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

namespace Nitride.Handlebars
{
    /// <summary>
    /// An operation that applies a common or shared template on the content of
    /// a document that includes theme or styling information.
    /// </summary>
    public class ApplyStyleHandlebarsTemplate<TModel> : NitrideOperationBase
    {
        private readonly HandlebarsTemplateCache cache;

        public ApplyStyleHandlebarsTemplate(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; }

        /// <summary>
        /// Gets or sets the callback used to determine which template to use
        /// for a given entity. This lets one have a per-page template change.
        /// </summary>
        public Func<Entity, string>? GetTemplateName { get; set; }

        public IHandlebars? Handlebars { get; set; }

        /// <inheritdoc />
        public override IEnumerable<Entity> Run(IEnumerable<Entity> input)
        {
            // Make sure we have sane data.
            this.CheckNotNull(x => x.CreateModelCallback);
            this.CheckNotNull(x => x.Handlebars);
            this.CheckNotNull(x => x.GetTemplateName);

            // Create and set up the Handlebars.
            return input
                .ForEachEntity<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 ApplyStyleHandlebarsTemplate<TModel> WithCreateModelCallback(
            Func<Entity, TModel>? callback)
        {
            this.CreateModelCallback = callback;
            return this;
        }

        public ApplyStyleHandlebarsTemplate<TModel> WithGetTemplateName(
            Func<Entity, string>? callback)
        {
            this.GetTemplateName = callback;
            return this;
        }

        public ApplyStyleHandlebarsTemplate<TModel> WithHandlebars(
            IHandlebars? handlebars)
        {
            this.Handlebars = handlebars;
            return this;
        }

        private Entity Apply(Entity entity, ITextContent content)
        {
            TModel model = this.CreateModelCallback!(entity);
            string name = this.GetTemplateName!(entity);
            HandlebarsTemplate<object, object> template =
                this.cache.GetNamedTemplate(name);
            string result = template(model!);

            return entity.SetTextContent(result);
        }
    }
}