using System;
using System.Collections.Generic;
using System.Linq;
using PolyTrader.Modules.Accounting.Models;
using PolyTrader.Modules.Accounting.Persistence;
using PolyTrader.Modules.Accounting.Services;
using Xunit;

namespace PolyTrader.Tests.Accounting
{
    /// <summary>
    /// Die Warnung über veraltete EZB-Kurse (#533). Die Schwelle liegt bei drei Tagen, weil genau so
    /// groß die planmäßige Wochenendlücke ist: Der Freitagskurs gilt bis Montag und ist dabei kein
    /// Mangel. Erst darüber hinaus fehlt wirklich etwas.
    /// </summary>
    public class CurrencyStalenessTests
    {
        private sealed class StubFx : IFxRateRepository
        {
            private readonly List<FxRate> _rates;
            public StubFx(params FxRate[] rates) => _rates = rates.ToList();
            public void Upsert(FxRate rate) => _rates.Add(rate);
            public List<FxRate> GetAll() => _rates.OrderBy(r => r.Date).ToList();
        }

        private sealed class ThrowingFx : IFxRateRepository
        {
            public void Upsert(FxRate rate) => throw new InvalidOperationException("DB weg");
            public List<FxRate> GetAll() => throw new InvalidOperationException("DB weg");
        }

        /// <summary>Leeres Ledger: Hier zählt allein die Währungsauflösung, nicht die Aggregation.</summary>
        private sealed class EmptyLedger : ILedgerRepository
        {
            public bool Upsert(LedgerEntry entry) => false;
            public DateTime? LatestTimestamp(int accountId) => null;
            public decimal SumNet(int accountId) => 0m;
            public int Count(int accountId) => 0;
            public List<LedgerEntry> Query(int? accountId, DateTime? from, DateTime? to, int limit) => new();
            public List<LedgerEntry> GetUpTo(int? accountId, DateTime to) => new();
        }

        private static AccountingReportService Build(IFxRateRepository fx) => new(new EmptyLedger(), fx);

        private static FxRate Rate(int year, int month, int day, decimal usdToEur = 0.86m) =>
            new() { Date = new DateTime(year, month, day), UsdToEur = usdToEur, Source = "ECB" };

        [Fact]
        public void Frisch_gerechneter_Kurs_warnt_nicht()
        {
            var ctx = Build(new StubFx(Rate(2026, 9, 9))).ResolveCurrency("EUR", new DateTime(2026, 9, 10));

            Assert.True(ctx.Available);
            Assert.False(ctx.IsStale);
            Assert.Null(ctx.Warning);
            Assert.Equal(1, ctx.RateAgeDays);
            Assert.Equal(new DateTime(2026, 9, 9), ctx.RateDate);
        }

        [Fact]
        public void Wochenende_gilt_noch_nicht_als_veraltet()
        {
            // Freitag 2026-09-04 → Montag 2026-09-07: drei Tage, der Normalfall.
            var ctx = Build(new StubFx(Rate(2026, 9, 4))).ResolveCurrency("EUR", new DateTime(2026, 9, 7));

            Assert.Equal(3, ctx.RateAgeDays);
            Assert.False(ctx.IsStale);
        }

        [Fact]
        public void Aelter_als_drei_Tage_warnt()
        {
            var ctx = Build(new StubFx(Rate(2026, 9, 4))).ResolveCurrency("EUR", new DateTime(2026, 9, 8));

            Assert.True(ctx.Available);      // benutzbar bleibt er
            Assert.True(ctx.IsStale);
            Assert.Equal(4, ctx.RateAgeDays);
            Assert.Contains("04.09.2026", ctx.Warning);
            Assert.Contains("4 Tage", ctx.Warning);
        }

        [Fact]
        public void Ohne_Kurse_ist_EUR_nicht_verfuegbar()
        {
            var ctx = Build(new StubFx()).ResolveCurrency("EUR", new DateTime(2026, 9, 10));

            Assert.False(ctx.Available);
            Assert.Equal(0m, ctx.Factor);
            Assert.Contains("Keine EZB-Tageskurse", ctx.Note);
        }

        [Fact]
        public void Rueckwirkende_Abrechnung_nimmt_den_Kurs_von_damals()
        {
            var fx = new StubFx(Rate(2026, 3, 31, 0.92m), Rate(2026, 9, 9, 0.86m));

            var maerz = Build(fx).ResolveCurrency("EUR", new DateTime(2026, 3, 31));

            Assert.Equal(0.92m, maerz.Factor);   // nicht der heutige Kurs
            Assert.False(maerz.IsStale);         // am Stichtag war er taggenau
        }

        [Fact]
        public void Datenbankausfall_sperrt_EUR_statt_zu_werfen()
        {
            var ctx = Build(new ThrowingFx()).ResolveCurrency("EUR", new DateTime(2026, 9, 10));

            Assert.False(ctx.Available);
            Assert.Equal(0m, ctx.Factor);
        }

        [Fact]
        public void USDC_und_USD_bleiben_ohne_Kurse_verfuegbar()
        {
            var svc = Build(new StubFx());

            var usdc = svc.ResolveCurrency("USDC", new DateTime(2026, 9, 10));
            var usd = svc.ResolveCurrency("USD", new DateTime(2026, 9, 10));

            Assert.True(usdc.Available);
            Assert.Equal(1.0m, usdc.Factor);
            Assert.True(usd.Available);
            Assert.False(usd.IsStale);
        }
    }
}