using Microsoft.EntityFrameworkCore;
using ROLAC.API.Data;
using ROLAC.API.DTOs.Finance;
using ROLAC.API.Entities;

namespace ROLAC.API.Services;

/// <summary>
/// Read-only aggregation producing the year-end 1099 recipient summary. CASH BASIS:
/// only Paid expenses whose PaidAt falls in the tax year, attributed to a tracked payee,
/// on a line whose category maps to a 1099 box (sub ?? group). Unmapped lines are excluded.
/// </summary>
public class Form1099ReportService : IForm1099ReportService
{
    private readonly AppDbContext _db;
    public Form1099ReportService(AppDbContext db) => _db = db;

    public async Task<List<Form1099BoxDto>> GetBoxesAsync() =>
        await _db.Form1099Boxes.AsNoTracking().Where(b => b.IsActive)
            .OrderBy(b => b.SortOrder)
            .Select(b => new Form1099BoxDto
            {
                Id = b.Id, BoxCode = b.BoxCode, Name_en = b.Name_en,
                Name_zh = b.Name_zh, FormType = b.FormType, SortOrder = b.SortOrder,
            }).ToListAsync();

    private IQueryable<PaidLine> ReportableLines(int taxYear) =>
        from e in _db.Expenses.Where(e => e.Status == "Paid" && e.PaidAt != null
                                          && e.PaidAt.Value.Year == taxYear && e.PayeeId != null)
        join p   in _db.Payee1099s.Where(p => p.Is1099Tracked) on e.PayeeId equals p.Id
        join l   in _db.ExpenseLines          on e.Id              equals l.ExpenseId
        join sub in _db.ExpenseSubCategories  on l.SubCategoryId   equals sub.Id
        join grp in _db.ExpenseCategoryGroups on l.CategoryGroupId equals grp.Id
        select new PaidLine
        {
            PayeeId   = p.Id,
            LegalName = p.LegalName,
            TinLast4  = p.TinLast4,
            W9Status  = p.W9Status,
            PaidAt    = e.PaidAt!.Value,
            Description = e.Description,
            CategoryName = grp.Name_en + " / " + sub.Name_en,
            Amount    = l.Amount,
            BoxId     = sub.Form1099BoxId ?? grp.Form1099BoxId,
        };

    public async Task<Form1099SummaryDto> GetAnnualSummaryAsync(int taxYear)
    {
        var boxes = await _db.Form1099Boxes.AsNoTracking().ToDictionaryAsync(b => b.Id, b => b.BoxCode);
        var lines = await ReportableLines(taxYear).Where(x => x.BoxId != null).ToListAsync();

        var dto = new Form1099SummaryDto { TaxYear = taxYear };
        foreach (var g in lines.GroupBy(x => x.PayeeId))
        {
            var first = g.First();
            var nec   = g.Where(x => boxes.GetValueOrDefault(x.BoxId!.Value) == Form1099.BoxNec1).Sum(x => x.Amount);
            var rents = g.Where(x => boxes.GetValueOrDefault(x.BoxId!.Value) == Form1099.BoxMisc1).Sum(x => x.Amount);
            var w9Missing = first.W9Status != Form1099.W9Status.OnFile;
            var meets = nec >= Form1099.ReportingThreshold || rents >= Form1099.ReportingThreshold;
            dto.Rows.Add(new Form1099RecipientRowDto
            {
                PayeeId = first.PayeeId, LegalName = first.LegalName, TinLast4 = first.TinLast4,
                W9Status = first.W9Status, NecTotal = nec, RentsTotal = rents,
                GrandTotal = nec + rents, MeetsThreshold = meets, W9Missing = w9Missing,
            });
        }
        dto.Rows = dto.Rows.OrderByDescending(r => r.GrandTotal).ToList();
        dto.TotalReportable       = dto.Rows.Sum(r => r.GrandTotal);
        dto.RecipientsAtThreshold = dto.Rows.Count(r => r.MeetsThreshold);
        dto.RecipientsMissingW9   = dto.Rows.Count(r => r.W9Missing);
        return dto;
    }

    public async Task<Form1099RecipientDetailDto?> GetRecipientDetailAsync(int payeeId, int taxYear)
    {
        var payee = await _db.Payee1099s.AsNoTracking().FirstOrDefaultAsync(p => p.Id == payeeId);
        if (payee is null) return null;
        var boxes = await _db.Form1099Boxes.AsNoTracking().ToDictionaryAsync(b => b.Id, b => b.BoxCode);
        var lines = await ReportableLines(taxYear).Where(x => x.PayeeId == payeeId && x.BoxId != null).ToListAsync();

        return new Form1099RecipientDetailDto
        {
            PayeeId = payee.Id, LegalName = payee.LegalName, TinLast4 = payee.TinLast4,
            W9Status = payee.W9Status, TaxYear = taxYear,
            Payments = lines.OrderBy(x => x.PaidAt).Select(x => new Form1099PaymentDto
            {
                PaidDate = DateOnly.FromDateTime(x.PaidAt.Date).ToString("yyyy-MM-dd"),
                Description = x.Description, CategoryName = x.CategoryName,
                BoxCode = boxes.GetValueOrDefault(x.BoxId!.Value) ?? "", Amount = x.Amount,
            }).ToList(),
        };
    }

    private sealed class PaidLine
    {
        public int PayeeId; public string LegalName = ""; public string? TinLast4; public string W9Status = "";
        public DateTimeOffset PaidAt; public string Description = ""; public string CategoryName = "";
        public decimal Amount; public int? BoxId;
    }
}