using System.Globalization;
using Fleet.Core;

namespace Fleet.Hosting;

/// <summary>
/// Writes logs locally and keeps a bounded ring of recent lines. Heartbeats carry only counters (see <see cref="TakeSummary"/>);
/// the text leaves the node when the control plane asks for it (see <see cref="Read"/>).
/// </summary>
public sealed class BufferedNodeLog : INodeLog, INodeLogSource
{
    private const int Capacity = 2048;
    private const int MaxFields = 20;
    private const int MaxMessageLength = 512;
    private const int MaxFieldValueLength = 256;
    private const int MaxPageBytes = 96 << 10;
    private const int MaxSummaryTypes = 8;

    private readonly object _gate = new();
    private readonly LinkedList<NodeLogEntry> _ring = [];
    private readonly Dictionary<(uint Type, string Level), long> _counts = [];
    private readonly INodeLog _local;
    private readonly TimeProvider _time;
    private long _lastId;
    private long _info;
    private long _warn;
    private long _error;

    public BufferedNodeLog(INodeLog local, TimeProvider time)
    {
        _local = local;
        _time = time;
    }

    public void Write(NodeLogLevel level, string message, params (string Key, object? Value)[] fields)
    {
        _local.Write(level, message, fields);

        var safeFields = new Dictionary<string, string>(Math.Min(fields.Length, MaxFields), StringComparer.Ordinal);
        foreach ((string key, object? value) in fields.Take(MaxFields))
        {
            string safeValue = IsSensitiveKey(key) ? "[redacted]" : Convert.ToString(value, CultureInfo.InvariantCulture) ?? "";
            safeFields[key.Length <= 64 ? key : key[..64]] = Truncate(safeValue, MaxFieldValueLength);
        }

        string levelName = level.ToString().ToLowerInvariant();
        var record = new NodeLogRecord(_time.GetUtcNow().ToUnixTimeMilliseconds(), levelName, Truncate(message, MaxMessageLength), safeFields);
        uint type = TypeOf(record.Message);
        lock (_gate)
        {
            _ring.AddLast(new NodeLogEntry(++_lastId, type, record));
            if (_ring.Count > Capacity)
            {
                _ring.RemoveFirst();
            }

            _counts[(type, levelName)] = _counts.GetValueOrDefault((type, levelName)) + 1;
            switch (level)
            {
                case NodeLogLevel.Error:
                    _error++;
                    break;
                case NodeLogLevel.Warn:
                    _warn++;
                    break;
                default:
                    _info++;
                    break;
            }
        }
    }

    public NodeLogSummary TakeSummary()
    {
        lock (_gate)
        {
            var summary = new NodeLogSummary(
                _lastId, _info, _warn, _error,
                [.. _counts.OrderByDescending(pair => pair.Value).Take(MaxSummaryTypes).Select(pair => new NodeLogTypeCount(pair.Key.Type, pair.Key.Level, pair.Value))]);
            _counts.Clear();
            _info = _warn = _error = 0;
            return summary;
        }
    }

    public NodeLogPage Read(long afterId, int limit, string? minLevel)
    {
        int rank = LevelRank(minLevel);
        lock (_gate)
        {
            var items = new List<NodeLogEntry>(Math.Min(Math.Max(limit, 0), 200));
            int bytes = 0;
            foreach (NodeLogEntry entry in _ring)
            {
                if (entry.Id <= afterId || LevelRank(entry.Record.Level) < rank)
                {
                    continue;
                }

                int entryBytes = 64 + entry.Record.Message.Length + entry.Record.Fields.Sum(pair => pair.Key.Length + pair.Value.Length + 8);
                if (items.Count >= Math.Clamp(limit, 0, 200) || (items.Count > 0 && bytes + entryBytes > MaxPageBytes))
                {
                    break;
                }

                items.Add(entry);
                bytes += entryBytes;
            }

            return new NodeLogPage(items, _lastId);
        }
    }

    /// <summary>The line's type: a stable 32-bit FNV-1a hash of its message text, so the same template always maps to the same number.</summary>
    public static uint TypeOf(string message)
    {
        uint hash = 2166136261;
        foreach (char c in message)
        {
            hash = (hash ^ c) * 16777619;
        }

        return hash;
    }

    private static int LevelRank(string? level) => level switch
    {
        "error" => 2,
        "warn" => 1,
        _ => 0,
    };

    private static bool IsSensitiveKey(string key)
    {
        string lower = key.ToLowerInvariant();
        return lower.Contains("token", StringComparison.Ordinal)
            || lower.Contains("secret", StringComparison.Ordinal)
            || lower.Contains("password", StringComparison.Ordinal)
            || lower.Contains("private", StringComparison.Ordinal)
            || lower.Contains("signature", StringComparison.Ordinal)
            || lower.Contains("authorization", StringComparison.Ordinal)
            || lower.Contains("cookie", StringComparison.Ordinal)
            || lower == "mac";
    }

    private static string Truncate(string value, int maxLength) => value.Length <= maxLength ? value : value[..maxLength];
}