write_labels.rs

//! Writes a sheet of peel-off labels: a grid of shelf labels, each carrying an
//! article name, its price, and the article number a till reads, closed by a
//! row of warehouse bin labels.
//!
//! This is the sheet a shop prints by the ream. The grid is driven by a stock
//! description — how many labels across and down, how big one is, and how far
//! apart their corners sit — so a reader retargets the sheet to their own
//! die-cut stock by changing six numbers. Every label is outlined and the page
//! margins carry cut marks, so what is drawn lines up with what is cut.
//!
//! Whether the codes scan is not for the page to say, and not for an eye: a
//! scanner says. `scripts/check_barcode.sh` points a decoder at the rendered
//! sheet and reads back every article number and every bin.
//!
//! Every word the page draws is held in `Words`, once per language, and
//! `HQF_PDF_LANG` picks which one is drawn. The prices, the article numbers,
//! the aisle and rack codes and what a scanner reads off the sheet are the same
//! in both.
//!
//! Usage: `cargo run --example write_labels -- tmp/labels.pdf [font.ttf]`
//!        `HQF_PDF_LANG=fr cargo run --example write_labels -- tmp/etiquettes.pdf`

use std::env;
use std::error::Error;
use std::fs;
use std::path::{Path, PathBuf};

use hqf_pdf::barcode::QUIET_ZONE as BAR_QUIET_ZONE;
use hqf_pdf::content::Content;
use hqf_pdf::cos::Name;
use hqf_pdf::datamatrix::QUIET_ZONE as MATRIX_QUIET_ZONE;
use hqf_pdf::{DataMatrix, Document, Ean13, Font, FontHandle, Page, Rgb, UpcA};

#[path = "shared/out.rs"]
mod out;

#[path = "shared/licence.rs"]
mod licence;

#[path = "shared/language.rs"]
mod language;

#[path = "shared/failure.rs"]
mod failure;

use language::Language;

/// The font the example draws with when none is given on the command line.
fn default_font() -> PathBuf {
    Path::new(env!("CARGO_MANIFEST_DIR"))
        .join("tests")
        .join("fonts")
        .join("DejaVuSans.ttf")
}

/// A4, in points.
const PAGE_WIDTH: f64 = 595.276;
const PAGE_HEIGHT: f64 = 841.89;

/// The die-cut stock the sheet is laid out for: how many labels across and
/// down, how big one is, and how far apart two neighbours' corners sit. The
/// pitch is the label plus the gutter the cutter leaves between two of them.
const COLUMNS: u32 = 3;
const ROWS: u32 = 5;
const LABEL_WIDTH: f64 = 170.0;
const LABEL_HEIGHT: f64 = 120.0;
const COLUMN_PITCH: f64 = 178.0;
const ROW_PITCH: f64 = 128.0;

/// The top edge of the first row of labels.
const SHEET_TOP: f64 = 742.0;

/// How long a cut mark is and how far it stands off the grid, in points.
const MARK_LENGTH: f64 = 11.0;
const MARK_OFFSET: f64 = 5.0;

/// The width of the narrowest bar, in points, and the side of one Data Matrix
/// module. Everything else in a code is a whole number of these.
const MODULE: f64 = 1.0;
const MATRIX_MODULE: f64 = 3.0;

/// The ink the prices are drawn in, the grey of the small print, and the black
/// the names and the codes are drawn in.
const ACCENT: Rgb = Rgb {
    r: 0.11,
    g: 0.33,
    b: 0.55,
};
const MUTED: Rgb = Rgb {
    r: 0.42,
    g: 0.42,
    b: 0.45,
};
const INK: Rgb = Rgb {
    r: 0.1,
    g: 0.1,
    b: 0.12,
};

/// The symbology an article number is drawn in, holding the digits without
/// their check digit.
enum Article {
    /// Twelve digits, drawn as an EAN-13 barcode.
    Ean13(&'static str),
    /// Eleven digits, drawn as a UPC-A barcode.
    UpcA(&'static str),
}

/// How many labels the sheet prints.
const LABEL_COUNT: usize = 15;

/// What a label carries under its name, apart from the words it is written in.
enum Face {
    /// A shelf label: the price of one pack, and the article number the till
    /// reads.
    Shelf { price: f64, article: Article },
    /// A bin label: where in the warehouse the stock stands, and the code a
    /// picker scans on arriving there.
    Bin {
        positions: [&'static str; 3],
        code: &'static str,
    },
}

