Possible approach for incremental schema building

IncrementalJsonSchemaBuilderExtensions.cs

using System.Collections.Generic;
using System.Linq;

namespace Json.Schema
{
	/// <summary>
	/// Provides a fluent interface for <see cref="JsonSchemaBuilder"/>.
	/// </summary>
	public static class IncrementalJsonSchemaBuilderExtensions
	{
		/// <summary>
		/// Add to an existing `allOf` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendAllOf(this JsonSchemaBuilder builder, JsonSchema schema)
		{
			var keyword = builder.Get<AllOfKeyword>();
			var schemas = keyword?.Schemas.ToList() ?? new List<JsonSchema>();
			schemas.Add(schema);
			builder.Add(new AllOfKeyword(schemas));
			return builder;
		}

		/// <summary>
		/// Add to an existing `anyOf` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendAnyOf(this JsonSchemaBuilder builder, JsonSchema schema)
		{
			var keyword = builder.Get<AnyOfKeyword>();
			var schemas = keyword?.Schemas.ToList() ?? new List<JsonSchema>();
			schemas.Add(schema);
			builder.Add(new AnyOfKeyword(schemas));
			return builder;
		}

		/// <summary>
		/// Add a definition to an existing `definitions` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="name">The definition name.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendDefinition(this JsonSchemaBuilder builder, string name, JsonSchema schema)
		{
			var keyword = builder.Get<DefinitionsKeyword>();
			var schemas = keyword?.Definitions.ToDictionary(x => x.Key, x => x.Value) ??
			              new Dictionary<string, JsonSchema>();
			schemas[name] = schema;
			builder.Add(new DefinitionsKeyword(schemas));
			return builder;
		}

		/// <summary>
		/// Add a definition to an existing `$defs` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="name">The definition name.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendDefs(this JsonSchemaBuilder builder, string name, JsonSchema schema)
		{
			var keyword = builder.Get<DefsKeyword>();
			var schemas = keyword?.Definitions.ToDictionary(x => x.Key, x => x.Value) ??
			              new Dictionary<string, JsonSchema>();
			schemas[name] = schema;
			builder.Add(new DefsKeyword(schemas));
			return builder;
		}

		/// <summary>
		/// Add to an existing `oneOf` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendOneOf(this JsonSchemaBuilder builder, JsonSchema schema)
		{
			var keyword = builder.Get<OneOfKeyword>();
			var schemas = keyword?.Schemas.ToList() ?? new List<JsonSchema>();
			schemas.Add(schema);
			builder.Add(new OneOfKeyword(schemas));
			return builder;
		}

		/// <summary>
		/// Add a property to an existing `properties` keyword.
		/// </summary>
		/// <param name="builder">The builder.</param>
		/// <param name="name">The property name.</param>
		/// <param name="schema">The new schema.</param>
		/// <returns>The builder.</returns>
		public static JsonSchemaBuilder AppendProperty(this JsonSchemaBuilder builder, string name, JsonSchema schema)
		{
			var keyword = builder.Get<PropertiesKeyword>();
			var schemas = keyword?.Properties.ToDictionary(x => x.Key, x => x.Value) ??
			              new Dictionary<string, JsonSchema>();
			schemas[name] = schema;
			builder.Add(new PropertiesKeyword(schemas));
			return builder;
		}
	}
}

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