// <copyright file="TestEvidenceService.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
// </copyright>

using System.Collections.Concurrent;
using System.Collections.Immutable;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Logging;

namespace StellaOps.Testing.Evidence;

/// <summary>
/// Default implementation of test evidence service.
/// </summary>
public sealed class TestEvidenceService : ITestEvidenceService
{
    private readonly ILogger<TestEvidenceService> _logger;
    private readonly TimeProvider _timeProvider;
    private readonly ConcurrentDictionary<string, TestEvidenceBundle> _bundles = new();

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        WriteIndented = false,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
    };

    /// <summary>
    /// Initializes a new instance of the <see cref="TestEvidenceService"/> class.
    /// </summary>
    /// <param name="logger">Logger instance.</param>
    /// <param name="timeProvider">Time provider for timestamps.</param>
    public TestEvidenceService(
        ILogger<TestEvidenceService> logger,
        TimeProvider timeProvider)
    {
        _logger = logger;
        _timeProvider = timeProvider;
    }

    /// <inheritdoc/>
    public Task<TestEvidenceSession> BeginSessionAsync(
        TestSessionMetadata metadata,
        CancellationToken ct = default)
    {
        var session = new TestEvidenceSession(metadata);

        _logger.LogInformation(
            "Started test evidence session {SessionId} for suite {TestSuiteId}",
            metadata.SessionId, metadata.TestSuiteId);

        return Task.FromResult(session);
    }

    /// <inheritdoc/>
    public Task RecordTestResultAsync(
        TestEvidenceSession session,
        TestResultRecord result,
        CancellationToken ct = default)
    {
        session.AddResult(result);

        _logger.LogDebug(
            "Recorded test result {TestId}: {Outcome}",
            result.TestId, result.Outcome);

        return Task.CompletedTask;
    }

    /// <inheritdoc/>
    public Task<TestEvidenceBundle> FinalizeSessionAsync(
        TestEvidenceSession session,
        CancellationToken ct = default)
    {
        if (session.IsFinalized)
        {
            throw new InvalidOperationException("Session is already finalized.");
        }

        session.MarkAsFinalized();

        var results = session.GetResults();
        var summary = ComputeSummary(results);
        var merkleRoot = ComputeMerkleRoot(results);
        var bundleId = GenerateBundleId(session.Metadata, merkleRoot);

        var bundle = new TestEvidenceBundle(
            BundleId: bundleId,
            MerkleRoot: merkleRoot,
            Metadata: session.Metadata,
            Summary: summary,
            Results: results,
            FinalizedAt: _timeProvider.GetUtcNow(),
            EvidenceLockerRef: $"evidence://{bundleId}");

        _bundles[bundleId] = bundle;

        _logger.LogInformation(
            "Finalized test evidence bundle {BundleId} with {TotalTests} tests ({Passed} passed, {Failed} failed)",
            bundleId, summary.TotalTests, summary.Passed, summary.Failed);

        return Task.FromResult(bundle);
    }

    /// <inheritdoc/>
    public Task<TestEvidenceBundle?> GetBundleAsync(
        string bundleId,
        CancellationToken ct = default)
    {
        _bundles.TryGetValue(bundleId, out var bundle);
        return Task.FromResult(bundle);
    }

    private static TestSummary ComputeSummary(ImmutableArray<TestResultRecord> results)
    {
        var byCategory = results
            .SelectMany(r => r.Categories.Select(c => (Category: c, Result: r)))
            .GroupBy(x => x.Category)
            .ToImmutableDictionary(g => g.Key, g => g.Count());

        var byBlastRadius = results
            .SelectMany(r => r.BlastRadiusAnnotations.Select(b => (BlastRadius: b, Result: r)))
            .GroupBy(x => x.BlastRadius)
            .ToImmutableDictionary(g => g.Key, g => g.Count());

        return new TestSummary(
            TotalTests: results.Length,
            Passed: results.Count(r => r.Outcome == TestOutcome.Passed),
            Failed: results.Count(r => r.Outcome == TestOutcome.Failed),
            Skipped: results.Count(r => r.Outcome == TestOutcome.Skipped),
            TotalDuration: TimeSpan.FromTicks(results.Sum(r => r.Duration.Ticks)),
            ResultsByCategory: byCategory,
            ResultsByBlastRadius: byBlastRadius);
    }

    private static string ComputeMerkleRoot(ImmutableArray<TestResultRecord> results)
    {
        if (results.IsEmpty)
        {
            return ComputeSha256("empty");
        }

        // Compute leaf hashes
        var leaves = results
            .OrderBy(r => r.TestId)
            .Select(r => ComputeResultHash(r))
            .ToList();

        // Build Merkle tree
        while (leaves.Count > 1)
        {
            var newLevel = new List<string>();

            for (int i = 0; i < leaves.Count; i += 2)
            {
                if (i + 1 < leaves.Count)
                {
                    newLevel.Add(ComputeSha256(leaves[i] + leaves[i + 1]));
                }
                else
                {
                    newLevel.Add(leaves[i]); // Odd leaf promoted
                }
            }

            leaves = newLevel;
        }

        return leaves[0];
    }

    private static string ComputeResultHash(TestResultRecord result)
    {
        var json = JsonSerializer.Serialize(result, JsonOptions);
        return ComputeSha256(json);
    }

    private static string GenerateBundleId(TestSessionMetadata metadata, string merkleRoot)
    {
        var input = $"{metadata.SessionId}:{metadata.TestSuiteId}:{merkleRoot}";
        var hash = ComputeSha256(input);
        return $"teb-{hash[..16]}";
    }

    private static string ComputeSha256(string input)
    {
        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(input));
        return Convert.ToHexString(bytes).ToLowerInvariant();
    }
}