/// The faces the sheet prints, in reading order: the grid fills across a row
/// before dropping to the next, and `Words::names` names them in that order.
const LABELS: [Face; LABEL_COUNT] = [
    Face::Shelf {
        price: 18.90,
        article: Article::Ean13("347000100013"),
    },
    Face::Shelf {
        price: 11.90,
        article: Article::Ean13("347000100020"),
    },
    Face::Shelf {
        price: 2.40,
        article: Article::Ean13("347000100037"),
    },
    Face::Shelf {
        price: 6.90,
        article: Article::Ean13("347000100044"),
    },
    Face::Shelf {
        price: 2.45,
        article: Article::Ean13("347000100051"),
    },
    Face::Shelf {
        price: 3.20,
        article: Article::Ean13("347000100068"),
    },
    Face::Shelf {
        price: 8.90,
        article: Article::Ean13("347000100075"),
    },
    Face::Shelf {
        price: 5.90,
        article: Article::Ean13("347000100082"),
    },
    Face::Shelf {
        price: 3.90,
        article: Article::Ean13("347000100099"),
    },
    Face::Shelf {
        price: 4.60,
        article: Article::Ean13("347000100105"),
    },
    Face::Shelf {
        price: 1.90,
        article: Article::Ean13("347000100112"),
    },
    Face::Shelf {
        price: 6.90,
        article: Article::Ean13("347000100129"),
    },
    Face::Shelf {
        price: 9.90,
        article: Article::UpcA("01234567890"),
    },
    Face::Bin {
        positions: ["A12", "R04", "S03"],
        code: "LOC:A12-R04-S03",
    },
    Face::Bin {
        positions: ["B07", "R11", "S02"],
        code: "LOC:B07-R11-S02",
    },
];

/// Every word the page draws, in one language.
///
/// What is not language stays out of it: the prices, the article numbers, the
/// aisle and rack codes and what the sheet is laid out for are drawn from
/// constants of their own and read the same in every language.
#[derive(Debug)]
struct Words {
    /// The words the document's title is built from.
    title: &'static str,
    /// The words set at the head of the sheet, over the grid.
    heading: &'static str,
    /// Which sheet of the run this one is.
    sheet_number: &'static str,
    /// What the labels are counted in, and what stands either side of the size
    /// of one, in the line under the heading.
    labels: &'static str,
    stock_before: &'static str,
    stock_after: &'static str,
    /// What stands before the day the sheet was printed, and that day.
    printed_label: &'static str,
    printed_on: &'static str,
    /// What each label names, in the order `LABELS` prints them.
    names: [&'static str; LABEL_COUNT],
    /// The line under each name: what one pack holds and what it comes to by
    /// weight or by volume, and, on a bin label, what the code beneath it is.
    subtitles: [&'static str; LABEL_COUNT],
    /// What stands before each of a bin label's three position codes.
    positions: [&'static str; 3],
    /// The sentence at the foot of the sheet, cut where the day the prices hold
    /// until goes into it.
    valid_before: &'static str,
    valid_until: &'static str,
}

impl Words {
    /// The words the sheet is written in, in `language`.
    fn of(language: Language) -> &'static Self {
        language::pick(&WORDS, language)
    }
}

/// The sheet in English.
const ENGLISH: Words = Words {
    title: "Shelf label sheet, 3 × 5 die-cut",
    heading: "SHELF LABELS",
    sheet_number: "Sheet 3 of 8",
    labels: "labels",
    stock_before: "on",
    stock_after: "pt die-cut stock",
    printed_label: "Printed",
    printed_on: "20 July 2026",
    names: [
        "Espresso beans, whole",
        "Olive oil, extra virgin",
        "Sea salt, coarse",
        "Basmati rice",
        "Dark chocolate, 70 %",
        "Orange juice, pressed",
        "Wildflower honey",
        "Green tea, loose leaf",
        "Sparkling water",
        "Sunflower seed oil",
        "Wholegrain pasta",
        "Roasted almonds",
        "Maple syrup, imported",
        "Dry goods reserve",
        "Chilled reserve",
    ],
    subtitles: [
        "1 kg pack · 18.90 EUR/kg",
        "750 ml bottle · 15.87 EUR/l",
        "1 kg pack · 2.40 EUR/kg",
        "2 kg pack · 3.45 EUR/kg",
        "100 g bar · 24.50 EUR/kg",
        "1 l carton · 3.20 EUR/l",
        "500 g jar · 17.80 EUR/kg",
        "125 g tin · 47.20 EUR/kg",
        "6 × 1 l · 0.65 EUR/l",
        "1 l bottle · 4.60 EUR/l",
        "500 g pack · 3.80 EUR/kg",
        "250 g pack · 27.60 EUR/kg",
        "250 ml bottle · 39.60 EUR/l",
        "BIN LOCATION",
        "BIN LOCATION",
    ],
    positions: ["Aisle", "Rack", "Shelf"],
    valid_before: "Prices valid until",
    valid_until: "31 August 2026",
};

