Add a frontmatter parser

lib/obsidian/parser.rb

@@ -6,6 +6,7 @@
 require_relative "parser/page"
 require_relative "parser/html_renderer"
 require_relative "parser/content_type"
+require_relative "parser/frontmatter_parser"
 
 require "forwardable"
 

lib/obsidian/parser/frontmatter_parser.rb

@@ -0,0 +1,27 @@
+require 'yaml'
+
+class Obsidian::MarkdownParser::FrontMatterParser
+  # Look for frontmatter delimited by '---' lines
+  # and try to interpret it as yaml.
+  # If it is valid YAML, then denotes properties.
+  # https://help.obsidian.md/Editing+and+formatting/Properties#Property+format
+  def parse(content)
+    enumerator = content.each_line
+    first_line = enumerator.next
+
+    if first_line.chomp != "---"
+      return {}
+    end
+
+    lines = []
+    while true
+      line = enumerator.next
+      break if line.chomp == "---"
+      lines << line
+    end
+
+    YAML.safe_load(lines.join)
+  rescue YAML::SyntaxError, StopIteration => ex
+    {}
+  end
+end

spec/obsidian/parser/frontmatter_parser.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+RSpec.describe(Obsidian::MarkdownParser::FrontMatterParser) do
+  subject(:parser) { described_class.new }
+  it "parses valid yaml" do
+    content = %(---
+foo: 1
+bar: banana
+---
+some text
+    )
+    expect(parser.parse(content)).to eq({"foo" => 1, "bar" => "banana"})
+  end
+
+  it "returns empty hash for invalid yaml" do
+    content = %(---
+{
+---
+some text
+    )
+    expect(parser.parse(content)).to eq({})
+  end
+
+  it "returns empty hash if the frontmatter is not terminated" do
+    content = %(---
+some text
+    )
+    expect(parser.parse(content)).to eq({})
+  end
+
+
+  it "returns empty hash if no frontmatter" do
+    content = "hello world"
+    expect(parser.parse(content)).to eq({})
+  end
+end