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Filename : arlstem.py
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# -*- coding: utf-8 -*-
#
# Natural Language Toolkit: ARLSTem Stemmer
#
# Copyright (C) 2001-2020 NLTK Project
#
# Author: Kheireddine Abainia (x-programer) <k.abainia@gmail.com>
# Algorithms: Kheireddine Abainia <k.abainia@gmail.com>
#                         Siham Ouamour
#                         Halim Sayoud
# URL: <http://nltk.org/>
# For license information, see LICENSE.TXT


"""
ARLSTem Arabic Stemmer
The details about the implementation of this algorithm are described in:
K. Abainia, S. Ouamour and H. Sayoud, A Novel Robust Arabic Light Stemmer ,
Journal of Experimental & Theoretical Artificial Intelligence (JETAI'17),
Vol. 29, No. 3, 2017, pp. 557-573.
The ARLSTem is a light Arabic stemmer that is based on removing the affixes
from the word (i.e. prefixes, suffixes and infixes). It was evaluated and
compared to several other stemmers using Paice's parameters (under-stemming
index, over-stemming index and stemming weight), and the results showed that
ARLSTem is promising and producing high performances. This stemmer is not
based on any dictionary and can be used on-line effectively.
"""
import re

from nltk.stem.api import StemmerI


class ARLSTem(StemmerI):
    """
    ARLSTem stemmer : a light Arabic Stemming algorithm without any dictionary.
    Department of Telecommunication & Information Processing. USTHB University,
    Algiers, Algeria.
    ARLSTem.stem(token) returns the Arabic stem for the input token.
    The ARLSTem Stemmer requires that all tokens are encoded using Unicode
    encoding.
    """

    def __init__(self):
        # different Alif with hamza
        self.re_hamzated_alif = re.compile(r"[\u0622\u0623\u0625]")
        self.re_alifMaqsura = re.compile(r"[\u0649]")
        self.re_diacritics = re.compile(r"[\u064B-\u065F]")

        # Alif Laam, Laam Laam, Fa Laam, Fa Ba
        self.pr2 = ["\u0627\u0644", "\u0644\u0644", "\u0641\u0644", "\u0641\u0628"]
        # Ba Alif Laam, Kaaf Alif Laam, Waaw Alif Laam
        self.pr3 = ["\u0628\u0627\u0644", "\u0643\u0627\u0644", "\u0648\u0627\u0644"]
        # Fa Laam Laam, Waaw Laam Laam
        self.pr32 = ["\u0641\u0644\u0644", "\u0648\u0644\u0644"]
        # Fa Ba Alif Laam, Waaw Ba Alif Laam, Fa Kaaf Alif Laam
        self.pr4 = [
            "\u0641\u0628\u0627\u0644",
            "\u0648\u0628\u0627\u0644",
            "\u0641\u0643\u0627\u0644",
        ]

        # Kaf Yaa, Kaf Miim
        self.su2 = ["\u0643\u064A", "\u0643\u0645"]
        # Ha Alif, Ha Miim
        self.su22 = ["\u0647\u0627", "\u0647\u0645"]
        # Kaf Miim Alif, Kaf Noon Shadda
        self.su3 = ["\u0643\u0645\u0627", "\u0643\u0646\u0651"]
        # Ha Miim Alif, Ha Noon Shadda
        self.su32 = ["\u0647\u0645\u0627", "\u0647\u0646\u0651"]

        # Alif Noon, Ya Noon, Waaw Noon
        self.pl_si2 = ["\u0627\u0646", "\u064A\u0646", "\u0648\u0646"]
        # Taa Alif Noon, Taa Ya Noon
        self.pl_si3 = ["\u062A\u0627\u0646", "\u062A\u064A\u0646"]

