using System.Reflection;
using System.Security.Claims;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Routing;
using Sentry;

namespace Api.SeaHavenIndustries.Observability;

public static class SentryObservability
{
    public const string ServiceName = "shoc-backend";
    public const string LocalDevelopmentRelease = "local-development";
    private const string ReleasePrefix = ServiceName + "@";
    private const int CommitShaLength = 40;

    public static string ResolveRelease(Assembly? assembly)
    {
        var informationalVersion = assembly?
            .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?
            .InformationalVersion;

        return ResolveRelease(informationalVersion);
    }

    public static string? ResolveCommitSha(Assembly? assembly)
    {
        var informationalVersion = assembly?
            .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?
            .InformationalVersion;

        return ResolveCommitSha(informationalVersion);
    }

    public static string ResolveRelease(string? informationalVersion) =>
        TryResolveCommitSha(informationalVersion, out var commitSha)
            ? ReleasePrefix + commitSha
            : LocalDevelopmentRelease;

    public static string? ResolveCommitSha(string? informationalVersion) =>
        TryResolveCommitSha(informationalVersion, out var commitSha)
            ? commitSha
            : null;

    public static bool IsReleaseInformationalVersion(string? value) =>
        TryResolveCommitSha(value, out _);

    private static bool TryResolveCommitSha(string? value, out string? commitSha)
    {
        commitSha = null;

        if (value is null || !value.StartsWith(ReleasePrefix, StringComparison.Ordinal))
            return false;

        var body = value[ReleasePrefix.Length..];
        var suffixSeparatorIndex = body.IndexOf('+');
        var sha = suffixSeparatorIndex < 0 ? body : body[..suffixSeparatorIndex];

        if (sha.Length != CommitShaLength || !sha.All(IsCommitShaHexDigit))
            return false;

        if (suffixSeparatorIndex >= 0
            && !string.Equals(body[(suffixSeparatorIndex + 1)..], sha, StringComparison.OrdinalIgnoreCase))
            return false;

        commitSha = sha.ToLowerInvariant();
        return true;
    }

    private static bool IsCommitShaHexDigit(char c) =>
        c is >= '0' and <= '9' or >= 'a' and <= 'f' or >= 'A' and <= 'F';

    public static void ConfigureRequest(IHub hub, HttpContext context)
    {
        var endpoint = context.GetEndpoint();
        var routeEndpoint = endpoint as RouteEndpoint;
        var routeTemplate = routeEndpoint?.RoutePattern.RawText;

        var actionDescriptor = endpoint?.Metadata.GetMetadata<ControllerActionDescriptor>();
        var userId = context.User.FindFirst(ClaimTypes.NameIdentifier)?.Value;
        var authenticated = !string.IsNullOrEmpty(userId);

        hub.ConfigureScope(scope =>
        {
            if (authenticated)
                scope.User = new SentryUser { Id = userId };

            scope.SetTag("actor.type", authenticated ? "authenticated" : "anonymous");
            scope.SetTag("operation.type", "http.server");

            if (actionDescriptor is not null)
                scope.SetTag("code.function", $"{actionDescriptor.ControllerName}.{actionDescriptor.ActionName}");

            scope.SetTag("http.method", context.Request.Method);

            if (!string.IsNullOrEmpty(routeTemplate))
                scope.SetTag("http.route", routeTemplate);

            var activeSpan = hub.GetSpan();
            if (activeSpan is not null)
            {
                scope.SetTag("trace_id", activeSpan.TraceId.ToString());
                scope.SetTag("transaction_id", activeSpan.SpanId.ToString());
            }
        });
    }

    public static SentryBackgroundTransactionHandle BeginBackgroundTransaction(
        IHub hub,
        string name,
        string function,
        string? description = null)
    {
        var scope = hub.PushScope();
        var transaction = hub.StartTransaction(name, "task");

        if (!string.IsNullOrEmpty(description))
            transaction.Description = description;

        hub.ConfigureScope(s => s.Transaction = transaction);

        foreach (var (key, value) in new[]
        {
            ("actor.type", "system"),
            ("operation.type", "background_job"),
            ("code.function", function),
            ("trace_id", transaction.TraceId.ToString()),
            ("transaction_id", transaction.SpanId.ToString()),
        })
        {
            transaction.SetTag(key, value);
            hub.ConfigureScope(s => s.SetTag(key, value));
        }

        return new SentryBackgroundTransactionHandle(transaction, scope);
    }
}

public static class SentryTelemetryScrubber
{
    private static readonly HashSet<string> SafeSpanDataKeys = new(StringComparer.Ordinal)
    {
        "actor.type",
        "code.function",
        "db.operation.name",
        "db.system",
        "http.method",
        "http.request.method",
        "http.response.status_code",
        "http.route",
        "http.status_code",
        "network.protocol.version",
        "operation.type",
        "server.address",
        "url.scheme",
    };

