1 files changed, 113 insertions, 0 deletions
diff --git a/mdit_py_plugins/substitution.py b/mdit_py_plugins/substitution.py
new file mode 100644
index 0000000..bae120b
--- /dev/null
+++ b/mdit_py_plugins/substitution.py
@@ -0,0 +1,113 @@
+from markdown_it import MarkdownIt
+from markdown_it.rules_block import StateBlock
+from markdown_it.rules_inline import StateInline
+
+
+def substitution_plugin(
+    md: MarkdownIt, start_delimiter: str = "{", end_delimiter: str = "}"
+):
+    """A plugin to create substitution tokens.
+
+    These, token should be handled by the renderer.
+
+    Example::
+
+        {{ block }}
+
+        a {{ inline }} b
+
+    """
+
+    start_char = ord(start_delimiter)
+    end_char = ord(end_delimiter)
+
+    def _substitution_inline(state: StateInline, silent: bool):
+        try:
+            if (
+                state.srcCharCode[state.pos] != start_char
+                or state.srcCharCode[state.pos + 1] != start_char
+            ):
+                return False
+        except IndexError:
+            return False
+
+        pos = state.pos + 2
+        found_closing = False
+        while True:
+            try:
+                end = state.srcCharCode.index(end_char, pos)
+            except ValueError:
+                return False
+            try:
+                if state.srcCharCode[end + 1] == end_char:
+                    found_closing = True
+                    break
+            except IndexError:
+                return False
+            pos = end + 2
+
+        if not found_closing:
+            return False
+
+        text = state.src[state.pos + 2 : end].strip()
+        state.pos = end + 2
+
+        if silent:
+            return True
+
+        token = state.push("substitution_inline", "span", 0)
+        token.block = False
+        token.content = text
+        token.attrSet("class", "substitution")
+        token.attrSet("text", text)
+        token.markup = f"{start_delimiter}{end_delimiter}"
+
+        return True
+
+    def _substitution_block(
+        state: StateBlock, startLine: int, endLine: int, silent: bool
+    ):
+        startPos = state.bMarks[startLine] + state.tShift[startLine]
+        end = state.eMarks[startLine]
+
+        # if it's indented more than 3 spaces, it should be a code block
+        if state.sCount[startLine] - state.blkIndent >= 4:
+            return False
+
+        lineText = state.src[startPos:end].strip()
+
+        try:
+            if (
+                lineText[0] != start_delimiter
+                or lineText[1] != start_delimiter
+                or lineText[-1] != end_delimiter
+                or lineText[-2] != end_delimiter
+                or len(lineText) < 5
+            ):
+                return False
+        except IndexError:
+            return False
+
+        text = lineText[2:-2].strip()
+
+        # special case if multiple on same line, e.g. {{a}}{{b}}
+        if (end_delimiter * 2) in text:
+            return False
+
+        state.line = startLine + 1
+
+        if silent:
+            return True
+
+        token = state.push("substitution_block", "div", 0)
+        token.block = True
+        token.content = text
+        token.attrSet("class", "substitution")
+        token.attrSet("text", text)
+        token.markup = f"{start_delimiter}{end_delimiter}"
+        token.map = [startLine, state.line]
+
+        return True
+
+    md.block.ruler.before("fence", "substitution_block", _substitution_block)
+    md.inline.ruler.before("escape", "substitution_inline", _substitution_inline)