"""Pluggable data sources for the wafer monitor.

A DataSource produces a MonitorSnapshot on demand. Today: CSV session + synthetic
demo. Future: live MQTT from NanoBerry. App.py only talks to this interface.
"""

from __future__ import annotations

from pathlib import Path
from typing import Protocol

from .Calibration import BaselineCalibration
from .CsvSource import find_session_files, load_camera_records_from_csv
from .VisionEngine import MonitorSnapshot, VisionEngine


class DataSource(Protocol):
    def latest_snapshot(self, baseline: BaselineCalibration) -> MonitorSnapshot: ...

    def description(self) -> str: ...


# ---------------------------------------------------------------------------
# P2.2 — CsvSessionSource for replaying a selected session.
#
# Resolves sibling files once from the seed path using P1.1, then re-reads
# those files on every latest_snapshot() call. If discovery returns no files,
# raises FileNotFoundError so a bad operator selection is visible immediately.
# ---------------------------------------------------------------------------
class CsvSessionSource:
    """Reads a captured session from a directory of CSV files.

    The operator selects the session folder (e.g. ``sessions/0540/``); this
    source discovers all cameras inside it automatically.  Re-reads files on
    every ``latest_snapshot()`` call so "Reload Current Session" always reflects
    the latest on-disk state without cache invalidation.
    """

    def __init__(self, folder: Path, engine: VisionEngine) -> None:
        self.folder = Path(folder)
        self.engine = engine
        # Discover once at construction so missing-folder errors are immediate.
        paths = find_session_files(self.folder)
        if not paths:
            raise FileNotFoundError(f"No NanoBerry CSV files found in {self.folder}")
        self._cam_count = len(paths)

    def latest_snapshot(self, baseline: BaselineCalibration) -> MonitorSnapshot:
        # Re-resolve on every call — supports "Reload Current Session".
        paths = find_session_files(self.folder)
        if not paths:
            raise FileNotFoundError(f"No NanoBerry CSV files found in {self.folder}")
        self._cam_count = len(paths)
        records = load_camera_records_from_csv(paths, baseline)
        return self.engine.snapshot_from_records(
            records,
            baseline,
            source_label=self.description(),
        )

    def description(self) -> str:
        return f"Session: {self.folder.name} ({self._cam_count} cams)"


# ---------------------------------------------------------------------------
# P2.3 — DemoSource as the default safe source.
#
# First launch should not depend on MASTER_SD being present or on the working
# directory. Wrapping VisionEngine.demo_snapshot() behind the same protocol
# means demo mode, CSV replay, and future MQTT all flow through P3.1 with no
# special-case read logic. The description is stable because P3.3 displays it
# directly in the status bar.
# ---------------------------------------------------------------------------
class DemoSource:
    """Synthetic perfect-world data — always works, used as fallback."""

    def __init__(self, engine: VisionEngine) -> None:
        self.engine = engine

    def latest_snapshot(self, baseline: BaselineCalibration) -> MonitorSnapshot:
        return self.engine.demo_snapshot(baseline)

    def description(self) -> str:
        return "Demo: Simulated Data"


# ---------------------------------------------------------------------------
# TODO P6.1: Post-scope hook for MqttSource implementing DataSource.
#
# THINKING:
#   Live MQTT should enter the app as another DataSource, not by changing
#   VisionEngine or App.read_wafer(). The source can own broker connection,
#   background subscription, and latest-frame buffers, then convert payloads to
#   CameraEdgeRecord before calling snapshot_from_records(). Keeping this as a
#   P6 task protects the beta session-loader milestone from broker/threading
#   risk while documenting the intended extension point.
#   Cross-reference: P6.2 adds the future App.py action that constructs it.
#
# Future signature:
#   class MqttSource:
#       def __init__(self, broker: str, engine: VisionEngine) -> None: ...
#       def latest_snapshot(self, baseline: BaselineCalibration) -> MonitorSnapshot: ...
# ---------------------------------------------------------------------------