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//! 对 ASCII 字符串和字符的操作。
//!
//! Rust 中的大多数字符串操作都作用于 UTF-8 字符串。
//! 但是，有时只考虑针对特定操作的 ASCII 字符集更有意义。
//!
//! [`escape_default`] 函数在给定字符的转义版本的字节上提供迭代器。
//!
//!

#![stable(feature = "core_ascii", since = "1.26.0")]

use crate::escape;
use crate::fmt;
use crate::iter::FusedIterator;
use crate::num::NonZeroUsize;

mod ascii_char;
#[unstable(feature = "ascii_char", issue = "110998")]
pub use ascii_char::AsciiChar as Char;

/// 在字节的转义版本上进行迭代的迭代器。
///
/// 该 `struct` 由 [`escape_default`] 函数创建。
/// 有关更多信息，请参见其文档。
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct EscapeDefault(escape::EscapeIterInner<4>);

/// 返回一个迭代器，该迭代器生成 `u8` 的转义版本。
///
/// 选择默认值时会偏向于生成在多种语言 (包括 C++ 11 和类似的 C 系列语言) 中都合法的字面量。
/// 确切的规则是：
///
/// * 制表符被转义为 `\t`。
/// * 回车符被转义为 `\r`。
/// * 换行符转为 `\n`。
/// * 单引号转义为 `\'`。
/// * 双引号转义为 `\"`。
/// * 反斜杠转义为 `\\`。
/// * `可打印 ASCII` 范围 `0x20` .. 中的任何字符 `0x7e` (含 `0x7e`) 不会转义。
/// * 任何其他字符都以 '\xNN' 形式给出十六进制转义。
/// * 此函数从不生成 Unicode 转义。
///
/// # Examples
///
/// ```
/// use std::ascii;
///
/// let escaped = ascii::escape_default(b'0').next().unwrap();
/// assert_eq!(b'0', escaped);
///
/// let mut escaped = ascii::escape_default(b'\t');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b't', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'\r');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'r', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'\n');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'n', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'\'');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'\'', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'"');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'"', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'\\');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'\\', escaped.next().unwrap());
///
/// let mut escaped = ascii::escape_default(b'\x9d');
///
/// assert_eq!(b'\\', escaped.next().unwrap());
/// assert_eq!(b'x', escaped.next().unwrap());
/// assert_eq!(b'9', escaped.next().unwrap());
/// assert_eq!(b'd', escaped.next().unwrap());
/// ```
///
///
#[stable(feature = "rust1", since = "1.0.0")]
pub fn escape_default(c: u8) -> EscapeDefault {
    let mut data = [Char::Null; 4];
    let range = escape::escape_ascii_into(&mut data, c);
    EscapeDefault(escape::EscapeIterInner::new(data, range))
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Iterator for EscapeDefault {
    type Item = u8;

    #[inline]
    fn next(&mut self) -> Option<u8> {
        self.0.next()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let n = self.0.len();
        (n, Some(n))
    }

    #[inline]
    fn count(self) -> usize {
        self.0.len()
    }

    #[inline]
    fn last(mut self) -> Option<u8> {
        self.0.next_back()
    }

    #[inline]
    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
        self.0.advance_by(n)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl DoubleEndedIterator for EscapeDefault {
    #[inline]
    fn next_back(&mut self) -> Option<u8> {
        self.0.next_back()
    }

    #[inline]
    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
        self.0.advance_back_by(n)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl ExactSizeIterator for EscapeDefault {
    #[inline]
    fn len(&self) -> usize {
        self.0.len()
    }
}

#[stable(feature = "fused", since = "1.26.0")]
impl FusedIterator for EscapeDefault {}

#[stable(feature = "ascii_escape_display", since = "1.39.0")]
impl fmt::Display for EscapeDefault {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.0.as_str())
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for EscapeDefault {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("EscapeDefault").finish_non_exhaustive()
    }
}