implement semver --increment to remove dependency

package.json

@@ -17,10 +17,5 @@
     "type": "git",
     "url": "git://github.com/davidchambers/xyz.git"
   },
-  "dependencies": {
-    "semver": "5.3.x"
-  },
-  "bundledDependencies": [
-    "semver"
-  ]
+  "dependencies": {}
 }

xyz

@@ -31,6 +31,11 @@ Options:
         'X.Y.Z' acts as a placeholder for the version number.
         'Version X.Y.Z' is assumed if this option is omitted.
 
+   --prerelease-label <label>
+        Specify the label to be used in the version number when publishing
+        a pre-release version (e.g. 'beta' is the label in '2.0.0-beta.0').
+        'rc' is assumed if this option is omitted.
+
    --publish-command <command>
         Specify the command to be run to publish the package. It may refer
         to the VERSION and PREVIOUS_VERSION environment variables. A no-op
@@ -60,27 +65,70 @@ Options:
         Print xyz's version number and exit.
 "
 
-# http://stackoverflow.com/a/246128/312785
-unset CDPATH
-path="${BASH_SOURCE[0]}"
-while [ -h "$path" ] ; do
-  dir="$(cd -P "$(dirname "$path")" && pwd)"
-  path="$(readlink "$path")"
-  [[ $path == /* ]] || path="$dir/$path"
-done
-dir="$(cd -P "$(dirname "$path")" && pwd)"
+inc() {
+  local prerelease_label="$1" increment="$2" version="$3"
+  local number='0|[1-9][0-9]*'
+  local part="$number|[-0-9A-Za-z]+"
+  local pattern="^($number)[.]($number)[.]($number)(-(($part)([.]($part))*))?$"
+  if ! [[ $version =~ $pattern ]] ; then
+    printf 'Invalid version: %s\n' "$version" >&2
+    return 1
+  fi
+  local -i x=${BASH_REMATCH[1]}
+  local -i y=${BASH_REMATCH[2]}
+  local -i z=${BASH_REMATCH[3]}
+  local qual=${BASH_REMATCH[5]}
+
+  local -a parts=("$prerelease_label" 0)
+  case $increment in
+    major)  (( y + z == 0 )) && [[ -n $qual ]] || x+=1 ; y=0 ; z=0 ;;
+    minor)      (( z == 0 )) && [[ -n $qual ]] || y+=1 ; z=0 ;;
+    patch)                      [[ -n $qual ]] || z+=1 ;;
+    premajor)                                     x+=1 ; y=0 ; z=0 ;;
+    preminor)                                     y+=1 ; z=0 ;;
+    prepatch)                                     z+=1 ;;
+    prerelease)
+      case ${BASH_REMATCH[6]} in
+        '') z+=1 ;;
+        $prerelease_label)
+          local idx
+          local -a xs
+          IFS=. read -r -a xs <<<"$qual"
+          for (( idx = ${#xs[@]} - 1 ; idx > 0 ; idx -= 1 )) ; do
+            pattern="^($number)$"
+            if [[ ${xs[idx]} =~ $pattern ]] ; then
+              parts=(${xs[@]})
+              (( parts[idx] += 1 ))
+              break
+            fi
+          done
+      esac
+      ;;
+    *)
+      echo "Invalid --increment" >&2
+      return 1
+  esac
+
+  version="$x.$y.$z"
+  if [[ $increment =~ ^pre ]] ; then
+    join() { local IFS=. ; echo "$*" ; }
+    version+="-$(join "${parts[@]}")"
+  fi
+  printf %s "$version"
+}
 
 branch=master
 edit=false
 increment=patch
 message_template='Version X.Y.Z'
+prerelease_label=rc
 publish_command='npm publish'
 repo=origin
 declare -a scripts
 tag_template=vX.Y.Z
 dry_run=false
 
-while (($# > 0)) ; do
+while (( $# > 0 )) ; do
   option="$1"
   shift
 
@@ -90,29 +138,25 @@ while (($# > 0)) ; do
       exit
       ;;
     -v|--version)
-      node -p "require('$dir/package.json').version"
+      node -p 'require("xyz/package.json").version'
       exit
       ;;
-    -b|--branch)          branch="$1"           ; shift ;;
-    -e|--edit)            edit=true             ;;
-    -i|--increment)       increment="$1"        ; shift ;;
-    -m|--message)         message_template="$1" ; shift ;;
-       --publish-command) publish_command="$1"  ; shift ;;
-    -r|--repo)            repo="$1"             ; shift ;;
-    -s|--script)          scripts+=("$1")       ; shift ;;
-    -t|--tag)             tag_template="$1"     ; shift ;;
-       --dry-run)         dry_run=true          ;;
+    -b|--branch)            branch="$1"           ; shift ;;
+    -e|--edit)              edit=true             ;;
+    -i|--increment)         increment="$1"        ; shift ;;
+    -m|--message)           message_template="$1" ; shift ;;
+       --prerelease-label)  prerelease_label="$1" ; shift ;;
+       --publish-command)   publish_command="$1"  ; shift ;;
+    -r|--repo)              repo="$1"             ; shift ;;
+    -s|--script)            scripts+=("$1")       ; shift ;;
+    -t|--tag)               tag_template="$1"     ; shift ;;
+       --dry-run)           dry_run=true          ;;
     *)
       echo "Unrecognized option $option" >&2
       exit 1
   esac
 done
 
-case "$increment" in
-  major|minor|patch|premajor|preminor|prepatch|prerelease) ;;
-  *) echo "Invalid --increment" >&2 ; exit 1 ;;
-esac
-
 [[ $(git rev-parse --abbrev-ref HEAD) == "$branch" ]] ||
   (echo "Current branch does not match specified --branch" >&2 ; exit 1)
 
@@ -125,8 +169,7 @@ name=$(node -p "require('./package.json').name" 2>/dev/null) ||
 version=$(node -p "require('./package.json').version" 2>/dev/null) ||
   (echo "Cannot read package version" >&2 ; exit 1)
 
-next_version=$("$dir/node_modules/.bin/semver" -i "$increment" "$version") ||
-  (echo "Cannot increment version number" >&2 ; exit 1)
+next_version=$(inc "$prerelease_label" "$increment" "$version")
 
 message="${message_template//X.Y.Z/$next_version}"
 tag="${tag_template//X.Y.Z/$next_version}"