using CoordinateSharp;
using PagerParser;
using System;
using System.ComponentModel.DataAnnotations.Schema;
using System.Text.RegularExpressions;

namespace PagerParser;

public class GpsPosition {
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int    GpsPositionId { get; set; }
    public double Latitude      { get; set; }
    public double Longitude     { get; set; }
}

public record MelwaysPage {
    public int    PageNo    { get; set; }
    public double Latitude  { get; set; }
    public double Longitude { get; set; }
}

// Derive roughly-accurate GPS coordinates from a Melways page number
// and grid number (e.g: 131 D7) by looking up the origin coordinates
// of the Melways page from a pre-defined table, then interpolating
// the grid number across the page to get a (very) rough position.
public class PositionCalculator {
    private const float PageWidth  = 0.0583403752108005f;
    private const float PageHeight = 0.0444074086328539f;

    private const int ColCount = 10;
    private const int RowCount = 12;

    private const float ColWidth  = PageWidth  / ColCount;
    private const float RowHeight = PageHeight / RowCount;

    private static readonly MelwaysPage[] MelwaysPages = {
        new MelwaysPage { PageNo = 94,  Latitude = -38.0062431030181, Longitude = 145.153465677450 },
        new MelwaysPage { PageNo = 95,  Latitude = -38.0061349929752, Longitude = 145.197873798763 },
        new MelwaysPage { PageNo = 96,  Latitude = -38.0060458242193, Longitude = 145.242282747795 },
        new MelwaysPage { PageNo = 98,  Latitude = -38.0501502394990, Longitude = 145.153538108815 },
        new MelwaysPage { PageNo = 110, Latitude = -38.0059397267576, Longitude = 145.286740799198 },
        new MelwaysPage { PageNo = 111, Latitude = -38.0058646642328, Longitude = 145.331164408607 },
        new MelwaysPage { PageNo = 128, Latitude = -38.0500712736303, Longitude = 145.197997939698 },
        new MelwaysPage { PageNo = 129, Latitude = -38.0499811306888, Longitude = 145.242424322651 },
        new MelwaysPage { PageNo = 130, Latitude = -38.0498760059982, Longitude = 145.286857218675 },
        new MelwaysPage { PageNo = 131, Latitude = -38.0497905233513, Longitude = 145.331303121527 },
        new MelwaysPage { PageNo = 212, Latitude = -38.0056782419614, Longitude = 145.375580424547 },
        new MelwaysPage { PageNo = 213, Latitude = -38.0055063939227, Longitude = 145.419999796841 },
        new MelwaysPage { PageNo = 214, Latitude = -38.0496145139129, Longitude = 145.375744441368 },
        new MelwaysPage { PageNo = 215, Latitude = -38.0494726543543, Longitude = 145.420190429893 },
        new MelwaysPage { PageNo = 315, Latitude = -38.0053618479218, Longitude = 145.464319398407 },
        new MelwaysPage { PageNo = 317, Latitude = -38.0493097638301, Longitude = 145.464666307851 }
    };

    public static GpsPosition? GetGpsPosition(ParsedPagerMessage message) {
        if(message.MelwaysMapNo is null || message.MelwaysGrid is null)
            return null;
        var page = MelwaysPages.FirstOrDefault(p => p.PageNo == message.MelwaysMapNo);
        if(page is null)
            return null;

        var match = Regex.Match(message.MelwaysGrid.ToUpper(), "^([A-HJ-K])([0-9]+)$");
        if(!match.Success)
            return null;

        var row = int.Parse(match.Groups[2].Value) - 1;
        var col = match.Groups[1].Value[0] - 'A';
        if(col > 7)
            col -= 1; // Compensate for Melways grids skipping 'I'

        var position = new GpsPosition {
            Latitude  = page.Latitude  - (row * RowHeight)  - (RowHeight  / 2),
            Longitude = page.Longitude + (col * ColWidth)   + (ColWidth   / 2)
        };

        if(message.GridReference is null)
            return position;

        // If we have a 6-digit grid reference, try to refine the location further
        // using the UTM coordinate system. Since zone information isn't included
        // in a 6-digit grid reference, we use the coordinates calculated from the
        // Melways as a starting point to find the zone.

        double gridRef = (double) message.GridReference;

        var origUTM = new Coordinate(position.Latitude, position.Longitude).UTM;
        var newUTM = new UniversalTransverseMercator(
            origUTM.LatZone,
            origUTM.LongZone,
            (Math.Floor(origUTM.Easting / 100000) * 100000) + (Math.Floor(gridRef / 1000) * 100),
            (Math.Floor(origUTM.Northing / 100000) * 100000) + ((gridRef % 1000) * 100));

        var coord = UniversalTransverseMercator.ConvertUTMtoLatLong(newUTM);

        position.Latitude  = coord.Latitude.ToDouble();
        position.Longitude = coord.Longitude.ToDouble();

        return position;
    }
}