//! Page geometry and text-width estimation.
//!
//! We use approximate Helvetica metrics rather than pulling real AFM tables
//! or a font-shaping crate. The approximation slightly overcounts width so
//! we err on the side of shorter lines rather than clipping the right edge.

use printpdf::Mm;

pub(crate) const PAGE_W: Mm = Mm(148.0);
pub(crate) const PAGE_H: Mm = Mm(210.0);
pub(crate) const MARGIN: Mm = Mm(14.0);

pub(crate) const BODY_PT: f32 = 11.0;
pub(crate) const H1_PT: f32 = 20.0;
pub(crate) const H2_PT: f32 = 16.0;
pub(crate) const H3_PT: f32 = 13.0;
pub(crate) const MONO_PT: f32 = 10.0;

pub(crate) const LINE_GAP: f32 = 1.35;
pub(crate) const BLOCK_GAP_MM: f32 = 3.5;
pub(crate) const HEADING_GAP_MM: f32 = 5.5;
pub(crate) const LIST_INDENT_MM: f32 = 6.0;
pub(crate) const QUOTE_INDENT_MM: f32 = 5.0;

pub(crate) fn content_width_mm() -> f32 {
    PAGE_W.0 - MARGIN.0 * 2.0
}

pub(crate) fn content_top_mm() -> f32 {
    PAGE_H.0 - MARGIN.0
}

pub(crate) fn content_bottom_mm() -> f32 {
    MARGIN.0
}

/// Approximate width in mm of `text` rendered in Helvetica at `pt`.
///
/// Uses a per-family average advance width of 0.52em (bold slightly wider).
/// 1pt = 25.4/72 mm.
pub(crate) fn text_width_mm(text: &str, pt: f32, bold: bool, mono: bool) -> f32 {
    let avg_em = if mono {
        0.60
    } else if bold {
        0.56
    } else {
        0.52
    };
    let mm_per_pt = 25.4 / 72.0;
    text.chars().count() as f32 * pt * avg_em * mm_per_pt
}

pub(crate) fn line_height_mm(pt: f32) -> f32 {
    pt * LINE_GAP * 25.4 / 72.0
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn width_grows_with_length_and_size() {
        let a = text_width_mm("hello", BODY_PT, false, false);
        let b = text_width_mm("hello world", BODY_PT, false, false);
        let c = text_width_mm("hello", H1_PT, false, false);
        assert!(b > a);
        assert!(c > a);
    }

    #[test]
    fn bold_wider_than_regular() {
        let r = text_width_mm("hello", BODY_PT, false, false);
        let b = text_width_mm("hello", BODY_PT, true, false);
        assert!(b > r);
    }
}