// <copyright file="FeedSnapshotSupport.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the BUSL-1.1.
// </copyright>

using System.Collections.Concurrent;
using System.Collections.Immutable;
using System.Text.Json;
using StellaOps.Replay.Core.FeedSnapshots;

namespace StellaOps.Replay.WebService;

internal sealed class InMemoryFeedSnapshotBlobStore : IFeedSnapshotBlobStore
{
    private readonly ConcurrentDictionary<string, FeedSnapshotBlob> _blobs = new(StringComparer.Ordinal);

    public Task StoreAsync(FeedSnapshotBlob blob, CancellationToken ct = default)
    {
        _blobs[blob.Digest] = blob;
        return Task.CompletedTask;
    }

    public Task<FeedSnapshotBlob?> GetByDigestAsync(string digest, CancellationToken ct = default)
    {
        _blobs.TryGetValue(digest, out var blob);
        return Task.FromResult(blob);
    }

    public Task<bool> ExistsAsync(string digest, CancellationToken ct = default)
    {
        return Task.FromResult(_blobs.ContainsKey(digest));
    }

    public Task DeleteAsync(string digest, CancellationToken ct = default)
    {
        _blobs.TryRemove(digest, out _);
        return Task.CompletedTask;
    }
}

internal sealed class InMemoryFeedSnapshotIndexStore : IFeedSnapshotIndexStore
{
    private readonly ConcurrentDictionary<string, List<FeedSnapshotIndexEntry>> _index = new(StringComparer.Ordinal);

    public Task IndexSnapshotAsync(FeedSnapshotIndexEntry entry, CancellationToken ct = default)
    {
        var entries = _index.GetOrAdd(entry.ProviderId, static _ => []);
        lock (entries)
        {
            entries.Add(entry);
        }

        return Task.CompletedTask;
    }

    public Task<FeedSnapshotIndexEntry?> FindSnapshotAtTimeAsync(
        string providerId,
        DateTimeOffset pointInTime,
        CancellationToken ct = default)
    {
        if (!_index.TryGetValue(providerId, out var entries))
        {
            return Task.FromResult<FeedSnapshotIndexEntry?>(null);
        }

        lock (entries)
        {
            var found = entries
                .Where(e => e.CapturedAt <= pointInTime)
                .OrderByDescending(e => e.CapturedAt)
                .FirstOrDefault();
            return Task.FromResult(found);
        }
    }

    public Task<ImmutableArray<FeedSnapshotIndexEntry>> ListSnapshotsAsync(
        string providerId,
        DateTimeOffset from,
        DateTimeOffset to,
        int limit,
        CancellationToken ct = default)
    {
        if (!_index.TryGetValue(providerId, out var entries))
        {
            return Task.FromResult(ImmutableArray<FeedSnapshotIndexEntry>.Empty);
        }

        lock (entries)
        {
            IEnumerable<FeedSnapshotIndexEntry> query = entries
                .Where(e => e.CapturedAt >= from && e.CapturedAt <= to)
                .OrderBy(e => e.CapturedAt);

            if (limit > 0)
            {
                query = query.Take(limit);
            }

            return Task.FromResult(query.ToImmutableArray());
        }
    }
}

internal sealed class JsonAdvisoryExtractor : IAdvisoryExtractor
{
    public Task<AdvisoryData?> ExtractAdvisoryAsync(
        string cveId,
        byte[] content,
        FeedSnapshotFormat format,
        CancellationToken ct = default)
    {
        if (string.IsNullOrWhiteSpace(cveId) || content.Length == 0)
        {
            return Task.FromResult<AdvisoryData?>(null);
        }

        try
        {
            using var doc = JsonDocument.Parse(content);
            var advisory = TryExtract(cveId, doc.RootElement);
            return Task.FromResult(advisory);
        }
        catch (JsonException)
        {
            return Task.FromResult<AdvisoryData?>(null);
        }
    }

    private static AdvisoryData? TryExtract(string cveId, JsonElement root)
    {
        if (root.ValueKind == JsonValueKind.Object)
        {
            if (TryParseAdvisoryObject(cveId, root, out var direct))
            {
                return direct;
            }

            if (TryGetPropertyIgnoreCase(root, "advisories", out var advisories) &&
                advisories.ValueKind == JsonValueKind.Array)
            {
                foreach (var item in advisories.EnumerateArray())
                {
                    if (item.ValueKind == JsonValueKind.Object &&
                        TryParseAdvisoryObject(cveId, item, out var parsed))
                    {
                        return parsed;
                    }
                }
            }

