add usage and arg parsing

scrape.sh

@@ -1,7 +1,93 @@
-#!/bin/sh
+#!/bin/bash
 
-if ! [ -d node_modules ]; then
-  yarn
-fi
+readonly ARGS="$@"
 
-exec node scrape.js
+function usage {
+  cat <<- EOF
+  ./scrape.sh [options]
+
+  Scrape facebook event pages.
+
+  This script will always return an JSON array.
+
+  OPTIONS:
+    -e --event                        Facebook event id. Scrape a single Facebook
+                                      event.
+    -p --page                         Facebook page id. Scrape all events of a
+                                      specific facebook page.
+    -a --pages                        Array of Facebook page ids. This is a space
+                                      seperated list of page ids.
+    -h --help -?                      print usage
+
+  EXAMPLES:
+  Scrape events of a facebook page with id 133713371337
+  ./scrape.sh --page 133713371337
+  ./scrape.sh -p 133713371337
+
+  Scrape a facebook event with id 420420420420
+  ./scrape.sh --event 420420420420
+  ./scrape.sh -e 420420420420
+
+  Scrape a facebook event with id 123 and all events from page 1323
+  ./scrape.sh --event 123 --page 1323
+EOF
+}
+
+function parse_args {
+  if [ "$1" = "" ]; then
+    echo ""
+  fi
+
+  while [[ $# -gt 0 ]]; do
+    key="$1"
+    case $key in
+      -e|--event)
+        shift
+        local event_id;
+        event_id=$1
+        ;;
+      -p|--page)
+        ;;
+      -a|--pages)
+        ;;
+      *)
+        usage
+        exit 1
+        ;;
+    esac
+    shift
+  done
+}
+
+function install_node_dependencies {
+  if ! [ -d node_modules ]; then
+    yarn
+  fi
+}
+
+function check_dependencies {
+  local missing;
+  missing=false;
+
+  if [ ! $(command -v node) ]; then
+    echo "Dependency missing. Please install node.js and make it available to the path as 'node'."
+    missing=true
+  fi
+
+  if [ ! $(command -v yarn) ]; then
+    echo "Dependency missing. Please install yarn and make it available to the path as 'yarn'."
+    missing=true
+  fi
+
+  install_node_dependencies
+
+  if [ "${missing}" != "false" ]; then
+    exit 1;
+  fi
+
+  return 0;
+}
+
+check_dependencies \
+  && parse_args "${ARGS}" \
+  && scrape