l trim, r trim, and trim in MongoDB's Aggregation Framework

gistfile1.txt

db.trim.insertMany([
{
	"_id" : ObjectId("59e0d1e8505f76f4acde0609"),
	"a" : "   \t\n\r   abc   \t\n\r   "
}
{ "_id" : ObjectId("59e4d34cd1fb8f891853bca4"), "a" : "xy" }
{ "_id" : ObjectId("59e4e55dd1fb8f891853bca5"), "a" : " " }
{ "_id" : ObjectId("59e4e56fd1fb8f891853bca6"), "a" : "  " }
{ "_id" : ObjectId("59e4e578d1fb8f891853bca7"), "a" : " a " }
])

db.trim.aggregate([
  {
    $project: {
      _id: 0,
      a: 1,
      a_split: {
        $let: {
          vars: {
            str_range: {
              $range: [0, { $strLenCP: "$a" }]
            }
          },
          in: {
            $let: {
              vars: {
                split_on_CP_str: {
                  $reduce: {
                    input: "$$str_range",
                    initialValue: {
                      split_string: [],
                      index: 0
                    },
                    in: {
                      split_string: {
                        $concatArrays: [
                          "$$value.split_string",
                          [
                            {
                              $substrCP: ["$a", "$$value.index", 1]
                            }
                          ]
                        ]
                      },
                      index: { $add: ["$$value.index", 1] }
                    }
                  }
                }
              },
              in: "$$split_on_CP_str.split_string"
            }
          }
        }
      },
      rtrimmed_a: {
        $substrCP: [
          "$a",
          0,
          {
            $max: {
              $let: {
                vars: {
                  str_range: {
                    $range: [0, { $strLenCP: "$a" }]
                  }
                },
                in: {
                  $let: {
                    vars: {
                      split_on_CP_str: {
                        $reduce: {
                          input: "$$str_range",
                          initialValue: {
                            split_string: [],
                            index: 0
                          },
                          in: {
                            split_string: {
                              $concatArrays: [
                                "$$value.split_string",
                                [
                                  {
                                    $let: {
                                      vars: {
                                        the_CP: {
                                          $substrCP: ["$a", "$$value.index", 1]
                                        }
                                      },
                                      in: {
                                        $cond: [
                                          {
                                            $eq: [
                                              {
                                                $indexOfCP: [
                                                  " \t\r\n",
                                                  "$$the_CP"
                                                ]
                                              },
                                              -1
                                            ]
                                          },
                                          { $add: ["$$value.index", 1] },
                                          0
                                        ]
                                      }
                                    }
                                  }
                                ]
                              ]
                            },
                            index: { $add: ["$$value.index", 1] }
                          }
                        }
                      }
                    },
                    in: "$$split_on_CP_str.split_string"
                  }
                }
              }
            }
          }
        ]
      },
      ltrimmed_a: {
        $substrCP: [
          "$a",
          {
            $min: {
              $let: {
                vars: {
                  str_range: {
                    $reverseArray: {
                      $range: [0, { $strLenCP: "$a" }]
                    }
                  }
                },
                in: {
                  $let: {
                    vars: {
                      split_on_CP_str: {
                        $reduce: {
                          input: "$$str_range",
                          initialValue: {
                            split_string: [],
                            index: { $subtract: [{ $size: "$$str_range" }, 1] }
                          },
                          in: {
                            split_string: {
                              $concatArrays: [
                                "$$value.split_string",
                                [
                                  {
                                    $let: {
                                      vars: {
                                        the_CP: {
                                          $substrCP: ["$a", "$$value.index", 1]
                                        }
                                      },
                                      in: {
                                        $cond: [
                                          {
                                            $eq: [
                                              {
                                                $indexOfCP: [
                                                  " \t\r\n",
                                                  "$$the_CP"
                                                ]
                                              },
                                              -1
                                            ]
                                          },
                                          "$$value.index",
                                          { $strLenCP: "$a" }
                                        ]
                                      }
                                    }
                                  }
                                ]
                              ]
                            },
                            index: { $subtract: ["$$value.index", 1] }
                          }
                        }
                      }
                    },
                    in: "$$split_on_CP_str.split_string"
                  }
                }
              }
            }
          },
          { $strLenCP: "$a" }
        ]
      }
    }
  },
  {
    $addFields: {
      fulltrim: {
        $cond: [
          { $eq: ["$ltrimmed_a", ""] },
          "",
          {
            $substrCP: [
              "$ltrimmed_a",
              0,
              {
                $max: {
                  $let: {
                    vars: {
                      str_range: {
                        $range: [0, { $strLenCP: "$ltrimmed_a" }]
                      }
                    },
                    in: {
                      $let: {
                        vars: {
                          split_on_CP_str: {
                            $reduce: {
                              input: "$$str_range",
                              initialValue: {
                                split_string: [],
                                index: 0
                              },
                              in: {
                                split_string: {
                                  $concatArrays: [
                                    "$$value.split_string",
                                    [
                                      {
                                        $let: {
                                          vars: {
                                            the_CP: {
                                              $substrCP: [
                                                "$ltrimmed_a",
                                                "$$value.index",
                                                1
                                              ]
                                            }
                                          },
                                          in: {
                                            $cond: [
                                              {
                                                $eq: [
                                                  {
                                                    $indexOfCP: [
                                                      " \t\r\n",
                                                      "$$the_CP"
                                                    ]
                                                  },
                                                  -1
                                                ]
                                              },
                                              { $add: ["$$value.index", 1] },
                                              0
                                            ]
                                          }
                                        }
                                      }
                                    ]
                                  ]
                                },
                                index: { $add: ["$$value.index", 1] }
                              }
                            }
                          }
                        },
                        in: "$$split_on_CP_str.split_string"
                      }
                    }
                  }
                }
              }
            ]
          }
        ]
      }
    }
  }
])