        # Alif Noon, Waaw Noon
        self.verb_su2 = ["\u0627\u0646", "\u0648\u0646"]
        # Siin Taa, Siin Yaa
        self.verb_pr2 = ["\u0633\u062A", "\u0633\u064A"]
        # Siin Alif, Siin Noon
        self.verb_pr22 = ["\u0633\u0627", "\u0633\u0646"]
        # Lam Noon, Lam Taa, Lam Yaa, Lam Hamza
        self.verb_pr33 = [
            "\u0644\u0646",
            "\u0644\u062A",
            "\u0644\u064A",
            "\u0644\u0623",
        ]
        # Taa Miim Alif, Taa Noon Shadda
        self.verb_suf3 = ["\u062A\u0645\u0627", "\u062A\u0646\u0651"]
        # Noon Alif, Taa Miim, Taa Alif, Waaw Alif
        self.verb_suf2 = [
            "\u0646\u0627",
            "\u062A\u0645",
            "\u062A\u0627",
            "\u0648\u0627",
        ]
        # Taa, Alif, Noon
        self.verb_suf1 = ["\u062A", "\u0627", "\u0646"]

    def stem(self, token):
        """
            call this function to get the word's stem based on ARLSTem .
        """
        try:
            if token is None:
                raise ValueError(
                    "The word could not be stemmed, because \
                                 it is empty !"
                )
            # remove Arabic diacritics and replace some letters with others
            token = self.norm(token)
            # strip common prefixes of the nouns
            pre = self.pref(token)
            if pre is not None:
                token = pre
            # strip the suffixes which are common to nouns and verbs
            token = self.suff(token)
            # transform a plural noun to a singular noun
            ps = self.plur2sing(token)
            if ps is None:
                # transform from the feminine form to the masculine form
                fm = self.fem2masc(token)
                if fm is not None:
                    return fm
                else:
                    if pre is None:  # if the prefixes are not stripped
                        # strip the verb prefixes and suffixes
                        return self.verb(token)
            else:
                return ps
            return token
        except ValueError as e:
            print(e)

    def norm(self, token):
        """
            normalize the word by removing diacritics, replacing hamzated Alif
            with Alif replacing AlifMaqsura with Yaa and removing Waaw at the
            beginning.
        """
        # strip Arabic diacritics
        token = self.re_diacritics.sub("", token)
        # replace Hamzated Alif with Alif bare
        token = self.re_hamzated_alif.sub("\u0627", token)
        # replace alifMaqsura with Yaa
        token = self.re_alifMaqsura.sub("\u064A", token)
        # strip the Waaw from the word beginning if the remaining is 3 letters
        # at least
        if token.startswith("\u0648") and len(token) > 3:
            token = token[1:]
        return token

    def pref(self, token):
        """
            remove prefixes from the words' beginning.
        """
        if len(token) > 5:
            for p3 in self.pr3:
                if token.startswith(p3):
                    return token[3:]
        if len(token) > 6:
            for p4 in self.pr4:
                if token.startswith(p4):
                    return token[4:]
        if len(token) > 5:
            for p3 in self.pr32:
                if token.startswith(p3):
                    return token[3:]
        if len(token) > 4:
            for p2 in self.pr2:
                if token.startswith(p2):
                    return token[2:]

    def suff(self, token):
        """
            remove suffixes from the word's end.
        """
        if token.endswith("\u0643") and len(token) > 3:
            return token[:-1]
        if len(token) > 4:
            for s2 in self.su2:
                if token.endswith(s2):
                    return token[:-2]
        if len(token) > 5:
            for s3 in self.su3:
                if token.endswith(s3):
                    return token[:-3]
        if token.endswith("\u0647") and len(token) > 3:
            token = token[:-1]
            return token
        if len(token) > 4:
            for s2 in self.su22:
                if token.endswith(s2):
                    return token[:-2]
        if len(token) > 5:
            for s3 in self.su32:
                if token.endswith(s3):
                    return token[:-3]
        if token.endswith("\u0646\u0627") and len(token) > 4:
            return token[:-2]
        return token

    def fem2masc(self, token):
        """
            transform the word from the feminine form to the masculine form.
        """
        if token.endswith("\u0629") and len(token) > 3:
            return token[:-1]

    def plur2sing(self, token):
        """
            transform the word from the plural form to the singular form.
        """
        if len(token) > 4:
            for ps2 in self.pl_si2:
                if token.endswith(ps2):
                    return token[:-2]
        if len(token) > 5:
            for ps3 in self.pl_si3:
                if token.endswith(ps3):
                    return token[:-3]
        if len(token) > 3 and token.endswith("\u0627\u062A"):
            return token[:-2]
        if len(token) > 3 and token.startswith("\u0627") and token[2] == "\u0627":
            return token[:2] + token[3:]
        if len(token) > 4 and token.startswith("\u0627") and token[-2] == "\u0627":
            return token[1:-2] + token[-1]

