// Copyright 2016 Google Inc. Use of this source code is governed by an
// MIT-style license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

import 'package:charcode/charcode.dart';
import 'package:string_scanner/string_scanner.dart';

import '../ast/sass.dart';
import '../util/character.dart';
import 'stylesheet.dart';

/// A parser for the indented syntax.
class SassParser extends StylesheetParser {
  int get currentIndentation => _currentIndentation;
  var _currentIndentation = 0;

  /// The indentation level of the next source line after the scanner's
  /// position, or `null` if that hasn't been computed yet.
  ///
  /// A source line is any line that's not entirely whitespace.
  int _nextIndentation;

  /// The beginning of the next source line after the scanner's position, or
  /// `null` if that hasn't been computed yet.
  ///
  /// A source line is any line that's not entirely whitespace.
  LineScannerState _nextIndentationEnd;

  /// Whether the document is indented using spaces or tabs.
  ///
  /// If this is `true`, the document is indented using spaces. If it's `false`,
  /// the document is indented using tabs. If it's `null`, we haven't yet seen
  /// the indentation character used by the document.
  bool _spaces;

  bool get indented => true;

  SassParser(String contents, {url, bool color: false})
      : super(contents, url: url, color: color);

  bool atEndOfStatement() {
    var next = scanner.peekChar();
    return next == null || isNewline(next);
  }

  bool lookingAtChildren() =>
      atEndOfStatement() && _peekIndentation() > currentIndentation;

  bool scanElse(int ifIndentation) {
    if (_peekIndentation() != ifIndentation) return false;
    var start = scanner.state;
    var startIndentation = currentIndentation;
    var startNextIndentation = _nextIndentation;
    var startNextIndentationEnd = _nextIndentationEnd;

    _readIndentation();
    if (scanner.scanChar($at) && scanIdentifier('else')) return true;

    scanner.state = start;
    _currentIndentation = startIndentation;
    _nextIndentation = startNextIndentation;
    _nextIndentationEnd = startNextIndentationEnd;
    return false;
  }

  List<Statement> children(Statement child()) {
    var children = <Statement>[];
    _whileIndentedLower(() {
      children.add(_child(child));
    });
    return children;
  }

  List<Statement> statements(Statement statement()) {
    var first = scanner.peekChar();
    if (first == $tab || first == $space) {
      scanner.error("Indenting at the beginning of the document is illegal.",
          position: 0, length: scanner.position);
    }

    var statements = <Statement>[];
    while (!scanner.isDone) {
      var child = _child(statement);
      if (child != null) statements.add(child);
      var indentation = _readIndentation();
      assert(indentation == 0);
    }
    return statements;
  }

  /// Consumes a child of the current statement.
  ///
  /// This consumes children that are allowed at all levels of the document; the
  /// [child] parameter is called to consume any children that are specifically
  /// allowed in the caller's context.
  Statement _child(Statement child()) {
    switch (scanner.peekChar()) {
      case $dollar:
        return variableDeclaration();
        break;

      case $slash:
        switch (scanner.peekChar(1)) {
          case $slash:
            return _silentComment();
            break;
          case $asterisk:
            return _loudComment();
            break;
          default:
            return child();
            break;
        }
        break;

      default:
        return child();
        break;
    }
  }

  /// Consumes an indented-style silent comment.
  Comment _silentComment() {
    var start = scanner.state;
    scanner.expect("//");

    var buffer = new StringBuffer();
    var parentIndentation = currentIndentation;
    while (true) {
      buffer.write("//");

      // Skip the first two indentation characters because we're already writing
      // "//".
      for (var i = 2; i < currentIndentation - parentIndentation; i++) {
        buffer.writeCharCode($space);
      }

      while (!scanner.isDone && !isNewline(scanner.peekChar())) {
        buffer.writeCharCode(scanner.readChar());
      }
      buffer.writeln();

      if (_peekIndentation() <= parentIndentation) break;
      _readIndentation();
    }

    return new Comment(buffer.toString(), scanner.spanFrom(start),
        silent: true);
  }

