var fs = Npm.require('fs');
var path = Npm.require('path');
var coffee = Npm.require('coffee-script');
var _ = Npm.require('underscore');

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
  // 1.6.3.
  //   - 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.

  var foundVarLine = false;
  lines = _.map(lines, function (line) {
    if (foundVarLine)
      return line;
    var match = /^var (.+)([,;])$/.exec(line);
    if (!match)
      return line;
    foundVarLine = true;

    // 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)
      return line;

    var vars = match[1].split(', ');
    vars = _.difference(vars, exports);
    if (!_.isEmpty(vars))
      return "var " + vars.join(', ') + match[2];
    // 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 '.
    return match[2] === ';' ? '' : 'var';
  });
  return lines.join('\n');
};

var addSharedHeader = function (source) {
  // 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 in case the first line is a linker @comment, which
  // should be at the beginning of a line.
  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.
  return source.replace(/^(?:(['"])use strict\1;\n)?/, function (match) {
    return match + header;
  });
};

var handler = function (compileStep) {
  var source = compileStep.read().toString('utf8');
  var options = {
    bare: true,
    filename: compileStep.inputPath,
    literate: path.extname(compileStep.inputPath) === '.litcoffee'
  };

  try {
    var output = coffee.compile(source, options);
  } catch (e) {
    // XXX better error handling, once the Plugin interface support it
    throw new Error(
      compileStep.inputPath + ':' +
      (e.location ? (e.location.first_line + ': ') : ' ') +
      e.message
    );
  }

  compileStep.addJavaScript({
    path: compileStep.inputPath + ".js",
    sourcePath: compileStep.inputPath,
    data: output,
    lineForLine: false,
    linkerUnitTransform: function (source, exports) {
      return addSharedHeader(stripExportedVars(source, exports));
    }
  });
};

Plugin.registerSourceHandler("coffee", handler);
Plugin.registerSourceHandler("litcoffee", handler);