//! A representation of [CSS layout properties](https://css-tricks.com/snippets/css/a-guide-to-flexbox/) in Rust, used for flexbox layout

use crate::geometry::{Rect, Size};
use crate::number::Number;

/// How [`Nodes`](crate::node::Node) are aligned relative to the cross axis
///
/// The default behavior is [`AlignItems::Stretch`].
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#align-items-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum AlignItems {
    /// Items are packed toward the start of the cross axis
    FlexStart,
    /// Items are packed toward the end of the cross axis
    FlexEnd,
    /// Items are packed along the center of the cross axis
    Center,
    /// Items are aligned such as their baselines align
    Baseline,
    /// Stretch to fill the container
    Stretch,
}

impl Default for AlignItems {
    fn default() -> Self {
        Self::Stretch
    }
}

/// Overrides the inherited [`AlignItems`] behavior for this node.
///
/// The behavior of any child nodes will be controlled by this node's [`AlignItems`] value.
///
/// The default behavior is [`AlignSelf::Auto`].
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#align-items-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum AlignSelf {
    /// Inherits the [`AlignItems`] behavior of the parent
    Auto,
    /// Items are packed toward the start of the cross axis
    FlexStart,
    /// Items are packed toward the end of the cross axis
    FlexEnd,
    /// Items are packed along the center of the cross axis
    Center,
    /// Items are aligned such as their baselines align
    Baseline,
    /// Distribute items evenly, but stretch them to fill the container
    Stretch,
}

impl Default for AlignSelf {
    fn default() -> Self {
        Self::Auto
    }
}

/// Sets the distribution of space between and around content items along the cross-axis
///
/// The default value is [`AlignContent::Stretch`].
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#align-content-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum AlignContent {
    /// Items are packed toward the start of the cross axis
    FlexStart,
    /// Items are packed toward the end of the cross axis
    FlexEnd,
    /// Items are packed along the center of the cross axis
    Center,
    /// Distribute items evenly, but stretch them to fill the container
    Stretch,
    /// Distribute items evenly, such that the first and last item are aligned with the edges
    SpaceBetween,
    /// Distribute items evenly,
    /// such that the space between items is the same as the space between the first and last item and the edges
    SpaceAround,
}

impl Default for AlignContent {
    fn default() -> Self {
        Self::Stretch
    }
}

/// Sets the layout used for the children of this node
///
/// [`Display::Flex`] is the default value.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum Display {
    /// The children will follow the flexbox layout algorithm
    #[cfg_attr(feature = "serde", serde(rename = "flex"))]
    Flex,
    /// The children will not be laid out, and will follow absolute positioning
    #[cfg_attr(feature = "serde", serde(rename = "none"))]
    None,
}

impl Default for Display {
    fn default() -> Self {
        Self::Flex
    }
}

/// The direction of the flexbox layout main axis.
///
/// There are always two perpendicular layout axes: main (or primary) and cross (or secondary).
/// Adding items will cause them to be positioned adjacent to each other along the main axis.
/// By varying this value throughout your tree, you can create complex axis-aligned layouts.
///
/// Items are always aligned relative to the cross axis, and justified relative to the main axis.
///
/// The default behavior is [`FlexDirection::Row`].
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#flex-direction-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum FlexDirection {
    /// Defines +x as the main axis
    ///
    /// Items will be added from left to right in a row.
    Row,
    /// Defines +y as the main axis
    ///
    /// Items will be added from top to bottom in a column.
    Column,
    /// Defines -x as the main axis
    ///
    /// Items will be added from right to left in a row.
    RowReverse,
    /// Defines -y as the main axis
    ///
    /// Items will be added from bottom to top in a column.
    ColumnReverse,
}

impl Default for FlexDirection {
    fn default() -> Self {
        Self::Row
    }
}

impl FlexDirection {
    #[inline]
    /// Is the direction [`FlexDirection::Row`] or [`FlexDirection::RowReverse`]?
    pub(crate) fn is_row(self) -> bool {
        matches!(self, Self::Row | Self::RowReverse)
    }

    #[inline]
    /// Is the direction [`FlexDirection::Column`] or [`FlexDirection::ColumnReverse`]?
    pub(crate) fn is_column(self) -> bool {
        matches!(self, Self::Column | Self::ColumnReverse)
    }

    #[inline]
    /// Is the direction [`FlexDirection::RowReverse`] or [`FlexDirection::ColumnReverse`]?
    pub(crate) fn is_reverse(self) -> bool {
        matches!(self, Self::RowReverse | Self::ColumnReverse)
    }
}

