using Microsoft.Extensions.Logging;
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 D (M5-T10) safety-net edge cases for
/// <see cref="DefaultAuditPayloadFilter"/>. Bundle B already pinned the
/// happy-path safety net (catastrophic-backtracking timeout →
/// <c>&lt;redacted: redactor error&gt;</c> + counter bump); this fixture covers
/// the pathological / config-mistake corners that production operators will
/// hit when typoing a regex or shipping a half-baked redactor list.
/// </summary>
/// <remarks>
/// <para>
/// The invariants under test:
/// </para>
/// <list type="bullet">
///   <item>An UNCOMPILABLE pattern (e.g. <c>[unclosed</c>) is logged at warning
///         on first encounter and cached as invalid so it never throws again,
///         but the redactor-failure COUNTER is not bumped at bind time —
///         per the contract on <see cref="IAuditRedactionFailureCounter"/>
///         the counter tracks RUNTIME redaction failures only.</item>
///   <item>One throwing regex in the middle of a list does NOT poison the
///         other patterns — the filter stops at the failing pattern,
///         over-redacts the offending field, but lets every other field keep
///         the prior cleanly-redacted state and lets the rest of the writer
///         pipeline run.</item>
///   <item>A live config change that introduces a broken pattern does not
///         crash the filter — the bad pattern is silently dropped (logged once)
///         and the still-valid patterns continue to redact normally.</item>
/// </list>
/// </remarks>
public class RedactionSafetyNetTests
{
    private static IOptionsMonitor<AuditLogOptions> Monitor(AuditLogOptions? opts = null) =>
        new StaticMonitor(opts ?? new AuditLogOptions());

    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 RegexNotCompilable_AtBindTime_LoggedAndSkipped()
    {
        // `[unclosed` is a structurally invalid character class — the .NET
        // regex engine throws ArgumentException at compile time. We assert:
        //   * the filter does NOT throw,
        //   * the OTHER (valid) pattern still redacts hunter2,
        //   * the failure counter is NOT incremented at compile time
        //     (it tracks runtime redaction failures only),
        //   * a warning is logged exactly once.
        const string badPattern = "[unclosed";
        const string goodPattern = "\"password\":\\s*\"[^\"]*\"";
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { badPattern, goodPattern },
        };
        var counter = new CountingRedactionFailureCounter();
        var spy = new SpyLogger<DefaultAuditPayloadFilter>();
        var filter = new DefaultAuditPayloadFilter(Monitor(opts), spy, counter);

        var evt = NewEvent(request: "{\"user\":\"alice\",\"password\":\"hunter2\"}");

        var result = filter.Apply(evt);

        Assert.NotNull(result.RequestSummary);
        Assert.DoesNotContain("hunter2", result.RequestSummary);
        Assert.Contains("<redacted>", result.RequestSummary);
        Assert.Equal(0, counter.Count);
        // Apply twice — the invalid-pattern compile must run AT MOST once;
        // the sentinel-cache entry stops repeat compile attempts.
        _ = filter.Apply(evt);
        var badPatternWarnings = spy.Entries
            .Where(e => e.Level == LogLevel.Warning && e.Message.Contains(badPattern))
            .Count();
        Assert.Equal(1, badPatternWarnings);
    }

    [Fact]
    public void MultipleRedactors_OneThrows_OthersStillApply_ToOtherFields()
    {
        // Pattern set: [valid-A, evil, valid-B]. The evil pattern is
        // catastrophic-backtracking on the RequestSummary input (all-'a's +
        // mismatching suffix) — that field is over-redacted with the error
        // marker as soon as evil throws. ResponseSummary is processed
        // INDEPENDENTLY; its input does not trigger evil's backtracking, so
        // valid-A and valid-B both still apply on that field. This proves a
        // per-field redactor failure does not poison the rest of the writer
        // call (the SQL-param stage, the truncation stage, and the other
        // fields all continue normally).
        const string validA = "SECRET-[A-Z0-9]+";
        const string evil = "^(a+)+$"; // catastrophic on long all-'a' string
        const string validB = "PIN-\\d{4}";
        var opts = new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { validA, evil, validB },
        };
        var counter = new CountingRedactionFailureCounter();
        var filter = new DefaultAuditPayloadFilter(
            Monitor(opts),
            NullLogger<DefaultAuditPayloadFilter>.Instance,
            counter);

        // Request: ALL 'a's + a non-'a' suffix character. valid-A does not
        // match (no SECRET-X prefix), so the buffer reaches `evil` untouched
        // and triggers the backtracking explosion.
        var request = new string('a', 30) + "!";
        // Response: short, mismatches the evil pattern cleanly (no
        // backtracking), so both valid-A and valid-B run and redact.
        const string response = "SECRET-ABC456 PIN-9999 other-text";

        var result = filter.Apply(NewEvent(request: request, response: response));

