Spark: fill spec value between flag values

I'm trying to figure out how to put a specific value between two flag values, for example:

there is

But it should be:

Desc: We define a range of lines between the first flag=1(inclusive) and the next one and create a new attribute with the value hash from id where the first flag is

You can use udf(), hashlib, and Window with rowsBetween():

from pyspark.sql import SparkSession
from pyspark.sql.functions import col, when, last, udf
from pyspark.sql.window import Window
from pyspark.sql.types import StringType
import hashlib


def _hash(df):
    sha = lambda id: hashlib.sha256(str(id).encode('utf-8')).hexdigest()[:5]
    U = udf(sha, StringType())
    df = df.withColumn("hash", when(col("flg") == 1, U(col("id"))))
    w = Window.orderBy("date").rowsBetween(Window.unboundedPreceding, 0)
    df = df.withColumn("hash", last("hash", True).over(w))
    df.show()


A = [
    (123, "01.01.2024", 1),
    (432, "02.01.2024", None),
    (5234, "03.01.2024", None),
    (12342, "06.01.2024", 1),
    (1256, "07.01.2024", None),
    (246, "08.01.2024", None),
    (846, "09.01.2024", None),
    (834, "15.01.2024", 1),
    (343, "11.01.2024", None),
    (364, "12.01.2024", None)
]
spark = SparkSession.builder.getOrCreate()
df = spark.createDataFrame(A, ["id", "date", "flg"])
_hash(df)

Prints

+-----+----------+----+-----+
|   id|      date| flg| hash|
+-----+----------+----+-----+
|  123|01.01.2024|   1|a665a|
|  432|02.01.2024|NULL|a665a|
| 5234|03.01.2024|NULL|a665a|
|12342|06.01.2024|   1|307fd|
| 1256|07.01.2024|NULL|307fd|
|  246|08.01.2024|NULL|307fd|
|  846|09.01.2024|NULL|307fd|
|  343|11.01.2024|NULL|307fd|
|  364|12.01.2024|NULL|307fd|
|  834|15.01.2024|   1|5c344|
+-----+----------+----+-----+