[Docs] Add note that WeasyPrint package is required

README.md

@@ -1,23 +1,22 @@
 # Pixelpress
-[![CircleCI](https://circleci.com/gh/nerdgeschoss/pixelpress/tree/master.svg?style=svg)](https://circleci.com/gh/nerdgeschoss/pixelpress/tree/master)
 
-Modeled after `ActionMailer` this gem allows you to render PDFs from HTML via Rails templating engine. Also you can preview your PDF templates via a supplied engine during development.
+Modeled after `ActionMailer`, this gem allows you to render PDFs from HTML via Rails' templating engine. Additionally, you can preview your PDF templates via a supplied Rails engine during development.
 
 ## Installation
 
-Add this line to your application's Gemfile:
+Add Pixelpress to your application's Gemfile:
 
 ```ruby
-gem 'pixelpress'
+gem "pixelpress"
 ```
 
 And then execute:
 
-    $ bundle
-
-Or install it yourself as:
+```bash
+$ bundle
+```
 
-    $ gem install pixelpress
+You'll also need [WeasyPrint](https://weasyprint.org/). It needs to be installed and added to your `PATH`, so that `which weasyprint` returns the location of the binary. Read their installation instructions here: https://doc.courtbouillon.org/weasyprint/stable/first_steps.html#installation
 
 ## Usage
 
@@ -26,37 +25,40 @@ Run the printer generator providing the name of your printer with methods to be
 rails generate pixelpress:printer NAME [method_name1 method_name2 ...] [options]
 ```
 
-This creates an `ApplicationPrinter` in `app/printers` and the corresponding subclass and also mounts the engine in your `config/routes.rb` file.
+This creates the new printer in `app/printers`. If you run it the first time, it will also add an `ApplicationPrinter` and mount the Rails engine in your `config/routes.rb` file.
 
 **Example**
+
 ```bash
-$ rails g pixelpress:printer invoice customer_invoice delivery_document 	
+$ rails g pixelpress:printer invoice customer_invoice delivery_document
 ```
-will generate `app/printers/invoice_printer.rb` file which looks like this:
+
+will generate an `app/printers/invoice_printer.rb` file with this content:
+
 ```ruby
 class InvoicePrinter < ApplicationPrinter
- 	def customer_invoice
- 		# put your code here
- 	end
+  def customer_invoice
+    # put your code here
+  end
 
- 	def delivery_document
- 		# put your code here
- 	end
+  def delivery_document
+    # put your code here
+  end
 end
 ```
 
-Also this command will generate the corresponding templates  as `.pdf.erb` files located in `app/views/printers/invoice/`:
+The command will also generate corresponding templates  as `.pdf.erb` files located in `app/views/printers/invoice/`:
 
 - `customer_invoice.pdf.erb`
 - `delivery_document.pdf.erb`
 
 You can preview your documents by running `rails s` and go to
 
 ```
-localhost:3000/rails/printers
+http://localhost:3000/rails/printers
 ```
 
-To use your printers in code, you can instantiate them just like mailers:
+To use your printers in code, you can use them similarly to how you'd use mailers:
 
 ```ruby
 InvoicePrinter.customer_invoice.pdf # render a temporary pdf file

lib/pixelpress/renderers/weasyprint_renderer.rb

@@ -1,18 +1,26 @@
 class Pixelpress::WeasyPrintRenderer
+  class WeasyPrintInstallationError < StandardError; end
+
   def render(input)
     output = Tempfile.new
 
     system executable_path, "--encoding", "utf-8", input.path, output.path, exception: true
     return output
   end
-  
+
   def version
     `#{executable_path} --version`.chomp.scan(/(\d+\.\d+)/).flatten.first
   end
 
   private
 
   def executable_path
-    `which weasyprint`.chomp || raise(StandardError, "could not find weasyprint")
+    path = `which weasyprint`.chomp
+
+    if path.blank?
+      raise WeasyPrintInstallationError.new("Unable to locate weasyprint binary. Please make sure it's in your PATH.")
+    end
+
+    path
   end
 end

spec/renderers/weasyprint_renderer_spec.rb

@@ -27,4 +27,14 @@
     page = reader.pages.sole
     expect(page.text).to eq("Hêllo Wörld")
   end
+
+  context "when the weasyprint binary can't be found" do
+    it "raises an error" do
+      expect(renderer).to receive(:`).with('which weasyprint').and_return("")
+
+      expect {
+        PDF::Reader.new(renderer.render(input))
+      }.to raise_error(/Unable to locate weasyprint/)
+    end
+  end
 end