#!/usr/bin/env bash

# v3.0.0
# https://github.com/fsaintjacques/semver-tool

set -o errexit -o nounset -o pipefail

NAT='0|[1-9][0-9]*'
ALPHANUM='[0-9]*[A-Za-z-][0-9A-Za-z-]*'
IDENT="$NAT|$ALPHANUM"
FIELD='[0-9A-Za-z-]+'

SEMVER_REGEX="\
^[vV]?\
($NAT)\\.($NAT)\\.($NAT)\
(\\-(${IDENT})(\\.(${IDENT}))*)?\
(\\+${FIELD}(\\.${FIELD})*)?$"

PROG=semver
PROG_VERSION="3.0.0"

USAGE="\
Usage:
  $PROG bump (major|minor|patch|release|prerel <prerel>|build <build>) <version>
  $PROG compare <version> <other_version>
  $PROG get (major|minor|patch|release|prerel|build) <version>
  $PROG --help
  $PROG --version

Arguments:
  <version>  A version must match the following regular expression:
             \"${SEMVER_REGEX}\"
             In English:
             -- The version must match X.Y.Z[-PRERELEASE][+BUILD]
                where X, Y and Z are non-negative integers.
             -- PRERELEASE is a dot separated sequence of non-negative integers and/or
                identifiers composed of alphanumeric characters and hyphens (with
                at least one non-digit). Numeric identifiers must not have leading
                zeros. A hyphen (\"-\") introduces this optional part.
             -- BUILD is a dot separated sequence of identifiers composed of alphanumeric
                characters and hyphens. A plus (\"+\") introduces this optional part.

  <other_version>  See <version> definition.

  <prerel>  A string as defined by PRERELEASE above.

  <build>   A string as defined by BUILD above.

Options:
  -v, --version          Print the version of this tool.
  -h, --help             Print this help message.

Commands:
  bump     Bump by one of major, minor, patch; zeroing or removing
           subsequent parts. \"bump prerel\" sets the PRERELEASE part and
           removes any BUILD part. \"bump build\" sets the BUILD part.
           \"bump release\" removes any PRERELEASE or BUILD parts.
           The bumped version is written to stdout.

  compare  Compare <version> with <other_version>, output to stdout the
           following values: -1 if <other_version> is newer, 0 if equal, 1 if
           older. The BUILD part is not used in comparisons.

  get      Extract given part of <version>, where part is one of major, minor,
           patch, prerel, build, or release.

See also:
  https://semver.org -- Semantic Versioning 2.0.0"

function error {
  echo -e "$1" >&2
  exit 1
}

function usage-help {
  error "$USAGE"
}

function usage-version {
  echo -e "${PROG}: $PROG_VERSION"
  exit 0
}

function validate-version {
  local version=$1
  if [[ "$version" =~ $SEMVER_REGEX ]]; then
    # if a second argument is passed, store the result in var named by $2
    if [ "$#" -eq "2" ]; then
      local major=${BASH_REMATCH[1]}
      local minor=${BASH_REMATCH[2]}
      local patch=${BASH_REMATCH[3]}
      local prere=${BASH_REMATCH[4]}
      local build=${BASH_REMATCH[8]}
      eval "$2=(\"$major\" \"$minor\" \"$patch\" \"$prere\" \"$build\")"
    else
      echo "$version"
    fi
  else
    error "version $version does not match the semver scheme 'X.Y.Z(-PRERELEASE)(+BUILD)'. See help for more information."
  fi
}

function is-nat {
  [[ "$1" =~ ^($NAT)$ ]]
}

function is-null {
  [ -z "$1" ]
}

function order-nat {
  [ "$1" -lt "$2" ] && {
    echo -1
    return
  }
  [ "$1" -gt "$2" ] && {
    echo 1
    return
  }
  echo 0
}

function order-string {
  [[ $1 < $2 ]] && {
    echo -1
    return
  }
  [[ $1 > $2 ]] && {
    echo 1
    return
  }
  echo 0
}

