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
// Copyright 2014-2017 The html5ever Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! The `BufferQueue` struct and helper types.
//!
//! This type is designed for the efficient parsing of string data, especially where many
//! significant characters are from the ascii range 0-63. This includes, for example, important
//! characters in xml/html parsing.
//!
//! Good and predictable performance is achieved by avoiding allocation where possible (a.k.a. zero
//! copy).
//!
//! [`BufferQueue`]: struct.BufferQueue.html

use std::{cell::RefCell, collections::VecDeque, mem};

use tendril::StrTendril;

pub use self::SetResult::{FromSet, NotFromSet};
use crate::util::smallcharset::SmallCharSet;

/// Result from [`pop_except_from`] containing either a character from a [`SmallCharSet`], or a
/// string buffer of characters not from the set.
///
/// [`pop_except_from`]: struct.BufferQueue.html#method.pop_except_from
/// [`SmallCharSet`]: ../struct.SmallCharSet.html
#[derive(PartialEq, Eq, Debug)]
pub enum SetResult {
    /// A character from the `SmallCharSet`.
    FromSet(char),
    /// A string buffer containing no characters from the `SmallCharSet`.
    NotFromSet(StrTendril),
}

/// A queue of owned string buffers, which supports incrementally consuming characters.
///
/// Internally it uses [`VecDeque`] and has the same complexity properties.
///
/// [`VecDeque`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html
#[derive(Debug)]
pub struct BufferQueue {
    /// Buffers to process.
    buffers: RefCell<VecDeque<StrTendril>>,
}

impl Default for BufferQueue {
    /// Create an empty BufferQueue.
    #[inline]
    fn default() -> Self {
        Self {
            buffers: RefCell::new(VecDeque::with_capacity(16)),
        }
    }
}

impl BufferQueue {
    /// Returns whether the queue is empty.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.buffers.borrow().is_empty()
    }

    /// Get the buffer at the beginning of the queue.
    #[inline]
    pub fn pop_front(&self) -> Option<StrTendril> {
        self.buffers.borrow_mut().pop_front()
    }

    /// Add a buffer to the beginning of the queue.
    ///
    /// If the buffer is empty, it will be skipped.
    pub fn push_front(&self, buf: StrTendril) {
        if buf.len32() == 0 {
            return;
        }
        self.buffers.borrow_mut().push_front(buf);
    }

    /// Add a buffer to the end of the queue.
    ///
    /// If the buffer is empty, it will be skipped.
    pub fn push_back(&self, buf: StrTendril) {
        if buf.len32() == 0 {
            return;
        }
        self.buffers.borrow_mut().push_back(buf);
    }

    /// Look at the next available character without removing it, if the queue is not empty.
    pub fn peek(&self) -> Option<char> {
        debug_assert!(
            !self.buffers.borrow().iter().any(|el| el.len32() == 0),
            "invariant \"all buffers in the queue are non-empty\" failed"
        );
        self.buffers
            .borrow()
            .front()
            .map(|b| b.chars().next().unwrap())
    }

    /// Pops and returns either a single character from the given set, or
    /// a buffer of characters none of which are in the set.
    ///
    /// # Examples
    ///
    /// ```
    /// # #[macro_use] extern crate markup5ever;
    /// # #[macro_use] extern crate tendril;
    /// # fn main() {
    /// use markup5ever::buffer_queue::{BufferQueue, SetResult};
    ///
    /// let mut queue = BufferQueue::default();
    /// queue.push_back(format_tendril!(r#"<some_tag attr="text">SomeText</some_tag>"#));
    /// let set = small_char_set!(b'<' b'>' b' ' b'=' b'"' b'/');
    /// let tag = format_tendril!("some_tag");
    /// let attr = format_tendril!("attr");
    /// let attr_val = format_tendril!("text");
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('<')));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(tag)));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet(' ')));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(attr)));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('=')));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::FromSet('"')));
    /// assert_eq!(queue.pop_except_from(set), Some(SetResult::NotFromSet(attr_val)));
    /// // ...
    /// # }
    /// ```
    pub fn pop_except_from(&self, set: SmallCharSet) -> Option<SetResult> {
        let (result, now_empty) = match self.buffers.borrow_mut().front_mut() {
            None => (None, false),
            Some(buf) => {
                let n = set.nonmember_prefix_len(buf);
                if n > 0 {
                    let out;
                    unsafe {
                        out = buf.unsafe_subtendril(0, n);
                        buf.unsafe_pop_front(n);
                    }
                    (Some(NotFromSet(out)), buf.is_empty())
                } else {
                    let c = buf.pop_front_char().expect("empty buffer in queue");
                    (Some(FromSet(c)), buf.is_empty())
                }
            },
        };

