import ChartJS, { ChartConfiguration } from 'chart.js/auto'

export interface HistogramConstructor {
    root: HTMLElement
    axisLabels?: { x: string, y: string }
    title?: string
    width?: number
}

export default class Histogram {
    private chart: ChartJS<'bar', number[]>
    private width: number

    constructor(opts: HistogramConstructor) {
        this.width = opts.width || 400
        const title = opts.title || 'Histogram'
        const axisLabels = opts.axisLabels || { x: 'Bins', y: 'Frequency' }

        const canvas = document.createElement('canvas')
        const draggable = document.createElement('drag-pane')
        draggable.setAttribute('heading', title )
        draggable.setAttribute('key', title)
        draggable.appendChild(canvas)
        opts.root.appendChild(draggable)
        canvas.width = this.width


        const defaultChartOptions: ChartConfiguration<'bar', number[]> = {
            type: 'bar',
            data: {
                labels: [],
                datasets: [{
                    label: title,
                    data: [],
                    backgroundColor: 'rgba(54, 162, 235, 0.2)',
                    borderColor: 'rgba(54, 162, 235, 1)',
                    borderWidth: 1
                }]
            },
            options: {
                scales: {
                    x: {
                        title: {
                            display: true,
                            text: axisLabels.x
                        }
                    },
                    y: {
                        title: {
                            display: true,
                            text: axisLabels.y
                        },
                        beginAtZero: true
                    }
                }
            }
        }

        this.chart = new ChartJS<'bar', number[]>(canvas, defaultChartOptions)
    }

    public applyData(data: number[], binSize: number): void {
        const { bins, frequencies } = this.calculateBins(data, binSize)
        this.chart.data.labels = bins
        this.chart.data.datasets[0].data = frequencies
        this.chart.update()
    }

    private calculateBins(data: number[], binSize: number): { bins: number[], frequencies: number[] } {
        const max = Math.max(...data)
        const min = Math.min(...data)
        // `bins` used as labels for the chart
        const bins = []
        const frequencies = []

        // gets the precision of the bin size float
        const precision = binSize.toString().split('.')[1]?.length || 1
        for (let start = min; start <= max; start += binSize) {
            bins.push(`${+(start).toFixed(precision)}-${ +(start + binSize).toFixed(precision)}`)
            frequencies.push(0)
        }

        data.forEach(value => {
            const binIndex = Math.floor((value - min) / binSize)
            frequencies[binIndex]++
        })

        return { bins, frequencies }
    }
}