using System.Collections.Concurrent;
using StellaOps.VexLens.Models;

namespace StellaOps.VexLens.Verification;

/// <summary>
/// In-memory implementation of <see cref="IIssuerDirectory"/>.
/// Suitable for testing and single-instance deployments.
/// </summary>
public sealed class InMemoryIssuerDirectory : IIssuerDirectory
{
    private readonly ConcurrentDictionary<string, IssuerRecord> _issuers = new(StringComparer.OrdinalIgnoreCase);
    private readonly ConcurrentDictionary<string, string> _fingerprintToIssuer = new(StringComparer.OrdinalIgnoreCase);
    private readonly TimeProvider _timeProvider;

    public InMemoryIssuerDirectory(TimeProvider? timeProvider = null)
    {
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    public Task<IssuerRecord?> GetIssuerAsync(
        string issuerId,
        CancellationToken cancellationToken = default)
    {
        _issuers.TryGetValue(issuerId, out var issuer);
        return Task.FromResult(issuer);
    }

    public Task<IssuerRecord?> GetIssuerByKeyFingerprintAsync(
        string fingerprint,
        CancellationToken cancellationToken = default)
    {
        if (_fingerprintToIssuer.TryGetValue(fingerprint, out var issuerId))
        {
            _issuers.TryGetValue(issuerId, out var issuer);
            return Task.FromResult(issuer);
        }

        return Task.FromResult<IssuerRecord?>(null);
    }

    public Task<IReadOnlyList<IssuerRecord>> ListIssuersAsync(
        IssuerListOptions? options = null,
        CancellationToken cancellationToken = default)
    {
        var query = _issuers.Values.AsEnumerable();

        if (options != null)
        {
            if (options.Category.HasValue)
            {
                query = query.Where(i => i.Category == options.Category.Value);
            }

            if (options.MinimumTrustTier.HasValue)
            {
                query = query.Where(i => i.TrustTier >= options.MinimumTrustTier.Value);
            }

            if (options.Status.HasValue)
            {
                query = query.Where(i => i.Status == options.Status.Value);
            }

            if (!string.IsNullOrWhiteSpace(options.SearchTerm))
            {
                var term = options.SearchTerm;
                query = query.Where(i =>
                    i.Name.Contains(term, StringComparison.OrdinalIgnoreCase) ||
                    i.IssuerId.Contains(term, StringComparison.OrdinalIgnoreCase));
            }

            if (options.Offset.HasValue)
            {
                query = query.Skip(options.Offset.Value);
            }

            if (options.Limit.HasValue)
            {
                query = query.Take(options.Limit.Value);
            }
        }

        var result = query
            .OrderBy(i => i.Name, StringComparer.OrdinalIgnoreCase)
            .ToList();

        return Task.FromResult<IReadOnlyList<IssuerRecord>>(result);
    }

    public Task<IssuerRecord> RegisterIssuerAsync(
        IssuerRegistration registration,
        CancellationToken cancellationToken = default)
    {
        var now = _timeProvider.GetUtcNow();
        var keyRecords = new List<KeyFingerprintRecord>();

        if (registration.InitialKeys != null)
        {
            foreach (var key in registration.InitialKeys)
            {
                keyRecords.Add(new KeyFingerprintRecord(
                    Fingerprint: key.Fingerprint,
                    KeyType: key.KeyType,
                    Algorithm: key.Algorithm,
                    Status: KeyFingerprintStatus.Active,
                    RegisteredAt: now,
                    ExpiresAt: key.ExpiresAt,
                    RevokedAt: null,
                    RevocationReason: null));

                _fingerprintToIssuer[key.Fingerprint] = registration.IssuerId;
            }
        }

        var record = new IssuerRecord(
            IssuerId: registration.IssuerId,
            Name: registration.Name,
            Category: registration.Category,
            TrustTier: registration.TrustTier,
            Status: IssuerStatus.Active,
            KeyFingerprints: keyRecords,
            Metadata: registration.Metadata,
            RegisteredAt: now,
            LastUpdatedAt: null,
            RevokedAt: null,
            RevocationReason: null);

        _issuers[registration.IssuerId] = record;

        return Task.FromResult(record);
    }

    public Task<bool> RevokeIssuerAsync(
        string issuerId,
        string reason,
        CancellationToken cancellationToken = default)
    {
        if (!_issuers.TryGetValue(issuerId, out var current))
        {
            return Task.FromResult(false);
        }

        var now = _timeProvider.GetUtcNow();
        var updated = current with
        {
            Status = IssuerStatus.Revoked,
            RevokedAt = now,
            RevocationReason = reason,
            LastUpdatedAt = now
        };

        _issuers[issuerId] = updated;

