From 791f617acbb3a189ffdf64833669859e0b403dcb Mon Sep 17 00:00:00 2001
From: Nick Chambers <uplime@spookyinternet.com>
Date: Sun, 25 Jul 2021 20:39:37 -0500
Subject: [PATCH] bash/roller: D&D-style dice roller

---
 bash/roller | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100755 bash/roller

diff --git a/bash/roller b/bash/roller
new file mode 100755
index 0000000..4299551
--- /dev/null
+++ b/bash/roller
@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+
+die() {
+  printf "invalid roll: $1\n" "${@:2}" >&2
+  exit 1
+}
+
+debug() {
+  if [[ -v opts[debug] ]]; then
+    printf "DEBUG: $1\n" "${@:2}"
+  fi
+}
+
+verbose() {
+  if [[ -v opts[verbose] ]]; then
+    printf "$1\n" "${@:2}"
+  fi
+}
+
+is_integer() {
+  if (( $# )); then
+    [[ $1 =~ ^[0-9]+$ ]]
+  else
+    return 1
+  fi
+}
+
+roll_die() {
+  if (( $# )); then
+    printf %d "$(( (RANDOM % $1) + 1 ))"
+  else
+    printf 0
+  fi
+}
+
+declare -A opts
+
+while (( $# )); do
+  case $1 in
+  -v)
+    opts[verbose]=1
+    ;;
+  -d)
+    opts[debug]=1
+    ;;
+  -x)
+    set -x
+    ;;
+  -*)
+    die "unknown option '%s'" "$1"
+    ;;
+  *)
+    break
+  esac
+
+  shift
+done
+
+if (( $# )); then
+  IFS=d read -r quantity rest <<< "$1"
+
+  if [[ -z $quantity ]]; then
+    quantity=1
+  elif ! is_integer "$quantity"; then
+    die "dice quantity is not a number"
+  fi
+
+  debug "quantity of dice is %d" "$quantity"
+
+  while (( ${#rest} )) && [[ ${rest:0:1} != @(+|-) ]]; do
+    sides+=${rest:0:1} rest=${rest:1}
+  done
+
+  if ! is_integer "$sides"; then
+    die "not a good number of die sides"
+  fi
+
+  debug "die has %d side(s)" "$sides"
+  total_mod=0
+
+  while (( ${#rest} )); do
+    mod_type=${rest:0:1} rest=${rest:1} next_mod=
+
+    while [[ -n $rest && ${rest:0:1} != @(+|-) ]]; do
+      next_mod+=${rest:0:1} rest=${rest:1}
+    done
+
+    if ! is_integer "$next_mod"; then
+      die "'%s' is not a proper modifier" "$next_mod"
+    elif [[ $mod_type = + ]]; then
+      (( total_mod += next_mod ))
+      debug "adding %d to modifier for a total of %d" "$next_mod" "$total_mod"
+    else
+      (( total_mod -= next_mod ))
+      debug "subtracting %d from modifier for a total of %d" "$next_mod" "$total_mod"
+    fi
+  done
+
+  score=0 count=0
+
+  while (( quantity-- )); do
+    roll=$(roll_die "$sides")
+    (( score += roll ))
+    debug "rolled a %d. score is now %d" "$roll" "$score"
+    verbose "roll %d: %d" "$(( count++ ))" "$roll"
+  done
+
+  verbose "score before modifier: %d" "$score"
+  (( score += total_mod ))
+  verbose "score after modifier: %d" "$score"
+  debug "score total after modifier is %d" "$score"
+
+  if [[ ! -v opts[verbose] ]]; then
+    printf '%d\n' "$score"
+  fi
+fi