using System.Collections.Generic;

using HandlebarsDotNet;

using Open.Threading;

namespace MfGames.Nitride.Handlebars;

/// <summary>
/// Implements a cache for templates to prevent compiling the same template
/// more than once.
/// </summary>
public class HandlebarsTemplateCache
{
    private readonly IHandlebars handlebars;

    private readonly ModificationSynchronizer locker;

    private readonly Dictionary<string, HandlebarsTemplate<object, object>> templates;

    public HandlebarsTemplateCache(IHandlebars handlebars)
    {
        this.handlebars = handlebars;
        this.locker = new ModificationSynchronizer();
        this.templates = new Dictionary<string, HandlebarsTemplate<object, object>>();
    }

    /// <summary>
    /// Caches the template by name based on the contents of the disk. It
    /// does it once in a multi-threaded manner to ensure it is only cached
    /// once in memory.
    /// </summary>
    /// <param name="literal">The string that contains the template.</param>
    /// <returns></returns>
    public HandlebarsTemplate<object, object> GetLiteralTemplate(string literal)
    {
        // Start with a read lock to see if we've already compiled it.
        this.locker.Modifying(
            () => !this.templates.ContainsKey(literal),
            () =>
            {
                HandlebarsTemplate<object, object> template = this.handlebars!.Compile(literal);

                this.templates[literal] = template;

                return true;
            });

        return this.locker.Reading(() => this.templates[literal]);
    }

    /// <summary>
    /// Caches the template by name based on the contents of the disk. It
    /// does it once in a multi-threaded manner to ensure it is only cached
    /// once in memory.
    /// </summary>
    /// <param name="templateName"></param>
    /// <returns></returns>
    public HandlebarsTemplate<object, object> GetNamedTemplate(string templateName)
    {
        string template = $"{{{{> {templateName}}}}}";

        return this.GetLiteralTemplate(template);
    }
}