using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using ZB.MOM.WW.CBDDC.Core;
using ZB.MOM.WW.CBDDC.Core.Storage;
using ZB.MOM.WW.CBDDC.Persistence.Surreal;

namespace ZB.MOM.WW.CBDDC.Persistence.Lmdb;

/// <summary>
///     Backfills LMDB oplog content from Surreal and validates parity.
/// </summary>
public sealed class LmdbOplogBackfillTool
{
    private readonly LmdbOplogStore _destination;
    private readonly ILogger<LmdbOplogBackfillTool> _logger;
    private readonly SurrealOplogStore _source;

    /// <summary>
    ///     Initializes a new instance of the <see cref="LmdbOplogBackfillTool" /> class.
    /// </summary>
    public LmdbOplogBackfillTool(
        SurrealOplogStore source,
        LmdbOplogStore destination,
        ILogger<LmdbOplogBackfillTool>? logger = null)
    {
        _source = source ?? throw new ArgumentNullException(nameof(source));
        _destination = destination ?? throw new ArgumentNullException(nameof(destination));
        _logger = logger ?? NullLogger<LmdbOplogBackfillTool>.Instance;
    }

    /// <summary>
    ///     Backfills one dataset from Surreal to LMDB and validates parity.
    /// </summary>
    public async Task<LmdbOplogBackfillReport> BackfillAsync(
        string datasetId,
        CancellationToken cancellationToken = default)
    {
        string normalizedDatasetId = DatasetId.Normalize(datasetId);
        var sourceEntries = (await _source.ExportAsync(normalizedDatasetId, cancellationToken))
            .OrderBy(entry => entry.Timestamp.PhysicalTime)
            .ThenBy(entry => entry.Timestamp.LogicalCounter)
            .ThenBy(entry => entry.Timestamp.NodeId, StringComparer.Ordinal)
            .ThenBy(entry => entry.Hash, StringComparer.Ordinal)
            .ToList();

        await _destination.MergeAsync(sourceEntries, normalizedDatasetId, cancellationToken);
        LmdbOplogBackfillReport report = await ValidateParityAsync(normalizedDatasetId, sourceEntries, cancellationToken);

        _logger.LogInformation(
            "LMDB oplog backfill {Result} for dataset {DatasetId}. Source={SourceCount}, Destination={DestinationCount}, HashSpotChecks={HashSpotChecks}, ChainSpotChecks={ChainSpotChecks}.",
            report.IsSuccess ? "succeeded" : "failed",
            report.DatasetId,
            report.SourceCount,
            report.DestinationCount,
            report.HashSpotCheckCount,
            report.ChainSpotCheckCount);

        return report;
    }

    /// <summary>
    ///     Validates parity only without running a backfill merge.
    /// </summary>
    public async Task<LmdbOplogBackfillReport> ValidateParityAsync(
        string datasetId,
        CancellationToken cancellationToken = default)
    {
        string normalizedDatasetId = DatasetId.Normalize(datasetId);
        var sourceEntries = (await _source.ExportAsync(normalizedDatasetId, cancellationToken)).ToList();
        return await ValidateParityAsync(normalizedDatasetId, sourceEntries, cancellationToken);
    }

    /// <summary>
    ///     Backfills and throws when parity validation fails.
    /// </summary>
    public async Task<LmdbOplogBackfillReport> BackfillOrThrowAsync(
        string datasetId,
        CancellationToken cancellationToken = default)
    {
        LmdbOplogBackfillReport report = await BackfillAsync(datasetId, cancellationToken);
        if (report.IsSuccess) return report;

        throw new InvalidOperationException(
            $"LMDB oplog backfill parity failed for dataset '{report.DatasetId}'. " +
            $"Source={report.SourceCount}, Destination={report.DestinationCount}, " +
            $"CountsMatch={report.CountsMatch}, CountsPerNodeMatch={report.CountsPerNodeMatch}, " +
            $"LatestHashPerNodeMatch={report.LatestHashPerNodeMatch}, HashSpotChecksPassed={report.HashSpotChecksPassed}, " +
            $"ChainSpotChecksPassed={report.ChainSpotChecksPassed}.");
    }

