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/*
.---------------------------------------------------------------------------.
|  Software: JSON-Patch PHP library                                         |
|   Version: 0.0.2                                                          |
|      Site: https://github.com/mikemccabe/json-patch-php                   |
| ------------------------------------------------------------------------- |
|   License: LGPL-3.0
'---------------------------------------------------------------------------'

Produce and apply JSON-patch objects.

Implements IETF JSON-patch (RFC 6902) and JSON-pointer (RFC 6901):

http://tools.ietf.org/html/rfc6902

http://tools.ietf.org/html/rfc6901

Entry points
------------

- get($doc, $pointer) - get a value from a JSON document
- diff($src, $dst) - return patches to create $dst from $src
- patch($doc, $patches) - apply patches to $doc and return result

Arguments are PHP arrays, i.e. the output of
json_decode($json_string, 1).

(Note that you MUST pass 1 as the second argument to json_decode to
get an array.  This library does not work with stdClass objects.)

All structures are implemented directly as PHP arrays.  An array is
considered to be 'associative' (e.g. like a JSON 'object') if it
contains at least one non-numeric key.

Because of this, empty arrays ([]) and empty objects ({}) compare the
same, and (for instance) an 'add' of a string key to an empty array
will succeed in this implementation where it might fail in others.

$simplexml_mode is provided to help with working with arrays produced
from XML in the style of simplexml - e.g. repeated XML elements are
expressed as arrays.  When $simplexml_mode is enabled, leaves with
scalar values are implicitly treated as length-1 arrays, so this test
will succeed:

    { "comment": "basic simplexml array promotion",
      "doc": { "foo":1 },
      "patch": [ { "op":"add", "path":"/foo/1", "value":2 } ],
      "expected": { "foo":[1, 2] } },

Also, when $simplexml_mode is true, 1-length arrays are converted to
scalars on return from patch().

*/

namespace mikemccabe\JsonPatch;

class JsonPatchException extends \Exception { }


class JsonPatch
{
  // Follow a json-pointer address into a JSON document and return
  // the designated leaf value
  public static function get($doc, $pointer, $simplexml_mode=false)
  {
    $parts = self::decompose_pointer($pointer);
    return self::get_helper($doc, $pointer, $parts, $simplexml_mode);
  }


  // Compute a list of json-patch structures representing the diff
  // between $src and $dst
  public static function diff($src, $dst)
  {
    return self::diff_values("", $src, $dst);
  }


  // Compute a new document from the supplied $doc and $patches.
  public static function patch($doc, $patches, $simplexml_mode=false)
  {
    // accept singleton patches
    if (count($patches) != 0 && !isset($patches[0]))
    {
      $patches = Array($patches);
    }

    foreach ($patches as $patch)
    {
      $op = $patch['op'];
      $path = $patch['path'];

      if (empty($op))
      {
        throw new JsonPatchException("'op' missing in "
                                     . json_encode($patch));
      }
      if (!is_string($path))
      {
        throw new JsonPatchException("'path' missing in "
                                     . json_encode($patch));
      }
      if (!in_array($op, array('add', 'remove', 'replace',
                               'move', 'copy', 'test', 'append')))
      {
        throw new JsonPatchException("Unrecognized op '$op' in "
                                     . json_encode($patch));
      }

      $parts = self::decompose_pointer($path);
      if (in_array($op, Array('test', 'add', 'replace', 'append')))
      {
        if (!array_key_exists('value', $patch))
        {
          throw new JsonPatchException("'value' missing in "
                                       . json_encode($patch));
        }
        $value = $patch['value'];
      }
      if (in_array($op, Array('move', 'copy')))
      {
        if (!array_key_exists('from', $patch))
        {
          throw new JsonPatchException("'from' missing in "
                                       . json_encode($patch));
        }
        $from_path = $patch['from'];
        $from_parts = self::decompose_pointer($from_path);
      }

