"""
Text similarity with simhash.
"""

import logging

from asyncpg import Connection
from simhash import Simhash, SimhashIndex

logger = logging.getLogger(__name__)
logger.setLevel(logging.ERROR)


postgresql_bigint_offset = 9223372036854775808
"""
Subtract this number to get a PostgreSQL bigint from a 64bit int.
"""


def get_features(txt: str) -> list[str]:
    """
    Extract features from string for use with Simhash.
    """
    width = 3
    txt = txt.replace(' ', '').lower()
    return [txt[i : i + width] for i in range(max(len(txt) - width + 1, 1))]


def simhash_to_bigint(simhash: Simhash) -> int:
    """
    Convert a simhash to PostgreSQL's bigint value range.
    """
    return simhash.value - postgresql_bigint_offset


def simhash_from_bigint(bigint: int) -> Simhash:
    """
    Convert a simhash from PostgreSQL's bigint to a Simhash instance.
    """
    return Simhash(bigint + postgresql_bigint_offset, log=logger)


def get_simhash(text: str) -> Simhash:
    """
    Return the Simhash of the given text.
    """
    return Simhash(get_features(text), log=logger)


async def get_simhash_index(conn: Connection, site_id: int) -> SimhashIndex:
    """
    Return a simhash index with hashes of all stored resources of the site.
    """
    sql = (
        "SELECT r.id, r.simhash FROM site_path sp, resource r"
        " WHERE sp.site_id=$1 AND sp.resource_id=r.id"
    )
    rows = await conn.fetch(sql, site_id)
    objs = [
        (
            str(row['id']),
            Simhash(row['simhash'] + postgresql_bigint_offset, log=logger),
        )
        for row in rows
    ]
    return SimhashIndex(objs, k=3, log=logger)


def create_simhash(
    index: SimhashIndex,
    resource_id: int,
    simhash_instance: Simhash,
) -> int:
    """
    Add a resource with given id and simhash to a simhash index.

    Return the simhash value shifted into PostgreSQL's bigint range.

    (The simhash field of the resource's database entry is not updated.)
    """
    index.add(str(resource_id), simhash_instance)
    return simhash_to_bigint(simhash_instance)


def search_simhash(index: SimhashIndex, simhash_inst: Simhash) -> list[int]:
    """
    Return the ids of similar resources from the index.
    """
    found = index.get_near_dups(simhash_inst)
    if found:
        return sorted([int(elem) for elem in found])
    return []