use anyhow::*;
use glob::glob;
use std::fs::{read_to_string, write, create_dir_all};
use std::path::PathBuf;

struct ShaderData {
    source: String,
    src_path: PathBuf,
    spv_path: PathBuf,
    kind: shaderc::ShaderKind,
}

impl ShaderData {
    // Load data from file
    pub fn load(src_path: PathBuf) -> Result<Self> {

        // Get extension and filename
        let filename = src_path.file_name().unwrap().to_str().unwrap();
        let extension = src_path.extension().context("File has no extension")?.to_str().unwrap();
            
        // Figure out kind from extension
        let kind = match extension {
            "vert" => shaderc::ShaderKind::Vertex,
            "frag" => shaderc::ShaderKind::Fragment,
            "comp" => shaderc::ShaderKind::Compute,
            _ => bail!("Unsupported shader: {}", src_path.display()),
        };

        // Create output path
        let directory = src_path.parent().unwrap().join(".bin");
        create_dir_all(directory.clone()).context("Failed to create output directory")?;
        let spv_path = directory.join(filename).with_extension(format!("{}.spv", extension));
 
        // Read file
        let source = read_to_string(src_path.clone())?;

        // Return struct
        Ok(Self{ source, src_path, spv_path, kind })
    }
}

fn main() -> Result<()> {

    // Collect all shaders recursively within /shaders/
    let mut shader_paths = [
        glob("./src/**/*.vert")?,
        glob("./src/**/*.frag")?,
        glob("./src/**/*.comp")?,
    ];
    let shaders = shader_paths.iter_mut().flatten()
        .map(|glob_result| ShaderData::load(glob_result?))
        .collect::<Vec<Result<_>>>().into_iter()
        .collect::<Result<Vec<_>>>()?;

    // Compile all shaders
    let mut compiler = shaderc::Compiler::new().context("Unable to create shader compiler")?;
    for shader in shaders {
        println!("cargo:rerun-if-changed={}", shader.src_path.as_os_str().to_str().unwrap());
        let compiled = compiler.compile_into_spirv(&shader.source, shader.kind, &shader.src_path.to_str().unwrap(), "main", None, )?;
        write(shader.spv_path, compiled.as_binary_u8())?;
    }

    Ok(())
}