using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Primitives;
using Volo.Abp.DependencyInjection;

namespace Volo.Abp.VirtualFileSystem;

//TODO: Work with directory & wildcard watches!
//TODO: Work with dictionaries!

/// <remarks>
/// Current implementation only supports file watch.
/// Does not support directory or wildcard watches.
/// </remarks>
public class DynamicFileProvider : DictionaryBasedFileProvider, IDynamicFileProvider, ISingletonDependency
{
    protected override IDictionary<string, IFileInfo> Files => DynamicFiles;

    protected ConcurrentDictionary<string, IFileInfo> DynamicFiles { get; }

    protected ConcurrentDictionary<string, ChangeTokenInfo> FilePathTokenLookup { get; }

    public DynamicFileProvider()
    {
        FilePathTokenLookup = new ConcurrentDictionary<string, ChangeTokenInfo>(StringComparer.OrdinalIgnoreCase); ;
        DynamicFiles = new ConcurrentDictionary<string, IFileInfo>();
    }

    public virtual void AddOrUpdate(IFileInfo fileInfo)
    {
        var filePath = fileInfo.GetVirtualOrPhysicalPathOrNull();
        DynamicFiles.AddOrUpdate(filePath!, fileInfo, (key, value) => fileInfo);
        ReportChange(filePath!);
    }

    public virtual bool Delete(string filePath)
    {
        if (!DynamicFiles.TryRemove(filePath, out _))
        {
            return false;
        }

        ReportChange(filePath);
        return true;
    }

    public override IChangeToken Watch(string filter)
    {
        return GetOrAddChangeToken(filter);
    }

    private IChangeToken GetOrAddChangeToken(string filePath)
    {
        if (!FilePathTokenLookup.TryGetValue(filePath, out var tokenInfo))
        {
            var cancellationTokenSource = new CancellationTokenSource();
            var cancellationChangeToken = new CancellationChangeToken(cancellationTokenSource.Token);
            tokenInfo = new ChangeTokenInfo(cancellationTokenSource, cancellationChangeToken);
            tokenInfo = FilePathTokenLookup.GetOrAdd(filePath, tokenInfo);
        }

        return tokenInfo.ChangeToken;
    }

    protected virtual void ReportChange(string filePath)
    {
        if (FilePathTokenLookup.TryRemove(filePath, out var tokenInfo))
        {
            tokenInfo.TokenSource.Cancel();
        }
    }

    protected struct ChangeTokenInfo
    {
        public ChangeTokenInfo(
            CancellationTokenSource tokenSource,
            CancellationChangeToken changeToken)
        {
            TokenSource = tokenSource;
            ChangeToken = changeToken;
        }

        public CancellationTokenSource TokenSource { get; }

        public CancellationChangeToken ChangeToken { get; }
    }
}