// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace Microsoft.TypeSpec.Generator.Input
{
    internal sealed class InputModelTypeConverter : JsonConverter<InputModelType>
    {
        private const string DynamicModelDecorator = "TypeSpec.HttpClient.CSharp.@dynamicModel";
        private readonly TypeSpecReferenceHandler _referenceHandler;

        public InputModelTypeConverter(TypeSpecReferenceHandler referenceHandler)
        {
            _referenceHandler = referenceHandler;
        }

        public override InputModelType? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
            => reader.ReadReferenceAndResolve<InputModelType>(_referenceHandler.CurrentResolver) ?? CreateModelType(ref reader, null, null, options, _referenceHandler.CurrentResolver);

        public override void Write(Utf8JsonWriter writer, InputModelType value, JsonSerializerOptions options)
            => throw new NotSupportedException("Writing not supported");

        internal static InputModelType CreateModelType(ref Utf8JsonReader reader, string? id, string? name, JsonSerializerOptions options, ReferenceResolver resolver)
        {
            if (id == null)
            {
                reader.TryReadReferenceId(ref id);
            }

            id = id ?? throw new JsonException();

            // create an empty model to resolve circular references
            var model = new InputModelType(
                name: name!,
                @namespace: null!,
                crossLanguageDefinitionId: null!,
                access: null,
                deprecation: null,
                summary: null,
                doc: null,
                usage: InputModelTypeUsage.None,
                properties: [],
                baseModel: null,
                derivedModels: [],
                discriminatorValue: null,
                discriminatorProperty: null,
                discriminatedSubtypes: null!,
                additionalProperties: null,
                modelAsStruct: false,
                serializationOptions: null!,
                isDynamicModel: false);
            resolver.AddReference(id, model);

            string? @namespace = null;
            string? crossLanguageDefinitionId = null;
            string? accessibility = null;
            string? deprecation = null;
            string? summary = null;
            string? doc = null;
            string? usageString = null;
            InputModelProperty? discriminatorProperty = null;
            string? discriminatorValue = null;
            InputType? additionalProperties = null;
            InputModelType? baseModel = null;
            IReadOnlyList<InputModelProperty>? properties = null;
            IReadOnlyDictionary<string, InputModelType>? discriminatedSubtypes = null;
            bool modelAsStruct = false;
            IReadOnlyList<InputDecoratorInfo>? decorators = null;
            InputSerializationOptions? serializationOptions = null;
            InputExternalTypeMetadata? external = null;

            // read all possible properties and throw away the unknown properties
            while (reader.TokenType != JsonTokenType.EndObject)
            {
                var isKnownProperty = reader.TryReadString("name", ref name)
                    || reader.TryReadString("namespace", ref @namespace)
                    || reader.TryReadString("crossLanguageDefinitionId", ref crossLanguageDefinitionId)
                    || reader.TryReadString("access", ref accessibility)
                    || reader.TryReadString("deprecation", ref deprecation)
                    || reader.TryReadString("summary", ref doc)
                    || reader.TryReadString("doc", ref doc)
                    || reader.TryReadString("usage", ref usageString)
                    || reader.TryReadComplexType("discriminatorProperty", options, ref discriminatorProperty)
                    || reader.TryReadString("discriminatorValue", ref discriminatorValue)
                    || reader.TryReadComplexType("additionalProperties", options, ref additionalProperties)
                    || reader.TryReadComplexType("baseModel", options, ref baseModel)
                    || reader.TryReadComplexType("properties", options, ref properties)
                    || reader.TryReadComplexType("discriminatedSubtypes", options, ref discriminatedSubtypes)
                    || reader.TryReadComplexType("decorators", options, ref decorators)
                    || reader.TryReadComplexType("serializationOptions", options, ref serializationOptions)
                    || reader.TryReadComplexType("external", options, ref external)
                    || reader.TryReadBoolean(nameof(InputModelType.ModelAsStruct), ref modelAsStruct); // TODO -- change this to fetch from the decorator list instead when the decorator is ready

                if (!isKnownProperty)
                {
                    reader.SkipProperty();
                }
            }

