// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of js;

class Printer implements NodeVisitor {
  final bool shouldCompressOutput;
  leg.Compiler compiler;
  leg.CodeBuffer outBuffer;
  int indentLevel = 0;
  bool inForInit = false;
  bool atStatementBegin = false;
  final DanglingElseVisitor danglingElseVisitor;
  final LocalNamer localNamer;
  bool pendingSemicolon = false;
  bool pendingSpace = false;
  static final identifierCharacterRegExp = new RegExp(r'^[a-zA-Z_0-9$]');
  static final expressionContinuationRegExp = new RegExp(r'^[-+([]');

  Printer(leg.Compiler compiler, { allowVariableMinification: true })
      : shouldCompressOutput = compiler.enableMinification,
        this.compiler = compiler,
        outBuffer = new leg.CodeBuffer(),
        danglingElseVisitor = new DanglingElseVisitor(compiler),
        localNamer = determineRenamer(compiler.enableMinification,
                                      allowVariableMinification);

  static LocalNamer determineRenamer(bool shouldCompressOutput,
                                     bool allowVariableMinification) {
    return (shouldCompressOutput && allowVariableMinification)
        ? new MinifyRenamer() : new IdentityNamer();
  }

  /// Always emit a newline, even under `enableMinification`.
  void forceLine() {
    out("\n");
  }
  /// Emits a newline for readability.
  void lineOut() {
    if (!shouldCompressOutput) forceLine();
  }
  void spaceOut() {
    if (!shouldCompressOutput) out(" ");
  }

  String lastAddedString = null;
  int get lastCharCode {
    if (lastAddedString == null) return 0;
    assert(lastAddedString.length != "");
    return lastAddedString.codeUnitAt(lastAddedString.length - 1);
  }

  void out(String str) {
    if (str != "") {
      if (pendingSemicolon) {
        if (!shouldCompressOutput) {
          outBuffer.add(";");
        } else if (str != "}") {
          // We want to output newline instead of semicolon because it makes
          // the raw stack traces much easier to read and it also makes line-
          // based tools like diff work much better.  JavaScript will
          // automatically insert the semicolon at the newline if it means a
          // parsing error is avoided, so we can only do this trick if the
          // next line is not something that can be glued onto a valid
          // expression to make a new valid expression.
          if (expressionContinuationRegExp.hasMatch(str)) {
            outBuffer.add(";");
          } else {
            outBuffer.add("\n");
          }
        }
      }
      if (pendingSpace &&
          (!shouldCompressOutput || identifierCharacterRegExp.hasMatch(str))) {
        outBuffer.add(" ");
      }
      pendingSpace = false;
      pendingSemicolon = false;
      outBuffer.add(str);
      lastAddedString = str;
    }
  }

  void outLn(String str) {
    out(str);
    lineOut();
  }

  void outSemicolonLn() {
    if (shouldCompressOutput) {
      pendingSemicolon = true;
    } else {
      out(";");
      forceLine();
    }
  }

  void outIndent(String str) { indent(); out(str); }
  void outIndentLn(String str) { indent(); outLn(str); }
  void indent() {
    if (!shouldCompressOutput) {
      for (int i = 0; i < indentLevel; i++) out("  ");
    }
  }

  void beginSourceRange(Node node) {
    if (node.sourcePosition != null) {
      outBuffer.beginMappedRange();
      outBuffer.setSourceLocation(node.sourcePosition);
    }
  }

  void endSourceRange(Node node) {
    if (node.endSourcePosition != null) {
      outBuffer.setSourceLocation(node.endSourcePosition);
    }
    if (node.sourcePosition != null) {
      outBuffer.endMappedRange();
    }
  }

  visit(Node node) {
    beginSourceRange(node);
    node.accept(this);
    endSourceRange(node);
  }

  visitCommaSeparated(List<Node> nodes, int hasRequiredType,
                      {bool newInForInit, bool newAtStatementBegin}) {
    for (int i = 0; i < nodes.length; i++) {
      if (i != 0) {
        atStatementBegin = false;
        out(",");
        spaceOut();
      }
      visitNestedExpression(nodes[i], hasRequiredType,
                            newInForInit: newInForInit,
                            newAtStatementBegin: newAtStatementBegin);
    }
  }

