chinese-transliteration/src/main/kotlin/com/marvinelsen/chinese/transliteration/api/PinyinSyllable.kt

package com.marvinelsen.chinese.transliteration.api

import java.io.InputStream

@Suppress("MagicNumber", "MaximumLineLength", "MaxLineLength")
data class PinyinSyllable(
    val pinyinSyllableWithoutTone: String,
    val tone: Tone,
) {
    companion object {
        private val pinyinToZhuyin = parseTranscriptions(
            this::class.java.getResourceAsStream("/pinyin_zhuyin_transcriptions.tsv")!!
        )
        private val zhuyinToPinyin = pinyinToZhuyin.entries.associate { it.value to it.key }
        private val zhuyinToneMarkRegex = """[ˊˇˋ˙]""".toRegex()

        fun isValidPinyinWithToneNumberSyllable(pinyinSyllable: String) =
            pinyinSyllable.last().isDigit() && pinyinSyllable.last().digitToInt() in 1..5 && pinyinSyllable
                .substring(0, pinyinSyllable.lastIndex)
                .lowercase() in pinyinToZhuyin

        fun fromPinyinWithToneNumber(pinyinWithToneNumber: String): PinyinSyllable {
            val pinyinWithoutNumber = pinyinWithToneNumber.substring(0, pinyinWithToneNumber.lastIndex)
            val lastCharacter = pinyinWithToneNumber.last()

            require(lastCharacter.isDigit()) {
                "'$pinyinWithToneNumber' is not a valid Pinyin with tone number syllable. Expected the last character to be a digit, but was '${pinyinWithToneNumber.last()}'"
            }
            require(lastCharacter.digitToInt() in 1..5) {
                "'$pinyinWithToneNumber' is not a valid Pinyin with tone number syllable. Expected the tone number 'n' to be in range 1 <= n <= 5, but was '${pinyinWithToneNumber.last()}'"
            }
            require(
                pinyinWithoutNumber.lowercase() in pinyinToZhuyin
            ) { "'$pinyinWithoutNumber' is not a valid Pinyin syllable." }

            return PinyinSyllable(
                pinyinSyllableWithoutTone = pinyinWithoutNumber,
                tone = Tone.fromDigit(lastCharacter)
            )
        }

        fun fromZhuyin(zhuyin: String): PinyinSyllable {
            val zhuyinWithoutToneMark = zhuyin.replace(zhuyinToneMarkRegex, "")

            require(zhuyinWithoutToneMark in zhuyinToPinyin) { "'$zhuyin' is not a valid Zhuyin syllable." }

            return PinyinSyllable(
                zhuyinToPinyin[zhuyinWithoutToneMark]!!,
                Tone.fromZhuyinToneMarkOrNull(zhuyin.last()) ?: Tone.fromZhuyinToneMarkOrNull(zhuyin.first())
                    ?: Tone.FIRST
            )
        }

        private fun parseTranscriptions(inputStream: InputStream) =
            inputStream.bufferedReader().useLines { lines ->
                lines.map { it.split('\t') }
                    .associate { it[0] to it[1] }
            }
    }

    fun format(transliterationSystem: TransliterationSystem) = when (transliterationSystem) {
        TransliterationSystem.ZHUYIN -> formatToZhuyin()
        TransliterationSystem.PINYIN_WITH_TONE_NUMBERS -> formatToPinyinWithToneNumbers()
        TransliterationSystem.PINYIN_WITH_TONE_MARKS -> formatToPinyinWithToneMarks()
    }

    private fun formatToZhuyin(): String {
        val zhuyinSyllable = pinyinToZhuyin[pinyinSyllableWithoutTone.lowercase()]
            ?: error("$pinyinSyllableWithoutTone is not a valid Pinyin syllable")
        val zhuyinToneMark = tone.format(TransliterationSystem.ZHUYIN)

        return when (tone) {
            Tone.FIRST, Tone.SECOND, Tone.THIRD, Tone.FORTH -> zhuyinSyllable + zhuyinToneMark
            Tone.FIFTH -> zhuyinToneMark + zhuyinSyllable
        }
    }

    private fun formatToPinyinWithToneNumbers(): String {
        check(pinyinSyllableWithoutTone.lowercase() in pinyinToZhuyin) {
            "'$pinyinSyllableWithoutTone is not a valid Pinyin syllable."
        }

        return pinyinSyllableWithoutTone + tone.format(TransliterationSystem.PINYIN_WITH_TONE_NUMBERS)
    }

    private fun formatToPinyinWithToneMarks(): String {
        check(pinyinSyllableWithoutTone.lowercase() in pinyinToZhuyin) {
            "'$pinyinSyllableWithoutTone is not a valid Pinyin syllable."
        }

        if (pinyinSyllableWithoutTone.lowercase() == "r" && tone == Tone.FIFTH) {
            return pinyinSyllableWithoutTone
        }

        val sanitizedPinyinSyllableWithoutTone = pinyinSyllableWithoutTone.replace("v", "ü").replace("u:", "ü")

        val characterToIndex = sanitizedPinyinSyllableWithoutTone.lowercase().withIndex().associate { it.value to it.index }
        val vowelIndex = when {
            'a' in characterToIndex -> characterToIndex['a']!!
            'o' in characterToIndex -> characterToIndex['o']!!
            'e' in characterToIndex -> characterToIndex['e']!!
            'i' in characterToIndex ->
                if (sanitizedPinyinSyllableWithoutTone.elementAtOrNull(characterToIndex['i']!! + 1) == 'u') {
                    characterToIndex['u']!!
                } else {
                    characterToIndex['i']!!
                }

            'u' in characterToIndex -> characterToIndex['u']!!
            'ü' in characterToIndex -> characterToIndex['ü']!!
            else -> error("No vowel found in Pinyin syllable '$sanitizedPinyinSyllableWithoutTone'")
        }

        return buildString {
            append(sanitizedPinyinSyllableWithoutTone)
            insert(vowelIndex + 1, tone.format(TransliterationSystem.PINYIN_WITH_TONE_MARKS))
        }
    }
}