using System;
using System.IO;

namespace AcDream.App.Rendering.Wb {

    /// <summary>
    /// Resolves WB-style shader resource names (e.g. "Shaders.Particle.vert") to
    /// the corresponding file under the acdream binary's Rendering/Shaders directory.
    ///
    /// WB embeds shaders as assembly resources under the Chorizite.OpenGLSDLBackend
    /// namespace. acdream ships shaders as plain files copied to the output directory.
    /// This class adapts between the two conventions so ParticleBatcher and
    /// ParticleEmitterRenderer can call GetEmbeddedResource without modification.
    ///
    /// Mapping rule: "Shaders.Foo.vert" → Rendering/Shaders/wb_foo.vert
    /// (lower-case, wb_ prefix to distinguish WB-origin shaders from acdream's own)
    /// </summary>
    public static class EmbeddedResourceReader {
        public static string GetEmbeddedResource(string filename) {
            // Convert "Shaders.Particle.vert" → "wb_particle.vert"
            // Strip leading "Shaders." then lowercase and prefix with wb_
            string leafName;
            const string shadersPrefix = "Shaders.";
            if (filename.StartsWith(shadersPrefix, StringComparison.Ordinal))
            {
                var rest = filename.Substring(shadersPrefix.Length); // e.g. "Particle.vert"
                leafName = "wb_" + rest.ToLowerInvariant(); // e.g. "wb_particle.vert"
            }
            else
            {
                leafName = "wb_" + filename.ToLowerInvariant();
            }

            var shadersDir = Path.Combine(AppContext.BaseDirectory, "Rendering", "Shaders");
            var fullPath = Path.Combine(shadersDir, leafName);

            if (!File.Exists(fullPath))
                throw new InvalidOperationException(
                    $"WB shader not found: '{fullPath}' (mapped from resource '{filename}'). " +
                    $"Ensure {leafName} is in src/AcDream.App/Rendering/Shaders/ with CopyToOutputDirectory.");

            return File.ReadAllText(fullPath);
        }
    }
}