  visitAll(List<Node> nodes) {
    nodes.forEach(visit);
  }

  visitProgram(Program program) {
    visitAll(program.body);
  }

  visitBlob(Blob node) {
    outBuffer.addBuffer(node.buffer);
  }

  bool blockBody(Node body, {bool needsSeparation, bool needsNewline}) {
    if (body is Block) {
      spaceOut();
      blockOut(body, false, needsNewline);
      return true;
    }
    if (shouldCompressOutput && needsSeparation) {
      // If [shouldCompressOutput] is false, then the 'lineOut' will insert
      // the separation.
      out(" ");
    } else {
      lineOut();
    }
    indentLevel++;
    visit(body);
    indentLevel--;
    return false;
  }

  void blockOutWithoutBraces(Node node) {
    if (node is Block) {
      beginSourceRange(node);
      Block block = node;
      block.statements.forEach(blockOutWithoutBraces);
      endSourceRange(node);
    } else {
      visit(node);
    }
  }

  void blockOut(Block node, bool shouldIndent, bool needsNewline) {
    if (shouldIndent) indent();
    beginSourceRange(node);
    out("{");
    lineOut();
    indentLevel++;
    node.statements.forEach(blockOutWithoutBraces);
    indentLevel--;
    indent();
    out("}");
    endSourceRange(node);
    if (needsNewline) lineOut();
  }

  visitBlock(Block block) {
    blockOut(block, true, true);
  }

  visitExpressionStatement(ExpressionStatement expressionStatement) {
    indent();
    visitNestedExpression(expressionStatement.expression, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: true);
    outSemicolonLn();
  }

  visitEmptyStatement(EmptyStatement nop) {
    outIndentLn(";");
  }

  void ifOut(If node, bool shouldIndent) {
    Node then = node.then;
    Node elsePart = node.otherwise;
    bool hasElse = node.hasElse;

    // Handle dangling elses.
    if (hasElse) {
      bool needsBraces = node.then.accept(danglingElseVisitor);
      if (needsBraces) {
        then = new Block(<Statement>[then]);
      }
    }
    if (shouldIndent) indent();
    out("if");
    spaceOut();
    out("(");
    visitNestedExpression(node.condition, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    bool thenWasBlock =
        blockBody(then, needsSeparation: false, needsNewline: !hasElse);
    if (hasElse) {
      if (thenWasBlock) {
        spaceOut();
      } else {
        indent();
      }
      out("else");
      if (elsePart is If) {
        pendingSpace = true;
        ifOut(elsePart, false);
      } else {
        blockBody(elsePart, needsSeparation: true, needsNewline: true);
      }
    }
  }

  visitIf(If node) {
    ifOut(node, true);
  }

  visitFor(For loop) {
    outIndent("for");
    spaceOut();
    out("(");
    if (loop.init != null) {
      visitNestedExpression(loop.init, EXPRESSION,
                            newInForInit: true, newAtStatementBegin: false);
    }
    out(";");
    if (loop.condition != null) {
      spaceOut();
      visitNestedExpression(loop.condition, EXPRESSION,
                            newInForInit: false, newAtStatementBegin: false);
    }
    out(";");
    if (loop.update != null) {
      spaceOut();
      visitNestedExpression(loop.update, EXPRESSION,
                            newInForInit: false, newAtStatementBegin: false);
    }
    out(")");
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  visitForIn(ForIn loop) {
    outIndent("for");
    spaceOut();
    out("(");
    visitNestedExpression(loop.leftHandSide, EXPRESSION,
                          newInForInit: true, newAtStatementBegin: false);
    out(" in");
    pendingSpace = true;
    visitNestedExpression(loop.object, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  visitWhile(While loop) {
    outIndent("while");
    spaceOut();
    out("(");
    visitNestedExpression(loop.condition, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  visitDo(Do loop) {
    outIndent("do");
    if (blockBody(loop.body, needsSeparation: true, needsNewline: false)) {
      spaceOut();
    } else {
      indent();
    }
    out("while");
    spaceOut();
    out("(");
    visitNestedExpression(loop.condition, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    outSemicolonLn();
  }

