use std::os::unix::fs::MetadataExt;
use std::path::PathBuf;
use std::time::Duration;
use anyhow::Context;

use chrono::{NaiveDateTime, Utc};
use image::{GenericImageView, Pixel};
use log::{debug, error, info};

/// Folder the camera images are uploaded to
const FOLDER_WITH_NEW_IMAGES: &str = "/dev/shm/camera";

/// File created in the uploads directory when the upload finishes.
const COMMIT_FILENAME : &str = "commit";

/// Folder where the cropped bird pics are saved
const FOLDER_WITH_BIRD_IMAGES: &str = "/backup/krmitko";

/// Image cropping config: left top X
const CROP_X : u32 = 1872;

/// Image cropping config: left top Y
const CROP_Y : u32 = 1329;

/// Image cropping config: crop width
const CROP_W : u32 = 1000;

/// Image cropping config: crop height
const CROP_H : u32 = 750;

/// Thumbnail width, used for bird detection (together with height creates the kernel size)
/// This is a compromise between sensitivity and susceptibility to false positives.
const THUMB_W: usize = 12;

/// Thumbnail height
const THUMB_H: usize = 8;

/// Threshold for bird detection.
/// Bird is detected if the sum of deviations from a median value in a picture exceeds this threshold.
const THRESHOLD_DEVIATION: u32 = 500;

fn main() {
    env_logger::init();

    let commit_file = PathBuf::from(FOLDER_WITH_NEW_IMAGES).join(COMMIT_FILENAME);

    loop {
        if !commit_file.exists() {
            debug!("No commit file, wait.");
            std::thread::sleep(Duration::from_secs(10));
            continue;
        }

        if let Err(e) = process_camera_pics() {
            error!("Error processing pics: {e}");
        }

        let _ = std::fs::remove_dir_all(FOLDER_WITH_NEW_IMAGES);
    }
}

fn process_camera_pics() -> anyhow::Result<()> {
    info!("Processing camera pics");

    let paths = std::fs::read_dir(FOLDER_WITH_NEW_IMAGES).context("Read folder with images")?;

    let mut crops = vec![];
    let mut thumbs = vec![];
    let mut timestamps = vec![];

    info!("Loading files");
    for dir_entry in paths {
        let Ok(dir_entry) = dir_entry else { continue; };
        let Ok(meta) = dir_entry.metadata() else { continue; };
        if !meta.is_file() || !dir_entry.file_name().to_string_lossy().ends_with(".jpg") {
            continue;
        }

        debug!("{}", dir_entry.path().display());

        let Ok(img) = image::open(dir_entry.path()) else {
            continue;
        };

        // File loaded fine, assume it's OK
        timestamps.push(meta.ctime());

        let crop = img.crop_imm(CROP_X, CROP_Y, CROP_W, CROP_H);
        let thumb = crop.thumbnail(THUMB_W as u32, THUMB_H as u32);

        crops.push(crop);

        let mut thumb_ar = [0u8; THUMB_H * THUMB_W];
        for y in 0..thumb.height() {
            for x in 0..thumb.width() {
                thumb_ar[(y * thumb.width() + x) as usize] = thumb.get_pixel(x, y).to_luma().0[0];
            }
        }

        thumbs.push(thumb_ar);
    }

    info!("Computing digests & medians");
    let mut transposed = vec![];
    for thumb in thumbs.iter() {
        for (b, item) in thumb.iter().enumerate() {
            if transposed.len() <= b {
                transposed.push(vec![]);
            }
            transposed[b].push(*item);
        }
    }

    let mut medians = [0; THUMB_H * THUMB_W];

    for (a, column) in transposed.iter().enumerate() {
        medians[a] = column[column.len() / 2]; // approximately median ...
    }

    debug!("Medians: {:?}", medians);

    info!("Finding deviations");
    for (thumb_num, thumb) in thumbs.iter().enumerate() {
        let deviation = thumb.iter().zip(medians.iter())
            .map(|(a, b)| (*a as i16 - *b as i16).abs() as u32).fold(0u32, |a, b| a + b);

        debug!("Thumb {thumb_num} summary diff from median is: {deviation}");

        if deviation > THRESHOLD_DEVIATION {
            info!("LIKELY BIRD!!!! in picture #{thumb_num}");

            let datetime_str = parse_unix_ts(timestamps[thumb_num]).format("%Y-%m-%d_%H-%M-%S");
            let path = format!("{}/{}.jpg", FOLDER_WITH_BIRD_IMAGES, datetime_str);
            let mut pb = PathBuf::from(path);

            // Ensure we do not overwrite a file if there are multiple in the same second!
            // This adds -2, -3 etc. to the file name
            let mut cnt = 2;
            while pb.exists() {
                pb.set_file_name(format!("{}-{cnt}.jpg", datetime_str));
                cnt += 1;
            }

            if let Err(e) = crops[thumb_num].save(pb) {
                error!("Fail to save pic: {e}");
            }
        }
    }

    Ok(())
}

fn parse_unix_ts(ts: i64) -> chrono::DateTime<Utc> {
    chrono::DateTime::<Utc>::from_naive_utc_and_offset(NaiveDateTime::from_timestamp_opt(ts, 0)
                                                           .expect("Bad timestamp"), Utc)
}