#!/bin/bash

# Convert a PDF into processed JPG images and split them into
# multiple PDF files, with a maximum of 100 images per output PDF.

set -e

if [ "$#" -ne 1 ]; then
    echo "Usage: $0 <pdf-file>"
    exit 1
fi

pdf_file="$1"

if [ ! -f "$pdf_file" ]; then
    echo "Error: '$pdf_file' does not exist."
    exit 1
fi

echo "Using $pdf_file"

# Resolve the input directory and filename.
pdf_dir="$(cd "$(dirname "$pdf_file")" && pwd)"
pdf_name="$(basename "$pdf_file")"
base_name="${pdf_name%.*}"

buffer_dir="$pdf_dir/.BUFFERFOLDER"

# Recreate the temporary working directory.
rm -rf "$buffer_dir"
mkdir -p "$buffer_dir"

cp "$pdf_file" "$buffer_dir/$pdf_name"

cd "$buffer_dir"

echo "Extracting images..."

# Extract PDF images as PNG.
pdfimages -png "$pdf_name" "$base_name"

count=0

shopt -s nullglob

for img in *.png; do
    jpg="${img%.png}.jpg"

    echo "Processing $jpg"

    # PNG -> JPG
    convert "$img" "$jpg"
    rm "$img"

    # Normalize image dimensions.
    convert "$jpg" -resize 2550x3300! "$jpg"

    # Use different crop dimensions for images containing "000".
    if [[ "$jpg" == *000* ]]; then
        convert "$jpg" -crop 2206x3200+200+50 "$jpg"
    else
        convert "$jpg" -crop 2106x3200+200+50 "$jpg"
    fi

    # Remove white background.
    convert "$jpg" -fuzz 20% -transparent White "$jpg"

    # Center image on a white 2550x3300 canvas.
    convert "$jpg" \
        -resize 2550x3300 \
        -gravity center \
        -background White \
        -extent 2550x3300 \
        "$jpg"

    # Group images into batches of 100.
    split_var=$((count / 100))
    split_dir="split_${split_var}"

    mkdir -p "$split_dir"
    mv "$jpg" "$split_dir/"

    ((count++)) || true
done

# Convert each group of images into a PDF.
for split_dir in split_*; do
    [ -d "$split_dir" ] || continue

    split_number="${split_dir#split_}"

    echo "Converting Part $split_number"

    convert "$split_dir"/*.jpg \
        "$pdf_dir/${base_name}_split_${split_number}.pdf"
done

# Remove temporary files.
cd "$pdf_dir"
rm -rf "$buffer_dir"

echo "Done."