  visitContinue(Continue node) {
    if (node.targetLabel == null) {
      outIndent("continue");
    } else {
      outIndent("continue ${node.targetLabel}");
    }
    outSemicolonLn();
  }

  visitBreak(Break node) {
    if (node.targetLabel == null) {
      outIndent("break");
    } else {
      outIndent("break ${node.targetLabel}");
    }
    outSemicolonLn();
  }

  visitReturn(Return node) {
    if (node.value == null) {
      outIndent("return");
    } else {
      outIndent("return");
      pendingSpace = true;
      visitNestedExpression(node.value, EXPRESSION,
                            newInForInit: false, newAtStatementBegin: false);
    }
    outSemicolonLn();
  }

  visitThrow(Throw node) {
    outIndent("throw");
    pendingSpace = true;
    visitNestedExpression(node.expression, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    outSemicolonLn();
  }

  visitTry(Try node) {
    outIndent("try");
    blockBody(node.body, needsSeparation: true, needsNewline: false);
    if (node.catchPart != null) {
      visit(node.catchPart);
    }
    if (node.finallyPart != null) {
      spaceOut();
      out("finally");
      blockBody(node.finallyPart, needsSeparation: true, needsNewline: true);
    } else {
      lineOut();
    }
  }

  visitCatch(Catch node) {
    spaceOut();
    out("catch");
    spaceOut();
    out("(");
    visitNestedExpression(node.declaration, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    blockBody(node.body, needsSeparation: false, needsNewline: true);
  }

  visitSwitch(Switch node) {
    outIndent("switch");
    spaceOut();
    out("(");
    visitNestedExpression(node.key, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out(")");
    spaceOut();
    outLn("{");
    indentLevel++;
    visitAll(node.cases);
    indentLevel--;
    outIndentLn("}");
  }

  visitCase(Case node) {
    outIndent("case");
    pendingSpace = true;
    visitNestedExpression(node.expression, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    outLn(":");
    if (!node.body.statements.isEmpty) {
      indentLevel++;
      blockOutWithoutBraces(node.body);
      indentLevel--;
    }
  }

  visitDefault(Default node) {
    outIndentLn("default:");
    if (!node.body.statements.isEmpty) {
      indentLevel++;
      blockOutWithoutBraces(node.body);
      indentLevel--;
    }
  }

  visitLabeledStatement(LabeledStatement node) {
    outIndent("${node.label}:");
    blockBody(node.body, needsSeparation: false, needsNewline: true);
  }

  void functionOut(Fun fun, Node name, VarCollector vars) {
    out("function");
    if (name != null) {
      out(" ");
      // Name must be a [Decl]. Therefore only test for primary expressions.
      visitNestedExpression(name, PRIMARY,
                            newInForInit: false, newAtStatementBegin: false);
    }
    localNamer.enterScope(vars);
    out("(");
    if (fun.params != null) {
      visitCommaSeparated(fun.params, PRIMARY,
                          newInForInit: false, newAtStatementBegin: false);
    }
    out(")");
    blockBody(fun.body, needsSeparation: false, needsNewline: false);
    localNamer.leaveScope();
  }

  visitFunctionDeclaration(FunctionDeclaration declaration) {
    VarCollector vars = new VarCollector();
    vars.visitFunctionDeclaration(declaration);
    indent();
    functionOut(declaration.function, declaration.name, vars);
    lineOut();
  }

  visitNestedExpression(Expression node, int requiredPrecedence,
                        {bool newInForInit, bool newAtStatementBegin}) {
    bool needsParentheses =
        // a - (b + c).
        (requiredPrecedence != EXPRESSION &&
         node.precedenceLevel < requiredPrecedence) ||
        // for (a = (x in o); ... ; ... ) { ... }
        (newInForInit && node is Binary && (node as Binary).op == "in") ||
        // (function() { ... })().
        // ({a: 2, b: 3}.toString()).
        (newAtStatementBegin && (node is NamedFunction ||
                                 node is Fun ||
                                 node is ObjectInitializer));
    if (needsParentheses) {
      inForInit = false;
      atStatementBegin = false;
      out("(");
      visit(node);
      out(")");
    } else {
      inForInit = newInForInit;
      atStatementBegin = newAtStatementBegin;
      visit(node);
    }
  }

