using StellaOps.Canonicalization.Json;
using StellaOps.Signals.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace StellaOps.Signals.Services;

internal static class ReachabilityFactDigestCalculator
{
    public static string Compute(ReachabilityFactDocument fact)
    {
        ArgumentNullException.ThrowIfNull(fact);

        var canonical = new CanonicalReachabilityFact(
            CallgraphId: fact.CallgraphId ?? string.Empty,
            SubjectKey: fact.SubjectKey ?? string.Empty,
            Subject: new CanonicalSubject(
                fact.Subject?.ImageDigest ?? string.Empty,
                fact.Subject?.Component ?? string.Empty,
                fact.Subject?.Version ?? string.Empty,
                fact.Subject?.ScanId ?? string.Empty),
            EntryPoints: NormalizeList(fact.EntryPoints),
            States: NormalizeStates(fact.States),
            RuntimeFacts: NormalizeRuntimeFacts(fact.RuntimeFacts),
            UncertaintyStates: NormalizeUncertaintyStates(fact.Uncertainty),
            Metadata: NormalizeMetadata(fact.Metadata),
            Score: fact.Score,
            RiskScore: fact.RiskScore,
            UnknownsCount: fact.UnknownsCount,
            UnknownsPressure: fact.UnknownsPressure,
            ComputedAt: fact.ComputedAt);

        var json = CanonicalJsonSerializer.Serialize(canonical);
        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
        SHA256.HashData(Encoding.UTF8.GetBytes(json), hash);
        return "sha256:" + Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static List<string> NormalizeList(IEnumerable<string>? values) =>
        values?
            .Where(v => !string.IsNullOrWhiteSpace(v))
            .Select(v => v.Trim())
            .Distinct(StringComparer.Ordinal)
            .OrderBy(v => v, StringComparer.Ordinal)
            .ToList() ?? new List<string>();

    private static List<CanonicalState> NormalizeStates(IEnumerable<ReachabilityStateDocument>? states)
    {
        if (states is null)
        {
            return new List<CanonicalState>();
        }

        return states
            .OrderBy(s => s.Target, StringComparer.Ordinal)
            .Select(state => new CanonicalState(
                Target: state.Target ?? string.Empty,
                Reachable: state.Reachable,
                Confidence: state.Confidence,
                Bucket: state.Bucket ?? "unknown",
                Weight: state.Weight,
                Score: state.Score,
                Path: NormalizeList(state.Path),
                RuntimeHits: NormalizeList(state.Evidence?.RuntimeHits),
                BlockedEdges: NormalizeList(state.Evidence?.BlockedEdges),
                GateMultiplierBps: Math.Clamp(state.Evidence?.GateMultiplierBps ?? 10000, 0, 10000),
                Gates: NormalizeGates(state.Evidence?.Gates)))
            .ToList();
    }

    private static List<CanonicalGate> NormalizeGates(IEnumerable<CallgraphGate>? gates)
    {
        if (gates is null)
        {
            return new List<CanonicalGate>();
        }

        return gates
            .Where(g => g is not null)
            .Select(g => new CanonicalGate(
                Type: g.Type.ToString(),
                GuardSymbol: g.GuardSymbol?.Trim() ?? string.Empty,
                DetectionMethod: g.DetectionMethod?.Trim() ?? string.Empty,
                Confidence: double.IsNaN(g.Confidence) ? 0.0 : Math.Clamp(g.Confidence, 0.0, 1.0),
                SourceFile: string.IsNullOrWhiteSpace(g.SourceFile) ? null : g.SourceFile.Trim(),
                LineNumber: g.LineNumber is > 0 ? g.LineNumber : null,
                Detail: g.Detail?.Trim() ?? string.Empty))
            .OrderBy(g => g.Type, StringComparer.Ordinal)
            .ThenBy(g => g.GuardSymbol, StringComparer.Ordinal)
            .ThenBy(g => g.DetectionMethod, StringComparer.Ordinal)
            .ThenBy(g => g.SourceFile, StringComparer.Ordinal)
            .ThenBy(g => g.LineNumber ?? 0)
            .ThenBy(g => g.Detail, StringComparer.Ordinal)
            .ToList();
    }

    private static List<CanonicalRuntimeFact> NormalizeRuntimeFacts(IEnumerable<RuntimeFactDocument>? facts)
    {
        if (facts is null)
        {
            return new List<CanonicalRuntimeFact>();
        }

