#!/bin/bash

SPLITSIZE="10M"     # Desired size of splitted files 
INFO="info.cfg"     # Desired name of document containing information
CHECKSUM="md5sum"   # Define application to create hashsums
FILE=""
MODE=""

while getopts s:i:c:f:t:help: opt; do
  case $opt in
  h)
      echo "This program is used to split large files into several small
files to avoid data loss and the need to re-download them from 
slow or unstable internet connections."
      echo
      echo "Necessary arguments to start this application:"
      echo "-t    Desired MODE. Possible values are \"server\" or \"client\""
      echo "      \"server\" splits the file on the server and needs a file for -f."
      echo "      \"client\" downloads the files and needs a download link for -f."
      echo "-f    File in the same directory to be splitted or link to be downloaded."
      echo
      echo "Optional arguments:"
      echo "-s    Define the desired size of splitted files. Default is $SPLITSIZE"
      echo "-i    Define the desired name of the info document. Default is $INFO"
      echo "-c    Define the program which should be used to calculate the hashsum. Default is $CHECKSUM"
      exit 0
      ;;
  s)
      SPLITSIZE=$OPTARG
      ;;
  i)
      INFO=$OPTARG
      ;;
  c)
      CHECKSUM=$OPTARG
      ;;
  f)
      FILE=$OPTARG
      ;;
  m)
      MODE=$OPTARG
      ;;
  esac
done

# DO NOT EDIT BELOW HERE
# ----------------------

if [ "$FILE" == "" ] || [ "$MODE" == "" ]; then
  echo "Missing arguments! Please define the mode with -m and the file/link with -f. More info with -h."
  exit 1
else
  echo "OK"
fi


# # # #
# FUNCTIONS
# # # #
function checkwait {
  read -p "Continue? Press Ctrl+C to cancel." END
}

function gethash {
  md5sum $1 | awk -F" " '{ print $1 }'
}

function comphash {
  HASH1=$(gethash $1)
  HASH2=$2
  if [ "$HASH1" == "$HASH2" ]; then
    echo "true"
  else
    echo "false"
  fi
}

function getdu {
  du -b $1 | awk -F" " '{ print $1 }'
}

function compdu {
  DU1=$(getdu $1)
  DU2=$2
  if [ "$DU1" == "$DU2" ]; then
    echo "true"
  else
    echo "false"
  fi
}

function compall {
  FILE=$1
  SIZE=$2
  HASH=$3
  if $(compdu $FILE $SIZE) && $(comphash $FILE $HASH); then
    echo="true"
  else
    echo="false"
  fi
}

function checkfolder {
  FOLDER=$1
  # Check if folder already exists. If not, create it
  if [ -d $FOLDER ]; then
    read -p "Destination folder \"$FOLDER\" already exists. Should it be emptied? [y/n]: " YN
    if [ $YN == "y" ]; then
      rm -rf $FOLDER
      mkdir $FOLDER
    else
      if [ "$MODE" == "server" ]; then
        echo "In server-mode, this isn't recommended. Aborting."
        exit 1
      fi
    fi
  elif [ -e $FOLDER ] && [ ! -d $FOLDER ]; then
    echo "Destination \"$FOLDER\" already exists but is not a folder. Please check."
    exit 1
  else
    mkdir $FOLDER
  fi
}


# # # #
# SERVER MODE
# # # #
if [ $MODE == "server" ]; then

# Check if file has spaces
if [ $(echo "$FILE" | grep -q " "; echo $?) == "0" ]; then
  read -p "Filename has spaces. Should it be renamed? [y/n]: " YN
  if [ $YN == "y" ]; then
    # replace spaces by underscores
    TMPFILENAME=$(echo "$FILE" | sed "s/ /_/g")
    mv "$FILE" "$TMPFILENAME"
    FILE=$TMPFILENAME
  else
    echo "Aborting."
    exit 1
  fi
fi

