using System.Data;
using Jiaowu.Api.Contracts;
using Jiaowu.Api.Domain.Academic;
using Jiaowu.Api.Domain.Identity;
using Jiaowu.Api.Infrastructure.Auth;
using Jiaowu.Api.Infrastructure.Excel;
using Jiaowu.Api.Infrastructure.Files;
using Jiaowu.Api.Infrastructure.Persistence;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

namespace Jiaowu.Api.Controllers;

[ApiController]
[Authorize]
[Route("api/campus-registrations")]
public sealed class CampusRegistrationsController(AppDbContext db, ICurrentUserDataScope scope) : ControllerBase
{
    private const string Managers = SystemRoles.SuperAdmin + "," + SystemRoles.AcademicAdmin + "," + SystemRoles.CollegeAdmin;

    [HttpGet("projects")]
    public async Task<ActionResult> GetProjects([FromQuery] string? keyword, CancellationToken ct)
    {
        var source = ScopedProjects().AsNoTracking();
        if (!string.IsNullOrWhiteSpace(keyword))
            source = source.Where(x => x.Name.Contains(keyword) || x.Code.Contains(keyword));
        if (scope.Current.IsInRole(SystemRoles.Student))
            source = source.Where(x => x.Status == CampusRegistrationProjectStatus.Published);
        var now = DateTime.UtcNow;
        return Ok(await source.OrderByDescending(x => x.RegistrationEndsAt).Select(x => new
        {
            x.Id, x.Code, x.Name, x.Description, x.RegistrationStartsAt, x.RegistrationEndsAt,
            x.Capacity, x.FeeAmount, x.RequiresReview, x.Status, x.ContactName, x.ContactPhone, x.Notes,
            CollegeName = x.College == null ? "全校" : x.College.Name,
            ConfirmedCount = x.Applications.Count(a => a.Status == CampusRegistrationApplicationStatus.Confirmed),
            IsAvailableNow = x.Status == CampusRegistrationProjectStatus.Published && now >= x.RegistrationStartsAt && now <= x.RegistrationEndsAt
        }).ToListAsync(ct));
    }

    [HttpPost("projects")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> CreateProject(ProjectRequest request, CancellationToken ct)
    {
        var error = ValidateProject(request);
        if (error is not null) return BadRequest(new { message = error });
        if (!CanManageCollege(request.CollegeId)) return Forbid();
        var code = request.Code.Trim().ToUpperInvariant();
        if (await db.CampusRegistrationProjects.AnyAsync(x => x.Code == code, ct)) return Conflict(new { message = "项目编码已存在。" });
        var project = new CampusRegistrationProject
        {
            Code = code, Name = request.Name.Trim(), Description = TrimOrNull(request.Description), CollegeId = request.CollegeId,
            RegistrationStartsAt = request.RegistrationStartsAt, RegistrationEndsAt = request.RegistrationEndsAt,
            Capacity = request.Capacity, FeeAmount = request.FeeAmount, RequiresReview = request.RequiresReview,
            Status = request.Status, ContactName = TrimOrNull(request.ContactName), ContactPhone = TrimOrNull(request.ContactPhone),
            Notes = TrimOrNull(request.Notes), CreatedByUserId = scope.Current.UserId
        };
        db.CampusRegistrationProjects.Add(project);
        await db.SaveChangesAsync(ct);
        return Created($"api/campus-registrations/projects/{project.Id}", new { project.Id });
    }

    [HttpPut("projects/{id:guid}")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> UpdateProject(Guid id, ProjectRequest request, CancellationToken ct)
    {
        var project = await db.CampusRegistrationProjects.FindAsync([id], ct);
        if (project is null) return NotFound();
        if (!CanManageProject(project)) return Forbid();
        var error = ValidateProject(request);
        if (error is not null) return BadRequest(new { message = error });
        if (!CanManageCollege(request.CollegeId)) return Forbid();
        var code = request.Code.Trim().ToUpperInvariant();
        if (await db.CampusRegistrationProjects.AnyAsync(x => x.Id != id && x.Code == code, ct)) return Conflict(new { message = "项目编码已存在。" });
        project.Code = code; project.Name = request.Name.Trim(); project.Description = TrimOrNull(request.Description); project.CollegeId = request.CollegeId;
        project.RegistrationStartsAt = request.RegistrationStartsAt; project.RegistrationEndsAt = request.RegistrationEndsAt; project.Capacity = request.Capacity;
        project.FeeAmount = request.FeeAmount; project.RequiresReview = request.RequiresReview; project.Status = request.Status;
        project.ContactName = TrimOrNull(request.ContactName); project.ContactPhone = TrimOrNull(request.ContactPhone); project.Notes = TrimOrNull(request.Notes);
        await db.SaveChangesAsync(ct);
        return NoContent();
    }