            if (TryGetPropertyIgnoreCase(root, "cves", out var cves))
            {
                if (cves.ValueKind == JsonValueKind.Object)
                {
                    foreach (var prop in cves.EnumerateObject())
                    {
                        if (string.Equals(prop.Name, cveId, StringComparison.OrdinalIgnoreCase) &&
                            prop.Value.ValueKind == JsonValueKind.Object &&
                            TryParseAdvisoryObject(cveId, prop.Value, out var parsed))
                        {
                            return parsed;
                        }
                    }
                }

                if (cves.ValueKind == JsonValueKind.Array)
                {
                    foreach (var item in cves.EnumerateArray())
                    {
                        if (item.ValueKind == JsonValueKind.Object &&
                            TryParseAdvisoryObject(cveId, item, out var parsed))
                        {
                            return parsed;
                        }
                    }
                }
            }
        }

        if (root.ValueKind == JsonValueKind.Array)
        {
            foreach (var item in root.EnumerateArray())
            {
                if (item.ValueKind == JsonValueKind.Object &&
                    TryParseAdvisoryObject(cveId, item, out var parsed))
                {
                    return parsed;
                }
            }
        }

        return null;
    }

    private static bool TryParseAdvisoryObject(string requestedCveId, JsonElement obj, out AdvisoryData? advisory)
    {
        advisory = null;
        var cveId = GetString(obj, "cveId", "cve", "cve_id", "id");
        if (string.IsNullOrWhiteSpace(cveId))
        {
            return false;
        }

        if (!string.Equals(cveId, requestedCveId, StringComparison.OrdinalIgnoreCase))
        {
            return false;
        }

        advisory = new AdvisoryData
        {
            CveId = cveId,
            Severity = GetString(obj, "severity"),
            CvssScore = GetDecimal(obj, "cvssScore", "cvss", "score"),
            CvssVector = GetString(obj, "cvssVector", "vector"),
            Description = GetString(obj, "description", "summary"),
            FixStatus = GetString(obj, "fixStatus", "fix_state", "status"),
            AffectedProducts = GetStringArray(obj, "affectedProducts", "affected_products", "packages"),
            References = GetStringArray(obj, "references", "refs", "links"),
            PublishedAt = GetDateTimeOffset(obj, "publishedAt", "published_at"),
            LastModifiedAt = GetDateTimeOffset(obj, "lastModifiedAt", "last_modified_at")
        };

        return true;
    }

    private static string? GetString(JsonElement obj, params string[] names)
    {
        foreach (var name in names)
        {
            if (TryGetPropertyIgnoreCase(obj, name, out var value))
            {
                if (value.ValueKind == JsonValueKind.String)
                {
                    return value.GetString();
                }

                if (value.ValueKind != JsonValueKind.Null && value.ValueKind != JsonValueKind.Undefined)
                {
                    return value.ToString();
                }
            }
        }

        return null;
    }

    private static decimal? GetDecimal(JsonElement obj, params string[] names)
    {
        foreach (var name in names)
        {
            if (!TryGetPropertyIgnoreCase(obj, name, out var value))
            {
                continue;
            }

            if (value.ValueKind == JsonValueKind.Number && value.TryGetDecimal(out var num))
            {
                return num;
            }

            if (value.ValueKind == JsonValueKind.String &&
                decimal.TryParse(value.GetString(), out var parsed))
            {
                return parsed;
            }
        }

        return null;
    }

    private static DateTimeOffset? GetDateTimeOffset(JsonElement obj, params string[] names)
    {
        foreach (var name in names)
        {
            if (!TryGetPropertyIgnoreCase(obj, name, out var value))
            {
                continue;
            }

            if (value.ValueKind == JsonValueKind.String &&
                DateTimeOffset.TryParse(value.GetString(), out var parsed))
            {
                return parsed;
            }
        }

        return null;
    }

    private static ImmutableArray<string> GetStringArray(JsonElement obj, params string[] names)
    {
        foreach (var name in names)
        {
            if (!TryGetPropertyIgnoreCase(obj, name, out var value) ||
                value.ValueKind != JsonValueKind.Array)
            {
                continue;
            }

            var values = new List<string>();
            foreach (var item in value.EnumerateArray())
            {
                if (item.ValueKind == JsonValueKind.String)
                {
                    var str = item.GetString();
                    if (!string.IsNullOrWhiteSpace(str))
                    {
                        values.Add(str);
                    }
                }
            }

            return values.ToImmutableArray();
        }

        return ImmutableArray<string>.Empty;
    }

    private static bool TryGetPropertyIgnoreCase(JsonElement obj, string name, out JsonElement value)
    {
        foreach (var prop in obj.EnumerateObject())
        {
            if (string.Equals(prop.Name, name, StringComparison.OrdinalIgnoreCase))
            {
                value = prop.Value;
                return true;
            }
        }

        value = default;
        return false;
    }
}