using System;
using System.Diagnostics;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using PKHeX.Core;

namespace PKHeX.Drawing
{
    public static class QRDecode
    {
        // QR Utility
        private const string DecodeAPI = "http://api.qrserver.com/v1/read-qr-code/?fileurl=";

        public static QRDecodeResult GetQRData(string address, out byte[] result)
        {
            result = Array.Empty<byte>();
            // Fetch data from QR code...

            if (!address.StartsWith("http"))
                return QRDecodeResult.BadPath;

            string url = DecodeAPI + WebUtility.UrlEncode(address);
            string data;
            try
            {
                var str = NetUtil.GetStringFromURL(url);
                if (str is null)
                    return QRDecodeResult.BadConnection;

                data = str;
                if (data.Contains("could not find"))
                    return QRDecodeResult.BadImage;

                if (data.Contains("filetype not supported"))
                    return QRDecodeResult.BadType;
            }
#pragma warning disable CA1031 // Do not catch general exception types
            catch { return QRDecodeResult.BadConnection; }
#pragma warning restore CA1031 // Do not catch general exception types

            // Quickly convert the json response to a data string
            try
            {
                result = DecodeQRJson(data);
                return QRDecodeResult.Success;
            }
#pragma warning disable CA1031 // Do not catch general exception types
            catch (Exception e)
#pragma warning restore CA1031 // Do not catch general exception types
            {
                Debug.WriteLine(e.Message);
                return QRDecodeResult.BadConversion;
            }
        }

        private static byte[] DecodeQRJson(string data)
        {
            const string cap = "\",\"error\":null}]}]";
            const string intro = "[{\"type\":\"qrcode\",\"symbol\":[{\"seq\":0,\"data\":\"";
            const string qrcode = "nQR-Code:";
            if (!data.StartsWith(intro))
                throw new FormatException();

            string pkstr = data[intro.Length..];

            // Remove multiple QR codes in same image
            var qr = pkstr.IndexOf(qrcode, StringComparison.Ordinal);
            if (qr != -1)
                pkstr = pkstr[..qr];

            // Trim outro
            var outroIndex = pkstr.IndexOf(cap, StringComparison.Ordinal);
            if (outroIndex == -1)
                throw new FormatException();

            pkstr = pkstr[..outroIndex];

            if (!pkstr.StartsWith("http") && !pkstr.StartsWith("null")) // G7
            {
                string fstr = Regex.Unescape(pkstr);
                byte[] raw = Encoding.Unicode.GetBytes(fstr);

                // Remove 00 interstitials and retrieve from offset 0x30, take PK7 Stored Size (always)
                byte[] result = new byte[0xE8];
                for (int i = 0; i < result.Length; i++)
                    result[i] = raw[(i + 0x30) * 2];
                return result;
            }
            // All except G7
            pkstr = pkstr[(pkstr.IndexOf('#') + 1)..]; // Trim URL
            pkstr = pkstr.Replace("\\", string.Empty); // Rectify response

            return Convert.FromBase64String(pkstr);
        }

        public static string ConvertMsg(this QRDecodeResult result) => result switch
        {
            QRDecodeResult.Success => string.Empty,
            QRDecodeResult.BadPath => MessageStrings.MsgQRUrlFailPath,
            QRDecodeResult.BadImage => MessageStrings.MsgQRUrlFailImage,
            QRDecodeResult.BadType => MessageStrings.MsgQRUrlFailType,
            QRDecodeResult.BadConnection => MessageStrings.MsgQRUrlFailConnection,
            QRDecodeResult.BadConversion => MessageStrings.MsgQRUrlFailConvert,
            _ => throw new ArgumentOutOfRangeException(nameof(result), result, null),
        };
    }
}