using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging.Abstractions;
using MsOptions = Microsoft.Extensions.Options;
using StellaOps.Signals.Models;
using StellaOps.Signals.Options;
using StellaOps.Signals.Persistence;
using StellaOps.Signals.Services;
using Xunit;

namespace StellaOps.Signals.Tests;

public class UnknownsDecayServiceTests
{
    private readonly MockTimeProvider _timeProvider;
    private readonly InMemoryUnknownsRepository _unknownsRepo;
    private readonly InMemoryDeploymentRefsRepository _deploymentRefs;
    private readonly InMemoryGraphMetricsRepository _graphMetrics;
    private readonly UnknownsScoringOptions _scoringOptions;
    private readonly UnknownsDecayOptions _decayOptions;

    public UnknownsDecayServiceTests()
    {
        _timeProvider = new MockTimeProvider(new DateTimeOffset(2025, 12, 15, 12, 0, 0, TimeSpan.Zero));
        _unknownsRepo = new InMemoryUnknownsRepository();
        _deploymentRefs = new InMemoryDeploymentRefsRepository();
        _graphMetrics = new InMemoryGraphMetricsRepository();
        _scoringOptions = new UnknownsScoringOptions();
        _decayOptions = new UnknownsDecayOptions();
    }

    private (UnknownsDecayService DecayService, UnknownsScoringService ScoringService) CreateServices()
    {
        var scoringService = new UnknownsScoringService(
            _unknownsRepo,
            _deploymentRefs,
            _graphMetrics,
            MsOptions.Options.Create(_scoringOptions),
            _timeProvider,
            NullLogger<UnknownsScoringService>.Instance);

        var decayService = new UnknownsDecayService(
            _unknownsRepo,
            scoringService,
            MsOptions.Options.Create(_scoringOptions),
            MsOptions.Options.Create(_decayOptions),
            _timeProvider,
            NullLogger<UnknownsDecayService>.Instance);

        return (decayService, scoringService);
    }

    #region ApplyDecayAsync Tests

    [Fact]
    public async Task ApplyDecayAsync_EmptySubject_ReturnsZeroCounts()
    {
        var (decayService, _) = CreateServices();

        var result = await decayService.ApplyDecayAsync("empty|1.0.0", CancellationToken.None);

        Assert.Equal("empty|1.0.0", result.SubjectKey);
        Assert.Equal(0, result.ProcessedCount);
        Assert.Equal(0, result.HotCount);
        Assert.Equal(0, result.WarmCount);
        Assert.Equal(0, result.ColdCount);
        Assert.Equal(0, result.BandChanges);
    }

    [Fact]
    public async Task ApplyDecayAsync_SingleUnknown_UpdatesAndPersists()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();
        const string subjectKey = "test|1.0.0";

        var unknown = new UnknownSymbolDocument
        {
            Id = "unknown-1",
            SubjectKey = subjectKey,
            LastAnalyzedAt = now.AddDays(-7),
            Flags = new UnknownFlags(),
            CreatedAt = now.AddDays(-10),
            Band = UnknownsBand.Cold
        };

        await _unknownsRepo.UpsertAsync(subjectKey, new[] { unknown }, CancellationToken.None);

        var result = await decayService.ApplyDecayAsync(subjectKey, CancellationToken.None);

        Assert.Equal(1, result.ProcessedCount);
        Assert.Equal(subjectKey, result.SubjectKey);

        // Verify the unknown was updated in the repository
        var updated = await _unknownsRepo.GetBySubjectAsync(subjectKey, CancellationToken.None);
        Assert.Single(updated);
        Assert.True(updated[0].UpdatedAt >= now);
    }

    [Fact]
    public async Task ApplyDecayAsync_BandChangesTracked()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();
        const string subjectKey = "test|1.0.0";

        // Create unknown that will change from COLD to HOT due to high staleness and flags
        var unknown = new UnknownSymbolDocument
        {
            Id = "unknown-1",
            SubjectKey = subjectKey,
            LastAnalyzedAt = now.AddDays(-14),
            Flags = new UnknownFlags
            {
                NoProvenanceAnchor = true,
                VersionRange = true,
                ConflictingFeeds = true,
                MissingVector = true
            },
            CreatedAt = now.AddDays(-20),
            Band = UnknownsBand.Cold // Initially cold
        };

        _deploymentRefs.SetDeploymentCount("pkg:npm/test@1.0.0", 100);
        await _unknownsRepo.UpsertAsync(subjectKey, new[] { unknown }, CancellationToken.None);

        var result = await decayService.ApplyDecayAsync(subjectKey, CancellationToken.None);

        // Band should have changed from COLD to HOT
        if (result.HotCount > 0)
        {
            Assert.Equal(1, result.BandChanges);
        }
    }