    private static readonly HashSet<string> SafeSpanTagKeys = new(StringComparer.Ordinal)
    {
        "actor.type",
        "code.function",
        "http.method",
        "http.route",
        "operation.type",
    };

    public static SentryEvent Scrub(SentryEvent @event)
    {
        ScrubRequest(@event.Request);
        @event.User = KeepOpaqueIdOnly(@event.User);
        return @event;
    }

    public static SentryTransaction Scrub(SentryTransaction transaction)
    {
        ScrubRequest(transaction.Request);
        transaction.User = KeepOpaqueIdOnly(transaction.User);
        transaction.SetTag("trace_id", transaction.TraceId.ToString());
        transaction.SetTag("transaction_id", transaction.SpanId.ToString());
        ScrubDictionary(transaction.Data, SafeSpanDataKeys);

        foreach (var span in transaction.Spans)
        {
            ScrubDictionary(span.Data, SafeSpanDataKeys);

            foreach (var tag in span.Tags.Keys.Where(key => !SafeSpanTagKeys.Contains(key)).ToArray())
                span.UnsetTag(tag);

            span.Description = span.Operation?.Contains("http", StringComparison.OrdinalIgnoreCase) == true
                ? NormalizeHttpDescription(span.Description)
                : null;
        }

        return transaction;
    }

    private static SentryUser KeepOpaqueIdOnly(SentryUser? user) =>
        string.IsNullOrWhiteSpace(user?.Id) ? new SentryUser() : new SentryUser { Id = user.Id };

    private static void ScrubRequest(SentryRequest? request)
    {
        if (request is null)
            return;

        request.Data = null;
        request.QueryString = null;
        request.Cookies = null;
        request.Headers.Clear();
        request.Env.Clear();
        request.Other.Clear();
    }

    private static void ScrubDictionary<TValue>(
        IReadOnlyDictionary<string, TValue> values,
        IReadOnlySet<string> allowedKeys)
    {
        if (values is not IDictionary<string, TValue> mutable)
            return;

        foreach (var key in mutable.Keys.Where(key => !allowedKeys.Contains(key)).ToArray())
            mutable.Remove(key);
    }

    private static string? NormalizeHttpDescription(string? description)
    {
        if (string.IsNullOrWhiteSpace(description))
            return null;

        var separator = description.IndexOf(' ');
        if (separator <= 0 || separator == description.Length - 1)
            return null;

        var method = description[..separator].ToUpperInvariant();
        if (method is not ("GET" or "POST" or "PUT" or "PATCH" or "DELETE" or "HEAD" or "OPTIONS"))
            return null;

        var rawUrl = description[(separator + 1)..];
        var path = Uri.TryCreate(rawUrl, UriKind.Absolute, out var absolute)
            ? absolute.GetLeftPart(UriPartial.Authority) + absolute.AbsolutePath
            : rawUrl.Split('?', '#')[0];

        return $"{method} {NormalizePathIdentifiers(path)}";
    }

    private static string NormalizePathIdentifiers(string path) =>
        string.Join('/', path.Split('/').Select(segment => IsIdentifierSegment(segment) ? ":id" : segment));

    private static bool IsIdentifierSegment(string segment)
    {
        if (string.IsNullOrEmpty(segment))
            return false;

        if (long.TryParse(segment, out _) || Guid.TryParse(segment, out _))
            return true;

        var allHex = segment.All(Uri.IsHexDigit);
        if (segment.Length >= 8 && allHex)
            return true;

        return segment.Length >= 16
            && segment.All(c => char.IsAsciiLetterOrDigit(c) || c is '.' or '_' or '~' or '-')
            && segment.Any(char.IsAsciiLetter)
            && segment.Any(char.IsAsciiDigit);
    }
}

public sealed class SentryBackgroundTransactionHandle : IDisposable
{
    private readonly ITransactionTracer _transaction;
    private readonly IDisposable _scope;
    private int _finished;

    internal SentryBackgroundTransactionHandle(ITransactionTracer transaction, IDisposable scope)
    {
        _transaction = transaction;
        _scope = scope;
    }

    public void FinishOk() => Finish(() => _transaction.Finish(SpanStatus.Ok));

    public void FinishCancelled() => Finish(() => _transaction.Finish(SpanStatus.Cancelled));

    public void FinishError(Exception exception) =>
        Finish(() => _transaction.Finish(exception, SpanStatus.InternalError));

    private void Finish(Action finish)
    {
        if (Interlocked.Exchange(ref _finished, 1) == 0)
            finish();
    }

    public void Dispose()
    {
        Finish(() => _transaction.Finish(SpanStatus.UnknownError));
        _scope.Dispose();
    }
}