app/backend/fluksio/flow/panels.py

"""Panels: which dashboards a given device shows.

A wall tablet in the hall and one in the workshop want different dashboards,
and the same dashboard may hang on both. Rather than nesting pages inside a
dashboard, a panel names an ordered set of whole dashboards — each keeps its
own canvas, its own draft and its own version, and the device switches between
them through a rail.

Stored beside the flows rather than in them, like the alerting configuration:
which screen hangs where is the deployment's concern, not any one dashboard's.
"""

from __future__ import annotations

import threading
from pathlib import Path

from pydantic import BaseModel, Field, field_validator

from fluksio.core.config import settings
from fluksio.flow.dashboards import DashboardNotFound, DashboardStore
from fluksio.flow.schemas import _validate_name


class PanelDef(BaseModel):
    """One device, and what it shows."""

    id: str
    title: str = ""
    #: Ordered. The first one is what the device opens after pairing, and the
    #: rail follows this order. A name that no longer resolves is simply a
    #: dashboard someone deleted; the panel skips it.
    dashboards: list[str] = Field(default_factory=list)
    #: Bigger controls, a bigger rail and no hover states, for a screen that is
    #: touched rather than pointed at. It belongs to the device rather than to
    #: any dashboard: the same dashboard may hang on a hallway tablet and on a
    #: desk browser, and only one of them has fingers on it.
    touch: bool = False
    #: Which generation of credential this panel honours. A token names the
    #: nonce it was minted at, so bumping this refuses the screen currently
    #: hanging here and leaves the panel, its dashboards and their arrangement
    #: exactly as they are — re-pairing one device without deleting anything.
    #: Not settable from outside: a save carries the stored value forward.
    nonce: int = 0

    @field_validator("id")
    @classmethod
    def _check_id(cls, value: str) -> str:
        return _validate_name(value)


class PanelsConfig(BaseModel):
    """Every panel this instance knows about."""

    panels: list[PanelDef] = Field(default_factory=list)


#: Held across a read-modify-write of the panels file.
#:
#: Both `save_panels` and `unpair_panel` are one of those, and interleaving
#: them silently undid a revocation: a save that read the file before an
#: unpair wrote it put the old nonce back, and the screen that had just been
#: unpaired kept working. The nonce carry-forward in the save handler was
#: written to make that impossible, and the window between its read and its
#: write is where it happened anyway.
edit_lock = threading.Lock()


def _path() -> Path:
    return settings.PANELS_FILE


def read_config() -> PanelsConfig:
    """The stored panels, or none. Blocking."""
    path = _path()
    if not path.exists():
        return PanelsConfig()
    try:
        return PanelsConfig.model_validate_json(path.read_text())
    except Exception:
        # A hand-edited file that no longer parses must not lock everyone out.
        return PanelsConfig()


def write_config(config: PanelsConfig) -> None:
    """Blocking."""
    path = _path()
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(config.model_dump_json(indent=2))


def find(panel_id: str) -> PanelDef | None:
    """The panel by that id, or None if it was removed.

    Read from disk on every call: this is what makes deleting a panel revoke
    its credential, so it has to see the current file rather than a cache.
    """
    for panel in read_config().panels:
        if panel.id == panel_id:
            return panel
    return None


def messages_for(panel_id: str, store: DashboardStore) -> set[str]:
    """Every message this panel's dashboards read or write.

    What a screen is entitled to see, as its own dashboards define it. Read
    from the published documents, since that is what a panel draws, and empty
    for a panel that is gone — which is the same answer as "nothing".

    A dashboard's own bound settings count, not only its widgets': the theme a
    panel is driven to is a message no tile on it draws, and a wall panel
    refused its own theme message is the one surface the setting exists for.
    """
    panel = find(panel_id)
    if panel is None:
        return set()
    names: set[str] = set()
    for dashboard in panel.dashboards:
        try:
            defn = store.read(dashboard)
        except DashboardNotFound:
            continue
        names.update(defn.setting_messages)
        for widget in defn.widgets:
            names.update(widget.messages)
            if widget.target:
                names.add(widget.target)
    return names