add high-level wrapper and document in README.md

Author: ashkulz

README.md

@@ -20,8 +20,29 @@ Or install it yourself as:
 
 ## Usage
 
-TODO: Write usage instructions here
+To encrypt, you can either pass in a file or binary data:
+```ruby
+require "ooxml_crypt"
+
+# pass in binary data, get binary data
+encrypted_data = OoxmlCrypt.encrypt(bindata, password)
+
+# or use file names
+OoxmlCrypt.encrypt_file(filename, password, encrypted_filename)
+```
+
+The same approach holds true for decryption:
+```ruby
+require "ooxml_crypt"
+
+# pass in binary data, get binary data
+decrypted_data = OoxmlCrypt.decrypt(bindata, password)
+
+# or use file names
+OoxmlCrypt.decrypt_file(filename, password, decrypted_filename)
+```
 
+An exception `OoxmlCrypt::Error` will be raised in case of errors.
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

lib/ooxml_crypt.rb

@@ -3,5 +3,73 @@
 require_relative "ooxml_crypt/version"
 require_relative "ooxml_crypt/ooxml_crypt"
 
+require "tempfile"
+
 module OoxmlCrypt
+  class Error < StandardError; end
+  class FileNotFound < Error; end
+  class EmptyPassword < Error; end
+
+  ERRORS = { # should be kept in sync with msoc.h
+    1  => "not supported format",
+    2  => "already encrypted",
+    3  => "already decrypted",
+    4  => "bad password",
+    5  => "bad parameter",
+    6  => "small max size",
+    7  => "no memory",
+    8  => "internal exception",
+    9  => "too large file",
+    10 => "inFile is empty",
+    11 => "outFile is empty",
+    12 => "password is empty",
+  }
+
+  def self.encrypt_file(input, password, output)
+    raise EmptyPassword if password.nil? || password.empty?
+    raise FileNotFound, input unless File.exist?(input)
+
+    result = OoxmlCryptNative.encrypt_file(input, password, output)
+    raise Error, ERRORS[-result] if result != 0
+  end
+
+  def self.decrypt_file(input, password, output)
+    raise EmptyPassword if password.nil? || password.empty?
+    raise FileNotFound, input unless File.exist?(input)
+
+    result = OoxmlCryptNative.decrypt_file(input, password, output)
+    raise Error, ERRORS[-result] if result != 0
+  end
+
+  def self.encrypt(data, password)
+    with_temp_files(data) do |input, output|
+      encrypt_file(input, password, output)
+    end
+  end
+
+  def self.decrypt(data, password)
+    with_temp_files(data) do |input, output|
+      decrypt_file(input, password, output)
+    end
+  end
+
+  private
+
+  def self.with_temp_files(data)
+    input = Tempfile.new("ooxml_crypt_input", binmode: true)
+    input.write(data)
+    input.close
+
+    output = Tempfile.new("ooxml_crypt_output", binmode: true)
+    output.close
+
+    yield input.path, output.path
+
+    result = File.binread(output.path)
+
+    input.unlink
+    output.unlink
+
+    result
+  end
 end