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

namespace xAiApi.Providers
{
    /// <summary>
    /// Composite extractor that delegates to appropriate extractor 
    /// based on MIME type ...
    /// </summary>    
    public class XCompositeFileContentExtractor : IXFileContentExtractor
    {
        //
        private readonly IEnumerable<IXFileContentExtractor> extractors;

        public XCompositeFileContentExtractor(
            IEnumerable<IXFileContentExtractor> extractors
        )
        {
            this.extractors = extractors;
        }

        /// <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;
        }
    }
}