using System;
using System.IO;
using MediaBrowser.Common.Configuration;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.JRay.Services;

/// <summary>
/// Injects (or removes) a script tag in the web client's <c>index.html</c>
/// that loads JRay's pause-overlay script. This follows the pattern used by
/// other Jellyfin plugins (e.g. Intro Skipper) since there is no official
/// plugin hook for player-overlay UI.
/// </summary>
public static class WebClientPatchService
{
    private const string Marker = "<!-- jray-overlay -->";
    private const string ScriptTag = "<script defer src=\"/Plugins/JRay/ClientScript\"></script>";
    private const string Injected = ScriptTag + Marker + "\n</body>";

    /// <summary>
    /// Ensures the web client's index.html either has or does not have the
    /// JRay overlay script injected, matching <paramref name="enableOverlay"/>.
    /// </summary>
    /// <param name="applicationPaths">The Jellyfin application paths.</param>
    /// <param name="enableOverlay">Whether the overlay script should be present.</param>
    /// <param name="logger">The logger.</param>
    public static void Apply(IApplicationPaths applicationPaths, bool enableOverlay, ILogger logger)
    {
        var indexPath = Path.Combine(applicationPaths.WebPath, "index.html");

        try
        {
            if (!File.Exists(indexPath))
            {
                logger.LogDebug("JRay: web client index.html not found at {Path}", indexPath);
                return;
            }

            var html = File.ReadAllText(indexPath);
            var hasMarker = html.Contains(Marker, StringComparison.Ordinal);

            if (enableOverlay && !hasMarker)
            {
                var patched = ReplaceLast(html, "</body>", Injected);
                File.WriteAllText(indexPath, patched);
                logger.LogInformation("JRay: injected pause-overlay script into {Path}", indexPath);
            }
            else if (!enableOverlay && hasMarker)
            {
                var patched = html.Replace(ScriptTag + Marker + "\n", string.Empty, StringComparison.Ordinal)
                    .Replace(ScriptTag + Marker, string.Empty, StringComparison.Ordinal);
                File.WriteAllText(indexPath, patched);
                logger.LogInformation("JRay: removed pause-overlay script from {Path}", indexPath);
            }
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
        {
            logger.LogWarning(ex, "JRay: failed to patch web client index.html at {Path}", indexPath);
        }
    }

    private static string ReplaceLast(string source, string find, string replace)
    {
        var index = source.LastIndexOf(find, StringComparison.Ordinal);
        if (index < 0)
        {
            return source;
        }

        return source[..index] + replace + source[(index + find.Length)..];
    }
}