const fs = require('fs');
const async = require('async');
const svgSprite = require('svg2sprite');
const sprite = svgSprite.collection();

const isSVG = (filename) => filename.split('.').pop() === 'svg';
const iconName = (filename) => filename.split('.')[0];

function saveSpritesheet(path, spritesheet) {
  if(path.indexOf('.svg') === -1) throw 'Error: Please specify a filename ending with .svg';

  fs.writeFile(path, spritesheet, (error) => { if (error) throw error });
}

function readSprite(filename, file) {
  sprite.add(iconName(filename), `<svg>${file}</svg>`);
}

function allSpritesRead(pathBuild) {
  let spritesheet = sprite.compile();

  if (pathBuild) {
    saveSpritesheet(pathBuild, spritesheet);
  }

  return spritesheet;
}

function generate(pathSrc, pathBuild) {
  return new Promise((resolve, reject) => {
    fs.readdir(pathSrc, (error, filenames) => {
      if (error) reject(error);

      async.eachSeries(filenames.filter(isSVG), (filename, cb) => {
        fs.readFile(pathSrc + filename, (error, fileData) => {
          if (error) reject(error);

          readSprite(filename, fileData);
          cb(fileData);
        });
      }, (error) => {
        if (error) reject(error);

        resolve(allSpritesRead(pathBuild));
      });
    });
  });
}

module.exports = generate;