import org.threeten.bp.format.DateTimeFormatter


class DateFormatterBuilder {

    enum class DateTimeUnit {
        YEAR,
        MONTH,
        DAY
    }

    private var prefix: ((DateTimeUnit, Boolean) -> String)? = null
    private var suffix: ((DateTimeUnit) -> String)? = null
    private var leadingZero: Boolean = false

    private var yearFormat: ((Boolean) -> String)? = null
    private var monthFormat: ((Boolean) -> String)? = null
    private var dayFormat: ((Boolean) -> String)? = null

    val hyphened: DateFormatterBuilder
        get() {
            prefix = { unit, inMiddle ->
                if (inMiddle) {
                    "-"
                } else {
                    ""
                }
            }
            suffix = null
            return this
        }

    val slashed: DateFormatterBuilder
        get() {
            prefix = { unit, inMiddle ->
                if (inMiddle) {
                    "/"
                } else {
                    ""
                }
            }
            suffix = null
            return this
        }

    val japanese: DateFormatterBuilder
        get() {
            suffix = {
                when (it) {
                    DateTimeUnit.YEAR -> "年"
                    DateTimeUnit.MONTH -> "月"
                    DateTimeUnit.DAY -> "日"
                }
            }
            prefix = null
            return this
        }

    val year: DateFormatterBuilder
        get() {
            yearFormat = {
                appendPrefixAndSuffix(if (leadingZero) "yyyy" else "y", DateTimeUnit.YEAR, it)
            }
            return this
        }

    val month: DateFormatterBuilder
        get() {
            monthFormat = {
                appendPrefixAndSuffix(if (leadingZero) "MM" else "M", DateTimeUnit.MONTH, it)
            }
            return this
        }

    val day: DateFormatterBuilder
        get() {
            dayFormat = {
                appendPrefixAndSuffix(if (leadingZero) "dd" else "d", DateTimeUnit.DAY, it)
            }
            return this
        }

    val withLeadingZero: DateFormatterBuilder
        get() {
            this.leadingZero = true
            return this
        }

    private fun appendPrefixAndSuffix(format: String, unit: DateTimeUnit, inMiddle: Boolean): String
            = "${prefix?.let { it(unit, inMiddle) } ?: ""}$format${suffix?.let { it(unit) } ?: ""}"

    fun build(): DateTimeFormatter {
        val sb = StringBuilder().apply {
            yearFormat?.let { append(it(this.length > 0)) }
            monthFormat?.let { append(it(this.length > 0)) }
            dayFormat?.let { append(it(this.length > 0)) }
        }
        return DateTimeFormatter.ofPattern(sb.toString())
    }
}