    [HttpPost("projects/{id:guid}/apply")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> Apply(Guid id, ApplyRequest request, CancellationToken ct)
    {
        var student = await db.Students.SingleOrDefaultAsync(x => x.UserId == scope.Current.UserId, ct);
        if (student is null) return BadRequest(new { message = "当前账号未关联学生档案。" });
        var project = await db.CampusRegistrationProjects.Include(x => x.Applications).SingleOrDefaultAsync(x => x.Id == id, ct);
        if (project is null || !CanStudentAccessProject(project, student)) return NotFound();
        var now = DateTime.UtcNow;
        if (project.Status != CampusRegistrationProjectStatus.Published || now < project.RegistrationStartsAt || now > project.RegistrationEndsAt) return Conflict(new { message = "当前不在报名时间内。" });
        if (await db.CampusRegistrationApplications.AnyAsync(x => x.ProjectId == id && x.StudentId == student.Id, ct)) return Conflict(new { message = "请勿重复报名。" });
        var confirmed = project.Applications.Count(x => x.Status == CampusRegistrationApplicationStatus.Confirmed);
        var status = confirmed >= project.Capacity ? CampusRegistrationApplicationStatus.Waitlisted : project.RequiresReview ? CampusRegistrationApplicationStatus.PendingReview : CampusRegistrationApplicationStatus.PendingPayment;
        var application = new CampusRegistrationApplication { ProjectId = id, StudentId = student.Id, Status = status, ApplicantNote = TrimOrNull(request.Note) };
        db.CampusRegistrationApplications.Add(application);
        if (status == CampusRegistrationApplicationStatus.PendingPayment) CreateOrder(application, project);
        await db.SaveChangesAsync(ct);
        return Created($"api/campus-registrations/applications/{application.Id}", new { application.Id, application.Status });
    }

    [HttpGet("mine")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> Mine(CancellationToken ct) => Ok(await ApplicationsForCurrentStudent()
        .OrderByDescending(x => x.CreatedAt).Select(ProjectApplicationDto()).ToListAsync(ct));

    [HttpGet("wallet/mine")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> GetMyWallet(CancellationToken ct)
    {
        var wallet = await db.CampusWalletAccounts.AsNoTracking()
            .SingleOrDefaultAsync(x => x.Student!.UserId == scope.Current.UserId, ct);
        return Ok(new { balance = wallet?.Balance ?? 0m });
    }

    [HttpPost("wallets/students/{studentId:guid}/adjust")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> AdjustWallet(Guid studentId, WalletAdjustmentRequest request, CancellationToken ct)
    {
        if (request.Amount == 0 || string.IsNullOrWhiteSpace(request.Reason))
            return BadRequest(new { message = "请填写非零调整金额和调整原因。" });
        var student = await db.Students.Include(x => x.AdministrativeClass).ThenInclude(x => x!.Major)
            .SingleOrDefaultAsync(x => x.Id == studentId, ct);
        if (student is null) return NotFound();
        if (!CanManageCollege(student.AdministrativeClass!.Major!.CollegeId)) return Forbid();
        var wallet = await db.CampusWalletAccounts.SingleOrDefaultAsync(x => x.StudentId == studentId, ct);
        if (wallet is null)
        {
            wallet = new CampusWalletAccount { StudentId = studentId, Balance = 0m };
            db.CampusWalletAccounts.Add(wallet);
        }
        var nextBalance = wallet.Balance + request.Amount;
        if (nextBalance < 0) return Conflict(new { message = "调整后余额不能小于零。" });
        wallet.Balance = nextBalance;
        db.CampusWalletTransactions.Add(new CampusWalletTransaction
        {
            WalletAccount = wallet, Amount = request.Amount, BalanceAfter = nextBalance,
            Type = CampusWalletTransactionType.AdministratorAdjustment, Reason = request.Reason.Trim(),
            OperatedByUserId = scope.Current.UserId
        });
        await db.SaveChangesAsync(ct);
        return Ok(new { balance = wallet.Balance });
    }

