"""Page through the store the way a person browses a shelf: newest first, filtered by who and what."""

from __future__ import annotations

from dataclasses import dataclass
from pathlib import Path

from .config import Settings
from .db import Database, row_to_atom
from .retrieval import decode_cursor, encode_cursor
from .schemas import AtomPage, Modality
from .storage import ObjectStore

# The visibility rule is spelled out in five literal statements — three here, one in store_search, one in vector_index — because the SQL gate rejects a concatenated statement and a view cannot take a parameter; backend/tests/test_visibility_rule.py fails if the copies disagree.


@dataclass(frozen=True)
class Picture:
    """The stored bytes behind an atom and how to label them when serving."""

    path: Path
    mime: str


def browse(
    settings: Settings,
    *,
    limit: int,
    cursor: str | None = None,
    modality: Modality | None = None,
    source_id: str | None = None,
    holder: str | None = None,
    as_holder: str | None = None,
) -> AtomPage:
    """One page plus the total, so a list can say what it left out instead of looking endless.

    `holder` narrows the shelf to one holder's memories; `as_holder` is whose eyes the page is
    read through: a holder id, the empty string for a caller who is nobody (only what nobody owns
    and what is marked for everyone), or None to read the whole library as the operator does.
    """
    offset = decode_cursor(cursor)
    wanted = (modality.value if modality else None, source_id, holder)
    filters = tuple(value for bound in wanted for value in (bound, bound))
    eyes = (as_holder, as_holder, as_holder, as_holder)
    database = Database(settings)
    with database.connect() as connection:
        total = int(
            connection.execute(
                "SELECT COUNT(*) FROM v_atoms_current"
                " WHERE (? IS NULL OR modality = ?) AND (? IS NULL OR source_id = ?) AND (? IS NULL OR holder_id = ?)"
                " AND (? IS NULL"
                "      OR holder_id = ''"
                "      OR json_extract(visibility_json, '$.scope') = 'everyone'"
                "      OR (? <> '' AND (holder_id = ?"
                "            OR EXISTS ("
                "                  SELECT 1 FROM json_each(json_extract(visibility_json, '$.holders'))"
                "                  WHERE value = ?"
                "            ))))",
                (*filters, *eyes),
            ).fetchone()[0]
        )
        rows = connection.execute(
            "SELECT * FROM v_atoms_current"
            " WHERE (? IS NULL OR modality = ?) AND (? IS NULL OR source_id = ?) AND (? IS NULL OR holder_id = ?)"
            " AND (? IS NULL"
            "      OR holder_id = ''"
            "      OR json_extract(visibility_json, '$.scope') = 'everyone'"
            "      OR (? <> '' AND (holder_id = ?"
            "            OR EXISTS ("
            "                  SELECT 1 FROM json_each(json_extract(visibility_json, '$.holders'))"
            "                  WHERE value = ?"
            "            ))))"
            " ORDER BY ingested_at DESC, atom_id DESC LIMIT ? OFFSET ?",
            (*filters, *eyes, limit + 1, offset),
        ).fetchall()
    atoms = [row_to_atom(row) for row in rows[:limit]]
    more = len(rows) > limit or offset + limit < total
    return AtomPage(
        atoms=atoms,
        total=total,
        next_cursor=encode_cursor(offset + limit) if atoms and more else None,
    )


def picture(settings: Settings, atom_id: str, as_holder: str | None = None) -> Picture | None:
    """The stored bytes behind one atom; None means there is no picture to show, for any of the three reasons."""
    database = Database(settings)
    with database.connect() as connection:
        row = connection.execute(
            "SELECT image_ref, mime FROM v_atoms_current JOIN sources USING (source_id)"
            " WHERE atom_id = ?"
            " AND (? IS NULL"
            "      OR holder_id = ''"
            "      OR json_extract(visibility_json, '$.scope') = 'everyone'"
            "      OR (? <> '' AND (holder_id = ?"
            "            OR EXISTS ("
            "                  SELECT 1 FROM json_each(json_extract(visibility_json, '$.holders'))"
            "                  WHERE value = ?"
            "            ))))",
            (atom_id, as_holder, as_holder, as_holder, as_holder),
        ).fetchone()
    if row is None or not row["image_ref"]:
        return None
    path = ObjectStore(settings).resolve(str(row["image_ref"]))
    if not path.exists():
        return None
    mime = str(row["mime"]) if row["mime"] else "image/png"
    return Picture(path=path, mime=mime)