// ==========================================================================
//  Squidex Headless CMS
// ==========================================================================
//  Copyright (c) Squidex UG (haftungsbeschraenkt)
//  All rights reserved. Licensed under the MIT license.
// ==========================================================================

using Squidex.Domain.Apps.Core.Contents;
using Squidex.Domain.Apps.Core.Schemas;
using Squidex.Infrastructure;
using Squidex.Infrastructure.Json.Objects;

#pragma warning disable RECS0033 // Convert 'if' to '||' expression

namespace Squidex.Domain.Apps.Core.ConvertContent
{
    public sealed class ContentConverter
    {
        private readonly List<IContentItemConverter> itemConverters = new List<IContentItemConverter>();
        private readonly List<IContentFieldAfterConverter> fieldAfterConverters = new List<IContentFieldAfterConverter>();
        private readonly List<IContentFieldConverter> fieldConverters = new List<IContentFieldConverter>();
        private readonly List<IContentValueConverter> valueConverters = new List<IContentValueConverter>();
        private readonly ResolvedComponents components;
        private readonly Schema schema;

        public ContentConverter(ResolvedComponents components, Schema schema)
        {
            this.components = components;
            this.schema = schema;
        }

        public ContentConverter Add(IConverter converter)
        {
            if (converter is IContentItemConverter itemConverter)
            {
                itemConverters.Add(itemConverter);
            }

            if (converter is IContentFieldConverter fieldConverter)
            {
                fieldConverters.Add(fieldConverter);
            }

            if (converter is IContentFieldAfterConverter fieldAfterConverter)
            {
                fieldAfterConverters.Add(fieldAfterConverter);
            }

            if (converter is IContentValueConverter valueConverter)
            {
                valueConverters.Add(valueConverter);
            }

            return this;
        }

        public ContentData Convert(ContentData content)
        {
            Guard.NotNull(schema);

            // The conversion process assumes that we have ownership of the data and can manipulate it.
            // Clones are only created to save allocations.
            var result = new ContentData(content.Count);

            foreach (var (fieldName, fieldData) in content)
            {
                if (fieldData == null || !schema.FieldsByName.TryGetValue(fieldName, out var field))
                {
                    continue;
                }

                // Some conversions are faster to do upfront, e.g. to remove hidden fields.
                var newData = ConvertField(field, fieldData);

                if (newData == null)
                {
                    continue;
                }

                newData = ConvertValues(field, newData);

                // Some conversions are faster to do later, e.g. fallback handling for languages.
                newData = ConvertFieldAfter(field, newData);

                if (newData != null)
                {
                    result.Add(field.Name, newData);
                }
            }

            return result;
        }

        private ContentFieldData? ConvertField(IRootField field, ContentFieldData? data)
        {
            foreach (var converter in fieldConverters)
            {
                data = converter.ConvertField(field, data!);

                if (data == null)
                {
                    break;
                }
            }

            return data;
        }

        private ContentFieldData? ConvertFieldAfter(IRootField field, ContentFieldData? data)
        {
            foreach (var converter in fieldAfterConverters)
            {
                data = converter.ConvertFieldAfter(field, data!);

                if (data == null)
                {
                    break;
                }
            }

            return data;
        }

        private (bool Remove, JsonValue) ConvertByType<T>(T field, JsonValue value, IField? parent) where T : IField
        {
            switch (field)
            {
                case IArrayField arrayField:
                    return ConvertArray(arrayField, value);

                case IField<ComponentFieldProperties>:
                    return ConvertComponent(value, field);

                case IField<ComponentsFieldProperties>:
                    return ConvertComponents(value, field);

                default:
                    return ConvertValue(field, value, parent);
            }
        }

        private (bool Remove, JsonValue) ConvertArray(IArrayField field, JsonValue value)
        {
            if (value.Value is not JsonArray array)
            {
                return (true, default);
            }

            for (int i = 0; i < array.Count; i++)
            {
                var oldValue = array[i];

                var (removed, newValue) = ConvertArrayItem(field, oldValue);

                if (removed)
                {
                    array.RemoveAt(i);
                    i--;
                }
                else if (!ReferenceEquals(newValue.Value, oldValue.Value))
                {
                    array[i] = newValue;
                }
            }

            return (false, array);
        }

        private (bool Remove, JsonValue) ConvertComponents(JsonValue value, IField parent)
        {
            if (value.Value is not JsonArray array)
            {
                return (true, default);
            }

            for (int i = 0; i < array.Count; i++)
            {
                var oldValue = array[i];

                var (removed, newValue) = ConvertComponent(oldValue, parent);

                if (removed)
                {
                    array.RemoveAt(i);
                    i--;
                }
                else if (!ReferenceEquals(newValue.Value, oldValue.Value))
                {
                    // Faster to check for reference equality than for deep equals.
                    array[i] = newValue;
                }
            }

            return (false, array);
        }

        private (bool Remove, JsonValue) ConvertComponent(JsonValue value, IField parent)
        {
            if (value.Value is not JsonObject obj || !obj.TryGetValue(Component.Discriminator, out var discriminator))
            {
                return (true, default);
            }

            if (!components.TryGetValue(DomainId.Create(discriminator.ToString()), out var component))
            {
                return (true, default);
            }

            return (false, ConvertNested(component.FieldCollection, obj, parent));
        }

        private (bool Remove, JsonValue) ConvertArrayItem(IArrayField field, JsonValue value)
        {
            if (value.Value is not JsonObject obj)
            {
                return (true, default);
            }

            return (false, ConvertNested(field.FieldCollection, obj, field));
        }

        private ContentFieldData ConvertValues(IField field, ContentFieldData source)
        {
            ContentFieldData? result = null;

            foreach (var (key, oldValue) in source)
            {
                var (removed, newData) = ConvertByType(field, oldValue, null);

                // Create a copy to avoid allocations if nothing has been changed.
                if (removed)
                {
                    result ??= new ContentFieldData(source);
                    result.Remove(key);
                }
                else if (!ReferenceEquals(newData.Value, oldValue.Value))
                {
                    // Faster to check for reference equality than for deep equals.
                    result ??= new ContentFieldData(source);
                    result[key] = newData;
                }
            }

            return result ?? source;
        }

        private JsonValue ConvertNested<T>(FieldCollection<T> fields, JsonObject source, IField parent) where T : IField
        {
            JsonObject? result = null;

            foreach (var (key, oldValue) in source)
            {
                var newValue = oldValue;

                var remove = false;

                if (fields.ByName.TryGetValue(key, out var field))
                {
                    (remove, newValue) = ConvertByType(field, oldValue, parent);
                }
                else if (key != Component.Discriminator)
                {
                    remove = true;
                }

                // Create a copy to avoid allocations if nothing has been changed.
                if (remove)
                {
                    result ??= new JsonObject(source);
                    result.Remove(key);
                }
                else if (!ReferenceEquals(newValue.Value, oldValue.Value))
                {
                    // Faster to check for reference equality than for deep equals.
                    result ??= new JsonObject(source);
                    result[key] = newValue;
                }
            }

            result ??= source;

            foreach (var converter in itemConverters)
            {
                result = converter.ConvertItem(parent, result);
            }

            return result ?? source;
        }

        private (bool Remove, JsonValue) ConvertValue(IField field, JsonValue value, IField? parent)
        {
            foreach (var converter in valueConverters)
            {
                // Use a tuple and not a nullable result to avoid boxing and allocations.
                (var remove, value) = converter.ConvertValue(field, value, parent);

                if (remove)
                {
                    return (true, default);
                }
            }

            return (false, value);
        }
    }
}