using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace StellaOps.Evidence.Budgets;

public interface IEvidenceBudgetService
{
    BudgetCheckResult CheckBudget(Guid scanId, EvidenceItem item);
    BudgetStatus GetBudgetStatus(Guid scanId);
    Task<PruneResult> PruneToFitAsync(Guid scanId, long targetBytes, CancellationToken ct);
}

public sealed class EvidenceBudgetService : IEvidenceBudgetService
{
    private readonly IEvidenceRepository _repository;
    private readonly IOptionsMonitor<EvidenceBudget> _options;
    private readonly ILogger<EvidenceBudgetService> _logger;

    public EvidenceBudgetService(
        IEvidenceRepository repository,
        IOptionsMonitor<EvidenceBudget> options,
        ILogger<EvidenceBudgetService> logger)
    {
        _repository = repository;
        _options = options;
        _logger = logger;
    }

    public BudgetCheckResult CheckBudget(Guid scanId, EvidenceItem item)
    {
        var budget = _options.CurrentValue;
        var currentUsage = GetCurrentUsage(scanId);

        var issues = new List<string>();

        // Check total budget
        var projectedTotal = currentUsage.TotalBytes + item.SizeBytes;
        if (projectedTotal > budget.MaxScanSizeBytes)
        {
            issues.Add($"Would exceed total budget: {projectedTotal:N0} > {budget.MaxScanSizeBytes:N0} bytes");
        }

        // Check per-type budget
        if (budget.MaxPerType.TryGetValue(item.Type, out var typeLimit))
        {
            var typeUsage = currentUsage.ByType.GetValueOrDefault(item.Type, 0);
            var projectedType = typeUsage + item.SizeBytes;
            if (projectedType > typeLimit)
            {
                issues.Add($"Would exceed {item.Type} budget: {projectedType:N0} > {typeLimit:N0} bytes");
            }
        }

        if (issues.Count == 0)
        {
            return BudgetCheckResult.WithinBudget();
        }

        return new BudgetCheckResult
        {
            IsWithinBudget = false,
            Issues = issues,
            RecommendedAction = budget.ExceededAction,
            CanAutoPrune = budget.ExceededAction == BudgetExceededAction.AutoPrune,
            BytesToFree = Math.Max(0, projectedTotal - budget.MaxScanSizeBytes)
        };
    }

    public BudgetStatus GetBudgetStatus(Guid scanId)
    {
        var budget = _options.CurrentValue;
        var usage = GetCurrentUsage(scanId);

        return new BudgetStatus
        {
            ScanId = scanId,
            TotalBudgetBytes = budget.MaxScanSizeBytes,
            UsedBytes = usage.TotalBytes,
            RemainingBytes = Math.Max(0, budget.MaxScanSizeBytes - usage.TotalBytes),
            UtilizationPercent = (decimal)usage.TotalBytes / budget.MaxScanSizeBytes * 100,
            ByType = usage.ByType.ToDictionary(
                kvp => kvp.Key,
                kvp => new TypeBudgetStatus
                {
                    Type = kvp.Key,
                    UsedBytes = kvp.Value,
                    LimitBytes = budget.MaxPerType.GetValueOrDefault(kvp.Key),
                    UtilizationPercent = budget.MaxPerType.TryGetValue(kvp.Key, out var limit)
                        ? (decimal)kvp.Value / limit * 100
                        : 0
                })
        };
    }

    public async Task<PruneResult> PruneToFitAsync(
        Guid scanId,
        long targetBytes,
        CancellationToken ct)
    {
        var budget = _options.CurrentValue;
        var usage = GetCurrentUsage(scanId);

        if (usage.TotalBytes <= targetBytes)
        {
            return PruneResult.NoPruningNeeded();
        }

        var bytesToPrune = usage.TotalBytes - targetBytes;
        var pruned = new List<PrunedItem>();

        // Get all evidence items, sorted by pruning priority
        var items = await _repository.GetByScanIdAsync(scanId, ct);
        var candidates = items
            .Where(i => !budget.AlwaysPreserve.Contains(i.Type))
            .OrderBy(i => GetPrunePriority(i))
            .ToList();

        long prunedBytes = 0;
        foreach (var item in candidates)
        {
            if (prunedBytes >= bytesToPrune)
                break;

