/*
 * Copyright 2019, gRPC Authors All rights reserved.
 *
 * 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 Foundation
import GRPC
import NIO
import NIOConcurrencyHelpers
import RouteGuideModel

class RouteGuideProvider: Routeguide_RouteGuideProvider {
  private let features: [Routeguide_Feature]
  private var notes: [Routeguide_Point: [Routeguide_RouteNote]] = [:]
  private var lock = Lock()

  init(features: [Routeguide_Feature]) {
    self.features = features
  }

  /// A simple RPC.
  ///
  /// Obtains the feature at a given position.
  ///
  /// A feature with an empty name is returned if there's no feature at the given position.
  func getFeature(
    request point: Routeguide_Point,
    context: StatusOnlyCallContext
  ) -> EventLoopFuture<Routeguide_Feature> {
    return context.eventLoop.makeSucceededFuture(self.checkFeature(at: point))
  }

  /// A server-to-client streaming RPC.
  ///
  /// Obtains the Features available within the given Rectangle. Results are streamed rather than
  /// returned at once (e.g. in a response message with a repeated field), as the rectangle may
  /// cover a large area and contain a huge number of features.
  func listFeatures(
    request: Routeguide_Rectangle,
    context: StreamingResponseCallContext<Routeguide_Feature>
  ) -> EventLoopFuture<GRPCStatus> {
    let left = min(request.lo.longitude, request.hi.longitude)
    let right = max(request.lo.longitude, request.hi.longitude)
    let top = max(request.lo.latitude, request.hi.latitude)
    let bottom = max(request.lo.latitude, request.hi.latitude)

    self.features.lazy.filter { feature in
      return !feature.name.isEmpty
        && feature.location.longitude >= left
        && feature.location.longitude <= right
        && feature.location.latitude >= bottom
        && feature.location.latitude <= top
    }.forEach {
      _ = context.sendResponse($0)
    }

    return context.eventLoop.makeSucceededFuture(.ok)
  }

  /// A client-to-server streaming RPC.
  ///
  /// Accepts a stream of Points on a route being traversed, returning a RouteSummary when traversal
  /// is completed.
  func recordRoute(
    context: UnaryResponseCallContext<Routeguide_RouteSummary>
  ) -> EventLoopFuture<(StreamEvent<Routeguide_Point>) -> Void> {
    var pointCount: Int32 = 0
    var featureCount: Int32 = 0
    var distance = 0.0
    var previousPoint: Routeguide_Point?
    let startTime = Date()

    return context.eventLoop.makeSucceededFuture({ event in
      switch event {
      case .message(let point):
        pointCount += 1
        if !self.checkFeature(at: point).name.isEmpty {
          featureCount += 1
        }

        // For each point after the first, add the incremental distance from the previous point to
        // the total distance value.
        if let previous = previousPoint {
          distance += previous.distance(to: point)
        }
        previousPoint = point

      case .end:
        let seconds = Date().timeIntervalSince(startTime)
        let summary = Routeguide_RouteSummary.with {
          $0.pointCount = pointCount
          $0.featureCount = featureCount
          $0.elapsedTime = Int32(seconds)
          $0.distance = Int32(distance)
        }
        context.responsePromise.succeed(summary)
      }
    })
  }

  /// A Bidirectional streaming RPC.
  ///
  /// Accepts a stream of RouteNotes sent while a route is being traversed, while receiving other
  /// RouteNotes (e.g. from other users).
  func routeChat(
    context: StreamingResponseCallContext<Routeguide_RouteNote>
  ) -> EventLoopFuture<(StreamEvent<Routeguide_RouteNote>) -> Void> {
    return context.eventLoop.makeSucceededFuture({ event in
      switch event {
      case .message(let note):
        // Get any notes at the location of request note.
        var notes = self.lock.withLock {
          self.notes[note.location, default: []]
        }

        // Respond with all previous notes at this location.
        for note in notes {
          _ = context.sendResponse(note)
        }

        // Add the new note and update the stored notes.
        notes.append(note)
        self.lock.withLockVoid {
          self.notes[note.location] = notes
        }

      case .end:
        context.statusPromise.succeed(.ok)
      }
    })
  }
}

extension RouteGuideProvider {
  private func getOrCreateNotes(for point: Routeguide_Point) -> [Routeguide_RouteNote] {
    return self.lock.withLock {
      self.notes[point, default: []]
    }
  }

  /// Returns a feature at the given location or an unnamed feature if none exist at that location.
  private func checkFeature(at location: Routeguide_Point) -> Routeguide_Feature {
    return self.features.first(where: {
      return $0.location.latitude == location.latitude && $0.location.longitude == location.longitude
    }) ?? Routeguide_Feature.with {
      $0.name = ""
      $0.location = location
    }
  }
}

fileprivate func degreesToRadians(_ degrees: Double) -> Double {
  return degrees * .pi / 180.0
}

fileprivate extension Routeguide_Point {
  func distance(to other: Routeguide_Point) -> Double {
    // Radius of Earth in meters
    let radius = 6_371_000.0
    // Points are in the E7 representation (degrees multiplied by 10**7 and rounded to the nearest
    // integer). See also `Routeguide_Point`.
    let coordinateFactor = 1.0e7

    let lat1 = degreesToRadians(Double(self.latitude) / coordinateFactor)
    let lat2 = degreesToRadians(Double(other.latitude) / coordinateFactor)
    let lon1 = degreesToRadians(Double(self.longitude) / coordinateFactor)
    let lon2 = degreesToRadians(Double(other.longitude) / coordinateFactor)

    let deltaLat = lat2 - lat1
    let deltaLon = lon2 - lon1

    let a = sin(deltaLat / 2) * sin(deltaLat / 2)
      + cos(lat1) * cos(lat2) * sin(deltaLon / 2) * sin(deltaLon / 2)
    let c = 2 * atan2(sqrt(a), sqrt(1 - a))

    return radius * c
  }
}