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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 super::{
    super::{reference, PatternError},
    super::{GenericPatternItem, PatternItem},
    Pattern,
};
use alloc::vec::Vec;
use core::str::FromStr;
use icu_provider::prelude::*;
use zerovec::ZeroVec;

#[derive(Debug, PartialEq, Eq, Clone, yoke::Yokeable, zerofrom::ZeroFrom)]
#[allow(clippy::exhaustive_structs)] // this type is stable
#[cfg_attr(
    feature = "datagen",
    derive(databake::Bake),
    databake(path = icu_datetime::pattern::runtime),
)]
pub struct GenericPattern<'data> {
    pub items: ZeroVec<'data, GenericPatternItem>,
}

/// A ZeroSlice containing a 0 and a 1 placeholder
#[cfg(feature = "experimental")]
pub(crate) const ZERO_ONE_SLICE: &zerovec::ZeroSlice<GenericPatternItem> = zerovec::zeroslice!(
    GenericPatternItem;
    GenericPatternItem::to_unaligned_const;
    [
        GenericPatternItem::Placeholder(0),
        GenericPatternItem::Placeholder(1),
    ]
);

impl<'data> GenericPattern<'data> {
    /// The function allows for creation of new DTF pattern from a generic pattern
    /// and replacement patterns.
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::datetime::pattern::runtime::{GenericPattern, Pattern};
    ///
    /// let date: Pattern = "Y-m-d".parse().expect("Failed to parse pattern");
    /// let time: Pattern = "HH:mm".parse().expect("Failed to parse pattern");
    ///
    /// let glue: GenericPattern = "{1} 'at' {0}"
    ///     .parse()
    ///     .expect("Failed to parse generic pattern");
    /// assert_eq!(
    ///     glue.combined(date, time)
    ///         .expect("Failed to combine patterns")
    ///         .to_string(),
    ///     "Y-m-d 'at' HH:mm"
    /// );
    /// ```
    pub fn combined(
        self,
        date: Pattern<'data>,
        time: Pattern<'data>,
    ) -> Result<Pattern<'static>, PatternError> {
        let size = date.items.len() + time.items.len();
        let mut result = Vec::with_capacity(self.items.len() + size);

        for item in self.items.iter() {
            match item {
                GenericPatternItem::Placeholder(0) => {
                    result.extend(time.items.iter());
                }
                GenericPatternItem::Placeholder(1) => {
                    result.extend(date.items.iter());
                }
                GenericPatternItem::Placeholder(idx) => {
                    #[allow(clippy::unwrap_used)] // idx is a valid base-10 digit
                    return Err(PatternError::UnknownSubstitution(
                        char::from_digit(idx as u32, 10).unwrap(),
                    ));
                }
                GenericPatternItem::Literal(ch) => result.push(PatternItem::Literal(ch)),
            }
        }

        Ok(Pattern::from(result))
    }
}

impl Default for GenericPattern<'_> {
    fn default() -> Self {
        Self {
            items: ZeroVec::new(),
        }
    }
}

impl From<&reference::GenericPattern> for GenericPattern<'_> {
    fn from(input: &reference::GenericPattern) -> Self {
        Self {
            items: ZeroVec::alloc_from_slice(&input.items),
        }
    }
}

impl From<&GenericPattern<'_>> for reference::GenericPattern {
    fn from(input: &GenericPattern<'_>) -> Self {
        Self {
            items: input.items.to_vec(),
        }
    }
}

#[cfg(feature = "datagen")]
impl core::fmt::Display for GenericPattern<'_> {
    fn fmt(&self, formatter: &mut core::fmt::Formatter) -> core::fmt::Result {
        let reference = reference::GenericPattern::from(self);
        reference.fmt(formatter)
    }
}

impl FromStr for GenericPattern<'_> {
    type Err = PatternError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let reference = reference::GenericPattern::from_str(s)?;
        Ok(Self::from(&reference))
    }
}

#[cfg(test)]
#[cfg(feature = "datagen")]
mod test {
    use super::*;

    #[test]
    fn test_runtime_generic_pattern_combine() {
        let pattern: GenericPattern = "{1} 'at' {0}"
            .parse()
            .expect("Failed to parse a generic pattern.");

        let date = "Y/m/d".parse().expect("Failed to parse a date pattern.");

        let time = "HH:mm".parse().expect("Failed to parse a time pattern.");

        let pattern = pattern
            .combined(date, time)
            .expect("Failed to combine date and time.");
        let pattern = reference::Pattern::from(pattern.items.to_vec());

        assert_eq!(pattern.to_string(), "Y/m/d 'at' HH:mm");
    }
}