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
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352

//! Functions for dealing with path expressions

use std::iter::Peekable;

/// Struct to store path token
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum PathToken {
  /// Root token $
  Root,
  /// named field token
  Field(String),
  /// integer index token
  Index(usize),
  /// * token
  Star,
  /// * index token
  StarIndex
}

fn peek<I>(chars: &mut Peekable<I>) -> Option<(usize, char)> where I: Iterator<Item = (usize, char)> {
  chars.peek().map(|tup| (tup.0.clone(), tup.1.clone()))
}

fn is_identifier_char(ch: char) -> bool {
  ch.is_alphabetic() || ch.is_numeric() || ch == '_' || ch == '-' || ch == ':' || ch == '#' || ch == '@'
}

// identifier -> a-zA-Z0-9+
fn identifier<I>(ch: char, chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  let mut id = String::new();
  id.push(ch);
  let mut next_char = peek(chars);
  while next_char.is_some() {
    let ch = next_char.unwrap();
    if is_identifier_char(ch.1) {
      chars.next();
      id.push(ch.1);
    } else if ch.1 == '.' || ch.1 == '\'' || ch.1 == '[' {
      break;
    } else {
      return Err(format!("\"{}\" is not allowed in an identifier in path expression \"{}\" at index {}",
                         ch.1, path, ch.0));
    }
    next_char = peek(chars);
  }
  tokens.push(PathToken::Field(id));
  Ok(())
}

// path_identifier -> identifier | *
fn path_identifier<I>(chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str, index: usize) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  match chars.next() {
    Some(ch) => match ch.1 {
      '*' => {
        tokens.push(PathToken::Star);
        Ok(())
      },
      c if is_identifier_char(c) => {
        identifier(c, chars, tokens, path)?;
        Ok(())
      },
      _ => Err(format!("Expected either a \"*\" or path identifier in path expression \"{}\" at index {}",
                       path, ch.0))
    },
    None => Err(format!("Expected a path after \".\" in path expression \"{}\" at index {}",
                        path, index))
  }
}

// string_path -> [^']+
fn string_path<I>(chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str, index: usize) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  let mut id = String::new();
  let mut next_char = peek(chars);
  if next_char.is_some() {
    chars.next();
    let mut ch = next_char.unwrap();
    next_char = peek(chars);
    while ch.1 != '\'' && next_char.is_some() {
      id.push(ch.1);
      chars.next();
      ch = next_char.unwrap();
      next_char = peek(chars);
    }
    if ch.1 == '\'' {
      if id.is_empty() {
        Err(format!("Empty strings are not allowed in path expression \"{}\" at index {}", path, ch.0))
      } else {
        tokens.push(PathToken::Field(id));
        Ok(())
      }
    } else {
      Err(format!("Unterminated string in path expression \"{}\" at index {}", path, ch.0))
    }
  } else {
    Err(format!("Unterminated string in path expression \"{}\" at index {}", path, index))
  }
}

// index_path -> [0-9]+
fn index_path<I>(chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  let mut id = String::new();
  let mut next_char = chars.next();
  id.push(next_char.unwrap().1);
  next_char = peek(chars);
  while next_char.is_some() {
    let ch = next_char.unwrap();
    if ch.1.is_numeric() {
      id.push(ch.1);
      chars.next();
    } else {
      break;
    }
    next_char = peek(chars);
  }

  if let Some(ch) = next_char {
    if ch.1 != ']' {
      return Err(format!("Indexes can only consist of numbers or a \"*\", found \"{}\" instead in path expression \"{}\" at index {}",
                         ch.1, path, ch.0))
    }
  }

