use std::fs;
use std::fs::DirEntry;
use std::fs::File;
use std::io::BufWriter;
use std::io::copy;
use std::path::Path;

use image::DynamicImage;
use image::GenericImageView;
use printpdf::{Image, Mm, PdfDocument};
use scraper::{Html, Selector};
use tempfile::TempDir;

use crate::error::EcloadError;

const BASEURL: &str = "https://www.e-codices.unifr.ch";
const DPI: f64 = 300.0;
const INCH_AS_MM: f64 = 25.4;

/// Provides functions to download e-codices.
pub struct EcLoader {}

arg_enum! {
    #[derive(PartialEq, Debug)]
    /// Defines the different sizes that e-codice pages can be.
    pub enum PageFormat {
        Small,
        Medium,
        Large,
        Max,
    }
}

impl PageFormat {
    /// Converts the formats in the represantation that the e-codice website uses.
    fn as_url_part(&self) -> &str {
        match self {
            PageFormat::Small => "small",
            PageFormat::Medium => "medium",
            PageFormat::Large => "large",
            PageFormat::Max => "max",
        }
    }
}

impl EcLoader {
    /// Download an e-codice from https://www.e-codices.unifr.ch.
    ///
    /// # Arguments
    ///
    /// * `id` - The combined id ot the e-codice. Consisting of the library id and the e-codice id (for example "bbb/0003").
    /// * `title` - Title of the pdf, this will also be the filename.
    /// * `out_dir` - Directory where the PDF gets saved (must already exist).
    /// * `format` - The size of the page to look for.
    pub fn download_codice(
        id: &str,
        title: &str,
        out_dir: &Path,
        format: PageFormat,
    ) -> Result<(), EcloadError> {
        let tmp_dir = tempfile::tempdir()?;
        debug!("temporary download directory: {}", tmp_dir.path().display());

        EcLoader::download_pages(id, format, &tmp_dir)
            .and_then(|_| EcLoader::build_pdf(title, out_dir, &tmp_dir))
    }

    /// Order files in a temporary directory
    ///
    /// # Arguments
    ///
    /// * `tmp_dir`- Reference to the temporary directory.
    fn get_ordered_tmp_files(tmp_dir: &TempDir) -> Result<Vec<DirEntry>, EcloadError> {
        let paths = fs::read_dir(tmp_dir.path())?;
        let mut sorted_paths: Vec<DirEntry> = paths.filter_map(|r| r.ok()).collect();

        sorted_paths.sort_by_key(|dir| dir.path());

        Ok(sorted_paths)
    }

    /// Calculate image dimensions in mm.
    ///
    /// # Arguments
    ///
    /// * `image` - Image for the calculation.
    fn mm_from_image(image: &DynamicImage) -> (Mm, Mm) {
        let (width, height) = image.dimensions();
        let mm_width = Mm(width as f64 * (INCH_AS_MM / DPI));
        let mm_height = Mm(height as f64 * (INCH_AS_MM / DPI));

        (mm_width, mm_height)
    }

    /// Convert an image to BMP.
    ///
    /// # Arguments
    ///
    /// * `img_path` - Path to the image that should be converted.
    ///
    /// # Remarks
    ///
    /// The BMP file gets saved to the same directory as the original, with the same name apart from
    /// the extension.
    fn get_img_as_bmp(img_path: &Path) -> Result<DynamicImage, EcloadError> {
        let image = image::open(img_path)?;
        let img_bmp_path = img_path.with_extension("bmp");
        image.save(&img_bmp_path)?;

        Ok(image::open(img_bmp_path)?)
    }

    /// Generate a PDF from images inside a directory.
    ///
    /// # Arguments
    ///
    /// * `title` - Title of the pdf, this will also be the filename.
    /// * `out_dir` - Directory where the PDF gets saved (must already exist).
    /// * `tmp_dir` - Reference to the temporary directory where the images for the pdf are.
    fn build_pdf(title: &str, out_dir: &Path, tmp_dir: &TempDir) -> Result<(), EcloadError> {
        let ordered_tmp_files = EcLoader::get_ordered_tmp_files(tmp_dir)?;
        let first_file = match ordered_tmp_files.first() {
            Some(file) => file,
            None => return Err(EcloadError::Error("no tmp files".to_string())),
        };

        let first_image_data = image::open(first_file.path())?;
        let (first_img_width, first_img_height) = EcLoader::mm_from_image(&first_image_data);

        let (doc, page1, layer1) =
            PdfDocument::new(title, first_img_width, first_img_height, "Layer 1");
        let mut current_layer = doc.get_page(page1).get_layer(layer1);

