import CoreLocation

extension Array where Element == CLLocation {

    /**
     Sample the locations using a given time interval.
     */
    func samplePeriodically(at interval: TimeInterval) -> [CLLocation] {
        guard interval > 0 else { return [] }
        guard let start = first, let end = last else { return self }
        let totalTime = end.timestamp.timeIntervalSince(start.timestamp)
        let numberOfSamples = Int((totalTime / interval).rounded(.up))
        return periodicSamples(interval: interval, numberOfSamples: numberOfSamples)
    }

    /**
     Sample the locations at a fixed period determined by the number of desired sampels
     */
    func samplePeriodically(numberOfSamples: Int) -> [CLLocation] {
        guard numberOfSamples > 0 else { return [] }
        guard let start = first, let end = last else { return self }
        let totalTime = end.timestamp.timeIntervalSince(start.timestamp)
        let timeInterval = totalTime / TimeInterval(count - 1)
        return periodicSamples(interval: timeInterval, numberOfSamples: numberOfSamples)
    }

    private func periodicSamples(interval: TimeInterval, numberOfSamples: Int) -> [CLLocation] {
        guard let start = first else { return [] }
        var currentIndex = 0
        var currentTime = start.timestamp

        var samples = [start]
        for _ in 1..<numberOfSamples {
            currentTime = currentTime.addingTimeInterval(interval)
            while true {
                let nextIndex = currentIndex + 1
                if nextIndex >= count { break }
                let nextTime = self[nextIndex].timestamp
                if nextTime > currentTime { break }
                currentIndex += 1
            }
            if currentIndex + 1 == count {
                samples.append(self[currentIndex])
            } else {
                let before = self[currentIndex]
                let after = self[currentIndex + 1]
                let interpolated = before.interpolate(currentTime, to: after)
                samples.append(interpolated)
            }
        }
        return samples
    }

    /// Computes path length by moving along center-to-center lines, intersecting uncertainty spheres
    func minimumTraveledDistance3D() -> CLLocationDistance {
        guard count > 1 else { return 0 }

        // Remove the uncertainty radius of the first location
        var current = self.first!
        var totalDistance: CLLocationDistance = -current.uncertaintyRadius3D
        for next in self[1...] {
            let (movement, point) = current.minimumDistance(to: next)
            current = point
            totalDistance += movement
        }
        return totalDistance
    }

    /// Calculates the minimum possible ascended altitude (meters),
    /// considering vertical accuracy as an uncertainty interval.
    func minimumAscendedAltitude() -> CLLocationDistance {
        guard let first = self.first else { return 0 }

        // Start with the highest possible value of the first point
        var currentAltitude = first.altitude + first.verticalAccuracy
        var ascended: CLLocationDistance = 0

        for next in self.dropFirst() {
            let newMin = next.altitude - next.verticalAccuracy
            let newMax = next.altitude + next.verticalAccuracy

            if newMin > currentAltitude {
                // Lower bound must be adjusted
                ascended += newMin - currentAltitude
                currentAltitude = newMin
            } else if newMax < currentAltitude {
                // Upper bound must be adjusted
                currentAltitude = newMax
            }
        }
        return ascended
    }

    /// Calculates the minimum possible ascended altitude (meters),
    /// considering a given vertical accuracy threshold
    func minimumAscendedAltitude(threshold: CLLocationDistance) -> CLLocationDistance {
        guard let first = self.first else { return 0 }

        // Start with the highest possible value of the first point
        var currentAltitude = first.altitude + threshold
        var ascended: CLLocationDistance = 0

        for next in self.dropFirst() {
            let newMin = next.altitude - threshold
            let newMax = next.altitude + threshold

            if newMin > currentAltitude {
                // Lower bound must be adjusted
                ascended += newMin - currentAltitude
                currentAltitude = newMin
            } else if newMax < currentAltitude {
                // Upper bound must be adjusted
                currentAltitude = newMax
            }
        }
        return ascended
    }

    func interpolateAltitudes(
        from startDate: Date,
        to endDate: Date
    ) -> [CLLocation] {