/// Sets the distribution of space between and around content items along the main-axis
///
/// The default value is [`JustifyContent::FlexStart`].
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#justify-content-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum JustifyContent {
    /// Items are packed toward the start of the main axis
    FlexStart,
    /// Items are packed toward the end of the main axis
    FlexEnd,
    /// Items are packed along the center of the main axis
    Center,
    /// Distribute items evenly, such that the first and last item are aligned with the edges
    SpaceBetween,
    /// Distribute items evenly,
    /// such that the space between items is twice same as the space between the first and last item and the edges
    SpaceAround,
    /// Distribute items evenly,
    /// such that the space between items is the same as the space between the first and last item and the edges
    SpaceEvenly,
}

impl Default for JustifyContent {
    fn default() -> Self {
        Self::FlexStart
    }
}

/// The positioning strategy for this item.
///
/// This controls both how the origin is determined for the [`Style::position`] field,
/// and whether or not the item will be controlled by flexbox's layout algorithm.
///
/// WARNING: this enum follows the behavior of [CSS's `position` property](https://developer.mozilla.org/en-US/docs/Web/CSS/position),
/// which can be unintuitive.
///
/// [`PositionType::Relative`] is the default value, in contrast to the default behavior in CSS.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum PositionType {
    /// The offset is computed relative to the final position given by the layout algorithm.
    /// Offsets do not affect the position of any other items; they are effectively a correction factor applied at the end.
    Relative,
    /// The offset is computed relative to this item's closest positioned ancestor, if any.
    /// Otherwise, it is placed relative to the origin.
    /// No space is created for the item in the page layout, and its size will not be altered.
    ///
    /// WARNING: to opt-out of layouting entirely, you must use [`Display::None`] instead on your [`Style`] object.
    Absolute,
}

impl Default for PositionType {
    fn default() -> Self {
        Self::Relative
    }
}

/// Controls whether flex items are forced onto one line or can wrap onto multiple lines.
///
/// Defaults to [`FlexWrap::NoWrap`]
///
/// [Specification](https://www.w3.org/TR/css-flexbox-1/#flex-wrap-property)
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum FlexWrap {
    /// Items will not wrap and stay on a single line
    NoWrap,
    /// Items will wrap according to this item's [`FlexDirection`]
    Wrap,
    /// Items will wrap in the oppposite direction to this item's [`FlexDirection`]
    WrapReverse,
}

impl Default for FlexWrap {
    fn default() -> Self {
        Self::NoWrap
    }
}

/// A unit of linear measurement
///
/// This is commonly combined with [`Rect`], [`Point`](crate::geometry::Point) and [`Size<T>`].
/// The default value is [`Dimension::Undefined`].
#[derive(Copy, Clone, PartialEq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum Dimension {
    /// The dimension is not given
    Undefined,
    /// The dimension should be automatically computed
    Auto,
    /// The dimension is stored in [points](https://en.wikipedia.org/wiki/Point_(typography))
    ///
    /// Each point is about 0.353 mm in size.
    Points(f32),
    /// The dimension is stored in percentage relative to the parent item.
    Percent(f32),
}

impl Default for Dimension {
    fn default() -> Self {
        Self::Undefined
    }
}

impl Dimension {
    /// Converts the given [`Dimension`] into a concrete value of points
    pub(crate) fn resolve(self, parent_dim: Number) -> Number {
        match self {
            Dimension::Points(points) => Number::Defined(points),
            Dimension::Percent(percent) => parent_dim * percent,
            _ => Number::Undefined,
        }
    }

    /// Is this value defined?
    pub(crate) fn is_defined(self) -> bool {
        matches!(self, Dimension::Points(_) | Dimension::Percent(_))
    }
}

impl Default for Rect<Dimension> {
    fn default() -> Self {
        Self { start: Default::default(), end: Default::default(), top: Default::default(), bottom: Default::default() }
    }
}

impl Default for Size<Dimension> {
    fn default() -> Self {
        Self { width: Dimension::Auto, height: Dimension::Auto }
    }
}

