From 2108ddd6f296f75a3f09352a862eb97b986d8735 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 26 Apr 2023 20:51:13 +0530
Subject: [PATCH] Add a rudimentary syntax highlighter for the markdown editor
 widget

Somebody that cares is welcome to improve it
---
 src/calibre/gui2/markdown_editor.py           |   5 +
 .../gui2/markdown_syntax_highlighter.py       | 345 ++++++++++++++++++
 2 files changed, 350 insertions(+)
 create mode 100644 src/calibre/gui2/markdown_syntax_highlighter.py

diff --git a/src/calibre/gui2/markdown_editor.py b/src/calibre/gui2/markdown_editor.py
index e54e1f1b91..50dc91e608 100644
--- a/src/calibre/gui2/markdown_editor.py
+++ b/src/calibre/gui2/markdown_editor.py
@@ -30,6 +30,11 @@ class MarkdownEdit(QPlainTextEdit):
 
     smarten_punctuation = pyqtSignal()
 
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        from calibre.gui2.markdown_syntax_highlighter import MarkdownHighlighter
+        self.highlighter = MarkdownHighlighter(self.document())
+
     def contextMenuEvent(self, ev):
         m = self.createStandardContextMenu()
         m.addSeparator()
diff --git a/src/calibre/gui2/markdown_syntax_highlighter.py b/src/calibre/gui2/markdown_syntax_highlighter.py
new file mode 100644
index 0000000000..1eae02e57e
--- /dev/null
+++ b/src/calibre/gui2/markdown_syntax_highlighter.py
@@ -0,0 +1,345 @@
+#!/usr/bin/env python
+# License: GPLv3 Copyright: 2023, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+import re
+from qt.core import (
+    QApplication, QBrush, QColor, QFont, QSyntaxHighlighter, QTextCharFormat,
+    QTextCursor, QTextLayout,
+)
+
+from calibre.gui2.palette import dark_link_color, light_link_color
+
+
+class MarkdownHighlighter(QSyntaxHighlighter):
+
+    MARKDOWN_KEYS_REGEX = {
+        'Bold' : re.compile('(?P<delim>\*\*)(?P<text>.+)(?P=delim)'),
+        'uBold': re.compile('(?P<delim>__)(?P<text>[^_]{2,})(?P=delim)'),
+        'Italic': re.compile('(?P<delim>\*)(?P<text>[^*]{2,})(?P=delim)'),
+        'uItalic': re.compile('(?P<delim>_)(?P<text>[^_]+)(?P=delim)'),
+        'Link': re.compile('(?u)(^|(?P<pre>[^!]))\[.*?\]:?[ \t]*\(?[^)]+\)?'),
+        'Image': re.compile('(?u)!\[.*?\]\(.+?\)'),
+        'HeaderAtx': re.compile('(?u)^\#{1,6}(.*?)\#*(\n|$)'),
+        'Header': re.compile('^(.+)[ \t]*\n(=+|-+)[ \t]*\n+'),
+        'CodeBlock': re.compile('^([ ]{4,}|\t).*'),
+        'UnorderedList': re.compile('(?u)^\s*(\* |\+ |- )+\s*'),
+        'UnorderedListStar': re.compile('^\s*(\* )+\s*'),
+        'OrderedList': re.compile('(?u)^\s*(\d+\. )\s*'),
+        'BlockQuote': re.compile('(?u)^\s*>+\s*'),
+        'BlockQuoteCount': re.compile('^[ \t]*>[ \t]?'),
+        'CodeSpan': re.compile('(?P<delim>`+).+?(?P=delim)'),
+        'HR': re.compile('(?u)^(\s*(\*|-)\s*){3,}$'),
+        'eHR': re.compile('(?u)^(\s*(\*|=)\s*){3,}$'),
+        'Html': re.compile('<.+?>')
+    }
+
+    light_theme =  {
+        "bold": {"color":"#859900", "font-weight":"bold", "font-style":"normal"},
+        "emphasis": {"color":"#b58900", "font-weight":"bold", "font-style":"italic"},
+        "link": {"color":light_link_color.name(), "font-weight":"normal", "font-style":"normal"},
+        "image": {"color":"#cb4b16", "font-weight":"normal", "font-style":"normal"},
+        "header": {"color":"#2aa198", "font-weight":"bold", "font-style":"normal"},
+        "unorderedlist": {"color":"red", "font-weight":"normal", "font-style":"normal"},
+        "orderedlist": {"color":"red", "font-weight":"normal", "font-style":"normal"},
+        "blockquote": {"color":"red", "font-weight":"normal", "font-style":"normal"},
+        "codespan": {"color":"#ff5800", "font-weight":"normal", "font-style":"normal"},
+        "codeblock": {"color":"#ff5800", "font-weight":"normal", "font-style":"normal"},
+        "line": {"color":"#2aa198", "font-weight":"normal", "font-style":"normal"},
+        "html": {"color":"#c000c0", "font-weight":"normal", "font-style":"normal"}
+    }
+
+    dark_theme =  {
+        "bold": {"color":"#859900", "font-weight":"bold", "font-style":"normal"},
+        "emphasis": {"color":"#b58900", "font-weight":"bold", "font-style":"italic"},
+        "link": {"color":dark_link_color.name(), "font-weight":"normal", "font-style":"normal"},
+        "image": {"color":"#cb4b16", "font-weight":"normal", "font-style":"normal"},
+        "header": {"color":"#2aa198", "font-weight":"bold", "font-style":"normal"},
+        "unorderedlist": {"color":"yellow", "font-weight":"normal", "font-style":"normal"},
+        "orderedlist": {"color":"yellow", "font-weight":"normal", "font-style":"normal"},
+        "blockquote": {"color":"yellow", "font-weight":"normal", "font-style":"normal"},
+        "codespan": {"color":"#90ee90", "font-weight":"normal", "font-style":"normal"},
+        "codeblock": {"color":"#ff9900", "font-weight":"normal", "font-style":"normal"},
+        "line": {"color":"#2aa198", "font-weight":"normal", "font-style":"normal"},
+        "html": {"color":"#F653A6", "font-weight":"normal", "font-style":"normal"}
+    }
+
+    def __init__(self, parent):
+        super().__init__(parent)
+        theme = self.dark_theme if QApplication.instance().is_dark_theme else self.light_theme
+        self.setTheme(theme)
+
+    def setTheme(self, theme):
+        self.theme = theme
+        self.MARKDOWN_KWS_FORMAT = {}