  tokens.push(PathToken::Index(id.parse().unwrap()));
  Ok(())
}

// bracket_path -> (string_path | index | *) ]
fn bracket_path<I>(chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str, index: usize) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  let mut ch = peek(chars);
  match ch {
    Some(c) => {
      if c.1 == '\'' {
        chars.next();
        string_path(chars, tokens, path, c.0)?
      } else if c.1.is_numeric() {
        index_path(chars, tokens, path)?
      } else if c.1 == '*' {
        chars.next();
        tokens.push(PathToken::StarIndex);
      } else if c.1 == ']' {
        return Err(format!("Empty bracket expressions are not allowed in path expression \"{}\" at index {}",
                           path, c.0));
      } else {
        return Err(format!("Indexes can only consist of numbers or a \"*\", found \"{}\" instead in path expression \"{}\" at index {}",
                           c.1, path, c.0));
      };
      ch = peek(chars);
      match ch {
        Some(c) => if c.1 != ']' {
          Err(format!("Unterminated brackets, found \"{}\" instead of \"]\" in path expression \"{}\" at index {}",
                      c.1, path, c.0))
        } else {
          chars.next();
          Ok(())
        },
        None => Err(format!("Unterminated brackets in path expression \"{}\" at index {}",
                            path, path.len() - 1))
      }
    },
    None => Err(format!("Expected a \"'\" (single qoute) or a digit in path expression \"{}\" after index {}",
                        path, index))
  }
}

// path_exp -> (dot-path | bracket-path)*
fn path_exp<I>(chars: &mut Peekable<I>, tokens: &mut Vec<PathToken>, path: &str) -> Result<(), String>
  where I: Iterator<Item=(usize, char)> {
  let mut next_char = chars.next();
  while next_char.is_some() {
    let ch = next_char.unwrap();
    match ch.1 {
      '.' => path_identifier(chars, tokens, path, ch.0)?,
      '[' => bracket_path(chars, tokens, path, ch.0)?,
      _ => return Err(format!("Expected a \".\" or \"[\" instead of \"{}\" in path expression \"{}\" at index {}",
                              ch.1, path, ch.0))
    }
    next_char = chars.next();
  }
  Ok(())
}

pub fn parse_path_exp(path: &str) -> Result<Vec<PathToken>, String> {
  let mut tokens = vec![];

  // parse_path_exp -> $ path_exp | empty
  let mut chars = path.chars().enumerate().peekable();
  match chars.next() {
    Some(ch) => {
      match ch.1 {
        '$' => {
          tokens.push(PathToken::Root);
          path_exp(&mut chars, &mut tokens, path)?;
          Ok(tokens)
        }
        c if c.is_alphabetic() || c.is_numeric() => {
          tokens.push(PathToken::Root);
          identifier(c, &mut chars, &mut tokens, path)?;
          path_exp(&mut chars, &mut tokens, path)?;
          Ok(tokens)
        }
        _ => Err(format!("Path expression \"{}\" does not start with a root marker \"$\"", path))
      }
    }
    None => Ok(tokens)
  }
}

#[cfg(test)]
mod tests {
  use super::*;
  use expectest::prelude::*;
  use expectest::expect;

  #[test]
  fn parse_path_exp_handles_empty_string() {
    expect!(parse_path_exp("")).to(be_ok().value(vec![]));
  }

  #[test]
  fn parse_path_exp_handles_root() {
    expect!(parse_path_exp("$")).to(be_ok().value(vec![PathToken::Root]));
  }

  #[test]
  fn parse_path_exp_handles_missing_root() {
    expect!(parse_path_exp("adsjhaskjdh"))
      .to(be_ok().value(vec![PathToken::Root, PathToken::Field("adsjhaskjdh".to_string())]));
  }

  #[test]
  fn parse_path_exp_handles_missing_path() {
    expect!(parse_path_exp("$adsjhaskjdh")).to(
      be_err().value("Expected a \".\" or \"[\" instead of \"a\" in path expression \"$adsjhaskjdh\" at index 1".to_string()));
  }

  #[test]
  fn parse_path_exp_handles_missing_path_name() {
    expect!(parse_path_exp("$.")).to(
      be_err().value("Expected a path after \".\" in path expression \"$.\" at index 1".to_string()));
    expect!(parse_path_exp("$.a.b.c.")).to(
      be_err().value("Expected a path after \".\" in path expression \"$.a.b.c.\" at index 7".to_string()));
  }

  #[test]
  fn parse_path_exp_handles_invalid_identifiers() {
    expect!(parse_path_exp("$.abc!")).to(
      be_err().value("\"!\" is not allowed in an identifier in path expression \"$.abc!\" at index 5".to_string()));
    expect!(parse_path_exp("$.a.b.c.}")).to(
      be_err().value("Expected either a \"*\" or path identifier in path expression \"$.a.b.c.}\" at index 8".to_string()));
  }

