//! # Material Module — Appearance Descriptor (shader_id → RenderPipeline)
//!
//! Defines `Material`, a lightweight appearance descriptor that pairs a shader identifier with
//! a shared RenderPipeline. Materials are created via PipelineCache to ensure pipeline reuse—
//! multiple materials referencing the same shader_id point to the identical compiled GPU pipeline.
//!
//! ## Architecture Notes (per ARCHI_APP.md)
//! - **Identifiants**: Each Material is registered in Scene by string identifier, enabling dynamic access
//!   during the render loop without borrow checker issues. The shader_id serves as the Handle<T> key.
//! - **Phase de Déclaration**: Materials are instantiated once in the declarative phase before the render loop begins.

use crate::pipeline::PipelineCache;
use std::sync::Arc;

/// Lightweight appearance descriptor: links a shader ID to a shared RenderPipeline.
/// Does not own the pipeline; holds an Arc for zero-copy sharing across objects using the same shader.
pub struct Material {
    /// Unique shader identifier used to look up or create a compiled RenderPipeline in PipelineCache.
    pub shader_id: String,
    /// Shared reference to the compiled GPU render pipeline. Multiple Materials can share one through Arc cloning.
    pub pipeline: Arc<wgpu::RenderPipeline>,
}

impl Material {
    /// Creates a new Material by requesting the cache to provide (or create) its RenderPipeline.
    /// Inputs: format (surface texture format required for fragment output), shader_id (unique key into PipelineCache),
    ///         cache (mutable reference for potential insertion of new pipelines).
    /// Returns a Material holding the Arc-wrapped pipeline. Called at scene initialization time only.
    pub fn new(format: wgpu::TextureFormat, shader_id: &str, cache: &mut PipelineCache) -> Self {
        // Request pipeline from cache — returns cached instance if already exists, creates new otherwise
        let pipeline = cache.get_or_create(format, shader_id);
        Self {
            shader_id: shader_id.to_string(),
            pipeline,
        }
    }
}