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use tui::{
    buffer::Buffer,
    layout::Rect,
    text::{Line, Span, Text},
    widgets::{Block, Paragraph, Widget},
};

#[derive(Default)]
pub struct List {
    /// The index at which the list last started. Used for scrolling
    pub offset: usize,
}

impl List {
    fn list_offset_for(&self, entry_in_view: Option<usize>, height: usize) -> usize {
        match entry_in_view {
            Some(pos) => match height as usize {
                h if (self.offset + h).saturating_sub(1) < pos => pos - h + 1,
                _ if self.offset > pos => pos,
                _ => self.offset,
            },
            None => 0,
        }
    }
}

#[derive(Default)]
pub struct ListProps<'b> {
    pub block: Option<Block<'b>>,
    pub entry_in_view: Option<usize>,
}

impl List {
    pub fn render<'a, 't>(
        &mut self,
        props: ListProps<'a>,
        items: impl IntoIterator<Item = Vec<Span<'t>>>,
        area: Rect,
        buf: &mut Buffer,
    ) {
        let ListProps {
            block,
            entry_in_view,
        } = props;

        let list_area = match block {
            Some(b) => {
                let inner_area = b.inner(area);
                b.render(area, buf);
                inner_area
            }
            None => area,
        };
        self.offset = self.list_offset_for(entry_in_view, list_area.height as usize);

        if list_area.width < 1 || list_area.height < 1 {
            return;
        }

        for (i, vec_of_spans) in items
            .into_iter()
            .skip(self.offset)
            .enumerate()
            .take(list_area.height as usize)
        {
            let (x, y) = (list_area.left(), list_area.top() + i as u16);
            Paragraph::new(Text::from(Line::from(vec_of_spans))).render(
                Rect {
                    x,
                    y,
                    width: list_area.width,
                    height: 1,
                },
                buf,
            );
        }
    }
}