  #[test]
  fn parse_path_exp_with_simple_identifiers() {
    expect!(parse_path_exp("$.a")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string())]));
    expect!(parse_path_exp("$.a.b.c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::Field("b".to_string()),
                         PathToken::Field("c".to_string())]));
    expect!(parse_path_exp("a.b.c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::Field("b".to_string()),
                         PathToken::Field("c".to_string())]));
  }

  #[test]
  fn parse_path_exp_handles_underscores_and_dashes() {
    expect!(parse_path_exp("$.user_id.user-id")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("user_id".to_string()),
                         PathToken::Field("user-id".to_string())])
    );
    expect!(parse_path_exp("$._id")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("_id".to_string())])
    );
    expect!(parse_path_exp("$.id:test")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("id:test".to_string())])
    );
  }

  #[test]
  fn parse_path_exp_handles_xml_names() {
    expect!(parse_path_exp("$.foo.@val")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("foo".to_string()),
                         PathToken::Field("@val".to_string())])
    );
    expect!(parse_path_exp("$.foo.#text")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("foo".to_string()),
                         PathToken::Field("#text".to_string())])
    );
    expect!(parse_path_exp("$.urn:ns:foo.urn:ns:something.#text")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("urn:ns:foo".to_string()),
                         PathToken::Field("urn:ns:something".to_string()), PathToken::Field("#text".to_string())])
    );
  }

  #[test]
  fn parse_path_exp_with_star_instead_of_identifiers() {
    expect!(parse_path_exp("$.*")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Star]));
    expect!(parse_path_exp("$.a.*.c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::Star,
                         PathToken::Field("c".to_string())]));
  }

  #[test]
  fn parse_path_exp_with_bracket_notation() {
    expect!(parse_path_exp("$['val1']")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("val1".to_string())]));
    expect!(parse_path_exp("$.a['val@1.'].c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::Field("val@1.".to_string()),
                         PathToken::Field("c".to_string())]));
    expect!(parse_path_exp("$.a[1].c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::Index(1),
                         PathToken::Field("c".to_string())]));
    expect!(parse_path_exp("$.a[*].c")).to(
      be_ok().value(vec![PathToken::Root, PathToken::Field("a".to_string()), PathToken::StarIndex,
                         PathToken::Field("c".to_string())]));
  }

  #[test]
  fn parse_path_exp_with_invalid_bracket_notation() {
    expect!(parse_path_exp("$[")).to(
      be_err().value("Expected a \"'\" (single qoute) or a digit in path expression \"$[\" after index 1".to_string()));
    expect!(parse_path_exp("$['")).to(
      be_err().value("Unterminated string in path expression \"$['\" at index 2".to_string()));
    expect!(parse_path_exp("$['Unterminated string")).to(
      be_err().value("Unterminated string in path expression \"$['Unterminated string\" at index 21".to_string()));
    expect!(parse_path_exp("$['']")).to(
      be_err().value("Empty strings are not allowed in path expression \"$['']\" at index 3".to_string()));
    expect!(parse_path_exp("$['test'.b.c")).to(
      be_err().value("Unterminated brackets, found \".\" instead of \"]\" in path expression \"$['test'.b.c\" at index 8".to_string()));
    expect!(parse_path_exp("$['test'")).to(
      be_err().value("Unterminated brackets in path expression \"$['test'\" at index 7".to_string()));
    expect!(parse_path_exp("$['test']b.c")).to(
      be_err().value("Expected a \".\" or \"[\" instead of \"b\" in path expression \"$[\'test\']b.c\" at index 9".to_string()));
  }

  #[test]
  fn parse_path_exp_with_invalid_bracket_index_notation() {
    expect!(parse_path_exp("$[dhghh]")).to(
      be_err().value("Indexes can only consist of numbers or a \"*\", found \"d\" instead in path expression \"$[dhghh]\" at index 2".to_string()));
    expect!(parse_path_exp("$[12abc]")).to(
      be_err().value("Indexes can only consist of numbers or a \"*\", found \"a\" instead in path expression \"$[12abc]\" at index 4".to_string()));
    expect!(parse_path_exp("$[]")).to(
      be_err().value("Empty bracket expressions are not allowed in path expression \"$[]\" at index 2".to_string()));
    expect!(parse_path_exp("$[-1]")).to(
      be_err().value("Indexes can only consist of numbers or a \"*\", found \"-\" instead in path expression \"$[-1]\" at index 2".to_string()));
  }
}