  visitVariableDeclarationList(VariableDeclarationList list) {
    out("var ");
    visitCommaSeparated(list.declarations, ASSIGNMENT,
                        newInForInit: inForInit, newAtStatementBegin: false);
  }

  visitSequence(Sequence sequence) {
    // Note that we only require that the entries are expressions and not
    // assignments. This means that nested sequences are not put into
    // parenthesis.
    visitCommaSeparated(sequence.expressions, EXPRESSION,
                        newInForInit: false,
                        newAtStatementBegin: atStatementBegin);
  }

  visitAssignment(Assignment assignment) {
    visitNestedExpression(assignment.leftHandSide, LEFT_HAND_SIDE,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);
    if (assignment.value != null) {
      spaceOut();
      String op = assignment.op;
      if (op != null) out(op);
      out("=");
      spaceOut();
      visitNestedExpression(assignment.value, ASSIGNMENT,
                            newInForInit: inForInit,
                            newAtStatementBegin: false);
    }
  }

  visitVariableInitialization(VariableInitialization initialization) {
    visitAssignment(initialization);
  }

  visitConditional(Conditional cond) {
    visitNestedExpression(cond.condition, LOGICAL_OR,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);
    spaceOut();
    out("?");
    spaceOut();
    // The then part is allowed to have an 'in'.
    visitNestedExpression(cond.then, ASSIGNMENT,
                          newInForInit: false, newAtStatementBegin: false);
    spaceOut();
    out(":");
    spaceOut();
    visitNestedExpression(cond.otherwise, ASSIGNMENT,
                          newInForInit: inForInit, newAtStatementBegin: false);
  }

  visitNew(New node) {
    out("new ");
    visitNestedExpression(node.target, CALL,
                          newInForInit: inForInit, newAtStatementBegin: false);
    out("(");
    visitCommaSeparated(node.arguments, ASSIGNMENT,
                        newInForInit: false, newAtStatementBegin: false);
    out(")");
  }

  visitCall(Call call) {
    visitNestedExpression(call.target, LEFT_HAND_SIDE,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);
    out("(");
    visitCommaSeparated(call.arguments, ASSIGNMENT,
                        newInForInit: false, newAtStatementBegin: false);
    out(")");
  }

  visitBinary(Binary binary) {
    Expression left = binary.left;
    Expression right = binary.right;
    String op = binary.op;
    int leftPrecedenceRequirement;
    int rightPrecedenceRequirement;
    switch (op) {
      case "||":
        leftPrecedenceRequirement = LOGICAL_OR;
        // x || (y || z) <=> (x || y) || z.
        rightPrecedenceRequirement = LOGICAL_OR;
        break;
      case "&&":
        leftPrecedenceRequirement = LOGICAL_AND;
        // x && (y && z) <=> (x && y) && z.
        rightPrecedenceRequirement = LOGICAL_AND;
        break;
      case "|":
        leftPrecedenceRequirement = BIT_OR;
        // x | (y | z) <=> (x | y) | z.
        rightPrecedenceRequirement = BIT_OR;
        break;
      case "^":
        leftPrecedenceRequirement = BIT_XOR;
        // x ^ (y ^ z) <=> (x ^ y) ^ z.
        rightPrecedenceRequirement = BIT_XOR;
        break;
      case "&":
        leftPrecedenceRequirement = BIT_AND;
        // x & (y & z) <=> (x & y) & z.
        rightPrecedenceRequirement = BIT_AND;
        break;
      case "==":
      case "!=":
      case "===":
      case "!==":
        leftPrecedenceRequirement = EQUALITY;
        rightPrecedenceRequirement = RELATIONAL;
        break;
      case "<":
      case ">":
      case "<=":
      case ">=":
      case "instanceof":
      case "in":
        leftPrecedenceRequirement = RELATIONAL;
        rightPrecedenceRequirement = SHIFT;
        break;
      case ">>":
      case "<<":
      case ">>>":
        leftPrecedenceRequirement = SHIFT;
        rightPrecedenceRequirement = ADDITIVE;
        break;
      case "+":
      case "-":
        leftPrecedenceRequirement = ADDITIVE;
        // We cannot remove parenthesis for "+" because
        //   x + (y + z) <!=> (x + y) + z:
        // Example:
        //   "a" + (1 + 2) => "a3";
        //   ("a" + 1) + 2 => "a12";
        rightPrecedenceRequirement = MULTIPLICATIVE;
        break;
      case "*":
      case "/":
      case "%":
        leftPrecedenceRequirement = MULTIPLICATIVE;
        // We cannot remove parenthesis for "*" because of precision issues.
        rightPrecedenceRequirement = UNARY;
        break;
      default:
        compiler.internalError("Forgot operator: $op");
    }

