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
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
use core::fmt;
use core::str;

use memchr::memchr;

use crate::{QuoteStyle, Terminator};

/// A builder for configuring a CSV writer.
///
/// This builder permits specifying the CSV delimiter, terminator, quoting
/// style and more.
#[derive(Debug)]
pub struct WriterBuilder {
    wtr: Writer,
}

impl WriterBuilder {
    /// Create a new builder for configuring a CSV writer.
    pub fn new() -> WriterBuilder {
        let wtr = Writer {
            state: WriterState::default(),
            requires_quotes: [false; 256],
            delimiter: b',',
            term: Terminator::Any(b'\n'),
            style: QuoteStyle::default(),
            quote: b'"',
            escape: b'\\',
            double_quote: true,
        };
        WriterBuilder { wtr: wtr }
    }

    /// Builder a CSV writer from this configuration.
    pub fn build(&self) -> Writer {
        use crate::Terminator::*;

        let mut wtr = self.wtr.clone();
        wtr.requires_quotes[self.wtr.delimiter as usize] = true;
        wtr.requires_quotes[self.wtr.quote as usize] = true;
        if !self.wtr.double_quote {
            // We only need to quote the escape character if the escape
            // character is used for escaping quotes.
            wtr.requires_quotes[self.wtr.escape as usize] = true;
        }
        match self.wtr.term {
            CRLF | Any(b'\n') | Any(b'\r') => {
                // This is a bit hokey. By default, the record terminator
                // is '\n', but we still need to quote '\r' (even if our
                // terminator is only `\n`) because the reader interprets '\r'
                // as a record terminator by default.
                wtr.requires_quotes[b'\r' as usize] = true;
                wtr.requires_quotes[b'\n' as usize] = true;
            }
            Any(b) => {
                wtr.requires_quotes[b as usize] = true;
            }
            _ => unreachable!(),
        }
        wtr
    }

    /// The field delimiter to use when writing CSV.
    ///
    /// The default is `b','`.
    pub fn delimiter(&mut self, delimiter: u8) -> &mut WriterBuilder {
        self.wtr.delimiter = delimiter;
        self
    }

    /// The record terminator to use when writing CSV.
    ///
    /// A record terminator can be any single byte. The default is `\n`.
    ///
    /// Note that RFC 4180 specifies that record terminators should be `\r\n`.
    /// To use `\r\n`, use the special `Terminator::CRLF` value.
    pub fn terminator(&mut self, term: Terminator) -> &mut WriterBuilder {
        self.wtr.term = term;
        self
    }

    /// The quoting style to use when writing CSV.
    ///
    /// By default, this is set to `QuoteStyle::Necessary`, which will only
    /// use quotes when they are necessary to preserve the integrity of data.
    ///
    /// Note that unless the quote style is set to `Never`, an empty field is
    /// quoted if it is the only field in a record.
    pub fn quote_style(&mut self, style: QuoteStyle) -> &mut WriterBuilder {
        self.wtr.style = style;
        self
    }

    /// The quote character to use when writing CSV.
    ///
    /// The default value is `b'"'`.
    pub fn quote(&mut self, quote: u8) -> &mut WriterBuilder {
        self.wtr.quote = quote;
        self
    }

    /// The escape character to use when writing CSV.
    ///
    /// This is only used when `double_quote` is set to `false`.
    ///
    /// The default value is `b'\\'`.
    pub fn escape(&mut self, escape: u8) -> &mut WriterBuilder {
        self.wtr.escape = escape;
        self
    }

    /// The quoting escape mechanism to use when writing CSV.
    ///
    /// When enabled (which is the default), quotes are escaped by doubling
    /// them. e.g., `"` escapes to `""`.
    ///
    /// When disabled, quotes are escaped with the escape character (which
    /// is `\\` by default).
    pub fn double_quote(&mut self, yes: bool) -> &mut WriterBuilder {
        self.wtr.double_quote = yes;
        self
    }
}

impl Default for WriterBuilder {
    fn default() -> WriterBuilder {
        WriterBuilder::new()
    }
}

