using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.EntityFrameworkCore;
using w4c_workflows.Data;
using w4c_workflows.Models;

namespace w4c_workflows.Services;

/// <summary>Resolved identity of an operator-key bearer.</summary>
public sealed record OperatorPrincipal(Guid KeyId, string TenantId, IReadOnlyList<string> Scopes)
{
    public bool HasScope(string scope) => Scopes.Contains(scope, StringComparer.Ordinal);
}

/// <summary>
/// Mints, verifies, lists and revokes per-tenant operator API keys. Only the
/// SHA-256 hash is persisted; the raw key is returned exactly once at mint time.
/// </summary>
public class ApiKeyService
{
    private const string KeyPrefix = "w4c_";

    /// <summary>
    /// <c>LastUsedAt</c> is informational, so it is written at most this often
    /// per key instead of on every authenticated request (which doubled the DB
    /// work on the auth hot path).
    /// </summary>
    private static readonly TimeSpan LastUsedWriteInterval = TimeSpan.FromMinutes(5);

    private readonly WorkflowsDbContext _db;

    public ApiKeyService(WorkflowsDbContext db)
    {
        _db = db;
    }

    /// <summary>
    /// Generates a fresh operator key, stores its hash, and returns the raw key
    /// (shown to the caller once — never persisted).
    /// </summary>
    public async Task<(Guid Id, string RawKey)> MintAsync(
        string tenantId, string label, IReadOnlyList<string> scopes, CancellationToken ct)
    {
        var raw = KeyPrefix + Base64Url(RandomNumberGenerator.GetBytes(32));

        var key = new ApiKey
        {
            Id = Guid.NewGuid(),
            TenantId = tenantId,
            KeyHash = Hash(raw),
            Label = label,
            ScopesJson = JsonSerializer.Serialize(scopes),
            CreatedAt = DateTime.UtcNow,
        };

        _db.ApiKeys.Add(key);
        await _db.SaveChangesAsync(ct);
        return (key.Id, raw);
    }

    /// <summary>
    /// Resolves a bearer token to an active key's tenant + scopes, touching
    /// last_used_at. Returns null for unknown/revoked keys (caller → 401).
    /// </summary>
    public async Task<OperatorPrincipal?> VerifyAsync(string? authHeader, CancellationToken ct)
    {
        if (string.IsNullOrEmpty(authHeader) ||
            !authHeader.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase))
            return null;

        var raw = authHeader["Bearer ".Length..].Trim();
        if (string.IsNullOrEmpty(raw))
            return null;

        var hash = Hash(raw);
        var key = await _db.ApiKeys
            .FirstOrDefaultAsync(k => k.KeyHash == hash && k.RevokedAt == null, ct);
        if (key == null)
            return null;

        // Throttled: skip the write when the key was already seen recently.
        var now = DateTime.UtcNow;
        if (key.LastUsedAt is null || now - key.LastUsedAt.Value >= LastUsedWriteInterval)
        {
            key.LastUsedAt = now;
            await _db.SaveChangesAsync(ct);
        }

        var scopes = ParseScopes(key.ScopesJson);
        return new OperatorPrincipal(key.Id, key.TenantId, scopes);
    }

    public Task<List<ApiKey>> ListAsync(string tenantId, CancellationToken ct)
        => _db.ApiKeys
            .Where(k => k.TenantId == tenantId)
            .OrderByDescending(k => k.CreatedAt)
            .ToListAsync(ct);

    public async Task<bool> RevokeAsync(string tenantId, Guid id, CancellationToken ct)
    {
        var key = await _db.ApiKeys
            .FirstOrDefaultAsync(k => k.Id == id && k.TenantId == tenantId, ct);
        if (key == null)
            return false;

        key.RevokedAt ??= DateTime.UtcNow;
        await _db.SaveChangesAsync(ct);
        return true;
    }

    public Task<int> CountActiveAsync(string tenantId, CancellationToken ct)
        => _db.ApiKeys.CountAsync(k => k.TenantId == tenantId && k.RevokedAt == null, ct);

    internal static string Hash(string raw) =>
        Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(raw))).ToLowerInvariant();

    private static IReadOnlyList<string> ParseScopes(string? json)
    {
        if (string.IsNullOrWhiteSpace(json))
            return Array.Empty<string>();
        try
        {
            return JsonSerializer.Deserialize<string[]>(json) ?? Array.Empty<string>();
        }
        catch
        {
            return Array.Empty<string>();
        }
    }

    private static string Base64Url(byte[] bytes) =>
        Convert.ToBase64String(bytes).TrimEnd('=').Replace('+', '-').Replace('/', '_');
}