A Simple Parser That Converts HTML from OneNote to Markdown

• Download OneNote2Markdown.zip - 438.4 KB
• Download Example.zip - 35.4 KB

Introduction

This article introduces OneNote2Markdown, a parser I made that converts the html file generated from OneNote (by sending to Word and save as html) to Markdown format, which can then be translated to a cleaner html by any online Markdown parser later.

• Written in F#, the tool works with OneNote 2010 and Word 2010. It handles normal paragraphs, headings, links, lists, inlined code and code blocks only.
• The tool reads from "input.html" and writes to "output.txt".
• The source code of the latest version can be viewed at Bitbucket. It requires HtmlAgilityPack to compile.
• The example pack contains this article in docx, html & Markdown formats, which would give a basic demonstration on how the tool works.

Background

I tend to take notes in OneNote. When I first time try to submit an article which is composed in OneNote, it is really a hassle to adapt the content to the template in Code Project manually. So I decided to make a parser which would automate most of the formatting work for me.

Implementation Overview

Preparations

• An Active Pattern to pattern match if a text node has a certain ancestor such as <b> or <i>.

  F#

  let (|HasAncestor|) tag (node: HtmlNode) =
      node.Ancestors(tag) |> Seq.isEmpty |> not

• A function to dig up a certain CSS property that a text node inherits from style attribute.

  F#

  let getPartialStyle cssProperty (node: HtmlNode) =
      let predicate node =
          // "property1:value1;property2:value2"
          let myMatch = Regex.Match(getStyle node, sprintf "%s:(.+?)(;|$)" cssProperty)
          if myMatch.Success then
              Some myMatch.Groups.[1].Value
          else None
      // Gets the value for the closest cssProperty.
      node.Ancestors("span") |> Seq.tryPick predicate

• A function to get a certain CSS property of a node from style attribute.

  F#

  let getPartialStyleSelf cssProperty (node: HtmlNode) =
      let myMatch = Regex.Match(getStyle node, sprintf "%s:(.+?)(;|$)" cssProperty)
      if myMatch.Success then
          Some myMatch.Groups.[1].Value
      else
          None

Headings

• Determines the heading type of a paragraph by checking its font-size & color CSS property as well as if it has <b> or <i> ancestor.

  F#

  match font, color, node with
  | Some "16.0pt", Some "#17365D", (HasAncestor "b" true)   -> H 1
  | Some "13.0pt", Some "#366092", (HasAncestor "b" true)   -> H 2
  | Some "11.0pt", Some "#366092", (HasAncestor "b" true)  & (HasAncestor "i" false) -> H 3
  | Some "11.0pt", Some "#366092", (HasAncestor "b" true)  & (HasAncestor "i" true)  -> H 4
  | Some "11.0pt", Some "#366092", (HasAncestor "b" false) & (HasAncestor "i" false) -> H 5
  | Some "11.0pt", Some "#366092", (HasAncestor "b" false) & (HasAncestor "i" true)  -> H 6
  | _ -> Normal

• Uses ## heading ## syntax so that Markdown parser doesn't eat the last # contained in the heading.

  F#

  let headIt n text =
      String.Format("{1} {0} {1}", text, (String (Array.create n '#')))

Code

• Any text whose font is Consolas is considered as code, otherwise not.

  F#

  match getPartialStyle "font-family" textNode with
  | Some "Consolas" -> varIt text
  | _ -> text

• Simplifies Markdown syntax by combining several inlined code pieces into one if they are separated by white-spaces (e.g. a b -> a b). Preserves the leading spaces so as to protect indentations and blank lines with code blocks (anything inside is non-trivial and will not be removed later, e.g. a -> a). However, the limitation exists that the text itself cannot contain `.

  F#

  let simplifyVar (text: string) =
      Regex.Replace(text, @"(?<=.)`(\s*)`", "$1")

• Differentiates code blocks from inlined code.

