#
# indexer.py
#
# Copyright 2018 Alan Orth.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# ---
#
# Connects to a DSpace Solr statistics core and ingests item views and downloads
# into a PostgreSQL database for use by other applications (like an API).
#
# This script is written for Python 3.5+ and requires several modules that you
# can install with pip (I recommend using a Python virtual environment):
#
#   $ pip install SolrClient psycopg2-binary
#
# See: https://solrclient.readthedocs.io/en/latest/SolrClient.html
# See: https://wiki.duraspace.org/display/DSPACE/Solr

from .config import SOLR_SERVER
from .database import DatabaseManager
import json
import psycopg2.extras
import re
import requests


# Enumerate the cores in Solr to determine if statistics have been sharded into
# yearly shards by DSpace's stats-util or not (for example: statistics-2018).
def get_statistics_shards():
    # Initialize an empty list for statistics core years
    statistics_core_years = []

    # URL for Solr status to check active cores
    solr_query_params = {
        'action': 'STATUS',
        'wt': 'json'
    }
    solr_url = SOLR_SERVER + '/admin/cores'
    res = requests.get(solr_url, params=solr_query_params)

    if res.status_code == requests.codes.ok:
        data = res.json()

        # Iterate over active cores from Solr's STATUS response (cores are in
        # the status array of this response).
        for core in data['status']:
            # Pattern to match, for example: statistics-2018
            pattern = re.compile('^statistics-[0-9]{4}$')

            if not pattern.match(core):
                continue

            # Append current core to list
            statistics_core_years.append(core)

    # Initialize a string to hold our shards (may end up being empty if the Solr
    # core has not been processed by stats-util).
    shards = str()

    if len(statistics_core_years) > 0:
        # Begin building a string of shards starting with the default one
        shards = '{}/statistics'.format(SOLR_SERVER)

        for core in statistics_core_years:
            # Create a comma-separated list of shards to pass to our Solr query
            #
            # See: https://wiki.apache.org/solr/DistributedSearch
            shards += ',{}/{}'.format(SOLR_SERVER, core)

    # Return the string of shards, which may actually be empty. Solr doesn't
    # seem to mind if the shards query parameter is empty and I haven't seen
    # any negative performance impact so this should be fine.
    return shards


def index_views():
    # get total number of distinct facets for items with a minimum of 1 view,
    # otherwise Solr returns all kinds of weird ids that are actually not in
    # the database. Also, stats are expensive, but we need stats.calcdistinct
    # so we can get the countDistinct summary.
    #
    # see: https://lucene.apache.org/solr/guide/6_6/the-stats-component.html
    solr_query_params = {
        'q': 'type:2',
        'fq': 'isBot:false AND statistics_type:view',
        'facet': 'true',
        'facet.field': 'id',
        'facet.mincount': 1,
        'facet.limit': 1,
        'facet.offset': 0,
        'stats': 'true',
        'stats.field': 'id',
        'stats.calcdistinct': 'true',
        'shards': shards,
        'rows': 0,
        'wt': 'json'
    }

    solr_url = SOLR_SERVER + '/statistics/select'

    res = requests.get(solr_url, params=solr_query_params)

    try:
        # get total number of distinct facets (countDistinct)
        results_totalNumFacets = res.json()['stats']['stats_fields']['id']['countDistinct']
    except TypeError:
        print('No item views to index, exiting.')

        exit(0)

    # divide results into "pages" (cast to int to effectively round down)
    results_per_page = 100
    results_num_pages = int(results_totalNumFacets / results_per_page)
    results_current_page = 0

    with DatabaseManager() as db:
        with db.cursor() as cursor:
            # create an empty list to store values for batch insertion
            data = []

            while results_current_page <= results_num_pages:
                # "pages" are zero based, but one based is more human readable
                print('Indexing item views (page {} of {})'.format(results_current_page + 1, results_num_pages + 1))

                solr_query_params = {
                    'q': 'type:2',
                    'fq': 'isBot:false AND statistics_type:view',
                    'facet': 'true',
                    'facet.field': 'id',
                    'facet.mincount': 1,
                    'facet.limit': results_per_page,
                    'facet.offset': results_current_page * results_per_page,
                    'shards': shards,
                    'rows': 0,
                    'wt': 'json',
                    'json.nl': 'map' # return facets as a dict instead of a flat list
                }

                solr_url = SOLR_SERVER + '/statistics/select'

                res = requests.get(solr_url, params=solr_query_params)

