using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Microsoft.Extensions.Logging;
using StellaOps.Auth.Abstractions;

namespace StellaOps.Policy.Gateway.Options;

/// <summary>
/// Root configuration for the Policy Gateway host.
/// </summary>
public sealed class PolicyGatewayOptions
{
    public const string SectionName = "PolicyGateway";

    public PolicyGatewayTelemetryOptions Telemetry { get; } = new();

    public PolicyGatewayResourceServerOptions ResourceServer { get; } = new();

    public PolicyGatewayPolicyEngineOptions PolicyEngine { get; } = new();

    public void Validate()
    {
        Telemetry.Validate();
        ResourceServer.Validate();
        PolicyEngine.Validate();
    }
}

/// <summary>
/// Logging and telemetry configuration for the gateway.
/// </summary>
public sealed class PolicyGatewayTelemetryOptions
{
    public LogLevel MinimumLogLevel { get; set; } = LogLevel.Information;

    public void Validate()
    {
        if (!Enum.IsDefined(typeof(LogLevel), MinimumLogLevel))
        {
            throw new InvalidOperationException("Unsupported log level configured for Policy Gateway telemetry.");
        }
    }
}

/// <summary>
/// JWT resource server configuration for incoming requests handled by the gateway.
/// </summary>
public sealed class PolicyGatewayResourceServerOptions
{
    public string Authority { get; set; } = "https://authority.stella-ops.local";

    public string? MetadataAddress { get; set; }
        = "https://authority.stella-ops.local/.well-known/openid-configuration";

    public IList<string> Audiences { get; } = new List<string> { "api://policy-gateway" };

    public IList<string> RequiredScopes { get; } = new List<string>
    {
        StellaOpsScopes.PolicyRead,
        StellaOpsScopes.PolicyAuthor,
        StellaOpsScopes.PolicyReview,
        StellaOpsScopes.PolicyApprove,
        StellaOpsScopes.PolicyOperate,
        StellaOpsScopes.PolicySimulate,
        StellaOpsScopes.PolicyRun,
        StellaOpsScopes.PolicyActivate
    };

    public IList<string> RequiredTenants { get; } = new List<string>();

    public IList<string> BypassNetworks { get; } = new List<string> { "127.0.0.1/32", "::1/128" };

    public bool RequireHttpsMetadata { get; set; } = true;

    public int BackchannelTimeoutSeconds { get; set; } = 30;

    public int TokenClockSkewSeconds { get; set; } = 60;

    public void Validate()
    {
        if (string.IsNullOrWhiteSpace(Authority))
        {
            throw new InvalidOperationException("Policy Gateway resource server configuration requires an Authority URL.");
        }

        if (!Uri.TryCreate(Authority.Trim(), UriKind.Absolute, out var authorityUri))
        {
            throw new InvalidOperationException("Policy Gateway resource server Authority URL must be absolute.");
        }

        if (RequireHttpsMetadata &&
            !authorityUri.IsLoopback &&
            !string.Equals(authorityUri.Scheme, Uri.UriSchemeHttps, StringComparison.OrdinalIgnoreCase))
        {
            throw new InvalidOperationException("Policy Gateway resource server Authority URL must use HTTPS when metadata requires HTTPS.");
        }

        if (BackchannelTimeoutSeconds <= 0)
        {
            throw new InvalidOperationException("Policy Gateway resource server back-channel timeout must be greater than zero seconds.");
        }

        if (TokenClockSkewSeconds < 0 || TokenClockSkewSeconds > 300)
        {
            throw new InvalidOperationException("Policy Gateway resource server token clock skew must be between 0 and 300 seconds.");
        }

        NormalizeList(Audiences, toLower: false);
        NormalizeList(RequiredScopes, toLower: true);
        NormalizeList(RequiredTenants, toLower: true);
        NormalizeList(BypassNetworks, toLower: false);
    }

    private static void NormalizeList(IList<string> values, bool toLower)
    {
        if (values.Count == 0)
        {
            return;
        }

        var unique = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        for (var index = values.Count - 1; index >= 0; index--)
        {
            var value = values[index];
            if (string.IsNullOrWhiteSpace(value))
            {
                values.RemoveAt(index);
                continue;
            }

            var normalized = value.Trim();
            if (toLower)
            {
                normalized = normalized.ToLowerInvariant();
            }

            if (!unique.Add(normalized))
            {
                values.RemoveAt(index);
                continue;
            }

            values[index] = normalized;
        }
    }
}

/// <summary>
/// Outbound Policy Engine configuration used by the gateway to forward requests.
/// </summary>
public sealed class PolicyGatewayPolicyEngineOptions
{
    public string BaseAddress { get; set; } = "https://policy-engine.stella-ops.local";

    public string Audience { get; set; } = "api://policy-engine";

    public PolicyGatewayClientCredentialsOptions ClientCredentials { get; } = new();

    public PolicyGatewayDpopOptions Dpop { get; } = new();

    public void Validate()
    {
        if (string.IsNullOrWhiteSpace(BaseAddress))
        {
            throw new InvalidOperationException("Policy Gateway requires a Policy Engine base address.");
        }

