import os

from fastapi import FastAPI
from opentelemetry import metrics, trace
from opentelemetry.exporter.prometheus import PrometheusMetricReader
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
from opentelemetry.instrumentation.logging import LoggingInstrumentor
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.resources import SERVICE_NAME, Resource
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import (
    BatchSpanProcessor,
    ConsoleSpanExporter,
)
from prometheus_client import start_http_server


_observability_initialized = False

def setup_observability(app: FastAPI) -> None:
    global _observability_initialized
    if _observability_initialized:
        return

    
    
    service_name = os.getenv("OTEL_SERVICE_NAME", "language-learning-api")
    metrics_host = os.getenv("OTEL_EXPORTER_PROMETHEUS_HOST", "0.0.0.0")
    metrics_port = int(os.getenv("OTEL_EXPORTER_PROMETHEUS_PORT", "9464"))

    resource = Resource.create({SERVICE_NAME: service_name})

    tracer_provider = TracerProvider(resource=resource)
    trace.set_tracer_provider(tracer_provider)

    tracer_provider.add_span_processor(BatchSpanProcessor(ConsoleSpanExporter()))

    metric_reader = PrometheusMetricReader()
    meter_provider = MeterProvider(resource=resource, metric_readers=[metric_reader])
    metrics.set_meter_provider(meter_provider)

    LoggingInstrumentor().instrument(set_logging_format=True)

    # Expose OTel metrics for Prometheus scraping on the standard endpoint.
    start_http_server(port=metrics_port, addr=metrics_host)

    
    
    _observability_initialized = True