perf(plugin-md-power): optimize plot rule (#408)

plugins/plugin-md-power/src/node/inline/plot.ts

@@ -4,8 +4,6 @@
 import type { PluginWithOptions } from 'markdown-it'
 import type { RuleInline } from 'markdown-it/lib/parser_inline.mjs'
 
-const [openTag, endTag] = ['!!', '!!']
-
 export const plotPlugin: PluginWithOptions<never> = md =>
   md.inline.ruler.before('emphasis', 'plot', createTokenizer())
 
@@ -15,9 +13,21 @@ function createTokenizer(): RuleInline {
     const max = state.posMax
     const start = state.pos
 
-    if (state.src.slice(start, start + 2) !== openTag)
+    if (
+      state.src.charCodeAt(start) !== 0x21
+      || state.src.charCodeAt(start + 1) !== 0x21
+    ) {
+      return false
+    }
+
+    const next = state.src.charCodeAt(start + 2)
+
+    // - !! xxx  |  !!!xxx
+    //     ^     |    ^
+    if (next === 0x20 || next === 0x21)
       return false
 
+    /* istanbul ignore if -- @preserve */
     if (silent)
       return false
 
@@ -28,39 +38,40 @@ function createTokenizer(): RuleInline {
     state.pos = start + 2
 
     while (state.pos < max) {
-      if (state.src.slice(state.pos - 1, state.pos + 1) === endTag) {
+      if (state.src.charCodeAt(state.pos) === 0x21
+        && state.src.charCodeAt(state.pos + 1) === 0x21) {
         found = true
         break
       }
 
       state.md.inline.skipToken(state)
     }
 
-    if (!found || start + 2 === state.pos) {
+    if (
+      !found
+      || start + 2 === state.pos
+      // - !!xxx !!
+      //        ^
+      || state.src.charCodeAt(state.pos - 1) === 0x20
+    ) {
       state.pos = start
 
       return false
     }
-    const content = state.src.slice(start + 2, state.pos - 1)
-
-    // 不允许前后带有空格
-    if (/^\s|\s$/.test(content)) {
-      state.pos = start
-      return false
-    }
+    const content = state.src.slice(start + 2, state.pos)
 
     // found!
-    state.posMax = state.pos - 1
+    state.posMax = state.pos
     state.pos = start + 2
 
     const open = state.push('plot_open', 'Plot', 1)
-    open.markup = openTag
+    open.markup = '!!'
 
     const text = state.push('text', '', 0)
     text.content = content
 
     const close = state.push('plot_close', 'Plot', -1)
-    close.markup = endTag
+    close.markup = '!!'
 
     state.pos = state.posMax + 2
     state.posMax = max