/// The result of writing CSV data.
///
/// A value of this type is returned from every interaction with `Writer`. It
/// informs the caller how to proceed, namely, by indicating whether more
/// input should be given (`InputEmpty`) or if a bigger output buffer is needed
/// (`OutputFull`).
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum WriteResult {
    /// This result occurs when all of the bytes from the given input have
    /// been processed.
    InputEmpty,
    /// This result occurs when the output buffer was too small to process
    /// all of the input bytes. Generally, this means the caller must call
    /// the corresponding method again with the rest of the input and more
    /// room in the output buffer.
    OutputFull,
}

/// A writer for CSV data.
///
/// # RFC 4180
///
/// This writer conforms to RFC 4180 with one exception: it doesn't guarantee
/// that all records written are of the same length. Instead, the onus is on
/// the caller to ensure that all records written are of the same length.
///
/// Note that the default configuration of a `Writer` uses `\n` for record
/// terminators instead of `\r\n` as specified by RFC 4180. Use the
/// `terminator` method on `WriterBuilder` to set the terminator to `\r\n` if
/// it's desired.
pub struct Writer {
    state: WriterState,
    requires_quotes: [bool; 256],
    delimiter: u8,
    term: Terminator,
    style: QuoteStyle,
    quote: u8,
    escape: u8,
    double_quote: bool,
}

impl Clone for Writer {
    fn clone(&self) -> Writer {
        let mut requires_quotes = [false; 256];
        for i in 0..256 {
            requires_quotes[i] = self.requires_quotes[i];
        }
        Writer {
            state: self.state.clone(),
            requires_quotes: requires_quotes,
            delimiter: self.delimiter,
            term: self.term,
            style: self.style,
            quote: self.quote,
            escape: self.escape,
            double_quote: self.double_quote,
        }
    }
}

impl fmt::Debug for Writer {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Writer")
            .field("state", &self.state)
            .field("delimiter", &self.delimiter)
            .field("term", &self.term)
            .field("style", &self.style)
            .field("quote", &self.quote)
            .field("escape", &self.escape)
            .field("double_quote", &self.double_quote)
            .finish()
    }
}

#[derive(Clone, Debug)]
struct WriterState {
    /// This is set whenever we've begun writing the contents of a field, even
    /// if the contents are empty. We use it to avoid re-computing whether
    /// quotes are necessary.
    in_field: bool,
    /// This is set whenever we've started writing a field that is enclosed in
    /// quotes. When the writer is finished, or if a delimiter or terminator
    /// are written, then a closing quote is inserted when this is true.
    quoting: bool,
    /// The number of total bytes written for the current record.
    ///
    /// If the writer is finished or a terminator is written when this is `0`,
    /// then an empty field is added as a pair of adjacent quotes.
    record_bytes: u64,
}

impl Writer {
    /// Creates a new CSV writer with the default configuration.
    pub fn new() -> Writer {
        Writer::default()
    }

    /// Finish writing CSV data to `output`.
    ///
    /// This must be called when one is done writing CSV data to `output`.
    /// In particular, it will write closing quotes if necessary.
    pub fn finish(&mut self, mut output: &mut [u8]) -> (WriteResult, usize) {
        let mut nout = 0;
        if self.state.record_bytes == 0 && self.state.in_field {
            assert!(!self.state.quoting);
            let (res, o) = self.write(&[self.quote, self.quote], output);
            if o == 0 {
                return (res, 0);
            }
            output = &mut moving(output)[o..];
            nout += o;
            self.state.record_bytes += o as u64;
        }
        if !self.state.quoting {
            return (WriteResult::InputEmpty, nout);
        }
        let (res, o) = self.write(&[self.quote], output);
        if o == 0 {
            return (res, nout);
        }
        nout += o;
        self.state.record_bytes = 0;
        self.state.in_field = false;
        self.state.quoting = false;
        (res, nout)
    }