    visitNestedExpression(left, leftPrecedenceRequirement,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);

    if (op == "in" || op == "instanceof") {
      // There are cases where the space is not required but without further
      // analysis we cannot know.
      out(" ");
      out(op);
      out(" ");
    } else {
      spaceOut();
      out(op);
      spaceOut();
    }
    visitNestedExpression(right, rightPrecedenceRequirement,
                          newInForInit: inForInit,
                          newAtStatementBegin: false);
  }

  visitPrefix(Prefix unary) {
    String op = unary.op;
    switch (op) {
      case "delete":
      case "void":
      case "typeof":
        // There are cases where the space is not required but without further
        // analysis we cannot know.
        out(op);
        out(" ");
        break;
      case "+":
      case "++":
        if (lastCharCode == charCodes.$PLUS) out(" ");
        out(op);
        break;
      case "-":
      case "--":
        if (lastCharCode == charCodes.$MINUS) out(" ");
        out(op);
        break;
      default:
        out(op);
    }
    visitNestedExpression(unary.argument, UNARY,
                          newInForInit: inForInit, newAtStatementBegin: false);
  }

  visitPostfix(Postfix postfix) {
    visitNestedExpression(postfix.argument, LEFT_HAND_SIDE,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);
    out(postfix.op);
  }

  visitVariableUse(VariableUse ref) {
    out(localNamer.getName(ref.name));
  }

  visitThis(This node) {
    out("this");
  }

  visitVariableDeclaration(VariableDeclaration decl) {
    out(localNamer.getName(decl.name));
  }

  visitParameter(Parameter param) {
    out(localNamer.getName(param.name));
  }

  bool isDigit(int charCode) {
    return charCodes.$0 <= charCode && charCode <= charCodes.$9;
  }

  bool isValidJavaScriptId(String field) {
    if (field.length < 3) return false;
    // Ignore the leading and trailing string-delimiter.
    for (int i = 1; i < field.length - 1; i++) {
      // TODO(floitsch): allow more characters.
      int charCode = field.codeUnitAt(i);
      if (!(charCodes.$a <= charCode && charCode <= charCodes.$z ||
            charCodes.$A <= charCode && charCode <= charCodes.$Z ||
            charCode == charCodes.$$ ||
            charCode == charCodes.$_ ||
            i != 1 && isDigit(charCode))) {
        return false;
      }
    }
    // TODO(floitsch): normally we should also check that the field is not a
    // reserved word.  We don't generate fields with reserved word names except
    // for 'super'.
    if (field == '"super"') return false;
    return true;
  }

  visitAccess(PropertyAccess access) {
    visitNestedExpression(access.receiver, CALL,
                          newInForInit: inForInit,
                          newAtStatementBegin: atStatementBegin);
    Node selector = access.selector;
    if (selector is LiteralString) {
      LiteralString selectorString = selector;
      String fieldWithQuotes = selectorString.value;
      if (isValidJavaScriptId(fieldWithQuotes)) {
        if (access.receiver is LiteralNumber) out(" ");
        out(".");
        out(fieldWithQuotes.substring(1, fieldWithQuotes.length - 1));
        return;
      }
    }
    out("[");
    visitNestedExpression(selector, EXPRESSION,
                          newInForInit: false, newAtStatementBegin: false);
    out("]");
  }

