use core::convert::TryFrom;

use crate::GlyphId;

use crate::parser::{FromData, LazyArray32, Stream};

#[derive(Clone, Copy)]

pub struct SequentialMapGroup {

    pub start_char_code: u32,

    pub end_char_code: u32,

    pub start_glyph_id: u32,

}

impl FromData for SequentialMapGroup {

    const SIZE: usize = 12;

    #[inline]

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

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

        Some(SequentialMapGroup {

            start_char_code: s.read::<u32>()?,

            end_char_code: s.read::<u32>()?,

            start_glyph_id: s.read::<u32>()?,

        })

    }

}

/// A [format 12](https://docs.microsoft.com/en-us/typography/opentype/spec/cmap#format-12-segmented-coverage)

/// subtable.

#[derive(Clone, Copy)]

pub struct Subtable12<'a> {

    groups: LazyArray32<'a, SequentialMapGroup>,

}

impl<'a> Subtable12<'a> {

    /// Parses a subtable from raw data.

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

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

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

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

        s.skip::<u32>(); // length

        s.skip::<u32>(); // language

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

        let groups = s.read_array32::<SequentialMapGroup>(count)?;

        Some(Self { groups })

    }

    /// Returns a glyph index for a code point.

    pub fn glyph_index(&self, code_point: u32) -> Option<GlyphId> {

        let (_, group) = self.groups.binary_search_by(|range| {

            use core::cmp::Ordering;

            if range.start_char_code > code_point {

                Ordering::Greater

            } else if range.end_char_code < code_point {

                Ordering::Less

            } else {

                Ordering::Equal

            }

        })?;

        let id = group

            .start_glyph_id

            .checked_add(code_point)?

            .checked_sub(group.start_char_code)?;

        u16::try_from(id).ok().map(GlyphId)

    }

    /// Iterate over each codepoint defined in this table.

    pub fn codepoints_iter(self) -> impl Iterator<Item = u32> + 'a {

        self.groups

            .into_iter()

            .flat_map(|group| group.start_char_code..=group.end_char_code)

    }

    /// Calls `f` for each codepoint defined in this table.

    pub fn codepoints(&self, f: impl FnMut(u32)) {

        self.codepoints_iter().for_each(f)

    }

}

impl core::fmt::Debug for Subtable12<'_> {

    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {

        write!(f, "Subtable12 {{ ... }}")

    }

}