                # Solr returns facets as a dict of dicts (see json.nl parameter)
                views = res.json()['facet_counts']['facet_fields']
                # iterate over the 'id' dict and get the item ids and views
                for item_id, item_views in views['id'].items():
                    data.append((item_id, item_views))

                # do a batch insert of values from the current "page" of results
                sql = 'INSERT INTO items(id, views) VALUES %s ON CONFLICT(id) DO UPDATE SET views=excluded.views'
                psycopg2.extras.execute_values(cursor, sql, data, template='(%s, %s)')
                db.commit()

                # clear all items from the list so we can populate it with the next batch
                data.clear()

                results_current_page += 1


def index_downloads():
    # get the total number of distinct facets for items with at least 1 download
    solr_query_params= {
        'q': 'type:0',
        'fq': 'isBot:false AND statistics_type:view AND bundleName:ORIGINAL',
        'facet': 'true',
        'facet.field': 'owningItem',
        'facet.mincount': 1,
        'facet.limit': 1,
        'facet.offset': 0,
        'stats': 'true',
        'stats.field': 'owningItem',
        'stats.calcdistinct': 'true',
        'shards': shards,
        'rows': 0,
        'wt': 'json'
    }

    solr_url = SOLR_SERVER + '/statistics/select'

    res = requests.get(solr_url, params=solr_query_params)

    try:
        # get total number of distinct facets (countDistinct)
        results_totalNumFacets = res.json()['stats']['stats_fields']['owningItem']['countDistinct']
    except TypeError:
        print('No item downloads to index, exiting.')

        exit(0)

    # divide results into "pages" (cast to int to effectively round down)
    results_per_page = 100
    results_num_pages = int(results_totalNumFacets / results_per_page)
    results_current_page = 0

    with DatabaseManager() as db:
        with db.cursor() as cursor:
            # create an empty list to store values for batch insertion
            data = []

            while results_current_page <= results_num_pages:
                # "pages" are zero based, but one based is more human readable
                print('Indexing item downloads (page {} of {})'.format(results_current_page + 1, results_num_pages + 1))

                solr_query_params = {
                    'q': 'type:0',
                    'fq': 'isBot:false AND statistics_type:view AND bundleName:ORIGINAL',
                    'facet': 'true',
                    'facet.field': 'owningItem',
                    'facet.mincount': 1,
                    'facet.limit': results_per_page,
                    'facet.offset': results_current_page * results_per_page,
                    'shards': shards,
                    'rows': 0,
                    'wt': 'json',
                    'json.nl': 'map' # return facets as a dict instead of a flat list
                }

                solr_url = SOLR_SERVER + '/statistics/select'

                res = requests.get(solr_url, params=solr_query_params)

                # Solr returns facets as a dict of dicts (see json.nl parameter)
                downloads = res.json()['facet_counts']['facet_fields']
                # iterate over the 'owningItem' dict and get the item ids and downloads
                for item_id, item_downloads in downloads['owningItem'].items():
                    data.append((item_id, item_downloads))

                # do a batch insert of values from the current "page" of results
                sql = 'INSERT INTO items(id, downloads) VALUES %s ON CONFLICT(id) DO UPDATE SET downloads=excluded.downloads'
                psycopg2.extras.execute_values(cursor, sql, data, template='(%s, %s)')
                db.commit()

                # clear all items from the list so we can populate it with the next batch
                data.clear()

                results_current_page += 1


with DatabaseManager() as db:
    with db.cursor() as cursor:
        # create table to store item views and downloads
        cursor.execute('''CREATE TABLE IF NOT EXISTS items
                  (id INT PRIMARY KEY, views INT DEFAULT 0, downloads INT DEFAULT 0)''')

    # commit the table creation before closing the database connection
    db.commit()

shards = get_statistics_shards()

index_views()
index_downloads()

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