namespace ExpenseFlow.Api;

public static class ApprovalPolicy
{
    // 各类别的单笔阈值，超过即需二级审批
    private static readonly Dictionary<string, decimal> Thresholds = new()
    {
        ["Meal"]      = 300m,
        ["Taxi"]      = 500m,
        ["Hotel"]     = 1500m,
        ["Equipment"] = 5000m,
    };

    public const decimal DefaultThreshold = 1000m;

    // 注意是严格大于：正好等于阈值不触发二级审批
    public static bool RequiresSecondApproval(string category, decimal amount) =>
        amount > (Thresholds.TryGetValue(category, out var t) ? t : DefaultThreshold);
}

using ExpenseFlow.Api;
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<ExpenseDbContext>(o =>
    o.UseSqlite("Data Source=expenses.db"));

var app = builder.Build();

using (var scope = app.Services.CreateScope())
{
    scope.ServiceProvider.GetRequiredService<ExpenseDbContext>().Database.EnsureCreated();
}

app.MapPost("/expenses", async (ExpenseRequest req, ExpenseDbContext db) =>
{
    if (req.Amount <= 0m)
        return Results.BadRequest("金额必须大于 0");

    var expense = new Expense
    {
        EmployeeId  = req.EmployeeId,
        Category    = req.Category,
        Amount      = req.Amount,
        Description = req.Description,
        SubmittedAt = DateTimeOffset.UtcNow,
        Status      = ExpenseStatus.Submitted,
        RequiresSecondApproval = ApprovalPolicy.RequiresSecondApproval(req.Category, req.Amount),
    };

    db.Expenses.Add(expense);
    await db.SaveChangesAsync();
    return Results.Created($"/expenses/{expense.Id}", expense);
});

app.MapGet("/expenses/{id:int}", async (int id, ExpenseDbContext db) =>
    await db.Expenses.FindAsync(id) is { } e ? Results.Ok(e) : Results.NotFound());

app.Run();

public record ExpenseRequest(string EmployeeId, string Category, decimal Amount, string Description);

public enum ExpenseStatus { Draft, Submitted, Approved, Rejected, Reimbursed }

public class Expense
{
    public int Id { get; set; }
    public string EmployeeId { get; set; } = "";
    public string Category { get; set; } = "";
    public decimal Amount { get; set; }
    public string Description { get; set; } = "";
    public DateTimeOffset SubmittedAt { get; set; }
    public ExpenseStatus Status { get; set; }
    public bool RequiresSecondApproval { get; set; }
}

public class ExpenseDbContext(DbContextOptions<ExpenseDbContext> options) : DbContext(options)
{
    public DbSet<Expense> Expenses => Set<Expense>();

    protected override void OnModelCreating(ModelBuilder b) =>
        b.Entity<Expense>().Property(e => e.Amount).HasPrecision(18, 2);
}

public partial class Program;

using ExpenseFlow.Api;

public class ApprovalPolicyTests
{
    [Theory]
    [InlineData("Meal",      280,  false)]
    [InlineData("Meal",      300,  false)]  // 正好等于阈值，不触发
    [InlineData("Meal",      300.01, true)]
    [InlineData("Hotel",     1500, false)]
    [InlineData("Equipment", 5001, true)]
    [InlineData("Unknown",   1200, true)]   // 未知类别走默认 1000
    public void Second_approval_kicks_in_above_category_threshold(
        string category, decimal amount, bool expected)
        => Assert.Equal(expected, ApprovalPolicy.RequiresSecondApproval(category, amount));
}

using System.Net;
using System.Net.Http.Json;
using Microsoft.AspNetCore.Mvc.Testing;

public class ExpensesEndpointTests(WebApplicationFactory<Program> factory)
    : IClassFixture<WebApplicationFactory<Program>>
{
    [Fact]
    public async Task Over_threshold_expense_is_flagged_for_second_approval()
    {
        var client = factory.CreateClient();

        var response = await client.PostAsJsonAsync("/expenses", new
        {
            EmployeeId  = "E1024",
            Category    = "Meal",
            Amount      = 880m,
            Description = "团队聚餐"
        });

        Assert.Equal(HttpStatusCode.Created, response.StatusCode);
        var created = await response.Content.ReadFromJsonAsync<Expense>();
        Assert.True(created!.RequiresSecondApproval);
    }

    [Fact]
    public async Task Non_positive_amount_is_rejected()
    {
        var client = factory.CreateClient();
        var response = await client.PostAsJsonAsync("/expenses", new
        {
            EmployeeId = "E1024", Category = "Taxi", Amount = 0m, Description = "空单"
        });

        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
    }
}