#!/bin/sh
[ -f "$HOME/Library/LaunchAgents/ssh-add-A.plist" ] || {
  [ -d "$HOME/Library/LaunchAgents" ] || mkdir -p "$HOME/Library/LaunchAgents"
  cat <<EOF | dd of="$HOME/Library/LaunchAgents/ssh-add-A.plist"
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>ssh-add-A</string>
    <key>ProgramArguments</key>
    <array>
      <string>/usr/bin/ssh-add</string>
      <string>-A</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
  </dict>
</plist>
EOF
}

cat_ssh_config(){
cat <<EOF
Host *
  ForwardAgent yes
  UseKeychain yes
  AddKeysToAgent yes
EOF
}
[ -f "$HOME/.ssh/config" ] && {
  if ! grep '[ 	]*UseKeychain yes$' "$HOME/.ssh/config"; then
    suffix="-$(stat -f '%Sm' -t '%Y%m%d%H%M%S' "$HOME/.ssh/config")"
    cp -p "$HOME/.ssh/config" "$HOME/.ssh/config$suffix"
    cat_ssh_config | tee -a "$HOME/.ssh/config" > /dev/null
  fi
} ||
cat_ssh_config | dd of="$HOME/.ssh/config"