1 files changed, 64 insertions, 0 deletions
diff --git a/indent/mermaid.vim b/indent/mermaid.vim
new file mode 100644
index 00000000..e1ade711
--- /dev/null
+++ b/indent/mermaid.vim
@@ -0,0 +1,64 @@
+if polyglot#init#is_disabled(expand('<sfile>:p'), 'mermaid', 'indent/mermaid.vim')
+  finish
+endif
+
+let s:indent_next_line_keywords = [
+      \ '^classDiagram',
+      \ '^classDiagram-v2',
+      \ '^erDiagram',
+      \ '^gantt',
+      \ '^graph',
+      \ '^flowchart',
+      \ '^pie',
+      \ '^sequenceDiagram',
+      \ '^stateDiagram',
+      \ '^stateDiagram-v2',
+      \ 'class.*{',
+      \ 'subgraph',
+      \ 'loop',
+      \ 'alt',
+      \ 'else',
+      \ 'opt',
+      \ 'par',
+      \ 'and',
+      \ 'rect',
+      \ '[^a-z]activate',
+      \ ]
+
+let s:deindent_current_line_keywords = [
+      \ '^\s\+classDiagram',
+      \ '^\s\+classDiagram-v2',
+      \ '^\s\+erDiagram',
+      \ '^\s\+gantt',
+      \ '^\s\+graph',
+      \ '^\s\+flowchart',
+      \ '^\s\+pie',
+      \ '^\s\+sequenceDiagram',
+      \ '^\s\+stateDiagram',
+      \ '^\s\+stateDiagram-v2',
+      \ '^\s\+end$',
+      \ '^\s\+}$',
+      \ '^\s\+deactivate$'
+      \ ]
+
+function! s:matches_any_word_in(text, list)
+  return empty(filter(copy(a:list), {_idx, val -> matchstr(a:text, val) != ""})) == v:false
+endfunction
+
+function! MermaidIndent()
+  let sw = shiftwidth()
+  let indent_level = indent(v:lnum - 1) / sw
+  let current_line = getline(v:lnum)
+  let line_above = getline(v:lnum - 1)
+
+  " TODO don't incorrect indent when has empty lines inside graph
+  if s:matches_any_word_in(current_line, s:deindent_current_line_keywords)
+    return (indent_level - 1) * sw
+  endif
+
+  if s:matches_any_word_in(line_above, s:indent_next_line_keywords)
+    return (indent_level + 1) * sw
+  endif
+
+  return indent_level * sw
+endfunction