    [HttpGet("wallets/students")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> GetStudentWallets(
        [FromQuery] string? keyword,
        [FromQuery] int? grade,
        [FromQuery] Guid? collegeId,
        [FromQuery] Guid? majorId,
        [FromQuery] Guid? administrativeClassId,
        [FromQuery] int page = 1,
        [FromQuery] int pageSize = 20,
        CancellationToken ct = default)
    {
        var students = db.Students.AsNoTracking().AsQueryable();
        if (scope.Current.RestrictedCollegeId is { } restrictedCollegeId)
        {
            if (collegeId.HasValue && collegeId != restrictedCollegeId) return Forbid();
            collegeId = restrictedCollegeId;
        }
        if (collegeId.HasValue) students = students.Where(x => x.AdministrativeClass!.Major!.CollegeId == collegeId);
        if (majorId.HasValue) students = students.Where(x => x.AdministrativeClass!.MajorId == majorId);
        if (administrativeClassId.HasValue) students = students.Where(x => x.AdministrativeClassId == administrativeClassId);
        if (grade.HasValue) students = students.Where(x => x.AdministrativeClass!.Grade == grade);
        if (!string.IsNullOrWhiteSpace(keyword))
        {
            var term = keyword.Trim();
            students = students.Where(x => x.StudentNumber.Contains(term) || x.Name.Contains(term));
        }
        var total = await students.CountAsync(ct);
        page = Math.Max(1, page); pageSize = Math.Clamp(pageSize, 1, 100);
        var items = await students.OrderBy(x => x.StudentNumber).Skip((page - 1) * pageSize).Take(pageSize)
            .Select(x => new
            {
                x.Id, x.StudentNumber, x.Name,
                CollegeName = x.AdministrativeClass!.Major!.College!.Name,
                MajorName = x.AdministrativeClass.Major.Name,
                ClassName = x.AdministrativeClass.Name,
                Balance = db.CampusWalletAccounts.Where(wallet => wallet.StudentId == x.Id)
                    .Select(wallet => (decimal?)wallet.Balance).FirstOrDefault() ?? 0m,
                LastChangedAt = db.CampusWalletTransactions.Where(transaction => transaction.WalletAccount!.StudentId == x.Id)
                    .OrderByDescending(transaction => transaction.CreatedAt).Select(transaction => (DateTime?)transaction.CreatedAt).FirstOrDefault()
            }).ToListAsync(ct);
        return Ok(new PagedResult<object>(items.Cast<object>().ToList(), total, page, pageSize));
    }

    [HttpGet("wallets/filter-options")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> GetWalletFilterOptions(CancellationToken ct)
    {
        var classes = db.AdministrativeClasses.AsNoTracking().AsQueryable();
        if (scope.Current.RestrictedCollegeId is { } collegeId)
            classes = classes.Where(x => x.Major!.CollegeId == collegeId);
        return Ok(new
        {
            colleges = await db.Colleges.AsNoTracking()
                .Where(x => scope.Current.RestrictedCollegeId == null || x.Id == scope.Current.RestrictedCollegeId)
                .OrderBy(x => x.Name).Select(x => new { x.Id, x.Name }).ToListAsync(ct),
            majors = await db.Majors.AsNoTracking()
                .Where(x => scope.Current.RestrictedCollegeId == null || x.CollegeId == scope.Current.RestrictedCollegeId)
                .OrderBy(x => x.Name).Select(x => new { x.Id, x.Name, x.CollegeId }).ToListAsync(ct),
            classes = await classes.OrderBy(x => x.Grade).ThenBy(x => x.Name)
                .Select(x => new { x.Id, x.Name, x.Grade, x.MajorId }).ToListAsync(ct)
        });
    }

    [HttpGet("wallets/adjustment-template.xlsx")]
    [Authorize(Roles = Managers)]
    public IActionResult DownloadWalletAdjustmentTemplate() => File(
        ExcelWorkbookHelper.Create("余额批量调整", ["学号", "调整金额", "调整原因"], [],
            ["调整金额：正数充值，负数扣减；调整后余额不得小于零。", "每行都会生成独立余额流水，调整原因必填。"]),
        ExcelWorkbookHelper.ContentType, DownloadFileName.Template("学生余额批量调整", ".xlsx"));