    [Fact]
    public async Task ApplyDecayAsync_MultipleUnknowns_ProcessesAll()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();
        const string subjectKey = "test|1.0.0";

        var unknowns = new[]
        {
            new UnknownSymbolDocument
            {
                Id = "unknown-1",
                SubjectKey = subjectKey,
                LastAnalyzedAt = now,
                Flags = new UnknownFlags(),
                CreatedAt = now.AddDays(-1),
                Band = UnknownsBand.Cold
            },
            new UnknownSymbolDocument
            {
                Id = "unknown-2",
                SubjectKey = subjectKey,
                LastAnalyzedAt = now.AddDays(-7),
                Flags = new UnknownFlags { NoProvenanceAnchor = true },
                CreatedAt = now.AddDays(-10),
                Band = UnknownsBand.Warm
            },
            new UnknownSymbolDocument
            {
                Id = "unknown-3",
                SubjectKey = subjectKey,
                LastAnalyzedAt = now.AddDays(-14),
                Flags = new UnknownFlags { NoProvenanceAnchor = true, VersionRange = true },
                CreatedAt = now.AddDays(-20),
                Band = UnknownsBand.Hot
            }
        };

        await _unknownsRepo.UpsertAsync(subjectKey, unknowns, CancellationToken.None);

        var result = await decayService.ApplyDecayAsync(subjectKey, CancellationToken.None);

        Assert.Equal(3, result.ProcessedCount);
        Assert.Equal(result.HotCount + result.WarmCount + result.ColdCount, result.ProcessedCount);
    }

    #endregion

    #region RunNightlyDecayBatchAsync Tests

    [Fact]
    public async Task RunNightlyDecayBatchAsync_ProcessesAllSubjects()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();

        // Create unknowns in multiple subjects
        await _unknownsRepo.UpsertAsync("subject-1|1.0.0", new[]
        {
            new UnknownSymbolDocument
            {
                Id = "u1",
                SubjectKey = "subject-1|1.0.0",
                LastAnalyzedAt = now.AddDays(-7),
                Flags = new UnknownFlags(),
                CreatedAt = now.AddDays(-10)
            }
        }, CancellationToken.None);

        await _unknownsRepo.UpsertAsync("subject-2|1.0.0", new[]
        {
            new UnknownSymbolDocument
            {
                Id = "u2",
                SubjectKey = "subject-2|1.0.0",
                LastAnalyzedAt = now.AddDays(-3),
                Flags = new UnknownFlags(),
                CreatedAt = now.AddDays(-5)
            }
        }, CancellationToken.None);

        var result = await decayService.RunNightlyDecayBatchAsync(CancellationToken.None);

        Assert.Equal(2, result.TotalSubjects);
        Assert.Equal(2, result.TotalUnknowns);
        Assert.True(result.Duration >= TimeSpan.Zero);
    }

    [Fact]
    public async Task RunNightlyDecayBatchAsync_RespectsMaxSubjectsLimit()
    {
        var decayOptions = new UnknownsDecayOptions { MaxSubjectsPerBatch = 1 };
        var scoringService = new UnknownsScoringService(
            _unknownsRepo,
            _deploymentRefs,
            _graphMetrics,
            MsOptions.Options.Create(_scoringOptions),
            _timeProvider,
            NullLogger<UnknownsScoringService>.Instance);

        var decayService = new UnknownsDecayService(
            _unknownsRepo,
            scoringService,
            MsOptions.Options.Create(_scoringOptions),
            MsOptions.Options.Create(decayOptions),
            _timeProvider,
            NullLogger<UnknownsDecayService>.Instance);

        var now = _timeProvider.GetUtcNow();

        // Create unknowns in multiple subjects
        await _unknownsRepo.UpsertAsync("subject-1|1.0.0", new[]
        {
            new UnknownSymbolDocument
            {
                Id = "u1",
                SubjectKey = "subject-1|1.0.0",
                LastAnalyzedAt = now.AddDays(-7),
                Flags = new UnknownFlags(),
                CreatedAt = now.AddDays(-10)
            }
        }, CancellationToken.None);

        await _unknownsRepo.UpsertAsync("subject-2|1.0.0", new[]
        {
            new UnknownSymbolDocument
            {
                Id = "u2",
                SubjectKey = "subject-2|1.0.0",
                LastAnalyzedAt = now.AddDays(-3),
                Flags = new UnknownFlags(),
                CreatedAt = now.AddDays(-5)
            }
        }, CancellationToken.None);

        var result = await decayService.RunNightlyDecayBatchAsync(CancellationToken.None);

        // Should only process 1 subject due to limit
        Assert.Equal(1, result.TotalSubjects);
        Assert.Equal(1, result.TotalUnknowns);
    }

    [Fact]
    public async Task RunNightlyDecayBatchAsync_CancellationRespected()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();

