# prepare.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/unicode-bidi-0.3.5/src/prepare.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright 2015 The Servo 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.

    //! 3.3.3 Preparations for Implicit Processing
    //!
    //! <http://www.unicode.org/reports/tr9/#Preparations_for_Implicit_Processing>

    use std::cmp::max;
    use std::ops::Range;
    use matches::matches;

    use super::BidiClass::{self, *};
    use super::level::Level;

    /// A maximal substring of characters with the same embedding level.
    ///
    /// Represented as a range of byte indices.
    pub type LevelRun = Range<usize>;

    /// Output of `isolating_run_sequences` (steps X9-X10)
    #[derive(Debug, PartialEq)]
    pub struct IsolatingRunSequence {
        pub runs: Vec<LevelRun>,
        pub sos: BidiClass, // Start-of-sequence type.
        pub eos: BidiClass, // End-of-sequence type.
    }

    /// Compute the set of isolating run sequences.
    ///
    /// An isolating run sequence is a maximal sequence of level runs such that for all level runs
    /// except the last one in the sequence, the last character of the run is an isolate initiator
    /// whose matching PDI is the first character of the next level run in the sequence.
    ///
    /// Note: This function does *not* return the sequences in order by their first characters.
    #[cfg_attr(feature = "flame_it", flamer::flame)]
    pub fn isolating_run_sequences(
        para_level: Level,
        original_classes: &[BidiClass],
        levels: &[Level],
    ) -> Vec<IsolatingRunSequence> {
        let runs = level_runs(levels, original_classes);

        // Compute the set of isolating run sequences.
        // <http://www.unicode.org/reports/tr9/#BD13>
        let mut sequences = Vec::with_capacity(runs.len());

        // When we encounter an isolate initiator, we push the current sequence onto the
        // stack so we can resume it after the matching PDI.
        let mut stack = vec![Vec::new()];

        for run in runs {
            assert!(run.len() > 0);
            assert!(!stack.is_empty());

            let start_class = original_classes[run.start];
            let end_class = original_classes[run.end - 1];

            let mut sequence = if start_class == PDI && stack.len() > 1 {
                // Continue a previous sequence interrupted by an isolate.
                stack.pop().unwrap()
            } else {
                // Start a new sequence.
                Vec::new()
            };

            sequence.push(run);

            if matches!(end_class, RLI | LRI | FSI) {
                // Resume this sequence after the isolate.
                stack.push(sequence);
            } else {
                // This sequence is finished.
                sequences.push(sequence);
            }
        }
        // Pop any remaning sequences off the stack.
        sequences.extend(stack.into_iter().rev().filter(|seq| !seq.is_empty()));

        // Determine the `sos` and `eos` class for each sequence.
        // <http://www.unicode.org/reports/tr9/#X10>
        sequences
            .into_iter()
            .map(|sequence: Vec<LevelRun>| {
                assert!(!sequence.is_empty());

                let start_of_seq = sequence[0].start;
                let end_of_seq = sequence[sequence.len() - 1].end;
                let seq_level = levels[start_of_seq];

                #[cfg(test)]
                for run in sequence.clone() {
                    for idx in run {
                        if not_removed_by_x9(&original_classes[idx]) {
                            assert_eq!(seq_level, levels[idx]);
                        }
                    }
                }

                // Get the level of the last non-removed char before the runs.
                let pred_level = match original_classes[..start_of_seq].iter().rposition(
                    not_removed_by_x9,
                ) {
                    Some(idx) => levels[idx],
                    None => para_level,
                };

                // Get the level of the next non-removed char after the runs.
                let succ_level = if matches!(original_classes[end_of_seq - 1], RLI | LRI | FSI) {
                    para_level
                } else {
                    match original_classes[end_of_seq..].iter().position(
                        not_removed_by_x9,
                    ) {
                        Some(idx) => levels[end_of_seq + idx],
                        None => para_level,
                    }
                };

                IsolatingRunSequence {
                    runs: sequence,
                    sos: max(seq_level, pred_level).bidi_class(),
                    eos: max(seq_level, succ_level).bidi_class(),
                }
            })
            .collect()
    }

    /// Finds the level runs in a paragraph.
    ///
    /// <http://www.unicode.org/reports/tr9/#BD7>
    fn level_runs(levels: &[Level], original_classes: &[BidiClass]) -> Vec<LevelRun> {
        assert_eq!(levels.len(), original_classes.len());

        let mut runs = Vec::new();
        if levels.is_empty() {
            return runs;
        }

        let mut current_run_level = levels[0];
        let mut current_run_start = 0;
        for i in 1..levels.len() {
            if !removed_by_x9(original_classes[i]) && levels[i] != current_run_level {
                // End the last run and start a new one.
                runs.push(current_run_start..i);
                current_run_level = levels[i];
                current_run_start = i;
            }
        }
        runs.push(current_run_start..levels.len());

        runs
    }

    /// Should this character be ignored in steps after X9?
    ///
    /// <http://www.unicode.org/reports/tr9/#X9>
    pub fn removed_by_x9(class: BidiClass) -> bool {
        matches!(class, RLE | LRE | RLO | LRO | PDF | BN)
    }

    // For use as a predicate for `position` / `rposition`
    pub fn not_removed_by_x9(class: &BidiClass) -> bool {
        !removed_by_x9(*class)
    }

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

        #[test]
        fn test_level_runs() {
            assert_eq!(level_runs(&Level::vec(&[]), &[]), &[]);
            assert_eq!(
                level_runs(&Level::vec(&[0, 0, 0, 1, 1, 2, 0, 0]), &[L; 8]),
                &[0..3, 3..5, 5..6, 6..8]
            );
        }