/// The sheet in French.
const FRENCH: Words = Words {
    title: "Planche d’étiquettes de rayon, prédécoupée 3 × 5",
    heading: "ÉTIQUETTES DE RAYON",
    sheet_number: "Feuille 3 sur 8",
    labels: "étiquettes",
    stock_before: "sur planche prédécoupée",
    stock_after: "pt",
    printed_label: "Imprimée le",
    printed_on: "20 juillet 2026",
    names: [
        "Café en grains, espresso",
        "Huile d’olive vierge extra",
        "Gros sel de mer",
        "Riz basmati",
        "Chocolat noir 70 %",
        "Jus d’orange pressé",
        "Miel toutes fleurs",
        "Thé vert en vrac",
        "Eau gazeuse",
        "Huile de tournesol",
        "Pâtes complètes",
        "Amandes grillées",
        "Sirop d’érable importé",
        "Réserve épicerie sèche",
        "Réserve froid positif",
    ],
    subtitles: [
        "sachet de 1 kg · 18.90 EUR/kg",
        "bouteille de 750 ml · 15.87 EUR/l",
        "sachet de 1 kg · 2.40 EUR/kg",
        "sachet de 2 kg · 3.45 EUR/kg",
        "tablette de 100 g · 24.50 EUR/kg",
        "brique de 1 l · 3.20 EUR/l",
        "pot de 500 g · 17.80 EUR/kg",
        "boîte de 125 g · 47.20 EUR/kg",
        "pack de 6 × 1 l · 0.65 EUR/l",
        "bouteille de 1 l · 4.60 EUR/l",
        "paquet de 500 g · 3.80 EUR/kg",
        "sachet de 250 g · 27.60 EUR/kg",
        "bouteille de 250 ml · 39.60 EUR/l",
        "EMPLACEMENT",
        "EMPLACEMENT",
    ],
    positions: ["Allée", "Travée", "Étagère"],
    valid_before: "Prix valables jusqu’au",
    valid_until: "31 août 2026",
};

/// The sheet in Dutch.
const DUTCH: Words = Words {
    title: "Blad schapetiketten, 3 × 5 gestanst",
    heading: "SCHAPETIKETTEN",
    sheet_number: "Blad 3 van 8",
    labels: "etiketten",
    stock_before: "op",
    stock_after: "pt gestanst materiaal",
    printed_label: "Gedrukt",
    printed_on: "20 juli 2026",
    names: [
        "Espressobonen, heel",
        "Olijfolie, extra vergine",
        "Zeezout, grof",
        "Basmatirijst",
        "Pure chocolade, 70 %",
        "Sinaasappelsap, geperst",
        "Bloemenhoning",
        "Groene thee, los",
        "Bruiswater",
        "Zonnebloemolie",
        "Volkorenpasta",
        "Geroosterde amandelen",
        "Ahornsiroop, geïmporteerd",
        "Voorraad droog",
        "Voorraad gekoeld",
    ],
    subtitles: [
        "Pak van 1 kg · 18,90 EUR/kg",
        "Fles van 750 ml · 15,87 EUR/l",
        "Pak van 1 kg · 2,40 EUR/kg",
        "Pak van 2 kg · 3,45 EUR/kg",
        "Reep van 100 g · 24,50 EUR/kg",
        "Pak van 1 l · 3,20 EUR/l",
        "Pot van 500 g · 17,80 EUR/kg",
        "Blik van 125 g · 47,20 EUR/kg",
        "6 × 1 l · 0,65 EUR/l",
        "Fles van 1 l · 4,60 EUR/l",
        "Pak van 500 g · 3,80 EUR/kg",
        "Pak van 250 g · 27,60 EUR/kg",
        "Fles van 250 ml · 39,60 EUR/l",
        "LOCATIE",
        "LOCATIE",
    ],
    positions: ["Gang", "Stelling", "Plank"],
    valid_before: "Prijzen geldig tot",
    valid_until: "31 augustus 2026",
};

