export interface TrendDataPoint {
  day: string;
  value: number;
}

export interface ChartConfig {
  chartData: any;
  chartOptions: any;
}

interface DatasetOverrides {
  label: string;
  backgroundColor: string | string[];
  datalabels?: object;
}

interface YAxisTicks {
  min: number;
  max: number;
  stepSize: number;
}

export class ChartBuilderUtils {
  private static readonly GREEN_DARK = '#2E7D32';
  private static readonly GRID_LINE = '#F0F0F0';
  private static readonly AXIS_LABEL = '#3a4450';
  private static readonly DATA_LABEL = '#222222';

  private static readonly SHARED_X_AXIS = [
    { gridLines: { display: false }, ticks: { fontColor: ChartBuilderUtils.AXIS_LABEL } }
  ];

  private static buildYAxis(ticks: YAxisTicks) {
    return [{ gridLines: { color: ChartBuilderUtils.GRID_LINE }, ticks: { fontColor: ChartBuilderUtils.AXIS_LABEL, beginAtZero: true, ...ticks } }];
  }

  /**
   * Computes a nice Y-axis scale from the actual data values.
   * `preferredMax` acts as both the zero-data fallback and a minimum floor —
   * the computed max will never be less than `preferredMax`.
   */
  private static niceYTicks(values: number[], preferredMax: number): YAxisTicks {
    const dataMax = values.length > 0 ? Math.max(...values) : 0;
    // Use whichever is larger: data-driven headroom or the preferred floor
    const raw = Math.max(dataMax * 1.2, preferredMax);
    const magnitude = Math.pow(10, Math.floor(Math.log10(raw / 5)));
    const stepSize = Math.ceil((raw / 5) / magnitude) * magnitude;
    const max = stepSize * 5;
    return { min: 0, max, stepSize };
  }

  private static buildBaseChartConfig(
    data: TrendDataPoint[],
    dataset: DatasetOverrides,
    yAxisTicks: YAxisTicks,
    tooltipUnit: string,
    plugins?: object
  ): ChartConfig {
    const values = data.map(d => d.value);
    return {
      chartData: {
        labels: data.map(d => d.day),
        datasets: [{
          label: dataset.label,
          data: values,
          fill: false,
          borderColor: ChartBuilderUtils.GREEN_DARK,
          backgroundColor: dataset.backgroundColor,
          pointBackgroundColor: ChartBuilderUtils.GREEN_DARK,
          pointRadius: 4,
          tension: 0.3,
          ...(dataset.datalabels ? { datalabels: dataset.datalabels } : {})
        }]
      },
      chartOptions: {
        responsive: true,
        maintainAspectRatio: false,
        legend: { display: false },
        ...(plugins ? { plugins } : {}),
        scales: {
          xAxes: ChartBuilderUtils.SHARED_X_AXIS,
          yAxes: ChartBuilderUtils.buildYAxis(yAxisTicks)
        },
        tooltips: {
          callbacks: { label: (item: any) => ` ${item.yLabel} ${tooltipUnit}` }
        }
      }
    };
  }

  private static interpolateGreenByValue(values: number[]): string[] {
    const light = { r: 165, g: 214, b: 167 };
    const dark = { r: 46, g: 125, b: 50 };
    const min = Math.min(...values);
    const max = Math.max(...values);
    return values.map(val => {
      const t = (max === min) ? 0 : (val - min) / (max - min);
      return `rgb(${Math.round(light.r + (dark.r - light.r) * t)},${Math.round(light.g + (dark.g - light.g) * t)},${Math.round(light.b + (dark.b - light.b) * t)})`;
    });
  }

  static hoursChart(data: TrendDataPoint[]): ChartConfig {
    const values = data.map(d => d.value);
    return ChartBuilderUtils.buildBaseChartConfig(
      data,
      { label: $localize`:Hours flown chart dataset label@@hoursChartLabel:Hours Flown`, backgroundColor: ChartBuilderUtils.GREEN_DARK },
      ChartBuilderUtils.niceYTicks(values, 5),
      $localize`:Hours unit abbreviation@@unitHrs:hrs`
    );
  }

  static hectaresChart(data: TrendDataPoint[], areaUnit = 'ha'): ChartConfig {
    const values = data.map(d => d.value);
    const preferredMax = areaUnit === 'ac' ? 2000 : 500;
    const datalabels = { anchor: 'end', align: 'end', color: ChartBuilderUtils.DATA_LABEL, font: { weight: 'bold' }, formatter: (v: number) => v };
    const datasetLabel = areaUnit === 'ac'
      ? $localize`:Acres sprayed chart dataset label@@acresChartLabel:Acres Sprayed`
      : $localize`:Hectares sprayed chart dataset label@@hectaresChartLabel:Hectares Sprayed`;
    return ChartBuilderUtils.buildBaseChartConfig(
      data,
      { label: datasetLabel, backgroundColor: ChartBuilderUtils.interpolateGreenByValue(values), datalabels },
      ChartBuilderUtils.niceYTicks(values, preferredMax),
      areaUnit,
      { datalabels }
    );
  }
}