using System.Security.Claims;
using Microsoft.AspNetCore.Http;
using Microsoft.EntityFrameworkCore;
using ROLAC.API.Data;
using ROLAC.API.DTOs.Giving;
using ROLAC.API.DTOs.Shared;
using ROLAC.API.Entities;
using ROLAC.API.Services.Storage;

namespace ROLAC.API.Services;

public class OfferingSessionService : IOfferingSessionService
{
    private readonly AppDbContext         _db;
    private readonly IHttpContextAccessor _http;
    private readonly IFileStorage         _storage;

    public OfferingSessionService(AppDbContext db, IHttpContextAccessor http, IFileStorage storage)
    {
        _db      = db;
        _http    = http;
        _storage = storage;
    }

    private string CurrentUserId =>
        _http.HttpContext?.User.FindFirstValue(ClaimTypes.NameIdentifier) ?? "system";

    public async Task<PagedResult<OfferingSessionListItemDto>> GetPagedAsync(
        int page, int pageSize, DateOnly? from, DateOnly? to)
    {
        var query = _db.OfferingSessions.AsNoTracking().AsQueryable();
        if (from.HasValue) query = query.Where(s => s.SessionDate >= from.Value);
        if (to.HasValue)   query = query.Where(s => s.SessionDate <= to.Value);

        var total = await query.CountAsync();
        var rows  = await query
            .OrderByDescending(s => s.SessionDate)
            .Skip((page - 1) * pageSize).Take(pageSize)
            .ToListAsync();

        var ids = rows.Select(r => r.Id).ToList();
        var counts = await _db.Givings.AsNoTracking()
            .Where(g => g.OfferingSessionId != null && ids.Contains(g.OfferingSessionId.Value))
            .GroupBy(g => g.OfferingSessionId!.Value)
            .Select(grp => new { Id = grp.Key, Count = grp.Count() })
            .ToDictionaryAsync(x => x.Id, x => x.Count);

        var items = rows.Select(s => new OfferingSessionListItemDto
        {
            Id = s.Id, SessionDate = s.SessionDate.ToString("yyyy-MM-dd"), Status = s.Status,
            CashTotal = s.CashTotal, CheckTotal = s.CheckTotal,
            SystemTotal = s.SystemTotal, Difference = s.Difference,
            LineCount = counts.TryGetValue(s.Id, out var c) ? c : 0,
            HasProof = s.ProofPdfPath != null,
        }).ToList();

        return new PagedResult<OfferingSessionListItemDto>
            { Items = items, TotalCount = total, Page = page, PageSize = pageSize };
    }

    public async Task<bool> DateExistsAsync(DateOnly date)
        => await _db.OfferingSessions.AnyAsync(s => s.SessionDate == date);

    // Distinguishes a unique-index collision on SessionDate (concurrent insert) from other DB errors.
    private async Task<bool> DateExistsConcurrentlyAsync(DateOnly date, int excludeId)
        => await _db.OfferingSessions.AsNoTracking().AnyAsync(s => s.SessionDate == date && s.Id != excludeId);

    public async Task<OfferingSessionDto?> GetByIdAsync(int id)
    {
        var s = await _db.OfferingSessions.AsNoTracking().FirstOrDefaultAsync(x => x.Id == id);
        if (s is null) return null;

        var lines = await _db.Givings.AsNoTracking()
            .Where(g => g.OfferingSessionId == id).ToListAsync();

        var catNames = await _db.GivingCategories.AsNoTracking()
            .ToDictionaryAsync(c => c.Id, c => c.Name_en);
        var memberIds = lines.Where(l => l.MemberId != null).Select(l => l.MemberId!.Value).ToHashSet();
        var memberNames = await _db.Members.AsNoTracking()
            .Where(m => memberIds.Contains(m.Id))
            .ToDictionaryAsync(m => m.Id, m => $"{m.FirstName_en} {m.LastName_en}");

        return new OfferingSessionDto
        {
            Id = s.Id, SessionDate = s.SessionDate, Status = s.Status,
            CashTotal = s.CashTotal, CheckTotal = s.CheckTotal,
            SystemTotal = s.SystemTotal, Difference = s.Difference, Notes = s.Notes,
            HasProof = s.ProofPdfPath != null,
            Givings = lines.Select(l => new OfferingGivingLineDto
            {
                Id = l.Id, MemberId = l.MemberId,
                MemberName = l.MemberId != null && memberNames.TryGetValue(l.MemberId.Value, out var n) ? n : null,
                GivingCategoryId = l.GivingCategoryId,
                CategoryName = catNames.TryGetValue(l.GivingCategoryId, out var cn) ? cn : "",
                Amount = l.Amount, PaymentMethod = l.PaymentMethod,
                CheckNumber = l.CheckNumber,
                ZelleReferenceCode = l.ZelleReferenceCode,
                PayPalTransactionId = l.PayPalTransactionId,
                IsAnonymous = l.IsAnonymous, Notes = l.Notes,
            }).ToList(),
        };
    }

