#!/usr/bin/env ruby

require 'pdfkit'
require 'yaml'
require 'optimist'
require 'date'
require 'money'

I18n.enforce_available_locales = false
Money.locale_backend = :currency
Money.rounding_mode = BigDecimal::ROUND_HALF_EVEN

module InvoiceGenerator
  def show_yml_example_and_exit
    puts <<eot
  from: |
    My multiline name
    Here's a second line
  client: |
    My multiline client
    Hey ho, second line here
  number: 2019-123
  notes: |
    If all your data are always the same, just the invoice number changes,
    save the the static data in a yml and pass the invoice number on command line
    by using (--number).

    Note that the date is always default to today, and the due-date to today + 15
  items:
    -
      - Nice item for %past_month% %year%
      - 1
      - 12334
    -
      - Other item, for %month%
      - 0.5
      - 100000
  currency: GBP
eot
    exit
  end

  def show_template_example_and_exit
    puts File.read(template_path)
    exit
  end

  def map_date_fields(opts)
    [:date, 'due-date'].each do |i|
      opts[i] = yield(opts[i])
    end
  end

  def read_params
    Optimist.options do
      opt :client,            'Contents of client field.', type: :string
      opt :currency,          'Currency used.', type: :string, default: 'USD'
      opt :date,              'Invoice date.', type: :date, default: Date.today
      opt 'due-date',         'Due date.', type: :date, default: (Date.today + 15)
      opt :from,              'Contents of from field.', type: :string
      opt :header,            'Contents of the header.', type: :string, default: 'Invoice'
      opt :notes,             'Contents of notes field.', type: :string
      opt :number,            'Invoice number.', type: :string
      opt 'show-yml-example', 'Show an example of a YML file that can be used by this script.'
      opt 'show-template-example', 'Show an example of a HTML template.'
      opt :stdin,             'Read YML file from STDIN.'
      opt :template,          'HTML template to use', type: :string
      opt :yml,               'YML file with values for parameters not given into command line.', default: 'invoice.yml'
    end
  end

  def read_yml(opts)
    if opts[:stdin]
      data = StringIO.new
      data << STDIN.read until STDIN.eof?
      yaml = data.string
    else
      yaml = File.read(opts[:yml])
    end
    YAML.safe_load(yaml).inject(opts) do |memo, item|
      memo[item[0].to_sym] = item[1]
      memo
    end
    fail('Items not in the right format, something is missing.') unless opts[:items].is_a?(Array)

    opts
  rescue Errno::ENOENT
    raise "YML file #{opts[:yml]} not found or can't be read."
  end

  def fix_date_options(opts)
    map_date_fields(opts) do |value|
      value.is_a?(Date) ? value : Date.parse(value)
    end
  end

  def add_extra_options(opts)
    today = Date.today
    opts[:month] = today.strftime('%B')
    opts[:past_month] = (today << 1).strftime('%B')
    opts[:year] = today.strftime('%Y')

    raw_balance = opts[:items].inject(0) do |balance, item|
      balance + (item[2] * item[1])
    end
    opts[:balance] = Money.new(raw_balance, opts[:currency]).format
  end

  def format_items(opts)
    opts[:items].map! do |i|
      fail 'Items must have 3 values' if i.size != 3

      i[3] = Money.new(i[2] * i[1], opts[:currency]).format
      i[2] = Money.new(i[2], opts[:currency]).format
      "<tr><td>#{i.join('</td><td>')}</td></tr>"
    end
    opts[:items] = opts[:items].join
  end

  def template_path
    File.join(File.dirname(__FILE__), 'invoicegenerator.html')
  end

  def generate_html(opts)
    map_date_fields(opts) do |value|
      value.strftime('%B %-d, %Y')
    end

    html = File.read(opts[:template] || template_path)
    opts.each do |opt, value|
      html.gsub!("%#{opt}%", value.to_s)
    end
    html
  end

  def main
    opts = read_params
    show_yml_example_and_exit if opts[:'show-yml-example_given']
    show_template_example_and_exit if opts[:'show-template-example_given']

    read_yml(opts)
    fix_date_options(opts)
    add_extra_options(opts)
    format_items(opts)
    html = generate_html(opts)

    kit = PDFKit.new(html.encode('iso-8859-1'))
    name = "invoice-#{opts[:number]}.pdf"
    puts "Generating #{name}..."
    kit.to_file(name)
  rescue Errno::ENOENT => e
    abort e.message
  rescue RuntimeError => e
    abort e.message
  end

  extend self
end