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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.
//! 3.3.2 Explicit Levels and Directions
//!
//! <http://www.unicode.org/reports/tr9/#Explicit_Levels_and_Directions>
use alloc::vec::Vec;
use super::char_data::{
is_rtl,
BidiClass::{self, *},
};
use super::level::Level;
/// Compute explicit embedding levels for one paragraph of text (X1-X8).
///
/// `processing_classes[i]` must contain the `BidiClass` of the char at byte index `i`,
/// for each char in `text`.
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn compute(
text: &str,
para_level: Level,
original_classes: &[BidiClass],
levels: &mut [Level],
processing_classes: &mut [BidiClass],
) {
assert_eq!(text.len(), original_classes.len());
// <http://www.unicode.org/reports/tr9/#X1>
let mut stack = DirectionalStatusStack::new();
stack.push(para_level, OverrideStatus::Neutral);
let mut overflow_isolate_count = 0u32;
let mut overflow_embedding_count = 0u32;
let mut valid_isolate_count = 0u32;
for (i, c) in text.char_indices() {
match original_classes[i] {
// Rules X2-X5c
RLE | LRE | RLO | LRO | RLI | LRI | FSI => {
let last_level = stack.last().level;
// X5a-X5c: Isolate initiators get the level of the last entry on the stack.
let is_isolate = match original_classes[i] {
RLI | LRI | FSI => true,
_ => false,
};
if is_isolate {
levels[i] = last_level;
match stack.last().status {
OverrideStatus::RTL => processing_classes[i] = R,
OverrideStatus::LTR => processing_classes[i] = L,
_ => {}
}
}
let new_level = if is_rtl(original_classes[i]) {
last_level.new_explicit_next_rtl()
} else {
last_level.new_explicit_next_ltr()
};
if new_level.is_ok() && overflow_isolate_count == 0 && overflow_embedding_count == 0
{
let new_level = new_level.unwrap();
stack.push(
new_level,
match original_classes[i] {
RLO => OverrideStatus::RTL,
LRO => OverrideStatus::LTR,
RLI | LRI | FSI => OverrideStatus::Isolate,
_ => OverrideStatus::Neutral,
},
);
if is_isolate {
valid_isolate_count += 1;
} else {
// The spec doesn't explicitly mention this step, but it is necessary.
// See the reference implementations for comparison.
levels[i] = new_level;
}
} else if is_isolate {
overflow_isolate_count += 1;
} else if overflow_isolate_count == 0 {
overflow_embedding_count += 1;
}
}
// <http://www.unicode.org/reports/tr9/#X6a>
PDI => {
if overflow_isolate_count > 0 {
overflow_isolate_count -= 1;
} else if valid_isolate_count > 0 {
overflow_embedding_count = 0;
loop {
// Pop everything up to and including the last Isolate status.
match stack.vec.pop() {
None
| Some(Status {
status: OverrideStatus::Isolate,
..
}) => break,
_ => continue,
}
}
valid_isolate_count -= 1;
}
let last = stack.last();
levels[i] = last.level;
match last.status {
OverrideStatus::RTL => processing_classes[i] = R,
OverrideStatus::LTR => processing_classes[i] = L,
_ => {}
}
}
// <http://www.unicode.org/reports/tr9/#X7>
PDF => {
if overflow_isolate_count > 0 {
continue;
}
if overflow_embedding_count > 0 {
overflow_embedding_count -= 1;
continue;
}
if stack.last().status != OverrideStatus::Isolate && stack.vec.len() >= 2 {
stack.vec.pop();
}
// The spec doesn't explicitly mention this step, but it is necessary.
// See the reference implementations for comparison.
levels[i] = stack.last().level;
}
// Nothing
B | BN => {}
// <http://www.unicode.org/reports/tr9/#X6>
_ => {
let last = stack.last();
levels[i] = last.level;
match last.status {
OverrideStatus::RTL => processing_classes[i] = R,
OverrideStatus::LTR => processing_classes[i] = L,
_ => {}
}
}
}
// Handle multi-byte characters.
for j in 1..c.len_utf8() {
levels[i + j] = levels[i];
processing_classes[i + j] = processing_classes[i];
}
}
}
/// Entries in the directional status stack:
struct Status {
level: Level,
status: OverrideStatus,
}
#[derive(PartialEq)]
enum OverrideStatus {
Neutral,
RTL,
LTR,
Isolate,
}
struct DirectionalStatusStack {
vec: Vec<Status>,
}
impl DirectionalStatusStack {
fn new() -> Self {
DirectionalStatusStack {
vec: Vec::with_capacity(Level::max_explicit_depth() as usize + 2),
}
}
fn push(&mut self, level: Level, status: OverrideStatus) {
self.vec.push(Status { level, status });
}
fn last(&self) -> &Status {
self.vec.last().unwrap()
}
}
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