/// The flexbox layout information for a single [`Node`](crate::node::Node).
///
/// The most important idea in flexbox is the notion of a "main" and "cross" axis, which are always perpendicular to each other.
/// The orientation of these axes are controlled via the [`FlexDirection`] field of this struct.
///
/// This struct follows the [CSS equivalent](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flexible_Box_Layout/Basic_Concepts_of_Flexbox) directly;
/// information about the behavior on the web should transfer directly.
///
/// Detailed information about the exact behavior of each of these fields
/// can be found on [MDN](https://developer.mozilla.org/en-US/docs/Web/CSS) by searching for the field name.
/// The distinction between margin, padding and border is explained well in
/// this [introduction to the box model](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Box_Model/Introduction_to_the_CSS_box_model).
///
/// If the behavior does not match the flexbox layout algorithm on the web, please file a bug!
#[derive(Copy, Clone, PartialEq, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[cfg_attr(feature = "serde", serde(default))]
pub struct Style {
    /// What layout strategy should be used?
    pub display: Display,
    /// What should the `position` value of this struct use as a base offset?
    pub position_type: PositionType,
    /// Which direction does the main axis flow in?
    pub flex_direction: FlexDirection,
    /// Should elements wrap, or stay in a single line?
    pub flex_wrap: FlexWrap,
    /// How should items be aligned relative to the cross axis?
    pub align_items: AlignItems,
    /// Should this item violate the cross axis alignment specified by its parent's [`AlignItems`]?
    pub align_self: AlignSelf,
    /// How should content contained within this item be aligned relative to the cross axis?
    pub align_content: AlignContent,
    /// How should items be aligned relative to the main axis?
    pub justify_content: JustifyContent,
    /// How should the position of this element be tweaked relative to the layout defined?
    pub position: Rect<Dimension>,
    /// How large should the margin be on each side?
    pub margin: Rect<Dimension>,
    /// How large should the padding be on each side?
    pub padding: Rect<Dimension>,
    /// How large should the border be on each side?
    pub border: Rect<Dimension>,
    /// The relative rate at which this item grows when it is expanding to fill space
    ///
    /// 1.0 is the default value, and this value must be positive.
    pub flex_grow: f32,
    /// The relative rate at which this item shrinks when it is contracting to fit into space
    ///
    /// 1.0 is the default value, and this value must be positive.
    pub flex_shrink: f32,
    /// Sets the initial main axis size of the item
    pub flex_basis: Dimension,
    /// Sets the initial size of the item
    // TODO: why does this exist as distinct from flex_basis? How do they interact?
    pub size: Size<Dimension>,
    /// Controls the minimum size of the item
    pub min_size: Size<Dimension>,
    /// Controls the maximum size of the item
    pub max_size: Size<Dimension>,
    /// Sets the preferred aspect ratio for the item
    ///
    /// The ratio is calculated as width divided by height.
    pub aspect_ratio: Number,
}

impl Default for Style {
    fn default() -> Self {
        Self {
            display: Default::default(),
            position_type: Default::default(),
            flex_direction: Default::default(),
            flex_wrap: Default::default(),
            align_items: Default::default(),
            align_self: Default::default(),
            align_content: Default::default(),
            justify_content: Default::default(),
            position: Default::default(),
            margin: Default::default(),
            padding: Default::default(),
            border: Default::default(),
            flex_grow: 0.0,
            flex_shrink: 1.0,
            flex_basis: Dimension::Auto,
            size: Default::default(),
            min_size: Default::default(),
            max_size: Default::default(),
            aspect_ratio: Default::default(),
        }
    }
}

impl Style {
    /// If the `direction` is row-oriented, the min width. Otherwise the min height
    pub(crate) fn min_main_size(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.min_size.width
        } else {
            self.min_size.height
        }
    }

    /// If the `direction` is row-oriented, the max width. Otherwise the max height
    pub(crate) fn max_main_size(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.max_size.width
        } else {
            self.max_size.height
        }
    }

    /// If the `direction` is row-oriented, the margin start. Otherwise the margin top
    pub(crate) fn main_margin_start(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.margin.start
        } else {
            self.margin.top
        }
    }

    /// If the `direction` is row-oriented, the margin end. Otherwise the margin bottom
    pub(crate) fn main_margin_end(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.margin.end
        } else {
            self.margin.bottom
        }
    }

    /// If the `direction` is row-oriented, the height. Otherwise the width
    pub(crate) fn cross_size(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.size.height
        } else {
            self.size.width
        }
    }

    /// If the `direction` is row-oriented, the min height. Otherwise the min width
    pub(crate) fn min_cross_size(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.min_size.height
        } else {
            self.min_size.width
        }
    }

    /// If the `direction` is row-oriented, the max height. Otherwise the max width
    pub(crate) fn max_cross_size(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.max_size.height
        } else {
            self.max_size.width
        }
    }

    /// If the `direction` is row-oriented, the margin top. Otherwise the margin start
    pub(crate) fn cross_margin_start(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.margin.top
        } else {
            self.margin.start
        }
    }

    /// If the `direction` is row-oriented, the margin bottom. Otherwise the margin end
    pub(crate) fn cross_margin_end(&self, direction: FlexDirection) -> Dimension {
        if direction.is_row() {
            self.margin.bottom
        } else {
            self.margin.end
        }
    }

    /// Computes the final alignment of this item based on the parent's [`AlignItems`] and this item's [`AlignSelf`]
    pub(crate) fn align_self(&self, parent: &Style) -> AlignSelf {
        if self.align_self == AlignSelf::Auto {
            match parent.align_items {
                AlignItems::FlexStart => AlignSelf::FlexStart,
                AlignItems::FlexEnd => AlignSelf::FlexEnd,
                AlignItems::Center => AlignSelf::Center,
                AlignItems::Baseline => AlignSelf::Baseline,
                AlignItems::Stretch => AlignSelf::Stretch,
            }
        } else {
            self.align_self
        }
    }
}