using System;
using System.IO;
using System.Linq;
using System.Threading;
using System.Reflection;
using xCommons.Extensions;
using xExceptions.Constants;
using System.Threading.Tasks;
using System.Collections.Generic;
using xAiApi.Interfaces.Extractors;

namespace xAiApi.Providers
{
    /// <summary>
    /// Composite extractor that delegates to appropriate extractor 
    /// based on MIME type ...
    /// </summary>    
    public class XFileContentExtractor : IXFileContentExtractor
    {
        //
        private readonly IList<IXFileContentExtractor> extractors = [];

        public XFileContentExtractor()
        {
            //
            var path = Path.Combine(AppContext.BaseDirectory);
            var files = Directory.GetFiles(path, "*.dll");
            foreach (var dll in files)
            {
                //
                // Retrieve DLL Assembly ...
                var assembly = Assembly.LoadFrom(dll);

                //
                // Extract Registerar Types ...
                var extractorTypes = assembly
                    .GetExportedTypes()
                    .Where(t =>
                        !t.IsAbstract &&
                        typeof(IXFileContentExtractor).IsAssignableFrom(t));
                foreach (var extractorType in extractorTypes)
                {
                    //
                    // Ignore XFileContentExtractor ...
                    if (extractorType.FullName.Contains(nameof(XFileContentExtractor)))
                    {
                        continue;
                    }

                    //
                    // Create Instance of Service ...
                    var instance = (IXFileContentExtractor)Activator.CreateInstance(extractorType);
                    if (!instance.IsNull())
                    {
                        //
                        // Add Registerar Instance to Collection ...
                        extractors.Add(instance);
                    }
                }
            }
        }

        /// <summary>
        /// Check if this extractor supports the specified MIME type ...
        /// </summary>
        public bool CanExtract(string mimeType)
        {
            return extractors.Any(e => e.CanExtract(mimeType));
        }

        /// <summary>
        /// Extract text content from file stream ...
        /// </summary>
        public async Task<string> ExtractAsync(
            Stream fileStream,
            string mimeType,
            CancellationToken cancellationToken = default
        )
        {
            //
            var extractor = extractors
                .FirstOrDefault(e => e.CanExtract(mimeType));
            if (extractor.IsNull())
            {
                //
                XException.NotAllowed.Throw(
                    $"Unsupported file type: {mimeType}"
                );
            }

            //
            var result = await extractor
                .ExtractAsync(
                    mimeType: mimeType,
                    fileStream: fileStream,
                    cancellationToken: cancellationToken
                );

            //
            return result;
        }
    }
}