from __future__ import annotations

import json
from dataclasses import asdict, dataclass, field
from datetime import datetime, timezone
from pathlib import Path


@dataclass
class TelemetryEvent:
    """A single structured telemetry event."""
    timestamp: str
    event_type: str
    target: str
    details: dict = field(default_factory=dict)

    def to_dict(self) -> dict:
        return asdict(self)


def _session_log_path(root: Path) -> Path:
    """Return the path to the session-log.jsonl file under .rdb/."""
    rdb_dir = root / ".rdb"
    rdb_dir.mkdir(parents=True, exist_ok=True)
    return rdb_dir / "session-log.jsonl"


def record_event(root: Path, event_type: str, target: str, details: dict | None = None) -> TelemetryEvent:
    """Record a telemetry event to the session log.

    Creates the .rdb/session-log.jsonl file if it does not exist.
    Each call appends one JSON line to the file.

    Args:
        root: Project root directory.
        event_type: Category of event, e.g. 'command', 'task', 'guardrail'.
        target: The entity the event relates to, e.g. 'rdb prompt'.
        details: Optional extra key-value pairs for context.

    Returns:
        The TelemetryEvent that was recorded.
    """
    event = TelemetryEvent(
        timestamp=datetime.now(timezone.utc).isoformat(),
        event_type=event_type,
        target=target,
        details=details or {},
    )

    log_path = _session_log_path(root)
    with open(log_path, "a", encoding="utf-8") as f:
        f.write(json.dumps(event.to_dict()) + "\n")

    return event


def read_events(root: Path) -> list[TelemetryEvent]:
    """Read all events from the session log.

    Returns an empty list if the log does not yet exist or is empty.
    Malformed lines are silently skipped.
    """
    log_path = _session_log_path(root)
    if not log_path.exists():
        return []

    events: list[TelemetryEvent] = []
    for line in log_path.read_text(encoding="utf-8").splitlines():
        line = line.strip()
        if not line:
            continue
        try:
            data = json.loads(line)
            events.append(TelemetryEvent(**data))
        except (json.JSONDecodeError, TypeError):
            pass

    return events