chore(#36): switch statement (@mrmlnc)

Author: michael-ciniawsky

README.md

@@ -43,6 +43,7 @@ You have full control over the delimiters used for injecting locals, as well as
 | **unescapeDelimiters** | `['{{{', '}}}']` | Array containing beginning and ending delimiters for unescaped locals |
 | **locals** | `{}` | Object containing any local variables you want to be available inside your expressions |
 | **conditionalTags** | `['if', 'elseif', 'else']` | Array containing names for tags used for `if/else if/else` statements |
+| **switchTags** | `['switch', 'case', 'default']` | Array containing names for tags used for `switch/case/default` statements |
 | **loopTags** | `['each']` | Array containing names for `for` loops |
 | **scopeTags** | `['scope']` | Array containing names for scopes |
 
@@ -155,6 +156,34 @@ else
   p Foo is probably just foo in the end.
 ```
 
+### Switch statement
+
+Switch statements act like streamline conditionals. They are useful for when you want to compare a single variable against a series of constants.
+
+```js
+locals: { foo: 'foo' }
+```
+
+```html
+<switch expression="foo">
+  <case n="'bar'">
+    <p>Foo really is bar! Revolutionary!</p>
+  </case>
+  <case n="'wow'">
+    <p>Foo is wow, oh man.</p>
+  </case>
+  <default>
+    <p>Foo is probably just foo in the end.</p>
+  </default>
+</switch>
+```
+
+```html
+<p>Foo is probably just foo in the end.</p>
+```
+
+Anything in the `expression` attribute is evaluated directly as an expressions.
+
 ### Loops
 
 You can use the `each` tag to build loops. It works with both arrays and objects. For example:

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
@@ -57,7 +57,7 @@ function executeScope (scope, locals, node) {
 
 /**
  * @author Jeff Escalante Denis (@jescalan),
- *         Malinochkin (mrmlnc),
+ *         Denis Malinochkin (mrmlnc),
  *         Michael Ciniawsky (@michael-ciniawsky)
  * @description Expressions Plugin for PostHTML
  * @license MIT
@@ -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]
@@ -225,11 +226,55 @@ function walk (opts, nodes) {
       return m
     }
 
+    // switch tag
+    if (node.tag === switches[0]) {
+      // throw an error if it's missing the "expression" 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
       if (!(node.attrs && node.attrs.loop)) {
-        throw new Error(`the "${conditionals[1]}" tag must have a "loop" attribute`)
+        throw new Error(`the "${loops[0]}" tag must have a "loop" attribute`)
       }
 
       // parse the "loop" param

test/expect/switch.html

@@ -0,0 +1,2 @@
+
+    <p>Hello, from Germany!</p>

test/expect/switch_customtag.html

@@ -0,0 +1,2 @@
+
+    <p>Hello, from United States!</p>

test/expect/switch_default.html

@@ -0,0 +1,2 @@
+
+    <p>Hello, from Earth!</p>

test/expect/switch_nested.html

@@ -0,0 +1,2 @@
+
+    <p>Hello, from Russia!</p>

test/expect/switch_number.html

@@ -0,0 +1,2 @@
+
+    <p>3</p>

test/fixtures/switch.html

@@ -0,0 +1,14 @@
+<switch expression="country">
+  <case n="'russia'">
+    <p>Hello, from Russia!</p>
+  </case>
+  <case n="'germany'">
+    <p>Hello, from Germany!</p>
+  </case>
+  <case n="'us'">
+    <p>Hello, from United States!</p>
+  </case>
+  <default>
+    <p>Hello, from Earth!</p>
+  </default>
+</switch>

test/fixtures/switch_bad_flow.html

@@ -0,0 +1,9 @@
+<switch expression="country">
+  <case n="'russia'">
+    <p>Hello, from Russia!</p>
+  </case>
+  <p>What?</p>
+  <default>
+    <p>Hello, from Earth!</p>
+  </default>
+</switch>

test/fixtures/switch_customtag.html

@@ -0,0 +1,14 @@
+<s expression="country">
+  <c n="'russia'">
+    <p>Hello, from Russia!</p>
+  </c>
+  <c n="'germany'">
+    <p>Hello, from Germany!</p>
+  </c>
+  <c n="'us'">
+    <p>Hello, from United States!</p>
+  </c>
+  <d>
+    <p>Hello, from Earth!</p>
+  </d>
+</s>