//! Macros to define CSS properties.

use crate::properties::ComputedValues;

/// Trait which all CSS property types should implement.

pub trait Property {

    /// Whether the property's computed value inherits from parent to child elements.

    ///

    /// For each property, the CSS or SVG specs say whether the property inherits

    /// automatically.  When a property is not specified in an element, the return value

    /// of this method determines whether the property's value is copied from the parent

    /// element (`true`), or whether it resets to the initial/default value (`false`).

    fn inherits_automatically() -> bool;

    /// Derive the CSS computed value from the parent element's

    /// [`ComputedValues`][crate::properties::ComputedValues] and the

    /// `self` value.

    ///

    /// The CSS or SVG specs say how to derive this for each property.

    fn compute(&self, _: &ComputedValues) -> Self;

}

/// Generates a type for a CSS property.

///

/// Writing a property by hand takes a bit of boilerplate:

///

/// * Define a type to represent the property's values.

///

/// * A [`Parse`] implementation to parse the property.

///

/// * A [`Default`] implementation to define the property's *initial* value.

///

/// * A [`Property`] implementation to define whether the property

/// inherits from the parent element, and how the property derives its

/// computed value.

///

/// When going from [`SpecifiedValues`] to [`ComputedValues`],

/// properties which inherit automatically from the parent element

/// will just have their values cloned.  Properties which do not

/// inherit will be reset back to their initial value (i.e. their

/// [`Default`]).

///

/// The default implementation of [`Property::compute()`] is to just

/// clone the property's value.  Properties which need more

/// sophisticated computation can override this.

///

/// This macro allows defining properties of different kinds; see the following

/// sections for examples.

///

/// # Simple identifiers

///

/// Many properties are just sets of identifiers and can be represented

/// by simple enums.  In this case, you can use the following:

///

/// ```text

/// make_property!(

///   /// Documentation here.

///   StrokeLinejoin,

///   default: Miter,

///   inherits_automatically: true,

///

///   identifiers:

///     "miter" => Miter,

///     "round" => Round,

///     "bevel" => Bevel,

/// );

/// ```

///

/// This generates a simple enum like the following, with implementations of [`Parse`],

/// [`Default`], and [`Property`].

///

/// ```

/// pub enum StrokeLinejoin { Miter, Round, Bevel }

/// ```

///

/// # Properties from an existing, general-purpose type

///

/// For example, both the `lightingColor` and `floodColor` properties can be represented

/// with a `cssparser::Color`, but their intial values are different.  In this case, the macro

/// can generate a newtype around `cssparser::Color` for each case:

///

/// ```text

/// make_property!(

///     /// Documentation here.

///     FloodColor,

///     default: cssparser::Color::RGBA(cssparser::RGBA::new(0, 0, 0, 0)),

///     inherits_automatically: false,

///     newtype_parse: cssparser::Color,

/// );

/// ```

///

/// # Properties from custom specific types

///

/// For example, font-related properties have custom, complex types that require an

/// implentation of `Property::compute` that is more than a simple `clone`.  In this case,

/// define the custom type separately, and use the macro to specify the default value and

/// the `Property` implementation.

///

/// [`Parse`]: crate::parsers::Parse

/// [`Property`]: crate::property_macros::Property

/// [`ComputedValues`]: crate::properties::ComputedValues

/// [`SpecifiedValues`]: crate::properties::SpecifiedValues

/// [`Property::compute()`]: crate::property_macros::Property::compute

///

#[doc(hidden)]

#[macro_export]

macro_rules! make_property {

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: ident,

     inherits_automatically: $inherits_automatically: expr,

     identifiers:

     $($str_prop: expr => $variant: ident,)+

    ) => {

        $(#[$attr])*

        #[repr(C)]

        pub enum $name {

            $($variant),+

        }

        impl_default!($name, $name::$default);

        impl_property!($name, $inherits_automatically);

        impl $crate::parsers::Parse for $name {

                    parser,

                    $($str_prop => $name::$variant,)+

        }

    };

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: ident,

     identifiers: { $($str_prop: expr => $variant: ident,)+ },

     property_impl: { $prop: item }

    ) => {

        $(#[$attr])*

        #[repr(C)]

        pub enum $name {

            $($variant),+

        }

        impl_default!($name, $name::$default);

        $prop

        impl $crate::parsers::Parse for $name {

                    parser,

                    $($str_prop => $name::$variant,)+

        }

    };

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: expr,

     inherits_automatically: $inherits_automatically: expr,

     newtype_parse: $type: ty,

    ) => {

        $(#[$attr])*

        impl_default!($name, $name($default));

        impl_property!($name, $inherits_automatically);

        impl $crate::parsers::Parse for $name {

        }

    };

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: expr,

     property_impl: { $prop: item }

    ) => {

        impl_default!($name, $default);

        $prop

    };

    ($name: ident,

     default: $default: expr,

     inherits_automatically: $inherits_automatically: expr,

    ) => {

        impl_default!($name, $default);

        impl_property!($name, $inherits_automatically);

    };

    ($name: ident,

     default: $default: expr,

     inherits_automatically: $inherits_automatically: expr,

     parse_impl: { $parse: item }

    ) => {

        impl_default!($name, $default);

        impl_property!($name, $inherits_automatically);

        $parse

    };

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: expr,

     newtype: $type: ty,

     property_impl: { $prop: item },

     parse_impl: { $parse: item }

    ) => {

        $(#[$attr])*

        impl_default!($name, $name($default));

        $prop

        $parse

    };

    // pending - only XmlLang

    ($(#[$attr:meta])*

     $name: ident,

     default: $default: expr,

     inherits_automatically: $inherits_automatically: expr,

     newtype: $type: ty,

     parse_impl: { $parse: item },

    ) => {

        $(#[$attr])*

        impl_default!($name, $name($default));

        impl_property!($name, $inherits_automatically);

        $parse

    };

    ($(#[$attr:meta])*

     $name: ident,

     inherits_automatically: $inherits_automatically: expr,

     fields: {

       $($field_name: ident : $field_type: ty, default: $field_default : expr,)+

     }

     parse_impl: { $parse: item }

    ) => {

        $(#[$attr])*

        pub struct $name {

        }

        impl_default!($name, $name { $($field_name: $field_default),+ });

        impl_property!($name, $inherits_automatically);

        $parse

    };

}

#[doc(hidden)]

#[macro_export]

macro_rules! impl_default {

    ($name:ident, $default:expr) => {

        impl Default for $name {

                $default

        }

    };

}

#[doc(hidden)]

#[macro_export]

macro_rules! impl_property {

    ($name:ident, $inherits_automatically:expr) => {

        impl $crate::property_macros::Property for $name {

                $inherits_automatically

        }

    };

}