strukto-ai--mirage/python/mirage/commands/builtin/postgres/head.py

# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========

from collections.abc import AsyncIterator
from functools import partial

from mirage.accessor.postgres import PostgresAccessor
from mirage.cache.index import IndexCacheStore
from mirage.commands.builtin.generic.head import head as generic_head
from mirage.commands.builtin.generic.head import head_multi
from mirage.commands.builtin.postgres._provision import head_tail_provision
from mirage.commands.builtin.utils.stream import _read_stdin_async
from mirage.commands.registry import command
from mirage.commands.spec import SPECS
from mirage.core.postgres.glob import resolve_glob
from mirage.core.postgres.read import read as postgres_read
from mirage.io.types import ByteSource, IOResult
from mirage.types import PathSpec


@command("head",
         resource="postgres",
         spec=SPECS["head"],
         provision=head_tail_provision)
async def head(
    accessor: PostgresAccessor,
    paths: list[PathSpec],
    *texts: str,
    stdin: AsyncIterator[bytes] | bytes | None = None,
    n: str | None = None,
    c: str | None = None,
    q: bool = False,
    v: bool = False,
    index: IndexCacheStore = None,
    **_extra: object,
) -> tuple[ByteSource | None, IOResult]:
    n_int = int(n) if n is not None else None
    c_int = int(c) if c is not None else None
    if paths:
        paths = await resolve_glob(accessor, paths, index)
        # Row reads push LIMIT into the query instead of fetching the whole
        # relation; non-row scopes ignore the limit kwarg.
        n_eff = n_int if n_int is not None else 10
        read_fn = postgres_read
        if c_int is None and n_eff > 0:
            read_fn = partial(postgres_read,
                              limit=min(n_eff,
                                        accessor.config.default_row_limit))
        return head_multi(paths,
                          read=read_fn,
                          accessor=accessor,
                          index=index,
                          n=n_int,
                          c=c_int,
                          show_headers=(v or len(paths) > 1)
                          and not q), IOResult()
    raw = await _read_stdin_async(stdin)
    if raw is None:
        raise ValueError("head: missing operand")
    return generic_head(raw, n=n_int, c=c_int), IOResult()