/// The sheet in Portuguese.
const PORTUGUESE: Words = Words {
    title: "Folha de etiquetas de prateleira, cortada 3 × 5",
    heading: "ETIQUETAS DE PRATELEIRA",
    sheet_number: "Folha 3 de 8",
    labels: "etiquetas",
    stock_before: "em",
    stock_after: "pt de suporte pré-cortado",
    printed_label: "Impresso",
    printed_on: "20 de julho de 2026",
    names: [
        "Café em grão",
        "Azeite virgem extra",
        "Sal marinho grosso",
        "Arroz basmati",
        "Chocolate negro, 70 %",
        "Sumo de laranja espremido",
        "Mel multifloral",
        "Chá verde a granel",
        "Água com gás",
        "Óleo de girassol",
        "Massa integral",
        "Amêndoas torradas",
        "Xarope de ácer, importado",
        "Reserva de secos",
        "Reserva refrigerada",
    ],
    subtitles: [
        "Pacote de 1 kg · 18,90 EUR/kg",
        "Garrafa de 750 ml · 15,87 EUR/l",
        "Pacote de 1 kg · 2,40 EUR/kg",
        "Pacote de 2 kg · 3,45 EUR/kg",
        "Tablete de 100 g · 24,50 EUR/kg",
        "Pacote de 1 l · 3,20 EUR/l",
        "Frasco de 500 g · 17,80 EUR/kg",
        "Lata de 125 g · 47,20 EUR/kg",
        "6 × 1 l · 0,65 EUR/l",
        "Garrafa de 1 l · 4,60 EUR/l",
        "Pacote de 500 g · 3,80 EUR/kg",
        "Pacote de 250 g · 27,60 EUR/kg",
        "Garrafa de 250 ml · 39,60 EUR/l",
        "LOCALIZAÇÃO",
        "LOCALIZAÇÃO",
    ],
    positions: ["Corredor", "Estante", "Prateleira"],
    valid_before: "Preços válidos até",
    valid_until: "31 de agosto de 2026",
};

/// The sheet in Italian.
const ITALIAN: Words = Words {
    title: "Foglio di etichette da scaffale, fustellato 3 × 5",
    heading: "ETICHETTE DA SCAFFALE",
    sheet_number: "Foglio 3 di 8",
    labels: "etichette",
    stock_before: "su",
    stock_after: "pt di supporto fustellato",
    printed_label: "Stampato",
    printed_on: "20 luglio 2026",
    names: [
        "Caffè in grani",
        "Olio extravergine di oliva",
        "Sale marino grosso",
        "Riso basmati",
        "Cioccolato fondente, 70 %",
        "Succo d’arancia spremuto",
        "Miele millefiori",
        "Tè verde sfuso",
        "Acqua frizzante",
        "Olio di semi di girasole",
        "Pasta integrale",
        "Mandorle tostate",
        "Sciroppo d’acero, importato",
        "Scorta secchi",
        "Scorta refrigerata",
    ],
    subtitles: [
        "Confezione da 1 kg · 18,90 EUR/kg",
        "Bottiglia da 750 ml · 15,87 EUR/l",
        "Confezione da 1 kg · 2,40 EUR/kg",
        "Confezione da 2 kg · 3,45 EUR/kg",
        "Tavoletta da 100 g · 24,50 EUR/kg",
        "Brick da 1 l · 3,20 EUR/l",
        "Vasetto da 500 g · 17,80 EUR/kg",
        "Latta da 125 g · 47,20 EUR/kg",
        "6 × 1 l · 0,65 EUR/l",
        "Bottiglia da 1 l · 4,60 EUR/l",
        "Confezione da 500 g · 3,80 EUR/kg",
        "Confezione da 250 g · 27,60 EUR/kg",
        "Bottiglia da 250 ml · 39,60 EUR/l",
        "UBICAZIONE",
        "UBICAZIONE",
    ],
    positions: ["Corsia", "Scaffale", "Ripiano"],
    valid_before: "Prezzi validi fino al",
    valid_until: "31 agosto 2026",
};

