#!/usr/bin/env bash

usage() {
  cat <<EOF
Interactively change the current namespace.

Usage:
  ns [-l | -u]

Examples:
  # Interactively change current namespace
  kubectl ns

  # List all namespaces of current cluster
  kubectl ns -l

  # Update local cache with namespaces of current cluster
  kubectl ns -u 

Flags:
  -l          List namespaces of current cluster
  -u          Update local cache with namespaces of current cluster
  -h, --help  Show this help message
EOF
}

fzf_missing() {
  cat <<EOF
You must install fzf to use this plugin:

    https://github.com/junegunn/fzf

INSTALLATION

Homebrew (macOS) and Linuxbrew (Linux):
    brew install fzf

From source (macOS, Linux):
    git clone https://github.com/junegunn/fzf.git ~/.fzf
    ~/.fzf/install

Other installation options:
    https://github.com/junegunn/fzf#installation 
EOF
}

CACHE="$HOME/.kube/kubectl-ns"

# Save cluster and namespace of current context in CLUSTER and NAMESPACE vars
get_data() {
  eval $(kubectl config view --minify | awk '/^ +namespace:/{n=$2} /^ +cluster:/{c=$2} END{if(n=="")n="default"; gsub("/","-",c); printf "CLUSTER=\"%s\" NAMESPACE=\"%s\"", c, n}')
}

# Retrieve namespaces of cluster of current context and save in local cache
update_cache() {
  echo -n "Updating local cache... "
  mkdir -p "$CACHE" 
  echo "This directory is a cache and can be safely deleted." >"$CACHE/README.txt"
  get_data
  kubectl get -o custom-columns=':.metadata.name' --no-headers ns >"$CACHE/$CLUSTER"
  echo done
}

# Test if cache exists for current cluster, and if not, create it
test_cache() {
  [[ -f "$CACHE/$CLUSTER" ]] || update_cache
}

# Print namespaces of current cluster from local cache
print_namespaces() {
  sed "s/^/  /;\|^  $NAMESPACE$|s/ /*/" "$CACHE/$CLUSTER"
}

# List namespaces from local cache
list_namespaces() {
  get_data
  test_cache
  print_namespaces
}

# Set namespace of current context to a new namespace (from local cache)
set_namespace() {
  which fzf >/dev/null || { fzf_missing; exit 1; }
  get_data
  test_cache
  local ns=$(print_namespaces | fzf -e | sed 's/^..//')
  if [[ -z "$ns" ]]; then
    echo "Aborted. Nothing has been changed."
  else
    kubectl config set-context --current --namespace "$ns" >/dev/null
    echo "Switched to namespace \"$ns\"."
  fi
}

case "$1" in
  "") set_namespace;;
  -l) list_namespaces;;
  -u) update_cache;;
  *)  usage;;
esac