using System;
using System.Collections.Generic;

using FluentValidation;

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 RenderContentTemplate<TModel> : OperationBase
{
    private readonly HandlebarsTemplateCache cache;

    // TODO: This does not use [WithProperties] because the source generator hasn't been taught how to do generics.

    private readonly IValidator<RenderContentTemplate<TModel>> validator;

    public RenderContentTemplate(IValidator<RenderContentTemplate<TModel>> validator, HandlebarsTemplateCache cache)
    {
        this.validator = validator;
        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.validator.ValidateAndThrow(this);

        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 RenderContentTemplate<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));
    }
}