adding feature to output CSV files

.rubocop.yml

@@ -112,6 +112,9 @@ Style/SlicingWithRange:
 Style/SpecialGlobalVars: # DANGER: unsafe rule!!
   Enabled: false
 
+Style/StringConcatenation:
+  Enabled: false
+
 Style/StringLiterals:
   Enabled: false
   EnforcedStyle: double_quotes

CHANGELOG.md

@@ -1,6 +1,9 @@
 
 # SmarterCSV 1.x Change Log
 
+## 1.11.0
+  * added feature to output CSV files ([issue #44](https://github.com/tilo/smarter_csv/issues/44))
+
 ## 1.10.3 (2024-03-10)
   * fixed issue when frozen options are handed in (thanks to Daniel Pepper)
   * cleaned-up rspec tests (thanks to Daniel Pepper)

lib/smarter_csv.rb

@@ -10,6 +10,7 @@
 require "smarter_csv/headers"
 require "smarter_csv/hash_transformations"
 require "smarter_csv/parse"
+require "smarter_csv/generator"
 
 # load the C-extension:
 case RUBY_ENGINE

lib/smarter_csv/generator.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module SmarterCSV
+  #
+  # Generate CSV files from batches of array_of_hashes data
+  # - automatically generates the header on-the-fly
+  # - automatically quotes fields containing the col_sep
+  #
+  # Optionally headers can be passed-in via the options,
+  # If any new headers are fund in the data, they will be appended to the headers.
+  #
+  class Generator
+    def initialize(file_path, options = {})
+      @options = options
+      @headers = options[:headers] || []
+      @col_sep = options[:col_sep] || ','
+      @force_quotes = options[:force_quotes]
+      @map_headers = options[:map_headers] || {}
+      @file = File.open(file_path, 'w+')
+    end
+
+    def append(array_of_hashes)
+      array_of_hashes.each do |hash|
+        hash_keys = hash.keys
+        new_keys = hash_keys - @headers
+        @headers.concat(new_keys)
+
+        # Reorder the hash to match the current headers order and fill missing fields
+        ordered_row = @headers.map { |header| hash[header] || '' }
+
+        @file.puts ordered_row.map { |value| escape_csv_field(value) }.join(@col_sep)
+      end
+    end
+
+    def finalize
+      # Map headers if :map_headers option is provided
+      mapped_headers = @headers.map { |header| @map_headers[header] || header }
+
+      # Rewind to the beginning of the file to write the headers
+      @file.rewind
+      @file.write(mapped_headers.join(@col_sep) + "\n")
+      @file.flush # Ensure all data is written to the file
+      @file.close
+    end
+
+    private
+
+    def escape_csv_field(field)
+      if @force_quotes || field.to_s.include?(@col_sep)
+        "\"#{field}\""
+      else
+        field.to_s
+      end
+    end
+  end
+end

spec/smarter_csv/generator_spec.rb

@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+RSpec.describe SmarterCSV::Generator do
+  let(:file_path) { 'test_output.csv' }
+
+  after(:each) do
+    File.delete(file_path) if File.exist?(file_path)
+  end
+
+  context 'when headers are given in advance' do
+    let(:options) { { headers: %w[name age city] } }
+    let(:data_batches) do
+      [
+        [
+          { name: 'John', age: 30, city: 'New York' },
+          { name: 'Jane', age: 25, country: 'USA' }
+        ],
+        [
+          { name: 'Mike', age: 35, city: 'Chicago', state: 'IL' }
+        ]
+      ]
+    end
+
+    it 'writes the given headers and data correctly' do
+      generator = SmarterCSV::Generator.new(file_path, options)
+      data_batches.each { |batch| generator.append(batch) }
+      generator.finalize
+
+      output = File.read(file_path)
+      expect(output).to include("name,age,city\n")
+      expect(output).to include("John,30,New York\n")
+      expect(output).to include("Jane,25,\n")
+      expect(output).to include("Mike,35,Chicago\n")
+    end
+  end
+
+  context 'when headers are automatically discovered' do
+    let(:data_batches) do
+      [
+        [
+          { name: 'John', age: 30, city: 'New York' },
+          { name: 'Jane', age: 25, country: 'USA' }
+        ],
+        [
+          { name: 'Mike', age: 35, city: 'Chicago', state: 'IL' }
+        ]
+      ]
+    end
+
+    it 'writes the discovered headers and data correctly' do
+      generator = SmarterCSV::Generator.new(file_path)
+      data_batches.each { |batch| generator.append(batch) }
+      generator.finalize
+
+      output = File.read(file_path)
+      expect(output).to include("name,age,city,country,state\n")
+      expect(output).to include("John,30,New York,,\n")
+      expect(output).to include("Jane,25,,USA,\n")
+      expect(output).to include("Mike,35,Chicago,,IL\n")
+    end
+  end
+
+  context 'when headers are mapped' do
+    let(:options) do
+      {
+        map_headers: { name: 'Full Name', age: 'Age', city: 'City', country: 'Country', state: 'State' }
+      }
+    end
+    let(:data_batches) do
+      [
+        [
+          { name: 'John', age: 30, city: 'New York' },
+          { name: 'Jane', age: 25, country: 'USA' }
+        ],
+        [
+          { name: 'Mike', age: 35, city: 'Chicago', state: 'IL' }
+        ]
+      ]
+    end
+
+    it 'writes the mapped headers and data correctly' do
+      generator = SmarterCSV::Generator.new(file_path, options)
+      data_batches.each { |batch| generator.append(batch) }
+      generator.finalize
+
+      output = File.read(file_path)
+      expect(output).to include("Full Name,Age,City,Country,State\n")
+      expect(output).to include("John,30,New York,,\n")
+      expect(output).to include("Jane,25,,USA,\n")
+      expect(output).to include("Mike,35,Chicago,,IL\n")
+    end
+  end
+end