//! Encoding and decoding QR codes.

use keyfork_bug as bug;

use image::{ImageBuffer, ImageReader, Luma};
use std::{
    io::{Cursor, Write},
    process::{Command, Stdio},
    time::{Duration, Instant},
};
use v4l::{
    buffer::Type,
    io::{traits::CaptureStream, userptr::Stream},
    video::Capture,
    Device, FourCC,
};

/// A QR code could not be generated.
#[derive(thiserror::Error, Debug)]
pub enum QRGenerationError {
    /// The resulting QR coode could not be read from the generator program.
    #[error("{0}")]
    Io(#[from] std::io::Error),

    /// The generator program produced invalid data.
    #[error("Could not decode output of qrencode (this is a bug!): {0}")]
    StringParse(#[from] std::string::FromUtf8Error),
}

/// An error occurred while scanning for a QR code.
#[derive(thiserror::Error, Debug)]
pub enum QRCodeScanError {
    /// The camera could not load the requested format.
    #[error("Camera could not use {expected} format, instead used {actual}")]
    CameraGaveBadFormat {
        /// The expected format, in FourCC format.
        expected: String,

        /// The actual format, in FourCC format.
        actual: String,
    },

    /// Interfacing with the camera resulted in an error.
    #[error("Unable to interface with camera: {0}")]
    CameraIO(#[from] std::io::Error),

    /// Decoding an image from the camera resulted in an error.
    #[error("Could not decode image: {0}")]
    ImageDecode(#[from] image::ImageError),
}

/// The level of error correction when generating a QR code.
#[derive(Default)]
pub enum ErrorCorrection {
    /// 7% of the QR code can be recovered.
    #[default]
    Lowest,

    /// 15% of the QR code can be recovered.
    Medium,

    /// 25% of the QR code can be recovered.
    Quartile,

    /// 30% of the QR code can be recovered.
    Highest,
}

/// Generate a terminal-printable QR code for a given string. Uses the `qrencode` CLI utility.
///
/// # Errors
/// The function may return an error if interacting with the QR code generation program fails.
pub fn qrencode(
    text: &str,
    error_correction: impl Into<Option<ErrorCorrection>>,
) -> Result<String, QRGenerationError> {
    let error_correction_arg = match error_correction.into().unwrap_or_default() {
        ErrorCorrection::Lowest => "L",
        ErrorCorrection::Medium => "M",
        ErrorCorrection::Quartile => "Q",
        ErrorCorrection::Highest => "H",
    };

    let mut qrencode = Command::new("qrencode")
        .arg("-t")
        .arg("ansiutf8")
        .arg("-m")
        .arg("2")
        .arg("-l")
        .arg(error_correction_arg)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .spawn()?;
    if let Some(stdin) = qrencode.stdin.as_mut() {
        stdin.write_all(text.as_bytes())?;
    }
    let output = qrencode.wait_with_output()?;
    let result = String::from_utf8(output.stdout)?;
    Ok(result)
}

const VIDEO_FORMAT_READ_ERROR: &str = "Failed to read video device format";

trait Scanner {
    fn scan_image(&mut self, image: ImageBuffer<Luma<u8>, Vec<u8>>) -> Option<String>;
}

#[cfg(feature = "decode-backend-zbar")]
mod zbar {
    use super::{ImageBuffer, Luma, Scanner};

    pub struct Zbar {
        scanner: keyfork_zbar::image_scanner::ImageScanner,
    }

    impl Zbar {
        #[allow(dead_code)]
        pub fn new() -> Self {
            Self::default()
        }
    }

    impl Default for Zbar {
        fn default() -> Self {
            Self {
                scanner: keyfork_zbar::image_scanner::ImageScanner::new(),
            }
        }
    }

    impl Scanner for Zbar {
        fn scan_image(
            &mut self,
            image: ImageBuffer<Luma<u8>, Vec<u8>>,
        ) -> Option<String> {
            let image = keyfork_zbar::image::Image::from(image);
            self.scanner.scan_image(&image).into_iter().next().map(|symbol| {
                String::from_utf8_lossy(symbol.data()).into()
            })
        }
    }
}

#[cfg(feature = "decode-backend-rqrr")]
mod rqrr {
    use super::{ImageBuffer, Luma, Scanner};

    pub struct Rqrr;

    impl Scanner for Rqrr {
        fn scan_image(
            &mut self,
            image: ImageBuffer<Luma<u8>, Vec<u8>>,
        ) -> Option<String> {
            let mut image = rqrr::PreparedImage::prepare(image);
            for grid in image.detect_grids() {
                if let Ok((_, content)) = grid.decode() {
                    return Some(content);
                }
            }
            None
        }
    }
}

#[allow(dead_code)]
fn dbg_elapsed(count: u64, instant: Instant) {
    let elapsed = instant.elapsed().as_secs();
    let framerate = count as f64 / elapsed as f64;
    eprintln!("framerate: {count}/{elapsed} = {framerate}");
}

/// Continuously scan the `index`-th camera for a QR code.
///
/// # Errors
///
/// The function may return an error if the hardware is unable to scan video or if an image could
/// not be decoded.
pub fn scan_camera(timeout: Duration, index: usize) -> Result<Option<String>, QRCodeScanError> {
    let device = Device::new(index)?;
    let mut fmt = device
        .format()
        .unwrap_or_else(bug::panic!(VIDEO_FORMAT_READ_ERROR));
    fmt.fourcc = FourCC::new(b"MPG1");
    device.set_format(&fmt)?;
    let mut stream = Stream::with_buffers(&device, Type::VideoCapture, 4)?;
    let start = Instant::now();
    cfg_if::cfg_if! {
        if #[cfg(feature = "decode-backend-zbar")] {
            let mut scanner = zbar::Zbar::default();
        } else if #[cfg(feature = "decode-backend-rqrr")] {
            let mut scanner = rqrr::Rqrr;
        } else {
            unimplemented!("neither decode-backend-zbar nor decode-backend-rqrr were selected")
        }
    };

    #[allow(unused)]
    let mut count = 0;

    while Instant::now().duration_since(start) < timeout {
        count += 1;
        let (buffer, _) = stream.next()?;
        let image = ImageReader::new(Cursor::new(buffer))
            .with_guessed_format()?
            .decode()?
            .to_luma8();
        if let Some(content) = scanner.scan_image(image) {
            // dbg_elapsed(count, start);
            return Ok(Some(content));
        }
    }

    // dbg_elapsed(count, start);

    Ok(None)
}