using System.Net;
using System.Threading.RateLimiting;
using Data.SeaHavenIndustries;
using Microsoft.AspNetCore.HttpOverrides;
using Microsoft.AspNetCore.RateLimiting;

namespace Api.SeaHavenIndustries.Infrastructure;

/// <summary>
/// Per-client limits on the anonymous password reset endpoints, plus the
/// forwarded-header trust that makes "per client" mean the caller and not the proxy.
/// </summary>
public static class PasswordResetRateLimiting
{
    public const string ForgetPasswordPolicy = "password-reset-request";
    public const string VerificationCodePolicy = "password-reset-verify";
    public const string ResetPasswordPolicy = "password-reset-confirm";

    public const int PermitLimit = 10;
    public static readonly TimeSpan Window = TimeSpan.FromMinutes(15);

    public const string RejectedMessage = "Too many requests. Please try again later.";

    /// <summary>
    /// The API runs on Elastic Beanstalk behind an application load balancer and the
    /// instance's nginx, so every request reaches Kestrel from loopback. X-Forwarded-For
    /// is read right to left through loopback and private (VPC) hops only; the first
    /// public address is the client. Entries a caller writes further left are ignored.
    /// </summary>
    public static IServiceCollection AddPasswordResetRateLimiting(this IServiceCollection services)
    {
        services.Configure<ForwardedHeadersOptions>(options =>
        {
            options.ForwardedHeaders = ForwardedHeaders.XForwardedFor;
            options.ForwardLimit = null;
            options.KnownNetworks.Clear();
            options.KnownProxies.Clear();
            options.KnownNetworks.Add(new Microsoft.AspNetCore.HttpOverrides.IPNetwork(IPAddress.Parse("127.0.0.0"), 8));
            options.KnownNetworks.Add(new Microsoft.AspNetCore.HttpOverrides.IPNetwork(IPAddress.Parse("10.0.0.0"), 8));
            options.KnownNetworks.Add(new Microsoft.AspNetCore.HttpOverrides.IPNetwork(IPAddress.Parse("172.16.0.0"), 12));
            options.KnownNetworks.Add(new Microsoft.AspNetCore.HttpOverrides.IPNetwork(IPAddress.Parse("192.168.0.0"), 16));
            options.KnownProxies.Add(IPAddress.IPv6Loopback);
        });

        services.AddRateLimiter(options =>
        {
            options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
            options.OnRejected = async (context, cancellationToken) =>
            {
                context.HttpContext.Response.StatusCode = StatusCodes.Status429TooManyRequests;
                await context.HttpContext.Response.WriteAsJsonAsync(
                    new Response { Status = "Error", Message = RejectedMessage },
                    cancellationToken);
            };

            AddPerClientPolicy(options, ForgetPasswordPolicy);
            AddPerClientPolicy(options, VerificationCodePolicy);
            AddPerClientPolicy(options, ResetPasswordPolicy);
        });

        return services;
    }

    public static string ClientPartitionKey(HttpContext context)
    {
        var address = context.Connection.RemoteIpAddress;
        if (address == null)
            return "unknown";
        return (address.IsIPv4MappedToIPv6 ? address.MapToIPv4() : address).ToString();
    }

    private static void AddPerClientPolicy(RateLimiterOptions options, string policyName)
    {
        options.AddPolicy(policyName, context => RateLimitPartition.GetFixedWindowLimiter(
            ClientPartitionKey(context),
            _ => new FixedWindowRateLimiterOptions
            {
                PermitLimit = PermitLimit,
                Window = Window,
                QueueLimit = 0,
                AutoReplenishment = true
            }));
    }
}