'use strict'

const fs = require('fs')
const glob = require('glob')
const path = require('path')
const LessCache = require('less-cache')

const CONFIG = require('../config')
const LESS_CACHE_VERSION = require('less-cache/package.json').version
const FALLBACK_VARIABLE_IMPORTS = '@import "variables/ui-variables";\n@import "variables/syntax-variables";\n'

module.exports = function () {
  const cacheDirPath = path.join(CONFIG.intermediateAppPath, 'less-compile-cache')
  console.log(`Generating pre-built less cache in ${cacheDirPath}`)

  // Group bundled packages into UI themes, syntax themes, and non-theme packages
  const uiThemes = []
  const syntaxThemes = []
  const nonThemePackages = []
  for (let packageName in CONFIG.appMetadata.packageDependencies) {
    const packageMetadata = require(path.join(CONFIG.intermediateAppPath, 'node_modules', packageName, 'package.json'))
    if (packageMetadata.theme === 'ui') {
      uiThemes.push(packageName)
    } else if (packageMetadata.theme === 'syntax') {
      syntaxThemes.push(packageName)
    } else {
      nonThemePackages.push(packageName)
    }
  }

  // Warm cache for every combination of the default UI and syntax themes,
  // because themes assign variables which may be used in any style sheet.
  for (let uiTheme of uiThemes) {
    for (let syntaxTheme of syntaxThemes) {
      // Build a LessCache instance with import paths based on the current theme combination
      const lessCache = new LessCache({
        cacheDir: cacheDirPath,
        fallbackDir: path.join(CONFIG.atomHomeDirPath, 'compile-cache', 'prebuild-less', LESS_CACHE_VERSION),
        syncCaches: true,
        resourcePath: CONFIG.intermediateAppPath,
        importPaths: [
          path.join(CONFIG.intermediateAppPath, 'node_modules', syntaxTheme, 'styles'),
          path.join(CONFIG.intermediateAppPath, 'node_modules', uiTheme, 'styles'),
          path.join(CONFIG.intermediateAppPath, 'static', 'variables'),
          path.join(CONFIG.intermediateAppPath, 'static'),
        ]
      })

      function cacheCompiledCSS(lessFilePath, importFallbackVariables) {
        let lessSource = fs.readFileSync(lessFilePath, 'utf8')
        if (importFallbackVariables) {
          lessSource = FALLBACK_VARIABLE_IMPORTS + lessSource
        }
        lessCache.cssForFile(lessFilePath, lessSource)
      }

      // Cache all styles in static; don't append variable imports
      for (let lessFilePath of glob.sync(path.join(CONFIG.intermediateAppPath, 'static', '**', '*.less'))) {
        cacheCompiledCSS(lessFilePath, false)
      }

      // Cache styles for all bundled non-theme packages
      for (let nonThemePackage of nonThemePackages) {
        for (let lessFilePath of glob.sync(path.join(CONFIG.intermediateAppPath, 'node_modules', nonThemePackage, '**', '*.less'))) {
          cacheCompiledCSS(lessFilePath, true)
        }
      }

      // Cache styles for this UI theme
      const uiThemeMainPath = path.join(CONFIG.intermediateAppPath, 'node_modules', uiTheme, 'index.less')
      cacheCompiledCSS(uiThemeMainPath, true)

      // Cache styles for this syntax theme
      const syntaxThemeMainPath = path.join(CONFIG.intermediateAppPath, 'node_modules', syntaxTheme, 'index.less')
      cacheCompiledCSS(syntaxThemeMainPath, true)
    }
  }
}