      if ($op === 'add')
      {
        $doc = self::do_op($doc, $op, $path, $parts, $value,
                           $simplexml_mode);
      }
      if ($op === 'append')
      {
        $doc = self::do_op($doc, $op, $path, $parts, $value,
                           $simplexml_mode);
      }
      else if ($op == 'replace')
      {
        $doc = self::do_op($doc, $op, $path, $parts, $value,
                           $simplexml_mode);
      }
      else if ($op == 'remove')
      {
        $doc = self::do_op($doc, $op, $path, $parts, null,
                           $simplexml_mode);
      }

      else if ($op == 'test')
      {
        self::test($doc, $path, $parts, $value,
                   $simplexml_mode);
      }

      else if ($op == 'copy')
      {
        $value = self::get_helper($doc, $from_path, $from_parts,
                                  $simplexml_mode);
        $doc = self::do_op($doc, 'add', $path, $parts, $value,
                           $simplexml_mode);
      }
      else if ($op == 'move')
      {
        $value = self::get_helper($doc, $from_path, $from_parts,
                                  $simplexml_mode);
        $doc = self::do_op($doc, 'remove', $from_path, $from_parts, null,
                           $simplexml_mode);
        $doc = self::do_op($doc, 'add', $path, $parts, $value,
                           $simplexml_mode);
      }
    }

    if ($simplexml_mode)
    {
      $doc = self::re_singletize($doc);
    }

    return $doc;
  }


  public static function compose_pointer($parts)
  {
    $result = "";
    foreach($parts as $part)
    {
      $part = self::escape_pointer_part($part);
      $result = $result . "/" . $part;
    }
    return $result;
  }


  public static function escape_pointer_part($part)
  {
    $part = str_replace('~', '~0', $part);
    $part = str_replace('/', '~1', $part);
    return $part;
  }


  // Private functions follow


  // Walk through the doc and turn every 1-length array into a
  // singleton value.  This follows SimpleXML behavior.
  private static function re_singletize($doc)
  {
    if (!is_array($doc))
    {
      return $doc;
    }

    if (array_key_exists(0, $doc) && count($doc) == 1)
    {
      return self::re_singletize($doc[0]);
    }

    $result = array();
    foreach(array_keys($doc) as $key)
    {
      $result[$key] = self::re_singletize($doc[$key]);
    }
    return $result;
  }


  private static function decompose_pointer($pointer)
  {
    $parts = explode('/', $pointer);
    if (array_shift($parts) !== "")
    {
      throw new JsonPatchException("path must start with / in $pointer");
    }
    for ($i = 0; $i < count($parts); $i++)
    {
      $parts[$i] = str_replace('~1', '/', $parts[$i]);
      $parts[$i] = str_replace('~0', '~', $parts[$i]);
    }
    return $parts;
  }


  // only 0 or counting number; '1e0' is excluded.
  private static function is_index($part)
  {
    return 1 === preg_match('/^(0|[1-9][0-9]*)$/', $part);
  }


  // diff support functions


  // Dispatch to a recursive diff_assoc or diff_array call if needed,
  // or emit a patch to replace the current value.
  private static function diff_values($path, $value, $other)
  {
    // manually handle the {}-looks-like-[] case, when other is associative
    if ((count($value) == 0 || count($other) == 0)
        && (self::is_associative($value) || self::is_associative($other)))
    {
      return self::diff_assoc($path, $value, $other);
    }
    else if (self::is_associative($value) && self::is_associative($other))
    {
      return self::diff_assoc($path, $value, $other);
    }
    else if (is_array($value) && !self::is_associative($value)
             && is_array($other) && !self::is_associative($value))
    {
      return self::diff_array($path, $value, $other);
    }
    else
    {
      if ($value !== $other)
      {
        return array(array("op" => "replace", "path" => "$path",
                           "value" => $other));
      }
    }
    return array();
  }


