using Microsoft.Extensions.Options;
using System.Collections.Concurrent;
using System.Text.Json;
using YD_TrainingCompetition_Api.Models;
using YD_TrainingCompetition_Api.Options;

namespace YD_TrainingCompetition_Api.Services;

public sealed class DeviceStateStore : IDeviceStateStore
{
    private readonly ConcurrentDictionary<string, DeviceTelemetry> _states = new(StringComparer.OrdinalIgnoreCase);
    private readonly ScoringOptions _options;
    private readonly ILogger<DeviceStateStore> _logger;

    public DeviceStateStore(IOptions<ScoringOptions> options, ILogger<DeviceStateStore> logger)
    {
        _options = options.Value;
        _logger = logger;
        LoadSnapshot();
    }

    public bool TryUpsert(DeviceTelemetry telemetry, out string? reason)
    {
        reason = null;

        if (string.IsNullOrWhiteSpace(telemetry.DeviceId))
        {
            reason = "deviceId is required";
            return false;
        }

        if (!_states.ContainsKey(telemetry.DeviceId) && _states.Count >= _options.MaxDevices)
        {
            reason = $"max device count({_options.MaxDevices}) reached";
            return false;
        }

        telemetry.Timestamp = telemetry.Timestamp == default ? DateTimeOffset.UtcNow : telemetry.Timestamp;
        _states[telemetry.DeviceId] = telemetry;
        PersistSnapshot();
        return true;
    }

    public IReadOnlyCollection<DeviceSnapshot> GetAll()
    {
        var now = DateTimeOffset.UtcNow;
        return _states.Values
            .OrderBy(x => x.DeviceId, StringComparer.OrdinalIgnoreCase)
            .Select(x => new DeviceSnapshot
            {
                Telemetry = x,
                LastSeen = x.Timestamp,
                Online = now - x.Timestamp <= TimeSpan.FromSeconds(_options.OfflineThresholdSeconds)
            })
            .ToArray();
    }

    public DeviceSnapshot? GetByDeviceId(string deviceId)
    {
        if (!_states.TryGetValue(deviceId, out var telemetry))
        {
            return null;
        }

        var now = DateTimeOffset.UtcNow;
        return new DeviceSnapshot
        {
            Telemetry = telemetry,
            LastSeen = telemetry.Timestamp,
            Online = now - telemetry.Timestamp <= TimeSpan.FromSeconds(_options.OfflineThresholdSeconds)
        };
    }

    private void LoadSnapshot()
    {
        try
        {
            if (!File.Exists(_options.SnapshotPath))
            {
                return;
            }

            var json = File.ReadAllText(_options.SnapshotPath);
            var data = JsonSerializer.Deserialize<List<DeviceTelemetry>>(json);
            if (data is null)
            {
                return;
            }

            foreach (var telemetry in data)
            {
                if (!string.IsNullOrWhiteSpace(telemetry.DeviceId))
                {
                    _states[telemetry.DeviceId] = telemetry;
                }
            }

            _logger.LogInformation("Loaded {Count} device snapshots from disk", _states.Count);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to load device snapshot");
        }
    }

    private void PersistSnapshot()
    {
        try
        {
            var directory = Path.GetDirectoryName(_options.SnapshotPath);
            if (!string.IsNullOrWhiteSpace(directory))
            {
                Directory.CreateDirectory(directory);
            }

            var json = JsonSerializer.Serialize(_states.Values, new JsonSerializerOptions
            {
                WriteIndented = false
            });

            File.WriteAllText(_options.SnapshotPath, json);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to persist device snapshot");
        }
    }
}