    public async Task<int> CreateAsync(CreateOfferingSessionRequest r)
    {
        if (await DateExistsAsync(r.SessionDate))
            throw new InvalidOperationException($"An offering session for {r.SessionDate:yyyy-MM-dd} already exists.");

        var systemTotal = r.Givings.Sum(g => g.Amount);
        var session = new OfferingSession
        {
            SessionDate = r.SessionDate, Status = "Submitted",
            CashTotal = r.CashTotal, CheckTotal = r.CheckTotal,
            SystemTotal = systemTotal,
            Difference  = (r.CashTotal + r.CheckTotal) - systemTotal,
            Notes = r.Notes,
            SubmittedAt = DateTimeOffset.UtcNow, SubmittedBy = CurrentUserId,
            Givings = r.Givings.Select(line => MapLine(line, r.SessionDate)).ToList(),
        };
        _db.OfferingSessions.Add(session);
        try
        {
            await _db.SaveChangesAsync();
        }
        catch (DbUpdateException)
        {
            if (await DateExistsConcurrentlyAsync(r.SessionDate, session.Id))
                throw new InvalidOperationException($"An offering session for {r.SessionDate:yyyy-MM-dd} already exists.");
            throw;
        }
        return session.Id;
    }

    public async Task ReopenAsync(int id)
    {
        var s = await _db.OfferingSessions.FindAsync(id)
            ?? throw new KeyNotFoundException($"OfferingSession {id} not found.");
        if (s.Status != "Submitted")
            throw new InvalidOperationException($"Only a Submitted session can be reopened (current: {s.Status}).");
        s.Status = "Draft";
        s.SubmittedAt = null; s.SubmittedBy = null;
        await _db.SaveChangesAsync();
    }

    public async Task ReplaceAsync(int id, CreateOfferingSessionRequest r)
    {
        var s = await _db.OfferingSessions
            .Include(x => x.Givings)
            .FirstOrDefaultAsync(x => x.Id == id)
            ?? throw new KeyNotFoundException($"OfferingSession {id} not found.");
        if (s.Status != "Draft")
            throw new InvalidOperationException($"Only a Draft (reopened) session can be edited (current: {s.Status}).");

        _db.Givings.RemoveRange(s.Givings);
        var systemTotal = r.Givings.Sum(g => g.Amount);
        s.CashTotal = r.CashTotal; s.CheckTotal = r.CheckTotal;
        s.SystemTotal = systemTotal;
        s.Difference  = (r.CashTotal + r.CheckTotal) - systemTotal;
        s.Notes = r.Notes;
        s.Status = "Submitted";
        s.SubmittedAt = DateTimeOffset.UtcNow; s.SubmittedBy = CurrentUserId;
        s.Givings = r.Givings.Select(line => MapLine(line, s.SessionDate)).ToList();
        await _db.SaveChangesAsync();
    }

    // ── Paper-proof PDF (one merged file per session) ────────────────────────

    public async Task SaveProofAsync(int id, Stream content, string fileName)
    {
        var s = await _db.OfferingSessions.FindAsync(id)
            ?? throw new KeyNotFoundException($"OfferingSession {id} not found.");

        var path = $"finance/offering-proofs/{s.SessionDate.Year}/{s.SessionDate.Month}/{s.Id}-proof.pdf";
        if (s.ProofPdfPath != null && s.ProofPdfPath != path)
            await _storage.DeleteAsync(s.ProofPdfPath);
        var saved = await _storage.SaveAsync(content, path);
        s.ProofPdfPath = saved;
        await _db.SaveChangesAsync();
    }

    public async Task<(Stream stream, string contentType)?> OpenProofAsync(int id)
    {
        var s = await _db.OfferingSessions.AsNoTracking().FirstOrDefaultAsync(x => x.Id == id)
            ?? throw new KeyNotFoundException($"OfferingSession {id} not found.");
        if (s.ProofPdfPath is null) return null;
        var stream = await _storage.OpenReadAsync(s.ProofPdfPath);
        if (stream is null) return null;
        return (stream, "application/pdf");
    }

    public async Task DeleteProofAsync(int id)
    {
        var s = await _db.OfferingSessions.FindAsync(id)
            ?? throw new KeyNotFoundException($"OfferingSession {id} not found.");
        if (s.ProofPdfPath is null) return;
        await _storage.DeleteAsync(s.ProofPdfPath);
        s.ProofPdfPath = null;
        await _db.SaveChangesAsync();
    }

    private static Giving MapLine(OfferingGivingLineRequest line, DateOnly sessionDate) => new()
    {
        MemberId            = line.IsAnonymous ? null : line.MemberId,
        GivingCategoryId    = line.GivingCategoryId,
        Amount              = line.Amount,
        PaymentMethod       = line.PaymentMethod,
        CheckNumber         = line.CheckNumber,
        ZelleReferenceCode  = line.ZelleReferenceCode,
        PayPalTransactionId = line.PayPalTransactionId,
        GivingDate          = sessionDate,
        IsAnonymous         = line.IsAnonymous,
        Notes               = line.Notes,
    };
}