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

namespace ROLAC.API.Services;

public class ExpenseService : IExpenseService
{
    private readonly AppDbContext _db;
    private readonly IHttpContextAccessor _http;
    private readonly IFileStorage _storage;

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

    // The JWT carries the user id in the "sub" claim (NameClaimType="sub", MapInboundClaims=false),
    // so ClaimTypes.NameIdentifier is absent at runtime. Check NameIdentifier first (unit tests set it),
    // then fall back to "sub" (real tokens). Required for the self-ownership guard to work in production.
    private string CurrentUserId =>
        _http.HttpContext?.User.FindFirstValue(ClaimTypes.NameIdentifier)
        ?? _http.HttpContext?.User.FindFirstValue("sub")
        ?? "system";

    public async Task<PagedResult<ExpenseListItemDto>> GetPagedAsync(
        int page, int pageSize, string? search, int? ministryId,
        int? categoryGroupId, string? status, DateOnly? from, DateOnly? to,
        int? subCategoryId = null, string? statuses = null)
    {
        var query = _db.Expenses.AsNoTracking().AsQueryable();
        if (ministryId.HasValue)      query = query.Where(e => e.MinistryId == ministryId.Value);
        if (categoryGroupId.HasValue) query = query.Where(e => e.CategoryGroupId == categoryGroupId.Value);
        if (subCategoryId.HasValue)   query = query.Where(e => e.SubCategoryId == subCategoryId.Value);
        // `statuses` (comma-separated) takes precedence over single `status`; lets the dashboard
        // request the Paid+Approved set in one call.
        if (!string.IsNullOrWhiteSpace(statuses))
        {
            var set = statuses.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
            query = query.Where(e => set.Contains(e.Status));
        }
        else if (!string.IsNullOrWhiteSpace(status))
        {
            query = query.Where(e => e.Status == status);
        }
        if (from.HasValue) query = query.Where(e => e.ExpenseDate >= from.Value);
        if (to.HasValue)   query = query.Where(e => e.ExpenseDate <= to.Value);
        if (!string.IsNullOrWhiteSpace(search))
        {
            var s = search.Trim().ToLower(); var term = search.Trim();
            query = query.Where(e =>
                e.Description.ToLower().Contains(s) ||
                (e.VendorName != null && e.VendorName.ToLower().Contains(s)) ||
                (e.CheckNumber != null && e.CheckNumber.ToLower().Contains(s)) ||
                (e.Member != null && (
                    (e.Member.FirstName_en + " " + e.Member.LastName_en).ToLower().Contains(s) ||
                    (e.Member.FirstName_zh != null && e.Member.FirstName_zh.Contains(term)) ||
                    (e.Member.LastName_zh  != null && e.Member.LastName_zh.Contains(term)))));
        }
        return await ProjectPagedAsync(query, page, pageSize);
    }

    public async Task<PagedResult<ExpenseListItemDto>> GetMineAsync(string userId, string? status, int page, int pageSize)
    {
        var query = _db.Expenses.AsNoTracking().Where(e => e.SubmittedBy == userId);
        if (!string.IsNullOrWhiteSpace(status)) query = query.Where(e => e.Status == status);
        return await ProjectPagedAsync(query, page, pageSize);
    }

    private async Task<PagedResult<ExpenseListItemDto>> ProjectPagedAsync(IQueryable<Expense> query, int page, int pageSize)
    {
        var total = await query.CountAsync();
        var rows = await query
            .OrderByDescending(e => e.ExpenseDate).ThenByDescending(e => e.Id)
            .Skip((page - 1) * pageSize).Take(pageSize).ToListAsync();

        var minNames = await _db.Ministries.AsNoTracking().ToDictionaryAsync(m => m.Id, m => $"{m.Name_en} / {m.Name_zh}");
        var grpNames = await _db.ExpenseCategoryGroups.AsNoTracking().ToDictionaryAsync(g => g.Id, g => $"{g.Name_en} / {g.Name_zh}");
        var subNames = await _db.ExpenseSubCategories.AsNoTracking().ToDictionaryAsync(s => s.Id, s => $"{s.Name_en} / {s.Name_zh}");
        var memberIds = rows.Where(r => r.MemberId != null).Select(r => r.MemberId!.Value).ToHashSet();
        var memNames = await _db.Members.AsNoTracking().Where(m => memberIds.Contains(m.Id))
            .ToDictionaryAsync(m => m.Id, m => $"{m.FirstName_en} {m.LastName_en}");

        var items = rows.Select(e => new ExpenseListItemDto
        {
            Id = e.Id, Type = e.Type, Status = e.Status, Amount = e.Amount, Description = e.Description,
            MinistryId = e.MinistryId, MinistryName = minNames.GetValueOrDefault(e.MinistryId, ""),
            CategoryGroupId = e.CategoryGroupId, CategoryGroupName = grpNames.GetValueOrDefault(e.CategoryGroupId, ""),
            SubCategoryId = e.SubCategoryId, SubCategoryName = subNames.GetValueOrDefault(e.SubCategoryId, ""),
            VendorName = e.VendorName, MemberId = e.MemberId,
            MemberName = e.MemberId != null ? memNames.GetValueOrDefault(e.MemberId.Value) : null,
            ExpenseDate = e.ExpenseDate.ToString("yyyy-MM-dd"),
            HasReceipt = e.ReceiptBlobPath != null,
            CheckNumber = e.CheckNumber,
        }).ToList();