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['bold']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['bold']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['bold']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['Bold'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['bold']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['bold']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['bold']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['uBold'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['emphasis']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['emphasis']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['emphasis']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['Italic'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['emphasis']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['emphasis']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['emphasis']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['uItalic'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['link']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['link']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['link']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['Link'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['image']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['image']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['image']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['Image'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['header']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['header']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['header']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['Header'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['header']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['header']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['header']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['HeaderAtx'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['unorderedlist']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['unorderedlist']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['unorderedlist']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['UnorderedList'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['orderedlist']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['orderedlist']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['orderedlist']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['OrderedList'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['blockquote']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['blockquote']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['blockquote']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['BlockQuote'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['codespan']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['codespan']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['codespan']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['CodeSpan'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['codeblock']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['codeblock']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['codeblock']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['CodeBlock'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['line']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['line']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['line']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['HR'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['line']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['line']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['line']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['eHR'] = format
+
+        format = QTextCharFormat()
+        format.setForeground(QBrush(QColor(theme['html']['color'])))
+        format.setFontWeight(QFont.Weight.Bold if theme['html']['font-weight']=='bold' else QFont.Weight.Normal)
+        format.setFontItalic(True if theme['html']['font-style']=='italic' else False)
+        self.MARKDOWN_KWS_FORMAT['HTML'] = format
+
+        self.rehighlight()
+
+    def highlightBlock(self, text):
+        self.highlightMarkdown(text,0)
+        self.highlightHtml(text)
+
+    def highlightMarkdown(self, text, strt):
+        cursor = QTextCursor(self.document())
+        bf = cursor.blockFormat()
+
+        #Block quotes can contain all elements so process it first
+        self.highlightBlockQuote(text, cursor, bf, strt)
+
+        #If empty line no need to check for below elements just return
+        if self.highlightEmptyLine(text, cursor, bf, strt):
+            return
+
+        #If horizontal line, look at pevious line to see if its a header, process and return
+        if self.highlightHorizontalLine(text, cursor, bf, strt):
+            return
+
+        if self.highlightAtxHeader(text, cursor, bf, strt):
+            return
+
+        self.highlightList(text, cursor, bf, strt)
+
+        self.highlightLink(text, cursor, bf, strt)
+
+        self.highlightImage(text, cursor, bf, strt)
+
+        self.highlightCodeSpan(text, cursor, bf, strt)
+
+        self.highlightEmphasis(text, cursor, bf, strt)
+
+        self.highlightBold(text, cursor, bf, strt)
+
+        self.highlightCodeBlock(text, cursor, bf, strt)
+
+    def highlightBlockQuote(self, text, cursor, bf, strt):
+        found = False
+        mo = re.search(self.MARKDOWN_KEYS_REGEX['BlockQuote'],text)
+        if mo:
+            self.setFormat(mo.start(), mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['BlockQuote'])
