mermaid-cli support (#6)

* support for mermaid if mermaid-cli is installed

.rubocop.yml

@@ -305,6 +305,9 @@ Style/HashTransformValues:
 RSpec/ExampleLength:
   Enabled: false
 
+RSpec/AnyInstance:
+  Enabled: false
+
 Naming/VariableNumber:
   Enabled: false
 

demo/demo.md

@@ -342,6 +342,29 @@ With a reference later in the document defining the URL location.
 
 ---
 
+# Mermaid
+
+if https://github.com/mermaid-js/mermaid-cli is installed, the following code block with mermaid fence is converted to and included as PNG
+
+```mermaid
+quadrantChart
+    title Reach and engagement of campaigns
+    x-axis Low Reach --> High Reach
+    y-axis Low Engagement --> High Engagement
+    quadrant-1 We should expand
+    quadrant-2 Need to promote
+    quadrant-3 Re-evaluate
+    quadrant-4 May be improved
+    Campaign A: [0.3, 0.6]
+    Campaign B: [0.45, 0.23]
+    Campaign C: [0.57, 0.69]
+    Campaign D: [0.78, 0.34]
+    Campaign E: [0.40, 0.34]
+    Campaign F: [0.35, 0.78]
+```
+
+---
+
 # Frontmatter
 
 Frontmatter YML is supported:
@@ -389,4 +412,3 @@ Duplicated footnote reference[^second].
 
 [^second]: Footnote text.
 
----

lib/md_to_pdf/elements/codeblock.rb

@@ -1,6 +1,11 @@
+require "open3"
+require "tempfile"
+
 module MarkdownToPDF
   module Codeblock
     def draw_codeblock(node, opts)
+      return if node.fence_info == "mermaid" && build_mermaid_block(node, opts)
+
       cell_style_opts = codeblock_style(opts)
       table_rows = build_codeblock_cell_rows(node, cell_style_opts)
       return if table_rows.empty?
@@ -22,6 +27,68 @@ def draw_codeblock(node, opts)
 
     private
 
+    def mermaid_cli_available?
+      return $mermaid_cli_available if defined?($mermaid_cli_available)
+
+      $mermaid_cli_available =
+        begin
+          _, status = Open3.capture2e("mmdc", "-V")
+          status.success?
+        rescue StandardError
+          false
+        end
+    end
+
+    def build_mermaid_block(node, _opts)
+      return false unless respond_to?(:mermaid_cli_enabled?) && mermaid_cli_enabled?
+      return false unless mermaid_cli_available?
+
+      image_file = Tempfile.new(['mermaid', ".png"])
+      begin
+        return false unless run_mermaid_cli(node.string_content, image_file.path, 'png',
+                                            { background: "transparent", theme: "neutral" })
+
+        image_obj, image_info = @pdf.build_image_object(image_file.path)
+        options = {
+          scale: [@pdf.bounds.width / image_info.width.to_f, 1].min
+        }
+        @pdf.embed_image(image_obj, image_info, options)
+        true
+      rescue StandardError
+        false
+      ensure
+        image_file.unlink
+      end
+    end
+
+    def run_mermaid_cli(mmdc, destination, format, options = {})
+      tmp_file('mermaid', 'mmdc', mmdc) do |filename|
+        args = ["-i", filename, '-e', format, '-o', destination]
+        args << '-C' << options[:css_file] if options[:css_file]
+        args << '-t' << options[:theme] if options[:theme]
+        args << '-w' << options[:width] if options[:width]
+        args << '-H' << options[:height] if options[:height]
+        args << '-s' << options[:scale] if options[:scale]
+        args << '-b' << options[:background] if options[:background]
+        args << '-p' << options[:puppeteer_config_file] if options[:puppeteer_config_file]
+        args << '-c' << options[:config_file] if options[:config_file]
+        _, status = Open3.capture2e("mmdc", *args)
+        status.success?
+      rescue StandardError
+        false
+      end
+    end
+
+    def tmp_file(basename, input_ext, code)
+      source_file = Tempfile.new([basename, ".#{input_ext}"])
+      begin
+        File.write(source_file.path, code)
+        yield source_file.path
+      ensure
+        source_file.unlink
+      end
+    end
+
     def build_codeblock_cell_rows(node, cell_style_opts)
       lines = node.string_content.gsub(' ', Prawn::Text::NBSP).split("\n")
       lines.map do |line|

lib/md_to_pdf/external.rb

@@ -26,6 +26,10 @@ def warn(text, element, node)
       puts "WARNING: #{text}\nGot #{element} at #{node ? node.source_position.inspect : '?'}\n\n"
     end
 
