EonaCat.DoxaApi/DoxaApi/Generation/SchemaBuilder.cs

using System.Collections;
using System.Reflection;
using EonaCat.DoxaApi.Models;

namespace EonaCat.DoxaApi.Generation
{
    public sealed class SchemaBuilder
    {
        private readonly Dictionary<string, SchemaModel> _registry;
        private readonly HashSet<Type> _inProgress = new();

        public SchemaBuilder(Dictionary<string, SchemaModel> registry)
        {
            _registry = registry;
        }

        public SchemaModel Build(Type type)
        {

            type = UnwrapAsyncAndActionResult(type);

            var underlying = Nullable.GetUnderlyingType(type);
            bool nullable = underlying is not null;
            if (underlying is not null)
            {
                type = underlying;
            }

            var schema = BuildCore(type);
            schema.Nullable = nullable || schema.Nullable;
            return schema;
        }

        private static Type UnwrapAsyncAndActionResult(Type type)
        {
            if (type == typeof(void))
            {
                return type;
            }

            if (type.IsGenericType)
            {
                var def = type.GetGenericTypeDefinition();
                if (def == typeof(Task<>) || def.Name.StartsWith("ValueTask`"))
                {
                    return UnwrapAsyncAndActionResult(type.GetGenericArguments()[0]);
                }

                if (def.Name is "ActionResult`1")
                {
                    return UnwrapAsyncAndActionResult(type.GetGenericArguments()[0]);
                }
            }

            if (type == typeof(Task))
            {
                return typeof(void);
            }

            return type;
        }

        private SchemaModel BuildCore(Type type)
        {
            if (type == typeof(void))
            {
                return new SchemaModel { Type = "void" };
            }

            if (type == typeof(string) || type == typeof(char))
            {
                return new SchemaModel { Type = "string" };
            }

            if (type == typeof(bool))
            {
                return new SchemaModel { Type = "boolean" };
            }

            if (type == typeof(byte) || type == typeof(sbyte) || type == typeof(short) ||
                type == typeof(ushort) || type == typeof(int) || type == typeof(uint) ||
                type == typeof(long) || type == typeof(ulong))
            {
                return new SchemaModel { Type = "integer", Format = type.Name.ToLowerInvariant() };
            }

            if (type == typeof(float) || type == typeof(double) || type == typeof(decimal))
            {
                return new SchemaModel { Type = "number", Format = type.Name.ToLowerInvariant() };
            }

            if (type == typeof(DateTime) || type == typeof(DateTimeOffset))
            {
                return new SchemaModel { Type = "string", Format = "date-time" };
            }

            if (type == typeof(DateOnly))
            {
                return new SchemaModel { Type = "string", Format = "date" };
            }

            if (type == typeof(TimeOnly) || type == typeof(TimeSpan))
            {
                return new SchemaModel { Type = "string", Format = "time" };
            }

            if (type == typeof(Guid))
            {
                return new SchemaModel { Type = "string", Format = "uuid" };
            }

            if (type == typeof(Uri))
            {
                return new SchemaModel { Type = "string", Format = "uri" };
            }

            if (type == typeof(object))
            {
                return new SchemaModel { Type = "object" };
            }

            if (type.IsEnum)
            {
                return new SchemaModel
                {
                    Type = "enum",
                    EnumValues = Enum.GetNames(type).ToList()
                };
            }

            if (IsDictionary(type, out var valueType))
            {
                return new SchemaModel
                {
                    Type = "object",
                    Items = Build(valueType!)
                };
            }

            var elementType = GetEnumerableElementType(type);
            if (elementType is not null)
            {
                return new SchemaModel
                {
                    Type = "array",
                    Items = Build(elementType)
                };
            }

            var refName = FriendlyTypeName(type);

            if (_registry.ContainsKey(refName))
            {
                return new SchemaModel { Type = "object", RefName = refName };
            }

            if (_inProgress.Contains(type))
            {
                return new SchemaModel { Type = "object", RefName = refName };
            }

            _inProgress.Add(type);

            var props = new Dictionary<string, SchemaModel>();
            var required = new List<string>();

            foreach (var prop in type.GetProperties(BindingFlags.Public | BindingFlags.Instance))
            {
                if (prop.GetIndexParameters().Length > 0)
                {
                    continue;
                }

                if (!prop.CanRead)
                {
                    continue;
                }

                var propSchema = Build(prop.PropertyType);
                props[ToCamelCase(prop.Name)] = propSchema;

                if (!propSchema.Nullable && Nullable.GetUnderlyingType(prop.PropertyType) is null
                    && (prop.PropertyType.IsValueType || IsNonNullableReferenceProperty(prop)))
                {
                    required.Add(ToCamelCase(prop.Name));
                }
            }

            _registry[refName] = new SchemaModel
            {
                Type = "object",
                Properties = props,
                Required = required.Count > 0 ? required : null
            };

            _inProgress.Remove(type);

            return new SchemaModel { Type = "object", RefName = refName };
        }

        private static bool IsNonNullableReferenceProperty(PropertyInfo prop)
        {

            try
            {
                var ctx = new NullabilityInfoContext();
                var info = ctx.Create(prop);
                return info.ReadState == NullabilityState.NotNull;
            }
            catch
            {
                return false;
            }
        }

        private static Type? GetEnumerableElementType(Type type)
        {
            if (type == typeof(string))
            {
                return null;
            }

            if (type.IsArray)
            {
                return type.GetElementType();
            }

            if (type.IsGenericType)
            {
                var def = type.GetGenericTypeDefinition();
                if (def == typeof(List<>) || def == typeof(IList<>) || def == typeof(ICollection<>) ||
                    def == typeof(IEnumerable<>) || def == typeof(IReadOnlyList<>) || def == typeof(IReadOnlyCollection<>) ||
                    def == typeof(HashSet<>) || def == typeof(Queue<>) || def == typeof(Stack<>))
                {
                    return type.GetGenericArguments()[0];
                }
            }

            foreach (var iface in type.GetInterfaces())
            {
                if (iface.IsGenericType && iface.GetGenericTypeDefinition() == typeof(IEnumerable<>))
                {
                    return iface.GetGenericArguments()[0];
                }
            }

            if (typeof(IEnumerable).IsAssignableFrom(type) && type != typeof(string))
            {
                return typeof(object);
            }

            return null;
        }

        private static bool IsDictionary(Type type, out Type? valueType)
        {
            valueType = null;
            if (!type.IsGenericType)
            {
                return false;
            }

            var def = type.GetGenericTypeDefinition();
            if (def == typeof(Dictionary<,>) || def == typeof(IDictionary<,>) || def == typeof(IReadOnlyDictionary<,>))
            {
                valueType = type.GetGenericArguments()[1];
                return true;
            }
            return false;
        }

        private static string FriendlyTypeName(Type type)
        {
            if (!type.IsGenericType)
            {
                return type.Name;
            }

            var name = type.Name[..type.Name.IndexOf('`')];
            var args = string.Join(",", type.GetGenericArguments().Select(FriendlyTypeName));
            return $"{name}<{args}>";
        }

        private static string ToCamelCase(string name)
        {
            if (string.IsNullOrEmpty(name) || char.IsLower(name[0]))
            {
                return name;
            }

            return char.ToLowerInvariant(name[0]) + name[1..];
        }
    }
}