+            unquote = re.sub(self.MARKDOWN_KEYS_REGEX['BlockQuoteCount'],'',text)
+            spcs = re.match(self.MARKDOWN_KEYS_REGEX['BlockQuoteCount'],text)
+            spcslen = 0
+            if spcs:
+                spcslen = len(spcs.group(0))
+            self.highlightMarkdown(unquote,spcslen)
+            found = True
+        return found
+
+    def highlightEmptyLine(self, text, cursor, bf, strt):
+        textAscii = str(text.replace('\u2029','\n'))
+        if textAscii.strip():
+            return False
+        else:
+            return True
+
+    def highlightHorizontalLine(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['HR'],text):
+            prevBlock = self.currentBlock().previous()
+            prevCursor = QTextCursor(prevBlock)
+            prev = prevBlock.text()
+            prevAscii = str(prev.replace('\u2029','\n'))
+            if prevAscii.strip():
+                #print "Its a header"
+                prevCursor.select(QTextCursor.LineUnderCursor)
+                #prevCursor.setCharFormat(self.MARKDOWN_KWS_FORMAT['Header'])
+                formatRange = QTextLayout.FormatRange()
+                formatRange.format = self.MARKDOWN_KWS_FORMAT['Header']
+                formatRange.length = prevCursor.block().length()
+                formatRange.start = 0
+                prevCursor.block().layout().setAdditionalFormats([formatRange])
+            self.setFormat(mo.start()+strt, mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['HR'])
+
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['eHR'],text):
+            prevBlock = self.currentBlock().previous()
+            prevCursor = QTextCursor(prevBlock)
+            prev = prevBlock.text()
+            prevAscii = str(prev.replace('\u2029','\n'))
+            if prevAscii.strip():
+                #print "Its a header"
+                prevCursor.select(QTextCursor.LineUnderCursor)
+                #prevCursor.setCharFormat(self.MARKDOWN_KWS_FORMAT['Header'])
+                formatRange = QTextLayout.FormatRange()
+                formatRange.format = self.MARKDOWN_KWS_FORMAT['Header']
+                formatRange.length = prevCursor.block().length()
+                formatRange.start = 0
+                prevCursor.block().layout().setAdditionalFormats([formatRange])
+            self.setFormat(mo.start()+strt, mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['HR'])
+        return found
+
+    def highlightAtxHeader(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['HeaderAtx'],text):
+            #bf.setBackground(QBrush(QColor(7,54,65)))
+            #cursor.movePosition(QTextCursor.End)
+            #cursor.mergeBlockFormat(bf)
+            self.setFormat(mo.start()+strt, mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['HeaderAtx'])
+            found = True
+        return found
+
+    def highlightList(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['UnorderedList'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['UnorderedList'])
+            found = True
+
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['OrderedList'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['OrderedList'])
+            found = True
+        return found
+
+    def highlightLink(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['Link'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['Link'])
+            found = True
+        return found
+
+    def highlightImage(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['Image'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['Image'])
+            found = True
+        return found
+
+    def highlightCodeSpan(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['CodeSpan'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['CodeSpan'])
+            found = True
+        return found
+
+    def highlightBold(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['Bold'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['Bold'])
+            found = True
+
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['uBold'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['uBold'])
+            found = True
+        return found
+
+    def highlightEmphasis(self, text, cursor, bf, strt):
+        found = False
+        unlist = re.sub(self.MARKDOWN_KEYS_REGEX['UnorderedListStar'],'',text)
+        spcs = re.match(self.MARKDOWN_KEYS_REGEX['UnorderedListStar'],text)
+        spcslen = 0
+        if spcs:
+            spcslen = len(spcs.group(0))
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['Italic'],unlist):
+            self.setFormat(mo.start()+strt+spcslen, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['Italic'])
+            found = True
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['uItalic'],text):
+            self.setFormat(mo.start()+strt, mo.end() - mo.start()-strt, self.MARKDOWN_KWS_FORMAT['uItalic'])
+            found = True
+        return found
+
+    def highlightCodeBlock(self, text, cursor, bf, strt):
+        found = False
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['CodeBlock'],text):
+            stripped = text.lstrip()
+            if stripped[0] not in ('*','-','+','>'):
+                self.setFormat(mo.start()+strt, mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['CodeBlock'])
+                found = True
+        return found
+
+    def highlightHtml(self, text):
+        for mo in re.finditer(self.MARKDOWN_KEYS_REGEX['Html'], text):
+            self.setFormat(mo.start(), mo.end() - mo.start(), self.MARKDOWN_KWS_FORMAT['HTML'])