#!/bin/sh

while [ $# -gt 0 ]
do
    case "$1" in
        --) shift; break;;
        -?) eval "OPT_${1#-}=y"
            shift
            ;;
        --*=*) kv=${1#--}
            k=${kv##=*}
            v=${kv%*=}
            eval "OPT_${k}=\$1" "$v"
            shift
            ;;
        -*) exit 1;;
        *) break;;
    esac
done

remote=${1:-origin}

SHOW=ahead
[ "$OPT_a" ] && SHOW=all
[ "$OPT_r" ] && SHOW=behind
[ "$OPT_u" ] && SHOW=upto
QUIET=
[ "$OPT_q" ] && QUIET=y
[ "$OPT_n" ] && NS_ONLY=y
[ "$OPT_N" ] && NS_ONLY=

show_message()
{
    show_${SHOW}_message
}

show_all_message()
{
    cat >&2 <<EOF
Showing all remote branches:

EOF
}

show_all_none_message()
{
    cat >&2 <<EOF
No remote branches.
EOF
}

show_ahead_message()
{
    cat >&2 <<EOF
Showing remote branches that are ahead (they have pushed onto your HEAD):

EOF
}

show_ahead_none_message()
{
    x=$(cat <<EOF)
No remote branches are ahead of your HEAD. %d other remote branches were not
listed.
EOF
    printf "$x\n" "$1" >&2

}

show_behind_message()
{
    cat >&2 <<EOF
Showing remote branches that are behind (your HEAD has commits on top of
the remote branch):

EOF
}

show_behind_none_message()
{
    x=$(cat <<EOF)
No remotes branches are behind your HEAD. %d other remote branches were not
listed.
EOF
    printf "$x\n" "$1" >&2

}

show_upto_message()
{
    cat >&2 <<EOF
Showing remote branches that are even with your HEAD.

EOF
}

show_upto_none_message()
{
x=$(cat <<EOF)
No remote branches are even with your HEAD. %d other remote branches were not
listed.
EOF
    printf "$x\n" "$1" >&2
}

have_ref()
{
    git rev-list --quiet "$1" 2>/dev/null
}

git_fetch()
{
    local hash="$1" ref="$2"
    have_ref "$hash" || git fetch "$remote" "$ref"
}

is_same_ref()
{
    [ "$1" = "$2 " ] || [ "$(git rev-parse "$1")" = "$(git rev-parse "$2")" ]
}

is_ancestor()
{
    if is_same_ref "$1" "$2"
    then false
    else git merge-base --is-ancestor "$1" "$2"
    fi
}

verdict()
{
    if is_same_ref HEAD "$1"
    then echo even
    elif is_ancestor "$1" HEAD
    then echo behind
    elif is_ancestor HEAD "$1"
    then echo ahead
    else echo diverged
    fi
}

show_this_remote_branch()
{
    local hash="$1"
    case "$SHOW" in
        all) VERDICT=$(verdict "$hash") ;;
        behind) is_ancestor "$hash" HEAD ;;
        ahead) is_ancestor HEAD "$hash" ;;
        upto) is_same_ref HEAD "$hash" ;;
    esac
}

handle_hash_ref()
{
    local hash="$1" ref="$2"
    git_fetch "$hash" "$ref" || exit

    if show_this_remote_branch "$hash"
    then
        if [ ! "$QUIET" -a "$listed" -eq 0 ]
        then
            show_message
        fi

        if [ "$SHOW" = all ]
        then
            >&2 printf 'remote: %s (%s)\n' "$ref" "$VERDICT"
        else
            >&2 printf 'remote: %s\n' "$ref"
        fi

        git show "$hash" | sed '/^$/q'
        listed=$((listed + 1))
    else
        skipped=$((skipped + 1))
    fi
}

read_hashes()
{
    while read hash ref; do
        [ "$hash" != From ] || continue
        case "$ref" in
            refs/namespaces/*) ;;
            *) [ ! "$NS_ONLY" ] || continue ;;
        esac
        handle_hash_ref "$hash" "$ref"
    done
}

finalize()
{
    if [ "$listed" -eq 0 ]
    then
        show_${SHOW}_none_message "$skipped"
    fi
}

skipped=0
listed=0
git ls-remote $remote | (read_hashes && finalize)