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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.

    //! 3.3.4 - 3.3.6. Resolve implicit levels and types.

    use std::cmp::max;

    use super::char_data::BidiClass;
    use super::prepare::{IsolatingRunSequence, LevelRun, not_removed_by_x9, removed_by_x9};
    use super::level::Level;

    use BidiClass::*;

    /// 3.3.4 Resolving Weak Types
    ///
    /// <http://www.unicode.org/reports/tr9/#Resolving_Weak_Types>
    #[cfg_attr(feature = "flame_it", flame)]
    pub fn resolve_weak(sequence: &IsolatingRunSequence, processing_classes: &mut [BidiClass]) {
        // FIXME (#8): This function applies steps W1-W6 in a single pass.  This can produce
        // incorrect results in cases where a "later" rule changes the value of `prev_class` seen
        // by an "earlier" rule.  We should either split this into separate passes, or preserve
        // extra state so each rule can see the correct previous class.

        // FIXME: Also, this could be the cause of increased failure for using longer-UTF-8 chars in
        // conformance tests, like BidiTest:69635 (AL ET EN)

        let mut prev_class = sequence.sos;
        let mut last_strong_is_al = false;
        let mut et_run_indices = Vec::new(); // for W5

        // Like sequence.runs.iter().flat_map(Clone::clone), but make indices itself clonable.
        fn id(x: LevelRun) -> LevelRun {
            x
        }
        let mut indices = sequence.runs.iter().cloned().flat_map(
            id as fn(LevelRun) -> LevelRun,
        );

        while let Some(i) = indices.next() {
            match processing_classes[i] {
                // <http://www.unicode.org/reports/tr9/#W1>
                NSM => {
                    processing_classes[i] = match prev_class {
                        RLI | LRI | FSI | PDI => ON,
                        _ => prev_class,
                    };
                }
                EN => {
                    if last_strong_is_al {
                        // W2. If previous strong char was AL, change EN to AN.
                        processing_classes[i] = AN;
                    } else {
                        // W5. If a run of ETs is adjacent to an EN, change the ETs to EN.
                        for j in &et_run_indices {
                            processing_classes[*j] = EN;
                        }
                        et_run_indices.clear();
                    }
                }
                // <http://www.unicode.org/reports/tr9/#W3>
                AL => processing_classes[i] = R,

                // <http://www.unicode.org/reports/tr9/#W4>
                ES | CS => {
                    let next_class = indices
                        .clone()
                        .map(|j| processing_classes[j])
                        .find(not_removed_by_x9)
                        .unwrap_or(sequence.eos);
                    processing_classes[i] = match (prev_class, processing_classes[i], next_class) {
                        (EN, ES, EN) | (EN, CS, EN) => EN,
                        (AN, CS, AN) => AN,
                        (_, _, _) => ON,
                    }
                }
                // <http://www.unicode.org/reports/tr9/#W5>
                ET => {
                    match prev_class {
                        EN => processing_classes[i] = EN,
                        _ => et_run_indices.push(i), // In case this is followed by an EN.
                    }
                }
                class => {
                    if removed_by_x9(class) {
                        continue;
                    }
                }
            }

            prev_class = processing_classes[i];
            match prev_class {
                L | R => {
                    last_strong_is_al = false;
                }
                AL => {
                    last_strong_is_al = true;
                }
                _ => {}
            }
            if prev_class != ET {
                // W6. If we didn't find an adjacent EN, turn any ETs into ON instead.
                for j in &et_run_indices {
                    processing_classes[*j] = ON;
                }
                et_run_indices.clear();
            }
        }

        // W7. If the previous strong char was L, change EN to L.
        let mut last_strong_is_l = sequence.sos == L;
        for run in &sequence.runs {
            for i in run.clone() {
                match processing_classes[i] {
                    EN if last_strong_is_l => {
                        processing_classes[i] = L;
                    }
                    L => {
                        last_strong_is_l = true;
                    }
                    R | AL => {
                        last_strong_is_l = false;
                    }
                    _ => {}
                }
            }
        }
    }

    /// 3.3.5 Resolving Neutral Types
    ///
    /// <http://www.unicode.org/reports/tr9/#Resolving_Neutral_Types>
    #[cfg_attr(feature = "flame_it", flame)]
    pub fn resolve_neutral(
        sequence: &IsolatingRunSequence,
        levels: &[Level],
        processing_classes: &mut [BidiClass],
    ) {
        let e: BidiClass = levels[sequence.runs[0].start].bidi_class();
        let mut indices = sequence.runs.iter().flat_map(Clone::clone);
        let mut prev_class = sequence.sos;

        while let Some(mut i) = indices.next() {
            // N0. Process bracket pairs.
            // TODO

            // Process sequences of NI characters.
            let mut ni_run = Vec::new();
            if is_NI(processing_classes[i]) {
                // Consume a run of consecutive NI characters.
                ni_run.push(i);
                let mut next_class;
                loop {
                    match indices.next() {
                        Some(j) => {
                            i = j;
                            if removed_by_x9(processing_classes[i]) {
                                continue;
                            }
                            next_class = processing_classes[j];
                            if is_NI(next_class) {
                                ni_run.push(i);
                            } else {
                                break;
                            }
                        }
                        None => {
                            next_class = sequence.eos;
                            break;
                        }
                    };
                }

                // N1-N2.
                //
                // <http://www.unicode.org/reports/tr9/#N1>
                // <http://www.unicode.org/reports/tr9/#N2>
                let new_class = match (prev_class, next_class) {
                    (L, L) => L,
                    (R, R) | (R, AN) | (R, EN) | (AN, R) | (AN, AN) | (AN, EN) | (EN, R) |
                    (EN, AN) | (EN, EN) => R,
                    (_, _) => e,
                };
                for j in &ni_run {
                    processing_classes[*j] = new_class;
                }
                ni_run.clear();
            }
            prev_class = processing_classes[i];
        }
    }

    /// 3.3.6 Resolving Implicit Levels
    ///
    /// Returns the maximum embedding level in the paragraph.
    ///
    /// <http://www.unicode.org/reports/tr9/#Resolving_Implicit_Levels>
    #[cfg_attr(feature = "flame_it", flame)]
    pub fn resolve_levels(original_classes: &[BidiClass], levels: &mut [Level]) -> Level {
        let mut max_level = Level::ltr();

        assert_eq!(original_classes.len(), levels.len());
        for i in 0..levels.len() {
            match (levels[i].is_rtl(), original_classes[i]) {
                (false, AN) | (false, EN) => levels[i].raise(2).expect("Level number error"),
                (false, R) | (true, L) | (true, EN) | (true, AN) => {
                    levels[i].raise(1).expect("Level number error")
                }
                (_, _) => {}
            }
            max_level = max(max_level, levels[i]);
        }

        max_level
    }

    /// Neutral or Isolate formatting character (B, S, WS, ON, FSI, LRI, RLI, PDI)
    ///
    /// <http://www.unicode.org/reports/tr9/#NI>
    #[allow(non_snake_case)]
    fn is_NI(class: BidiClass) -> bool {
        matches!(class, B | S | WS | ON | FSI | LRI | RLI | PDI)
    }