        // From <http://www.unicode.org/reports/tr9/#BD13>
        #[rustfmt::skip]
        #[test]
        fn test_isolating_run_sequences() {

            // == Example 1 ==
            // text1·RLE·text2·PDF·RLE·text3·PDF·text4
            // index        0    1  2    3    4  5    6  7
            let classes = &[L, RLE, L, PDF, RLE, L, PDF, L];
            let levels =  &[0,   1, 1,   1,   1, 1,   1, 0];
            let para_level = Level::ltr();
            let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
            sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
            assert_eq!(
                sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
                vec![vec![0..2], vec![2..7], vec![7..8]]
            );

            // == Example 2 ==
            // text1·RLI·text2·PDI·RLI·text3·PDI·text4
            // index        0    1  2    3    4  5    6  7
            let classes = &[L, RLI, L, PDI, RLI, L, PDI, L];
            let levels =  &[0,   0, 1,   0,   0, 1,   0, 0];
            let para_level = Level::ltr();
            let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
            sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
            assert_eq!(
                sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
                vec![vec![0..2, 3..5, 6..8], vec![2..3], vec![5..6]]
            );

            // == Example 3 ==
            // text1·RLI·text2·LRI·text3·RLE·text4·PDF·text5·PDI·text6·PDI·text7
            // index        0    1  2    3  4    5  6    7  8    9  10  11  12
            let classes = &[L, RLI, L, LRI, L, RLE, L, PDF, L, PDI, L, PDI,  L];
            let levels =  &[0,   0, 1,   1, 2,   3, 3,   3, 2,   1, 1,   0,  0];
            let para_level = Level::ltr();
            let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
            sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
            assert_eq!(
                sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
                vec![vec![0..2, 11..13], vec![2..4, 9..11], vec![4..6], vec![6..8], vec![8..9]]
            );
        }

        // From <http://www.unicode.org/reports/tr9/#X10>
        #[rustfmt::skip]
        #[test]
        fn test_isolating_run_sequences_sos_and_eos() {

            // == Example 1 ==
            // text1·RLE·text2·LRE·text3·PDF·text4·PDF·RLE·text5·PDF·text6
            // index        0    1  2    3  4    5  6    7    8  9   10  11
            let classes = &[L, RLE, L, LRE, L, PDF, L, PDF, RLE, L, PDF,  L];
            let levels =  &[0,   1, 1,   2, 2,   2, 1,   1,   1, 1,   1,  0];
            let para_level = Level::ltr();
            let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
            sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));

            // text1
            assert_eq!(
                &sequences[0],
                &IsolatingRunSequence {
                    runs: vec![0..2],
                    sos: L,
                    eos: R,
                }
            );

            // text2
            assert_eq!(
                &sequences[1],
                &IsolatingRunSequence {
                    runs: vec![2..4],
                    sos: R,
                    eos: L,
                }
            );

            // text3
            assert_eq!(
                &sequences[2],
                &IsolatingRunSequence {
                    runs: vec![4..6],
                    sos: L,
                    eos: L,
                }
            );

            // text4 text5
            assert_eq!(
                &sequences[3],
                &IsolatingRunSequence {
                    runs: vec![6..11],
                    sos: L,
                    eos: R,
                }
            );

            // text6
            assert_eq!(
                &sequences[4],
                &IsolatingRunSequence {
                    runs: vec![11..12],
                    sos: R,
                    eos: L,
                }
            );

            // == Example 2 ==
            // text1·RLI·text2·LRI·text3·PDI·text4·PDI·RLI·text5·PDI·text6
            // index        0    1  2    3  4    5  6    7    8  9   10  11
            let classes = &[L, RLI, L, LRI, L, PDI, L, PDI, RLI, L, PDI,  L];
            let levels =  &[0,   0, 1,   1, 2,   1, 1,   0,   0, 1,   0,  0];
            let para_level = Level::ltr();
            let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
            sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));

            // text1·RLI·PDI·RLI·PDI·text6
            assert_eq!(
                &sequences[0],
                &IsolatingRunSequence {
                    runs: vec![0..2, 7..9, 10..12],
                    sos: L,
                    eos: L,
                }
            );

            // text2·LRI·PDI·text4
            assert_eq!(
                &sequences[1],
                &IsolatingRunSequence {
                    runs: vec![2..4, 5..7],
                    sos: R,
                    eos: R,
                }
            );

            // text3
            assert_eq!(
                &sequences[2],
                &IsolatingRunSequence {
                    runs: vec![4..5],
                    sos: L,
                    eos: L,
                }
            );

            // text5
            assert_eq!(
                &sequences[3],
                &IsolatingRunSequence {
                    runs: vec![9..10],
                    sos: R,
                    eos: R,
                }
            );
        }

        #[test]
        fn test_removed_by_x9() {
            let rem_classes = &[RLE, LRE, RLO, LRO, PDF, BN];
            let not_classes = &[L, RLI, AL, LRI, PDI];
            for x in rem_classes {
                assert_eq!(removed_by_x9(*x), true);
            }
            for x in not_classes {
                assert_eq!(removed_by_x9(*x), false);
            }
        }

        #[test]
        fn test_not_removed_by_x9() {
            let non_x9_classes = &[L, R, AL, EN, ES, ET, AN, CS, NSM, B, S, WS, ON, LRI, RLI, FSI, PDI];
            for x in non_x9_classes {
                assert_eq!(not_removed_by_x9(&x), true);
            }
        }
    }