import round from "./round.js"

/**
 * Format a number with a specific style.
 * @example
 * Basic usage
 * ```js
 * const string = formatNumber(1234.567, { sign: true, round: true })
 * // returns "+1,235"
 * ```
 * @param number The number to format.
 * @param options An object containing the formatting options.
 * @param options.style The style to use for formatting. Can be "cbc" or "rc".
 * @param options.sign If true, "-" or "+" are added in front of the number.
 * @param options.round If true, the number will be rounded.
 * @param options.decimals The number of decimals to keep when rounding.
 * @param options.significantDigits The number of significant digits to keep.
 * @param options.fixed If true, display a fixed number of decimals by keeping 0 digits.
 * @param options.nearestInteger The base to use to round the number.
 * @param options.prefix A string to add before the number.
 * @param options.suffix A string to add after the number.
 *
 * @category Formatting
 */

export default function formatNumber(
    number: number,
    options: {
        style?: "cbc" | "rc"
        sign?: boolean
        round?: boolean
        decimals?: number
        significantDigits?: number
        fixed?: boolean
        nearestInteger?: number
        prefix?: string
        suffix?: string
    } = {}
): string {
    if (typeof number !== "number") {
        throw new Error("Not a number")
    }

    const mergedOptions: {
        style: "cbc" | "rc"
        sign: boolean
        round: boolean
        decimals?: number
        nearestInteger?: number
        significantDigits?: number
        fixed: boolean
        prefix: string
        suffix: string
    } = {
        style: "cbc",
        sign: false,
        round: false,
        fixed: false,
        prefix: "",
        suffix: "",
        ...options,
    }

    if (
        mergedOptions.round ||
        typeof mergedOptions.decimals === "number" ||
        typeof mergedOptions.nearestInteger === "number" ||
        typeof mergedOptions.significantDigits === "number"
    ) {
        number = round(number, {
            decimals: mergedOptions.decimals,
            nearestInteger: mergedOptions.nearestInteger,
            significantDigits: mergedOptions.significantDigits,
        })
    }

    const regex = /\B(?=(\d{3})+(?!\d))/g
    const [integers, decimals] = mergedOptions.fixed
        ? number.toFixed(mergedOptions.decimals).split(".")
        : number.toString().split(".")

    let formattedNumber = ""

    if (mergedOptions.style === "cbc") {
        const formattedIntegers = integers.replace(regex, ",")
        if (decimals) {
            formattedNumber = `${formattedIntegers}.${decimals}`
        } else {
            formattedNumber = formattedIntegers
        }
    } else if (mergedOptions.style === "rc") {
        const string = mergedOptions.fixed
            ? number.toFixed(mergedOptions.decimals)
            : number.toString()
        if (string.length === 4) {
            formattedNumber = string.replace(".", ",")
        } else {
            const formattedIntegers = integers.replace(regex, " ")
            if (decimals) {
                formattedNumber = `${formattedIntegers},${decimals}`
            } else {
                formattedNumber = formattedIntegers
            }
        }
    } else {
        throw new Error("Unknown style")
    }

    if (mergedOptions.sign && number > 0) {
        formattedNumber = `+${formattedNumber}`
    }

    return `${mergedOptions.prefix}${formattedNumber}${mergedOptions.suffix}`
}