/// The sheet in Spanish.
const SPANISH: Words = Words {
    title: "Hoja de etiquetas de estante, troquelada 3 × 5",
    heading: "ETIQUETAS DE ESTANTE",
    sheet_number: "Hoja 3 de 8",
    labels: "etiquetas",
    stock_before: "en",
    stock_after: "pt de soporte troquelado",
    printed_label: "Impreso",
    printed_on: "20 de julio de 2026",
    names: [
        "Café en grano",
        "Aceite de oliva virgen extra",
        "Sal marina gruesa",
        "Arroz basmati",
        "Chocolate negro, 70 %",
        "Zumo de naranja exprimido",
        "Miel de milflores",
        "Té verde a granel",
        "Agua con gas",
        "Aceite de girasol",
        "Pasta integral",
        "Almendras tostadas",
        "Sirope de arce, importado",
        "Reserva de secos",
        "Reserva refrigerada",
    ],
    subtitles: [
        "Paquete de 1 kg · 18,90 EUR/kg",
        "Botella de 750 ml · 15,87 EUR/l",
        "Paquete de 1 kg · 2,40 EUR/kg",
        "Paquete de 2 kg · 3,45 EUR/kg",
        "Tableta de 100 g · 24,50 EUR/kg",
        "Brik de 1 l · 3,20 EUR/l",
        "Tarro de 500 g · 17,80 EUR/kg",
        "Lata de 125 g · 47,20 EUR/kg",
        "6 × 1 l · 0,65 EUR/l",
        "Botella de 1 l · 4,60 EUR/l",
        "Paquete de 500 g · 3,80 EUR/kg",
        "Paquete de 250 g · 27,60 EUR/kg",
        "Botella de 250 ml · 39,60 EUR/l",
        "UBICACIÓN",
        "UBICACIÓN",
    ],
    positions: ["Pasillo", "Estantería", "Balda"],
    valid_before: "Precios válidos hasta el",
    valid_until: "31 de agosto de 2026",
};

/// The sheet in German.
const GERMAN: Words = Words {
    title: "Bogen mit Regaletiketten, 3 × 5 gestanzt",
    heading: "REGALETIKETTEN",
    sheet_number: "Bogen 3 von 8",
    labels: "Etiketten",
    stock_before: "auf",
    stock_after: "pt Stanzmaterial",
    printed_label: "Gedruckt",
    printed_on: "20. Juli 2026",
    names: [
        "Espressobohnen, ganz",
        "Olivenöl, nativ extra",
        "Meersalz, grob",
        "Basmatireis",
        "Zartbitterschokolade, 70 %",
        "Orangensaft, gepresst",
        "Wildblütenhonig",
        "Grüner Tee, lose",
        "Mineralwasser mit Kohlensäure",
        "Sonnenblumenöl",
        "Vollkornnudeln",
        "Geröstete Mandeln",
        "Ahornsirup, importiert",
        "Reserve Trockenwaren",
        "Reserve Kühlware",
    ],
    subtitles: [
        "1-kg-Packung · 18,90 EUR/kg",
        "750-ml-Flasche · 15,87 EUR/l",
        "1-kg-Packung · 2,40 EUR/kg",
        "2-kg-Packung · 3,45 EUR/kg",
        "100-g-Tafel · 24,50 EUR/kg",
        "1-l-Karton · 3,20 EUR/l",
        "500-g-Glas · 17,80 EUR/kg",
        "125-g-Dose · 47,20 EUR/kg",
        "6 × 1 l · 0,65 EUR/l",
        "1-l-Flasche · 4,60 EUR/l",
        "500-g-Packung · 3,80 EUR/kg",
        "250-g-Packung · 27,60 EUR/kg",
        "250-ml-Flasche · 39,60 EUR/l",
        "LAGERPLATZ",
        "LAGERPLATZ",
    ],
    positions: ["Gang", "Regal", "Fach"],
    valid_before: "Preise gültig bis",
    valid_until: "31. August 2026",
};

/// Every language the example is written in. A language is added by writing its
/// own set of words and naming it here.
static WORDS: [(Language, &Words); 7] = [
    (Language::English, &ENGLISH),
    (Language::French, &FRENCH),
    (Language::German, &GERMAN),
    (Language::Spanish, &SPANISH),
    (Language::Italian, &ITALIAN),
    (Language::Portuguese, &PORTUGUESE),
    (Language::Dutch, &DUTCH),
];

/// The left edge of the first column, which is what centres the grid on the
/// page.
fn sheet_left() -> f64 {
    (PAGE_WIDTH - f64::from(COLUMNS - 1).mul_add(COLUMN_PITCH, LABEL_WIDTH)) / 2.0
}

/// The last digit of an EAN-13 or UPC-A number: the one that makes the weighted
/// sum of the whole a multiple of ten. Read from the right, the digit just
/// before it weighs three and the weights alternate from there.
fn check_digit(digits: &str) -> u32 {
    let weighted: u32 = digits
        .chars()
        .rev()
        .enumerate()
        .filter_map(|(index, digit)| {
            digit
                .to_digit(10)
                .map(|value| if index % 2 == 0 { value * 3 } else { value })
        })
        .sum();
    (10 - weighted % 10) % 10
}