  // Walk associative arrays $src and $dst, returning a list of patches
  private static function diff_assoc($path, $src, $dst)
  {
    $result = array();
    if (count($src) == 0 && count($dst) != 0)
    {
      $result[] = array("op" => "replace", "path" => "$path", "value" => $dst);
    }
    else
    {
      foreach (array_keys($src) as $key)
      {
        $ekey = self::escape_pointer_part($key);
        if (!array_key_exists($key, $dst))
        {
          $result[] = array("op" => "remove", "path" => "$path/$ekey");
        }
        else
        {
          $result = array_merge($result,
                                self::diff_values("$path/$ekey",
                                                  $src[$key], $dst[$key]));
        }
      }
      foreach (array_keys($dst) as $key)
      {
        if (!array_key_exists($key, $src))
        {
          $ekey = self::escape_pointer_part($key);
          $result[] = array("op" => "add", "path" => "$path/$ekey",
                            "value" => $dst[$key]);
        }
      }
    }
    return $result;
  }


  // Walk simple arrays $src and $dst, returning a list of patches
  private static function diff_array($path, $src, $dst)
  {
    $result = array();
    $lsrc = count($src);
    $ldst = count($dst);
    $max = ($lsrc > $ldst) ? $lsrc : $ldst;

    // Walk backwards through arrays, starting with longest
    $i = $max - 1;
    while ($i >= 0) // equivalent for loop didn't work?
    {
      if ($i < $lsrc && $i < $ldst && 
          array_key_exists($i, $src) && array_key_exists($i, $dst))
      {
        $result = array_merge($result,
                              self::diff_values("$path/$i",
                                                $src[$i], $dst[$i]));
      }
      else if ($i < $ldst && array_key_exists($i, $dst))
      {
        $result[] = array("op" => "add", "path" => "$path/$i",
                          "value" => $dst[$i]);
      }
      else if ($i < $lsrc && !array_key_exists($i, $dst))
      {
        $result[] = array("op" => "remove", "path" => "$path/$i");
      }
      $i--;
    }
    return $result;
  }


  // patch support functions


  // Implements the 'test' op
  private static function test($doc, $path, $parts, $value, $simplexml_mode)
  {
    $found = self::get_helper($doc, $path, $parts, $simplexml_mode);

    if (!self::considered_equal($found, $value))
    {
      throw new JsonPatchException("test target value different - expected "
                                   . json_encode($value) . ", found "
                                   . json_encode($found));
    }
  }


  // Helper for get() and 'copy', 'move', 'test' ops - get a value from a doc.
  private static function get_helper($doc, $path, $parts, $simplexml_mode)
  {
    if (count($parts) == 0)
    {
      return $doc;
    }

    $part = array_shift($parts);
    if (!is_array($doc) || !array_key_exists($part, $doc))
    {
      throw new JsonPatchException("Path '$path' not found");
    }
    if ($simplexml_mode
        && count($parts) > 0
        && $parts[0] == '0'
        && self::is_associative($doc)
        && !(is_array($doc[$part]) && !self::is_associative($doc[$part])))
    {
      return self::get_helper(array($doc[$part]), $path, $parts,
                              $simplexml_mode);
    }
    else
    {
      return self::get_helper($doc[$part], $path, $parts,
                              $simplexml_mode);
    }
  }


  // Test whether a php array looks 'associative' - does it have
  // any non-numeric keys?
  //
  // note: is_associative(array()) === false
  private static function is_associative($a)
  {
    if (!is_array($a))
    {
      return false;
    }
    foreach (array_keys($a) as $key)
    {
      if (is_string($key))
      {
        return true;
      }
    }
    // Also treat php gappy arrays as associative.
    // (e.g. {"0":"a", "2":"c"})
    $len = count($a);
    for ($i = 0; $i < $len; $i++)
    {
      if (!array_key_exists($i, $a))
      {
        return true;
      }
    }
    return false;
  }