  /// Consumes an indented-style loud context.
  Comment _loudComment() {
    var start = scanner.state;
    scanner.expect("/*");

    var first = true;
    var buffer = new StringBuffer("/*");
    var parentIndentation = currentIndentation;
    while (true) {
      if (!first) {
        buffer.writeln();
        buffer.write(" * ");
      }
      first = false;

      for (var i = 3; i < currentIndentation - parentIndentation; i++) {
        buffer.writeCharCode($space);
      }

      while (!scanner.isDone && !isNewline(scanner.peekChar())) {
        buffer.writeCharCode(scanner.readChar());
      }

      if (_peekIndentation() <= parentIndentation) break;
      _readIndentation();
    }
    buffer.write(" */");

    print(buffer);
    return new Comment(buffer.toString(), scanner.spanFrom(start),
        silent: false);
  }

  void whitespace() {
    // This overrides whitespace consumption so that it doesn't consume newlines
    // or loud comments.
    while (!scanner.isDone) {
      var next = scanner.peekChar();
      if (next != $tab && next != $space) break;
      scanner.readChar();
    }

    if (scanner.peekChar() == $slash && scanner.peekChar(1) == $slash) {
      silentComment();
    }
  }

  /// As long as the scanner's position is indented beneath the starting line,
  /// runs [body] to consume the next statement.
  void _whileIndentedLower(void body()) {
    var parentIndentation = currentIndentation;
    int childIndentation;
    while (_peekIndentation() > parentIndentation) {
      var indentation = _readIndentation();
      childIndentation ??= indentation;
      if (childIndentation != indentation) {
        scanner.error(
            "Inconsistent indentation, expected $childIndentation spaces.",
            position: scanner.position - scanner.column,
            length: scanner.column);
      }

      body();
    }
  }

  /// Consumes indentation whitespace and returns the indentation level of the
  /// next line.
  int _readIndentation() {
    if (_nextIndentation == null) _peekIndentation();
    _currentIndentation = _nextIndentation;
    scanner.state = _nextIndentationEnd;
    _nextIndentation = null;
    _nextIndentationEnd = null;
    return currentIndentation;
  }

  /// Returns the indentation level of the next line.
  int _peekIndentation() {
    if (_nextIndentation != null) return _nextIndentation;

    if (scanner.isDone) {
      _nextIndentation = 0;
      _nextIndentationEnd = scanner.state;
      return 0;
    }

    var start = scanner.state;
    if (!scanCharIf(isNewline)) {
      scanner.error("Expected newline.", position: scanner.position);
    }

    bool containsTab;
    bool containsSpace;
    do {
      containsTab = false;
      containsSpace = false;
      _nextIndentation = 0;

      while (true) {
        var next = scanner.peekChar();
        if (next == $space) {
          containsSpace = true;
        } else if (next == $tab) {
          containsTab = true;
        } else {
          break;
        }
        _nextIndentation++;
        scanner.readChar();
      }

      if (scanner.isDone) {
        _nextIndentation = 0;
        _nextIndentationEnd = scanner.state;
        scanner.state = start;
        return 0;
      }
    } while (scanCharIf(isNewline));

    _checkIndentationConsistency(containsTab, containsSpace);

    _spaces ??= containsSpace;
    _nextIndentationEnd = scanner.state;
    scanner.state = start;
    return _nextIndentation;
  }

  /// Ensures that the document uses consistent characters for indentation.
  ///
  /// The [containsTab] and [containsSpace] parameters refer to a single line of
  /// indentation that has just been parsed.
  void _checkIndentationConsistency(bool containsTab, bool containsSpace) {
    if (containsTab) {
      if (containsSpace) {
        scanner.error("Tabs and spaces may not be mixed.",
            position: scanner.position - scanner.column,
            length: scanner.column);
      } else if (_spaces == true) {
        scanner.error("Expected spaces, was tabs.",
            position: scanner.position - scanner.column,
            length: scanner.column);
      }
    } else if (_spaces == false) {
      scanner.error("Expected tabs, was spaces.",
          position: scanner.position - scanner.column, length: scanner.column);
    }
  }
}