feat(index): add switch statement

Author: mrmlnc

lib/index.js

@@ -10,7 +10,7 @@ const revertBackupedLocals = require('./backup').revert
 const placeholders = require('./placeholders')
 
 let delimitersSettings = []
-let conditionals, loops, scopes
+let conditionals, switches, loops, scopes
 
 /**
  * @description Creates a set of local variables within the loop, and evaluates all nodes within the loop, returning their contents
@@ -84,6 +84,7 @@ module.exports = function postHTMLExpressions (options) {
     delimiters: ['{{', '}}'],
     unescapeDelimiters: ['{{{', '}}}'],
     conditionalTags: ['if', 'elseif', 'else'],
+    switchTags: ['switch', 'case', 'default'],
     loopTags: ['each'],
     scopeTags: ['scope']
   }, options)
@@ -92,6 +93,7 @@ module.exports = function postHTMLExpressions (options) {
   loops = options.loopTags
   scopes = options.scopeTags
   conditionals = options.conditionalTags
+  switches = options.switchTags
 
   // make a RegExp's to search for placeholders
   let before = escapeRegexpString(options.delimiters[0])
@@ -169,7 +171,6 @@ function walk (opts, nodes) {
 
       // сalculate the first path of condition expression
       let expressionIndex = 1
-
       let expression = `if (${node.attrs.condition}) { 0 } `
 
       const branches = [node.content]
@@ -225,6 +226,50 @@ function walk (opts, nodes) {
       return m
     }
 
+    // switch tag
+    if (node.tag === switches[0]) {
+      // throw an error if it's missing the "condition" attribute
+      if (!(node.attrs && node.attrs.expression)) {
+        throw new Error(`the "${switches[0]}" tag must have a "expression" attribute`)
+      }
+
+      // сalculate the first path of condition expression
+      let expressionIndex = 0
+      let expression = `switch(${node.attrs.expression}) {`
+
+      const branches = []
+
+      for (let i = 0; i < node.content.length; i++) {
+        const currentNode = node.content[i]
+        if (typeof currentNode === 'string') {
+          continue
+        }
+
+        if (currentNode.tag === switches[1]) {
+          // throw an error if it's missing the "n" attribute
+          if (!(currentNode.attrs && currentNode.attrs.n)) {
+            throw new Error(`the "${switches[1]}" tag must have a "n" attribute`)
+          }
+          expression += `case ${currentNode.attrs.n}: {${expressionIndex++}}; break; `
+        } else if (currentNode.tag === switches[2]) {
+          expression += `default: {${expressionIndex++}}`
+        } else {
+          throw new Error(`the "${switches[0]}" tag can contain only "${switches[1]}" tags and one "${switches[2]}" tag`)
+        }
+        branches.push(currentNode)
+      }
+
+      expression += '}'
+
+      // evaluate the expression, get the winning switch branch
+      const branch = branches[vm.runInContext(expression, ctx)]
+
+      // recursive evaluate of branch
+      Array.prototype.push.apply(m, walk(opts, branch.content))
+
+      return m
+    }
+
     // parse loops
     if (node.tag === loops[0]) {
       // handle syntax error