// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Globalization;
 
namespace Aspire.Hosting.ApplicationModel;
 
internal class ExpressionResolver(string containerHostName, CancellationToken cancellationToken, bool sourceIsContainer)
{
 
    async Task<string?> EvalEndpointAsync(EndpointReference endpointReference, EndpointProperty property)
    {
        // We need to use the root resource, e.g. AzureStorageResource instead of AzureBlobResource
        // Otherwise, we get the wrong values for IsContainer and Name
        var target = endpointReference.Resource.GetRootResource();
 
        return (property, target.IsContainer()) switch
        {
            // If Container -> Container, we go directly to the container name and target port, bypassing the host
            (EndpointProperty.Host or EndpointProperty.IPV4Host, true) => target.Name,
            (EndpointProperty.Port, true) => await endpointReference.Property(EndpointProperty.TargetPort).GetValueAsync(cancellationToken).ConfigureAwait(false),
            // If Container -> Exe, we need to go through the container host
            (EndpointProperty.Host or EndpointProperty.IPV4Host, false) => containerHostName,
            (EndpointProperty.Url, _) => string.Format(CultureInfo.InvariantCulture, "{0}://{1}:{2}",
                                            endpointReference.Scheme,
                                            await EvalEndpointAsync(endpointReference, EndpointProperty.Host).ConfigureAwait(false),
                                            await EvalEndpointAsync(endpointReference, EndpointProperty.Port).ConfigureAwait(false)),
            (EndpointProperty.HostAndPort, _) => string.Format(CultureInfo.InvariantCulture, "{0}:{1}",
                                            await EvalEndpointAsync(endpointReference, EndpointProperty.Host).ConfigureAwait(false),
                                            await EvalEndpointAsync(endpointReference, EndpointProperty.Port).ConfigureAwait(false)),
            _ => await endpointReference.Property(property).GetValueAsync(cancellationToken).ConfigureAwait(false)
        };
    }
 
    async Task<ResolvedValue> EvalExpressionAsync(ReferenceExpression expr)
    {
        // This logic is similar to ReferenceExpression.GetValueAsync, except that we recurse on
        // our own resolver method
        var args = new object?[expr.ValueProviders.Count];
        var isSensitive = false;
 
        for (var i = 0; i < expr.ValueProviders.Count; i++)
        {
            var result = await ResolveInternalAsync(expr.ValueProviders[i]).ConfigureAwait(false);
            args[i] = result?.Value;
            if (result?.IsSensitive is true)
            {
                isSensitive = true;
            }
        }
 
        // Identically to ReferenceExpression.GetValueAsync, we return null if the format is empty
        var value = expr.Format.Length == 0 ? null : string.Format(CultureInfo.InvariantCulture, expr.Format, args);
 
        return new ResolvedValue(value, isSensitive);
    }
 
    async Task<ResolvedValue> EvalValueProvider(IValueProvider vp)
    {
        var value = await vp.GetValueAsync(cancellationToken).ConfigureAwait(false);
 
        if (vp is ParameterResource pr)
        {
            return new ResolvedValue(value, pr.Secret);
        }
 
        // No need to do extra work, since the below will only be valid for containers.
        if (!sourceIsContainer)
        {
            return new ResolvedValue(value, false);
        }
 
        if (vp is HostUrl && value != null)
        {
            // HostUrl is a bit of a hack that is not modeled as an expression
            // So in this one case, we need to fix up the container host name 'manually'
            // Internally, this is only used for OTEL_EXPORTER_OTLP_ENDPOINT, but HostUrl
            // is public, so we don't control how it is used
            try
            {
                var uri = new UriBuilder(value);
                if (uri.Host is "localhost" or "127.0.0.1" or "[::1]")
                {
                    var hasEndingSlash = value.EndsWith('/');
                    uri.Host = containerHostName;
                    value = uri.ToString();
 
                    // Remove trailing slash if we didn't have one before (UriBuilder always adds one)
                    if (!hasEndingSlash && value.EndsWith('/'))
                    {
                        value = value[..^1];
                    }
                }
            }
            catch (UriFormatException)
            {
                // HostUrl was meant to only be used with valid URLs. However, this was not
                // previously enforced. So we need to handle the case where it's not a valid URL,
                // by falling back to a simple string replacement.
                value = value.Replace("localhost", containerHostName, StringComparison.OrdinalIgnoreCase)
                             .Replace("127.0.0.1", containerHostName)
                             .Replace("[::1]", containerHostName);
            }
        }
 
        return new ResolvedValue(value, false);
    }
 
    async Task<ResolvedValue> ResolveConnectionStringReferenceAsync(ConnectionStringReference cs)
    {
        // We are substituting our own logic for ConnectionStringReference's GetValueAsync.
        // However, ConnectionStringReference#GetValueAsync will throw if the connection string is not optional but is not present.
        // so we need to do the same here.
        var value = await ResolveInternalAsync(cs.Resource.ConnectionStringExpression).ConfigureAwait(false);
 
        // Throw if the connection string is required but not present
        if (string.IsNullOrEmpty(value.Value) && !cs.Optional)
        {
            cs.ThrowConnectionStringUnavailableException();
        }
 
        return value;
    }
 
    /// <summary>
    /// Resolve an expression. When it is being used from inside a container, endpoints may be evaluated (either in a container-to-container or container-to-exe communication).
    /// </summary>
    async ValueTask<ResolvedValue> ResolveInternalAsync(object? value)
    {
        return value switch
        {
            ConnectionStringReference cs => await ResolveConnectionStringReferenceAsync(cs).ConfigureAwait(false),
            IResourceWithConnectionString cs and not ConnectionStringParameterResource => await ResolveInternalAsync(cs.ConnectionStringExpression).ConfigureAwait(false),
            ReferenceExpression ex => await EvalExpressionAsync(ex).ConfigureAwait(false),
            EndpointReference endpointReference when sourceIsContainer => new ResolvedValue(await EvalEndpointAsync(endpointReference, EndpointProperty.Url).ConfigureAwait(false), false),
            EndpointReferenceExpression ep when sourceIsContainer => new ResolvedValue(await EvalEndpointAsync(ep.Endpoint, ep.Property).ConfigureAwait(false), false),
            IValueProvider vp => await EvalValueProvider(vp).ConfigureAwait(false),
            _ => throw new NotImplementedException()
        };
    }
 
    static async ValueTask<ResolvedValue> ResolveWithContainerSourceAsync(IValueProvider valueProvider, string containerHostName, bool sourceIsContainer, CancellationToken cancellationToken)
    {
        var resolver = new ExpressionResolver(containerHostName, cancellationToken, sourceIsContainer);
        return await resolver.ResolveInternalAsync(valueProvider).ConfigureAwait(false);
    }
 
    internal static async ValueTask<ResolvedValue> ResolveAsync(bool sourceIsContainer, IValueProvider valueProvider, string containerHostName, CancellationToken cancellationToken)
    {
        return await ResolveWithContainerSourceAsync(valueProvider, containerHostName, sourceIsContainer, cancellationToken).ConfigureAwait(false);
    }
}
 
internal record ResolvedValue(string? Value, bool IsSensitive);