using Blacklight.Core;
using System;
using System.Collections.Generic;
using System.Reflection;

namespace Glass.Blacklight
{
    /// <summary>
    /// Holds the texture made for each font page, so fonts that name the same page share one.
    /// </summary>
    public sealed class PageTextureCache
    {
        private readonly Dictionary<(Assembly Assembly, string Resource), Texture> textures =
            new Dictionary<(Assembly Assembly, string Resource), Texture>();

        /// <summary>
        /// Gets how many different pages have a texture.
        /// </summary>
        public int Count => textures.Count;

        /// <summary>
        /// Returns the texture for the page <paramref name="resource"/> of <paramref name="assembly"/>, making it with
        /// <paramref name="create"/> the first time it's asked for.
        /// </summary>
        public Texture GetOrCreate(Assembly assembly, string resource, Func<Texture> create)
        {
            if (assembly == null)
            {
                throw new ArgumentNullException(nameof(assembly));
            }

            if (resource == null)
            {
                throw new ArgumentNullException(nameof(resource));
            }

            if (create == null)
            {
                throw new ArgumentNullException(nameof(create));
            }

            if (!textures.TryGetValue((assembly, resource), out Texture returnMe))
            {
                returnMe = create();
                textures.Add((assembly, resource), returnMe);
            }

            return returnMe;
        }
    }
}