    /// Write a single CSV field from `input` to `output` while employing this
    /// writer's quoting style.
    ///
    /// This returns the result of writing field data, in addition to the
    /// number of bytes consumed from `input` and the number of bytes
    /// written to `output`.
    ///
    /// The result of writing field data is either `WriteResult::InputEmpty`
    /// or `WriteResult::OutputFull`. The former occurs when all bytes in
    /// `input` were copied to `output`, while the latter occurs when `output`
    /// is too small to fit everything from `input`. The maximum number of
    /// bytes that can be written to `output` is `2 + (2 * input.len())`
    /// because of quoting. (The worst case is a field consisting entirely
    /// of quotes.)
    ///
    /// Multiple successive calls to `field` will write more data to the same
    /// field. Subsequent fields can be written by calling either `delimiter`
    /// or `terminator` first.
    ///
    /// If this writer's quoting style is `QuoteStyle::Necessary`, then `input`
    /// should contain the *entire* field. Otherwise, whether the field needs
    /// to be quoted or not cannot be determined.
    pub fn field(
        &mut self,
        input: &[u8],
        mut output: &mut [u8],
    ) -> (WriteResult, usize, usize) {
        let (mut nin, mut nout) = (0, 0);

        if !self.state.in_field {
            self.state.quoting = self.should_quote(input);
            if self.state.quoting {
                let (res, o) = self.write(&[self.quote], output);
                if o == 0 {
                    return (res, 0, 0);
                }
                output = &mut moving(output)[o..];
                nout += o;
                self.state.record_bytes += o as u64;
            }
            self.state.in_field = true;
        }
        let (res, i, o) = if self.state.quoting {
            quote(input, output, self.quote, self.escape, self.double_quote)
        } else {
            write_optimistic(input, output)
        };
        nin += i;
        nout += o;
        self.state.record_bytes += o as u64;
        (res, nin, nout)
    }

    /// Write the configured field delimiter to `output`.
    ///
    /// If the output buffer does not have enough room to fit
    /// a field delimiter, then nothing is written to `output`
    /// and `WriteResult::OutputFull` is returned. Otherwise,
    /// `WriteResult::InputEmpty` is returned along with the number of bytes
    /// written to `output` (which is `1` in case of an unquoted
    /// field, or `2` in case of an end quote and a field separator).
    pub fn delimiter(
        &mut self,
        mut output: &mut [u8],
    ) -> (WriteResult, usize) {
        let mut nout = 0;
        if self.state.quoting {
            let (res, o) = self.write(&[self.quote], output);
            if o == 0 {
                return (res, o);
            }
            output = &mut moving(output)[o..];
            nout += o;
            self.state.record_bytes += o as u64;
            self.state.quoting = false;
        }
        let (res, o) = self.write(&[self.delimiter], output);
        if o == 0 {
            return (res, nout);
        }
        nout += o;
        self.state.record_bytes += o as u64;
        self.state.in_field = false;
        (res, nout)
    }

    /// Write the configured record terminator to `output`.
    ///
    /// If the output buffer does not have enough room to fit a record
    /// terminator, then no part of the terminator is written and
    /// `WriteResult::OutputFull` is returned. Otherwise,
    /// `WriteResult::InputEmpty` is returned along with the number of bytes
    /// written to `output` (which is always `1` or `2`).
    pub fn terminator(
        &mut self,
        mut output: &mut [u8],
    ) -> (WriteResult, usize) {
        let mut nout = 0;
        if self.state.record_bytes == 0 {
            assert!(!self.state.quoting);
            let (res, o) = self.write(&[self.quote, self.quote], output);
            if o == 0 {
                return (res, 0);
            }
            output = &mut moving(output)[o..];
            nout += o;
            self.state.record_bytes += o as u64;
        }
        if self.state.quoting {
            let (res, o) = self.write(&[self.quote], output);
            if o == 0 {
                return (res, o);
            }
            output = &mut moving(output)[o..];
            nout += o;
            self.state.record_bytes += o as u64;
            self.state.quoting = false;
        }
        let (res, o) = match self.term {
            Terminator::CRLF => write_pessimistic(&[b'\r', b'\n'], output),
            Terminator::Any(b) => write_pessimistic(&[b], output),
            _ => unreachable!(),
        };
        if o == 0 {
            return (res, nout);
        }
        nout += o;
        self.state.record_bytes = 0;
        self.state.in_field = false;
        (res, nout)
    }

