#!/usr/bin/env bash

# Bash substring parse cheatsheet
# -------------------------------
#   %.*  filename.blah.foo.txt -> filename.blah.foo
#   %%.* filename.blah.foo.txt -> filename
#   #*.  filename.blah.foo.txt -> foo.blah.txt
#   ##*. filename.blah.foo.txt -> txt



# split:
# Splits the specified file into the specified number of segments. Output file
# is created within the 'out' directory.
#
# @file         Source file to split into multiple segments
# @splitcount   Number of segments to split @file into.
split() {
  local file="${1}"
  local splitcount="${2}"

  local lc="$(wc -l ${file} | cut -d ' ' -f 1)"
  local lps=$(( lc / splitcount + 1 ))  # Calculate lines per segment
  local segment=0                   # Current file segment int
  local segline=0                   # Current line in the current segment
  local outfile=''                  # Current output file segment path

  # Filename without extension (filename.txt -> filename)
  local filebase="${file%.*}"
  # File extension (filename.txt -> txt)
  local fileext=".${file##*.}"

  # If file extension is the same as the file base (with a preceeding dot), the
  # source file has no extention. Set this variable to empty so the extention
  # will be the segment number
  [ "${fileext}" = ".${filebase}" ] && fileext=''

  # Create output directory to keep things a bit more organized
  [ ! -d out ] && mkdir out

  # Ensure IFS is only separating on newlines
  local oldifs="${IFS}"
  export IFS=$'\n'


  # Update the outfile path
  outfile="out/${filebase}.${segment}${fileext}"
  # Truncate the current output segment file. If we skip this and the file
  # already exists, we will append to an existing file, corrupting output.
  > "${outfile}"
  printf "Writing to '%s' segment\n" "${outfile}"


  # Iterrate over the source file, line by line.
  for line in $(cat ${file}); do
    if [ "${segline}" -eq "${lps}" ]; then
      # Increment the file segment counter
      segment=$(( segment + 1 ))
      # Reset the segment line counter
      segline=0

      # Update the outfile path
      outfile="out/${filebase}.${segment}${fileext}"
      > "${outfile}"
      printf "Writing to '%s' segment\n" "${outfile}"
    fi

    # Append line to segment file
    printf -- "%s\n" "${line}" >> "${outfile}"

    # Increment the segment line counter so we can ensure we don't write past
    # the 'lines per segement' (lps) var.
    segline=$(( segline + 1 ))
  done

  export IFS="${oldifs}"
}


main() {
  local file="${1}"
  local count="${2}"

  # Ensure file and segment count are specified
  [ -z "${file}" ] && printf "Filename required\n" && return 1
  [ -z "${count}" ] && printf "Segment count required\n" && return 1

  # Split (Croatia)!
  split "${file}" "${count}"
}

main ${@}