    [HttpGet("wallets/export.xlsx")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> ExportWallets(CancellationToken ct)
    {
        var students = db.Students.AsNoTracking().AsQueryable();
        if (scope.Current.RestrictedCollegeId is { } collegeId)
            students = students.Where(x => x.AdministrativeClass!.Major!.CollegeId == collegeId);
        var rows = await students.OrderBy(x => x.StudentNumber).Select(x => new { x.StudentNumber, x.Name, CollegeName = x.AdministrativeClass!.Major!.College!.Name, MajorName = x.AdministrativeClass.Major.Name, ClassName = x.AdministrativeClass.Name, Balance = db.CampusWalletAccounts.Where(a => a.StudentId == x.Id).Select(a => (decimal?)a.Balance).FirstOrDefault() ?? 0m }).ToListAsync(ct);
        return File(ExcelWorkbookHelper.Create("学生余额", ["学号", "姓名", "学院", "专业", "行政班", "当前余额"], rows.Select(x => (IReadOnlyList<object?>)[x.StudentNumber, x.Name, x.CollegeName, x.MajorName, x.ClassName, x.Balance])), ExcelWorkbookHelper.ContentType, DownloadFileName.Export("学生余额", ".xlsx"));
    }

    [HttpPost("wallets/import-adjustments")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> ImportWalletAdjustments(IFormFile file, CancellationToken ct)
    {
        IReadOnlyList<ExcelRow> rows;
        try { rows = await ExcelWorkbookHelper.ReadAsync(file, ["学号", "调整金额", "调整原因"], ct); }
        catch (InvalidDataException ex) { return BadRequest(new { message = ex.Message }); }
        var errors = new List<string>(); var inputs = new List<(string Number, decimal Amount, string Reason)>();
        foreach (var row in rows) { if (!decimal.TryParse(row["调整金额"], out var amount) || amount == 0 || string.IsNullOrWhiteSpace(row["学号"]) || string.IsNullOrWhiteSpace(row["调整原因"])) errors.Add($"第 {row.RowNumber} 行：请填写学号、非零调整金额和调整原因。"); else inputs.Add((row["学号"], amount, row["调整原因"].Trim())); }
        var students = await db.Students.Include(x => x.AdministrativeClass).ThenInclude(x => x!.Major).Where(x => inputs.Select(i => i.Number).Contains(x.StudentNumber)).ToDictionaryAsync(x => x.StudentNumber, ct);
        foreach (var input in inputs) if (!students.TryGetValue(input.Number, out var student) || !CanManageCollege(student.AdministrativeClass!.Major!.CollegeId)) errors.Add($"学号 {input.Number} 不存在或不在当前管理范围内。");
        if (errors.Count > 0) return BadRequest(new { message = string.Join("；", errors.Take(20)) });
        var accounts = await db.CampusWalletAccounts.Where(x => inputs.Select(i => students[i.Number].Id).Contains(x.StudentId)).ToDictionaryAsync(x => x.StudentId, ct);
        foreach (var input in inputs) { var student = students[input.Number]; if (!accounts.TryGetValue(student.Id, out var account)) { account = new CampusWalletAccount { StudentId = student.Id }; db.CampusWalletAccounts.Add(account); accounts[student.Id] = account; } var balance = account.Balance + input.Amount; if (balance < 0) { errors.Add($"学号 {input.Number} 调整后余额不能小于零。"); continue; } account.Balance = balance; db.CampusWalletTransactions.Add(new CampusWalletTransaction { WalletAccount = account, Amount = input.Amount, BalanceAfter = balance, Type = CampusWalletTransactionType.AdministratorAdjustment, Reason = input.Reason, OperatedByUserId = scope.Current.UserId }); }
        if (errors.Count > 0) return BadRequest(new { message = string.Join("；", errors) });
        await db.SaveChangesAsync(ct); return Ok(new { adjusted = inputs.Count });
    }

    [HttpPost("applications/{id:guid}/cancel")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> Cancel(Guid id, CancellationToken ct)
    {
        var application = await db.CampusRegistrationApplications.Include(x => x.Project).Include(x => x.PaymentOrder).SingleOrDefaultAsync(x => x.Id == id && x.Student!.UserId == scope.Current.UserId, ct);
        if (application is null) return NotFound();
        if (application.Status is CampusRegistrationApplicationStatus.Confirmed or CampusRegistrationApplicationStatus.Rejected or CampusRegistrationApplicationStatus.Cancelled) return Conflict(new { message = "当前报名不能撤销。" });
        application.Status = CampusRegistrationApplicationStatus.Cancelled; application.CancelledAt = DateTime.UtcNow;
        if (application.PaymentOrder?.Status == CampusPaymentOrderStatus.Pending) application.PaymentOrder.Status = CampusPaymentOrderStatus.Cancelled;
        try
        {
            await db.SaveChangesAsync(ct);
            return NoContent();
        }
        catch (DbUpdateConcurrencyException)
        {
            return Conflict(new { message = "该报名已被其他管理员处理，请刷新后查看最新状态。" });
        }
    }

