//! Generic CSS alignment code that is shared between both the Flexbox and CSS Grid algorithms.
use crate::style::AlignContent;

/// Generic alignment function that is used:
///   - For both align-content and justify-content alignment
///   - For both the Flexbox and CSS Grid algorithms
/// CSS Grid does not apply gaps as part of alignment, so the gap parameter should
/// always be set to zero for CSS Grid.
pub(crate) fn compute_alignment_offset(
    free_space: f32,
    num_items: usize,
    gap: f32,
    alignment_mode: AlignContent,
    layout_is_flex_reversed: bool,
    is_first: bool,
) -> f32 {
    if is_first {
        match alignment_mode {
            AlignContent::Start => 0.0,
            AlignContent::FlexStart => {
                if layout_is_flex_reversed {
                    free_space
                } else {
                    0.0
                }
            }
            AlignContent::End => free_space,
            AlignContent::FlexEnd => {
                if layout_is_flex_reversed {
                    0.0
                } else {
                    free_space
                }
            }
            AlignContent::Center => free_space / 2.0,
            AlignContent::Stretch => 0.0,
            AlignContent::SpaceBetween => 0.0,
            AlignContent::SpaceAround => {
                if free_space >= 0.0 {
                    (free_space / num_items as f32) / 2.0
                } else {
                    free_space / 2.0
                }
            }
            AlignContent::SpaceEvenly => {
                if free_space >= 0.0 {
                    free_space / (num_items + 1) as f32
                } else {
                    free_space / 2.0
                }
            }
        }
    } else {
        let free_space = free_space.max(0.0);
        gap + match alignment_mode {
            AlignContent::Start => 0.0,
            AlignContent::FlexStart => 0.0,
            AlignContent::End => 0.0,
            AlignContent::FlexEnd => 0.0,
            AlignContent::Center => 0.0,
            AlignContent::Stretch => 0.0,
            AlignContent::SpaceBetween => free_space / (num_items - 1) as f32,
            AlignContent::SpaceAround => free_space / num_items as f32,
            AlignContent::SpaceEvenly => free_space / (num_items + 1) as f32,
        }
    }
}