using StellaOps.Zastava.Core.Contracts;
using StellaOps.Zastava.Observer.Configuration;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace StellaOps.Zastava.Observer.Runtime;

internal static class RuntimeFactsBuilder
{
    public static RuntimeFactsPublishRequest? Build(
        IReadOnlyCollection<RuntimeEventEnvelope> envelopes,
        ReachabilityRuntimeOptions options)
    {
        ArgumentNullException.ThrowIfNull(envelopes);
        ArgumentNullException.ThrowIfNull(options);

        if (!options.Enabled || envelopes.Count == 0)
        {
            return null;
        }

        if (string.IsNullOrWhiteSpace(options.CallgraphId))
        {
            return null;
        }

        var facts = new List<RuntimeFactEventPayload>(envelopes.Count);
        ReachabilitySubjectPayload? subject = null;

        foreach (var envelope in envelopes)
        {
            var fact = TryBuildFact(envelope);
            if (fact is null)
            {
                continue;
            }

            facts.Add(fact);
            subject ??= BuildSubject(envelope, options);
        }

        if (facts.Count == 0)
        {
            return null;
        }

        subject ??= BuildFallbackSubject(options);
        if (subject is null)
        {
            return null;
        }

        facts.Sort(CompareFacts);

        return new RuntimeFactsPublishRequest
        {
            CallgraphId = options.CallgraphId.Trim(),
            Subject = subject,
            Events = facts
        };
    }

    private static RuntimeFactEventPayload? TryBuildFact(RuntimeEventEnvelope envelope)
    {
        ArgumentNullException.ThrowIfNull(envelope);

        var evt = envelope.Event;
        if (evt.Kind != RuntimeEventKind.ContainerStart || evt.Process is null)
        {
            return null;
        }

        var symbolId = BuildSymbolId(evt.Process);
        if (string.IsNullOrWhiteSpace(symbolId))
        {
            return null;
        }

        var fact = new RuntimeFactEventPayload
        {
            SymbolId = symbolId,
            CodeId = Normalize(evt.Process.BuildId),
            BuildId = Normalize(evt.Process.BuildId),
            LoaderBase = null,
            Purl = null,
            SymbolDigest = null,
            HitCount = 1,
            ObservedAt = evt.When,
            ProcessId = evt.Process.Pid,
            ProcessName = ResolveProcessName(evt.Process.Entrypoint),
            ContainerId = evt.Workload.ContainerId,
            Metadata = BuildMetadata(evt.Process)
        };

        return fact;
    }

    private static string? BuildSymbolId(RuntimeProcess process)
    {
        if (!string.IsNullOrWhiteSpace(process.BuildId))
        {
            return $"sym:binary:{process.BuildId.Trim().ToLowerInvariant()}";
        }

        var trace = process.EntryTrace?.FirstOrDefault(t =>
            !string.IsNullOrWhiteSpace(t.Target) || !string.IsNullOrWhiteSpace(t.File));

        var seed = trace?.Target ?? trace?.File ?? process.Entrypoint.FirstOrDefault();
        if (string.IsNullOrWhiteSpace(seed))
        {
            return null;
        }

        var stable = ComputeStableFragment(seed);
        return $"sym:shell:{stable}";
    }

    private static ReachabilitySubjectPayload? BuildSubject(RuntimeEventEnvelope envelope, ReachabilityRuntimeOptions options)
    {
        var workload = envelope.Event.Workload;
        var imageRef = workload.ImageRef;

        var digest = ExtractImageDigest(imageRef);
        var (component, version) = ExtractComponentAndVersion(imageRef);

        digest ??= Normalize(options.SubjectImageDigest);
        component ??= Normalize(options.SubjectComponent);
        version ??= Normalize(options.SubjectVersion);

        var scanId = Normalize(options.SubjectScanId);

        if (string.IsNullOrWhiteSpace(digest) && string.IsNullOrWhiteSpace(scanId)
            && (string.IsNullOrWhiteSpace(component) || string.IsNullOrWhiteSpace(version)))
        {
            return null;
        }

        return new ReachabilitySubjectPayload
        {
            ScanId = scanId,
            ImageDigest = digest,
            Component = component,
            Version = version
        };
    }

    private static ReachabilitySubjectPayload? BuildFallbackSubject(ReachabilityRuntimeOptions options)
    {
        var digest = Normalize(options.SubjectImageDigest);
        var component = Normalize(options.SubjectComponent);
        var version = Normalize(options.SubjectVersion);
        var scanId = Normalize(options.SubjectScanId);

        if (string.IsNullOrWhiteSpace(digest) && string.IsNullOrWhiteSpace(scanId)
            && (string.IsNullOrWhiteSpace(component) || string.IsNullOrWhiteSpace(version)))
        {
            return null;
        }