# Check if command is executed in directory of file or not
if [ $(basename "$FILE") != "$FILE" ]; then
  echo "Please execute command in the same directory than the file itself."
  exit 1
fi

# Check if file exists
if [ ! -e "$FILE" ]; then
  echo "File does not exist. Aborting."
  exit 1
fi

# Check if it's a file or a directory
if [ ! -f "$FILE" ]; then
  echo "File is not a file. This script doesn't work with directories."
  exit 1
fi

FOLDER="dl-$FILE"

checkfolder $FOLDER

INFONAME=$INFO
INFO="$FOLDER/$INFONAME"

echo "[INFO] Calculating size and HASH sum..."
BIGNAME=$(basename $FILE)
BIGSIZE=$(getdu $FILE)
BIGHASH=$(gethash $FILE)

echo "BIGNAME=$BIGNAME" >> $INFO
echo "BIGSIZE=$BIGSIZE" >> $INFO
echo "BIGHASH=$BIGHASH" >> $INFO
echo >> $INFO

echo "[INFO] Splitting big file into smaller parts..."
split --verbose -a 4 -b $SPLITSIZE $FILE $FOLDER/dl-

# List all splitted files, measure size and hashsum
echo "[INFO] Creating info document with necessary specs..."
SMALLNO=$(ls $FOLDER | grep -v $INFONAME | wc -l)
echo "SMALLNO=$SMALLNO" >> $INFO
NO=0
ls $FOLDER | grep -v $INFONAME | while read -r line; do 
  
  SMALLNAME=$line
  SMALLSIZE=$(getdu $FOLDER/$SMALLNAME)
  SMALLHASH=$(gethash $FOLDER/$SMALLNAME)
  
  echo "SMALLNAME[$NO]=$SMALLNAME" >> $INFO
  echo "SMALLSIZE[$NO]=$SMALLSIZE" >> $INFO
  echo "SMALLHASH[$NO]=$SMALLHASH" >> $INFO
  
  let NO=NO+1
done

echo "[SUCCESS] You can now download the splitted files with the client function of this program!"
echo "[INFO] Please move the folder \"$FOLDER\" to a web-accessible directory and use this folder as the first argument for this script."

fi # /SERVER MODE


# # # #
# CLIENT MODE
# # # #
if [ $MODE == "client" ]; then

URL=$FILE

# Check if remote directory is valid and has an info.cfg file
if [ $(wget -q --spider $URL/$INFO ; echo $?) != "0" ]; then
  echo "Remote directory does not exists or has invalid info.cfg file. Aborting."
  exit 1
fi

if [ -e $INFO ]; then rm $INFO; fi
wget -q $URL/$INFO

# Rename info.cfg to avoid colissions and source it
mv $INFO $BIGNAME-$INFO
INFO=$BIGNAME-$INFO
source $INFO

FOLDER="dl-$BIGNAME"

# Print basic status
echo
echo "Total filesize: $BIGSIZE"
echo "HASH: $BIGHASH"
echo "Number of splitted files: $SMALLNO"
echo "Download folder: "$(readlink -f $FOLDER)""
echo
checkwait
echo

checkfolder $FOLDER   # Checks and creates folder

until [ "$STATUS" == "F" ]; do
  for ((i = 0; i < ${#SMALLNAME[*]}; i++)); do
    SMALLNAME=${SMALLNAME[$i]}
    SMALLSIZE=${SMALLSIZE[$i]}
    SMALLHASH=${SMALLHASH[$i]}
    
    SMALLURL=$URL/$SMALLNAME
    SMALLPATH=$FOLDER/$SMALLNAME
    
    let NO=i+1
    echo
    echo "------------------"
    echo "Starting file: $SMALLNAME ($SMALLSIZE bytes)"
    echo "This is file $NO of total $SMALLNO files."
    echo "Already downloaded "$(getdu $FOLDER)" of $BIGSIZE bytes."
    echo 
      
