added plugin for displaying prompt responsively

(cherry picked from commit 25a04de1e51358fc8b119c047343a060ee34ced6)
(cherry picked from commit 3f47be12e38c82d09ddaa4ba59269fa642d18840)

plugins/responsive-prompt/responsive-prompt.plugin.zsh

@@ -0,0 +1,49 @@
+#!/usr/env/bin zsh
+# Make your Terminal Prompt responsive :)
+#
+# Author: Nikhil Gupta <me@nikhgupta.com>
+# Version: 0.0.1
+#
+# Please, read the README.md
+#
+[[ -n "${PROMPT_FILE}" ]]          || PROMPT_FILE="${HOME}/.zshrc"
+[[ -n "${PROMPT_BREAKPOINTS}" ]]   || PROMPT_BREAKPOINTS=(120 90 60 0)
+[[ -n "${PROMPT_NEWLINE_AFTER}" ]] || PROMPT_NEWLINE_AFTER=40
+
+
+# Calculate length of the prompt being rendered. Additionally, set
+# a variable that adds a newline character when prompt length exceeds
+# $PROMPT_NEWLINE_AFTER
+_calculate_prompt_length() {
+  local prompt_exp="${(%%)PROMPT}"
+  local prompt_stripped="$(echo $prompt_exp | sed -r 's/\x1B\[([0-9]{1,2}(;[0-9]{1,2})?)?[m|K]//g')"
+  local prompt_length="${#prompt_stripped}"
+
+  unset prompt_newline
+  if [[ $prompt_length -gt $PROMPT_NEWLINE_AFTER ]]; then
+    prompt_newline=$'\n'
+  else
+    prompt_newline=$''
+  fi
+}
+
+# Look for change in $COLUMNS, and loop through all breakpoints to setup
+# the appropriate prompt for the new column size.
+_responsive_prompt(){
+  _calculate_prompt_length
+  [[ $COLUMNS -eq $last_columns ]] && return
+  for breakpoint in $PROMPT_BREAKPOINTS; do
+    [[ $COLUMNS -lt $breakpoint ]] && continue
+    if which "_prompt_$breakpoint" &>/dev/null; then
+      eval "_prompt_$breakpoint"
+      break
+    else
+      source $PROMPT_FILE
+    fi
+  done
+  _calculate_prompt_length
+  last_columns=$COLUMNS
+}
+
+# this function should run when prompt is about to be rendered.
+precmd_functions+=( _responsive_prompt )