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

    public async Task<ExpenseDto?> GetByIdAsync(int id)
    {
        var e = await _db.Expenses.AsNoTracking().FirstOrDefaultAsync(x => x.Id == id);
        if (e is null) return null;
        var minName = await _db.Ministries.Where(m => m.Id == e.MinistryId).Select(m => m.Name_en).FirstOrDefaultAsync() ?? "";
        var grpName = await _db.ExpenseCategoryGroups.Where(g => g.Id == e.CategoryGroupId).Select(g => g.Name_en).FirstOrDefaultAsync() ?? "";
        var subName = await _db.ExpenseSubCategories.Where(s => s.Id == e.SubCategoryId).Select(s => s.Name_en).FirstOrDefaultAsync() ?? "";
        string? memName = e.MemberId != null
            ? await _db.Members.Where(m => m.Id == e.MemberId).Select(m => m.FirstName_en + " " + m.LastName_en).FirstOrDefaultAsync()
            : null;
        return new ExpenseDto
        {
            Id = e.Id, Type = e.Type, Status = e.Status, Amount = e.Amount, Description = e.Description,
            MinistryId = e.MinistryId, MinistryName = minName,
            CategoryGroupId = e.CategoryGroupId, CategoryGroupName = grpName,
            SubCategoryId = e.SubCategoryId, SubCategoryName = subName,
            VendorName = e.VendorName, MemberId = e.MemberId, MemberName = memName,
            ExpenseDate = e.ExpenseDate.ToString("yyyy-MM-dd"), HasReceipt = e.ReceiptBlobPath != null,
            CheckNumber = e.CheckNumber, Notes = e.Notes, ReviewNotes = e.ReviewNotes,
            SubmittedBy = e.SubmittedBy, SubmittedAt = e.SubmittedAt, ReviewedAt = e.ReviewedAt, PaidAt = e.PaidAt,
        };
    }

    public async Task<int> CreateAsync(CreateExpenseRequest r, bool isFinance)
    {
        var e = new Expense
        {
            MinistryId = r.MinistryId, CategoryGroupId = r.CategoryGroupId, SubCategoryId = r.SubCategoryId,
            Type = r.Type, Amount = r.Amount, Description = r.Description, VendorName = r.VendorName,
            CheckNumber = r.CheckNumber, ExpenseDate = r.ExpenseDate, Notes = r.Notes,
        };

        if (r.Type == "VendorPayment")
        {
            if (!isFinance) throw new InvalidOperationException("Only finance can create vendor payments.");
            // Enters the approval queue: PendingApproval -> Approve -> Pay (issue check).
            e.Status = "PendingApproval";
            e.SubmittedBy = CurrentUserId; e.SubmittedAt = DateTimeOffset.UtcNow;
            e.MemberId = null;
        }
        else // StaffReimbursement
        {
            // Finance entering on behalf of a member goes straight to the approval queue;
            // a member's own self-service entry stays a Draft until they explicitly Submit it.
            e.Status = isFinance ? "PendingApproval" : "Draft";
            e.SubmittedBy = CurrentUserId;
            if (isFinance) e.SubmittedAt = DateTimeOffset.UtcNow;
            e.MemberId = isFinance ? r.MemberId : await CallerMemberIdAsync();
            e.VendorName = null;
        }

        _db.Expenses.Add(e);
        await _db.SaveChangesAsync();
        return e.Id;
    }

    private async Task<int?> CallerMemberIdAsync()
    {
        var uid = CurrentUserId;
        return await _db.Users.Where(u => u.Id == uid).Select(u => u.MemberId).FirstOrDefaultAsync();
    }

    public async Task UpdateAsync(int id, UpdateExpenseRequest r, bool isFinance)
    {
        // FirstOrDefaultAsync (not FindAsync) so the soft-delete query filter applies.
        var e = await _db.Expenses.FirstOrDefaultAsync(x => x.Id == id)
            ?? throw new KeyNotFoundException($"Expense {id} not found.");
        if (!isFinance && !(e.SubmittedBy == CurrentUserId && e.Status == "Draft"))
            throw new InvalidOperationException("You can only edit your own draft reimbursements.");