    private async Task<LmdbOplogBackfillReport> ValidateParityAsync(
        string datasetId,
        List<OplogEntry> sourceEntries,
        CancellationToken cancellationToken)
    {
        var sourceOrdered = sourceEntries
            .OrderBy(entry => entry.Timestamp.PhysicalTime)
            .ThenBy(entry => entry.Timestamp.LogicalCounter)
            .ThenBy(entry => entry.Timestamp.NodeId, StringComparer.Ordinal)
            .ThenBy(entry => entry.Hash, StringComparer.Ordinal)
            .ToList();

        var destinationOrdered = (await _destination.ExportAsync(datasetId, cancellationToken))
            .OrderBy(entry => entry.Timestamp.PhysicalTime)
            .ThenBy(entry => entry.Timestamp.LogicalCounter)
            .ThenBy(entry => entry.Timestamp.NodeId, StringComparer.Ordinal)
            .ThenBy(entry => entry.Hash, StringComparer.Ordinal)
            .ToList();

        bool countsMatch = sourceOrdered.Count == destinationOrdered.Count;
        IReadOnlyDictionary<string, int> sourceCountByNode = CountByNode(sourceOrdered);
        IReadOnlyDictionary<string, int> destinationCountByNode = CountByNode(destinationOrdered);
        bool countsPerNodeMatch = DictionaryEqual(sourceCountByNode, destinationCountByNode);

        IReadOnlyDictionary<string, string> sourceLatestHashByNode = LatestHashByNode(sourceOrdered);
        IReadOnlyDictionary<string, string> destinationLatestHashByNode = LatestHashByNode(destinationOrdered);
        bool latestHashPerNodeMatch = DictionaryEqual(sourceLatestHashByNode, destinationLatestHashByNode);

        (bool hashSpotChecksPassed, int hashSpotCheckCount) = await RunHashSpotChecksAsync(
            datasetId,
            sourceOrdered,
            cancellationToken);
        (bool chainSpotChecksPassed, int chainSpotCheckCount) = await RunChainSpotChecksAsync(
            datasetId,
            sourceOrdered,
            cancellationToken);

        return new LmdbOplogBackfillReport(
            datasetId,
            sourceOrdered.Count,
            destinationOrdered.Count,
            sourceCountByNode,
            destinationCountByNode,
            sourceLatestHashByNode,
            destinationLatestHashByNode,
            hashSpotCheckCount,
            chainSpotCheckCount,
            countsMatch,
            countsPerNodeMatch,
            latestHashPerNodeMatch,
            hashSpotChecksPassed,
            chainSpotChecksPassed);
    }

    private async Task<(bool Passed, int Count)> RunHashSpotChecksAsync(
        string datasetId,
        IReadOnlyList<OplogEntry> sourceEntries,
        CancellationToken cancellationToken)
    {
        if (sourceEntries.Count == 0) return (true, 0);

        var sampleIndexes = BuildSampleIndexes(sourceEntries.Count, Math.Min(10, sourceEntries.Count));
        foreach (int index in sampleIndexes)
        {
            string hash = sourceEntries[index].Hash;
            OplogEntry? destinationEntry = await _destination.GetEntryByHashAsync(hash, datasetId, cancellationToken);
            if (destinationEntry == null) return (false, sampleIndexes.Count);
        }

        return (true, sampleIndexes.Count);
    }

    private async Task<(bool Passed, int Count)> RunChainSpotChecksAsync(
        string datasetId,
        IReadOnlyList<OplogEntry> sourceEntries,
        CancellationToken cancellationToken)
    {
        if (sourceEntries.Count < 2) return (true, 0);

        var sourceByHash = sourceEntries.ToDictionary(entry => entry.Hash, StringComparer.Ordinal);
        var checks = sourceEntries
            .Where(entry => !string.IsNullOrWhiteSpace(entry.PreviousHash) &&
                            sourceByHash.ContainsKey(entry.PreviousHash))
            .Take(5)
            .Select(entry => (StartHash: entry.PreviousHash, EndHash: entry.Hash))
            .ToList();

