run_update_history.sh

#!/bin/bash

# Backward updates mechanism

set -e

source /usr/local/etc/library.sh

# Updates folder contains the "history" of updates
updates="$1"
[ -d "$updates" ] || { echo "$updates does not exist. Abort" >&2; exit 1; }

# Get the array of updates dir
# The files in updates dir are sorted by tag number
# Files names follow the syntax of a tag: x.y.z.sh
while read line ; do
  updates_list+=("$line")
done < <( ls -1 "$updates" | sort -V)

starting_checkpoint=0
len=${#updates_list[@]}
end_of_list=$((len - 1))

# The latest checkpoint is the newer version in updates dir
latest_checkpoint=${updates_list[$end_of_list]}
latest_checkpoint_version=$( basename "$latest_checkpoint" .sh )
current_version=$( grep -oP "\d+\.\d+\.\d+" /usr/local/etc/ncp-version | cut -d'v' -f1 )

# Compare current version with latest checkpoint
# If the current version is more recent than the latest checkpoint there is no need for backward updates

if is_more_recent_than "$latest_checkpoint_version" "$current_version" ; then

  # Execute a series of updates of older versions

  # Binary search to find the right checkpoint to begin the updates
  # Checkpoints are considered the updates files
  # An update file will update the system to the version it has as a tag
  # <tag>.sh will update ncp to <tag> version

  # An update is *applicable* when it is more recent than the current version
  # An older update/checkpoint is not *applicable* to our system
    
  lower_bound=0
  upper_bound=$end_of_list
  while [ $lower_bound -le $upper_bound ]; do
    x=$((upper_bound + lower_bound))
    mid=$((x / 2))

    #Compare mid's version with current version

    mid_version=$( basename ${updates_list[$mid]} .sh )

    if is_more_recent_than "$mid_version" "$current_version" ; then 
      # Mid's version update is applicable to the current version
      # Check if the previous checkpoint (mid-1) is applicable

      previous=$((mid - 1))
      previous_version=$( basename ${updates_list[$previous]} .sh )
      if [ "$mid" -gt 0 ] ; then
        #Compare previous's version with current version
	# If the previous checkpoint is not applicable then mid is the starting checkpoint
	# Otherwise keep on binary searching
	if is_more_recent_than "$current_version" "$previous_version" ; then
          starting_checkpoint=$mid
	  break
	fi
      else
        # mid is at 0, so this is the starting checkpoint
	starting_checkpoint=$mid
	break
      fi
      # Continue searching for starting checkpoint
      upper_bound=$((mid - 1))

    else
      # Mid's version update is not applicable to the current version
      # Check if the next checkpoint (mid+1) is applicable

      next=$((mid + 1))
      next_version=$( basename ${updates_list[$next]} .sh )

      #Compare next's version with current version
      # If next checkpoint is not applicable then next is the starting checkpoint
      # Otherwise keep on binary searching
      if is_more_recent_than "$current_version" "$next_version" ; then
        # Continue searching for starting checkpoint
	lower_bound=$((mid + 1))
      else
        # The next version is the starting checkpoint
	starting_checkpoint=$next
	break
      fi
    fi
  done

  # Starting checkpoint has been found so update the system for the rest updates

  for(( i="$starting_checkpoint"; i<="$end_of_list"; i++)); do
    update_file=${updates_list[i]}
    tag_update=$( basename "$update_file" .sh )
    echo -e "Updating system to version $tag_update . . ."
    ./"$updates"/"$update_file" || exit 1
    echo -e "System updated successfully to version $tag_update"
    echo "v$tag_update" > /usr/local/etc/ncp-version
  done
fi