        // Also revoke all keys
        foreach (var key in current.KeyFingerprints)
        {
            _fingerprintToIssuer.TryRemove(key.Fingerprint, out _);
        }

        return Task.FromResult(true);
    }

    public Task<IssuerRecord> AddKeyFingerprintAsync(
        string issuerId,
        KeyFingerprintRegistration keyRegistration,
        CancellationToken cancellationToken = default)
    {
        if (!_issuers.TryGetValue(issuerId, out var current))
        {
            throw new InvalidOperationException($"Issuer '{issuerId}' not found");
        }

        var now = _timeProvider.GetUtcNow();
        var newKey = new KeyFingerprintRecord(
            Fingerprint: keyRegistration.Fingerprint,
            KeyType: keyRegistration.KeyType,
            Algorithm: keyRegistration.Algorithm,
            Status: KeyFingerprintStatus.Active,
            RegisteredAt: now,
            ExpiresAt: keyRegistration.ExpiresAt,
            RevokedAt: null,
            RevocationReason: null);

        var updatedKeys = current.KeyFingerprints.Append(newKey).ToList();
        var updated = current with
        {
            KeyFingerprints = updatedKeys,
            LastUpdatedAt = now
        };

        _issuers[issuerId] = updated;
        _fingerprintToIssuer[keyRegistration.Fingerprint] = issuerId;

        return Task.FromResult(updated);
    }

    public Task<bool> RevokeKeyFingerprintAsync(
        string issuerId,
        string fingerprint,
        string reason,
        CancellationToken cancellationToken = default)
    {
        if (!_issuers.TryGetValue(issuerId, out var current))
        {
            return Task.FromResult(false);
        }

        var keyIndex = current.KeyFingerprints
            .Select((k, i) => (k, i))
            .FirstOrDefault(x => x.k.Fingerprint == fingerprint);

        if (keyIndex.k == null)
        {
            return Task.FromResult(false);
        }

        var now = _timeProvider.GetUtcNow();
        var revokedKey = keyIndex.k with
        {
            Status = KeyFingerprintStatus.Revoked,
            RevokedAt = now,
            RevocationReason = reason
        };

        var updatedKeys = current.KeyFingerprints.ToList();
        updatedKeys[keyIndex.i] = revokedKey;

        var updated = current with
        {
            KeyFingerprints = updatedKeys,
            LastUpdatedAt = now
        };

        _issuers[issuerId] = updated;
        _fingerprintToIssuer.TryRemove(fingerprint, out _);

        return Task.FromResult(true);
    }

    public Task<IssuerTrustValidation> ValidateTrustAsync(
        string issuerId,
        string? keyFingerprint,
        CancellationToken cancellationToken = default)
    {
        var warnings = new List<string>();

        if (!_issuers.TryGetValue(issuerId, out var issuer))
        {
            return Task.FromResult(new IssuerTrustValidation(
                IsTrusted: false,
                EffectiveTrustTier: TrustTier.Unknown,
                IssuerStatus: IssuerTrustStatus.NotRegistered,
                KeyStatus: null,
                Warnings: ["Issuer is not registered in the directory"]));
        }

        var issuerStatus = issuer.Status switch
        {
            IssuerStatus.Active => IssuerTrustStatus.Trusted,
            IssuerStatus.Suspended => IssuerTrustStatus.Suspended,
            IssuerStatus.Revoked => IssuerTrustStatus.Revoked,
            _ => IssuerTrustStatus.NotRegistered
        };

        if (issuerStatus != IssuerTrustStatus.Trusted)
        {
            return Task.FromResult(new IssuerTrustValidation(
                IsTrusted: false,
                EffectiveTrustTier: TrustTier.Untrusted,
                IssuerStatus: issuerStatus,
                KeyStatus: null,
                Warnings: [$"Issuer status is {issuer.Status}"]));
        }

        KeyTrustStatus? keyStatus = null;

        if (!string.IsNullOrWhiteSpace(keyFingerprint))
        {
            var key = issuer.KeyFingerprints
                .FirstOrDefault(k => k.Fingerprint.Equals(keyFingerprint, StringComparison.OrdinalIgnoreCase));

            if (key == null)
            {
                keyStatus = KeyTrustStatus.NotRegistered;
                warnings.Add("Key fingerprint is not registered for this issuer");
            }
            else if (key.Status == KeyFingerprintStatus.Revoked)
            {
                keyStatus = KeyTrustStatus.Revoked;
                warnings.Add($"Key was revoked: {key.RevocationReason}");
            }
            else if (key.ExpiresAt.HasValue && key.ExpiresAt.Value < _timeProvider.GetUtcNow())
            {
                keyStatus = KeyTrustStatus.Expired;
                warnings.Add($"Key expired on {key.ExpiresAt.Value:O}");
            }
            else
            {
                keyStatus = KeyTrustStatus.Valid;
            }
        }

        var isTrusted = issuerStatus == IssuerTrustStatus.Trusted &&
                        (keyStatus == null || keyStatus == KeyTrustStatus.Valid);

        var effectiveTier = isTrusted ? issuer.TrustTier : TrustTier.Untrusted;

        return Task.FromResult(new IssuerTrustValidation(
            IsTrusted: isTrusted,
            EffectiveTrustTier: effectiveTier,
            IssuerStatus: issuerStatus,
            KeyStatus: keyStatus,
            Warnings: warnings));
    }
}