using System.Text;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ScadaLink.AuditLog.Configuration;
using ScadaLink.AuditLog.Payload;
using ScadaLink.Commons.Entities.Audit;
using ScadaLink.Commons.Types.Enums;

namespace ScadaLink.AuditLog.Tests.Payload;

/// <summary>
/// Bundle B (M5-T4) tests for body regex redaction in
/// <see cref="DefaultAuditPayloadFilter"/>. The body-redactor stage runs
/// regex replace against RequestSummary / ResponseSummary / ErrorDetail /
/// Extra, replacing every match with <c>&lt;redacted&gt;</c>. Regexes come
/// from <see cref="AuditLogOptions.GlobalBodyRedactors"/> plus the per-target
/// <see cref="PerTargetRedactionOverride.AdditionalBodyRedactors"/>. Each
/// regex is compiled with a 50 ms timeout so catastrophic-backtracking
/// patterns trip a <see cref="System.Text.RegularExpressions.RegexMatchTimeoutException"/>;
/// when that happens the offending field is over-redacted with
/// <c>&lt;redacted: redactor error&gt;</c> and the
/// <see cref="IAuditRedactionFailureCounter"/> is incremented. The stage runs
/// BEFORE truncation.
/// </summary>
public class BodyRegexRedactionTests
{
    private static IOptionsMonitor<AuditLogOptions> Monitor(AuditLogOptions? opts = null) =>
        new StaticMonitor(opts ?? new AuditLogOptions());

    private static DefaultAuditPayloadFilter Filter(
        AuditLogOptions? opts = null,
        IAuditRedactionFailureCounter? counter = null) =>
        new(Monitor(opts), NullLogger<DefaultAuditPayloadFilter>.Instance, counter);

    private static AuditEvent NewEvent(
        AuditStatus status = AuditStatus.Delivered,
        string? request = null,
        string? response = null,
        string? errorDetail = null,
        string? extra = null,
        string? target = null) => new()
    {
        EventId = Guid.NewGuid(),
        OccurredAtUtc = DateTime.UtcNow,
        Channel = AuditChannel.ApiOutbound,
        Kind = AuditKind.ApiCall,
        Status = status,
        Target = target,
        RequestSummary = request,
        ResponseSummary = response,
        ErrorDetail = errorDetail,
        Extra = extra,
    };

    [Fact]
    public void GlobalRegex_HunterPassword_Redacted()
    {
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { "\"password\":\\s*\"[^\"]*\"" },
        };
        const string input = "{\"user\":\"alice\",\"password\":\"hunter2\"}";
        var evt = NewEvent(request: input);

        var result = Filter(opts).Apply(evt);

        Assert.NotNull(result.RequestSummary);
        Assert.Contains("<redacted>", result.RequestSummary);
        Assert.DoesNotContain("hunter2", result.RequestSummary);
        Assert.Contains("alice", result.RequestSummary);
    }

    [Fact]
    public void PerTargetRegex_OnlyAppliedToMatchingTarget()
    {
        var opts = new AuditLogOptions
        {
            PerTargetOverrides = new Dictionary<string, PerTargetRedactionOverride>
            {
                ["esg.A"] = new PerTargetRedactionOverride
                {
                    AdditionalBodyRedactors = new List<string> { "SECRET-[A-Z0-9]+" },
                },
            },
        };

        const string input = "token=SECRET-XYZ123 normal-text";

        var matchedEvt = NewEvent(request: input, target: "esg.A");
        var matchedResult = Filter(opts).Apply(matchedEvt);
        Assert.Contains("<redacted>", matchedResult.RequestSummary!);
        Assert.DoesNotContain("SECRET-XYZ123", matchedResult.RequestSummary!);

        var unmatchedEvt = NewEvent(request: input, target: "esg.B");
        var unmatchedResult = Filter(opts).Apply(unmatchedEvt);
        Assert.Equal(input, unmatchedResult.RequestSummary);
    }