  F#

  let tryGetPureCode (text: string) =
      let myMatch = (Regex.Match(text, @"^`([^`]*)`$"))
      if myMatch.Success then
          Some (myMatch.Result "$1")
      else
          None

Lists

• Distinguishes between ordered lists and unordered lists by the symbol. Lists without symbols are considered as normal paragraphs without indentation.

  F#

  let listIt x text =
      match x with
      | "o" | "·" -> sprintf "*  %s" text
      | _         -> sprintf "1. %s" text

• Gets the indentation by margin-left:54.0pt CSS property.

  F#

  let getIndent (node: HtmlNode) =
      let getMargin (x: string) =
          let unit = 27 // each level is 27
          let array = x.Split '.'
          let (success, x) = Int32.TryParse array.[0]
          if success then x / unit
          else failwith "indent parse error!"
      match getPartialStyleSelf "margin-left" node with
      | Some x -> getMargin x
      | None -> 0

Links

• Checks if a piece of text contains the link by looking for <a> in its ancestors.

  F#

  match textNode with
  | (HasAncestor "a" true) ->
      let ancestor_a = textNode.Ancestors("a") |> Seq.head
      linkIt text (ancestor_a.GetAttributeValue("href", "none"))
  | _ -> text

Finalization 

• Gets the correct indentations and paragraph spacing for the whole content.

  F#

  /// Assumes in OneNote there are no spaces in front of a code block (indent by tabs).
  /// Assumes in OneNote the internal indentations of a code block are either all tabs or all spaces, never mixed.
  let review paragraphs =
      // indentOffset is used for nesting indentations.
      // If a benchmark line with indentation a, actually indents x, we set indentOffset = a - x.
      // So any line with indentation b, does actually indent b - indentOffset = b - a + x.
      let mutable listIndentOffset = 0
      let mutable codeIndentOffset = 0
      let oldCopy = paragraphs |> Seq.toArray
      let newCopy = Array.zeroCreate oldCopy.Length
      // Looks at the current paragraph and the previous paragraph.
      // I don't care about the first paragraph as it will be the title.
      // Uses "\r\n" so that Notepad reads correctly.
      for i in 1 .. oldCopy.Length - 1 do
          match oldCopy.[i - 1], oldCopy.[i] with
          | (Code _ | Listing _) , (Heading text | Basic text) ->
              // Code block / list block ends, prepends and appends new lines, and resets both indentOffsets.
              newCopy.[i] <- sprintf "\r\n%s\r\n" text
              listIndentOffset <- 0
              codeIndentOffset <- 0
  
          | (Heading _ | Basic _), (Heading text | Basic text) ->
              // Appends a new line.
              newCopy.[i] <- sprintf "%s\r\n" text
  
          | Code (_, a)          , Code (text, b)              ->
              // Don't add a new line in between code blocks.
              newCopy.[i] <- indentIt (b - codeIndentOffset) text
  
          | (Heading _ | Basic _), Code (text, b)              ->
              // Code block starts, cache codeIndentOffset
              // Indents 1 level only as Heading or Basic indents none.
              newCopy.[i] <- indentIt 1 text
              codeIndentOffset <- b - 1
  
          | Listing (_, a)       , Code (text, b)              ->
              // Code block within a list requires 1 additional level on top of the list indentation.
              // Code block starts, cache codeIndentOffset.
              // Prepends a new line.
              newCopy.[i] <- sprintf "\r\n%s" (indentIt (b - listIndentOffset + 1) text)
              codeIndentOffset <- listIndentOffset - 1
  
          | Listing (_, a)       , Listing (text, b)           ->
              // Don't add  a new line in between list blocks.
              newCopy.[i] <- indentIt (b - listIndentOffset) text
  
          | Code (_, a)          , Listing (text, b)           ->
              // Code block ends, reset codeIndentOffset.
              // Prepends a new line.
              codeIndentOffset <- 0
              newCopy.[i] <- sprintf "\r\n%s" (indentIt (b - listIndentOffset) text)
  
          | (Heading _ | Basic _), Listing (text, b)           ->
              // List block starts, cache listIndentOffset
              listIndentOffset <- b
              newCopy.[i] <- text
      newCopy