tanisa/src/converter.ts

An utility to convert Malagasy 🇲🇬 numbers, including decimals, into their word representations.

import { MalagasyNumerals } from './dictionary'
import { TanisaOptions, LargeNumberUnit } from './interface'

export class Tanisa {
  public toWords(number: number | string, options?: TanisaOptions): string {
    const ignoreDecimal = options?.ignoreDecimal ?? false
    const decimalPlaces = options?.decimalPlaces ?? -1

    const numStr = String(number).trim()
    const [integerPartStr, decimalPartStr] = numStr.split('.')
    const integerPartNum = parseInt(integerPartStr || '0', 10)

    if (
      isNaN(integerPartNum) ||
      (decimalPartStr &&
        decimalPartStr.length > 0 &&
        isNaN(parseInt(decimalPartStr, 10)))
    ) {
      throw new TypeError(`Invalid number input: "${number}"`)
    }

    if (numStr.trim().startsWith('-') && integerPartNum !== 0) {
      throw new RangeError('Negative numbers are not supported.')
    }

    if (
      integerPartNum >= MalagasyNumerals.MAX_SUPPORTED_INTEGER ||
      integerPartStr == MalagasyNumerals.MAX_SUPPORTED_INTEGER.toString()
    ) {
      throw new RangeError(
        `Number ${integerPartNum} exceeds the maximum supported value (${MalagasyNumerals.MAX_SUPPORTED_INTEGER}).`
      )
    }

    const integerWords = this.convertInteger(integerPartNum)

    let decimalWords = ''
    const processDecimals =
      decimalPartStr &&
      decimalPartStr.length > 0 &&
      !ignoreDecimal &&
      decimalPlaces !== 0

    if (processDecimals) {
      let effectiveDecimalPartStr = decimalPartStr

      if (decimalPlaces > 0 && decimalPartStr.length > decimalPlaces) {
        effectiveDecimalPartStr = decimalPartStr.substring(0, decimalPlaces)
      }

      if (parseInt(effectiveDecimalPartStr || '0', 10) > 0) {
        let tempDecimalWords = ''
        for (let i = 0; i < effectiveDecimalPartStr.length; i++) {
          const digit = effectiveDecimalPartStr[i]
          if (digit === '0') {
            tempDecimalWords += MalagasyNumerals.GLUE_DECIMAL_ZERO
          } else {
            const remainingDecimal = effectiveDecimalPartStr.substring(i)
            tempDecimalWords += this.convertInteger(
              parseInt(remainingDecimal, 10)
            )
            break
          }
        }
        if (tempDecimalWords) {
          decimalWords = MalagasyNumerals.GLUE_FAINGO + tempDecimalWords
        }
      }
    }

    return integerWords + decimalWords
  }

  private convertInteger(num: number): string {
    if (num === 0) {
      return MalagasyNumerals.ZERO
    }

    for (const unit of MalagasyNumerals.LARGE_NUMBER_UNITS) {
      if (num >= unit.threshold) {
        return this.formatLargeNumber(num, unit)
      }
    }

    return this.convertBelowThousand(num)
  }

  private formatLargeNumber(num: number, unit: LargeNumberUnit): string {
    const multiple = Math.floor(num / unit.threshold)
    const remainder = num % unit.threshold

    let prefix = ''
    // Use prefix only if multiple is greater than 1 OR
    // if multiple is 1 AND the unit is larger than 'arivo' (1000)
    if (multiple > 1) {
      prefix = this.convertInteger(multiple) + ' '
    } else if (multiple === 1 && unit.threshold > 1000) {
      prefix = MalagasyNumerals.DIGITS[1] + ' '
    }
    // If multiple is 1 and unit is 'arivo', no prefix is needed ("arivo", not "iray arivo")
    const basePart = prefix + unit.name

    if (remainder > 0) {
      const remainderText = this.convertInteger(remainder)
      return remainderText + MalagasyNumerals.GLUE_SY + basePart
    } else {
      return basePart
    }
  }

  private convertBelowThousand(num: number): string {
    // Assumes 0 < num < 1000
    if (num >= 100) {
      const hundredMultiple = Math.floor(num / 100)
      const remainder = num % 100
      const hundredWord = MalagasyNumerals.HUNDREDS[hundredMultiple]

      if (remainder === 0) {
        return hundredWord
      } else {
        const remainderWords = this.convertBelowHundred(remainder)
        let glue = MalagasyNumerals.GLUE_AMBY as string
        // Special rule: Use "sy" if hundred base >= 200 AND remainder >= 10
        if (hundredMultiple >= 2 && remainder >= 10) {
          glue = MalagasyNumerals.GLUE_SY
        }
        // Use "iraika" for remainder 1 when connecting
        const finalRemainderWords =
          remainder === 1 ? MalagasyNumerals.CUSTOM_ONE : remainderWords
        return finalRemainderWords + glue + hundredWord
      }
    }
    return this.convertBelowHundred(num)
  }

  private convertBelowHundred(num: number): string {
    if (num >= 10) {
      const tenMultiple = Math.floor(num / 10)
      const remainder = num % 10
      const tenWord = MalagasyNumerals.TENS[tenMultiple]

      if (remainder === 0) {
        return tenWord
      } else {
        // Always use "amby" for tens+digits
        const digitWord =
          remainder === 1
            ? MalagasyNumerals.CUSTOM_ONE
            : MalagasyNumerals.DIGITS[remainder]
        return digitWord + MalagasyNumerals.GLUE_AMBY + tenWord
      }
    }
    return MalagasyNumerals.DIGITS[num]
  }
}