    [HttpGet("applications")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> GetApplications([FromQuery] Guid? projectId, [FromQuery] CampusRegistrationApplicationStatus? status, CancellationToken ct)
    {
        var source = ScopedApplications().AsNoTracking();
        if (projectId.HasValue) source = source.Where(x => x.ProjectId == projectId);
        if (status.HasValue) source = source.Where(x => x.Status == status);
        return Ok(await source.OrderByDescending(x => x.CreatedAt).Select(ProjectApplicationDto()).ToListAsync(ct));
    }

    [HttpGet("applications/export.xlsx")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> ExportApplications([FromQuery] Guid? projectId, CancellationToken ct)
    {
        var rows = await ScopedApplications().AsNoTracking().Where(x => !projectId.HasValue || x.ProjectId == projectId).OrderByDescending(x => x.CreatedAt)
            .Select(x => new { x.Project!.Code, ProjectName = x.Project.Name, x.Student!.StudentNumber, StudentName = x.Student.Name, Status = x.Status.ToString(), x.CreatedAt, Amount = x.PaymentOrder == null ? 0m : x.PaymentOrder.Amount, PaymentStatus = x.PaymentOrder == null ? "—" : x.PaymentOrder.Status.ToString(), x.ReviewComment }).ToListAsync(ct);
        var content = ExcelWorkbookHelper.Create("校园报名与缴费", ["项目编码", "项目名称", "学号", "姓名", "报名状态", "提交时间", "应收金额", "支付状态", "审核意见"], rows.Select(x => (IReadOnlyList<object?>)[x.Code, x.ProjectName, x.StudentNumber, x.StudentName, x.Status, x.CreatedAt, x.Amount, x.PaymentStatus, x.ReviewComment]).ToList());
        return File(content, ExcelWorkbookHelper.ContentType, DownloadFileName.Export("校园报名与缴费", ".xlsx"));
    }

    [HttpPost("applications/{id:guid}/review")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> Review(Guid id, ReviewRequest request, CancellationToken ct)
    {
        var application = await db.CampusRegistrationApplications.Include(x => x.Project).SingleOrDefaultAsync(x => x.Id == id, ct);
        if (application is null) return NotFound(); if (!CanManageProject(application.Project!)) return Forbid();
        if (application.Status != CampusRegistrationApplicationStatus.PendingReview) return Conflict(new { message = "该报名当前无需审核。" });
        application.ReviewedByUserId = scope.Current.UserId; application.ReviewedAt = DateTime.UtcNow; application.ReviewComment = TrimOrNull(request.Comment);
        if (!request.Approved) application.Status = CampusRegistrationApplicationStatus.Rejected;
        else if (await ConfirmedCount(application.ProjectId, ct) >= application.Project!.Capacity) application.Status = CampusRegistrationApplicationStatus.Waitlisted;
        else { application.Status = CampusRegistrationApplicationStatus.PendingPayment; CreateOrder(application, application.Project!); }
        try
        {
            await db.SaveChangesAsync(ct);
            return NoContent();
        }
        catch (DbUpdateConcurrencyException)
        {
            return Conflict(new { message = "该报名已被其他管理员处理，请刷新后查看最新状态。" });
        }
    }