+    def mermaid_cli_enabled?
+      true
+    end
+
     private
 
     def validate_image(url, node)

spec/fixtures/mermaid/mermaid.md

@@ -0,0 +1,28 @@
+```mermaid
+gantt
+    title A Gantt Diagram
+    dateFormat YYYY-MM-DD
+    section Section
+        A task          :a1, 2014-01-01, 30d
+        Another task    :after a1, 20d
+    section Another
+        Task in Another :2014-01-12, 12d
+        another task    :24d
+```
+
+```mermaid
+quadrantChart
+    title Reach and engagement of campaigns
+    x-axis Low Reach --> High Reach
+    y-axis Low Engagement --> High Engagement
+    quadrant-1 We should expand
+    quadrant-2 Need to promote
+    quadrant-3 Re-evaluate
+    quadrant-4 May be improved
+    Campaign A: [0.3, 0.6]
+    Campaign B: [0.45, 0.23]
+    Campaign C: [0.57, 0.69]
+    Campaign D: [0.78, 0.34]
+    Campaign E: [0.40, 0.34]
+    Campaign F: [0.35, 0.78]
+```

spec/markdown_to_pdf/codeblock_mermaid_spec.rb

@@ -0,0 +1,54 @@
+require 'pdf_helpers'
+
+describe MarkdownToPDF::Codeblock do
+  include_context 'with pdf'
+
+  it 'keeps using the code block if mermaid cli is not available' do
+    allow_any_instance_of(described_class)
+      .to receive(:mermaid_cli_available?)
+            .and_return(false)
+    generator.parse_file('mermaid/mermaid.md')
+    expect_pdf_images([])
+    expect_pdf([
+                 { x: 36.0, y: 744.756, text: "gantt" },
+                 { x: 36.0, y: 728.884, text: "    title A Gantt Diagram" },
+                 { x: 36.0, y: 713.012, text: "    dateFormat YYYY-MM-DD" },
+                 { x: 36.0, y: 697.14, text: "    section Section" },
+                 { x: 36.0, y: 681.268, text: "        A task          :a1, 2014-01-01, 30d" },
+                 { x: 36.0, y: 665.396, text: "        Another task    :after a1, 20d" },
+                 { x: 36.0, y: 649.524, text: "    section Another" },
+                 { x: 36.0, y: 633.652, text: "        Task in Another :2014-01-12, 12d" },
+                 { x: 36.0, y: 617.78, text: "        another task    :24d" },
+                 { x: 36.0, y: 603.908, text: "quadrantChart" },
+                 { x: 36.0, y: 588.036, text: "    title Reach and engagement of campaigns" },
+                 { x: 36.0, y: 572.164, text: "    x-axis Low Reach --> High Reach" },
+                 { x: 36.0, y: 556.292, text: "    y-axis Low Engagement --> High Engagement" },
+                 { x: 36.0, y: 540.42, text: "    quadrant-1 We should expand" },
+                 { x: 36.0, y: 524.548, text: "    quadrant-2 Need to promote" },
+                 { x: 36.0, y: 508.676, text: "    quadrant-3 Re-evaluate" },
+                 { x: 36.0, y: 492.804, text: "    quadrant-4 May be improved" },
+                 { x: 36.0, y: 476.932, text: "    Campaign A: [0.3, 0.6]" },
+                 { x: 36.0, y: 461.06, text: "    Campaign B: [0.45, 0.23]" },
+                 { x: 36.0, y: 445.188, text: "    Campaign C: [0.57, 0.69]" },
+                 { x: 36.0, y: 429.316, text: "    Campaign D: [0.78, 0.34]" },
+                 { x: 36.0, y: 413.444, text: "    Campaign E: [0.40, 0.34]" },
+                 { x: 36.0, y: 397.572, text: "    Campaign F: [0.35, 0.78]" }])
+  end
+
+  it 'replaces mermaid diagram code block with images' do
+    allow_any_instance_of(described_class)
+      .to receive(:mermaid_cli_available?)
+            .and_return(true)
+    allow_any_instance_of(described_class)
+      .to receive(:run_mermaid_cli) do |_caller, _mmdc, destination, _format, _options|
+      png = Base64.decode64("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAACklEQVR4nGMAAQAABQABDQottAAAAABJRU5ErkJggg==")
+      File.write(destination, png)
+      true
+    end
+    generator.parse_file('mermaid/mermaid.md')
+    expect_pdf_images([
+                        { x: 36.0, y: 755.0, width: 1.0, height: 1.0 },
+                        { x: 36.0, y: 754.0, width: 1.0, height: 1.0 }])
+    expect_pdf([])
+  end
+end

spec/pdf_helpers.rb

@@ -49,6 +49,10 @@ def render_file(filename)
   def hyphenate(text)
     text # @hyphens.hyphenate(text)
   end
+
+  def mermaid_cli_enabled?
+    true
+  end
 end
 
 RSpec.shared_context 'with pdf' do