/// The number as it is printed under the bars: the digits given, followed by
/// the check digit they imply.
fn full_number(digits: &str) -> String {
    format!("{digits}{}", check_digit(digits))
}

/// A price, as a shelf label writes it: "18.90 EUR".
fn price_text(value: f64) -> String {
    format!("{value:.2} EUR")
}

/// Draws a line of text, left-aligned, in a colour of its own.
fn text(content: &mut Content, font: &FontHandle, size: f64, x: f64, y: f64, color: Rgb, s: &str) {
    let _ = content.set_fill(color);
    content.begin_text();
    let _ = content.set_font(font, size);
    let _ = content.text_origin(x, y);
    content.show_glyphs(&font.glyphs(s));
    content.end_text();
}

/// Draws a line of text whose right edge sits at `right`.
fn text_right(
    content: &mut Content,
    font: &FontHandle,
    size: f64,
    right: f64,
    y: f64,
    color: Rgb,
    s: &str,
) {
    text(
        content,
        font,
        size,
        right - font.measure(s, size),
        y,
        color,
        s,
    );
}

/// Draws a line of text centred on `centre`.
fn text_centred(
    content: &mut Content,
    font: &FontHandle,
    size: f64,
    centre: f64,
    y: f64,
    color: Rgb,
    s: &str,
) {
    text(
        content,
        font,
        size,
        centre - font.measure(s, size) / 2.0,
        y,
        color,
        s,
    );
}

/// A straight line between two points, in the given ink and thickness.
fn line(
    content: &mut Content,
    from: (f64, f64),
    to: (f64, f64),
    width: f64,
    color: Rgb,
) -> Result<(), hqf_pdf::Error> {
    content.set_stroke(color)?;
    content.set_line_width(width)?;
    content.move_to(from.0, from.1)?;
    content.line_to(to.0, to.1)?;
    content.stroke();
    Ok(())
}

/// Draws the cut marks: a tick in the margin against every column edge and
/// every row edge, which is what a guillotine or a die is registered against.
fn cut_marks(content: &mut Content) -> Result<(), hqf_pdf::Error> {
    let left = sheet_left();
    let grid_bottom = SHEET_TOP - f64::from(ROWS - 1).mul_add(ROW_PITCH, LABEL_HEIGHT);
    let grid_right = f64::from(COLUMNS - 1).mul_add(COLUMN_PITCH, left + LABEL_WIDTH);
    let ink = Rgb::gray(0.45);

    for column in 0..COLUMNS {
        let label_left = f64::from(column).mul_add(COLUMN_PITCH, left);
        for x in [label_left, label_left + LABEL_WIDTH] {
            let above = SHEET_TOP + MARK_OFFSET;
            let below = grid_bottom - MARK_OFFSET;
            line(content, (x, above), (x, above + MARK_LENGTH), 0.5, ink)?;
            line(content, (x, below), (x, below - MARK_LENGTH), 0.5, ink)?;
        }
    }

    for row in 0..ROWS {
        let label_top = f64::from(row).mul_add(-ROW_PITCH, SHEET_TOP);
        for y in [label_top, label_top - LABEL_HEIGHT] {
            let outer = left - MARK_OFFSET;
            let far = grid_right + MARK_OFFSET;
            line(content, (outer, y), (outer - MARK_LENGTH, y), 0.5, ink)?;
            line(content, (far, y), (far + MARK_LENGTH, y), 0.5, ink)?;
        }
    }

    Ok(())
}

/// Draws one label's die-cut outline, from its lower-left corner.
fn outline(content: &mut Content, x: f64, bottom: f64) -> Result<(), hqf_pdf::Error> {
    content.set_stroke(Rgb::gray(0.74))?;
    content.set_line_width(0.4)?;
    content.rect(x, bottom, LABEL_WIDTH, LABEL_HEIGHT)?;
    content.stroke();
    Ok(())
}

/// Draws a shelf label's face: the price, the price per unit, and the article
/// number as bars with its digits under them.
fn shelf_face(
    content: &mut Content,
    font: &FontHandle,
    x: f64,
    bottom: f64,
    subtitle: &str,
    price: f64,
    article: &Article,
) -> Result<(), Box<dyn Error>> {
    text(content, font, 7.5, x + 12.0, bottom + 92.0, MUTED, subtitle);
    text(
        content,
        font,
        18.0,
        x + 12.0,
        bottom + 68.0,
        ACCENT,
        &price_text(price),
    );

    let (modules, printed) = match article {
        Article::Ean13(digits) => {
            let printed = full_number(digits);
            (Ean13::new(&printed)?.module_count(), printed)
        }
        Article::UpcA(digits) => {
            let printed = full_number(digits);
            (UpcA::new(&printed)?.module_count(), printed)
        }
    };

