1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190

use super::error::SyntaxError;
use super::error::SyntaxErrorType;
use super::error::SyntaxResult;
use super::lex::lex_next;
use super::lex::Lexer;
use super::lex::LexerCheckpoint;
use super::source::SourceRange;
use super::token::Token;
use super::token::TokenType;
use crate::ast::Expression;
use crate::ast::ModuleItem;
use crate::ast::Node;
use crate::ast::Statement;
use crate::symbol::Scope;
use crate::symbol::ScopeType;

#[must_use]
pub struct MaybeToken {
  typ: TokenType,
  range: SourceRange,
  matched: bool,
}

impl MaybeToken {
  pub fn is_match(&self) -> bool {
    self.matched
  }

  pub fn match_loc(&self) -> Option<SourceRange> {
    if self.matched {
      Some(self.range)
    } else {
      None
    }
  }

  pub fn error(&self, err: SyntaxErrorType) -> SyntaxError {
    debug_assert!(!self.matched);
    SyntaxError::from_loc(self.range, err, Some(self.typ))
  }

  pub fn and_then<R, F: FnOnce() -> SyntaxResult<R>>(self, f: F) -> SyntaxResult<Option<R>> {
    Ok(if self.matched { Some(f()?) } else { None })
  }
}

pub struct ParserCheckpoint {
  checkpoint: LexerCheckpoint,
}

pub struct Parser<'a> {
  lexer: Lexer<'a>,
  pub(crate) scope: Scope, // The current scope, which will be changed while parsing. It's a field instead of passed via method args to avoid having to propagate that to every method.
}

impl<'a> Parser<'a> {
  pub fn new(lexer: Lexer<'a>, root_scope: Scope) -> Parser<'a> {
    Parser {
      lexer,
      scope: root_scope,
    }
  }

  // Creates a new scope as a child of the current one and updates the current scope reference to it, returning the old scope.
  pub fn enter_new_scope(&mut self, typ: ScopeType) -> Scope {
    let old = self.scope.clone();
    let new = old.new_child(typ);
    self.scope = new;
    old
  }

  pub fn return_to_scope(&mut self, old: Scope) {
    self.scope = old;
  }

  pub fn new_expression(&self, loc: SourceRange, expr: Expression) -> Node<Expression> {
    Node {
      loc,
      stx: Box::new(expr),
      scope: self.scope.clone(),
    }
  }

  pub fn new_statement(&self, loc: SourceRange, stmt: Statement) -> Node<Statement> {
    Node {
      loc,
      stx: Box::new(stmt),
      scope: self.scope.clone(),
    }
  }

  pub fn new_module_item(&self, loc: SourceRange, item: ModuleItem) -> Node<ModuleItem> {
    Node {
      loc,
      stx: Box::new(item),
      scope: self.scope.clone(),
    }
  }

  pub fn lexer_mut(&mut self) -> &mut Lexer<'a> {
    &mut self.lexer
  }

  pub fn source(&self, range: SourceRange) -> &[u8] {
    &self.lexer[range]
  }

  pub fn source_as_string(&self, range: SourceRange) -> String {
    unsafe { String::from_utf8_unchecked(self.source(range).to_vec()) }
  }

  pub fn source_range(&self) -> SourceRange {
    self.lexer.source_range()
  }

  pub fn checkpoint(&self) -> ParserCheckpoint {
    ParserCheckpoint {
      checkpoint: self.lexer.checkpoint(),
    }
  }

  pub fn since_checkpoint(&self, checkpoint: ParserCheckpoint) -> SourceRange {
    self.lexer.since_checkpoint(checkpoint.checkpoint)
  }

  pub fn restore_checkpoint(&mut self, checkpoint: ParserCheckpoint) -> () {
    self.lexer.apply_checkpoint(checkpoint.checkpoint);
  }

  fn forward<K: FnOnce(&Token) -> bool>(&mut self, keep: K) -> SyntaxResult<(bool, Token)> {
    let cp = self.checkpoint();
    let t = lex_next(&mut self.lexer)?;
    let k = keep(&t);
    if !k {
      self.restore_checkpoint(cp);
    };
    Ok((k, t))
  }

  pub fn peek(&mut self) -> SyntaxResult<Token> {
    self.forward(|_| false).map(|r| r.1)
  }

  pub fn consume(&mut self) -> SyntaxResult<Token> {
    self.forward(|_| true).map(|r| r.1)
  }

  pub fn consume_if_pred<F: FnOnce(&Token) -> bool>(
    &mut self,
    pred: F,
  ) -> SyntaxResult<MaybeToken> {
    let (matched, t) = self.forward(pred)?;
    Ok(MaybeToken {
      typ: t.typ,
      matched,
      range: t.loc,
    })
  }

  pub fn consume_if(&mut self, typ: TokenType) -> SyntaxResult<MaybeToken> {
    self.consume_if_pred(|t| t.typ == typ)
  }

  pub fn require_predicate<P: FnOnce(TokenType) -> bool>(
    &mut self,
    pred: P,
    expected: &'static str,
  ) -> SyntaxResult<Token> {
    let t = self.consume()?;
    if !pred(t.typ) {
      Err(t.error(SyntaxErrorType::ExpectedSyntax(expected)))
    } else {
      Ok(t)
    }
  }

  pub fn require(&mut self, typ: TokenType) -> SyntaxResult<Token> {
    let t = self.consume()?;
    if t.typ != typ {
      Err(t.error(SyntaxErrorType::RequiredTokenNotFound(typ)))
    } else {
      Ok(t)
    }
  }

  pub fn require_identifier_as_string(&mut self) -> SyntaxResult<(SourceRange, String)> {
    let loc = self.require(TokenType::Identifier)?.loc;
    Ok((loc, self.source_as_string(loc)))
  }
}