// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using Microsoft.Extensions.Primitives;
 
namespace Microsoft.AspNetCore.OutputCaching;
 
/// <summary>
/// When applied, the cached content will be different for every value of the provided headers.
/// </summary>
internal sealed class VaryByHeaderPolicy : IOutputCachePolicy
{
    private readonly StringValues _headerNames;
 
    private VaryByHeaderPolicy()
    {
    }
 
    public VaryByHeaderPolicy(string header, params string[] headerNames)
    {
        ArgumentNullException.ThrowIfNull(header);
 
        _headerNames = header;
 
        if (headerNames != null && headerNames.Length > 0)
        {
            _headerNames = StringValues.Concat(_headerNames, headerNames);
        }
    }
 
    public VaryByHeaderPolicy(string[] headerNames)
    {
        ArgumentNullException.ThrowIfNull(headerNames);
 
        _headerNames = headerNames;
    }
 
    /// <inheritdoc />
    ValueTask IOutputCachePolicy.CacheRequestAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        // No vary by header?
        if (_headerNames.Count == 0)
        {
            context.CacheVaryByRules.HeaderNames = _headerNames;
            return ValueTask.CompletedTask;
        }
 
        context.CacheVaryByRules.HeaderNames = StringValues.Concat(context.CacheVaryByRules.HeaderNames, _headerNames);
 
        return ValueTask.CompletedTask;
    }
 
    /// <inheritdoc />
    ValueTask IOutputCachePolicy.ServeFromCacheAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        return ValueTask.CompletedTask;
    }
 
    /// <inheritdoc />
    ValueTask IOutputCachePolicy.ServeResponseAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        return ValueTask.CompletedTask;
    }
}