            model.Name = name ?? throw new JsonException("InputModelType must have name");
            model.Namespace = @namespace ?? string.Empty;
            model.CrossLanguageDefinitionId = crossLanguageDefinitionId ?? string.Empty;
            model.Access = accessibility;
            model.Deprecation = deprecation;
            model.Summary = summary;
            model.Doc = doc;
            var parsedUsage = Enum.TryParse<InputModelTypeUsage>(usageString, ignoreCase: true, out var usage) ? usage : InputModelTypeUsage.None;

            if (!parsedUsage.HasFlag(InputModelTypeUsage.Xml))
            {
                parsedUsage |= InputModelTypeUsage.Json;
            }
            model.Usage = parsedUsage;
            model.DiscriminatorValue = discriminatorValue;
            model.DiscriminatorProperty = discriminatorProperty;
            model.AdditionalProperties = additionalProperties;
            model.BaseModel = baseModel;
            model.SerializationOptions = serializationOptions ?? new();
            if (properties != null)
            {
                model.Properties = properties;
            }
            if (discriminatedSubtypes != null)
            {
                model.DiscriminatedSubtypes = discriminatedSubtypes;
            }
            else if (model.DiscriminatorProperty != null)
            {
                model.DiscriminatedSubtypes = new Dictionary<string, InputModelType>();
            }
            model.ModelAsStruct = modelAsStruct;
            if (decorators != null)
            {
                model.Decorators = decorators;
                if (model.Decorators.Any(d => d.Name.Equals(DynamicModelDecorator)))
                {
                    MarkModelsAsDynamicRecursive(model, []);
                }
            }
            model.External = external;

            // if this model has a base, it means this model is a derived model of the base model, add it into the list.
            if (baseModel != null)
            {
                baseModel.AddDerivedModel(model);
            }

            return model;
        }

        private static void MarkModelsAsDynamicRecursive(InputType inputType, HashSet<InputType> visited)
        {
            if (!visited.Add(inputType))
            {
                return;
            }

            if (inputType is InputModelType modelType)
            {
                modelType.IsDynamicModel = true;

                // Mark all derived/discriminated models as dynamic
                foreach (var derivedModel in modelType.DerivedModels)
                {
                    MarkModelsAsDynamicRecursive(derivedModel, visited);
                }
                foreach (var discriminatedModel in modelType.DiscriminatedSubtypes.Values)
                {
                    MarkModelsAsDynamicRecursive(discriminatedModel, visited);
                }

                // Mark the base discriminated model as dynamic
                var baseModel = modelType.BaseModel;
                if (baseModel?.DiscriminatorProperty != null || baseModel?.DiscriminatorValue != null)
                {
                    MarkModelsAsDynamicRecursive(baseModel, visited);
                }

                foreach (var property in modelType.Properties)
                {
                    switch (property.Type)
                    {
                        case InputModelType propertyType:
                            MarkModelsAsDynamicRecursive(propertyType, visited);
                            break;
                        case InputArrayType arrayType:
                            MarkModelsAsDynamicRecursive(arrayType.ValueType, visited);
                            break;
                        case InputDictionaryType dictionaryType:
                            MarkModelsAsDynamicRecursive(dictionaryType.ValueType, visited);
                            break;
                        case InputNullableType nullableType:
                            MarkModelsAsDynamicRecursive(nullableType.Type, visited);
                            break;
                        case InputUnionType unionType:
                            foreach (var type in unionType.VariantTypes)
                            {
                                MarkModelsAsDynamicRecursive(type, visited);
                            }
                            break;
                    }
                }
            }
            else if (inputType is InputUnionType unionType)
            {
                foreach (var type in unionType.VariantTypes)
                {
                    MarkModelsAsDynamicRecursive(type, visited);
                }
            }
            else if (inputType is InputArrayType arrayType)
            {
                MarkModelsAsDynamicRecursive(arrayType.ValueType, visited);
            }
            else if (inputType is InputDictionaryType dictionaryType)
            {
                MarkModelsAsDynamicRecursive(dictionaryType.ValueType, visited);
            }
        }
    }
}