    /// Returns true if and only if the given input field *requires* quotes to
    /// preserve the integrity of `input` while taking into account the current
    /// configuration of this writer (except for the configured quoting style).
    #[inline]
    fn needs_quotes(&self, mut input: &[u8]) -> bool {
        let mut needs = false;
        while !needs && input.len() >= 8 {
            needs = self.requires_quotes[input[0] as usize]
                || self.requires_quotes[input[1] as usize]
                || self.requires_quotes[input[2] as usize]
                || self.requires_quotes[input[3] as usize]
                || self.requires_quotes[input[4] as usize]
                || self.requires_quotes[input[5] as usize]
                || self.requires_quotes[input[6] as usize]
                || self.requires_quotes[input[7] as usize];
            input = &input[8..];
        }
        needs || input.iter().any(|&b| self.is_special_byte(b))
    }

    /// Returns true if and only if the given byte corresponds to a special
    /// byte in this CSV writer's configuration.
    ///
    /// Note that this does **not** take into account this writer's quoting
    /// style.
    #[inline]
    pub fn is_special_byte(&self, b: u8) -> bool {
        self.requires_quotes[b as usize]
    }

    /// Returns true if and only if we should put the given field data
    /// in quotes. This takes the quoting style into account.
    #[inline]
    pub fn should_quote(&self, input: &[u8]) -> bool {
        match self.style {
            QuoteStyle::Always => true,
            QuoteStyle::Never => false,
            QuoteStyle::NonNumeric => is_non_numeric(input),
            QuoteStyle::Necessary => self.needs_quotes(input),
            _ => unreachable!(),
        }
    }

    /// Return the delimiter used for this writer.
    #[inline]
    pub fn get_delimiter(&self) -> u8 {
        self.delimiter
    }

    /// Return the terminator used for this writer.
    #[inline]
    pub fn get_terminator(&self) -> Terminator {
        self.term
    }

    /// Return the quoting style used for this writer.
    #[inline]
    pub fn get_quote_style(&self) -> QuoteStyle {
        self.style
    }

    /// Return the quote character used for this writer.
    #[inline]
    pub fn get_quote(&self) -> u8 {
        self.quote
    }

    /// Return the escape character used for this writer.
    #[inline]
    pub fn get_escape(&self) -> u8 {
        self.escape
    }

    /// Return whether this writer doubles quotes or not. When the writer
    /// does not double quotes, it will escape them using the escape character.
    #[inline]
    pub fn get_double_quote(&self) -> bool {
        self.double_quote
    }

    fn write(&self, data: &[u8], output: &mut [u8]) -> (WriteResult, usize) {
        if data.len() > output.len() {
            (WriteResult::OutputFull, 0)
        } else {
            output[..data.len()].copy_from_slice(data);
            (WriteResult::InputEmpty, data.len())
        }
    }
}

impl Default for Writer {
    fn default() -> Writer {
        WriterBuilder::new().build()
    }
}

impl Default for WriterState {
    fn default() -> WriterState {
        WriterState { in_field: false, quoting: false, record_bytes: 0 }
    }
}

/// Returns true if and only if the given input is non-numeric.
pub fn is_non_numeric(input: &[u8]) -> bool {
    let s = match str::from_utf8(input) {
        Err(_) => return true,
        Ok(s) => s,
    };
    // I suppose this could be faster if we wrote validators of numbers instead
    // of using the actual parser, but that's probably a lot of work for a bit
    // of a niche feature.
    !s.parse::<f64>().is_ok() && !s.parse::<i128>().is_ok()
}