  visitNamedFunction(NamedFunction namedFunction) {
    VarCollector vars = new VarCollector();
    vars.visitNamedFunction(namedFunction);
    functionOut(namedFunction.function, namedFunction.name, vars);
  }

  visitFun(Fun fun) {
    VarCollector vars = new VarCollector();
    vars.visitFun(fun);
    functionOut(fun, null, vars);
  }

  visitLiteralBool(LiteralBool node) {
    out(node.value ? "true" : "false");
  }

  visitLiteralString(LiteralString node) {
    out(node.value);
  }

  visitLiteralNumber(LiteralNumber node) {
    int charCode = node.value.codeUnitAt(0);
    if (charCode == charCodes.$MINUS && lastCharCode == charCodes.$MINUS) {
      out(" ");
    }
    out(node.value);
  }

  visitLiteralNull(LiteralNull node) {
    out("null");
  }

  visitArrayInitializer(ArrayInitializer node) {
    out("[");
    List<ArrayElement> elements = node.elements;
    int elementIndex = 0;
    for (int i = 0; i < node.length; i++) {
      if (elementIndex < elements.length &&
          elements[elementIndex].index == i) {
        visitNestedExpression(elements[elementIndex].value, ASSIGNMENT,
                              newInForInit: false, newAtStatementBegin: false);
        elementIndex++;
        // We can avoid a trailing "," if there was an element just before. So
        // `[1]` and `[1,]` are the same, but `[,]` and `[]` are not.
        if (i != node.length - 1) {
          out(",");
          spaceOut();
        }
      } else {
        out(",");
      }
    }
    out("]");
  }

  visitArrayElement(ArrayElement node) {
    throw "Unreachable";
  }

  visitObjectInitializer(ObjectInitializer node) {
    // Print all the properties on one line until we see a function-valued
    // property.  Ideally, we would use a proper pretty-printer to make the
    // decision based on layout.
    bool onePerLine = false;
    List<Property> properties = node.properties;
    out("{");
    ++indentLevel;
    for (int i = 0; i < properties.length; i++) {
      Expression value = properties[i].value;
      if (value is Fun || value is NamedFunction) onePerLine = true;
      if (i != 0) {
        out(",");
        if (!onePerLine) spaceOut();
      }
      if (onePerLine) {
        forceLine();
        indent();
      }
      visitProperty(properties[i]);
    }
    --indentLevel;
    if (onePerLine) lineOut();
    out("}");
  }

  visitProperty(Property node) {
    if (node.name is LiteralString) {
      LiteralString nameString = node.name;
      String name = nameString.value;
      if (isValidJavaScriptId(name)) {
        out(name.substring(1, name.length - 1));
      } else {
        out(name);
      }
    } else {
      assert(node.name is LiteralNumber);
      LiteralNumber nameNumber = node.name;
      out(nameNumber.value);
    }
    out(":");
    spaceOut();
    visitNestedExpression(node.value, ASSIGNMENT,
                          newInForInit: false, newAtStatementBegin: false);
  }

  visitRegExpLiteral(RegExpLiteral node) {
    out(node.pattern);
  }

  visitLiteralExpression(LiteralExpression node) {
    String template = node.template;
    List<Expression> inputs = node.inputs;

    List<String> parts = template.split('#');
    int inputsLength = inputs == null ? 0 : inputs.length;
    if (parts.length != inputsLength + 1) {
      compiler.internalError('Wrong number of arguments for JS: $template');
    }
    // Code that uses JS must take care of operator precedences, and
    // put parenthesis if needed.
    out(parts[0]);
    for (int i = 0; i < inputsLength; i++) {
      visit(inputs[i]);
      out(parts[i + 1]);
    }
  }

  visitLiteralStatement(LiteralStatement node) {
    outLn(node.code);
  }

  visitJSExpression(JSExpression node) {
    compiler.internalError('JSPrinter should never see a JSExpression');
  }

  visitInterpolatedExpression(InterpolatedExpression node) {
    visit(node.value);
  }

  void visitComment(Comment node) {
    if (shouldCompressOutput) return;
    String comment = node.comment.trim();
    if (comment.isEmpty) return;
    for (var line in comment.split('\n')) {
      if (comment.startsWith('//')) {
        outIndentLn(line.trim());
      } else {
        outIndentLn('// ${line.trim()}');
      }
    }
  }
}


class OrderedSet<T> {
  final Set<T> set;
  final List<T> list;

