using System.Security.Cryptography;
using Microsoft.Extensions.Caching.Memory;

namespace Rmsys.Api.Endpoints;

/// <summary>
/// 图形验证码：服务端生成 SVG（不依赖 System.Drawing，Linux/Windows 都能跑），
/// 验证码文本存内存缓存，3 分钟过期、校验一次即作废（防重放）。
/// </summary>
public static class CaptchaEndpoints
{
    private const string Chars = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";   // 去掉 0/O/1/I/L 易混字符
    private const int Length = 4;
    private const int TtlSeconds = 180;

    public static void MapCaptchaEndpoints(this WebApplication app)
    {
        app.MapGet("/api/auth/captcha", (IMemoryCache cache) =>
        {
            var code = NewCode();
            var id = Guid.NewGuid().ToString("N");
            cache.Set("captcha:" + id, code, TimeSpan.FromSeconds(TtlSeconds));

            var svg = BuildSvg(code);
            // 只有显式设置 RMSYS_CAPTCHA_DEBUG=1 才回传答案（仅供联调/自测）。
            // 安装包部署时不设置该变量，生产环境永远不会泄露答案。
            var debug = Environment.GetEnvironmentVariable("RMSYS_CAPTCHA_DEBUG") == "1";
            if (debug)
                return Results.Ok(new { ok = true, id, svg, code, ttl = TtlSeconds });

            return Results.Ok(new { ok = true, id, svg, ttl = TtlSeconds });
        });

        /// <summary>登录时校验：命中即删除（一次一用）</summary>
        app.MapPost("/api/auth/captcha/check", (CaptchaCheckReq req, IMemoryCache cache) =>
        {
            var ok = Consume(cache, req.id, req.code);
            return Results.Ok(new { ok });
        });
    }

    /// <summary>校验并从缓存移除；失败也移除（避免被反复猜）</summary>
    public static bool Consume(IMemoryCache cache, string? id, string? input)
    {
        if (string.IsNullOrWhiteSpace(id) || string.IsNullOrWhiteSpace(input)) return false;
        var key = "captcha:" + id;
        if (!cache.TryGetValue<string>(key, out var code) || string.IsNullOrEmpty(code)) return false;
        cache.Remove(key);
        return string.Equals(code, input.Trim(), StringComparison.OrdinalIgnoreCase);
    }

    private static string NewCode()
    {
        var buf = new char[Length];
        for (var i = 0; i < Length; i++) buf[i] = Chars[RandomNumberGenerator.GetInt32(Chars.Length)];
        return new string(buf);
    }

    private static string BuildSvg(string code)
    {
        var rnd = RandomNumberGenerator.Create();
        int R(int min, int max) { var b = new byte[4]; rnd.GetBytes(b); return min + (int)(BitConverter.ToUInt32(b, 0) % (uint)(max - min)); }
        double D(double min, double max) => min + (rnd.NextDoubleLike() * (max - min));

        const int w = 132, h = 44;
        var sb = new System.Text.StringBuilder();
        sb.Append($"<svg xmlns='http://www.w3.org/2000/svg' width='{w}' height='{h}' viewBox='0 0 {w} {h}'>");
        sb.Append($"<rect width='{w}' height='{h}' fill='#F6F2E9'/>");

        // 干扰线
        for (var i = 0; i < 3; i++)
        {
            var c = i % 2 == 0 ? "#D8C7A8" : "#C9B99B";
            sb.Append($"<line x1='{R(0, 12)}' y1='{R(4, h - 4)}' x2='{R(w - 12, w)}' y2='{R(4, h - 4)}' stroke='{c}' stroke-width='1.2'/>");
        }
        // 干扰点
        for (var i = 0; i < 26; i++)
            sb.Append($"<circle cx='{R(2, w - 2)}' cy='{R(2, h - 2)}' r='{D(0.6, 1.4):F1}' fill='#BFAE8E' opacity='0.55'/>");

        // 字符：逐个随机旋转、轻微上下浮动，颜色在深红/墨黑/棕色间取
        var colors = new[] { "#8C1515", "#3A3A3A", "#7A4B12", "#1F4E79" };
        var glyphs = new List<string>();
        for (var i = 0; i < code.Length; i++)
        {
            var x = 22 + i * 27 + R(-8, 9);   // 抖动足以打乱「按 x 排序」，又不影响人眼阅读
            var y = 31 + R(-3, 4);
            var rot = R(-20, 21);
            var col = colors[R(0, colors.Length)];
            var size = R(24, 29);
            glyphs.Add($"<text x='{x}' y='{y}' fill='{col}' font-size='{size}' font-family='Georgia,DejaVu Serif,serif' "
                     + $"font-weight='700' transform='rotate({rot} {x} {y})'>{System.Security.SecurityElement.Escape(code[i].ToString())}</text>");
        }

        // 反脚本提取（一）：混入与底色同色的诱饵字符，照 DOM 顺序读会读错
        for (var i = 0; i < 2; i++)
        {
            var dx = R(6, w - 20);
            var dy = R(20, h - 6);
            glyphs.Add($"<text x='{dx}' y='{dy}' fill='#F6F2E9' font-size='{R(22, 28)}' font-family='Georgia,serif'>"
                     + Chars[R(0, Chars.Length)] + "</text>");
        }

        // 反脚本提取（二）：打乱绘制顺序，可见字符也不再是 DOM 里的先后顺序
        for (var i = glyphs.Count - 1; i > 0; i--)
        {
            var j = R(0, i + 1);
            (glyphs[i], glyphs[j]) = (glyphs[j], glyphs[i]);
        }
        foreach (var g in glyphs) sb.Append(g);
        sb.Append("</svg>");
        return sb.ToString();
    }

    private static double NextDoubleLike(this RandomNumberGenerator r)
    {
        var b = new byte[4];
        r.GetBytes(b);
        return BitConverter.ToUInt32(b, 0) / (double)uint.MaxValue;
    }

    public record CaptchaCheckReq(string? id, string? code);
}