import Charts
import CoreData
import Foundation
import SwiftUI

struct ForecastChart: View {
    @StateObject var state: Bolus.StateModel
    @Environment(\.colorScheme) var colorScheme
    @Binding var units: GlucoseUnits

    @State private var startMarker = Date(timeIntervalSinceNow: -4 * 60 * 60)

    private var endMarker: Date {
        state
            .forecastDisplayType == .lines ? Date(timeIntervalSinceNow: TimeInterval(hours: 3)) :
            Date(timeIntervalSinceNow: TimeInterval(
                Int(1.5) * 5 * state
                    .minCount * 60
            )) // min is 1.5h -> (1.5*1h = 1.5*(5*12*60))
    }

    private var glucoseFormatter: NumberFormatter {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal

        if units == .mmolL {
            formatter.maximumFractionDigits = 1
            formatter.minimumFractionDigits = 1
            formatter.roundingMode = .halfUp
        } else {
            formatter.maximumFractionDigits = 0
        }
        return formatter
    }

    var body: some View {
        VStack {
            forecastChartLabels
                .padding(.bottom, 8)

            forecastChart
        }
    }

    private var forecastChartLabels: some View {
        HStack {
            HStack {
                Image(systemName: "fork.knife")
                Text("\(state.carbs.description) g")
            }
            .font(.footnote)
            .foregroundStyle(.orange)
            .padding(8)
            .background {
                RoundedRectangle(cornerRadius: 10)
                    .fill(Color.orange.opacity(0.2))
            }

            Spacer()

            HStack {
                Image(systemName: "syringe.fill")
                Text("\(state.amount.description) U")
            }
            .font(.footnote)
            .foregroundStyle(.blue)
            .padding(8)
            .background {
                RoundedRectangle(cornerRadius: 10)
                    .fill(Color.blue.opacity(0.2))
            }

            Spacer()

            HStack {
                Image(systemName: "arrow.right.circle")

                if let simulatedDetermination = state.simulatedDetermination, let eventualBG = simulatedDetermination.eventualBG {
                    HStack {
                        Text(
                            (units == .mgdL ? Decimal(eventualBG).description : eventualBG.formattedAsMmolL) + units.rawValue
                        )
                    }
                } else {
                    Text("---")
                }
            }
            .font(.footnote)
            .foregroundStyle(.primary)
            .padding(8)
            .background {
                RoundedRectangle(cornerRadius: 10)
                    .fill(Color.primary.opacity(0.2))
            }
        }
    }

    private var forecastChart: some View {
        Chart {
            drawGlucose()
            drawCurrentTimeMarker()

            if state.forecastDisplayType == .lines {
                drawForecastLines()
            } else {
                drawForecastsCone()
            }
        }
        .chartXAxis { forecastChartXAxis }
        .chartXScale(domain: startMarker ... endMarker)
        .chartYAxis { forecastChartYAxis }
        .chartYScale(domain: units == .mgdL ? 0 ... 300 : 0.asMmolL ... 300.asMmolL)
        .backport.chartForegroundStyleScale(state: state)
    }

    private func drawGlucose() -> some ChartContent {
        ForEach(state.glucoseFromPersistence) { item in
            let glucoseToDisplay = state.units == .mgdL ? Decimal(item.glucose) : Decimal(item.glucose).asMmolL

            // low and high glucose is parsed in state to mmol/L; parse it back to mg/dl here for comparison
            let lowGlucose = units == .mgdL ? state.lowGlucose : state.lowGlucose.asMgdL
            let highGlucose = units == .mgdL ? state.highGlucose : state.highGlucose.asMgdL
            let targetGlucose = (state.determination.first?.currentTarget ?? state.currentBGTarget as NSDecimalNumber) as Decimal

            let pointMarkColor: Color = FreeAPS.getDynamicGlucoseColor(
                glucoseValue: Decimal(item.glucose),
                highGlucoseColorValue: highGlucose,
                lowGlucoseColorValue: lowGlucose,
                targetGlucose: targetGlucose,
                glucoseColorScheme: state.glucoseColorScheme,
                offset: 20
            )

            if !state.isSmoothingEnabled {
                PointMark(
                    x: .value("Time", item.date ?? Date(), unit: .second),
                    y: .value("Value", glucoseToDisplay)
                )
                .foregroundStyle(pointMarkColor)
                .symbolSize(18)
            } else {
                PointMark(
                    x: .value("Time", item.date ?? Date(), unit: .second),
                    y: .value("Value", glucoseToDisplay)
                )
                .symbol {
                    Image(systemName: "record.circle.fill")
                        .font(.system(size: 6))
                        .bold()
                        .foregroundStyle(pointMarkColor)
                }
            }
        }
    }