    [HttpPost("orders/{id:guid}/confirm-offline")]
    [Authorize(Roles = Managers)]
    public async Task<ActionResult> ConfirmOffline(Guid id, OfflinePaymentRequest request, CancellationToken ct)
    {
        var order = await db.CampusPaymentOrders.Include(x => x.Application).ThenInclude(x => x!.Project).SingleOrDefaultAsync(x => x.Id == id, ct);
        if (order is null) return NotFound(); if (!CanManageProject(order.Application!.Project!)) return Forbid();
        if (order.Status != CampusPaymentOrderStatus.Pending || order.PaymentMethod != CampusPaymentMethod.Offline) return Conflict(new { message = "该订单不能线下确认。" });
        if (await ConfirmedCount(order.Application.ProjectId, ct) >= order.Application.Project!.Capacity) { order.Application.Status = CampusRegistrationApplicationStatus.Waitlisted; await db.SaveChangesAsync(ct); return Conflict(new { message = "名额已满，报名已转为候补。" }); }
        order.Status = CampusPaymentOrderStatus.Paid; order.ConfirmedAt = DateTime.UtcNow; order.ConfirmedByUserId = scope.Current.UserId; order.ReferenceNumber = TrimOrNull(request.ReferenceNumber); order.Note = TrimOrNull(request.Note);
        order.Application.Status = CampusRegistrationApplicationStatus.Confirmed; order.Application.ConfirmedAt = DateTime.UtcNow;
        try
        {
            await db.SaveChangesAsync(ct);
            return NoContent();
        }
        catch (DbUpdateConcurrencyException)
        {
            return Conflict(new { message = "该订单已被其他管理员处理，请刷新后查看最新状态。" });
        }
    }

    [HttpPost("orders/{id:guid}/pay-balance")]
    [Authorize(Roles = SystemRoles.Student)]
    public async Task<ActionResult> PayByBalance(Guid id, CancellationToken ct)
    {
        var order = await db.CampusPaymentOrders.Include(x => x.Application).ThenInclude(x => x!.Project)
            .SingleOrDefaultAsync(x => x.Id == id && x.Application!.Student!.UserId == scope.Current.UserId, ct);
        if (order is null) return NotFound();
        if (order.Status != CampusPaymentOrderStatus.Pending || order.Application!.Status != CampusRegistrationApplicationStatus.PendingPayment)
            return Conflict(new { message = "该订单当前不能使用余额支付。" });
        if (await ConfirmedCount(order.Application.ProjectId, ct) >= order.Application.Project!.Capacity)
        {
            order.Application.Status = CampusRegistrationApplicationStatus.Waitlisted;
            await db.SaveChangesAsync(ct);
            return Conflict(new { message = "名额已满，报名已转为候补。" });
        }
        await using var transaction = await db.Database.BeginTransactionAsync(IsolationLevel.Serializable, ct);
        var debited = await db.CampusWalletAccounts
            .Where(x => x.StudentId == order.Application.StudentId && x.Balance >= order.Amount)
            .ExecuteUpdateAsync(setters => setters
                .SetProperty(x => x.Balance, x => x.Balance - order.Amount)
                .SetProperty(x => x.UpdatedAt, _ => DateTime.UtcNow), ct);
        if (debited == 0)
        {
            await transaction.RollbackAsync(ct);
            return Conflict(new { message = "余额不足，请联系管理员调整余额或选择线下缴费。" });
        }
        var balanceAfter = await db.CampusWalletAccounts.AsNoTracking()
            .Where(x => x.StudentId == order.Application.StudentId)
            .Select(x => x.Balance).SingleAsync(ct);
        db.CampusWalletTransactions.Add(new CampusWalletTransaction
        {
            WalletAccountId = await db.CampusWalletAccounts.Where(x => x.StudentId == order.Application.StudentId)
                .Select(x => x.Id).SingleAsync(ct), Amount = -order.Amount, BalanceAfter = balanceAfter,
            Type = CampusWalletTransactionType.Payment, Reason = $"支付报名项目：{order.Application.Project!.Name}",
            PaymentOrderId = order.Id, OperatedByUserId = scope.Current.UserId
        });
        order.Status = CampusPaymentOrderStatus.Paid; order.PaymentMethod = CampusPaymentMethod.Balance;
        order.ConfirmedAt = DateTime.UtcNow; order.ConfirmedByUserId = scope.Current.UserId;
        order.Application.Status = CampusRegistrationApplicationStatus.Confirmed; order.Application.ConfirmedAt = DateTime.UtcNow;
        try { await db.SaveChangesAsync(ct); await transaction.CommitAsync(ct); return NoContent(); }
        catch (DbUpdateConcurrencyException) { return Conflict(new { message = "订单或余额已变化，请刷新后重试。" }); }
        catch (DbUpdateException) { return Conflict(new { message = "该订单已完成支付或余额已变化，请刷新后查看最新状态。" }); }
    }

