using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Schaad.Accounting.Datasets;
using Schaad.Accounting.Datasets.Charts;
using Schaad.Accounting.Interfaces;

namespace Schaad.Accounting.Services
{
    public class ChartService : IChartService
    {
        private readonly ISettingsService settingsService;
        private readonly IViewService viewService;

        public ChartService(ISettingsService settingsService, IViewService viewService)
        {
            this.settingsService = settingsService;
            this.viewService = viewService;
        }

        public async Task<IReadOnlyList<DataSerie>> GetExpensesPerMonthAsync()
        {
            var expenseTransactions = (await viewService.GetTransactionViewListAsync())
                .Where(t => t.TargetAccount.Class == ClassIds.Expenses)
                .ToList();

            var distinctSubClasses = expenseTransactions
                .Select(t => t.TargetAccount.SubClass)
                .Distinct()
                .Count();

            return distinctSubClasses > 1
                ? GetSubClassExpensesPerMonth(expenseTransactions)
                : await GetAccountExpensesPerMonthAsync();
        }

        private List<DataSerie> GetSubClassExpensesPerMonth(List<TransactionDataset> expenseTransactions)
        {
            var year = settingsService.GetYear();
            var maxMonth = expenseTransactions
                .OrderByDescending(t => t.ValueDate)
                .FirstOrDefault()?.ValueDate.Month ?? 12;

            var list = new List<DataSerie>();
            foreach (var grp in expenseTransactions.GroupBy(t => t.TargetAccount.SubClass))
            {
                var groupedByMonth = grp
                    .GroupBy(t => t.ValueDate.Month)
                    .ToDictionary(g => g.Key, g => g.Sum(t => t.Value));
                EnsureEntryForEveryMonth(groupedByMonth, maxMonth);

                list.Add(new DataSerie(
                    Id: grp.Key.ToString(),
                    Name: grp.First().TargetAccount.Name,
                    X: groupedByMonth.OrderBy(g => g.Key).Select(g => new DateOnly(year, g.Key, 1)).ToList(),
                    Y: groupedByMonth.OrderBy(g => g.Key).Select(g => g.Value).ToList()
                ));
            }
            return list;
        }

        private async Task<List<DataSerie>> GetAccountExpensesPerMonthAsync()
        {
            var year = settingsService.GetYear();
            var allTransactions = await viewService.GetTransactionViewListAsync();
            var expenseAccounts = (await viewService.GetAccountViewListAsync()).Where(a => a.Class == ClassIds.Expenses);

            var list = new List<DataSerie>();
            foreach (var account in expenseAccounts)
            {
                var transactions = allTransactions.Where(t => t.TargetAccountId == account.Id).ToList();
                if (transactions.Count == 0)
                {
                    continue;
                }

                var maxMonth = transactions.Max(t => t.ValueDate.Month);
                var groupedByMonth = transactions
                    .GroupBy(t => t.ValueDate.Month)
                    .ToDictionary(g => g.Key, g => g.Sum(t => t.Value));
                EnsureEntryForEveryMonth(groupedByMonth, maxMonth);

                list.Add(new DataSerie(
                    Id: account.Id,
                    Name: account.Name,
                    X: groupedByMonth.OrderBy(g => g.Key).Select(g => new DateOnly(year, g.Key, 1)).ToList(),
                    Y: groupedByMonth.OrderBy(g => g.Key).Select(g => g.Value).ToList()
                ));
            }
            return list;
        }

        private static void EnsureEntryForEveryMonth(Dictionary<int, decimal> values, int maxMonth = 12)
        {
            for (int i = 1; i <= maxMonth; i++)
            {
                if (values.ContainsKey(i) == false)
                {
                    values.Add(i, 0);
                }
            }
        }
    }
}