using System.Globalization;
using System.Net.Http.Json;
using System.Text.Json.Serialization;
using LehrerApp.Core.Models;

namespace LehrerApp.Api;

public interface IGeocoder
{
    Task<GeocodingResult?> GeocodeAsync(SchoolLocationRequest address, CancellationToken cancellationToken);
}

public sealed record GeocodingResult(double Latitude, double Longitude, string DisplayName);

/// <summary>Einmalige, explizit ausgelöste Adressauflösung über den öffentlichen OSM-Nominatim-
/// Dienst. Kein Autocomplete; die dauerhafte Ergebnisspeicherung übernimmt SchoolWeatherStore.</summary>
public sealed class NominatimGeocoder(HttpClient http) : IGeocoder
{
    private static readonly SemaphoreSlim RequestGate = new(1, 1);
    private static DateTime _lastRequestAt = DateTime.MinValue;

    public async Task<GeocodingResult?> GeocodeAsync(SchoolLocationRequest address,
        CancellationToken cancellationToken)
    {
        var structured = Query(new Dictionary<string, string>
        {
            ["street"] = address.Street,
            ["postalcode"] = address.PostalCode,
            ["city"] = address.City,
        });
        var result = await SearchRespectingRateLimitAsync(structured, cancellationToken);
        if (result is not null) return result;

        // Manche Schulen/Ortsteile sind bei OSM anders adressiert. Ein kontrollierter zweiter
        // Versuch mit der gesamten Suchzeile ist robuster, bleibt aber weit weg vom 1-rps-Limit.
        var freeForm = string.Join(", ", new[]
        {
            address.SchoolName, address.Street, $"{address.PostalCode} {address.City}", "Deutschland",
        }.Where(x => !string.IsNullOrWhiteSpace(x)));
        return await SearchRespectingRateLimitAsync(
            Query(new Dictionary<string, string> { ["q"] = freeForm }), cancellationToken);
    }

    private async Task<GeocodingResult?> SearchRespectingRateLimitAsync(string query,
        CancellationToken cancellationToken)
    {
        await RequestGate.WaitAsync(cancellationToken);
        try
        {
            var wait = TimeSpan.FromSeconds(1) - (DateTime.UtcNow - _lastRequestAt);
            if (wait > TimeSpan.Zero) await Task.Delay(wait, cancellationToken);
            _lastRequestAt = DateTime.UtcNow;
            var candidates = await http.GetFromJsonAsync<List<NominatimCandidate>>(
                $"search?format=jsonv2&limit=1&countrycodes=de{query}", cancellationToken);
            var candidate = candidates?.FirstOrDefault();
            if (candidate is null ||
                !double.TryParse(candidate.Lat, NumberStyles.Float, CultureInfo.InvariantCulture, out var latitude) ||
                !double.TryParse(candidate.Lon, NumberStyles.Float, CultureInfo.InvariantCulture, out var longitude))
                return null;
            return new(latitude, longitude, candidate.DisplayName ?? "");
        }
        finally { RequestGate.Release(); }
    }

    private static string Query(IReadOnlyDictionary<string, string> values) => string.Concat(
        values.Where(x => !string.IsNullOrWhiteSpace(x.Value))
              .Select(x => $"&{Uri.EscapeDataString(x.Key)}={Uri.EscapeDataString(x.Value.Trim())}"));

    private sealed class NominatimCandidate
    {
        [JsonPropertyName("lat")]
        public string? Lat { get; set; }
        [JsonPropertyName("lon")]
        public string? Lon { get; set; }
        [JsonPropertyName("display_name")]
        public string? DisplayName { get; set; }
    }
}