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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Vector drawing of QR code using Cairo.
//! 
//! ## Examples
//!
//! ### PDF
//!
//! PDF example from the `examples/` directory:
//! ```rust
//! let surface = cairo::PdfSurface::new(100.0, 100.0, "example.pdf").unwrap();
//! let cr = cairo::Context::new(&surface);
//! qr2cairo::draw(&cr, 100.0, 100.0, "qr2cairo").unwrap();
//! cr.show_page();
//! ```
//! 
//! This generates this PDF: [example.pdf](https://www.willemp.be/qr2cairo/example.pdf).
//!
//! ### GTK 
//! 
//! GTK example (note: no GTK required to use qr2cairo):
//! 
//! ```sh
//! $ cd examples/gtk ; cargo run
//! ```
//! 
//! ![qr2cairo gtk example](https://www.willemp.be/qr2cairo/screenshot-qr2cairo-0.1.0-gtk.svg)
//! 
//! ### SVG
//! 
//! The underlying qrcode crate can
//! [create SVGs](https://docs.rs/qrcode/0.12.0/qrcode/render/svg/index.html).

extern crate qrcode;
use self::qrcode::types::Color::Dark as QrDark;
use self::qrcode::QrCode;
pub use qrcode::types::QrError;

/// Number of blocks that must be kept blank/light/white around the QR code.
const QUIET_ZONE: usize = 4;

/// Which color to draw the dark blocks of the QR code with.
///
/// Values are red, green, blue, alpha (i.e. opacity) from 0.0 to 1.0.
const LIGHT_COLOR_RGBA: (f64, f64, f64, f64) = (1.0, 1.0, 1.0, 1.0);

/// Which color to draw the light blocks of the QR code with.
const DARK_COLOR_RGBA: (f64, f64, f64, f64) = (0.0, 0.0, 0.0, 1.0);

/// Draw the given text as QR code to the given cairo context
///
/// # Arguments
///
/// * `cr`: what to draw on
/// * `width`: horizontal length in pixels of the draweable area
/// * `height`: vertical length in pixels of the draweable area
/// * `text`: what to draw as QR code
pub fn draw(cr: &cairo::Context, width: f64, height: f64, text: &str) -> Result<(), QrError> {
    Qr2Cairo::new(width, height, text)?.draw(cr);
    Ok(())
}

struct Qr2Cairo {
    width: f64,
    height: f64,
    qr_code: QrCode,
}

impl Qr2Cairo {
    pub fn new(width: f64, height: f64, text: &str) -> Result<Qr2Cairo, QrError> {
        let qr_code = QrCode::new(text)?;
        return Ok(Qr2Cairo {
            width,
            height,
            qr_code,
        });
    }

    /// Renders a QR code to the given cairo context `cr`.
    pub fn draw(&self, cr: &cairo::Context) {
        self.set_up_scaling(cr);
        self.draw_background(cr);
        self.draw_dark_boxes(cr);
    }

    /// Draw the dark part (i.e. not the background) of the QR code.
    fn draw_dark_boxes(&self, cr: &cairo::Context) {
        let vec = self.qr_code.to_colors();
        let (r, g, b, a) = DARK_COLOR_RGBA;
        cr.set_source_rgba(r, g, b, a);
        for row in 0..self.width_in_blocks_without_quiet() {
            for col in 0..self.width_in_blocks_without_quiet() {
                let vec_pos = row * self.width_in_blocks_without_quiet() + col;
                if vec[vec_pos] == QrDark {
                    cr.rectangle(
                        (QUIET_ZONE + col) as f64,
                        (QUIET_ZONE + row) as f64,
                        1.0,
                        1.0,
                    );
                }
            }
        }
        cr.fill();
    }

    /// Set up scaling and resizing such that we can draw with units of 1.0
    ///
    /// After this function, a distance of 1.0 in cairo will be one block of the QR code.
    fn set_up_scaling(&self, cr: &cairo::Context) {
        let drawingsize = f64::min(self.width, self.height);
        let px_per_block = drawingsize / (self.width_in_blocks() as f64);
        let move_x = f64::max(0.0, self.width - drawingsize) / 2.0;
        let move_y = f64::max(0.0, self.height - drawingsize) / 2.0;
        cr.translate(move_x, move_y);
        cr.scale(px_per_block, px_per_block);
    }

    /// Draw light background.
    ///
    /// Only draw light background only under the qr code (not the entire space) to not blind users
    /// with dark theme.
    fn draw_background(&self, cr: &cairo::Context) {
        let (r, g, b, a) = LIGHT_COLOR_RGBA;
        cr.set_source_rgba(r, g, b, a);
        cr.rectangle(
            0.0,
            0.0,
            self.width_in_blocks() as f64,
            self.width_in_blocks() as f64,
        );
        cr.fill();
    }

    /// How many blocks of the QR code, is the QR code wide (and tall), excluding quiet zone.
    fn width_in_blocks_without_quiet(&self) -> usize {
        self.qr_code.width()
    }

    /// How many blocks of the QR code, is the QR code wide (and tall), including quiet zone.
    fn width_in_blocks(&self) -> usize {
        self.width_in_blocks_without_quiet() + QUIET_ZONE * 2
    }
}