//
//  BasalDeliveryTable.swift
//  OmniKit
//
//  Created by Pete Schwamb on 4/4/18.
//  Copyright © 2018 Pete Schwamb. All rights reserved.
//

import Foundation

public struct BasalTableEntry {
    let segments: Int
    let pulses: Int
    let alternateSegmentPulse: Bool
    
    public init(encodedData: Data) {
        segments = Int(encodedData[0] >> 4) + 1
        pulses = (Int(encodedData[0] & 0b11) << 8) + Int(encodedData[1])
        alternateSegmentPulse = (encodedData[0] >> 3) & 0x1 == 1
    }
    
    public init(segments: Int, pulses: Int, alternateSegmentPulse: Bool) {
        self.segments = segments
        self.pulses = pulses
        self.alternateSegmentPulse = alternateSegmentPulse
    }
    
    public var data: Data {
        let pulsesHighBits = UInt8((pulses >> 8) & 0b11)
        let pulsesLowBits = UInt8(pulses & 0xff)
        return Data([
            UInt8((segments - 1) << 4) + UInt8((alternateSegmentPulse ? 1 : 0) << 3) + pulsesHighBits,
            UInt8(pulsesLowBits)
            ])
    }
    
    public func checksum() -> UInt16 {
        let checksumPerSegment = (pulses & 0xff) + (pulses >> 8)
        return UInt16(checksumPerSegment * segments + (alternateSegmentPulse ? segments / 2 : 0))
    }
}

extension BasalTableEntry: CustomDebugStringConvertible {
    public var debugDescription: String {
        return "BasalTableEntry(segments:\(segments), pulses:\(pulses), alternateSegmentPulse:\(alternateSegmentPulse))"
    }
}


public struct BasalDeliveryTable {
    static let segmentDuration: TimeInterval = .minutes(30)
    
    let entries: [BasalTableEntry]
    
    public init(entries: [BasalTableEntry]) {
        self.entries = entries
    }
    
    
    public init(schedule: BasalSchedule) {
        
        struct TempSegment {
            let pulses: Int
        }
        
        let numSegments = 48
        let maxSegmentsPerEntry = 16
        
        var halfPulseRemainder = false
        
        let expandedSegments = stride(from: 0, to: numSegments, by: 1).map { (index) -> TempSegment in
            let rate = schedule.rateAt(offset: Double(index) * .minutes(30))
            let pulsesPerHour = Int(round(rate / Pod.pulseSize))
            let pulsesPerSegment = pulsesPerHour >> 1
            let halfPulse = pulsesPerHour & 0b1 != 0
            
            let segment = TempSegment(pulses: pulsesPerSegment + ((halfPulseRemainder && halfPulse) ? 1 : 0))
            halfPulseRemainder = halfPulseRemainder != halfPulse

            return segment
        }
        
        var tableEntries = [BasalTableEntry]()

        let addEntry = { (segments: [TempSegment], alternateSegmentPulse: Bool) in
            tableEntries.append(BasalTableEntry(
                segments: segments.count,
                pulses: segments.first!.pulses,
                alternateSegmentPulse: alternateSegmentPulse
            ))
        }

        var altSegmentPulse = false
        var segmentsToMerge = [TempSegment]()
        
        for segment in expandedSegments {
            guard let firstSegment = segmentsToMerge.first else {
                segmentsToMerge.append(segment)
                continue
            }
            
            let delta = segment.pulses - firstSegment.pulses
            
            if segmentsToMerge.count == 1 {
                altSegmentPulse = delta == 1
            }
            
            let expectedDelta: Int
            
            if !altSegmentPulse {
                expectedDelta = 0
            } else {
                expectedDelta = segmentsToMerge.count % 2
            }
            
            if expectedDelta != delta || segmentsToMerge.count == maxSegmentsPerEntry {
                addEntry(segmentsToMerge, altSegmentPulse)
                segmentsToMerge.removeAll()
            }
            
            segmentsToMerge.append(segment)
        }
        addEntry(segmentsToMerge, altSegmentPulse)