        return facts
            .Select(f => new CanonicalRuntimeFact(
                SymbolId: f.SymbolId ?? string.Empty,
                CodeId: f.CodeId,
                SymbolDigest: f.SymbolDigest,
                Purl: f.Purl,
                BuildId: f.BuildId,
                LoaderBase: f.LoaderBase,
                ProcessId: f.ProcessId,
                ProcessName: f.ProcessName,
                SocketAddress: f.SocketAddress,
                ContainerId: f.ContainerId,
                EvidenceUri: f.EvidenceUri,
                HitCount: f.HitCount,
                ObservedAt: f.ObservedAt,
                Metadata: NormalizeMetadata(f.Metadata)))
            .OrderBy(f => f.SymbolId, StringComparer.Ordinal)
            .ThenBy(f => f.CodeId, StringComparer.Ordinal)
            .ThenBy(f => f.LoaderBase, StringComparer.Ordinal)
            .ToList();
    }

    private static SortedDictionary<string, string?> NormalizeMetadata(IDictionary<string, string?>? metadata)
    {
        var normalized = new SortedDictionary<string, string?>(StringComparer.Ordinal);
        if (metadata is null)
        {
            return normalized;
        }

        foreach (var kvp in metadata)
        {
            if (string.IsNullOrWhiteSpace(kvp.Key))
            {
                continue;
            }

            normalized[kvp.Key.Trim()] = kvp.Value?.Trim();
        }

        return normalized;
    }

    private static List<CanonicalUncertaintyState> NormalizeUncertaintyStates(UncertaintyDocument? uncertainty)
    {
        if (uncertainty?.States is not { Count: > 0 })
        {
            return new List<CanonicalUncertaintyState>();
        }

        return uncertainty.States
            .Where(s => s is not null && !string.IsNullOrWhiteSpace(s.Code))
            .Select(s => new CanonicalUncertaintyState(
                Code: s.Code.Trim(),
                Name: s.Name?.Trim() ?? string.Empty,
                Entropy: Math.Clamp(s.Entropy, 0.0, 1.0),
                Evidence: NormalizeUncertaintyEvidence(s.Evidence),
                Timestamp: s.Timestamp))
            .OrderBy(s => s.Code, StringComparer.Ordinal)
            .ThenBy(s => s.Name, StringComparer.Ordinal)
            .ToList();
    }

    private static List<CanonicalUncertaintyEvidence> NormalizeUncertaintyEvidence(IEnumerable<UncertaintyEvidenceDocument>? evidence)
    {
        if (evidence is null)
        {
            return new List<CanonicalUncertaintyEvidence>();
        }

        return evidence
            .Select(e => new CanonicalUncertaintyEvidence(
                Type: e.Type?.Trim() ?? string.Empty,
                SourceId: e.SourceId?.Trim() ?? string.Empty,
                Detail: e.Detail?.Trim() ?? string.Empty))
            .OrderBy(e => e.Type, StringComparer.Ordinal)
            .ThenBy(e => e.SourceId, StringComparer.Ordinal)
            .ThenBy(e => e.Detail, StringComparer.Ordinal)
            .ToList();
    }

    private sealed record CanonicalReachabilityFact(
        string CallgraphId,
        string SubjectKey,
        CanonicalSubject Subject,
        List<string> EntryPoints,
        List<CanonicalState> States,
        List<CanonicalRuntimeFact> RuntimeFacts,
        List<CanonicalUncertaintyState> UncertaintyStates,
        SortedDictionary<string, string?> Metadata,
        double Score,
        double RiskScore,
        int UnknownsCount,
        double UnknownsPressure,
        DateTimeOffset ComputedAt);

    private sealed record CanonicalSubject(
        string ImageDigest,
        string Component,
        string Version,
        string ScanId);

    private sealed record CanonicalState(
        string Target,
        bool Reachable,
        double Confidence,
        string Bucket,
        double Weight,
        double Score,
        List<string> Path,
        List<string> RuntimeHits,
        List<string> BlockedEdges,
        int GateMultiplierBps,
        List<CanonicalGate> Gates);

    private sealed record CanonicalGate(
        string Type,
        string GuardSymbol,
        string DetectionMethod,
        double Confidence,
        string? SourceFile,
        int? LineNumber,
        string Detail);

    private sealed record CanonicalRuntimeFact(
        string SymbolId,
        string? CodeId,
        string? SymbolDigest,
        string? Purl,
        string? BuildId,
        string? LoaderBase,
        int? ProcessId,
        string? ProcessName,
        string? SocketAddress,
        string? ContainerId,
        string? EvidenceUri,
        int HitCount,
        DateTimeOffset? ObservedAt,
        SortedDictionary<string, string?> Metadata);

    private sealed record CanonicalUncertaintyState(
        string Code,
        string Name,
        double Entropy,
        List<CanonicalUncertaintyEvidence> Evidence,
        DateTimeOffset? Timestamp);

    private sealed record CanonicalUncertaintyEvidence(
        string Type,
        string SourceId,
        string Detail);
}