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

        // ResponseSummary: clean — both valid regexes still applied; the evil
        // one ran without throwing on this short input.
        Assert.NotNull(result.ResponseSummary);
        Assert.DoesNotContain("SECRET-ABC456", result.ResponseSummary);
        Assert.DoesNotContain("PIN-9999", result.ResponseSummary);
        Assert.Contains("<redacted>", result.ResponseSummary);
        Assert.Contains("other-text", result.ResponseSummary);
    }

    // Edge case 3 (RedactorReturnsNonStringExceptionType) intentionally
    // skipped — the brief permits dropping it: there is no portable way to
    // artificially trigger an OutOfMemoryException inside System.Text.RegularExpressions
    // from a unit test without writing native interop, and the existing
    // per-stage try/catch already covers Exception (which OOM and similar
    // would derive from). Bundle B's RegexThrowsTimeout coverage exercises
    // the same catch path with a deterministic trigger.

    [Fact]
    public void ConfigChange_WithBadRegex_LiveTrafficKeepsApplyingValidRegexes()
    {
        // Initial config: one valid global redactor — hunter2 is redacted.
        // Reload: ADD a malformed pattern alongside the original. Per the
        // safety contract, the bad pattern is logged + skipped, the original
        // valid pattern keeps redacting, and the filter NEVER throws on the
        // hot path. The counter must not be bumped at reload time (the
        // CompiledRegex sentinel covers the bind error before runtime even
        // sees it).
        var monitor = new MutableMonitor(new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string> { "\"password\":\\s*\"[^\"]*\"" },
        });
        var counter = new CountingRedactionFailureCounter();
        var spy = new SpyLogger<DefaultAuditPayloadFilter>();
        var filter = new DefaultAuditPayloadFilter(monitor, spy, counter);

        var evt = NewEvent(request: "{\"user\":\"alice\",\"password\":\"hunter2\"}");

        var before = filter.Apply(evt);
        Assert.DoesNotContain("hunter2", before.RequestSummary!);

        // Reload: malformed pattern added to the list.
        monitor.Set(new AuditLogOptions
        {
            GlobalBodyRedactors = new List<string>
            {
                "\"password\":\\s*\"[^\"]*\"",
                "[unclosed",
            },
        });

        var after = filter.Apply(evt);
        Assert.NotNull(after.RequestSummary);
        Assert.DoesNotContain("hunter2", after.RequestSummary);
        Assert.Contains("<redacted>", after.RequestSummary);
        Assert.Equal(0, counter.Count);
        // Compile-time warning logged for the broken pattern.
        Assert.Contains(
            spy.Entries,
            e => e.Level == LogLevel.Warning && e.Message.Contains("[unclosed"));
    }

    /// <summary>Counts <see cref="IAuditRedactionFailureCounter.Increment"/> calls.</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;
    }

    /// <summary>
    /// IOptionsMonitor test double that supports a live <see cref="Set"/> —
    /// mirrors the helper used in
    /// <see cref="ScadaLink.AuditLog.Tests.Configuration.AuditLogOptionsBindingTests"/>;
    /// kept private here so the safety-net test file remains self-contained.
    /// </summary>
    private sealed class MutableMonitor : IOptionsMonitor<AuditLogOptions>
    {
        private AuditLogOptions _current;
        public MutableMonitor(AuditLogOptions initial) => _current = initial;
        public AuditLogOptions CurrentValue => _current;
        public AuditLogOptions Get(string? name) => _current;
        public IDisposable? OnChange(Action<AuditLogOptions, string?> listener) => null;
        public void Set(AuditLogOptions value) => _current = value;
    }

    /// <summary>
    /// Minimal ILogger that records each formatted log line so tests can
    /// assert on the compile-time warning emission contract — counting
    /// warnings and grepping the message text.
    /// </summary>
    private sealed class SpyLogger<T> : ILogger<T>
    {
        private readonly List<LogEntry> _entries = new();

        public IReadOnlyList<LogEntry> Entries
        {
            get { lock (_entries) return _entries.ToArray(); }
        }

        public IDisposable BeginScope<TState>(TState state) where TState : notnull => NullScope.Instance;
        public bool IsEnabled(LogLevel logLevel) => true;
        public void Log<TState>(
            LogLevel logLevel,
            EventId eventId,
            TState state,
            Exception? exception,
            Func<TState, Exception?, string> formatter)
        {
            var msg = formatter(state, exception);
            lock (_entries) _entries.Add(new LogEntry(logLevel, msg));
        }

        private sealed class NullScope : IDisposable
        {
            public static readonly NullScope Instance = new();
            public void Dispose() { }
        }
    }

    public sealed record LogEntry(LogLevel Level, string Message);
}