// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// 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.

//! Unicode-intensive string manipulations.
//!
//! This module provides functionality to `str` that requires the Unicode methods provided by the
//! unicode parts of the CharExt trait.

use core::char;
use core::iter::Filter;
use core::slice;
use core::str::Split;

/// An iterator over the non-whitespace substrings of a string,
/// separated by any amount of whitespace.
#[stable(feature = "split_whitespace", since = "1.1.0")]
pub struct SplitWhitespace<'a> {
    inner: Filter<Split<'a, fn(char) -> bool>, fn(&&str) -> bool>,
}

/// Methods for Unicode string slices
#[allow(missing_docs)] // docs in libcollections
pub trait UnicodeStr {
    fn split_whitespace<'a>(&'a self) -> SplitWhitespace<'a>;
    fn is_whitespace(&self) -> bool;
    fn is_alphanumeric(&self) -> bool;
    fn trim<'a>(&'a self) -> &'a str;
    fn trim_left<'a>(&'a self) -> &'a str;
    fn trim_right<'a>(&'a self) -> &'a str;
}

impl UnicodeStr for str {
    #[inline]
    fn split_whitespace(&self) -> SplitWhitespace {
        fn is_not_empty(s: &&str) -> bool { !s.is_empty() }
        let is_not_empty: fn(&&str) -> bool = is_not_empty; // coerce to fn pointer

        fn is_whitespace(c: char) -> bool { c.is_whitespace() }
        let is_whitespace: fn(char) -> bool = is_whitespace; // coerce to fn pointer

        SplitWhitespace { inner: self.split(is_whitespace).filter(is_not_empty) }
    }

    #[inline]
    fn is_whitespace(&self) -> bool { self.chars().all(|c| c.is_whitespace()) }

    #[inline]
    fn is_alphanumeric(&self) -> bool { self.chars().all(|c| c.is_alphanumeric()) }

    #[inline]
    fn trim(&self) -> &str {
        self.trim_matches(|c: char| c.is_whitespace())
    }

    #[inline]
    fn trim_left(&self) -> &str {
        self.trim_left_matches(|c: char| c.is_whitespace())
    }

    #[inline]
    fn trim_right(&self) -> &str {
        self.trim_right_matches(|c: char| c.is_whitespace())
    }
}

// https://tools.ietf.org/html/rfc3629
static UTF8_CHAR_WIDTH: [u8; 256] = [
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x1F
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x3F
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x5F
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x7F
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0x9F
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0xBF
0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // 0xDF
3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, // 0xEF
4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0, // 0xFF
];

/// Given a first byte, determine how many bytes are in this UTF-8 character
#[inline]
pub fn utf8_char_width(b: u8) -> usize {
    return UTF8_CHAR_WIDTH[b as usize] as usize;
}

/// Determines if a vector of `u16` contains valid UTF-16
pub fn is_utf16(v: &[u16]) -> bool {
    let mut it = v.iter();
    macro_rules! next { ($ret:expr) => {
            match it.next() { Some(u) => *u, None => return $ret }
        }
    }
    loop {
        let u = next!(true);

        match char::from_u32(u as u32) {
            Some(_) => {}
            None => {
                let u2 = next!(false);
                if u < 0xD7FF || u > 0xDBFF ||
                    u2 < 0xDC00 || u2 > 0xDFFF { return false; }
            }
        }
    }
}

/// An iterator that decodes UTF-16 encoded codepoints from a vector
/// of `u16`s.
#[derive(Clone)]
pub struct Utf16Items<'a> {
    iter: slice::Iter<'a, u16>
}
/// The possibilities for values decoded from a `u16` stream.
#[derive(Copy, PartialEq, Eq, Clone, Debug)]
pub enum Utf16Item {
    /// A valid codepoint.
    ScalarValue(char),
    /// An invalid surrogate without its pair.
    LoneSurrogate(u16)
}

impl Utf16Item {
    /// Convert `self` to a `char`, taking `LoneSurrogate`s to the
    /// replacement character (U+FFFD).
    #[inline]
    pub fn to_char_lossy(&self) -> char {
        match *self {
            Utf16Item::ScalarValue(c) => c,
            Utf16Item::LoneSurrogate(_) => '\u{FFFD}'
        }
    }
}