        // Ensure valid range
        guard startDate < endDate else { return self }

        // Find first and last locations in the window
        guard
            let startLocation = first(where: { $0.timestamp >= startDate }),
            let endLocation = last(where: { $0.timestamp <= endDate })
        else {
            return self // No valid range found
        }

        let startAltitude = startLocation.altitude
        let endAltitude = endLocation.altitude
        let duration = endDate.timeIntervalSince(startDate)

        return map { loc in
            let t = loc.timestamp.timeIntervalSince1970

            if loc.timestamp >= startDate && loc.timestamp <= endDate {
                let progress = (loc.timestamp.timeIntervalSince(startDate)) / duration
                let newAltitude = startAltitude + progress * (endAltitude - startAltitude)

                return CLLocation(
                    coordinate: loc.coordinate,
                    altitude: newAltitude,
                    horizontalAccuracy: loc.horizontalAccuracy,
                    verticalAccuracy: loc.verticalAccuracy,
                    course: loc.course,
                    speed: loc.speed,
                    timestamp: loc.timestamp
                )
            } else {
                return loc // outside window, unchanged
            }
        }
    }
}

extension CLLocation {

    /// Combined uncertainty sphere radius (meters) from horizontal+vertical accuracy
    var uncertaintyRadius3D: CLLocationDistance {
        let h = max(0, horizontalAccuracy)
        let v = max(0, verticalAccuracy)
        return sqrt(h * h + v * v)
    }

    func verticalDistance(from other: CLLocation) -> CLLocationDistance {
        abs(self.altitude - other.altitude)
    }

    func minimumDistance(to other: CLLocation) -> (distance: CLLocationDistance, point: CLLocation) {
        let horizontalDistance = distance(from: other)
        let horizontalMovement = Swift.max(0, horizontalDistance - Swift.max(0, other.horizontalAccuracy))

        let latitude: CLLocationDegrees
        let longitude: CLLocationDegrees
        if horizontalDistance == 0 || horizontalMovement == 0 {
            latitude = coordinate.latitude
            longitude = coordinate.longitude
        } else {
            let horizontalRatio = horizontalMovement / horizontalDistance
            latitude = coordinate.latitude.move(horizontalRatio, to: other.coordinate.latitude)
            longitude = coordinate.longitude.move(horizontalRatio, to: other.coordinate.longitude)
        }

        let verticalDistance = verticalDistance(from: other)
        let verticalMovement = Swift.max(0, verticalDistance - Swift.max(0, other.verticalAccuracy))

        let altitude: CLLocationDistance
        if verticalDistance == 0 || verticalMovement == 0 {
            altitude = self.altitude
        } else {
            let verticalRatio = verticalMovement / verticalDistance
            altitude = self.altitude.move(verticalRatio, to: other.altitude)
        }

        let movement = sqrt(horizontalMovement * horizontalMovement + verticalMovement * verticalMovement)
        let point = CLLocation(
            coordinate: .init(latitude: latitude, longitude: longitude),
            altitude: altitude,
            horizontalAccuracy: 0,
            verticalAccuracy: 0,
            timestamp: other.timestamp
        )
        return (movement, point)
    }

    func interpolate(_ time: Date, to other: CLLocation) -> CLLocation {
        if self.timestamp > other.timestamp {
            return other.interpolate(time, to: self)
        }
        let totalDuration = other.timestamp.timeIntervalSince(self.timestamp)
        if totalDuration == 0 { return move(0.5, to: other) }
        let ratio = time.timeIntervalSince(self.timestamp) / totalDuration
        return move(ratio, to: other)
    }

    func move(_ ratio: Double, to other: CLLocation) -> CLLocation {
        if ratio <= 0 { return self }
        if ratio >= 1 { return other }

        let time = timestamp.addingTimeInterval(other.timestamp.timeIntervalSince(timestamp) * ratio)

        return CLLocation(
            coordinate: .init(
                latitude: coordinate.latitude.move(ratio, to: other.coordinate.latitude),
                longitude: coordinate.longitude.move(ratio, to: other.coordinate.longitude)),
            altitude: altitude.move(ratio, to: other.altitude),
            horizontalAccuracy: move(from: horizontalAccuracy, to: other.horizontalAccuracy, by: ratio),
            verticalAccuracy: move(from: verticalAccuracy, to: other.verticalAccuracy, by: ratio),
            course: move(from: course, to: other.course, by: ratio),
            courseAccuracy: move(from: courseAccuracy, to: other.courseAccuracy, by: ratio),
            speed: move(from: speed, to: other.speed, by: ratio),
            speedAccuracy: move(from: speedAccuracy, to: other.speedAccuracy, by: ratio),
            timestamp: time)
    }

    private func move(from source: Double, to other: Double, by ratio: Double) -> Double {
        if source == -1 {
            return other
        }
        if other == -1 {
            return source
        }
        return source.move(ratio, to: other)
    }
}

extension Double {

    /**
     Move to a different value by the given ratio of their distance.
     */
    func move(_ ratio: Double, to other: Double) -> Double {
        self + (other - self) * ratio
    }
}