    private func timeForIndex(_ index: Int32) -> Date {
        let currentTime = Date()
        let timeInterval = TimeInterval(index * 300)
        return currentTime.addingTimeInterval(timeInterval)
    }

    private func drawForecastsCone() -> some ChartContent {
        // Draw AreaMark for the forecast bounds
        ForEach(0 ..< max(state.minForecast.count, state.maxForecast.count), id: \.self) { index in
            if index < state.minForecast.count, index < state.maxForecast.count {
                let yMinMaxDelta = Decimal(state.minForecast[index] - state.maxForecast[index])
                let xValue = timeForIndex(Int32(index))

                // if distance between respective min and max is 0, provide a default range
                if yMinMaxDelta == 0 {
                    let yMinValue = units == .mgdL ? Decimal(state.minForecast[index] - 1) :
                        Decimal(state.minForecast[index] - 1)
                        .asMmolL
                    let yMaxValue = units == .mgdL ? Decimal(state.minForecast[index] + 1) :
                        Decimal(state.minForecast[index] + 1)
                        .asMmolL

                    AreaMark(
                        x: .value("Time", xValue <= endMarker ? xValue : endMarker),
                        yStart: .value("Min Value", units == .mgdL ? yMinValue : yMinValue.asMmolL),
                        yEnd: .value("Max Value", units == .mgdL ? yMaxValue : yMaxValue.asMmolL)
                    )
                    .foregroundStyle(Color.blue.opacity(0.5))
                    .interpolationMethod(.catmullRom)

                } else {
                    let yMinValue = Decimal(state.minForecast[index]) <= 300 ? Decimal(state.minForecast[index]) : Decimal(300)
                    let yMaxValue = Decimal(state.maxForecast[index]) <= 300 ? Decimal(state.maxForecast[index]) : Decimal(300)

                    AreaMark(
                        x: .value("Time", timeForIndex(Int32(index)) <= endMarker ? timeForIndex(Int32(index)) : endMarker),
                        yStart: .value("Min Value", units == .mgdL ? yMinValue : yMinValue.asMmolL),
                        yEnd: .value("Max Value", units == .mgdL ? yMaxValue : yMaxValue.asMmolL)
                    )
                    .foregroundStyle(Color.blue.opacity(0.5))
                    .interpolationMethod(.catmullRom)
                }
            }
        }
    }

    private func drawForecastLines() -> some ChartContent {
        let predictions = state.predictionsForChart

        // Prepare the prediction data with only the first 36 values, i.e. 3 hours in the future
        let predictionData = [
            ("iob", predictions?.iob?.prefix(36)),
            ("zt", predictions?.zt?.prefix(36)),
            ("cob", predictions?.cob?.prefix(36)),
            ("uam", predictions?.uam?.prefix(36))
        ]

        return ForEach(predictionData, id: \.0) { name, values in
            if let values = values {
                ForEach(values.indices, id: \.self) { index in
                    LineMark(
                        x: .value("Time", timeForIndex(Int32(index))),
                        y: .value("Value", units == .mgdL ? Decimal(values[index]) : Decimal(values[index]).asMmolL)
                    )
                    .foregroundStyle(by: .value("Prediction Type", name))
                }
            }
        }
    }

    private func drawCurrentTimeMarker() -> some ChartContent {
        RuleMark(
            x: .value(
                "",
                Date(timeIntervalSince1970: TimeInterval(NSDate().timeIntervalSince1970)),
                unit: .second
            )
        ).lineStyle(.init(lineWidth: 2, dash: [3])).foregroundStyle(Color(.systemGray2))
    }

    private var forecastChartXAxis: some AxisContent {
        AxisMarks(values: .stride(by: .hour, count: 2)) { _ in
            AxisGridLine(stroke: .init(lineWidth: 0.5, dash: [2, 3]))
            AxisValueLabel(format: .dateTime.hour(.defaultDigits(amPM: .narrow)), anchor: .top)
                .font(.caption2)
                .foregroundStyle(Color.secondary)
        }
    }

    private var forecastChartYAxis: some AxisContent {
        AxisMarks(position: .trailing) { _ in
            AxisGridLine(stroke: .init(lineWidth: 0.5, dash: [2, 3]))
            AxisTick(length: 3, stroke: .init(lineWidth: 3)).foregroundStyle(Color.secondary)
            AxisValueLabel().font(.caption2).foregroundStyle(Color.secondary)
        }
    }
}