    [Fact]
    public void RegexThrowsTimeout_FieldBecomesRedactedMarker_CounterIncrements()
    {
        // Catastrophic backtracking pattern: alternation with overlapping
        // groups + non-matching suffix forces the engine into exponential
        // work that blows past the 50 ms timeout. Append a non-'a' character
        // so the suffix anchor fails and the engine has to exhaust every
        // permutation.
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { "^(a+)+$" },
        };
        // 30 'a's followed by '!' — small enough to keep the test fast, big
        // enough to overflow the 50 ms regex timeout on every machine the CI
        // grid runs on.
        var input = new string('a', 30) + "!";
        var counter = new CountingRedactionFailureCounter();
        var evt = NewEvent(request: input);

        var result = Filter(opts, counter).Apply(evt);

        Assert.Equal("<redacted: redactor error>", result.RequestSummary);
        Assert.True(counter.Count >= 1, $"expected counter >= 1, got {counter.Count}");
    }

    [Fact]
    public void NoRegexConfigured_FieldUnchanged()
    {
        var opts = new AuditLogOptions(); // no GlobalBodyRedactors, no per-target
        const string input = "{\"password\":\"hunter2\"}";
        var evt = NewEvent(request: input);

        var result = Filter(opts).Apply(evt);

        Assert.Equal(input, result.RequestSummary);
    }

    [Fact]
    public void RedactionAppliedBeforeTruncation()
    {
        // A pattern that matches a long secret in the body. The full input is
        // > 8 KB so truncation must run. After redaction:
        //  * the marker survives the cap (redaction ran first),
        //  * the original secret bytes do NOT survive,
        //  * PayloadTruncated is set.
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { "SECRET-[A-Z0-9]+" },
        };
        var secret = "SECRET-ABCDEF123";
        var padding = new string('x', 9 * 1024);
        var input = secret + padding;
        Assert.True(Encoding.UTF8.GetByteCount(input) > 8192);

        var evt = NewEvent(AuditStatus.Delivered, request: input);

        var result = Filter(opts).Apply(evt);

        Assert.NotNull(result.RequestSummary);
        Assert.True(Encoding.UTF8.GetByteCount(result.RequestSummary!) <= 8192);
        Assert.Contains("<redacted>", result.RequestSummary);
        Assert.DoesNotContain(secret, result.RequestSummary);
        Assert.True(result.PayloadTruncated);
    }

    [Fact]
    public void CatastrophicBacktrackingRegex_AtCompileTime_RejectedAtStartup()
    {
        // .NET's regex engine has no compile-time detection for catastrophic
        // backtracking (only structural validation), so the filter's
        // protection is RUNTIME — the 50 ms per-match timeout. We assert the
        // safety net behaviour: a known evil pattern compiles cleanly but
        // matches time out at runtime, the field is over-redacted, and the
        // failure counter is incremented. Future engines that DO support
        // compile-time analysis can tighten this further; the contract here
        // is that the user-facing action is never aborted.
        var evilPattern = "^(a+)+$";
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { evilPattern },
        };
        var input = new string('a', 30) + "!";
        var counter = new CountingRedactionFailureCounter();
        var evt = NewEvent(request: input);

        var result = Filter(opts, counter).Apply(evt);

        Assert.Equal("<redacted: redactor error>", result.RequestSummary);
        Assert.True(counter.Count >= 1);
    }

    /// <summary>Test double that counts increments.</summary>
    private sealed class CountingRedactionFailureCounter : IAuditRedactionFailureCounter
    {
        private int _count;
        public int Count => _count;
        public void Increment() => System.Threading.Interlocked.Increment(ref _count);
    }

    /// <summary>IOptionsMonitor test double — returns the same snapshot on every read.</summary>
    private sealed class StaticMonitor : IOptionsMonitor<AuditLogOptions>
    {
        private readonly AuditLogOptions _value;
        public StaticMonitor(AuditLogOptions value) => _value = value;
        public AuditLogOptions CurrentValue => _value;
        public AuditLogOptions Get(string? name) => _value;
        public IDisposable? OnChange(Action<AuditLogOptions, string?> listener) => null;
    }
}