import { subWeeks, subMonths, subYears } from 'date-fns';
import type { TimeRange, ChartDataPoint } from '@/lib/types';

function toTradingDayKey(value: string): string {
  const parsed = Date.parse(value);
  if (!Number.isFinite(parsed)) {
    return value;
  }

  return new Date(parsed).toISOString().slice(0, 10);
}

/**
 * Filter chart data by time range
 */
export function filterByTimeRange<T extends ChartDataPoint>(
  data: T[],
  range: TimeRange
): T[] {
  if (data.length === 0) return data;

  const now = new Date();
  const cutoffDate = {
    '1W': subWeeks(now, 1),
    '1M': subMonths(now, 1),
    '3M': subMonths(now, 3),
    '1Y': subYears(now, 1),
    '3Y': subYears(now, 3),
    '5Y': subYears(now, 5),
    '10Y': subYears(now, 10),
    '20Y': subYears(now, 20)
  }[range];

  return data.filter(point => new Date(point.date) >= cutoffDate);
}

/**
 * Check if data point has OHLCV fields
 */
export function isOHLCVData(data: ChartDataPoint): data is {
  date: string;
  open: number;
  high: number;
  low: number;
  close: number;
  volume: number;
} {
  return 'open' in data && 'high' in data && 'low' in data && 'close' in data && 'volume' in data;
}

/**
 * Check if data point has simple price field
 */
export function isPriceData(data: ChartDataPoint): data is { date: string; price: number } {
  return 'price' in data;
}

/**
 * Normalize data to ensure consistent structure
 * Converts price data to OHLCV-like structure for candlestick charts
 */
function normalizeChartData<T extends ChartDataPoint>(data: T[]): T[] {
  if (!data || data.length === 0) return [];

  // Sort by date ascending
  return [...data].sort((a, b) =>
    new Date(a.date).getTime() - new Date(b.date).getTime()
  );
}

/**
 * Sample data for performance with large datasets
 * Keeps every Nth point when dataset is too large
 */
function sampleData<T extends ChartDataPoint>(
  data: T[],
  maxPoints: number = 1000
): T[] {
  if (data.length <= maxPoints) return data;

  const samplingRate = Math.ceil(data.length / maxPoints);
  const sampled: T[] = [];

  for (let i = 0; i < data.length; i += samplingRate) {
    sampled.push(data[i]);
  }

  // Always include the last point
  if (sampled[sampled.length - 1] !== data[data.length - 1]) {
    sampled.push(data[data.length - 1]);
  }

  return sampled;
}

/**
 * Calculate min/max values for Y-axis domain
 */
function calculateYAxisDomain<T extends ChartDataPoint>(
  data: T[],
  padding: number = 0.1
): [number, number] {
  if (data.length === 0) return [0, 100];

  let min = Infinity;
  let max = -Infinity;

  data.forEach(point => {
    if (isOHLCVData(point)) {
      min = Math.min(min, point.low);
      max = Math.max(max, point.high);
    } else if (isPriceData(point)) {
      min = Math.min(min, point.price);
      max = Math.max(max, point.price);
    }
  });

  // Add padding
  const range = max - min;
  const paddedMin = min - (range * padding);
  const paddedMax = max + (range * padding);

  return [paddedMin, paddedMax];
}

/**
 * Calculate volume max for volume indicator Y-axis
 */
function calculateVolumeMax<T extends ChartDataPoint>(data: T[]): number {
  if (data.length === 0 || !isOHLCVData(data[0])) return 0;

  return Math.max(...data.map(d => (isOHLCVData(d) ? d.volume : 0)));
}

/**
 * Merge multiple data series by date for combination charts
 */
export function mergeDataSeries<T extends ChartDataPoint>(
  seriesArray: Array<{ id: string; data: T[] }>
): Array<{ date: string } & Record<string, string | number>> {
  if (!seriesArray || seriesArray.length === 0) return [];

  // Create map indexed by normalized trading day.
  const dateMap = new Map<string, { date: string } & Record<string, string | number>>();
  const seriesPointMaps = seriesArray.map((series) => {
    const pointMap = new Map<string, number>();

    series.data.forEach(point => {
      const date = toTradingDayKey(point.date);

      if (isOHLCVData(point)) {
        pointMap.set(date, point.close);
      } else if (isPriceData(point)) {
        pointMap.set(date, point.price);
      }
    });

    pointMap.forEach((_value, date) => {
      const existing = dateMap.get(date) || { date } as { date: string } & Record<string, string | number>;
      dateMap.set(date, existing);
    });

    return {
      id: series.id,
      pointMap
    };
  });

  const mergedDates = Array.from(dateMap.keys()).sort((a, b) =>
    new Date(a).getTime() - new Date(b).getTime()
  );

  // Fill forward each series to keep benchmark/comparison lines aligned on trading days.
  seriesPointMaps.forEach(({ id, pointMap }) => {
    let lastKnownValue: number | null = null;

    mergedDates.forEach((date) => {
      const currentValue = pointMap.get(date);
      if (typeof currentValue === 'number') {
        lastKnownValue = currentValue;
      }

      const existing = dateMap.get(date);
      if (existing && lastKnownValue !== null) {
        existing[id] = lastKnownValue;
      }
    });
  });

  return mergedDates.map((date) => dateMap.get(date)!);
}