using System;
using System.Net.Http;

namespace StellaOps.AirGap.Policy;

/// <summary>
/// Provides helpers for creating <see cref="HttpClient"/> instances that respect the configured <see cref="IEgressPolicy"/>.
/// </summary>
public static class EgressHttpClientFactory
{
    /// <summary>
    /// Creates an <see cref="HttpClient"/> after validating the supplied egress request against the policy.
    /// </summary>
    /// <param name="egressPolicy">The policy used to validate outbound requests.</param>
    /// <param name="request">Describes the destination and intent for the outbound call.</param>
    /// <param name="configure">Optional configuration hook applied to the newly created client.</param>
    /// <returns>An <see cref="HttpClient"/> that has been pre-authorised by the policy.</returns>
    public static HttpClient Create(IEgressPolicy egressPolicy, EgressRequest request, Action<HttpClient>? configure = null)
    {
        ArgumentNullException.ThrowIfNull(egressPolicy);

        egressPolicy.EnsureAllowed(request);

        var client = new HttpClient();
        configure?.Invoke(client);
        return client;
    }

    /// <summary>
    /// Creates an <see cref="HttpClient"/> from a caller-provided factory after validating the supplied egress request.
    /// </summary>
    /// <param name="egressPolicy">The policy used to validate outbound requests.</param>
    /// <param name="request">Describes the destination and intent for the outbound call.</param>
    /// <param name="clientFactory">Factory used to supply a configured client (for example, from IHttpClientFactory).</param>
    /// <param name="configure">Optional configuration hook applied to the newly created client.</param>
    /// <returns>An <see cref="HttpClient"/> that has been pre-authorised by the policy.</returns>
    public static HttpClient Create(
        IEgressPolicy egressPolicy,
        EgressRequest request,
        Func<HttpClient> clientFactory,
        Action<HttpClient>? configure = null)
    {
        ArgumentNullException.ThrowIfNull(egressPolicy);
        ArgumentNullException.ThrowIfNull(clientFactory);

        egressPolicy.EnsureAllowed(request);

        var client = clientFactory();
        if (client is null)
        {
            throw new InvalidOperationException("EgressHttpClientFactory received a null HttpClient from the factory.");
        }

        configure?.Invoke(client);
        return client;
    }

    /// <summary>
    /// Creates and configures an <see cref="HttpClient"/> after validating the supplied egress request against the policy.
    /// </summary>
    /// <param name="egressPolicy">The policy used to validate outbound requests.</param>
    /// <param name="component">Component initiating the request.</param>
    /// <param name="destination">Destination that will be contacted.</param>
    /// <param name="intent">Intent label describing why the request is needed.</param>
    /// <param name="configure">Optional configuration hook applied to the newly created client.</param>
    /// <returns>An <see cref="HttpClient"/> that has been pre-authorised by the policy.</returns>
    public static HttpClient Create(
        IEgressPolicy egressPolicy,
        string component,
        Uri destination,
        string intent,
        Action<HttpClient>? configure = null)
        => Create(egressPolicy, new EgressRequest(component, destination, intent), configure);

    /// <summary>
    /// Creates a configured <see cref="HttpClient"/> using a caller-provided factory after policy validation.
    /// </summary>
    /// <param name="egressPolicy">The policy used to validate outbound requests.</param>
    /// <param name="component">Component initiating the request.</param>
    /// <param name="destination">Destination that will be contacted.</param>
    /// <param name="intent">Intent label describing why the request is needed.</param>
    /// <param name="clientFactory">Factory used to supply a configured client.</param>
    /// <param name="configure">Optional configuration hook applied to the newly created client.</param>
    /// <returns>An <see cref="HttpClient"/> that has been pre-authorised by the policy.</returns>
    public static HttpClient Create(
        IEgressPolicy egressPolicy,
        string component,
        Uri destination,
        string intent,
        Func<HttpClient> clientFactory,
        Action<HttpClient>? configure = null)
        => Create(egressPolicy, new EgressRequest(component, destination, intent), clientFactory, configure);
}