module Jekyll::Algolia::Utils

def self.compact_empty(hash)

hash - The input hash

Public: Remove all keys with a nil value or an empty array from a hash 
def self.compact_empty(hash)
  new_hash = {}
  hash.each do |key, value|
    next if value.nil?
    next if value.respond_to?(:empty?) && value.empty?
    new_hash[key] = value
  end
  new_hash
end

def self.find_by_key(items, key, value)

It is basically a wrapper around [].find, handling more edge-cases

value - The value of the key to filter
key - The key to search for
items - The array of hashes to search

Public: Find an item from an array based on the value of one of its key 
def self.find_by_key(items, key, value)
  return nil if items.nil?
  items.find do |item|
    item[key] == value
  end
end

def self.html_to_text(html)

html - String representation of the HTML node

Public: Convert an HTML string to its content only 
def self.html_to_text(html)
  return nil if html.nil?
  text = Nokogiri::HTML(html).text
  text.tr("\n", ' ').squeeze(' ').strip
end

def self.instance_of?(input, classname)

classname - the string representation of the class
input - the variable to test

Public: Check if a variable is an instance of a specific class 
def self.instance_of?(input, classname)
  return input.instance_of? Object.const_get(classname)
rescue StandardError
  # The class might not even exist
  return false
end

def self.keys_to_symbols(hash)

hash - The input hash, with string keys

Public: Convert a hash with string keys to a hash with symbol keys 
def self.keys_to_symbols(hash)
  Hash[hash.map { |key, value| [key.to_sym, value] }]
end

def self.match?(string, regex)

needed for older versions.
Newer versions of Ruby have easy ways to test this, but a wrapper is

regex - The regex to match against
string - The string to test

Public: Check if a string matches a regex 
def self.match?(string, regex)
  # Ruby 2.4 introduces .match?
  return regex.match?(string) if regex.respond_to?(:match?)
  # Older versions of Ruby have to deal with =~ returning nil if no match
  # is found
  !(string =~ regex).nil?
end

def self.monkey_patch(instance, method, block)

https://stackoverflow.com/questions/803020/redefining-a-single-ruby-method-on-a-single-instance-with-a-lambda/16631789
Solution found on

block - The new block to use for replacing (as a proc)
method - The method symbol to overwrite
instance - The instance to overwrite

Public: Allow redefining an instance method on the fly with a new one 
def self.monkey_patch(instance, method, block)
  metaclass = class << instance; self; end
  metaclass.send(:define_method, method, block)
end