#!/bin/bash

# usage:
#   cd xen.git
#   docs/support-matrix-generate [-D]                               \
#       refs/remotes/origin/master                                  \
#           https://xenbits.xen.org/docs/unstable/SUPPORT.html      \
#       refs/remotes/origin/stable-NN                               \
#           https://xenbits.xen.org/docs/NN-testing/SUPPORT.html    \
#
# NN is a *literal* in the above rune!  It will be substituted with
# the appropriate version number.
#
# The idea is that we use staging's version of this script, and it
# looks into the git history and various git remote tracking refs to
# find the various versions of SUPPORT.md.
#
# The arguments specify the git refs to look in, and also the URLs for
# the SUPPORT.html (which are needed so that we can make
# cross-reference links).  We provide the ref and url (i) for unstable
# (ii) in template form for all previous versions.

# Algorithm:
#
# We start with `refs/remotes/origin/master' and process its
# SUPPORT.md into json.
#
# Then we try to find the next previous revision.  This is done by
# extracting the current version number from xen/Makefile.  (We make
# some slight assumption about how xen/Makefile's variables are
# written, because we want to be able to do this without checking out
# the whole tree for the version in question.)  Then we use git log on
# xen/Makefile to try to find a commit where the version changed.
# This gives us the previous version number, NN.
#
# That is substituted into the `refs/remotes/origin/stable-NN'
# argument to get the tip of the relevant branch.  That in turns
# contains another SUPPORT.md.  We keep going until either the ref
# itself is missing, or we get to a ref with no SUPPORT.md.

set -e
set -o posix
set -o pipefail

fail () { echo >&2 "$0: $1"; exit 12; }

args=()

case "$1" in
    -D) args+=("$1"); shift ;;
    -*) fail 'bad usage' ;;
    --) shift; break ;;
esac

case "$#" in
    4) ;;
    *) fail 'bad usage' ;;
esac

current_ref=$1
current_url=$2
pattern_ref=$3
pattern_url=$4

tmp_prefix="docs/tmp.support-matrix"
tmp_mdfile="$tmp_prefix.md"
tmp_revisions="$tmp_prefix.revisions.html"

versionfile=xen/Makefile
tmp_versionfile="$tmp_prefix.xen.make"

cat docs/misc/support-matrix-head.html

debug () {
    echo "<!-- $* -->"
}

select_commitish () {
    commitish=$1
    debug "select_commitish $commitish"
    obj="$(printf "%s:SUPPORT.md" "$commitish")"
    exists="$(printf "%s" "$obj" | git cat-file --batch-check)"
    >"$tmp_mdfile"
    case "$exists" in
        *' missing')
            rm "$tmp_mdfile"
            ;;
        *' blob '*)
            git cat-file blob "$obj" >"$tmp_mdfile"
            ;;
        *) fail "?? $current_url $exists ?";;
    esac
}

commitish_version () {
    case "$commitish" in
        refs/*)
            # this is how to find out if a ref exists
            local gfer=$(git for-each-ref "[r]${commitish#r}")
            if [ "x$gfer" = x ]; then return; fi
            ;;
    esac

    git cat-file blob "$commitish:$versionfile" >"$tmp_versionfile"

    local maj=$(sed -n 's/.*XEN_VERSION.*= \([0-9]\+\)/\1/p' < "$tmp_versionfile")
    local min=$(sed -n 's/.*XEN_SUBVERSION.*= \([0-9]\+\)/\1/p' < "$tmp_versionfile")

    if [ -z $maj ] || [ -z $min ];
    then
        fail "Unable to identify Xen version for $commitish";
    fi

    printf "%d.%d\n" "$maj" "$min"
}

exec 4>"$tmp_revisions"

while true; do
    select_commitish "$current_ref"
    current_version=$(commitish_version)
    debug "current_version=$current_version"

    if ! [ -e "$tmp_mdfile" ]; then break; fi

    cat >&4 <<END
<tr>
<td align="center">$current_version</td>
END
    git >&4 log -n1 --pretty=tformat:'
<td><code>%ci</code></td>
<td><code>%H</code></td>
' "$current_ref"
    cat >&4 <<END
</tr>
END

    current_jsonfile="$tmp_prefix.$current_version.json"
    pandoc -t json <"$tmp_mdfile" >"$current_jsonfile"

    args+=("$current_jsonfile" "$current_url")

    # find previous version
    search_commit="$current_ref"
    while true; do
        search_commit=$(git log --pretty=format:%H -n1 \
                        -G 'XEN.*VERSION' $search_commit -- $versionfile)
        if ! [ "$search_commit" ]; then search_version=''; break; fi

        search_commit="$search_commit~"
        select_commitish "$search_commit"
        search_version=$(commitish_version)
        debug "search_version=$search_version"
        if [ "x$search_version" != "x$current_version" ]; then break; fi
    done

    if [ "x$search_version" = x ]; then break; fi

    # have found the previous version
    current_ref=${pattern_ref/NN/$search_version}
    current_url=${pattern_url/NN/$search_version}
done

debug "${args[*]}"
docs/parse-support-md "${args[@]}"

cat <<END
    <h2>Source materials</h2>
      Generated from xen.git
      by docs/support-matrix-generate and docs/parse-support-md.
      <p>
      Input revisions of SUPPORT.md used:
    <table>
    <tr>
      <th>Version</th>
      <th align="left">Commit date</th>
      <th align="left">Git commit</th>
END

cat "$tmp_revisions"

generated=$(TZ=UTC date --iso-8601=minutes)

cat <<END
    </table>
    <p>
    Last checked/updated/regenerated: ${generated/T/ }
  </body>
</html>
END