lib/src/piece/infix.dart

// Copyright (c) 2023, 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.
import '../back_end/code_writer.dart';
import 'piece.dart';

/// A piece for a series of binary expressions at the same precedence, like:
///
///     a + b + c
abstract base class InfixPiece extends Piece {
  /// The series of operands.
  ///
  /// Since we don't split on both sides of the operator, the operators will be
  /// embedded in the operand pieces. If the operator is a hanging one, it will
  /// be in the preceding operand, so `1 + 2` becomes "Infix(`1 +`, `2`)".
  /// A leading operator like `foo as int` becomes "Infix(`foo`, `as int`)".
  final List<Piece> _operands;

  /// What kind of indentation should be applied to the subsequent operands.
  final Indent _indent;

  /// Creates an [InfixPiece] for the given series of [operands].
  factory InfixPiece(
    List<Piece> operands, {
    required bool is3Dot7,
    bool conditional = false,
    Indent indent = Indent.expression,
  }) {
    if (is3Dot7) {
      return _InfixPiece3Dot7(operands, indent);
    } else {
      return _InfixPiece(operands, indent, conditional);
    }
  }

  /// Creates an [InfixPiece] for a conditional (`?:`) expression.
  factory InfixPiece.conditional(
    List<Piece> operands, {
    required bool is3Dot7,
  }) {
    if (is3Dot7) {
      return _InfixPiece3Dot7(operands, Indent.expression);
    } else {
      return _InfixPiece(operands, Indent.infix, true);
    }
  }

  InfixPiece._(this._operands, this._indent);

  @override
  List<State> get additionalStates => const [State.split];

  @override
  Set<Shape> allowedChildShapes(State state, Piece child) =>
      Shape.anyIf(state == State.split);

  @override
  void forEachChild(void Function(Piece piece) callback) {
    _operands.forEach(callback);
  }

  @override
  State? fixedStateForPageWidth(int pageWidth) {
    var totalLength = 0;

    for (var operand in _operands) {
      // If any operand contains a newline, then we have to split.
      if (operand.containsHardNewline) return State.split;

      totalLength += operand.totalCharacters;
      if (totalLength > pageWidth) break;
    }

    // If the total length doesn't fit in the page, then we have to split.
    if (totalLength > pageWidth) return State.split;

    return null;
  }
}

/// InfixPiece subclass for 3.8 and newer style.
final class _InfixPiece extends InfixPiece {
  /// Whether this piece is for a conditional expression.
  final bool _isConditional;

  _InfixPiece(super.operands, super.indent, this._isConditional) : super._();

  @override
  void format(CodeWriter writer, State state) {
    writer.pushIndent(_indent);

    // If this is a conditional expression (or chain of them), then allow the
    // leading condition to be headline formatted in an assignment, like:
    //
    //     variable = condition
    //         ? thenBranch
    //         : elseBranch;
    //
    // We only do this for conditional expressions and not other infix operators
    // because with other operators, the operands are homogeneous and it makes
    // more sense to split before the first one so that they are aligned in
    // parallel:
    //
    //     variable =
    //         operand +
    //         another;
    if (_isConditional) writer.setShapeMode(ShapeMode.beforeHeadline);
    writer.format(_operands[0]);
    if (_isConditional) writer.setShapeMode(ShapeMode.afterHeadline);

    for (var i = 1; i < _operands.length; i++) {
      writer.splitIf(state == State.split);

      // If this is a branch of a conditional expression, then indent the
      // branch's contents past the `?` or `:`.
      if (_isConditional) writer.pushIndent(Indent.block);

      // We can format each operand separately if the operand is on its own
      // line. This happens when the operator is split and we aren't the first
      // or last operand.
      var separate = state == State.split && i < _operands.length - 1;
      writer.format(_operands[i], separate: separate);
      if (_isConditional) writer.popIndent();
    }

    writer.popIndent();
  }
}

/// [InfixPiece] subclass for 3.7 style.
final class _InfixPiece3Dot7 extends InfixPiece {
  _InfixPiece3Dot7(super.operands, super.indent) : super._();

  @override
  void format(CodeWriter writer, State state) {
    writer.pushIndent(_indent);

    for (var i = 0; i < _operands.length; i++) {
      // We can format each operand separately if the operand is on its own
      // line. This happens when the operator is split and we aren't the first
      // or last operand.
      var separate = state == State.split && i > 0 && i < _operands.length - 1;

      writer.format(_operands[i], separate: separate);
      if (i < _operands.length - 1) writer.splitIf(state == State.split);
    }

    writer.popIndent();
  }
}