# given two (named) arrays containing NAT and/or ALPHANUM fields, compare them
# one by one according to semver 2.0.0 spec. Return -1, 0, 1 if left array ($1)
# is less-than, equal, or greater-than the right array ($2).  The longer array
# is considered greater-than the shorter if the shorter is a prefix of the longer.
#
function compare-fields {
  local l="$1[@]"
  local r="$2[@]"
  local leftfield=("${!l}")
  local rightfield=("${!r}")
  local left
  local right

  local i=$((-1))
  local order=$((0))

  while true; do
    [ $order -ne 0 ] && {
      echo $order
      return
    }

    : $((i++))
    left="${leftfield[$i]}"
    right="${rightfield[$i]}"

    is-null "$left" && is-null "$right" && {
      echo 0
      return
    }
    is-null "$left" && {
      echo -1
      return
    }
    is-null "$right" && {
      echo 1
      return
    }

    is-nat "$left" && is-nat "$right" && {
      order=$(order-nat "$left" "$right")
      continue
    }
    is-nat "$left" && {
      echo -1
      return
    }
    is-nat "$right" && {
      echo 1
      return
    }
    {
      order=$(order-string "$left" "$right")
      continue
    }
  done
}

# shellcheck disable=SC2206     # checked by "validate"; ok to expand prerel id's into array
function compare-version {
  local order
  validate-version "$1" V
  validate-version "$2" V_

  # compare major, minor, patch

  local left=("${V[0]}" "${V[1]}" "${V[2]}")
  local right=("${V_[0]}" "${V_[1]}" "${V_[2]}")

  order=$(compare-fields left right)
  [ "$order" -ne 0 ] && {
    echo "$order"
    return
  }

  # compare pre-release ids when M.m.p are equal

  local prerel="${V[3]:1}"
  local prerel_="${V_[3]:1}"
  local left=(${prerel//./ })
  local right=(${prerel_//./ })

  # if left and right have no pre-release part, then left equals right
  # if only one of left/right has pre-release part, that one is less than simple M.m.p

  [ -z "$prerel" ] && [ -z "$prerel_" ] && {
    echo 0
    return
  }
  [ -z "$prerel" ] && {
    echo 1
    return
  }
  [ -z "$prerel_" ] && {
    echo -1
    return
  }

  # otherwise, compare the pre-release id's

  compare-fields left right
}

function command-bump {
  local new
  local version
  local sub_version
  local command

  case $# in
  2) case $1 in
    major | minor | patch | release)
      command=$1
      version=$2
      ;;
    *) usage-help ;;
    esac ;;
  3) case $1 in
    prerel | build)
      command=$1
      sub_version=$2 version=$3
      ;;
    *) usage-help ;;
    esac ;;
  *) usage-help ;;
  esac

  validate-version "$version" parts
  # shellcheck disable=SC2154
  local major="${parts[0]}"
  local minor="${parts[1]}"
  local patch="${parts[2]}"
  local prere="${parts[3]}"
  local build="${parts[4]}"

  case "$command" in
  major) new="$((major + 1)).0.0" ;;
  minor) new="${major}.$((minor + 1)).0" ;;
  patch) new="${major}.${minor}.$((patch + 1))" ;;
  release) new="${major}.${minor}.${patch}" ;;
  prerel) new=$(validate-version "${major}.${minor}.${patch}-${sub_version}") ;;
  build) new=$(validate-version "${major}.${minor}.${patch}${prere}+${sub_version}") ;;
  *) usage-help ;;
  esac

  echo "$new"
  exit 0
}

function command-compare {
  local v
  local v_

  case $# in
  2)
    v=$(validate-version "$1")
    v_=$(validate-version "$2")
    ;;
  *) usage-help ;;
  esac

  set +u # need unset array element to evaluate to null
  compare-version "$v" "$v_"
  exit 0
}

# shellcheck disable=SC2034
function command-get {
  local part version

  if [[ "$#" -ne "2" ]] || [[ -z "$1" ]] || [[ -z "$2" ]]; then
    usage-help
    exit 0
  fi

  part="$1"
  version="$2"

  validate-version "$version" parts
  local major="${parts[0]}"
  local minor="${parts[1]}"
  local patch="${parts[2]}"
  local prerel="${parts[3]:1}"
  local build="${parts[4]:1}"
  local release="${major}.${minor}.${patch}"

  case "$part" in
  major | minor | patch | release | prerel | build) echo "${!part}" ;;
  *) usage-help ;;
  esac

  exit 0
}

case $# in
0)
  echo "Unknown command: $*"
  usage-help
  ;;
esac

case $1 in
--help | -h)
  echo -e "$USAGE"
  exit 0
  ;;
--version | -v) usage-version ;;
bump)
  shift
  command-bump "$@"
  ;;
get)
  shift
  command-get "$@"
  ;;
compare)
  shift
  command-compare "$@"
  ;;
*)
  echo "Unknown arguments: $*"
  usage-help
  ;;
esac