        if (!Uri.TryCreate(BaseAddress.Trim(), UriKind.Absolute, out var baseUri))
        {
            throw new InvalidOperationException("Policy Gateway Policy Engine base address must be an absolute URI.");
        }

        if (!string.Equals(baseUri.Scheme, Uri.UriSchemeHttps, StringComparison.OrdinalIgnoreCase) && !baseUri.IsLoopback)
        {
            throw new InvalidOperationException("Policy Gateway Policy Engine base address must use HTTPS unless targeting loopback.");
        }

        if (string.IsNullOrWhiteSpace(Audience))
        {
            throw new InvalidOperationException("Policy Gateway requires a Policy Engine audience value for client credential flows.");
        }

        ClientCredentials.Validate();
        Dpop.Validate();
    }

    public Uri BaseUri => new(BaseAddress, UriKind.Absolute);
}

/// <summary>
/// Client credential configuration for the gateway when calling the Policy Engine.
/// </summary>
public sealed class PolicyGatewayClientCredentialsOptions
{
    public bool Enabled { get; set; } = true;

    public string ClientId { get; set; } = "policy-gateway";

    public string? ClientSecret { get; set; }
        = "change-me";

    public IList<string> Scopes { get; } = new List<string>
    {
        StellaOpsScopes.PolicyRead,
        StellaOpsScopes.PolicyAuthor,
        StellaOpsScopes.PolicyReview,
        StellaOpsScopes.PolicyApprove,
        StellaOpsScopes.PolicyOperate,
        StellaOpsScopes.PolicySimulate,
        StellaOpsScopes.PolicyRun,
        StellaOpsScopes.PolicyActivate
    };

    public int BackchannelTimeoutSeconds { get; set; } = 30;

    public void Validate()
    {
        if (!Enabled)
        {
            return;
        }

        if (string.IsNullOrWhiteSpace(ClientId))
        {
            throw new InvalidOperationException("Policy Gateway client credential configuration requires a client identifier when enabled.");
        }

        if (Scopes.Count == 0)
        {
            throw new InvalidOperationException("Policy Gateway client credential configuration requires at least one scope when enabled.");
        }

        var normalized = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        for (var index = Scopes.Count - 1; index >= 0; index--)
        {
            var scope = Scopes[index];
            if (string.IsNullOrWhiteSpace(scope))
            {
                Scopes.RemoveAt(index);
                continue;
            }

            var trimmed = scope.Trim().ToLowerInvariant();
            if (!normalized.Add(trimmed))
            {
                Scopes.RemoveAt(index);
                continue;
            }

            Scopes[index] = trimmed;
        }

        if (Scopes.Count == 0)
        {
            throw new InvalidOperationException("Policy Gateway client credential configuration requires at least one non-empty scope when enabled.");
        }

        if (BackchannelTimeoutSeconds <= 0)
        {
            throw new InvalidOperationException("Policy Gateway client credential back-channel timeout must be greater than zero seconds.");
        }
    }

    public IReadOnlyList<string> NormalizedScopes => new ReadOnlyCollection<string>(Scopes);

    public TimeSpan BackchannelTimeout => TimeSpan.FromSeconds(BackchannelTimeoutSeconds);
}

/// <summary>
/// DPoP sender-constrained credential configuration for outbound Policy Engine calls.
/// </summary>
public sealed class PolicyGatewayDpopOptions
{
    public bool Enabled { get; set; } = false;

    public string KeyPath { get; set; } = string.Empty;

    public string? KeyPassphrase { get; set; }
        = null;

    public string Algorithm { get; set; } = "ES256";

    public TimeSpan ProofLifetime { get; set; } = TimeSpan.FromMinutes(2);

    public TimeSpan ClockSkew { get; set; } = TimeSpan.FromSeconds(30);

    public void Validate()
    {
        if (!Enabled)
        {
            return;
        }

        if (string.IsNullOrWhiteSpace(KeyPath))
        {
            throw new InvalidOperationException("Policy Gateway DPoP configuration requires a key path when enabled.");
        }

        if (string.IsNullOrWhiteSpace(Algorithm))
        {
            throw new InvalidOperationException("Policy Gateway DPoP configuration requires an algorithm when enabled.");
        }

        var normalizedAlgorithm = Algorithm.Trim().ToUpperInvariant();
        if (normalizedAlgorithm is not ("ES256" or "ES384"))
        {
            throw new InvalidOperationException("Policy Gateway DPoP configuration supports only ES256 or ES384 algorithms.");
        }

        if (ProofLifetime <= TimeSpan.Zero)
        {
            throw new InvalidOperationException("Policy Gateway DPoP proof lifetime must be greater than zero.");
        }

        if (ClockSkew < TimeSpan.Zero || ClockSkew > TimeSpan.FromMinutes(5))
        {
            throw new InvalidOperationException("Policy Gateway DPoP clock skew must be between 0 seconds and 5 minutes.");
        }

        Algorithm = normalizedAlgorithm;
    }
}