using Microsoft.Extensions.Configuration;
using StellaOps.Doctor.Models;
using StellaOps.Doctor.Plugins;
using System.Globalization;
using System.Security.Cryptography.X509Certificates;

namespace StellaOps.Doctor.Plugins.Security.Checks;

/// <summary>
/// Validates TLS certificate configuration and expiration.
/// </summary>
public sealed class TlsCertificateCheck : IDoctorCheck
{
    /// <inheritdoc />
    public string CheckId => "check.security.tls.certificate";

    /// <inheritdoc />
    public string Name => "TLS Certificate";

    /// <inheritdoc />
    public string Description => "Validates TLS certificate validity and expiration";

    /// <inheritdoc />
    public DoctorSeverity DefaultSeverity => DoctorSeverity.Fail;

    /// <inheritdoc />
    public IReadOnlyList<string> Tags => ["security", "tls", "certificate"];

    /// <inheritdoc />
    public TimeSpan EstimatedDuration => TimeSpan.FromSeconds(5);

    /// <inheritdoc />
    public bool CanRun(DoctorPluginContext context)
    {
        var certPath = context.Configuration.GetValue<string>("Tls:CertificatePath")
            ?? context.Configuration.GetValue<string>("Kestrel:Certificates:Default:Path");
        return !string.IsNullOrWhiteSpace(certPath);
    }

    /// <inheritdoc />
    public Task<DoctorCheckResult> RunAsync(DoctorPluginContext context, CancellationToken ct)
    {
        var result = context.CreateResult(CheckId, "stellaops.doctor.security", DoctorCategory.Security.ToString());

        var certPath = context.Configuration.GetValue<string>("Tls:CertificatePath")
            ?? context.Configuration.GetValue<string>("Kestrel:Certificates:Default:Path");

        if (string.IsNullOrWhiteSpace(certPath))
        {
            return Task.FromResult(result
                .Skip("TLS certificate path not configured")
                .WithEvidence("Configuration", e => e.Add("CertificatePath", "(not set)"))
                .Build());
        }

        if (!File.Exists(certPath))
        {
            return Task.FromResult(result
                .Fail($"TLS certificate file not found: {certPath}")
                .WithEvidence("TLS configuration", e =>
                {
                    e.Add("CertificatePath", certPath);
                    e.Add("FileExists", "false");
                })
                .WithCauses("Certificate file path is incorrect", "Certificate file was deleted")
                .WithRemediation(r => r
                    .AddManualStep(1, "Verify path", "Check Tls:CertificatePath configuration")
                    .AddManualStep(2, "Generate certificate", "Generate or obtain a valid TLS certificate")
                    .WithRunbookUrl("docs/doctor/articles/security/security-tls-certificate.md"))
                .WithVerification("stella doctor --check check.security.tls.certificate")
                .Build());
        }

        try
        {
            var certPassword = context.Configuration.GetValue<string>("Tls:CertificatePassword")
                ?? context.Configuration.GetValue<string>("Kestrel:Certificates:Default:Password");

            using var cert = string.IsNullOrEmpty(certPassword)
                ? X509CertificateLoader.LoadCertificateFromFile(certPath)
                : X509CertificateLoader.LoadPkcs12FromFile(certPath, certPassword);

            var now = context.TimeProvider.GetUtcNow();
            var daysUntilExpiry = (cert.NotAfter - now.DateTime).TotalDays;

            if (now.DateTime < cert.NotBefore)
            {
                return Task.FromResult(result
                    .Fail("TLS certificate is not yet valid")
                    .WithEvidence("TLS certificate", e =>
                    {
                        e.Add("Subject", cert.Subject);
                        e.Add("Issuer", cert.Issuer);
                        e.Add("NotBefore", cert.NotBefore.ToString("O", CultureInfo.InvariantCulture));
                        e.Add("NotAfter", cert.NotAfter.ToString("O", CultureInfo.InvariantCulture));
                    })
                    .WithCauses("Certificate validity period has not started")
                    .Build());
            }

            if (now.DateTime > cert.NotAfter)
            {
                return Task.FromResult(result
                    .Fail("TLS certificate has expired")
                    .WithEvidence("TLS certificate", e =>
                    {
                        e.Add("Subject", cert.Subject);
                        e.Add("Issuer", cert.Issuer);
                        e.Add("ExpiredOn", cert.NotAfter.ToString("O", CultureInfo.InvariantCulture));
                        e.Add("DaysExpired", Math.Abs(daysUntilExpiry).ToString("F0", CultureInfo.InvariantCulture));
                    })
                    .WithCauses("Certificate has exceeded its validity period")
                    .WithRemediation(r => r
                        .AddManualStep(1, "Renew certificate", "Obtain a new TLS certificate")
                        .AddManualStep(2, "Update configuration", "Update Tls:CertificatePath with new certificate")
                        .WithRunbookUrl("docs/doctor/articles/security/security-tls-certificate.md"))
                    .WithVerification("stella doctor --check check.security.tls.certificate")
                    .Build());
            }

            if (daysUntilExpiry < 30)
            {
                return Task.FromResult(result
                    .Warn($"TLS certificate expires in {daysUntilExpiry:F0} days")
                    .WithEvidence("TLS certificate", e =>
                    {
                        e.Add("Subject", cert.Subject);
                        e.Add("Issuer", cert.Issuer);
                        e.Add("NotAfter", cert.NotAfter.ToString("O", CultureInfo.InvariantCulture));
                        e.Add("DaysUntilExpiry", daysUntilExpiry.ToString("F0", CultureInfo.InvariantCulture));
                    })
                    .WithCauses("Certificate is approaching expiration")
                    .WithRemediation(r => r
                        .AddManualStep(1, "Plan renewal", "Schedule certificate renewal before expiration")
                        .WithRunbookUrl("docs/doctor/articles/security/security-tls-certificate.md"))
                    .Build());
            }

            return Task.FromResult(result
                .Pass($"TLS certificate valid for {daysUntilExpiry:F0} days")
                .WithEvidence("TLS certificate", e =>
                {
                    e.Add("Subject", cert.Subject);
                    e.Add("Issuer", cert.Issuer);
                    e.Add("NotBefore", cert.NotBefore.ToString("O", CultureInfo.InvariantCulture));
                    e.Add("NotAfter", cert.NotAfter.ToString("O", CultureInfo.InvariantCulture));
                    e.Add("DaysUntilExpiry", daysUntilExpiry.ToString("F0", CultureInfo.InvariantCulture));
                    e.Add("Thumbprint", cert.Thumbprint);
                })
                .Build());
        }
        catch (Exception ex)
        {
            return Task.FromResult(result
                .Fail($"Failed to load TLS certificate: {ex.Message}")
                .WithEvidence("TLS configuration", e =>
                {
                    e.Add("CertificatePath", certPath);
                    e.Add("ErrorType", ex.GetType().Name);
                    e.Add("Error", ex.Message);
                })
                .WithCauses(
                    "Certificate file is corrupted",
                    "Certificate password is incorrect",
                    "Certificate format not supported")
                .Build());
        }
    }
}