using System;
using System.Collections.Generic;
using Gallium;
using HandlebarsDotNet;
using Nitride.Contents;

namespace Nitride.Handlebars
{
    /// <summary>
    /// An operation that uses the content to create a template that is then
    /// applied against the content and metadata and then replaces the content
    /// of that entity.
    /// </summary>
    public class ApplyContentHandlebarsTemplate<TModel> : NitrideOperationBase
    {
        private readonly HandlebarsTemplateCache cache;

        public ApplyContentHandlebarsTemplate(HandlebarsTemplateCache cache)
        {
            this.cache = cache;
        }

        /// <summary>
        /// Gets or sets the callback used to create a model from a given
        /// entity. This allows for the website to customize what information is
        /// being passed to the template.
        /// </summary>
        public Func<Entity, TModel>? CreateModelCallback { get; set; }

        /// <inheritdoc />
        public override IEnumerable<Entity> Run(IEnumerable<Entity> input)
        {
            this.CheckNotNull(x => x.CreateModelCallback);

            return input
                .ForEachEntity<HasHandlebarsTemplate, ITextContent>(this.Apply);
        }

        /// <summary>
        /// Sets the callback for the template and returns the operation to
        /// chain operations.
        /// </summary>
        /// <param name="callback">The callback to set.</param>
        /// <returns>The ApplyContentHandlebarsTemplate to chain requests.</returns>
        public ApplyContentHandlebarsTemplate<TModel> WithCreateModelCallback(
            Func<Entity, TModel>? callback)
        {
            this.CreateModelCallback = callback;
            return this;
        }

        private Entity Apply(
            Entity entity,
            HasHandlebarsTemplate _,
            ITextContent content)
        {
            // Create the model using the callback.
            TModel model = this.CreateModelCallback!(entity);

            // Create a template from the contents.
            string text = content.GetText();
            HandlebarsTemplate<object, object> template =
                this.cache.GetLiteralTemplate(text);

            // Render the template and create a new entity with the updated
            // text.
            string result = template(model!);

            return entity
                .Remove<HasHandlebarsTemplate>()
                .SetTextContent(new StringTextContent(result));
        }
    }
}