//! `head` — Font Header table.
//!
//! Contains global font metrics and flags.
//! Reference: <https://learn.microsoft.com/en-us/typography/opentype/spec/head>

use crate::font::parse::Reader;
use crate::font::FontError;

/// Parsed `head` table.
#[derive(Debug)]
pub struct HeadTable {
    /// Major version (should be 1).
    pub major_version: u16,
    /// Minor version (should be 0).
    pub minor_version: u16,
    /// Font revision (fixed-point 16.16).
    pub font_revision: i32,
    /// Units per em (typically 1000 or 2048).
    pub units_per_em: u16,
    /// Bounding box: minimum x.
    pub x_min: i16,
    /// Bounding box: minimum y.
    pub y_min: i16,
    /// Bounding box: maximum x.
    pub x_max: i16,
    /// Bounding box: maximum y.
    pub y_max: i16,
    /// Mac style flags (bit 0 = bold, bit 1 = italic).
    pub mac_style: u16,
    /// Smallest readable size in pixels.
    pub lowest_rec_ppem: u16,
    /// 0 = short offsets in loca, 1 = long offsets.
    pub index_to_loc_format: i16,
}

impl HeadTable {
    /// Parse the `head` table from raw bytes.
    pub fn parse(data: &[u8]) -> Result<HeadTable, FontError> {
        let r = Reader::new(data);
        // Minimum head table size is 54 bytes.
        if r.len() < 54 {
            return Err(FontError::MalformedTable("head"));
        }

        let major_version = r.u16(0)?;
        let minor_version = r.u16(2)?;
        let font_revision = r.i32(4)?;
        // skip checksumAdjustment(4) + magicNumber(4) + flags(2)
        let units_per_em = r.u16(18)?;
        // skip created(8) + modified(8)
        let x_min = r.i16(36)?;
        let y_min = r.i16(38)?;
        let x_max = r.i16(40)?;
        let y_max = r.i16(42)?;
        let mac_style = r.u16(44)?;
        let lowest_rec_ppem = r.u16(46)?;
        // skip fontDirectionHint(2)
        let index_to_loc_format = r.i16(50)?;

        Ok(HeadTable {
            major_version,
            minor_version,
            font_revision,
            units_per_em,
            x_min,
            y_min,
            x_max,
            y_max,
            mac_style,
            lowest_rec_ppem,
            index_to_loc_format,
        })
    }
}