'use strict';

const Promise = require('bluebird');

const fs = Promise.promisifyAll(require('fs'));

const path = require('path');

const jsStringEscape = require('js-string-escape');

const difference = require('lodash.difference');

const debug_ = require('debug');

const debug = debug_('purs-loader');

const debugVerbose = debug_('purs-loader:verbose');

const PsModuleMap = require('./purs-module-map');

function updatePsModuleMap(psModule) {
  const options = psModule.options;

  const cache = psModule.cache;

  const filePurs = psModule.srcPath;

  if (!cache.psModuleMap) {
    debugVerbose('module mapping does not exist - making a new module map');

    cache.psModuleMap = PsModuleMap.makeMap(options.src);

    return cache.psModuleMap;
  }
  else {
    debugVerbose('module mapping exists - updating module map for %s', filePurs);

    cache.psModuleMap = cache.psModuleMap.then(psModuleMap =>
      PsModuleMap.makeMapEntry(filePurs).then(result => {
        const map = Object.assign(psModuleMap, result);

        return map;
      })
    );

    return cache.psModuleMap;
  }
}

 // Reference the bundle.
function makeBundleJS(psModule) {
  const bundleOutput = psModule.options.bundleOutput;

  const name = psModule.name;

  const srcDir = psModule.srcDir;

  const escaped = jsStringEscape(path.relative(srcDir, bundleOutput));

  const result = `module.exports = require("${escaped}")["${name}"]`;

  return Promise.resolve(result);
}

// Replace require paths to output files generated by psc with paths
// to purescript sources, which are then also run through this loader.
// Additionally, the imports replaced are tracked so that in the event
// the compiler fails to compile the PureScript source, we can tack on
// any new imports in order to allow webpack to watch the new files
// before they have been successfully compiled.
function makeJS(psModule, psModuleMap, js) {
  const requireRE = /require\(['"]\.\.\/([\w\.]+)(?:\/index\.js)?['"]\)/g;

  const foreignRE = /require\(['"]\.\/foreign(?:\.js)?['"]\)/g;

  const name = psModule.name;

  const imports = psModuleMap[name].imports;

  var replacedImports = [];

  const result = js
    .replace(requireRE, (m, p1) => {
      const moduleValue = psModuleMap[p1];

      if (!moduleValue) {
        debug('module %s was not found in the map, replacing require with null', p1);

        return 'null';
      }
      else {
        const escapedPath = jsStringEscape(moduleValue.src);

        replacedImports.push(p1);

        return `require("${escapedPath}")`;
      }
    })
    .replace(foreignRE, () => {
      const escapedPath = jsStringEscape(psModuleMap[name].ffi);

      return `require("${escapedPath}")`;
    })
  ;

  const additionalImports = difference(imports, replacedImports);

  if (!additionalImports.length) {
    return Promise.resolve(result);
  }
  else {
    debug('rebuilding module map due to additional imports for %s: %o', name, additionalImports);

    psModule.cache.psModuleMap = null;

    return updatePsModuleMap(psModule).then(updatedPsModuleMap => {
      const additionalImportsResult = additionalImports.map(import_ => {
        const moduleValue = updatedPsModuleMap[import_];

        if (!moduleValue) {
          debug('module %s was not found in the map, skipping require', import_);

          return null;
        }
        else {
          const escapedPath = jsStringEscape(moduleValue.src);

          return `var ${import_.replace(/\./g, '_')} = require("${escapedPath}")`;
        }
      }).filter(a => a !== null).join('\n');

      return result + '\n' + additionalImportsResult;
    });
  }
}

module.exports = function toJavaScript(psModule) {
  const options = psModule.options;

  const cache = psModule.cache;

  const bundlePath = path.resolve(options.bundleOutput);

  const jsPath = options.bundle ? bundlePath : psModule.jsPath;

  const js = fs.readFileAsync(jsPath, 'utf8').catch(() => '');

  const psModuleMap = updatePsModuleMap(psModule);

  debugVerbose('loading JavaScript for %s', psModule.name);

  return Promise.props({js: js, psModuleMap: psModuleMap}).then(result =>
    options.bundle ?
      makeBundleJS(psModule) :
      makeJS(psModule, result.psModuleMap, result.js)
  );
};