use base64::Engine;
use thiserror::Error;
use std::io;

#[allow(dead_code)]
#[derive(Error, Debug)]
pub enum UriReadError {
    #[error("IOError: '{0}'")]
    IoError(io::Error),

    // From is implemented for this field in each loader module
    #[error("Base64 decoding error: '{0}'")]
    Base64Decode(base64::DecodeError),

    #[error("Some data was missing from the uri")]
    None
}

/// Read a buffer's uri string into a byte buffer.
///
/// * `containing_path`: The path of the containing folder of the buffers "parent",
///     the parent being where this buffer is defined in,
///     i.e. parent="resources/models/player.gltf", containing="resource/models"
pub(crate) fn gltf_read_buffer_uri(containing_path: &str, uri: &str) -> Result<Vec<u8>, UriReadError> {
    if let Some((mime, data)) = uri.strip_prefix("data")
            .and_then(|uri| uri.split_once(',')) {
        let (_mime, is_base64) = match mime.strip_suffix(";base64") {
            Some(mime) => (mime, true),
            None => (mime, false),
        };
    
        if is_base64 {
            base64::engine::general_purpose::STANDARD.decode(data)
                .map_err(UriReadError::Base64Decode)
        } else {
            Ok(data.as_bytes().to_vec())
        }
    } else {
        let full_path = format!("{containing_path}/{uri}");
        std::fs::read(full_path).map_err(UriReadError::IoError)
    }
}