    # File doesn't exist yet, so start fresh download
    if [ ! -e $SMALLPATH ]; then
      echo "[INFO] File doesn't exist yet. Starting new download."
      wget -O $SMALLPATH -nv --show-progress $SMALLURL
      if $(compall $SMALLPATH $SMALLSIZE $SMALLHASH); then
        STATUS="C"
      else 
        # Downloaded file is not valid. Restart for-loop
        echo "[ERROR] Downloaded file is corrupt. Restarting."
        STATUS="E"
        break
      fi
      
    # File already exists but not finished yet
    elif [ -e $SMALLPATH ] && ! $(compdu $SMALLPATH $SMALLSIZE); then
      echo "[INFO] Continuing download."
      wget -c -O $SMALLPATH -nv --show-progress $SMALLURL
      if $(compall $SMALLPATH $SMALLSIZE $SMALLHASH); then
        STATUS="C"
      else 
        # Downloaded file is not valid. Restart for-loop
        echo "[ERROR] Downloaded file is corrupt. Restarting."
        STATUS="E"
        break
      fi
      
    # File already exists, has correct size, but has wrong HASH
    elif [ -e $SMALLPATH ] && $(compdu $SMALLPATH SMALLSIZE) && ! $(comphash $SMALLPATH $SMALLHASH); then
      echo "[ERROR] HASH is different but file has same size."
      echo "[INFO] Deleting file and starting new download." 
      checkwait
      rm $SMALLPATH
      wget -O $SMALLPATH -nv --show-progress $SMALLURL
      if $(compall $SMALLPATH $SMALLSIZE $SMALLHASH); then
        STATUS="C"
      else 
        # Downloaded file is not valid. Restart for-loop
        echo "[ERROR] Downloaded file is corrupt. Restarting."
        STATUS="E"
        break
      fi
    
    # File already exists, has correct size, and has correct HASH
    elif [ -e $SMALLPATH ] && $(compdu $SMALLPATH $SMALLSIZE) && $(comphash $SMALLPATH $SMALLHASH); then
      echo "[SUCCESS] File already exists and is valid."
      STATUS="C"
      
    # This shouldn't happen...
    else
      echo "Dafuq?!"
      STATUS="E"
    fi
    
    # Check if download is finished
    if [ $NO -lt $SMALLNO ]; then
      echo "[INFO] Starting next download."
      STATUS="C"
    elif [ $NO -ge $SMALLNO ] && [ "$STATUS" == "C" ]; then
      echo "[SUCCESS] Downloading finished."
      STATUS="F"
    else
      echo "Dafuq^2"
    fi
    
  done # /for smallnames
done


read -p "Download seems to be finished. Should the splitted files be rebuilt to the original big file again? [y/n] " YN
if [ $YN == "y" ]; then
  # Destination file already exists
  if [ -e $BIGNAME ]; then
    read -p "Destination file already exists. Should it be overwritten? [y/n] " YN
    
    if [ $YN == "y" ]; then
      cat $FOLDER/dl-* > $BIGNAME
    else
      echo "[INFO] Skipping rebuilding."
    fi
  # Destination file doesn't exist yet
  else
    cat $FOLDER/dl-* > $BIGNAME
  fi
fi

# Check big file for HASH and size
sleep 2   # In rare cases, this can prevent a wrong du size
echo "[INFO] Checking correct size and HASH hashsum for rebuilt big file..."

# Compare sizes
if $(compdu $BIGNAME $BIGSIZE); then
  echo "[SUCCESS] The size of the completed file is corrent."
else
  echo "[ERROR] The size of the completed file is incorrect."
fi

# Compare HASH sum
if $(comphash $BIGNAME $BIGHASH); then
  echo "[SUCCESS] The HASH sum of the completed file is corrent."
else
  echo "[ERROR] The HASH sum of the completed file is incorrect."
fi


# Clean directories
read -p "Clean the download directory and info.cfg file? [y/n] " YN
if [ $YN == "y" ]; then
  rm $INFO
  rm -r $FOLDER
fi

fi # /CLIENT MODE