            // Move to archive tier or delete
            await _repository.MoveToTierAsync(item.Id, RetentionTier.Archive, ct);
            pruned.Add(new PrunedItem(item.Id, item.Type, item.SizeBytes));
            prunedBytes += item.SizeBytes;
        }

        _logger.LogInformation(
            "Pruned {Count} items ({Bytes:N0} bytes) for scan {ScanId}",
            pruned.Count, prunedBytes, scanId);

        return new PruneResult
        {
            Success = prunedBytes >= bytesToPrune,
            BytesPruned = prunedBytes,
            ItemsPruned = pruned,
            BytesRemaining = usage.TotalBytes - prunedBytes
        };
    }

    private static int GetPrunePriority(EvidenceItem item)
    {
        // Lower = prune first
        return item.Type switch
        {
            EvidenceType.RuntimeCapture => 1,
            EvidenceType.CallGraph => 2,
            EvidenceType.Advisory => 3,
            EvidenceType.PathWitness => 4,
            EvidenceType.PolicyTrace => 5,
            EvidenceType.Sbom => 6,
            EvidenceType.Vex => 7,
            EvidenceType.Attestation => 8,
            EvidenceType.Verdict => 9, // Never prune
            _ => 5
        };
    }

    private UsageStats GetCurrentUsage(Guid scanId)
    {
        // Implementation to calculate current usage from repository
        var items = _repository.GetByScanIdAsync(scanId, CancellationToken.None)
            .GetAwaiter().GetResult();

        var totalBytes = items.Sum(i => i.SizeBytes);
        var byType = items
            .GroupBy(i => i.Type)
            .ToDictionary(g => g.Key, g => g.Sum(i => i.SizeBytes));

        return new UsageStats
        {
            TotalBytes = totalBytes,
            ByType = byType
        };
    }
}

public sealed record BudgetCheckResult
{
    public required bool IsWithinBudget { get; init; }
    public IReadOnlyList<string> Issues { get; init; } = [];
    public BudgetExceededAction RecommendedAction { get; init; }
    public bool CanAutoPrune { get; init; }
    public long BytesToFree { get; init; }

    public static BudgetCheckResult WithinBudget() => new() { IsWithinBudget = true };
}

public sealed record BudgetStatus
{
    public required Guid ScanId { get; init; }
    public required long TotalBudgetBytes { get; init; }
    public required long UsedBytes { get; init; }
    public required long RemainingBytes { get; init; }
    public required decimal UtilizationPercent { get; init; }
    public required IReadOnlyDictionary<EvidenceType, TypeBudgetStatus> ByType { get; init; }
}

public sealed record TypeBudgetStatus
{
    public required EvidenceType Type { get; init; }
    public required long UsedBytes { get; init; }
    public long? LimitBytes { get; init; }
    public decimal UtilizationPercent { get; init; }
}

public sealed record PruneResult
{
    public required bool Success { get; init; }
    public long BytesPruned { get; init; }
    public IReadOnlyList<PrunedItem> ItemsPruned { get; init; } = [];
    public long BytesRemaining { get; init; }

    public static PruneResult NoPruningNeeded() => new() { Success = true };
}

public sealed record PrunedItem(Guid ItemId, EvidenceType Type, long SizeBytes);

public sealed record UsageStats
{
    public long TotalBytes { get; init; }
    public IReadOnlyDictionary<EvidenceType, long> ByType { get; init; } = new Dictionary<EvidenceType, long>();
}

// Supporting interfaces and types

public interface IEvidenceRepository
{
    Task<IReadOnlyList<EvidenceItem>> GetByScanIdAsync(Guid scanId, CancellationToken ct);
    Task<IReadOnlyList<EvidenceItem>> GetByScanIdAndTypeAsync(Guid scanId, EvidenceType type, CancellationToken ct);
    Task<IReadOnlyList<EvidenceItem>> GetOlderThanAsync(RetentionTier tier, DateTimeOffset cutoff, CancellationToken ct);
    Task MoveToTierAsync(Guid itemId, RetentionTier tier, CancellationToken ct);
    Task UpdateContentAsync(Guid itemId, byte[] content, CancellationToken ct);
}

public sealed record EvidenceItem
{
    public required Guid Id { get; init; }
    public required Guid ScanId { get; init; }
    public required EvidenceType Type { get; init; }
    public required long SizeBytes { get; init; }
    public required RetentionTier Tier { get; init; }
    public required DateTimeOffset CreatedAt { get; init; }
    public string? ArchiveKey { get; init; }
}