export type GridAggregationFunction<T = number, R = number> = (
    values: T[]
) => R | null

function isNumber(value: unknown): value is number {
    return typeof value === 'number' && !Number.isNaN(value)
}

export const sum: GridAggregationFunction = (values) => {
    let sum = 0
    for (const value of values) {
        if (isNumber(value)) {
            sum += value
        }
    }

    return sum
}

export const avg: GridAggregationFunction = (values) => {
    if (values.length === 0) {
        return null
    }
    let sum = 0
    let valuesCount = 0
    for (const value of values) {
        if (isNumber(value)) {
            valuesCount += 1
            sum += value
        }
    }
    return sum / valuesCount
}

export const min: GridAggregationFunction<
    number | Date,
    number | Date | null
> = (values) => {
    if (values.length === 0) {
        return null
    }
    let min: number | Date = +Infinity
    for (const value of values) {
        if (value != null && value < min) {
            min = value
        }
    }
    return min
}

export const max: GridAggregationFunction<
    number | Date,
    number | Date | null
> = (values) => {
    if (values.length === 0) {
        return null
    }

    let max: number | Date = -Infinity
    for (const value of values) {
        if (value != null && value > max) {
            max = value
        }
    }

    return max
}

export const size: GridAggregationFunction<string | number | Date, number> = (
    values
) => values.filter((value) => value != null).length

export const AGGREGATION_FUNCTIONS = {
    sum,
    avg,
    min,
    max,
    size,
}