//! A [Font Variations Table](

//! https://docs.microsoft.com/en-us/typography/opentype/spec/fvar) implementation.

use core::num::NonZeroU16;

use crate::parser::{Fixed, FromData, LazyArray16, Offset, Offset16, Stream, f32_bound};

use crate::{NormalizedCoordinate, Tag};

/// A [variation axis](https://docs.microsoft.com/en-us/typography/opentype/spec/fvar#variationaxisrecord).

#[repr(C)]

#[allow(missing_docs)]

#[derive(Clone, Copy, PartialEq, Debug)]

pub struct VariationAxis {

    pub tag: Tag,

    pub min_value: f32,

    pub def_value: f32,

    pub max_value: f32,

    /// An axis name in the `name` table.

    pub name_id: u16,

    pub hidden: bool,

}

impl FromData for VariationAxis {

    const SIZE: usize = 20;

    fn parse(data: &[u8]) -> Option<Self> {

        let mut s = Stream::new(data);

        let tag = s.read::<Tag>()?;

        let min_value = s.read::<Fixed>()?;

        let def_value = s.read::<Fixed>()?;

        let max_value = s.read::<Fixed>()?;

        let flags = s.read::<u16>()?;

        let name_id = s.read::<u16>()?;

        Some(VariationAxis {

            tag,

            min_value: def_value.0.min(min_value.0),

            def_value: def_value.0,

            max_value: def_value.0.max(max_value.0),

            name_id,

            hidden: flags & 1 == 1,

        })

    }

}

impl VariationAxis {

    /// Returns a normalized variation coordinate for this axis.

    pub(crate) fn normalized_value(&self, mut v: f32) -> NormalizedCoordinate {

        // Based on

        // https://docs.microsoft.com/en-us/typography/opentype/spec/avar#overview

        v = f32_bound(self.min_value, v, self.max_value);

        if v == self.def_value {

            v = 0.0;

        } else if v < self.def_value {

            v = (v - self.def_value) / (self.def_value - self.min_value);

        } else {

            v = (v - self.def_value) / (self.max_value - self.def_value);

        }

        NormalizedCoordinate::from(v)

    }

}

/// A [Font Variations Table](

/// https://docs.microsoft.com/en-us/typography/opentype/spec/fvar).

#[derive(Clone, Copy, Debug)]

pub struct Table<'a> {

    /// A list of variation axes.

    pub axes: LazyArray16<'a, VariationAxis>,

}

impl<'a> Table<'a> {

    /// Parses a table from raw data.

    pub fn parse(data: &'a [u8]) -> Option<Self> {

        let mut s = Stream::new(data);

        let version = s.read::<u32>()?;

        if version != 0x00010000 {

            return None;

        }

        let axes_array_offset = s.read::<Offset16>()?;

        s.skip::<u16>(); // reserved

        let axis_count = s.read::<u16>()?;

        // 'If axisCount is zero, then the font is not functional as a variable font,

        // and must be treated as a non-variable font;

        // any variation-specific tables or data is ignored.'

        let axis_count = NonZeroU16::new(axis_count)?;

        let mut s = Stream::new_at(data, axes_array_offset.to_usize())?;

        let axes = s.read_array16::<VariationAxis>(axis_count.get())?;

        Some(Table { axes })

    }

}