//! A build module of the application which minifies the project's css and js files on build which
//! helps reduce the initial page by loading the files faster.

#![forbid(unsafe_code, clippy::panic)]
#![deny(missing_docs, clippy::missing_docs_in_private_items, clippy::perf)]
#![warn(clippy::cognitive_complexity, rust_2018_idioms)]

// ------- Imports -------
use lightningcss::stylesheet::{MinifyOptions, ParserOptions, PrinterOptions, StyleSheet};
use minify_js::{minify, Session, TopLevelMode};
use std::{
    fs::{read_dir, read_to_string, File, OpenOptions},
    io::{Read, Write},
};

// ------- Constants -------
const COMMON_STATIC_SOURCE_CODE_FOLDER: &str = "./public/static/";
const STYLE_FOLDERS: [&str; 2] = ["themes", "colorschemes"];
const PACKAGE_ENVIRONMENT_VARIABLE: &str = "PKG_ENV";
const PRODUCTION_PKG_ENV_VARIABLE_VALUE: &str = "prod";

/// A main function which minifies both css and js files using `lightningcss` and `minify_js` when
/// the `PKG_ENV` environment and it is set to the value of `prod`.
///
/// # Error
///
/// This function returns the unit type when the minification process runs successfully otherwise
/// it returns a standard error.
fn main() -> Result<(), Box<dyn std::error::Error>> {
    if let Ok(pkg_env_var) = std::env::var(PACKAGE_ENVIRONMENT_VARIABLE) {
        if pkg_env_var.to_lowercase() == PRODUCTION_PKG_ENV_VARIABLE_VALUE {
            // A for loop that loops over each file name containing in the `colorschemes` and `themes` folders
            // and minifies it using the `lightningcss` minifier.
            for folder_name in STYLE_FOLDERS {
                for file in read_dir(format!("{COMMON_STATIC_SOURCE_CODE_FOLDER}{folder_name}/"))? {
                    let file_path = file?.path();
                    let source = read_to_string(file_path.clone())?;

                    let mut stylesheet = StyleSheet::parse(&source, ParserOptions::default())
                        .map_err(|err| format!("{err}\n{:?}", file_path.file_name().unwrap()))?;

                    stylesheet.minify(MinifyOptions::default())?;
                    let minified_css = stylesheet.to_css(PrinterOptions::default())?;

                    let mut old_css_file = OpenOptions::new()
                        .write(true)
                        .truncate(true)
                        .open(file_path)?;
                    old_css_file.write_all(minified_css.code.as_bytes())?;
                    old_css_file.flush()?;
                }
            }

            // A for loop that loops over each file name containing in the `public/static` folder and minifies
            // it using the `minify-js` minifier.
            for file in read_dir(COMMON_STATIC_SOURCE_CODE_FOLDER)? {
                let file_path = file?.path();
                if file_path.is_file() {
                    let mut code = Vec::new();
                    let mut js_file = File::open(file_path.clone())?;
                    js_file.read_to_end(&mut code)?;

                    drop(js_file);

                    let mut out = Vec::new();
                    minify(&Session::new(), TopLevelMode::Global, &code, &mut out)
                        .map_err(|err| format!("{err}\n{:?}", file_path.file_name().unwrap()))?;

                    let mut old_js_file = OpenOptions::new()
                        .write(true)
                        .truncate(true)
                        .open(file_path)?;
                    old_js_file.write_all(&out)?;
                    old_js_file.flush()?;
                }
            }
        }
    }
    Ok(())
}