        // Unborrow self for this part.
        if now_empty {
            self.buffers.borrow_mut().pop_front();
        }

        result
    }

    /// Consume bytes matching the pattern, using a custom comparison function `eq`.
    ///
    /// Returns `Some(true)` if there is a match, `Some(false)` if there is no match, or `None` if
    /// it wasn't possible to know (more data is needed).
    ///
    /// The custom comparison function is used elsewhere to compare ascii-case-insensitively.
    ///
    /// # Examples
    ///
    /// ```
    /// # extern crate markup5ever;
    /// # #[macro_use] extern crate tendril;
    /// # fn main() {
    /// use markup5ever::buffer_queue::BufferQueue;
    ///
    /// let mut queue = BufferQueue::default();
    /// queue.push_back(format_tendril!("testtext"));
    /// let test_str = "test";
    /// assert_eq!(queue.eat("test", |&a, &b| a == b), Some(true));
    /// assert_eq!(queue.eat("text", |&a, &b| a == b), Some(true));
    /// assert!(queue.is_empty());
    /// # }
    /// ```
    pub fn eat<F: Fn(&u8, &u8) -> bool>(&self, pat: &str, eq: F) -> Option<bool> {
        let mut buffers_exhausted = 0;
        let mut consumed_from_last = 0;

        self.buffers.borrow().front()?;

        for pattern_byte in pat.bytes() {
            if buffers_exhausted >= self.buffers.borrow().len() {
                return None;
            }
            let buf = &self.buffers.borrow()[buffers_exhausted];

            if !eq(&buf.as_bytes()[consumed_from_last], &pattern_byte) {
                return Some(false);
            }

            consumed_from_last += 1;
            if consumed_from_last >= buf.len() {
                buffers_exhausted += 1;
                consumed_from_last = 0;
            }
        }

        // We have a match. Commit changes to the BufferQueue.
        for _ in 0..buffers_exhausted {
            self.buffers.borrow_mut().pop_front();
        }

        match self.buffers.borrow_mut().front_mut() {
            None => assert_eq!(consumed_from_last, 0),
            Some(ref mut buf) => buf.pop_front(consumed_from_last as u32),
        }

        Some(true)
    }

    /// Get the next character if one is available, removing it from the queue.
    ///
    /// This function manages the buffers, removing them as they become empty.
    pub fn next(&self) -> Option<char> {
        let (result, now_empty) = match self.buffers.borrow_mut().front_mut() {
            None => (None, false),
            Some(buf) => {
                let c = buf.pop_front_char().expect("empty buffer in queue");
                (Some(c), buf.is_empty())
            },
        };

        if now_empty {
            self.buffers.borrow_mut().pop_front();
        }

        result
    }

    pub fn replace_with(&self, other: BufferQueue) {
        let _ = mem::replace(&mut *self.buffers.borrow_mut(), other.buffers.take());
    }

    pub fn swap_with(&self, other: &BufferQueue) {
        mem::swap(
            &mut *self.buffers.borrow_mut(),
            &mut *other.buffers.borrow_mut(),
        );
    }
}

#[cfg(test)]
#[allow(non_snake_case)]
mod test {
    use tendril::SliceExt;

    use super::BufferQueue;
    use super::SetResult::{FromSet, NotFromSet};

    #[test]
    fn smoke_test() {
        let bq = BufferQueue::default();
        assert_eq!(bq.peek(), None);
        assert_eq!(bq.next(), None);

        bq.push_back("abc".to_tendril());
        assert_eq!(bq.peek(), Some('a'));
        assert_eq!(bq.next(), Some('a'));
        assert_eq!(bq.peek(), Some('b'));
        assert_eq!(bq.peek(), Some('b'));
        assert_eq!(bq.next(), Some('b'));
        assert_eq!(bq.peek(), Some('c'));
        assert_eq!(bq.next(), Some('c'));
        assert_eq!(bq.peek(), None);
        assert_eq!(bq.next(), None);
    }

    #[test]
    fn can_unconsume() {
        let bq = BufferQueue::default();
        bq.push_back("abc".to_tendril());
        assert_eq!(bq.next(), Some('a'));

        bq.push_front("xy".to_tendril());
        assert_eq!(bq.next(), Some('x'));
        assert_eq!(bq.next(), Some('y'));
        assert_eq!(bq.next(), Some('b'));
        assert_eq!(bq.next(), Some('c'));
        assert_eq!(bq.next(), None);
    }

    #[test]
    fn can_pop_except_set() {
        let bq = BufferQueue::default();
        bq.push_back("abc&def".to_tendril());
        let pop = || bq.pop_except_from(small_char_set!('&'));
        assert_eq!(pop(), Some(NotFromSet("abc".to_tendril())));
        assert_eq!(pop(), Some(FromSet('&')));
        assert_eq!(pop(), Some(NotFromSet("def".to_tendril())));
        assert_eq!(pop(), None);
    }

    #[test]
    fn can_eat() {
        // This is not very comprehensive.  We rely on the tokenizer
        // integration tests for more thorough testing with many
        // different input buffer splits.
        let bq = BufferQueue::default();
        bq.push_back("a".to_tendril());
        bq.push_back("bc".to_tendril());
        assert_eq!(bq.eat("abcd", u8::eq_ignore_ascii_case), None);
        assert_eq!(bq.eat("ax", u8::eq_ignore_ascii_case), Some(false));
        assert_eq!(bq.eat("ab", u8::eq_ignore_ascii_case), Some(true));
        assert_eq!(bq.next(), Some('c'));
        assert_eq!(bq.next(), None);
    }
}