using System;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Threading;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using HC_APTBS.Models;
using HC_APTBS.Services;

namespace HC_APTBS.ViewModels.Pages
{
    /// <summary>
    /// Developer Tools — EEPROM unlock password library. Persisted via
    /// <see cref="IConfigurationService.EepromPasswords"/>.
    ///
    /// <para>"Apply" sends the standard KWP unlock packet
    /// <c>[0x18 0x00 Zone KeyHi KeyLo]</c> over the persistent K-Line session
    /// (per <c>docs/kline_eeprom_spec.md</c>) and logs ACK/NAK in the parent's
    /// transaction log. "Add" pushes a new entry built from the small inline editor.</para>
    ///
    /// <para>Compiled into Debug builds only — see <c>HC_APTBS.csproj</c>.</para>
    /// </summary>
    public sealed partial class DeveloperToolsPasswordsViewModel : ObservableObject
    {
        private readonly DeveloperPageViewModel _parent;
        private readonly IKwpService _kwp;
        private readonly IConfigurationService _config;
        private readonly IAppLogger _log;
        private const string LogId = nameof(DeveloperToolsPasswordsViewModel);

        public DeveloperToolsPasswordsViewModel(
            DeveloperPageViewModel parent,
            IKwpService kwp,
            IConfigurationService config,
            IAppLogger log)
        {
            _parent = parent;
            _kwp    = kwp;
            _config = config;
            _log    = log;
        }

        /// <summary>Persistent collection from <see cref="IConfigurationService.EepromPasswords"/>.</summary>
        public ObservableCollection<EepromPassword> Items => _config.EepromPasswords;

        /// <summary>Currently selected entry. Drives Apply / Delete enable state.</summary>
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(ApplySelectedCommand))]
        [NotifyCanExecuteChangedFor(nameof(DeleteSelectedCommand))]
        private EepromPassword? _selected;

        // ── Inline "Add new" editor ──────────────────────────────────────────────

        /// <summary>Display name for the new entry.</summary>
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(AddCommand))]
        private string _newName = string.Empty;

        /// <summary>Zone byte for the new entry, hex (e.g. "03").</summary>
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(AddCommand))]
        private string _newZoneHex = "00";

        /// <summary>16-bit key for the new entry, hex (e.g. "00FF").</summary>
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(AddCommand))]
        private string _newKeyHex = "0000";

        // ── Commands ──────────────────────────────────────────────────────────────

        /// <summary>Sends <c>[0x18 0x00 Zone KeyHi KeyLo]</c> for the selected password.</summary>
        [RelayCommand(CanExecute = nameof(CanApplySelected))]
        private async Task ApplySelectedAsync()
        {
            if (Selected is null) return;

            byte[] payload =
            {
                0x18,
                0x00,
                Selected.Zone,
                (byte)(Selected.Key >> 8),
                (byte)(Selected.Key & 0xFF),
            };
            var hex = DeveloperPageViewModel.FormatHex(payload);
            _parent.AppendLog(DeveloperLogDirection.Tx, $"[Apply '{Selected.Name}'] {hex}");
            _parent.SetStatus($"Applying '{Selected.Name}' (zone 0x{Selected.Zone:X2}, key 0x{Selected.Key:X4})…");

            try
            {
                var responses = await _kwp.SendRawCustomAsync(payload, CancellationToken.None);
                if (responses.Count == 0)
                {
                    _parent.AppendLog(DeveloperLogDirection.Info, "(no response)");
                    _parent.SetStatus("No response — session may not be open.");
                    return;
                }
                foreach (var pkt in responses)
                    _parent.AppendLog(DeveloperLogDirection.Rx, DeveloperPageViewModel.FormatHex(pkt));

                // Heuristic: a NAK is a single 3-byte packet with title 0x0A;
                // anything else is treated as success at the protocol layer.
                bool nak = responses.Count == 1 && responses[0].Length >= 3 && responses[0][2] == 0x0A;
                _parent.SetStatus(nak
                    ? $"'{Selected.Name}' rejected (NAK)."
                    : $"'{Selected.Name}' accepted.");
            }
            catch (Exception ex)
            {
                _parent.AppendLog(DeveloperLogDirection.Info, $"ERROR: {ex.Message}");
                _parent.SetStatus($"Apply failed: {ex.Message}");
                _log.Warning(LogId, $"ApplySelected failed: {ex.Message}");
            }
        }

        private bool CanApplySelected() => Selected is not null;

        /// <summary>Adds a new entry from the inline editor and persists.</summary>
        [RelayCommand(CanExecute = nameof(CanAdd))]
        private void Add()
        {
            var name = (NewName ?? string.Empty).Trim();
            if (name.Length == 0)
            {
                _parent.SetStatus("Enter a name before adding a password.");
                return;
            }
            if (!TryParseHexByte(NewZoneHex, out byte zone))
            {
                _parent.SetStatus($"Bad zone hex '{NewZoneHex}'.");
                return;
            }
            if (!TryParseHexUshort(NewKeyHex, out ushort key))
            {
                _parent.SetStatus($"Bad key hex '{NewKeyHex}'.");
                return;
            }

            Items.Add(new EepromPassword { Name = name, Zone = zone, Key = key });
            _config.SaveEepromPasswords();
            _parent.AppendLog(DeveloperLogDirection.Info,
                $"ADDED password '{name}' (zone 0x{zone:X2}, key 0x{key:X4})");
            _parent.SetStatus($"Added '{name}'.");

            NewName    = string.Empty;
            NewZoneHex = "00";
            NewKeyHex  = "0000";
        }

        private bool CanAdd() =>
            !string.IsNullOrWhiteSpace(NewName)
            && TryParseHexByte(NewZoneHex, out _)
            && TryParseHexUshort(NewKeyHex, out _);

        /// <summary>Removes the selected entry from the library and persists.</summary>
        [RelayCommand(CanExecute = nameof(CanDeleteSelected))]
        private void DeleteSelected()
        {
            if (Selected is null) return;
            var name = Selected.Name;
            Items.Remove(Selected);
            _config.SaveEepromPasswords();
            _parent.AppendLog(DeveloperLogDirection.Info, $"DELETED password '{name}'");
            _parent.SetStatus($"Deleted '{name}'.");
            Selected = null;
        }

        private bool CanDeleteSelected() => Selected is not null;

        // ── Helpers ───────────────────────────────────────────────────────────────

        private static bool TryParseHexByte(string text, out byte value)
        {
            value = 0;
            if (string.IsNullOrWhiteSpace(text)) return false;
            var t = text.Trim();
            if (t.StartsWith("0x", StringComparison.OrdinalIgnoreCase)) t = t.Substring(2);
            return byte.TryParse(t, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out value);
        }

        private static bool TryParseHexUshort(string text, out ushort value)
        {
            value = 0;
            if (string.IsNullOrWhiteSpace(text)) return false;
            var t = text.Trim();
            if (t.StartsWith("0x", StringComparison.OrdinalIgnoreCase)) t = t.Substring(2);
            return ushort.TryParse(t, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out value);
        }
    }
}