  OrderedSet() : set = new Set<T>(), list = <T>[];

  void add(T x) {
    if (!set.contains(x)) {
      set.add(x);
      list.add(x);
    }
  }

  void forEach(void fun(T x)) {
    list.forEach(fun);
  }
}

// Collects all the var declarations in the function.  We need to do this in a
// separate pass because JS vars are lifted to the top of the function.
class VarCollector extends BaseVisitor {
  bool nested;
  final OrderedSet<String> vars;
  final OrderedSet<String> params;

  VarCollector() : nested = false,
                   vars = new OrderedSet<String>(),
                   params = new OrderedSet<String>();

  void forEachVar(void fn(String v)) => vars.forEach(fn);
  void forEachParam(void fn(String p)) => params.forEach(fn);

  void collectVarsInFunction(Fun fun) {
    if (!nested) {
      nested = true;
      if (fun.params != null) {
        for (int i = 0; i < fun.params.length; i++) {
          params.add(fun.params[i].name);
        }
      }
      visitBlock(fun.body);
      nested = false;
    }
  }

  void visitFunctionDeclaration(FunctionDeclaration declaration) {
    // Note that we don't bother collecting the name of the function.
    collectVarsInFunction(declaration.function);
  }

  void visitNamedFunction(NamedFunction namedFunction) {
    // Note that we don't bother collecting the name of the function.
    collectVarsInFunction(namedFunction.function);
  }

  void visitFun(Fun fun) {
    collectVarsInFunction(fun);
  }

  void visitThis(This node) {}

  void visitVariableDeclaration(VariableDeclaration decl) {
    vars.add(decl.name);
  }
}


/**
 * Returns true, if the given node must be wrapped into braces when used
 * as then-statement in an [If] that has an else branch.
 */
class DanglingElseVisitor extends BaseVisitor<bool> {
  leg.Compiler compiler;

  DanglingElseVisitor(this.compiler);

  bool visitProgram(Program node) => false;

  bool visitNode(Statement node) {
    compiler.internalError("Forgot node: $node");
  }

  bool visitBlock(Block node) => false;
  bool visitExpressionStatement(ExpressionStatement node) => false;
  bool visitEmptyStatement(EmptyStatement node) => false;
  bool visitIf(If node) {
    if (!node.hasElse) return true;
    return node.otherwise.accept(this);
  }
  bool visitFor(For node) => node.body.accept(this);
  bool visitForIn(ForIn node) => node.body.accept(this);
  bool visitWhile(While node) => node.body.accept(this);
  bool visitDo(Do node) => false;
  bool visitContinue(Continue node) => false;
  bool visitBreak(Break node) => false;
  bool visitReturn(Return node) => false;
  bool visitThrow(Throw node) => false;
  bool visitTry(Try node) {
    if (node.finallyPart != null) {
      return node.finallyPart.accept(this);
    } else {
      return node.catchPart.accept(this);
    }
  }
  bool visitCatch(Catch node) => node.body.accept(this);
  bool visitSwitch(Switch node) => false;
  bool visitCase(Case node) => false;
  bool visitDefault(Default node) => false;
  bool visitFunctionDeclaration(FunctionDeclaration node) => false;
  bool visitLabeledStatement(LabeledStatement node)
      => node.body.accept(this);
  bool visitLiteralStatement(LiteralStatement node) => true;

  bool visitExpression(Expression node) => false;
}


leg.CodeBuffer prettyPrint(Node node, leg.Compiler compiler,
                           { allowVariableMinification: true }) {
  Printer printer =
      new Printer(compiler,
                  allowVariableMinification: allowVariableMinification);
  printer.visit(node);
  return printer.outBuffer;
}


abstract class LocalNamer {
  String getName(String oldName);
  String declareVariable(String oldName);
  String declareParameter(String oldName);
  void enterScope(VarCollector vars);
  void leaveScope();
}


class IdentityNamer implements LocalNamer {
  String getName(String oldName) => oldName;
  String declareVariable(String oldName) => oldName;
  String declareParameter(String oldName) => oldName;
  void enterScope(VarCollector vars) {}
  void leaveScope() {}
}


class MinifyRenamer implements LocalNamer {
  final List<Map<String, String>> maps = [];
  final List<int> parameterNumberStack = [];
  final List<int> variableNumberStack = [];
  int parameterNumber = 0;
  int variableNumber = 0;