/// Escape quotes `input` and writes the result to `output`.
///
/// If `input` does not have a `quote`, then the contents of `input` are
/// copied verbatim to `output`.
///
/// If `output` is not big enough to store the fully quoted contents of
/// `input`, then `WriteResult::OutputFull` is returned. The `output` buffer
/// will require a maximum of storage of `2 * input.len()` in the worst case
/// (where every byte is a quote).
///
/// In streaming contexts, `quote` should be called in a loop until
/// `WriteResult::InputEmpty` is returned. It is possible to write an infinite
/// loop if your output buffer is less than 2 bytes in length (the minimum
/// storage space required to store an escaped quote).
///
/// In addition to the `WriteResult`, the number of consumed bytes from `input`
/// and the number of bytes written to `output` are also returned.
///
/// `quote` is the quote byte and `escape` is the escape byte. If
/// `double_quote` is true, then quotes are escaped by doubling them,
/// otherwise, quotes are escaped with the `escape` byte.
///
/// N.B. This function is provided for low level usage. It is called
/// automatically if you're using a `Writer`.
pub fn quote(
    mut input: &[u8],
    mut output: &mut [u8],
    quote: u8,
    escape: u8,
    double_quote: bool,
) -> (WriteResult, usize, usize) {
    let (mut nin, mut nout) = (0, 0);
    loop {
        match memchr(quote, input) {
            None => {
                let (res, i, o) = write_optimistic(input, output);
                nin += i;
                nout += o;
                return (res, nin, nout);
            }
            Some(next_quote) => {
                let (res, i, o) =
                    write_optimistic(&input[..next_quote], output);
                input = &input[i..];
                output = &mut moving(output)[o..];
                nin += i;
                nout += o;
                if let WriteResult::OutputFull = res {
                    return (res, nin, nout);
                }
                if double_quote {
                    let (res, o) = write_pessimistic(&[quote, quote], output);
                    if let WriteResult::OutputFull = res {
                        return (res, nin, nout);
                    }
                    nout += o;
                    output = &mut moving(output)[o..];
                } else {
                    let (res, o) = write_pessimistic(&[escape, quote], output);
                    if let WriteResult::OutputFull = res {
                        return (res, nin, nout);
                    }
                    nout += o;
                    output = &mut moving(output)[o..];
                }
                nin += 1;
                input = &input[1..];
            }
        }
    }
}

/// Copy the bytes from `input` to `output`. If `output` is too small to fit
/// everything from `input`, then copy `output.len()` bytes from `input`.
/// Otherwise, copy everything from `input` into `output`.
///
/// In the first case (`output` is too small), `WriteResult::OutputFull` is
/// returned, in addition to the number of bytes consumed from `input` and
/// the number of bytes written to `output`.
///
/// In the second case (`input` is no bigger than `output`),
/// `WriteResult::InputEmpty` is returned, in addition to the number of bytes
/// consumed from `input` and the number of bytes written to `output`.
fn write_optimistic(
    input: &[u8],
    output: &mut [u8],
) -> (WriteResult, usize, usize) {
    if input.len() > output.len() {
        let input = &input[..output.len()];
        output.copy_from_slice(input);
        (WriteResult::OutputFull, output.len(), output.len())
    } else {
        output[..input.len()].copy_from_slice(input);
        (WriteResult::InputEmpty, input.len(), input.len())
    }
}

/// Copy the bytes from `input` to `output` only if `input` is no bigger than
/// `output`. If `input` is bigger than `output`, then return
/// `WriteResult::OutputFull` and copy nothing into `output`. Otherwise,
/// return `WriteResult::InputEmpty` and the number of bytes copied into
/// `output`.
fn write_pessimistic(input: &[u8], output: &mut [u8]) -> (WriteResult, usize) {
    if input.len() > output.len() {
        (WriteResult::OutputFull, 0)
    } else {
        output[..input.len()].copy_from_slice(input);
        (WriteResult::InputEmpty, input.len())
    }
}

/// This avoids reborrowing.
/// See: https://bluss.github.io/rust/fun/2015/10/11/stuff-the-identity-function-does/
fn moving<T>(x: T) -> T {
    x
}

#[cfg(test)]
mod tests {
    use crate::writer::WriteResult::*;
    use crate::writer::{quote, QuoteStyle, Writer, WriterBuilder};

