var fs = Npm.require('fs');
var path = Npm.require('path');
var _ = Npm.require('underscore');
var sourcemap = Npm.require('source-map');
var LRU = Npm.require('lru-cache');

// The coffee-script compiler overrides Error.prepareStackTrace, mostly for the
// use of coffee.run which we don't use.  This conflicts with the tool's use of
// Error.prepareStackTrace to properly show error messages in linked code.  Save
// the tool's one and restore it after coffee-script clobbers it.
var prepareStackTrace = Error.prepareStackTrace;
var coffee = Npm.require('coffee-script');
Error.prepareStackTrace = prepareStackTrace;

var CACHE_SIZE = process.env.METEOR_COFFEESCRIPT_CACHE_SIZE || 1024*1024*10;
var CACHE_DEBUG = !! process.env.METEOR_TEST_PRINT_CACHE_DEBUG;

var stripExportedVars = function (source, exports) {
  if (!exports || _.isEmpty(exports))
    return source;
  var lines = source.split("\n");

  // We make the following assumptions, based on the output of CoffeeScript
  // 1.7.1.
  //   - The var declaration in question is not indented and is the first such
  //     var declaration.  (CoffeeScript only produces one var line at each
  //     scope and there's only one top-level scope.)  All relevant variables
  //     are actually on this line.
  //   - The user hasn't used a ###-comment containing a line that looks like
  //     a var line, to produce something like
  //        /* bla
  //        var foo;
  //        */
  //     before an actual var line.  (ie, we do NOT attempt to figure out if
  //     we're inside a /**/ comment, which is produced by ### comments.)
  //   - The var in question is not assigned to in the declaration, nor are any
  //     other vars on this line. (CoffeeScript does produce some assignments
  //     but only for internal helpers generated by CoffeeScript, and they end
  //     up on subsequent lines.)
  // XXX relax these assumptions by doing actual JS parsing (eg with jsparse).
  //     I'd do this now, but there's no easy way to "unparse" a jsparse AST.
  //     Or alternatively, hack the compiler to allow us to specify unbound
  //     symbols directly.

  for (var i = 0; i < lines.length; i++) {
    var line = lines[i];
    var match = /^var (.+)([,;])$/.exec(line);
    if (!match)
      continue;

    // If there's an assignment on this line, we assume that there are ONLY
    // assignments and that the var we are looking for is not declared. (Part
    // of our strong assumption about the layout of this code.)
    if (match[1].indexOf('=') !== -1)
      continue;

    // We want to replace the line with something no shorter, so that all
    // records in the source map continue to point at valid
    // characters.
    var replaceLine = function (x) {
      if (x.length >= lines[i].length) {
        lines[i] = x;
      } else {
        lines[i] = x + new Array(1 + (lines[i].length - x.length)).join(' ');
      }
    };

    var vars = match[1].split(', ');
    vars = _.difference(vars, exports);
    if (!_.isEmpty(vars)) {
      replaceLine("var " + vars.join(', ') + match[2]);
    } else {
      // We got rid of all the vars on this line. Drop the whole line if this
      // didn't continue to the next line, otherwise keep just the 'var '.
      if (match[2] === ';')
        replaceLine('');
      else
        replaceLine('var');
    }
    break;
  }

  return lines.join('\n');
};

var addSharedHeader = function (source, sourceMap) {
  var sourceMapJSON = JSON.parse(sourceMap);

  // We want the symbol "share" to be visible to all CoffeeScript files in the
  // package (and shared between them), but not visible to JavaScript
  // files. (That's because we don't want to introduce two competing ways to
  // make package-local variables into JS ("share" vs assigning to non-var
  // variables).) The following hack accomplishes that: "__coffeescriptShare"
  // will be visible at the package level and "share" at the file level.  This
  // should work both in "package" mode where __coffeescriptShare will be added
  // as a var in the package closure, and in "app" mode where it will end up as
  // a global.
  //
  // This ends in a newline to make the source map easier to adjust.
  var header = ("__coffeescriptShare = typeof __coffeescriptShare === 'object' " +
                "? __coffeescriptShare : {}; " +
                "var share = __coffeescriptShare;\n");