impl<'a> Iterator for Utf16Items<'a> {
    type Item = Utf16Item;

    fn next(&mut self) -> Option<Utf16Item> {
        let u = match self.iter.next() {
            Some(u) => *u,
            None => return None
        };

        if u < 0xD800 || 0xDFFF < u {
            // not a surrogate
            Some(Utf16Item::ScalarValue(unsafe { char::from_u32_unchecked(u as u32) }))
        } else if u >= 0xDC00 {
            // a trailing surrogate
            Some(Utf16Item::LoneSurrogate(u))
        } else {
            // preserve state for rewinding.
            let old = self.iter.clone();

            let u2 = match self.iter.next() {
                Some(u2) => *u2,
                // eof
                None => return Some(Utf16Item::LoneSurrogate(u))
            };
            if u2 < 0xDC00 || u2 > 0xDFFF {
                // not a trailing surrogate so we're not a valid
                // surrogate pair, so rewind to redecode u2 next time.
                self.iter = old.clone();
                return Some(Utf16Item::LoneSurrogate(u))
            }

            // all ok, so lets decode it.
            let c = (((u - 0xD800) as u32) << 10 | (u2 - 0xDC00) as u32) + 0x1_0000;
            Some(Utf16Item::ScalarValue(unsafe { char::from_u32_unchecked(c) }))
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (low, high) = self.iter.size_hint();
        // we could be entirely valid surrogates (2 elements per
        // char), or entirely non-surrogates (1 element per char)
        (low / 2, high)
    }
}

/// Create an iterator over the UTF-16 encoded codepoints in `v`,
/// returning invalid surrogates as `LoneSurrogate`s.
///
/// # Examples
///
/// ```
/// #![feature(unicode)]
///
/// extern crate rustc_unicode;
///
/// use rustc_unicode::str::Utf16Item::{ScalarValue, LoneSurrogate};
///
/// fn main() {
///     // 𝄞mus<invalid>ic<invalid>
///     let v = [0xD834, 0xDD1E, 0x006d, 0x0075,
///              0x0073, 0xDD1E, 0x0069, 0x0063,
///              0xD834];
///
///     assert_eq!(rustc_unicode::str::utf16_items(&v).collect::<Vec<_>>(),
///                vec![ScalarValue('𝄞'),
///                     ScalarValue('m'), ScalarValue('u'), ScalarValue('s'),
///                     LoneSurrogate(0xDD1E),
///                     ScalarValue('i'), ScalarValue('c'),
///                     LoneSurrogate(0xD834)]);
/// }
/// ```
pub fn utf16_items<'a>(v: &'a [u16]) -> Utf16Items<'a> {
    Utf16Items { iter : v.iter() }
}

/// Iterator adaptor for encoding `char`s to UTF-16.
#[derive(Clone)]
pub struct Utf16Encoder<I> {
    chars: I,
    extra: u16
}

impl<I> Utf16Encoder<I> {
    /// Create a UTF-16 encoder from any `char` iterator.
    pub fn new(chars: I) -> Utf16Encoder<I> where I: Iterator<Item=char> {
        Utf16Encoder { chars: chars, extra: 0 }
    }
}

impl<I> Iterator for Utf16Encoder<I> where I: Iterator<Item=char> {
    type Item = u16;

    #[inline]
    fn next(&mut self) -> Option<u16> {
        if self.extra != 0 {
            let tmp = self.extra;
            self.extra = 0;
            return Some(tmp);
        }

        let mut buf = [0; 2];
        self.chars.next().map(|ch| {
            let n = CharExt::encode_utf16(ch, &mut buf).unwrap_or(0);
            if n == 2 { self.extra = buf[1]; }
            buf[0]
        })
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (low, high) = self.chars.size_hint();
        // every char gets either one u16 or two u16,
        // so this iterator is between 1 or 2 times as
        // long as the underlying iterator.
        (low, high.and_then(|n| n.checked_mul(2)))
    }
}

impl<'a> Iterator for SplitWhitespace<'a> {
    type Item = &'a str;

    fn next(&mut self) -> Option<&'a str> { self.inner.next() }
}
impl<'a> DoubleEndedIterator for SplitWhitespace<'a> {
    fn next_back(&mut self) -> Option<&'a str> { self.inner.next_back() }
}