    // OMG I HATE BYTE STRING LITERALS SO MUCH.
    fn b(s: &str) -> &[u8] {
        s.as_bytes()
    }
    fn s(b: &[u8]) -> &str {
        ::core::str::from_utf8(b).unwrap()
    }

    macro_rules! assert_field {
        (
            $wtr:expr, $inp:expr, $out:expr,
            $expect_in:expr, $expect_out:expr,
            $expect_res:expr, $expect_data:expr
        ) => {{
            let (res, i, o) = $wtr.field($inp, $out);
            assert_eq!($expect_res, res, "result");
            assert_eq!($expect_in, i, "input");
            assert_eq!($expect_out, o, "output");
            assert_eq!($expect_data, s(&$out[..o]), "data");
        }};
    }

    macro_rules! assert_write {
        (
            $wtr:expr, $which:ident, $out:expr,
            $expect_out:expr, $expect_res:expr, $expect_data:expr
        ) => {{
            let (res, o) = $wtr.$which($out);
            assert_eq!($expect_res, res, "result");
            assert_eq!($expect_out, o, "output");
            assert_eq!($expect_data, s(&$out[..o]), "data");
        }};
    }

    #[test]
    fn writer_one_field() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(wtr, b("abc"), &mut out[n..], 3, 3, InputEmpty, "abc");
        n += 3;

        assert_write!(wtr, finish, &mut out[n..], 0, InputEmpty, "");
    }

    #[test]
    fn writer_one_empty_field_terminator() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];

        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, terminator, &mut out[..], 3, InputEmpty, "\"\"\n");
        assert_write!(wtr, finish, &mut out[..], 0, InputEmpty, "");
    }

    #[test]
    fn writer_one_empty_field_finish() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];

        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, finish, &mut out[..], 2, InputEmpty, "\"\"");
    }

    #[test]
    fn writer_many_one_empty_field_finish() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];

        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, terminator, &mut out[..], 3, InputEmpty, "\"\"\n");
        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, finish, &mut out[..], 2, InputEmpty, "\"\"");
    }

    #[test]
    fn writer_many_one_empty_field_terminator() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];

        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, terminator, &mut out[..], 3, InputEmpty, "\"\"\n");
        assert_field!(wtr, b(""), &mut out[..], 0, 0, InputEmpty, "");
        assert_write!(wtr, terminator, &mut out[..], 3, InputEmpty, "\"\"\n");
        assert_write!(wtr, finish, &mut out[..], 0, InputEmpty, "");
    }

    #[test]
    fn writer_one_field_quote() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(
            wtr,
            b("a\"bc"),
            &mut out[n..],
            4,
            6,
            InputEmpty,
            "\"a\"\"bc"
        );
        n += 6;

        assert_write!(wtr, finish, &mut out[n..], 1, InputEmpty, "\"");
    }

    #[test]
    fn writer_one_field_stream() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(wtr, b("abc"), &mut out[n..], 3, 3, InputEmpty, "abc");
        n += 3;
        assert_field!(wtr, b("x"), &mut out[n..], 1, 1, InputEmpty, "x");
        n += 1;

        assert_write!(wtr, finish, &mut out[n..], 0, InputEmpty, "");
    }

    #[test]
    fn writer_one_field_stream_quote() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(
            wtr,
            b("abc\""),
            &mut out[n..],
            4,
            6,
            InputEmpty,
            "\"abc\"\""
        );
        n += 6;
        assert_field!(wtr, b("x"), &mut out[n..], 1, 1, InputEmpty, "x");
        n += 1;

        assert_write!(wtr, finish, &mut out[n..], 1, InputEmpty, "\"");
    }

    #[test]
    fn writer_one_field_stream_quote_partial() {
        let mut wtr = Writer::new();
        let out = &mut [0; 4];

        assert_field!(wtr, b("ab\"xyz"), out, 2, 3, OutputFull, "\"ab");
        assert_field!(wtr, b("\"xyz"), out, 3, 4, OutputFull, "\"\"xy");
        assert_field!(wtr, b("z"), out, 1, 1, InputEmpty, "z");
        assert_write!(wtr, finish, out, 1, InputEmpty, "\"");
    }

