using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace MSearch.Domain;

public sealed partial class SearchService(ILogger<SearchService> logger, IEnumerable<ISearchProvider> searchProviders)
{
    private readonly IReadOnlyCollection<ISearchProvider> searchProviders = [.. searchProviders];

    public IAsyncEnumerable<SearchResult> Search(string term, CancellationToken cancellationToken)
    {
        var query = new SearchQuery(term);

        var channel = Channel.CreateUnbounded<SearchResult>(new() { SingleReader = true });
        StartProviders(query, channel.Writer, cancellationToken);
        return channel.Reader.ReadAllAsync(cancellationToken);
    }

    private async void StartProviders(
        SearchQuery query,
        ChannelWriter<SearchResult> writer,
        CancellationToken cancellationToken
    )
    {
        try
        {
            var searchTasks = searchProviders.Select(sp => StartProvider(query, sp, writer, cancellationToken));
            await Task.WhenAll(searchTasks);
        }
        finally
        {
            var completed = writer.TryComplete();
            if (!completed)
            {
                LogUncompletedChannel();
            }
        }
    }

    private async Task StartProvider(
        SearchQuery query,
        ISearchProvider provider,
        ChannelWriter<SearchResult> writer,
        CancellationToken cancellationToken
    )
    {
        try
        {
            await foreach (var result in provider.Search(query, cancellationToken))
            {
                await writer.WriteAsync(result, cancellationToken);
            }
        }
        catch (Exception ex)
        {
            LogSearchProviderException(ex);
        }
    }

    [LoggerMessage(LogLevel.Error, "Failed when processing search provider results.")]
    private partial void LogSearchProviderException(Exception exception);

    [LoggerMessage(LogLevel.Warning, "Could not close channel after writing all search results. Leaving channel open.")]
    private partial void LogUncompletedChannel();
}