using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
// Explicit: an unqualified Configuration.* inside this namespace binds to Host.Configuration, not to
// the ZB.MOM.WW.OtOpcUa.Configuration assembly.
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Core.Authorization;
using ZB.MOM.WW.OtOpcUa.OpcUaServer.Security;

namespace ZB.MOM.WW.OtOpcUa.Host.OpcUa;

/// <summary>
///     Production <see cref="IOpcUaUserAuthenticator"/> for the machine-to-machine data plane (#520):
///     the client presents the static username <c>apikey</c> with an
///     <c>otua_&lt;keyId&gt;_&lt;secret&gt;</c> credential as the password. Replaces the LDAP adapter.
/// </summary>
/// <remarks>
///     <para>
///         <b>This runs inline on session activation.</b> The SDK raises <c>ImpersonateUser</c>
///         synchronously while holding a SessionManager-wide event lock, so a slow authenticator does not
///         stall one request — it serializes every session activation server-wide. That is why
///         verification is a single indexed lookup plus one HMAC, with no directory call and no retry —
///         the main practical advantage of keys over the LDAP bind this replaces.
///     </para>
///     <para>
///         ⚠️ <b>"No network I/O" is TRUE ONLY ON A DRIVER-ONLY NODE</b> (arch-review 03/S18). The claim
///         describes <see cref="ArtifactApiKeyStore"/>, which is two dictionary probes on an in-memory
///         snapshot. On an <b>admin or fused</b> node <see cref="IApiKeyStore"/> is
///         <see cref="ConfigDbApiKeyStore"/>, and a UserName activation costs <b>two</b> EF round trips
///         (the key row, then the principal's <c>NodeAcl</c> rows) — inside this same lock. What bounds
///         that is <see cref="BoundedApiKeyStore"/>, which wraps it in production; the deadline it applies
///         surfaces here as an ordinary throw and is denied by the catch-all below, like any other store
///         failure.
///     </para>
///     <para>
///         <b>Fail closed, and say little.</b> Every rejection returns the same opaque message. The
///         reason is logged server-side but never returned, so a caller cannot distinguish "no such key"
///         from "wrong secret" from "key disabled" and use the server as an oracle.
///     </para>
/// </remarks>
public sealed class ApiKeyOpcUaUserAuthenticator : IOpcUaUserAuthenticator
{
    /// <summary>
    ///     Returned for every failure mode, deliberately uninformative. Public so a test can assert that
    ///     the failure modes really are indistinguishable, rather than restating the literal and passing
    ///     even if the implementation started differentiating them.
    /// </summary>
    public const string DenyMessage = "Invalid API key.";

    private readonly IApiKeyStore _store;
    private readonly IOptions<ApiKeyOptions> _options;
    private readonly ILogger<ApiKeyOpcUaUserAuthenticator> _log;
    private readonly TimeProvider _time;

    /// <summary>Initializes a new instance of the <see cref="ApiKeyOpcUaUserAuthenticator"/> class.</summary>
    /// <param name="store">The API key source.</param>
    /// <param name="options">The <c>Security:ApiKeys</c> options.</param>
    /// <param name="log">The logger.</param>
    /// <param name="time">Time provider, injected so expiry is testable.</param>
    public ApiKeyOpcUaUserAuthenticator(
        IApiKeyStore store,
        IOptions<ApiKeyOptions> options,
        ILogger<ApiKeyOpcUaUserAuthenticator> log,
        TimeProvider? time = null)
    {
        _store = store;
        _options = options;
        _log = log;
        _time = time ?? TimeProvider.System;
    }

    /// <inheritdoc />
    public async Task<OpcUaUserAuthResult> AuthenticateUserNameAsync(
        string username, string password, CancellationToken ct)
    {
        var opts = _options.Value;

        // The username carries no information, but check it rather than ignore it: a client sending the
        // wrong username gets an explicit denial it can diagnose, instead of "any username works".
        if (!string.Equals(username, opts.Username, StringComparison.Ordinal))
        {
            _log.LogInformation(
                "ApiKeyAuth: denied — username {Presented} is not the configured {Expected}",
                username, opts.Username);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        if (!ApiKeySecret.TryParse(password, out var apiKeyId, out var secret))
        {
            _log.LogInformation("ApiKeyAuth: denied — credential is not a well-formed otua_ key");
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        var now = _time.GetUtcNow().UtcDateTime;