        // Create unknowns in multiple subjects
        for (int i = 0; i < 10; i++)
        {
            await _unknownsRepo.UpsertAsync($"subject-{i}|1.0.0", new[]
            {
                new UnknownSymbolDocument
                {
                    Id = $"u{i}",
                    SubjectKey = $"subject-{i}|1.0.0",
                    LastAnalyzedAt = now.AddDays(-7),
                    Flags = new UnknownFlags(),
                    CreatedAt = now.AddDays(-10)
                }
            }, CancellationToken.None);
        }

        using var cts = new CancellationTokenSource();
        cts.Cancel();

        await Assert.ThrowsAsync<OperationCanceledException>(() =>
            decayService.RunNightlyDecayBatchAsync(cts.Token));
    }

    #endregion

    #region ApplyDecayToUnknownAsync Tests

    [Fact]
    public async Task ApplyDecayToUnknownAsync_UpdatesScoringFields()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();

        var unknown = new UnknownSymbolDocument
        {
            Id = "unknown-1",
            SubjectKey = "test|1.0.0",
            Purl = "pkg:npm/test@1.0.0",
            LastAnalyzedAt = now.AddDays(-7),
            Flags = new UnknownFlags { NoProvenanceAnchor = true },
            CreatedAt = now.AddDays(-10),
            Score = 0,
            Band = UnknownsBand.Cold
        };

        _deploymentRefs.SetDeploymentCount("pkg:npm/test@1.0.0", 50);

        var result = await decayService.ApplyDecayToUnknownAsync(unknown, CancellationToken.None);

        // Verify scoring fields were updated
        Assert.True(result.Score > 0);
        Assert.True(result.PopularityScore > 0);
        Assert.True(result.StalenessScore > 0);
        Assert.True(result.UncertaintyScore > 0);
        Assert.NotNull(result.NextScheduledRescan);
        Assert.NotNull(result.NormalizationTrace);
    }

    [Fact]
    public async Task ApplyDecayToUnknownAsync_SetsNextRescanBasedOnBand()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();

        // Create unknown that will be scored as COLD
        var coldUnknown = new UnknownSymbolDocument
        {
            Id = "cold-unknown",
            SubjectKey = "test|1.0.0",
            LastAnalyzedAt = now, // Fresh
            Flags = new UnknownFlags(),
            CreatedAt = now.AddDays(-1)
        };

        var result = await decayService.ApplyDecayToUnknownAsync(coldUnknown, CancellationToken.None);

        Assert.Equal(UnknownsBand.Cold, result.Band);
        Assert.Equal(now.AddDays(_scoringOptions.ColdRescanDays), result.NextScheduledRescan);
    }

    #endregion

    #region Decay Result Aggregation Tests

    [Fact]
    public async Task ApplyDecayAsync_ResultCountsAreAccurate()
    {
        var (decayService, _) = CreateServices();
        var now = _timeProvider.GetUtcNow();
        const string subjectKey = "test|1.0.0";

        // Create unknowns that will end up in different bands
        var unknowns = new List<UnknownSymbolDocument>();

        // This will be COLD (fresh, no flags)
        unknowns.Add(new UnknownSymbolDocument
        {
            Id = "cold-1",
            SubjectKey = subjectKey,
            LastAnalyzedAt = now,
            Flags = new UnknownFlags(),
            CreatedAt = now.AddDays(-1)
        });

        // Add more with varying staleness and flags
        for (int i = 0; i < 5; i++)
        {
            unknowns.Add(new UnknownSymbolDocument
            {
                Id = $"unknown-{i}",
                SubjectKey = subjectKey,
                LastAnalyzedAt = now.AddDays(-i * 2),
                Flags = new UnknownFlags
                {
                    NoProvenanceAnchor = i > 2,
                    VersionRange = i > 3
                },
                CreatedAt = now.AddDays(-i * 2 - 5)
            });
        }

        await _unknownsRepo.UpsertAsync(subjectKey, unknowns, CancellationToken.None);

        var result = await decayService.ApplyDecayAsync(subjectKey, CancellationToken.None);

        Assert.Equal(6, result.ProcessedCount);
        Assert.Equal(6, result.HotCount + result.WarmCount + result.ColdCount);
        Assert.True(result.ColdCount >= 1); // At least the fresh one should be cold
    }

