SilentDragonPaper/lib/src/pdf.rs

extern crate printpdf;

use qrcode::QrCode;
use qrcode::types::Color;

use std::io::BufWriter;
use std::convert::From;
use std::fs::File;
use printpdf::*;

/**
 * Save the list of wallets (address + private keys) to the given PDF file name.
 */
pub fn save_to_pdf(addresses: &str, filename: &str) {
    let (doc, page1, layer1) = PdfDocument::new("Zec Sapling Paper Wallet", Mm(210.0), Mm(297.0), "Layer 1");
    let current_layer = doc.get_page(page1).get_layer(layer1);
    let font  = doc.add_builtin_font(BuiltinFont::Courier).unwrap();
    let font_bold = doc.add_builtin_font(BuiltinFont::CourierBold).unwrap();

    let keys = json::parse(&addresses).unwrap();
    for kv in keys.members() {
        add_address_to_page(&current_layer, &font, &font_bold, kv["address"].as_str().unwrap(), 0);

        add_pk_to_page(&current_layer, &font, &font_bold, kv["private_key"].as_str().unwrap(), 1);

        // Is the shape stroked? Is the shape closed? Is the shape filled?
        let line1 = Line {
            points: vec![(Point::new(Mm(5.0), Mm(160.0)), false), (Point::new(Mm(205.0), Mm(160.0)), false)],
            is_closed: true,
            has_fill: false,
            has_stroke: true,
            is_clipping_path: false,
        };

        let outline_color = printpdf::Color::Rgb(Rgb::new(0.0, 0.0, 0.0, None));

        current_layer.set_outline_color(outline_color);
        current_layer.set_outline_thickness(2.0);

        // Draw first line
        current_layer.add_shape(line1);
    };
    
    doc.save(&mut BufWriter::new(File::create(filename).unwrap())).unwrap();
}

/**
 * Generate a qrcode. The outout is a vector of RGB values of size (qrcode_modules * scalefactor) + padding
 */
fn qrcode_scaled(data: &str, scalefactor: usize) -> (Vec<u8>, usize) {
    let code = QrCode::new(data.as_bytes()).unwrap();
    let output_size = code.width();

    let imgdata = code.to_colors();

    // Add padding around the QR code, otherwise some scanners can't seem to read it. 
    let padding     = 10;
    let scaledsize  = output_size * scalefactor;
    let finalsize   = scaledsize + (2 * padding);

    // Build a scaled image
    let scaledimg: Vec<u8> = (0..(finalsize*finalsize)).flat_map( |i| {
        let x = i / finalsize;
        let y = i % finalsize;
        if x < padding || y < padding || x >= (padding+scaledsize) || y >= (padding+scaledsize) {
            vec![255u8; 3]
        } else {
            if imgdata[(x - padding)/scalefactor * output_size + (y - padding)/scalefactor] != Color::Light {vec![0u8; 3] } else { vec![255u8; 3] }
        }
    }).collect();

    return (scaledimg, finalsize);
}

/**
 * Add the address section to the PDF at `pos`. Note that each page can fit only 2 wallets, so pos has to effectively be either 0 or 1.
 */
fn add_address_to_page(current_layer: &PdfLayerReference, font: &IndirectFontRef, font_bold: &IndirectFontRef,address: &str, pos: u32) {
    let (scaledimg, finalsize) = qrcode_scaled(address, 10);

    let ypos = 297.0 - 5.0 - (50.0 * ((pos+1) as f64));
    add_qrcode_image_to_page(current_layer, scaledimg, finalsize, Mm(10.0), Mm(ypos));

    current_layer.use_text("Address", 14, Mm(55.0), Mm(ypos+27.5), &font_bold);
    let strs = split_to_max(&address, 44, 8);
    for i in 0..strs.len() {
        current_layer.use_text(strs[i].clone(), 12, Mm(55.0), Mm(ypos+15.0-((i*5) as f64)), &font);
    }
}

/**
 * Add the private key section to the PDF at `pos`, which can effectively be only 0 or 1.
 */
fn add_pk_to_page(current_layer: &PdfLayerReference, font: &IndirectFontRef, font_bold: &IndirectFontRef, pk: &str, pos: u32) {
    let (scaledimg, finalsize) = qrcode_scaled(pk, 10);

    let ypos = 297.0 - 5.0 - (50.0 * ((pos+1) as f64));
    add_qrcode_image_to_page(current_layer, scaledimg, finalsize, Mm(145.0), Mm(ypos-17.5));

    current_layer.use_text("Private Key", 14, Mm(10.0), Mm(ypos+27.5), &font_bold);
    let strs = split_to_max(&pk, 45, 10);
    for i in 0..strs.len() {
        current_layer.use_text(strs[i].clone(), 12, Mm(10.0), Mm(ypos+15.0-((i*5) as f64)), &font);
    }
}

/**
 * Insert the given QRCode into the PDF at the given x,y co-ordinates. The qr code is a vector of RGB values. 
 */
fn add_qrcode_image_to_page(current_layer: &PdfLayerReference, qr: Vec<u8>, qrsize: usize, x: Mm, y: Mm) {
    // you can also construct images manually from your data:
    let image_file_2 = ImageXObject {
            width: Px(qrsize),
            height: Px(qrsize),
            color_space: ColorSpace::Rgb,
            bits_per_component: ColorBits::Bit8,
            interpolate: true,
            /* put your bytes here. Make sure the total number of bytes =
            width * height * (bytes per component * number of components)
            (e.g. 2 (bytes) x 3 (colors) for RGB 16bit) */
            image_data: qr,
            image_filter: None, /* does not work yet */
            clipping_bbox: None, /* doesn't work either, untested */
    };
    
    let image2 = Image::from(image_file_2);
    image2.add_to_layer(current_layer.clone(), Some(x), Some(y), None, None, None, None);
}

/**
 * Split a string into multiple lines, each with a `max` length and add spaces in each line at `blocksize` intervals
 */
fn split_to_max(s: &str, max: usize, blocksize: usize) -> Vec<String> {
    let mut ans: Vec<String> = Vec::new();

    // Split into lines. 
    for i in 0..((s.len() / max)+1) {
        let start = i * max;
        let end   = if start + max > s.len() { s.len() } else { start + max };

        let line = &s[start..end];

        // Now, add whitespace into the individual lines to better readability.
        let mut spaced_line = String::default();
        for j in 0..((line.len() / blocksize)+1) {
            let start = j * blocksize;
            let end   = if start + blocksize > line.len() {line.len()} else {start + blocksize};

            spaced_line.push_str(" ");
            spaced_line.push_str(&line[start..end]);
        }

        // If there was nothing to split in the blocks, just add the whole line
        if spaced_line.is_empty() {
            spaced_line = line.to_string();
        }

        ans.push(spaced_line.trim().to_string());
    }

    // Add spaces
    return ans;
}