    private IQueryable<CampusRegistrationProject> ScopedProjects() => scope.Current.RestrictedCollegeId is { } collegeId ? db.CampusRegistrationProjects.Where(x => x.CollegeId == null || x.CollegeId == collegeId) : db.CampusRegistrationProjects;
    private IQueryable<CampusRegistrationApplication> ScopedApplications() => scope.Current.RestrictedCollegeId is { } collegeId ? db.CampusRegistrationApplications.Where(x => x.Project!.CollegeId == null || x.Project.CollegeId == collegeId) : db.CampusRegistrationApplications;
    private IQueryable<CampusRegistrationApplication> ApplicationsForCurrentStudent() => db.CampusRegistrationApplications.Where(x => x.Student!.UserId == scope.Current.UserId);
    private bool CanManageCollege(Guid? collegeId) => scope.Current.RestrictedCollegeId is not { } restricted || collegeId is null || collegeId == restricted;
    private bool CanManageProject(CampusRegistrationProject project) => CanManageCollege(project.CollegeId);
    private static bool CanStudentAccessProject(CampusRegistrationProject project, Student student) => project.CollegeId is null || project.CollegeId == student.AdministrativeClass!.Major!.CollegeId;
    private Task<int> ConfirmedCount(Guid projectId, CancellationToken ct) => db.CampusRegistrationApplications.CountAsync(x => x.ProjectId == projectId && x.Status == CampusRegistrationApplicationStatus.Confirmed, ct);
    private void CreateOrder(CampusRegistrationApplication application, CampusRegistrationProject project)
    {
        var free = project.FeeAmount == 0;
        var order = new CampusPaymentOrder
        {
            ApplicationId = application.Id,
            OrderNumber = $"CR{DateTime.UtcNow:yyyyMMddHHmmss}{Guid.NewGuid():N}"[..38],
            Amount = project.FeeAmount,
            PaymentMethod = free ? CampusPaymentMethod.Free : CampusPaymentMethod.Offline,
            Status = free ? CampusPaymentOrderStatus.Paid : CampusPaymentOrderStatus.Pending,
            ConfirmedAt = free ? DateTime.UtcNow : null,
            ConfirmedByUserId = free ? scope.Current.UserId : null
        };
        db.CampusPaymentOrders.Add(order);
        if (free) { application.Status = CampusRegistrationApplicationStatus.Confirmed; application.ConfirmedAt = DateTime.UtcNow; }
    }
    private static string? ValidateProject(ProjectRequest r) => string.IsNullOrWhiteSpace(r.Code) || r.Code.Trim().Length > 40 ? "请填写不超过 40 字的项目编码。" : string.IsNullOrWhiteSpace(r.Name) || r.Name.Trim().Length > 120 ? "请填写不超过 120 字的项目名称。" : r.RegistrationEndsAt <= r.RegistrationStartsAt ? "报名结束时间必须晚于开始时间。" : r.Capacity < 1 ? "名额必须至少为 1。" : r.FeeAmount < 0 ? "金额不能为负数。" : null;
    private static string? TrimOrNull(string? value) => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
    private static System.Linq.Expressions.Expression<Func<CampusRegistrationApplication, object>> ProjectApplicationDto() => x => new { x.Id, x.ProjectId, ProjectCode = x.Project!.Code, ProjectName = x.Project.Name, x.Status, x.ApplicantNote, x.CreatedAt, x.ReviewComment, x.ConfirmedAt, x.CancelledAt, StudentId = x.StudentId, StudentNumber = x.Student!.StudentNumber, StudentName = x.Student.Name, Order = x.PaymentOrder == null ? null : new { x.PaymentOrder.Id, x.PaymentOrder.OrderNumber, x.PaymentOrder.Amount, x.PaymentOrder.PaymentMethod, x.PaymentOrder.Status, x.PaymentOrder.ReferenceNumber } };
}

public sealed record ProjectRequest(string Code, string Name, string? Description, Guid? CollegeId, DateTime RegistrationStartsAt, DateTime RegistrationEndsAt, int Capacity, decimal FeeAmount, bool RequiresReview, CampusRegistrationProjectStatus Status, string? ContactName, string? ContactPhone, string? Notes);
public sealed record ApplyRequest(string? Note);
public sealed record ReviewRequest(bool Approved, string? Comment);
public sealed record OfflinePaymentRequest(string? ReferenceNumber, string? Note);
public sealed record WalletAdjustmentRequest(decimal Amount, string? Reason);