#!/usr/bin/env bash

# Print all (transitive) dependenents of the specified go package.

set -euo pipefail

if [ $# -ne 1 ]; then
    echo "Usage: $0 <module>" >&2
    exit 64
fi
declare -r MODULE=$1

GRAPH=$(go mod graph)
declare -r GRAPH

depends_on() {
    local pkg=$1
    echo "$GRAPH" | awk '$2 == "'"$pkg"'" { print $1 }' | sort | uniq
}

declare -A PKGS=()
supertree() {
    local pkg=$1
    local namepfx=${2:-}
    local pfx=${3:-}
    if (( ${PKGS[$pkg]:-0} )); then
        echo "$namepfx$pkg (*)"
    else
        PKGS[$pkg]=1
        echo "$namepfx$pkg"
        local parent=''
        for p in $(depends_on "$pkg") ; do
            if [ -n "$parent" ]; then supertree "$parent" "$pfx├── " "$pfx│   " ; fi
            parent=$p
        done
        if [ -n "$parent" ]; then supertree "$parent" "$pfx└── " "$pfx    " ; fi
    fi
}

if [[ "$MODULE" == *@* ]]; then
    # The dependency specifies an exact version, so print the packages that
    # depend on it.
    supertree "$MODULE"
else
    # The dependency does not specify an exact version, find all versions of
    # the package and print the packages that depend on each of them.
    first=1
    for pkg in $(echo "$GRAPH" | awk '{ print $1 }' | sort | uniq) ; do
        if [ "${pkg%@*}" = "$MODULE" ]; then
            if (( first )); then first=0; else echo; fi
            supertree "$pkg"
        fi
    done
fi