    // A barcode whose margin a neighbouring label eats does not scan. The bars
    // are centred in the label, and what the centring leaves either side is
    // held against the quiet zone the symbology asks for.
    let bars_width = f64::from(u32::try_from(modules)?) * MODULE;
    let side_margin = (LABEL_WIDTH - bars_width) / 2.0;
    let quiet = f64::from(u32::try_from(BAR_QUIET_ZONE)?) * MODULE;
    if side_margin < quiet {
        return Err("the label is narrower than the barcode and its quiet zone".into());
    }

    // Bars are read by the contrast between them and the paper: they are drawn
    // in black whatever ink the price above them was set in.
    let bars_left = x + side_margin;
    content.set_fill(Rgb::gray(0.0))?;
    match article {
        Article::Ean13(digits) => {
            let code = Ean13::new(&full_number(digits))?;
            content.draw_ean13(&code, bars_left, bottom + 22.0, bars_width, 30.0)?;
        }
        Article::UpcA(digits) => {
            let code = UpcA::new(&full_number(digits))?;
            content.draw_upc_a(&code, bars_left, bottom + 22.0, bars_width, 30.0)?;
        }
    }

    text_centred(
        content,
        font,
        7.5,
        x + LABEL_WIDTH / 2.0,
        bottom + 11.0,
        INK,
        &printed,
    );
    Ok(())
}

/// Draws a bin label's face: the Data Matrix code a picker scans, and beside it
/// the aisle, rack and shelf a human reads.
fn bin_face(
    content: &mut Content,
    font: &FontHandle,
    corner: (f64, f64),
    words: &Words,
    subtitle: &str,
    positions: &[&str; 3],
    carried: &str,
) -> Result<(), Box<dyn Error>> {
    let (x, bottom) = corner;
    text(content, font, 7.5, x + 12.0, bottom + 92.0, MUTED, subtitle);

    let code = DataMatrix::new(carried)?;
    content.set_fill(Rgb::gray(0.0))?;
    let side = f64::from(u32::try_from(code.width())?) * MATRIX_MODULE;
    let quiet = f64::from(u32::try_from(MATRIX_QUIET_ZONE)?) * MATRIX_MODULE;

    // The quiet zone is the caller's: the code is drawn that far inside the
    // label's left margin, and the placement lines start clear of it.
    content.draw_data_matrix(&code, x + 12.0 + quiet, bottom + 26.0, side)?;

    let lines_left = x + 12.0 + quiet.mul_add(2.0, side) + 12.0;
    for (index, (label, placed)) in words.positions.iter().zip(positions).enumerate() {
        let y = f64::from(u32::try_from(index)?).mul_add(-13.0, bottom + 70.0);
        text(
            content,
            font,
            9.0,
            lines_left,
            y,
            INK,
            &format!("{label} {placed}"),
        );
    }

    text(content, font, 7.0, x + 12.0, bottom + 11.0, INK, carried);
    Ok(())
}

/// Draws the head of the sheet: who printed it, what stock it is laid out for,
/// and how many labels it carries.
fn header(content: &mut Content, font: &FontHandle, words: &Words) -> Result<(), hqf_pdf::Error> {
    let left = sheet_left();
    let right = f64::from(COLUMNS - 1).mul_add(COLUMN_PITCH, left + LABEL_WIDTH);

    text(content, font, 13.0, left, 800.0, INK, "HQF Development");
    text(
        content,
        font,
        7.5,
        left,
        788.0,
        MUTED,
        "High Quality Foundations · contact@hqf-pdf.com",
    );

    text_right(content, font, 16.0, right, 799.0, ACCENT, words.heading);
    text_right(
        content,
        font,
        8.0,
        right,
        785.0,
        MUTED,
        &format!(
            "{} · {} {} · {COLUMNS} × {ROWS} {} {LABEL_WIDTH:.0} × \
             {LABEL_HEIGHT:.0} {}",
            words.sheet_number,
            LABELS.len(),
            words.labels,
            words.stock_before,
            words.stock_after
        ),
    );
    text_right(
        content,
        font,
        8.0,
        right,
        773.0,
        MUTED,
        &format!("{} {}", words.printed_label, words.printed_on),
    );

