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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::parser::{get_subtag_iterator, ParserError};
use std::ops::RangeInclusive;
use std::str::FromStr;
use tinystr::TinyStr8;

/// A value used in a list of [`Keywords`](super::Keywords).
///
/// The value has to be a sequence of one or more alphanumerical strings
/// separated by `-`.
/// Each part of the sequence has to be no shorter than three characters and no
/// longer than 8.
///
///
/// # Examples
///
/// ```
/// use icu::locid::extensions::unicode::Value;
///
/// let value1: Value = "gregory".parse()
///     .expect("Failed to parse a Value.");
/// let value2: Value = "islamic-civil".parse()
///     .expect("Failed to parse a Value.");
///
/// assert_eq!(&value1.to_string(), "gregory");
/// assert_eq!(&value2.to_string(), "islamic-civil");
/// ```
#[derive(Debug, PartialEq, Eq, Clone, Hash, PartialOrd, Ord)]
pub struct Value(Box<[TinyStr8]>);

const VALUE_LENGTH: RangeInclusive<usize> = 3..=8;
const TRUE_VALUE: TinyStr8 = tinystr::tinystr8!("true");

impl Value {
    /// A constructor which takes a utf8 slice, parses it and
    /// produces a well-formed [`Value`].
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::locid::extensions::unicode::Value;
    ///
    /// let value = Value::from_bytes(b"buddhist")
    ///     .expect("Parsing failed.");
    ///
    /// assert_eq!(&value.to_string(), "buddhist");
    /// ```
    pub fn from_bytes(input: &[u8]) -> Result<Self, ParserError> {
        let mut v = vec![];

        if !input.is_empty() {
            for subtag in get_subtag_iterator(input) {
                if !Self::is_type_subtag(subtag) {
                    return Err(ParserError::InvalidExtension);
                }
                let val =
                    TinyStr8::from_bytes(subtag).map_err(|_| ParserError::InvalidExtension)?;
                if val != TRUE_VALUE {
                    v.push(val);
                }
            }
        }
        Ok(Self(v.into_boxed_slice()))
    }

    pub(crate) fn from_vec_unchecked(input: Vec<TinyStr8>) -> Self {
        Self(input.into_boxed_slice())
    }

    pub(crate) fn is_type_subtag(t: &[u8]) -> bool {
        VALUE_LENGTH.contains(&t.len()) && !t.iter().any(|c: &u8| !c.is_ascii_alphanumeric())
    }

    pub(crate) fn parse_subtag(t: &[u8]) -> Result<Option<TinyStr8>, ParserError> {
        let s = TinyStr8::from_bytes(t).map_err(|_| ParserError::InvalidSubtag)?;
        if !VALUE_LENGTH.contains(&t.len()) || !s.is_ascii_alphanumeric() {
            return Err(ParserError::InvalidExtension);
        }

        let s = s.to_ascii_lowercase();

        if s == TRUE_VALUE {
            Ok(None)
        } else {
            Ok(Some(s))
        }
    }
}

impl FromStr for Value {
    type Err = ParserError;

    fn from_str(source: &str) -> Result<Self, Self::Err> {
        Self::from_bytes(source.as_bytes())
    }
}

impl_writeable_for_tinystr_list!(Value, "", "islamic", "civil");