using System.Globalization;
using System.Text.Json.Nodes;
using Microsoft.AspNetCore.Mvc;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NamingConventions;

namespace StellaOps.Router.Gateway.OpenApi;

/// <summary>
/// Endpoints for serving OpenAPI documentation.
/// </summary>
public static class OpenApiEndpoints
{
    private static readonly ISerializer YamlSerializer = new SerializerBuilder()
        .WithNamingConvention(CamelCaseNamingConvention.Instance)
        .Build();

    /// <summary>
    /// Maps OpenAPI endpoints to the application.
    /// </summary>
    public static IEndpointRouteBuilder MapRouterOpenApiEndpoints(this IEndpointRouteBuilder endpoints)
    {
        endpoints.MapGet("/.well-known/openapi", GetOpenApiDiscovery)
            .ExcludeFromDescription();

        endpoints.MapGet("/openapi.json", GetOpenApiJson)
            .ExcludeFromDescription();

        endpoints.MapGet("/openapi.yaml", GetOpenApiYaml)
            .ExcludeFromDescription();

        return endpoints;
    }

    private static IResult GetOpenApiDiscovery(
        [FromServices] IRouterOpenApiDocumentCache cache,
        HttpContext context)
    {
        var (_, etag, generatedAt) = cache.GetDocument();

        var discovery = new
        {
            openapi_json = "/openapi.json",
            openapi_yaml = "/openapi.yaml",
            etag,
            generated_at = generatedAt.ToString("O", CultureInfo.InvariantCulture)
        };

        context.Response.Headers.CacheControl = "public, max-age=60";
        return Results.Ok(discovery);
    }

    private static IResult GetOpenApiJson(
        [FromServices] IRouterOpenApiDocumentCache cache,
        HttpContext context)
    {
        var (documentJson, etag, _) = cache.GetDocument();

        // Check If-None-Match header
        if (context.Request.Headers.TryGetValue("If-None-Match", out var ifNoneMatch))
        {
            if (ifNoneMatch == etag)
            {
                context.Response.Headers.ETag = etag;
                context.Response.Headers.CacheControl = "public, max-age=60";
                return Results.StatusCode(304);
            }
        }

        context.Response.Headers.ETag = etag;
        context.Response.Headers.CacheControl = "public, max-age=60";
        return Results.Content(documentJson, "application/json; charset=utf-8");
    }

    private static IResult GetOpenApiYaml(
        [FromServices] IRouterOpenApiDocumentCache cache,
        HttpContext context)
    {
        var (documentJson, etag, _) = cache.GetDocument();

        // Check If-None-Match header
        if (context.Request.Headers.TryGetValue("If-None-Match", out var ifNoneMatch))
        {
            if (ifNoneMatch == etag)
            {
                context.Response.Headers.ETag = etag;
                context.Response.Headers.CacheControl = "public, max-age=60";
                return Results.StatusCode(304);
            }
        }

        // Convert JSON to YAML
        var jsonNode = JsonNode.Parse(documentJson);
        var yamlContent = ConvertToYaml(jsonNode);

        context.Response.Headers.ETag = etag;
        context.Response.Headers.CacheControl = "public, max-age=60";
        return Results.Content(yamlContent, "application/yaml; charset=utf-8");
    }

    private static string ConvertToYaml(JsonNode? node)
    {
        if (node is null)
            return string.Empty;

        var obj = ConvertJsonNodeToObject(node);
        return YamlSerializer.Serialize(obj);
    }

    private static object? ConvertJsonNodeToObject(JsonNode? node)
    {
        return node switch
        {
            null => null,
            JsonObject obj => obj.ToDictionary(
                kvp => kvp.Key,
                kvp => ConvertJsonNodeToObject(kvp.Value)),
            JsonArray arr => arr.Select(ConvertJsonNodeToObject).ToList(),
            JsonValue val => val.GetValue<object>(),
            _ => null
        };
    }
}