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//! A simple horizontal or vertical layout with padding and child spacing.

use std::collections::HashMap;

use crate::{scalar, Scalar, Dimensions, Context, LayoutChildrenArgs, MinimumSizeArgs};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Axis {
    Horizontal,
    Vertical,
}

#[derive(Debug, Clone)]
pub struct Settings {
    pub axis: Axis,
    pub padding: Scalar,
    pub child_spacing: Scalar,
}

pub fn minimum_size<C: Context>(args: &MinimumSizeArgs<'_, C>, settings: &Settings) -> Dimensions {
    let Settings { axis, padding, child_spacing } = *settings;
    
    let mut minimum_size = Dimensions::zero();
    let num_children = crate::visible_children(args.slots, args.slot_id).count();
    let child_spacing = if num_children > 0 {
        child_spacing * ((num_children - 1) as Scalar)
    } else {
        scalar::ZERO
    };
    match axis {
        Axis::Horizontal => {
            minimum_size.width += padding * scalar::TWO + child_spacing;
        }
        Axis::Vertical => {
            minimum_size.height += padding * scalar::TWO + child_spacing;
        }
    }
    for child_id in crate::visible_children(args.slots, args.slot_id) {
        let child_minimum_size = args.minimum_size_cache[&child_id];
        match axis {
            Axis::Horizontal => {
                minimum_size.width += child_minimum_size.width;
                minimum_size.height = minimum_size.height.max(child_minimum_size.height);
            }
            Axis::Vertical => {
                minimum_size.width = minimum_size.width.max(child_minimum_size.width);
                minimum_size.height += child_minimum_size.height;
            }
        }
    }
    match axis {
        Axis::Horizontal => {
            minimum_size.height += padding * scalar::TWO;
        }
        Axis::Vertical => {
            minimum_size.width += padding * scalar::TWO;
        }
    }
    minimum_size
}

pub fn layout_children<C: Context>(args: &mut LayoutChildrenArgs<'_, C>, settings: &Settings) {
    let Settings { axis, padding, child_spacing } = *settings;
    
    let bounds = args.slots.get(args.slot_id).bounds;
    let children = crate::visible_children(args.slots, args.slot_id).collect::<Vec<_>>();
    let num_children = children.len();
    let size = match axis {
        Axis::Horizontal => bounds.size.width,
        Axis::Vertical => bounds.size.height,
    };
    let available_size = size - padding * scalar::TWO - child_spacing * ((num_children - 1) as Scalar);

    let mut irregular_sizes = HashMap::new();
    let mut num_regular_children = num_children;
    let mut reserved_size = scalar::ZERO;

    let mut expand_children = Vec::new();
    // Children not set as `expand` will always be their minimum size.
    for child_id in children.iter().rev() {
        let child = args.slots.get(*child_id);
        let child_minimum_size = args.minimum_size_cache[child_id];
        let (axis_expand, minimum_size) = match axis {
            Axis::Horizontal => (child.info.expand_x, child_minimum_size.width),
            Axis::Vertical => (child.info.expand_y, child_minimum_size.height),
        };
        if !axis_expand {
            irregular_sizes.insert(*child_id, minimum_size);
            num_regular_children -= 1;
            reserved_size += minimum_size;
        } else {
            expand_children.push((*child_id, minimum_size));
        }
    }

    // Children set as `expand` will be at least their minimum size or at most the "regular" size.
    // (The leftover size that is distributed equally (for now) between children marked `expand`.)
    // We need to figure out which children will be irregularly-sized.
    //
    // It makes sense to check this on children ordered from largest to smallest minimum sizes.
    expand_children.sort_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap());
    for (child_id, minimum_size) in expand_children.into_iter().rev() {
        let regular_size = if num_regular_children > 0 {
            (available_size - reserved_size) / num_regular_children as Scalar
        } else {
            scalar::ZERO
        };
        if minimum_size > regular_size {
            irregular_sizes.insert(child_id, minimum_size);
            num_regular_children -= 1;
            reserved_size += minimum_size;
        }
    }

    let regular_size = if num_regular_children > 0 {
        (available_size - reserved_size) / num_regular_children as Scalar
    } else {
        scalar::ZERO
    };
    let mut offset = padding;
    for (i, child_id) in children.iter().enumerate() {
        let child = args.slots.get_mut(*child_id);
        let other_expand = match axis {
            Axis::Horizontal => child.info.expand_y,
            Axis::Vertical => child.info.expand_x,
        };
        let child_size = irregular_sizes
            .get(child_id)
            .cloned()
            .unwrap_or(regular_size);
        let child_minimum_size = args.minimum_size_cache[child_id];
        match axis {
            Axis::Horizontal => {
                child.bounds.x = offset;
                child.bounds.y = padding;
                child.bounds.size.width = child_size.max(child_minimum_size.width);
                child.bounds.size.height = if other_expand {
                    (bounds.size.height - (padding * scalar::TWO)).max(child_minimum_size.height)
                } else {
                    child_minimum_size.height
                };
                offset += child.bounds.size.width;
            }
            Axis::Vertical => {
                child.bounds.x = padding;
                child.bounds.y = offset;
                child.bounds.size.width = if other_expand {
                    (bounds.size.width - (padding * scalar::TWO)).max(child_minimum_size.width)
                } else {
                    child_minimum_size.width
                };
                child.bounds.size.height = child_size.max(child_minimum_size.height);
                offset += child.bounds.size.height;
            }
        }
        if i < children.len() - 1 {
            offset += child_spacing;
        }
    }
}