/*
Copyright 2022 Splunk Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import { RandomIdGenerator } from '@opentelemetry/sdk-trace-base';
import { AppState } from 'react-native';
import { trace, diag } from '@opentelemetry/api';
import { setNativeSessionId } from './native';

const idGenerator = new RandomIdGenerator();

interface Session {
  startTime: number;
  id: string;
}

let session: Session = {
  startTime: Date.now(),
  id: idGenerator.generateTraceId(),
};

const tracer = trace.getTracer('session');
//FIXME add conf
const MAX_SESSION_AGE = 4 * 60 * 60 * 1000;
const SESSION_TIMEOUT = 15 * 60 * 1000;
const sessionLogging = false;
let lastActivityTime = Date.now();
const State = {
  FOREGROUND: 'active',
  BACKGROUND: 'background',
  TRANSITIONING_TO_FOREGROUND: 'transitioning',
};
let currentState: String = AppState.currentState;

AppState.addEventListener('change', (nextAppState) => {
  if (sessionLogging) {
    diag.debug('Session:AppStateChange: ', currentState, nextAppState);
  }
  if (nextAppState === State.FOREGROUND && currentState === State.BACKGROUND) {
    if (sessionLogging) {
      diag.debug('Session:AppStateChange:TRANSITIONING_TO_FOREGROUND');
    }
    currentState = State.TRANSITIONING_TO_FOREGROUND;
    return;
  }
  currentState = nextAppState;
});

let isUpdatingSessionId = false;

export function getSessionId() {
  // In order to prevent infinite loop when newSessionId() logic calls getSessionId(),
  // don't update session id if it's already being updated.
  if (isUpdatingSessionId) {
    return session.id;
  }

  if (hasExpired() || hasTimedOut()) {
    bump();
    newSessionId();
  } else {
    bump();
  }
  return session.id;
}

function bump() {
  lastActivityTime = Date.now();
  if (sessionLogging) {
    diag.debug('Session:bump:', new Date(lastActivityTime));
  }
  // when the app spent >15 minutes without any activity (spans) in the background,
  // after moving to the foreground the first span should trigger the sessionId timeout.
  if (currentState === State.TRANSITIONING_TO_FOREGROUND) {
    currentState = State.FOREGROUND;
  }
}

function hasTimedOut() {
  // don't apply sessionId timeout to apps in the foreground
  if (currentState === State.FOREGROUND) {
    if (sessionLogging) {
      diag.debug('Session:hasTimedOut: State.FOREGROUND');
    }
    return false;
  }
  const elapsedTime = Date.now() - lastActivityTime;
  if (sessionLogging) {
    diag.debug(
      'Session:hasTimedOut',
      elapsedTime,
      SESSION_TIMEOUT - elapsedTime
    );
  }
  return elapsedTime >= SESSION_TIMEOUT;
}

function hasExpired() {
  const timeElapsed = Date.now() - session.startTime;
  if (sessionLogging) {
    diag.debug(
      'Session:hasExpired',
      timeElapsed,
      MAX_SESSION_AGE - timeElapsed
    );
  }
  return Date.now() - session.startTime >= MAX_SESSION_AGE;
}

function newSessionId() {
  isUpdatingSessionId = true;
  const previousId = session.id;
  session.startTime = Date.now();
  session.id = idGenerator.generateTraceId();
  setNativeSessionId(session.id);
  if (sessionLogging) {
    diag.debug('Session:newSessionId:', previousId, session.id);
  }
  const span = tracer.startSpan('sessionId.change', {
    attributes: {
      'splunk.rum.previous_session_id': previousId,
    },
  });
  span.end();
  isUpdatingSessionId = false;
}

export function _generatenewSessionId() {
  newSessionId();
  if (sessionLogging) {
    diag.debug('CLIENT:session:generateNewId: ', session.id);
  }
}