class SimpleCov::Formatter::HTMLFormatter

coverage.json and coverage_data.js from the same in-memory hash.
Uses JSONFormatter.build_hash to serialize the result, then writes both
alongside pre-compiled static assets (index.html, application.js/css).
Generates an HTML coverage report by writing a coverage_data.js file

def atomic_write(dest, content)

from opening the existing path for writing.
/nix/store) are replaced cleanly instead of triggering EACCES
- read-only existing files (e.g. assets shipped at 0444 from
- parallel writers can't race on an unlink-then-write window, and
atomic and overwrite-safe, so:
same directory, then `File.rename` onto the final path. rename is
Write `content` at `dest` via a uniquely-named temp file in the 
def atomic_write(dest, content)
  temp = "#{dest}.#{Process.pid}.#{rand(2**32).to_s(36)}"
  begin
    File.binwrite(temp, content)
    File.rename(temp, dest)
  ensure
    FileUtils.rm_f(temp)
  end
end

def copy_static_assets(dest_dir = output_path) 

def copy_static_assets(dest_dir = output_path)
  Dir[File.join(public_dir, "*")].each do |src|
    atomic_write(File.join(dest_dir, File.basename(src)), File.binread(src))
  end
end

def entry_point_filename 

def entry_point_filename
  "index.html"
end

def format(result) 

def format(result)
  # `coverage_data.js` feeds the client-side viewer, which renders
  # source from the embedded array — it always needs `source`,
  # regardless of `SimpleCov.source_in_json`. The side-file
  # `coverage.json` honors the setting so downstream tools that
  # read source from disk can opt into a smaller payload. When
  # the setting is at its default (true), the two files share a
  # single serialization.
  FileUtils.mkdir_p(output_path)
  viewer_json = JSON.pretty_generate(JSONFormatter.build_hash(result, include_source: true))
  coverage_json = SimpleCov.source_in_json ? viewer_json : JSON.pretty_generate(JSONFormatter.build_hash(result))
  atomic_write(File.join(output_path, JSONFormatter::FILENAME), coverage_json)
  atomic_write(File.join(output_path, DATA_FILENAME), "window.SIMPLECOV_DATA = #{viewer_json};\n")
  copy_static_assets
  # stderr, not stdout: this is a status message, not the program's
  # output. Keeps the line out of pipelines like `rspec -f json`. And
  # $stderr.puts, not `warn`: a status line should not reach
  # `Warning.warn` hooks or vanish under `-W0` (see #1225).
  $stderr.puts output_message(result) unless @silent # rubocop:disable Style/StderrPuts
end

def format_from_json(json_path, output_dir)

needing a live SimpleCov::Result or even a running test suite.
Generate HTML from a pre-existing coverage.json file without 
def format_from_json(json_path, output_dir)
  FileUtils.mkdir_p(output_dir)
  json = File.read(json_path)
  atomic_write(File.join(output_dir, DATA_FILENAME), "window.SIMPLECOV_DATA = #{json};\n")
  copy_static_assets(output_dir)
end

def public_dir 

def public_dir
  # `.to_s` collapses `__dir__`'s nil arm (only possible under eval,
  # which can't happen for a file on disk) so the path is a String.
  File.join(__dir__.to_s, "html_formatter/public/")
end