        let mut is_first_page = true;
        let mut page_count = 1;
        for entry in ordered_tmp_files {
            let filename_os = entry.file_name();
            let filename = match filename_os.to_str() {
                Some(filename) => filename,
                None => continue,
            };

            if !filename.ends_with(".jpg") {
                continue;
            }

            info!("saving page {} to pdf...", page_count);
            let image_bmp = match EcLoader::get_img_as_bmp(&entry.path()) {
                Ok(image_data) => image_data,
                Err(err) => {
                    error!("could not decode {}: {:?}", entry.path().display(), err);
                    continue;
                }
            };

            let mut image_file = File::open(entry.path().with_extension("bmp")).unwrap();
            let image = Image::try_from(image::bmp::BMPDecoder::new(&mut image_file)).unwrap();

            let (img_width, img_height) = EcLoader::mm_from_image(&image_bmp);
            debug!("dimensions: {:?} x {:?}", img_width, img_height);

            if !is_first_page {
                let (new_page, new_layer) = doc.add_page(img_width, img_height, "Layer 1");
                current_layer = doc.get_page(new_page).get_layer(new_layer);
            }

            image.add_to_layer(
                current_layer.clone(),
                None,
                None,
                None,
                None,
                None,
                Some(DPI),
            );

            is_first_page = false;
            page_count += 1;
        }

        let pdf_file_path = out_dir.join(format!("{}.pdf", title));
        info!("saved to {}", pdf_file_path.display());
        let pdf_file = File::create(pdf_file_path)?;
        doc.save(&mut BufWriter::new(pdf_file))?;

        Ok(())
    }

    fn get_thumbnail_url(id: &str) -> String {
        format!("{}/en/thumbs/{}", BASEURL, id)
    }

    /// Download all the pages of an e-codice to a temporary directory.
    ///
    /// # Arguments
    ///
    /// * `id` - The combined id ot the e-codice. Consisting of the library id and the e-codice id (for example "bbb/0003").
    /// * `format` - The size of the page to look for.
    /// * `tmp_dir` - Reference to a temporary directory where the downloaded files get saved.
    fn download_pages(id: &str, format: PageFormat, tmp_dir: &TempDir) -> Result<(), EcloadError> {
        let thumbnail_url = EcLoader::get_thumbnail_url(id);
        let mut response = reqwest::get(thumbnail_url.as_str())?;
        let html = response.text()?;
        let fragment = Html::parse_fragment(&html);

        let li_selector = Selector::parse("div.thumbnail-image > a").unwrap();

        let mut page_count = 0;
        for element in fragment.select(&li_selector) {
            let page_link = match element.value().attr("href") {
                Some(href) => href.to_string(),
                None => {
                    continue;
                }
            };

            debug!("searching download links for {}...", page_link);
            let download_link = match EcLoader::get_download_link(&page_link, &format) {
                Ok(download_link) => download_link,
                Err(err) => {
                    error!(
                        "could not find download link for {} with format {}: {:?}",
                        &page_link, format, err
                    );
                    continue;
                }
            };
            debug!("found {}", download_link);

            info!("downloading {}...", download_link);
            let page_file_path = tmp_dir
                .path()
                .join(format!("{:0>5}.jpg", page_count.to_string()));

            let mut page_download = match reqwest::get(&download_link) {
                Ok(response) => response,
                Err(err) => {
                    error!("could not download {}: {:?}", download_link, err);
                    continue;
                }
            };

            let mut dest = File::create(page_file_path)?;
            copy(&mut page_download, &mut dest)?;

            page_count += 1;
        }

        Ok(())
    }

    /// Finds the image url for a specified size for an e-codice page.
    ///
    /// # Arguments
    ///
    /// * `page_link` - The specific e-codice page url.
    /// * `format` - The size of the page to look for.
    fn get_download_link(page_link: &str, format: &PageFormat) -> Result<String, EcloadError> {
        let mut response = reqwest::get(page_link)?;
        let html = response.text()?;
        let fragment = Html::parse_fragment(&html);

        let a_selector = Selector::parse("ul.download-page-list > li > a").unwrap();
        for element in fragment.select(&a_selector) {
            let download_link = match element.value().attr("href") {
                Some(href) => href.to_string(),
                None => {
                    continue;
                }
            };

            if download_link.ends_with(format.as_url_part()) {
                return Ok(download_link);
            }
        }

        Err(EcloadError::Error(
            "could not find download link".to_string(),
        ))
    }
}