        foreach (var check in checks)
        {
            string[] sourceChain = (await _source.GetChainRangeAsync(check.StartHash, check.EndHash, datasetId, cancellationToken))
                .Select(entry => entry.Hash)
                .ToArray();
            string[] destinationChain =
                (await _destination.GetChainRangeAsync(check.StartHash, check.EndHash, datasetId, cancellationToken))
                .Select(entry => entry.Hash)
                .ToArray();

            if (!sourceChain.SequenceEqual(destinationChain, StringComparer.Ordinal))
                return (false, checks.Count);
        }

        return (true, checks.Count);
    }

    private static IReadOnlyDictionary<string, int> CountByNode(IEnumerable<OplogEntry> entries)
    {
        return entries
            .Where(entry => !string.IsNullOrWhiteSpace(entry.Timestamp.NodeId))
            .GroupBy(entry => entry.Timestamp.NodeId, StringComparer.Ordinal)
            .ToDictionary(group => group.Key, group => group.Count(), StringComparer.Ordinal);
    }

    private static IReadOnlyDictionary<string, string> LatestHashByNode(IEnumerable<OplogEntry> entries)
    {
        return entries
            .Where(entry => !string.IsNullOrWhiteSpace(entry.Timestamp.NodeId))
            .GroupBy(entry => entry.Timestamp.NodeId, StringComparer.Ordinal)
            .ToDictionary(
                group => group.Key,
                group => group
                    .OrderByDescending(entry => entry.Timestamp.PhysicalTime)
                    .ThenByDescending(entry => entry.Timestamp.LogicalCounter)
                    .ThenByDescending(entry => entry.Hash, StringComparer.Ordinal)
                    .First()
                    .Hash,
                StringComparer.Ordinal);
    }

    private static bool DictionaryEqual<T>(
        IReadOnlyDictionary<string, T> left,
        IReadOnlyDictionary<string, T> right)
    {
        if (left.Count != right.Count) return false;
        foreach (var pair in left)
        {
            if (!right.TryGetValue(pair.Key, out T? rightValue)) return false;
            if (!EqualityComparer<T>.Default.Equals(pair.Value, rightValue)) return false;
        }

        return true;
    }

    private static List<int> BuildSampleIndexes(int totalCount, int sampleCount)
    {
        if (sampleCount <= 0 || totalCount <= 0) return [];
        if (sampleCount >= totalCount) return Enumerable.Range(0, totalCount).ToList();

        var indexes = new HashSet<int>();
        for (var i = 0; i < sampleCount; i++)
        {
            int index = (int)Math.Round(i * (totalCount - 1d) / (sampleCount - 1d));
            indexes.Add(Math.Clamp(index, 0, totalCount - 1));
        }

        return indexes.OrderBy(value => value).ToList();
    }
}

/// <summary>
///     Parity report produced by the LMDB backfill tool.
/// </summary>
public sealed record LmdbOplogBackfillReport(
    string DatasetId,
    int SourceCount,
    int DestinationCount,
    IReadOnlyDictionary<string, int> SourceCountByNode,
    IReadOnlyDictionary<string, int> DestinationCountByNode,
    IReadOnlyDictionary<string, string> SourceLatestHashByNode,
    IReadOnlyDictionary<string, string> DestinationLatestHashByNode,
    int HashSpotCheckCount,
    int ChainSpotCheckCount,
    bool CountsMatch,
    bool CountsPerNodeMatch,
    bool LatestHashPerNodeMatch,
    bool HashSpotChecksPassed,
    bool ChainSpotChecksPassed)
{
    /// <summary>
    ///     Gets a value indicating whether parity validation passed all checks.
    /// </summary>
    public bool IsSuccess =>
        CountsMatch &&
        CountsPerNodeMatch &&
        LatestHashPerNodeMatch &&
        HashSpotChecksPassed &&
        ChainSpotChecksPassed;
}