"""OTel initialization — called at app startup (U1: OTel now required)."""

import logging

from opentelemetry import trace, metrics
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.export import PeriodicExportingMetricReader
from opentelemetry.sdk.resources import Resource
from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
from opentelemetry.exporter.otlp.proto.grpc.metric_exporter import OTLPMetricExporter
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor

logger = logging.getLogger(__name__)


def setup_telemetry(app, config: dict | None = None):
    """Initialize OpenTelemetry if configured.

    U1: opentelemetry-* deps now required (pyproject.toml). ImportError
    fallbacks removed — a missing package is a hard install error. The
    `enabled=False` config switch remains the supported way to disable.

    Args:
        app: FastAPI application instance
        config: Telemetry configuration dict with keys:
            - enabled (bool): Whether to enable telemetry
            - service_name (str): Service name for OTel resource
            - otlp_endpoint (str): OTLP gRPC endpoint URL
            - export_traces (bool): Whether to export traces
            - export_metrics (bool): Whether to export metrics
    """
    if not config or not config.get("enabled", False):
        logger.info("Telemetry disabled")
        return

    service_name = config.get("service_name", "fischer-agentkit")
    resource = Resource.create({"service.name": service_name})

    # Tracing setup
    if config.get("export_traces", True):
        endpoint = config.get("otlp_endpoint", "http://localhost:4317")
        provider = TracerProvider(resource=resource)
        provider.add_span_processor(
            BatchSpanProcessor(OTLPSpanExporter(endpoint=endpoint, insecure=True))
        )
        trace.set_tracer_provider(provider)
        logger.info(f"Tracing enabled, exporting to {endpoint}")

    # Metrics setup
    if config.get("export_metrics", True):
        endpoint = config.get("otlp_endpoint", "http://localhost:4317")
        reader = PeriodicExportingMetricReader(OTLPMetricExporter(endpoint=endpoint, insecure=True))
        # ponytail: OTel SDK 1.16+ 将 readers kwarg 改名为 metric_readers；
        # 旧代码用 readers=[...] 是已存在 bug，被 ImportError fallback 掩盖。
        provider = MeterProvider(resource=resource, metric_readers=[reader])
        metrics.set_meter_provider(provider)
        logger.info(f"Metrics enabled, exporting to {endpoint}")

    # FastAPI auto-instrumentation
    FastAPIInstrumentor.instrument_app(app, excluded_urls="health,metrics")
    logger.info("FastAPI auto-instrumentation enabled")