  MinifyRenamer();

  void enterScope(VarCollector vars) {
    maps.add(new Map<String, String>());
    variableNumberStack.add(variableNumber);
    parameterNumberStack.add(parameterNumber);
    vars.forEachVar(declareVariable);
    vars.forEachParam(declareParameter);
  }

  void leaveScope() {
    maps.removeLast();
    variableNumber = variableNumberStack.removeLast();
    parameterNumber = parameterNumberStack.removeLast();
  }

  String getName(String oldName) {
    // Go from inner scope to outer looking for mapping of name.
    for (int i = maps.length - 1; i >= 0; i--) {
      var map = maps[i];
      var replacement = map[oldName];
      if (replacement != null) return replacement;
    }
    return oldName;
  }

  static const LOWER_CASE_LETTERS = 26;
  static const LETTERS = LOWER_CASE_LETTERS;
  static const DIGITS = 10;

  static int nthLetter(int n) {
    return (n < LOWER_CASE_LETTERS) ?
           charCodes.$a + n :
           charCodes.$A + n - LOWER_CASE_LETTERS;
  }

  // Parameters go from a to z and variables go from z to a.  This makes each
  // argument list and each top-of-function var declaration look similar and
  // helps gzip compress the file.  If we have more than 26 arguments and
  // variables then we meet somewhere in the middle of the alphabet.  After
  // that we give up trying to be nice to the compression algorithm and just
  // use the same namespace for arguments and variables, starting with A, and
  // moving on to a0, a1, etc.
  String declareVariable(String oldName) {
    var newName;
    if (variableNumber + parameterNumber < LOWER_CASE_LETTERS) {
      // Variables start from z and go backwards, for better gzipability.
      newName = getNameNumber(oldName, LOWER_CASE_LETTERS - 1 - variableNumber);
    } else {
      // After 26 variables and parameters we allocate them in the same order.
      newName = getNameNumber(oldName, variableNumber + parameterNumber);
    }
    variableNumber++;
    return newName;
  }

  String declareParameter(String oldName) {
    var newName;
    if (variableNumber + parameterNumber < LOWER_CASE_LETTERS) {
      newName = getNameNumber(oldName, parameterNumber);
    } else {
      newName = getNameNumber(oldName, variableNumber + parameterNumber);
    }
    parameterNumber++;
    return newName;
  }

  String getNameNumber(String oldName, int n) {
    if (maps.isEmpty) return oldName;

    String newName;
    if (n < LETTERS) {
      // Start naming variables a, b, c, ..., z, A, B, C, ..., Z.
      newName = new String.fromCharCodes([nthLetter(n)]);
    } else {
      // Then name variables a0, a1, a2, ..., a9, b0, b1, ..., Z9, aa0, aa1, ...
      // For all functions with fewer than 500 locals this is just as compact
      // as using aa, ab, etc. but avoids clashes with keywords.
      n -= LETTERS;
      int digit = n % DIGITS;
      n ~/= DIGITS;
      int alphaChars = 1;
      int nameSpaceSize = LETTERS;
      // Find out whether we should use the 1-character namespace (size 52), the
      // 2-character namespace (size 52*52), etc.
      while (n >= nameSpaceSize) {
        n -= nameSpaceSize;
        alphaChars++;
        nameSpaceSize *= LETTERS;
      }
      var codes = <int>[];
      for (var i = 0; i < alphaChars; i++) {
        nameSpaceSize ~/= LETTERS;
        codes.add(nthLetter((n ~/ nameSpaceSize) % LETTERS));
      }
      codes.add(charCodes.$0 + digit);
      newName = new String.fromCharCodes(codes);
    }
    assert(new RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
    maps.last[oldName] = newName;
    return newName;
  }
}