        e.MinistryId = r.MinistryId; e.CategoryGroupId = r.CategoryGroupId; e.SubCategoryId = r.SubCategoryId;
        e.Amount = r.Amount; e.Description = r.Description; e.CheckNumber = r.CheckNumber;
        e.ExpenseDate = r.ExpenseDate; e.Notes = r.Notes;
        if (e.Type == "VendorPayment") e.VendorName = r.VendorName;
        await _db.SaveChangesAsync();
    }

    public async Task DeleteAsync(int id, bool isFinance)
    {
        var e = await _db.Expenses.FirstOrDefaultAsync(x => x.Id == id)
            ?? throw new KeyNotFoundException($"Expense {id} not found.");
        if (!isFinance && !(e.SubmittedBy == CurrentUserId && e.Status == "Draft"))
            throw new InvalidOperationException("You can only delete your own draft reimbursements.");
        e.IsDeleted = true; e.DeletedAt = DateTimeOffset.UtcNow; e.DeletedBy = CurrentUserId;
        await _db.SaveChangesAsync();
    }

    // FirstOrDefaultAsync (not FindAsync) so the soft-delete query filter applies.
    private async Task<Expense> RequireAsync(int id) =>
        await _db.Expenses.FirstOrDefaultAsync(x => x.Id == id)
            ?? throw new KeyNotFoundException($"Expense {id} not found.");

    public async Task SubmitAsync(int id)
    {
        var e = await RequireAsync(id);
        if (e.SubmittedBy != CurrentUserId) throw new InvalidOperationException("Only the submitter can submit this reimbursement.");
        if (e.Status != "Draft") throw new InvalidOperationException($"Cannot submit from status '{e.Status}'.");
        e.Status = "PendingApproval"; e.SubmittedAt = DateTimeOffset.UtcNow;
        await _db.SaveChangesAsync();
    }

    public async Task ApproveAsync(int id)
    {
        var e = await RequireAsync(id);
        if (e.Status != "PendingApproval") throw new InvalidOperationException($"Cannot approve from status '{e.Status}'.");
        e.Status = "Approved"; e.ReviewedBy = CurrentUserId; e.ReviewedAt = DateTimeOffset.UtcNow;
        await _db.SaveChangesAsync();
    }

    public async Task RejectAsync(int id, string? reviewNotes)
    {
        var e = await RequireAsync(id);
        if (e.Status != "PendingApproval") throw new InvalidOperationException($"Cannot reject from status '{e.Status}'.");
        e.Status = "Rejected"; e.ReviewedBy = CurrentUserId; e.ReviewedAt = DateTimeOffset.UtcNow; e.ReviewNotes = reviewNotes;
        await _db.SaveChangesAsync();
    }

    public async Task PayAsync(int id, string? checkNumber, DateOnly? paidAt)
    {
        var e = await RequireAsync(id);
        if (e.Status != "Approved") throw new InvalidOperationException($"Cannot mark paid from status '{e.Status}'.");
        e.Status = "Paid";
        if (!string.IsNullOrWhiteSpace(checkNumber)) e.CheckNumber = checkNumber;
        e.PaidBy = CurrentUserId;
        e.PaidAt = paidAt.HasValue
            ? new DateTimeOffset(paidAt.Value.ToDateTime(TimeOnly.MinValue), TimeSpan.Zero)
            : DateTimeOffset.UtcNow;
        await _db.SaveChangesAsync();
    }

    public async Task SaveReceiptAsync(int id, Stream content, string fileName, bool isFinance)
    {
        var e = await RequireAsync(id);
        if (!isFinance && e.SubmittedBy != CurrentUserId)
            throw new InvalidOperationException("You can only attach receipts to your own reimbursements.");

        var safe = Path.GetFileName(fileName).Replace(' ', '_');
        var path = $"finance/receipts/{e.ExpenseDate.Year}/{e.ExpenseDate.Month}/{e.Id}-{safe}";
        if (e.ReceiptBlobPath != null && e.ReceiptBlobPath != path)
            await _storage.DeleteAsync(e.ReceiptBlobPath);
        var saved = await _storage.SaveAsync(content, path);
        e.ReceiptBlobPath = saved;
        await _db.SaveChangesAsync();
    }

    public async Task<(Stream stream, string contentType)?> OpenReceiptAsync(int id, bool isFinance)
    {
        var e = await RequireAsync(id);
        if (!isFinance && e.SubmittedBy != CurrentUserId)
            throw new InvalidOperationException("Not authorized to view this receipt.");
        if (e.ReceiptBlobPath is null) return null;
        var stream = await _storage.OpenReadAsync(e.ReceiptBlobPath);
        if (stream is null) return null;
        var ext = Path.GetExtension(e.ReceiptBlobPath).ToLowerInvariant();
        var contentType = ext switch
        {
            ".png" => "image/png", ".webp" => "image/webp", ".pdf" => "application/pdf",
            _ => "image/jpeg",
        };
        return (stream, contentType);
    }
}