    #[test]
    fn writer_two_fields() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(wtr, b("abc"), &mut out[n..], 3, 3, InputEmpty, "abc");
        n += 3;
        assert_write!(wtr, delimiter, &mut out[n..], 1, InputEmpty, ",");
        n += 1;
        assert_field!(wtr, b("yz"), &mut out[n..], 2, 2, InputEmpty, "yz");
        n += 2;

        assert_write!(wtr, finish, &mut out[n..], 0, InputEmpty, "");

        assert_eq!("abc,yz", s(&out[..n]));
    }

    #[test]
    fn writer_two_fields_non_numeric() {
        let mut wtr =
            WriterBuilder::new().quote_style(QuoteStyle::NonNumeric).build();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(wtr, b("abc"), &mut out[n..], 3, 4, InputEmpty, "\"abc");
        n += 4;
        assert_write!(wtr, delimiter, &mut out[n..], 2, InputEmpty, "\",");
        n += 2;
        assert_field!(wtr, b("5.2"), &mut out[n..], 3, 3, InputEmpty, "5.2");
        n += 3;
        assert_write!(wtr, delimiter, &mut out[n..], 1, InputEmpty, ",");
        n += 1;
        assert_field!(wtr, b("98"), &mut out[n..], 2, 2, InputEmpty, "98");
        n += 2;

        assert_write!(wtr, finish, &mut out[n..], 0, InputEmpty, "");

        assert_eq!("\"abc\",5.2,98", s(&out[..n]));
    }

    #[test]
    fn writer_two_fields_quote() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(
            wtr,
            b("a,bc"),
            &mut out[n..],
            4,
            5,
            InputEmpty,
            "\"a,bc"
        );
        n += 5;
        assert_write!(wtr, delimiter, &mut out[n..], 2, InputEmpty, "\",");
        n += 2;
        assert_field!(wtr, b("\nz"), &mut out[n..], 2, 3, InputEmpty, "\"\nz");
        n += 3;

        assert_write!(wtr, finish, &mut out[n..], 1, InputEmpty, "\"");
        n += 1;

        assert_eq!("\"a,bc\",\"\nz\"", s(&out[..n]));
    }

    #[test]
    fn writer_two_fields_two_records() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(wtr, b("abc"), &mut out[n..], 3, 3, InputEmpty, "abc");
        n += 3;
        assert_write!(wtr, delimiter, &mut out[n..], 1, InputEmpty, ",");
        n += 1;
        assert_field!(wtr, b("yz"), &mut out[n..], 2, 2, InputEmpty, "yz");
        n += 2;
        assert_write!(wtr, terminator, &mut out[n..], 1, InputEmpty, "\n");
        n += 1;
        assert_field!(wtr, b("foo"), &mut out[n..], 3, 3, InputEmpty, "foo");
        n += 3;
        assert_write!(wtr, delimiter, &mut out[n..], 1, InputEmpty, ",");
        n += 1;
        assert_field!(wtr, b("quux"), &mut out[n..], 4, 4, InputEmpty, "quux");
        n += 4;

        assert_write!(wtr, finish, &mut out[n..], 0, InputEmpty, "");

        assert_eq!("abc,yz\nfoo,quux", s(&out[..n]));
    }

    #[test]
    fn writer_two_fields_two_records_quote() {
        let mut wtr = Writer::new();
        let out = &mut [0; 1024];
        let mut n = 0;