  // If the file begins with "use strict", we need to keep that as the first
  // statement.
  source = source.replace(/^(?:((['"])use strict\2;)\n)?/, function (match, useStrict) {
    if (match) {
      // There's a "use strict"; we keep this as the first statement and insert
      // our header at the end of the line that it's on. This doesn't change
      // line numbers or the part of the line that previous may have been
      // annotated, so we don't need to update the source map.
      return useStrict + "  " + header;
    } else {
      // There's no use strict, so we can just add the header at the very
      // beginning. This adds a line to the file, so we update the source map to
      // add a single un-annotated line to the beginning.
      sourceMapJSON.mappings = ";" + sourceMapJSON.mappings;
      return header;
    }
  });
  return {
    source: source,
    sourceMap: JSON.stringify(sourceMapJSON)
  };
};

var CoffeeCompiler = function () {
  var self = this;
  // Maps from a cache key (encoding the source hash, exports, and the other
  // options passed to coffee.compile) to a {source,sourceMap} object (both
  // strings).  Note that this is the result of both coffee.compile and the
  // post-processing that we do.
  self._cache = new LRU({
    max: CACHE_SIZE,
    // Cache is measured in bytes.
    length: function (value) {
      return value.source.length + value.sourceMap.length;
    }
  });
  self._diskCache = null;
  // For testing.
  self._callCount = 0;
};

_.extend(CoffeeCompiler.prototype, {
  processFilesForTarget: function (inputFiles) {
    var self = this;
    var cacheMisses = [];

    inputFiles.forEach(function (inputFile) {
      var source = inputFile.getContentsAsString();
      var outputFilePath = inputFile.getPathInPackage() + ".js";
      var extension = inputFile.getExtension();
      var literate = extension !== 'coffee';

      var options = {
        bare: true,
        filename: inputFile.getPathInPackage(),
        literate: literate,
        // Return a source map.
        sourceMap: true,
        // Include the original source in the source map (sourcesContent field).
        inline: true,
        // This becomes the "file" field of the source map.
        generatedFile: "/" + outputFilePath,
        // This becomes the "sources" field of the source map.
        sourceFiles: [inputFile.getDisplayPath()]
      };

      var cacheKey = JSON.stringify([inputFile.getSourceHash(),
                                     inputFile.getDeclaredExports(),
                                     options]);
      var sourceWithMap = self._cache.get(cacheKey);
      if (! sourceWithMap) {
        cacheMisses.push(inputFile.getDisplayPath());
        try {
          var output = coffee.compile(source, options);
        } catch (e) {
          inputFile.error({
            message: e.message,
            line: e.location && (e.location.first_line + 1),
            column: e.location && (e.location.first_column + 1)
          });

          return;
        }

        var stripped = stripExportedVars(
          output.js,
          _.pluck(inputFile.getDeclaredExports(), 'name'));
        sourceWithMap = addSharedHeader(stripped, output.v3SourceMap);
        self._cache.set(cacheKey, sourceWithMap);
      }

      inputFile.addJavaScript({
        path: outputFilePath,
        sourcePath: inputFile.getPathInPackage(),
        data: sourceWithMap.source,
        sourceMap: sourceWithMap.sourceMap,
        bare: inputFile.getFileOptions().bare
      });
    });

    // Rewrite the cache to disk.
    // XXX BBP we should just write individual entries separately.
    self._writeCache();

    if (CACHE_DEBUG) {
      cacheMisses.sort();
      console.log("Ran coffee.compile (#%s) on: %s",
                  ++self._callCount, JSON.stringify(cacheMisses));
    }
  },
  setDiskCacheDirectory: function (diskCache) {
    var self = this;
    if (self._diskCache)
      throw Error("setDiskCacheDirectory called twice?");
    self._diskCache = diskCache;
    self._readCache();
  },
  // XXX BBP this is an inefficiently designed cache that will cause quadratic
  // behavior due to writing the whole cache on each write, and has no error
  // handling, and uses sync, and has an exists/read race condition, and might
  // not work on Windows
  _cacheFile: function () {
    var self = this;
    return path.join(self._diskCache, 'cache.json');
  },
  _readCache: function () {
    var self = this;
    var cacheFile = self._cacheFile();
    if (! fs.existsSync(cacheFile))
      return;
    var cacheJSON = JSON.parse(fs.readFileSync(cacheFile));
    _.each(cacheJSON, function (value, cacheKey) {
      self._cache.set(cacheKey, value);
    });
    if (CACHE_DEBUG) {
      console.log("Loaded coffeescript cache");
    }
  },
  _writeCache: function () {
    var self = this;
    if (! self._diskCache)
      return;
    var cacheJSON = {};
    self._cache.forEach(function (value, cacheKey) {
      cacheJSON[cacheKey] = value;
    });
    fs.writeFileSync(self._cacheFile(), JSON.stringify(cacheJSON));
  }
});

Plugin.registerCompiler({
  extensions: ['coffee', 'litcoffee', 'coffee.md']
}, function () {
  return new CoffeeCompiler();
});