        self.entries = tableEntries
    }
    
    public init(tempBasalRate: Double, duration: TimeInterval) {
        self.entries = BasalDeliveryTable.rateToTableEntries(rate: tempBasalRate, duration: duration)
    }
    
    private static func rateToTableEntries(rate: Double, duration: TimeInterval) -> [BasalTableEntry] {
        var tableEntries = [BasalTableEntry]()
        
        let pulsesPerHour = Int(round(rate / Pod.pulseSize))
        let pulsesPerSegment = pulsesPerHour >> 1
        let alternateSegmentPulse = pulsesPerHour & 0b1 != 0
        
        var remaining = Int(round(duration / BasalDeliveryTable.segmentDuration))
        
        while remaining > 0 {
            let segments = min(remaining, 16)
            let tableEntry = BasalTableEntry(segments: segments, pulses: Int(pulsesPerSegment), alternateSegmentPulse: segments > 1 ? alternateSegmentPulse : false)
            tableEntries.append(tableEntry)
            remaining -= segments
        }
        return tableEntries
    }
    
    public func numSegments() -> Int {
        return entries.reduce(0) { $0 + $1.segments }
    }
}

extension BasalDeliveryTable: CustomDebugStringConvertible {
    public var debugDescription: String {
        return "BasalDeliveryTable(\(entries))"
    }
}

public struct RateEntry {
    let totalPulses: Double
    let delayBetweenPulses: TimeInterval
    
    public init(totalPulses: Double, delayBetweenPulses: TimeInterval) {
        self.totalPulses = totalPulses
        self.delayBetweenPulses = delayBetweenPulses
    }
    
    public var rate: Double {
        if totalPulses == 0 {
            return 0
        } else {
            return round(TimeInterval(hours: 1) / delayBetweenPulses) / Pod.pulsesPerUnit
        }
    }
    
    public var duration: TimeInterval {
        if totalPulses == 0 {
            return delayBetweenPulses
        } else {
            return round(delayBetweenPulses * Double(totalPulses))
        }
    }
    
    public var data: Data {
        var data = Data()
        data.appendBigEndian(UInt16(round(totalPulses * 10)))
        if totalPulses == 0 {
            data.appendBigEndian(UInt32(delayBetweenPulses.hundredthsOfMilliseconds) * 10)
        } else {
            data.appendBigEndian(UInt32(delayBetweenPulses.hundredthsOfMilliseconds))
        }
        return data
    }
    
    public static func makeEntries(rate: Double, duration: TimeInterval) -> [RateEntry] {
        let maxPulsesPerEntry: Double = 6400
        var entries = [RateEntry]()
        
        var remainingSegments = Int(round(duration.minutes / 30))
        
        let pulsesPerSegment = round(rate / Pod.pulseSize) / 2
        let maxSegmentsPerEntry = pulsesPerSegment > 0 ? Int(maxPulsesPerEntry / pulsesPerSegment) : 1
        
        var remainingPulses = rate * duration.hours / Pod.pulseSize
        let delayBetweenPulses = TimeInterval(hours: 1) / rate * Pod.pulseSize
        
        while (remainingSegments > 0) {
            if rate == 0 {
                entries.append(RateEntry(totalPulses: 0, delayBetweenPulses: .minutes(30)))
                remainingSegments -= 1
            } else {
                let numSegments = min(maxSegmentsPerEntry, Int(round(remainingPulses / pulsesPerSegment)))
                if numSegments == 0 {
                    break // prevent infinite loop and subsequent malloc crash with certain bad rate values
                }
                remainingSegments -= numSegments
                let pulseCount = pulsesPerSegment * Double(numSegments)
                let entry = RateEntry(totalPulses: pulseCount, delayBetweenPulses: delayBetweenPulses)
                entries.append(entry)
                remainingPulses -= pulseCount
            }
        }
        return entries
    }
}

extension RateEntry: CustomDebugStringConvertible {
    public var debugDescription: String {
        return "RateEntry(rate:\(rate) duration:\(duration.stringValue))"
    }
}