        assert_field!(
            wtr,
            b("a,bc"),
            &mut out[n..],
            4,
            5,
            InputEmpty,
            "\"a,bc"
        );
        n += 5;
        assert_write!(wtr, delimiter, &mut out[n..], 2, InputEmpty, "\",");
        n += 2;
        assert_field!(wtr, b("\nz"), &mut out[n..], 2, 3, InputEmpty, "\"\nz");
        n += 3;
        assert_write!(wtr, terminator, &mut out[n..], 2, InputEmpty, "\"\n");
        n += 2;
        assert_field!(
            wtr,
            b("f\"oo"),
            &mut out[n..],
            4,
            6,
            InputEmpty,
            "\"f\"\"oo"
        );
        n += 6;
        assert_write!(wtr, delimiter, &mut out[n..], 2, InputEmpty, "\",");
        n += 2;
        assert_field!(
            wtr,
            b("quux,"),
            &mut out[n..],
            5,
            6,
            InputEmpty,
            "\"quux,"
        );
        n += 6;

        assert_write!(wtr, finish, &mut out[n..], 1, InputEmpty, "\"");
        n += 1;

        assert_eq!("\"a,bc\",\"\nz\"\n\"f\"\"oo\",\"quux,\"", s(&out[..n]));
    }

    macro_rules! assert_quote {
        (
            $inp:expr, $out:expr,
            $expect_in:expr, $expect_out:expr,
            $expect_res:expr, $expect_data:expr
        ) => {
            assert_quote!(
                $inp,
                $out,
                $expect_in,
                $expect_out,
                $expect_res,
                $expect_data,
                true
            );
        };
        (
            $inp:expr, $out:expr,
            $expect_in:expr, $expect_out:expr,
            $expect_res:expr, $expect_data:expr,
            $double_quote:expr
        ) => {{
            let (res, i, o) = quote($inp, $out, b'"', b'\\', $double_quote);
            assert_eq!($expect_res, res, "result");
            assert_eq!($expect_in, i, "input");
            assert_eq!($expect_out, o, "output");
            assert_eq!(b($expect_data), &$out[..o], "data");
        }};
    }

    #[test]
    fn quote_empty() {
        let inp = b("");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 0, 0, InputEmpty, "");
    }

    #[test]
    fn quote_no_quotes() {
        let inp = b("foobar");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 6, 6, InputEmpty, "foobar");
    }

    #[test]
    fn quote_one_quote() {
        let inp = b("\"");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 1, 2, InputEmpty, r#""""#);
    }

    #[test]
    fn quote_two_quotes() {
        let inp = b("\"\"");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 2, 4, InputEmpty, r#""""""#);
    }

    #[test]
    fn quote_escaped_one() {
        let inp = b("\"");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 1, 2, InputEmpty, r#"\""#, false);
    }

    #[test]
    fn quote_escaped_two() {
        let inp = b("\"\"");
        let out = &mut [0; 1024];

        assert_quote!(inp, out, 2, 4, InputEmpty, r#"\"\""#, false);
    }

    #[test]
    fn quote_misc() {
        let inp = b(r#"foo "bar" baz "quux"?"#);
        let out = &mut [0; 1024];

        assert_quote!(
            inp,
            out,
            21,
            25,
            InputEmpty,
            r#"foo ""bar"" baz ""quux""?"#
        );
    }

    #[test]
    fn quote_stream_no_quotes() {
        let mut inp = b("fooba");
        let out = &mut [0; 2];

        assert_quote!(inp, out, 2, 2, OutputFull, "fo");
        inp = &inp[2..];
        assert_quote!(inp, out, 2, 2, OutputFull, "ob");
        inp = &inp[2..];
        assert_quote!(inp, out, 1, 1, InputEmpty, "a");
    }

    #[test]
    fn quote_stream_quotes() {
        let mut inp = b(r#"a"bc"d""#);
        let out = &mut [0; 2];

        assert_quote!(inp, out, 1, 1, OutputFull, "a");
        inp = &inp[1..];
        assert_quote!(inp, out, 1, 2, OutputFull, r#""""#);
        inp = &inp[1..];
        assert_quote!(inp, out, 2, 2, OutputFull, "bc");
        inp = &inp[2..];
        assert_quote!(inp, out, 1, 2, OutputFull, r#""""#);
        inp = &inp[1..];
        assert_quote!(inp, out, 1, 1, OutputFull, "d");
        inp = &inp[1..];
        assert_quote!(inp, out, 1, 2, InputEmpty, r#""""#);
    }
}