        if (suffixStart >= 0)
        {
            suffix = url[suffixStart..];
            url = url[..suffixStart];
        }

        if (string.IsNullOrEmpty(url))
        {
            return CodeReadmeLinkResolution.Keep;
        }

        if (
            url.StartsWith("//", StringComparison.Ordinal)
            || (
                Uri.TryCreate(url, UriKind.Absolute, out var uri)
                && ExternalSchemes.Contains(uri.Scheme)
            )
        )
        {
            return CodeReadmeLinkResolution.External;
        }

        var segments = new List<string>(basePaths.Count);
        foreach (var item in basePaths)
        {
            if (!string.IsNullOrWhiteSpace(item))
            {
                segments.Add(item);
            }
        }

        url = url.Replace('\\', '/').TrimStart('/');
        foreach (var part in url.Split('/', StringSplitOptions.RemoveEmptyEntries))
        {
            if (part == ".")
            {
                continue;
            }

            if (part == "..")
            {
                if (segments.Count > 0)
                {
                    segments.RemoveAt(segments.Count - 1);
                }

                continue;
            }

            segments.Add(part);
        }

        var repoPath = string.Join('/', segments);
        return CodeReadmeLinkResolution.Repo(repoPath, suffix.Length == 0 ? null : suffix);
    }
}