        ApiKeyLookup? lookup;
        try
        {
            lookup = await _store.FindAsync(apiKeyId, now, ct).ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            // The contract forbids throwing: an exception here escapes into the SDK's session-activation
            // path and surfaces as BadInternalError. A store outage denies, it does not crash.
            _log.LogError(ex, "ApiKeyAuth: key store threw for key id {ApiKeyId}", apiKeyId);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        if (lookup is null)
        {
            _log.LogInformation("ApiKeyAuth: denied — no enabled, unexpired key with id {ApiKeyId}", apiKeyId);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        bool verified;
        try
        {
            verified = ApiKeySecret.Verify(secret, opts.Pepper, lookup.Key.SecretHash);
        }
        catch (ArgumentException ex)
        {
            // Thrown only when the pepper is unset. This is a deployment error, not a bad credential —
            // log it loudly, because otherwise it presents as "every key is rejected" with no clue why.
            _log.LogError(ex,
                "ApiKeyAuth: {Section}:Pepper is not configured — every key will be rejected until it is",
                ApiKeyOptions.SectionName);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        if (!verified)
        {
            _log.LogInformation("ApiKeyAuth: denied — secret mismatch for key id {ApiKeyId}", apiKeyId);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        if (string.Equals(lookup.Key.Principal, OpcUaPrincipals.Anonymous, StringComparison.OrdinalIgnoreCase))
        {
            // Defence in depth against a key authored with the reserved principal (authoring blocks it).
            // Allowing it would let a credentialled client silently inherit whatever anonymous was
            // granted, and vice versa — two identities that are meant to be distinct sharing one grant.
            _log.LogError(
                "ApiKeyAuth: denied — key {ApiKeyId} uses the reserved principal '{Principal}'",
                apiKeyId, OpcUaPrincipals.Anonymous);
            return OpcUaUserAuthResult.Deny(DenyMessage);
        }

        var roles = ApiKeyInterimRoleMapper.Map(lookup.Grants, lookup.Key.Principal);

        _log.LogInformation(
            "ApiKeyAuth: granted key {Name} ({ApiKeyId}) as principal {Principal} with roles [{Roles}]",
            lookup.Key.Name, apiKeyId, lookup.Key.Principal, string.Join(",", roles));

        // AllowKey, not Allow: the key id rides along so an open session can be re-checked against a later
        // deployment that revoked this key. Without it a revoked key keeps working until the client
        // happens to disconnect, which on a machine-to-machine data plane can be indefinitely.
        return OpcUaUserAuthResult.AllowKey(lookup.Key.Principal, roles, apiKeyId);
    }

    /// <inheritdoc />
    /// <remarks>
    ///     Resolves the <c>anonymous</c> principal's grants through the same mapper a key's principal
    ///     goes through, so anonymous is authorized by ordinary ACL rows rather than by a special case.
    ///     Whether anonymous may connect at all is the host's decision
    ///     (<c>OpcUa:AllowAnonymous</c>) and is settled before this is called.
    /// </remarks>
    public async Task<OpcUaUserAuthResult> AuthenticateAnonymousAsync(CancellationToken ct)
    {
        IReadOnlyList<NodeAcl> grants;
        try
        {
            grants = await _store.FindGrantsAsync(OpcUaPrincipals.Anonymous, ct).ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            // Deny rather than admit-with-no-roles. Admitting would be the pre-#520 behaviour, and doing
            // it precisely when we could not read what anonymous is allowed to do is the wrong default:
            // once reads are gated (stage 6) a no-roles admission stops being harmless.
            _log.LogError(ex, "ApiKeyAuth: key store threw resolving anonymous grants");
            return OpcUaUserAuthResult.Deny("Anonymous access is unavailable.");
        }

        var roles = ApiKeyInterimRoleMapper.Map(grants, OpcUaPrincipals.Anonymous);
        _log.LogInformation(
            "ApiKeyAuth: anonymous admitted with roles [{Roles}]",
            roles.Count == 0 ? "none" : string.Join(",", roles));

        return OpcUaUserAuthResult.Allow(OpcUaPrincipals.Anonymous, roles);
    }
}