feat(changelog script): Have script produce markdown, add settings

This completely revamps the changelog script. It now generates links to
the relevant commits in the format of:

     - [`sha-1 hash`](link on github) subsystem: commit message

Additionally, the types of commits shown in the changelog and the root
repository for the link may be set at runtime. Example:

    $ TYPES='feat(;Features' ./generate-changelog.sh v0.9.0
    $ REPOROOT="http://github.com/Xe/deis" ./generate-changelog.sh v0.9.0

This is purely cosmetic and to enable this script to be reused more
easily. The script is now documented and sourceable as a library for
further reuse.

REBASE EDIT: Link generation is deduplicated (commit was rebased) so that
the commit message is no longer a link to the commit, only the commit hash
is. This also no longer uses a temporary file and uses bash command
output redirection as a backwards pip to directly pull the changes from
git into a while loop. Thanks again @bacongobbler for the guidance on this
latest rebase.

Technique found here: http://linuxshellaccount.blogspot.com/2008/08/using-bash-to-feed-command-output-to.html

Author: Xe

contrib/util/generate-changelog.sh

@@ -1,30 +1,85 @@
-#!/bin/sh
+#!/bin/bash
+# vim: et tw=0 sw=4 ts=4
 
 usage() {
     echo "Usage: $0 <from> [to]"
+    echo "The REPOROOT and TYPES variables may be used to customize"
+    echo "what is scraped from the commit logs. Current settings are:"
+    echo
+    echo "   REPOROOT = $REPOROOT"
+    echo "   TYPES = $TYPES"
+    echo
 }
 
+# Print the information scraped from git
 retrieve() {
-    git --no-pager log --oneline --no-merges --oneline --format=" - %h %s" --grep="$1" $FROM..$TO
+    while read commit hash message
+    do
+        # Extract the subsystem where type(subsystem): message
+        SUBSYSTEM=$(echo $message | cut -d'(' -f2 | cut -d')' -f1 | sed 's/\*/\(all\)/g')
+        # Extract the message where type(subsystem): message
+        MESSAGE=$(echo $message | awk -F ")" '{ print $2}' | sed 's/://' | cut -f2- -d' ')
+        # Generate a link to the full legal commit on GitHub
+        LINK="$REPOROOT/commit/$hash"
+        # Echo all this in a way that makes the commit hash and message a link
+        # to the commit in markdown
+        echo ' -' "[\`$commit\`]($LINK)" "$SUBSYSTEM": "$MESSAGE"
+    done < <(git --no-pager log --oneline --no-merges --oneline --format="%h %H %s" --grep="$1" "$FROM".."$TO")
+    # Scrape the information from git
 }
 
+# Wrap feature type and show its relevant commits
 subheading() {
-    echo "#### $1\n"
+    echo "#### $1"
+    echo
     retrieve "$2"
     echo
 }
 
-FROM=$1
-TO=${2:-"HEAD"}
+main() {
+    # if REPOROOT is already in the environment, don't overload it and use that
+    if [ -z "$REPOROOT" ];
+    then
+        REPOROOT="http://github.com/deis/deis"
+    fi
 
-if [ -z $1 ];
-then
-    usage
-    exit 1
-fi
+    # if TYPES is already in the environment, don't overload it and use that
+    if [ -z "$TYPES" ];
+    then
+        # Based on https://github.com/deis/deis/blob/master/CONTRIBUTING.md
+        # The format is in the form of $shortname;$longname $shortname;longname.
+        TYPES="feat(;Features fix(;Fixes docs(;Documentation chore(;Maintenance"
+    fi
+
+    # Print usage summary if user didn't specify a beginning
+    if [ -z "$1" ];
+    then
+        usage
+        exit 1
+    fi
 
-echo "### $FROM -> $TO\n"
+    FROM=$1
+    TO=${2:-"HEAD"}
 
-subheading "Features" "feat("
-subheading "Fixes" "fix("
-subheading "Documentation" "docs("
+    printf "### $FROM -> $TO \n\n"
+
+    # Iterate over the types of messages specified
+    for LEGALTYPE in $TYPES
+    do
+        SHORT=$(echo "$LEGALTYPE" | cut -f1 -d';')
+        LONG=$(echo "$LEGALTYPE" | cut -f2 -d';')
+
+        subheading $LONG $SHORT
+    done
+}
+
+if (( $SHLVL == 2 ))
+then
+    # If this is being run as a command
+    main $*
+    exit
+else
+    # Otherwise this is being sourced
+    unset -f main
+    unset -f usage
+fi