    line(content, (left, 762.0), (right, 762.0), 1.0, ACCENT)
}

/// Draws the foot of the sheet: how long the prices hold, and who to send the
/// sheet back to.
fn footer(content: &mut Content, font: &FontHandle, words: &Words) -> Result<(), hqf_pdf::Error> {
    let left = sheet_left();
    let right = f64::from(COLUMNS - 1).mul_add(COLUMN_PITCH, left + LABEL_WIDTH);

    line(content, (left, 78.0), (right, 78.0), 0.5, Rgb::gray(0.8))?;
    let mentions = format!(
        "{} {} · HQF Development · 42 lot les Genêts, \
         13480 Calas, France · contact@hqf-pdf.com",
        words.valid_before, words.valid_until
    );
    text_centred(
        content,
        font,
        7.0,
        f64::midpoint(left, right),
        66.0,
        MUTED,
        &mentions,
    );
    Ok(())
}

fn main() -> std::process::ExitCode {
    failure::reported(run())
}

fn run() -> Result<(), Box<dyn Error>> {
    let language = Language::from_environment()?;
    let words = Words::of(language);

    let mut args = env::args().skip(1);
    // A named file is written as named; the default one carries the language,
    // so the two languages do not overwrite each other in `tmp/`.
    let path = args
        .next()
        .unwrap_or_else(|| language.file_name(&out::default_path("labels")));
    let font_path = args.next().map_or_else(default_font, PathBuf::from);

    let mut doc = Document::new();
    doc.set_license(licence::licensed());
    doc.set_info(Name::new("Title"), words.title);

    let font = doc.add_font(Font::parse(fs::read(&font_path)?)?);

    let mut content = Content::new();
    header(&mut content, &font, words)?;
    cut_marks(&mut content)?;

    // The grid fills across a row before dropping to the next, so a label's
    // place on the page follows from its place in the list and the two pitches.
    let left = sheet_left();
    for (index, face) in LABELS.iter().enumerate() {
        let place = u32::try_from(index)?;
        let x = f64::from(place % COLUMNS).mul_add(COLUMN_PITCH, left);
        let bottom = f64::from(place / COLUMNS).mul_add(-ROW_PITCH, SHEET_TOP) - LABEL_HEIGHT;
        let subtitle = words.subtitles[index];

        outline(&mut content, x, bottom)?;
        text(
            &mut content,
            &font,
            10.5,
            x + 12.0,
            bottom + 104.0,
            INK,
            words.names[index],
        );

        match face {
            Face::Shelf { price, article } => {
                shelf_face(&mut content, &font, x, bottom, subtitle, *price, article)?;
            }
            Face::Bin { positions, code } => {
                bin_face(
                    &mut content,
                    &font,
                    (x, bottom),
                    words,
                    subtitle,
                    positions,
                    code,
                )?;
            }
        }
    }

    footer(&mut content, &font, words)?;

    let mut page = Page::new(PAGE_WIDTH, PAGE_HEIGHT);
    page.content = content.into_bytes();
    doc.add_page(page)?;

    let bytes = doc.to_bytes()?;
    if let Some(parent) = Path::new(&path).parent() {
        fs::create_dir_all(parent)?;
    }
    fs::write(&path, &bytes)?;

    println!(
        "wrote {path}: {} bytes, {} labels",
        bytes.len(),
        LABELS.len()
    );
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::{WORDS, language};

    /// The lines two languages are allowed to write the same way, where two
    /// languages spell a word alike. Every word is a word of the language it is
    /// written in.
    const SPARED: [&str; 10] = [
        // Written the same way in German.
        r#""6 × 1 l · 0.65 EUR/l""#,
        // Written the same way in Spanish.
        r#""6 × 1 l · 0,65 EUR/l""#,
        // Written the same way in Portuguese.
        r#""Arroz basmati""#,
        r#""Chocolate negro, 70 %""#,
        r#""Lata de 125 g · 47,20 EUR/kg""#,
        r#""Reserva de secos""#,
        r#""Reserva refrigerada""#,
        r#"labels: "etiquetas""#,
        r#"valid_until: "31 de agosto de 2026""#,
        // Written the same way in Dutch.
        r#""Gang""#,
    ];

    #[test]
    fn every_language_draws_the_sheet_in_its_own_words() {
        let untranslated = language::untranslated_lines(&WORDS, &SPARED);

        assert!(
            untranslated.is_empty(),
            "the label sheet says these in more than one language: {untranslated:?}"
        );
    }
}