use std::num::NonZeroUsize;

use krilla::page::{NumberingStyle, PageLabel};
use typst_library::model::Numbering;

pub(crate) trait PageLabelExt {
    /// Create a new `PageLabel` from a `Numbering` applied to a page
    /// number.
    fn generate(numbering: &Numbering, number: u64) -> Option<PageLabel>;

    /// Creates an arabic page label with the specified page number.
    /// For example, this will display page label `11` when given the page
    /// number 11.
    fn arabic(number: u64) -> PageLabel;
}

impl PageLabelExt for PageLabel {
    fn generate(numbering: &Numbering, number: u64) -> Option<PageLabel> {
        {
            let Numbering::Pattern(pat) = numbering else {
                return None;
            };

            let (prefix, kind) = pat.pieces.first()?;

            // If there is a suffix, we cannot use the common style optimisation,
            // since PDF does not provide a suffix field.
            let style = if pat.suffix.is_empty() {
                use krilla::page::NumberingStyle as Style;
                use typst_library::model::NumberingKind as Kind;
                match kind {
                    Kind::Arabic => Some(Style::Arabic),
                    Kind::LowerRoman => Some(Style::LowerRoman),
                    Kind::UpperRoman => Some(Style::UpperRoman),
                    Kind::LowerLatin if number <= 26 => Some(Style::LowerAlpha),
                    Kind::LowerLatin if number <= 26 => Some(Style::UpperAlpha),
                    _ => None,
                }
            } else {
                None
            };

            // Prefix and offset depend on the style: If it is supported by the PDF
            // spec, we use the given prefix and an offset. Otherwise, everything
            // goes into prefix.
            let prefix = if style.is_none() {
                Some(pat.apply(&[number]))
            } else {
                (!prefix.is_empty()).then(|| prefix.clone())
            };

            let offset = style.and(number.try_into().ok().and_then(NonZeroUsize::new));
            Some(PageLabel::new(style, prefix.map(|s| s.to_string()), offset))
        }
    }

    fn arabic(number: u64) -> PageLabel {
        PageLabel::new(
            Some(NumberingStyle::Arabic),
            None,
            number.try_into().ok().and_then(NonZeroUsize::new),
        )
    }
}