  // Recursively sort array keys
  private static function rksort($a)
  {
    if (!is_array($a))
    {
      return $a;
    }
    foreach (array_keys($a) as $key)
    {
      $a[$key] = self::rksort($a[$key]);
    }
    // SORT_STRING seems required, as otherwise numeric indices
    // (e.g. "4") aren't sorted.
    ksort($a, SORT_STRING);
    return $a;
  }


  // Per http://tools.ietf.org/html/rfc6902#section-4.6
  public static function considered_equal($a1, $a2)
  {
    return json_encode(self::rksort($a1)) === json_encode(self::rksort($a2));
  }


  // Apply a single op to modify the given document.
  //
  // As php arrays are not passed by reference, this function works
  // recursively, rebuilding complete subarrays that need changing;
  // the revised subarray is changed in the parent array before
  // returning it.
  private static function do_op($doc, $op, $path, $parts, $value,
                                $simplexml_mode)
  {
    // Special-case toplevel
    if (count($parts) == 0)
    {
      if ($op == 'add' || $op == 'replace')
      {
        return $value;
      }
      else if ($op == 'remove')
      {
        throw new JsonPatchException("Can't remove whole document");
      }
      else
      {
        throw new JsonPatchException("'$op' can't operate on whole document");
      }
    }

    $part = array_shift($parts);

    // recur until we get to the target
    if (count($parts) > 0)
    {
      if (!array_key_exists($part, $doc))
      {
        throw new JsonPatchException("Path '$path' not found");
      }
      // recur, adding resulting sub-doc into doc returned to caller

      // special case for simplexml-style behavior - make singleton
      // scalar leaves look like 1-length arrays
      if ($simplexml_mode
          && count($parts) > 0
          && ($parts[0] == '0' || $parts[0] == '1' || $parts[0] == '-')
          && self::is_associative($doc)
          && !(is_array($doc[$part]) && !self::is_associative($doc[$part])))
      {
        $doc[$part] = self::do_op(array($doc[$part]), $op, $path, $parts,
                                  $value, $simplexml_mode);
      }
      else
      {
        $doc[$part] = self::do_op($doc[$part], $op, $path, $parts,
                                  $value, $simplexml_mode);
      }
      return $doc;
    }

    // at target
    if (!is_array($doc))
    {
      throw new JsonPatchException('Target must be array or associative array');
    }

    if (!self::is_associative($doc)) // N.B. returns false for empty arrays
    {
      if (count($doc) && !self::is_index($part)
          && !($part == '-' && ($op == 'add' || $op == 'append')))
      {
        throw new JsonPatchException("Non-array key '$part' used on array");
      }
      else
      {
        // check range, if numeric
        if (self::is_index($part) &&
            ($part < 0 || (($op == 'remove' && $part >= count($doc))
                           || ($op != 'remove' && $part > count($doc)))))
        {
          throw new JsonPatchException("Can't operate outside of array bounds");
        }
      }
    }

    if ($op == 'add' || $op == 'append')
    {
      if (!self::is_associative($doc)
          && (self::is_index($part) || $part == '-'))
      {
        // If index is '-', use array length
        $index = ($part == '-') ? count($doc) : $part;
        if ($op == 'append')
        {
          array_splice($doc, $index, 0, $value);
        }
        else
        {
          array_splice($doc, $index, 0, Array($value));
        }
      }
      else
      {
        $doc[$part] = $value;
      }
    }

    else if ($op == 'replace')
    {
      if (!self::is_associative($doc) && self::is_index($part))
      {
        array_splice($doc, $part, 1, Array($value));
      }
      else
      {
        if (!array_key_exists($part, $doc))
        {
          throw new JsonPatchException("replace target '$path' not set");
        }
        $doc[$part] = $value;
      }
    }

    else if ($op == 'remove')
    {
      if (!self::is_associative($doc) && self::is_index($part))
      {
        array_splice($doc, $part, 1);
      }
      else
      {
        if (!array_key_exists($part, $doc))
        {
          throw new JsonPatchException("remove target '$path' not set");
        }
        unset($doc[$part]);
      }
    }
    return $doc;
  }
}