// =====================================================================
//  RETAIL PHARMACY PLATFORM — Counter Helper
//  HelperConfig.cs
//
//  The token is generated once, at first run, and never transmitted
//  anywhere. The setup wizard on the local node reads it from this file
//  and stores it in the node's `setting` table (scope COUNTER, key
//  helper_token). Both sides are on the same machine, so it never
//  crosses a wire.
// =====================================================================

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace CounterHelper;

public sealed class HelperConfig
{
    [JsonPropertyName("port")]            public int Port { get; set; } = 7331;
    [JsonPropertyName("token")]           public string Token { get; set; } = "";
    [JsonPropertyName("counter_id")]      public string CounterId { get; set; } = "";
    [JsonPropertyName("default_printer")] public string DefaultPrinter { get; set; } = "";
    [JsonPropertyName("data_dir")]        public string DataDir { get; set; } = "";
    [JsonPropertyName("update_url")]      public string UpdateUrl { get; set; } = "";
    [JsonPropertyName("update_pubkey")]   public string UpdatePubKey { get; set; } = "";

    private static string DefaultDataDir =>
        Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData),
                     "CaresoftCounter");

    public static HelperConfig Load()
    {
        var dir  = DefaultDataDir;
        Directory.CreateDirectory(dir);
        var path = Path.Combine(dir, "helper.json");

        HelperConfig cfg;
        if (File.Exists(path))
        {
            cfg = JsonSerializer.Deserialize<HelperConfig>(File.ReadAllText(path)) ?? new HelperConfig();
        }
        else
        {
            cfg = new HelperConfig();
        }

        if (string.IsNullOrWhiteSpace(cfg.DataDir)) cfg.DataDir = dir;
        if (string.IsNullOrWhiteSpace(cfg.Token))   cfg.Token   = NewToken();

        // Pick a sensible default printer on first run so the setup
        // wizard has something to test with rather than an empty box.
        if (string.IsNullOrWhiteSpace(cfg.DefaultPrinter))
        {
            try
            {
                var printers = RawPrinter.List();
                foreach (var p in printers)
                {
                    var u = p.ToUpperInvariant();
                    // The hardware actually behind Indian chemist counters.
                    if (u.Contains("LX-300") || u.Contains("EPSON") ||
                        u.Contains("TVS") || u.Contains("POS") || u.Contains("THERMAL"))
                    { cfg.DefaultPrinter = p; break; }
                }
                if (string.IsNullOrWhiteSpace(cfg.DefaultPrinter) && printers.Count > 0)
                    cfg.DefaultPrinter = printers[0];
            }
            catch { /* leave blank; the wizard will ask */ }
        }

        Save(cfg, path);
        return cfg;
    }

    private static void Save(HelperConfig cfg, string path)
    {
        var tmp = path + ".tmp";
        File.WriteAllText(tmp, JsonSerializer.Serialize(cfg,
            new JsonSerializerOptions { WriteIndented = true }));
        if (File.Exists(path)) File.Delete(path);
        File.Move(tmp, path);
    }

    /// <summary>32 bytes of CSPRNG, hex encoded.</summary>
    private static string NewToken()
    {
        var b = new byte[32];
        RandomNumberGenerator.Fill(b);
        return Convert.ToHexString(b).ToLowerInvariant();
    }
}