        return new ReachabilitySubjectPayload
        {
            ScanId = scanId,
            ImageDigest = digest,
            Component = component,
            Version = version
        };
    }

    private static Dictionary<string, string?>? BuildMetadata(RuntimeProcess process)
    {
        if (process.EntryTrace is null || process.EntryTrace.Count == 0)
        {
            return null;
        }

        var sb = new StringBuilder();
        foreach (var trace in process.EntryTrace)
        {
            if (trace is null)
            {
                continue;
            }

            var op = string.IsNullOrWhiteSpace(trace.Op) ? "exec" : trace.Op;
            var target = trace.Target ?? trace.File;
            if (string.IsNullOrWhiteSpace(target))
            {
                continue;
            }

            if (sb.Length > 0)
            {
                sb.Append(" | ");
            }
            sb.Append(op).Append(':').Append(target);
        }

        if (sb.Length == 0)
        {
            return null;
        }

        return new Dictionary<string, string?>(StringComparer.Ordinal)
        {
            ["entryTrace"] = sb.ToString()
        };
    }

    private static string? ExtractImageDigest(string? imageRef)
    {
        if (string.IsNullOrWhiteSpace(imageRef))
        {
            return null;
        }

        var digestStart = imageRef.IndexOf("sha256:", StringComparison.OrdinalIgnoreCase);
        if (digestStart >= 0)
        {
            return imageRef[digestStart..].Trim();
        }

        var atIndex = imageRef.IndexOf('@');
        if (atIndex > 0 && atIndex + 1 < imageRef.Length)
        {
            return imageRef[(atIndex + 1)..].Trim();
        }

        return null;
    }

    private static (string? Component, string? Version) ExtractComponentAndVersion(string? imageRef)
    {
        if (string.IsNullOrWhiteSpace(imageRef))
        {
            return (null, null);
        }

        var lastSlash = imageRef.LastIndexOf('/');
        var lastColon = imageRef.LastIndexOf(':');

        if (lastColon < 0 || lastColon < lastSlash)
        {
            return (null, null);
        }

        var component = imageRef[(lastSlash + 1)..lastColon];
        var version = imageRef[(lastColon + 1)..];

        if (string.IsNullOrWhiteSpace(component) || string.IsNullOrWhiteSpace(version))
        {
            return (null, null);
        }

        return (component.Trim(), version.Trim());
    }

    private static string? ResolveProcessName(IReadOnlyList<string>? entrypoint)
    {
        if (entrypoint is null || entrypoint.Count == 0)
        {
            return null;
        }

        var first = entrypoint[0];
        if (string.IsNullOrWhiteSpace(first))
        {
            return null;
        }

        var lastSlash = first.LastIndexOf('/');
        return lastSlash >= 0 ? first[(lastSlash + 1)..] : first;
    }

    private static string ComputeStableFragment(string seed)
    {
        var normalized = seed.Trim().ToLowerInvariant();
        var bytes = Encoding.UTF8.GetBytes(normalized);
        Span<byte> hash = stackalloc byte[32];
        _ = SHA256.TryHashData(bytes, hash, out _);
        return Convert.ToHexString(hash[..16]).ToLowerInvariant();
    }

    private static int CompareFacts(RuntimeFactEventPayload left, RuntimeFactEventPayload right)
    {
        var timeComparison = Nullable.Compare(left.ObservedAt, right.ObservedAt);
        if (timeComparison != 0)
        {
            return timeComparison;
        }

        return string.Compare(left.SymbolId, right.SymbolId, StringComparison.Ordinal);
    }

    private static string? Normalize(string? value)
        => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
}

internal sealed class RuntimeFactsPublishRequest
{
    public ReachabilitySubjectPayload Subject { get; set; } = new();

    public string CallgraphId { get; set; } = string.Empty;

    public List<RuntimeFactEventPayload> Events { get; set; } = new();
}

internal sealed class ReachabilitySubjectPayload
{
    public string? ScanId { get; set; }

    public string? ImageDigest { get; set; }

    public string? Component { get; set; }

    public string? Version { get; set; }
}

internal sealed class RuntimeFactEventPayload
{
    public string SymbolId { get; set; } = string.Empty;

    public string? CodeId { get; set; }

    public string? SymbolDigest { get; set; }

    public string? Purl { get; set; }

    public string? BuildId { get; set; }

    public string? LoaderBase { get; set; }

    public int? ProcessId { get; set; }

    public string? ProcessName { get; set; }

    public string? SocketAddress { get; set; }

    public string? ContainerId { get; set; }

    public string? EvidenceUri { get; set; }

    public int HitCount { get; set; } = 1;

    public DateTimeOffset? ObservedAt { get; set; }

    public Dictionary<string, string?>? Metadata { get; set; }
}

internal sealed class RuntimeFactsException : Exception
{
    public RuntimeFactsException(string message, Exception? innerException = null) : base(message, innerException)
    {
    }
}