    #endregion

    #region Test Infrastructure

    private sealed class MockTimeProvider : TimeProvider
    {
        private DateTimeOffset _now;

        public MockTimeProvider(DateTimeOffset now) => _now = now;

        public override DateTimeOffset GetUtcNow() => _now;

        public void Advance(TimeSpan duration) => _now = _now.Add(duration);
    }

    private sealed class InMemoryUnknownsRepository : IUnknownsRepository
    {
        private readonly List<UnknownSymbolDocument> _stored = new();

        public Task UpsertAsync(string subjectKey, IEnumerable<UnknownSymbolDocument> items, CancellationToken cancellationToken)
        {
            _stored.RemoveAll(x => x.SubjectKey == subjectKey);
            _stored.AddRange(items);
            return Task.CompletedTask;
        }

        public Task<IReadOnlyList<UnknownSymbolDocument>> GetBySubjectAsync(string subjectKey, CancellationToken cancellationToken)
        {
            return Task.FromResult<IReadOnlyList<UnknownSymbolDocument>>(
                _stored.Where(x => x.SubjectKey == subjectKey).ToList());
        }

        public Task<int> CountBySubjectAsync(string subjectKey, CancellationToken cancellationToken)
        {
            return Task.FromResult(_stored.Count(x => x.SubjectKey == subjectKey));
        }

        public Task BulkUpdateAsync(IEnumerable<UnknownSymbolDocument> items, CancellationToken cancellationToken)
        {
            foreach (var item in items)
            {
                var existing = _stored.FindIndex(x => x.Id == item.Id);
                if (existing >= 0)
                    _stored[existing] = item;
                else
                    _stored.Add(item);
            }
            return Task.CompletedTask;
        }

        public Task<IReadOnlyList<string>> GetAllSubjectKeysAsync(CancellationToken cancellationToken)
        {
            return Task.FromResult<IReadOnlyList<string>>(
                _stored.Select(x => x.SubjectKey).Distinct().ToList());
        }

        public Task<IReadOnlyList<UnknownSymbolDocument>> GetDueForRescanAsync(UnknownsBand band, int limit, CancellationToken cancellationToken)
        {
            return Task.FromResult<IReadOnlyList<UnknownSymbolDocument>>(
                _stored.Where(x => x.Band == band).Take(limit).ToList());
        }

        public Task<IReadOnlyList<UnknownSymbolDocument>> QueryAsync(UnknownsBand? band, int limit, int offset, CancellationToken cancellationToken)
        {
            var query = _stored.AsEnumerable();
            if (band.HasValue)
                query = query.Where(x => x.Band == band.Value);
            return Task.FromResult<IReadOnlyList<UnknownSymbolDocument>>(
                query.Skip(offset).Take(limit).ToList());
        }

        public Task<UnknownSymbolDocument?> GetByIdAsync(string id, CancellationToken cancellationToken)
        {
            return Task.FromResult(_stored.FirstOrDefault(x => x.Id == id));
        }
    }

    private sealed class InMemoryDeploymentRefsRepository : IDeploymentRefsRepository
    {
        private readonly Dictionary<string, int> _counts = new();

        public void SetDeploymentCount(string purl, int count) => _counts[purl] = count;

        public Task<int> CountDeploymentsAsync(string purl, CancellationToken cancellationToken)
        {
            return Task.FromResult(_counts.TryGetValue(purl, out var count) ? count : 0);
        }

        public Task<IReadOnlyList<string>> GetDeploymentIdsAsync(string purl, int limit, CancellationToken cancellationToken)
        {
            return Task.FromResult<IReadOnlyList<string>>(Array.Empty<string>());
        }

        public Task UpsertAsync(DeploymentRef deployment, CancellationToken cancellationToken) => Task.CompletedTask;

        public Task BulkUpsertAsync(IEnumerable<DeploymentRef> deployments, CancellationToken cancellationToken) => Task.CompletedTask;

        public Task<DeploymentSummary?> GetSummaryAsync(string purl, CancellationToken cancellationToken) =>
            Task.FromResult<DeploymentSummary?>(null);
    }

    private sealed class InMemoryGraphMetricsRepository : IGraphMetricsRepository
    {
        private readonly Dictionary<string, GraphMetrics> _metrics = new();

        public void SetMetrics(string symbolId, string callgraphId, GraphMetrics metrics)
        {
            _metrics[$"{symbolId}:{callgraphId}"] = metrics;
        }

        public Task<GraphMetrics?> GetMetricsAsync(string symbolId, string callgraphId, CancellationToken cancellationToken)
        {
            _metrics.TryGetValue($"{symbolId}:{callgraphId}", out var metrics);
            return Task.FromResult(metrics);
        }

        public Task UpsertAsync(GraphMetrics metrics, CancellationToken cancellationToken) => Task.CompletedTask;

        public Task BulkUpsertAsync(IEnumerable<GraphMetrics> metrics, CancellationToken cancellationToken) => Task.CompletedTask;

        public Task<IReadOnlyList<string>> GetStaleCallgraphsAsync(TimeSpan maxAge, int limit, CancellationToken cancellationToken) =>
            Task.FromResult<IReadOnlyList<string>>(Array.Empty<string>());

        public Task DeleteByCallgraphAsync(string callgraphId, CancellationToken cancellationToken) => Task.CompletedTask;
    }

    #endregion
}