<?php
 
 namespace Illuminate\View\Concerns;
 
 use InvalidArgumentException;
 
 trait ManagesStacks
 {
     /**
      * All of the finished, captured push sections.
      *
      * @var array
      */
     protected $pushes = [];
 
     /**
      * All of the finished, captured prepend sections.
      *
      * @var array
      */
     protected $prepends = [];
 
     /**
      * The stack of in-progress push sections.
      *
      * @var array
      */
     protected $pushStack = [];
 
     /**
      * Start injecting content into a push section.
      *
      * @param  string  $section
      * @param  string  $content
      * @return void
      */
     public function startPush($section, $content = '')
     {
         if ($content === '') {
             if (ob_start()) {
                 $this->pushStack[] = $section;
             }
         } else {
             $this->extendPush($section, $content);
         }
     }
 
     /**
      * Stop injecting content into a push section.
      *
      * @return string
      *
      * @throws \InvalidArgumentException
      */
     public function stopPush()
     {
         if (empty($this->pushStack)) {
             throw new InvalidArgumentException('Cannot end a push stack without first starting one.');
         }
 
         return tap(array_pop($this->pushStack), function ($last) {
             $this->extendPush($last, ob_get_clean());
         });
     }
 
     /**
      * Append content to a given push section.
      *
      * @param  string  $section
      * @param  string  $content
      * @return void
      */
     protected function extendPush($section, $content)
     {
         if (! isset($this->pushes[$section])) {
             $this->pushes[$section] = [];
         }
 
         if (! isset($this->pushes[$section][$this->renderCount])) {
             $this->pushes[$section][$this->renderCount] = $content;
         } else {
             $this->pushes[$section][$this->renderCount] .= $content;
         }
     }
 
     /**
      * Start prepending content into a push section.
      *
      * @param  string  $section
      * @param  string  $content
      * @return void
      */
     public function startPrepend($section, $content = '')
     {
         if ($content === '') {
             if (ob_start()) {
                 $this->pushStack[] = $section;
             }
         } else {
             $this->extendPrepend($section, $content);
         }
     }
 
     /**
      * Stop prepending content into a push section.
      *
      * @return string
      *
      * @throws \InvalidArgumentException
      */
     public function stopPrepend()
     {
         if (empty($this->pushStack)) {
             throw new InvalidArgumentException('Cannot end a prepend operation without first starting one.');
         }
 
         return tap(array_pop($this->pushStack), function ($last) {
             $this->extendPrepend($last, ob_get_clean());
         });
     }
 
     /**
      * Prepend content to a given stack.
      *
      * @param  string  $section
      * @param  string  $content
      * @return void
      */
     protected function extendPrepend($section, $content)
     {
         if (! isset($this->prepends[$section])) {
             $this->prepends[$section] = [];
         }
 
         if (! isset($this->prepends[$section][$this->renderCount])) {
             $this->prepends[$section][$this->renderCount] = $content;
         } else {
             $this->prepends[$section][$this->renderCount] = $content.$this->prepends[$section][$this->renderCount];
         }
     }
 
     /**
      * Get the string contents of a push section.
      *
      * @param  string  $section
      * @param  string  $default
      * @return string
      */
     public function yieldPushContent($section, $default = '')
     {
         if (! isset($this->pushes[$section]) && ! isset($this->prepends[$section])) {
             return $default;
         }
 
         $output = '';
 
         if (isset($this->prepends[$section])) {
             $output .= implode(array_reverse($this->prepends[$section]));
         }
 
         if (isset($this->pushes[$section])) {
             $output .= implode($this->pushes[$section]);
         }
 
         return $output;
     }
 
     /**
      * Flush all of the stacks.
      *
      * @return void
      */
     public function flushStacks()
     {
         $this->pushes = [];
         $this->prepends = [];
         $this->pushStack = [];
     }
 }