    def verb(self, token):
        """
            stem the verb prefixes and suffixes or both
        """
        vb = self.verb_t1(token)
        if vb is not None:
            return vb
        vb = self.verb_t2(token)
        if vb is not None:
            return vb
        vb = self.verb_t3(token)
        if vb is not None:
            return vb
        vb = self.verb_t4(token)
        if vb is not None:
            return vb
        vb = self.verb_t5(token)
        if vb is not None:
            return vb
        return self.verb_t6(token)

    def verb_t1(self, token):
        """
            stem the present prefixes and suffixes
        """
        if len(token) > 5 and token.startswith("\u062A"):  # Taa
            for s2 in self.pl_si2:
                if token.endswith(s2):
                    return token[1:-2]
        if len(token) > 5 and token.startswith("\u064A"):  # Yaa
            for s2 in self.verb_su2:
                if token.endswith(s2):
                    return token[1:-2]
        if len(token) > 4 and token.startswith("\u0627"):  # Alif
            # Waaw Alif
            if len(token) > 5 and token.endswith("\u0648\u0627"):
                return token[1:-2]
            # Yaa
            if token.endswith("\u064A"):
                return token[1:-1]
            # Alif
            if token.endswith("\u0627"):
                return token[1:-1]
            # Noon
            if token.endswith("\u0646"):
                return token[1:-1]
        # ^Yaa, Noon$
        if len(token) > 4 and token.startswith("\u064A") and token.endswith("\u0646"):
            return token[1:-1]
        # ^Taa, Noon$
        if len(token) > 4 and token.startswith("\u062A") and token.endswith("\u0646"):
            return token[1:-1]

    def verb_t2(self, token):
        """
            stem the future prefixes and suffixes
        """
        if len(token) > 6:
            for s2 in self.pl_si2:
                # ^Siin Taa
                if token.startswith(self.verb_pr2[0]) and token.endswith(s2):
                    return token[2:-2]
            # ^Siin Yaa, Alif Noon$
            if token.startswith(self.verb_pr2[1]) and token.endswith(self.pl_si2[0]):
                return token[2:-2]
            # ^Siin Yaa, Waaw Noon$
            if token.startswith(self.verb_pr2[1]) and token.endswith(self.pl_si2[2]):
                return token[2:-2]
        # ^Siin Taa, Noon$
        if (
            len(token) > 5
            and token.startswith(self.verb_pr2[0])
            and token.endswith("\u0646")
        ):
            return token[2:-1]
        # ^Siin Yaa, Noon$
        if (
            len(token) > 5
            and token.startswith(self.verb_pr2[1])
            and token.endswith("\u0646")
        ):
            return token[2:-1]

    def verb_t3(self, token):
        """
            stem the present suffixes
        """
        if len(token) > 5:
            for su3 in self.verb_suf3:
                if token.endswith(su3):
                    return token[:-3]
        if len(token) > 4:
            for su2 in self.verb_suf2:
                if token.endswith(su2):
                    return token[:-2]
        if len(token) > 3:
            for su1 in self.verb_suf1:
                if token.endswith(su1):
                    return token[:-1]

    def verb_t4(self, token):
        """
            stem the present prefixes
        """
        if len(token) > 3:
            for pr1 in self.verb_suf1:
                if token.startswith(pr1):
                    return token[1:]
            if token.startswith("\u064A"):
                return token[1:]

    def verb_t5(self, token):
        """
            stem the future prefixes
        """
        if len(token) > 4:
            for pr2 in self.verb_pr22:
                if token.startswith(pr2):
                    return token[2:]
            for pr2 in self.verb_pr2:
                if token.startswith(pr2):
                    return token[2:]
        return token

    def verb_t6(self, token):
        """
            stem the order prefixes
        """
        if len(token) > 4:
            for pr3 in self.verb_pr33:
                if token.startswith(pr3):
                    return token[2:]
        return token