using System.IO;
using System.Reflection;
using Lskj.AgentPet.Host.Core;

namespace Lskj.AgentPet.Host;

internal sealed class EmbeddedPetResource
{
    public EmbeddedPetResource(byte[] bytes, string contentType, bool document)
    {
        Bytes = bytes ?? throw new ArgumentNullException(nameof(bytes));
        ContentType = contentType ?? throw new ArgumentNullException(nameof(contentType));
        IsDocument = document;
    }

    public byte[] Bytes { get; }
    public string ContentType { get; }
    public bool IsDocument { get; }
}

internal static class EmbeddedPetResources
{
    public const string PageUrl = "https://lserp-pet.local/index.html";
    private const int MaximumResourceBytes = 2 * 1024 * 1024;
    private const int MaximumTotalBytes = 4 * 1024 * 1024;

    private static readonly ResourceSpec[] Specs =
    {
        new(PageUrl, "Lskj.AgentPet.Web.index.html", "text/html; charset=utf-8", true),
        new("https://lserp-pet.local/pet.css", "Lskj.AgentPet.Web.pet.css", "text/css; charset=utf-8", false),
        new("https://lserp-pet.local/pet-runtime.js", "Lskj.AgentPet.Web.pet-runtime.js", "text/javascript; charset=utf-8", false),
        new("https://lserp-pet.local/bridge-client.js", "Lskj.AgentPet.Web.bridge-client.js", "text/javascript; charset=utf-8", false),
        new("https://lserp-pet.local/pet-shell.js", "Lskj.AgentPet.Web.pet-shell.js", "text/javascript; charset=utf-8", false)
    };

    public static IReadOnlyDictionary<string, EmbeddedPetResource> Load()
    {
        Assembly assembly = typeof(EmbeddedPetResources).Assembly;
        Dictionary<string, EmbeddedPetResource> result =
            new(StringComparer.Ordinal);
        int totalBytes = 0;
        foreach (ResourceSpec spec in Specs)
        {
            using Stream? stream = assembly.GetManifestResourceStream(spec.Name);
            if (stream is null
                || !stream.CanRead
                || stream.Length <= 0
                || stream.Length > MaximumResourceBytes)
            {
                throw new HostError(
                    "pet_web_resource_invalid",
                    "签名桌宠程序集缺少有效的嵌入式页面资源。");
            }
            totalBytes = checked(totalBytes + (int)stream.Length);
            if (totalBytes > MaximumTotalBytes)
            {
                throw new HostError(
                    "pet_web_resource_invalid",
                    "签名桌宠页面资源超过安全上限。");
            }

            byte[] bytes = new byte[(int)stream.Length];
            int offset = 0;
            while (offset < bytes.Length)
            {
                int read = stream.Read(bytes, offset, bytes.Length - offset);
                if (read <= 0)
                    throw new HostError(
                        "pet_web_resource_invalid",
                        "无法完整读取签名桌宠页面资源。");
                offset += read;
            }
            result.Add(
                spec.Url,
                new EmbeddedPetResource(bytes, spec.ContentType, spec.Document));
        }
        return result;
    }

    private sealed class ResourceSpec
    {
        public ResourceSpec(
            string url,
            string name,
            string contentType,
            bool document)
        {
            Url = url;
            Name = name;
            ContentType = contentType;
            Document = document;
        }

        public string Url { get; }
        public string Name { get; }
        public string ContentType { get; }
        public bool Document { get; }
    }
}