package net.pterodactylus.sone.text

import freenet.keys.*
import net.pterodactylus.sone.data.*
import net.pterodactylus.sone.data.impl.*
import net.pterodactylus.sone.database.*
import net.pterodactylus.sone.text.LinkType.*
import net.pterodactylus.sone.text.LinkType.USK
import net.pterodactylus.sone.utils.*
import org.bitpedia.util.*
import java.net.*
import javax.inject.*

/**
 * [Parser] implementation that can recognize Freenet URIs.
 */
class SoneTextParser @Inject constructor(private val soneProvider: SoneProvider?, private val postProvider: PostProvider?) {

	fun parse(source: String, context: SoneTextParserContext?) =
			source.split("\n")
					.dropWhile { it.trim() == "" }
					.dropLastWhile { it.trim() == "" }
					.mergeMultipleEmptyLines()
					.flatMap { splitLineIntoParts(it, context) }
					.removeEmptyPlainTextParts()
					.mergeAdjacentPlainTextParts()

	private fun splitLineIntoParts(line: String, context: SoneTextParserContext?) =
			generateSequence(PlainTextPart("") as Part to line) { remainder ->
				if (remainder.second == "")
					null
				else
					LinkType.values()
							.mapNotNull { it.findNext(remainder.second) }
							.minBy { it.position }
							.let {
								when {
									it == null -> PlainTextPart(remainder.second) to ""
									it.position == 0 -> it.toPart(context) to it.remainder
									else -> PlainTextPart(remainder.second.substring(0, it.position)) to (it.link + it.remainder)
								}
							}
			}.map { it.first }.toList()

	private val NextLink.linkWithoutBacklink: String
		get() {
			val backlink = link.indexOf("/../")
			val query = link.indexOf("?")
			return if ((backlink > -1) && ((query == -1) || (query > -1) && (backlink < query)))
				link.substring(0, backlink)
			else
				link
		}

	private fun NextLink.toPart(context: SoneTextParserContext?) = when (linkType) {
		KSK, CHK -> try {
			FreenetURI(linkWithoutBacklink).let { freenetUri ->
				FreenetLinkPart(
						linkWithoutBacklink,
						freenetUri.allMetaStrings?.lastOrNull { it != "" } ?: freenetUri.docName ?: linkWithoutBacklink.substring(0, 9),
						linkWithoutBacklink.split('?').first()
				)
			}
		} catch (e: MalformedURLException) {
			PlainTextPart(linkWithoutBacklink)
		}
		SSK, USK ->
			try {
				FreenetURI(linkWithoutBacklink).let { uri ->
					uri.allMetaStrings
							?.takeIf { (it.size > 1) || ((it.size == 1) && (it.single() != "")) }
							?.lastOrNull()
							?: uri.docName
							?: "${uri.keyType}@${uri.routingKey.asFreenetBase64}"
				}.let { FreenetLinkPart(linkWithoutBacklink.removeSuffix("/"), it, trusted = context?.routingKey?.contentEquals(FreenetURI(linkWithoutBacklink).routingKey) == true) }
			} catch (e: MalformedURLException) {
				PlainTextPart(linkWithoutBacklink)
			}
		SONE -> link.substring(7).let { SonePart(soneProvider?.getSone(it) ?: IdOnlySone(it)) }
		POST -> postProvider?.getPost(link.substring(7))?.let { PostPart(it) } ?: PlainTextPart(link)
		FREEMAIL -> link.indexOf('@').let { atSign ->
			link.substring(atSign + 1, link.length - 9).let { freemailId ->
				FreemailPart(link.substring(0, atSign), freemailId, freemailId.decodedId)
			}
		}
		HTTP, HTTPS -> LinkPart(link, link
				.withoutProtocol
				.withoutWwwPrefix
				.withoutUrlParameters
				.withoutMiddlePathComponents
				.withoutTrailingSlash)
	}

}

private fun List<String>.mergeMultipleEmptyLines() = fold(emptyList<String>()) { previous, current ->
	if (previous.isEmpty()) {
		previous + current
	} else {
		if ((previous.last() == "\n") && (current == "")) {
			previous
		} else {
			previous + ("\n" + current)
		}
	}
}

private fun List<Part>.mergeAdjacentPlainTextParts() = fold(emptyList<Part>()) { parts, part ->
	if ((parts.lastOrNull() is PlainTextPart) && (part is PlainTextPart)) {
		parts.dropLast(1) + PlainTextPart(parts.last().text + part.text)
	} else {
		parts + part
	}
}

private fun List<Part>.removeEmptyPlainTextParts() = filterNot { it == PlainTextPart("") }

private val String.decodedId: String get() = Base32.decode(this).asFreenetBase64
private val String.withoutProtocol get() = substring(indexOf("//") + 2)
private val String.withoutUrlParameters get() = split('?').first()

private val String.withoutWwwPrefix
	get() = split("/")
			.replaceFirst { it.split(".").dropWhile { it == "www" }.joinToString(".") }
			.joinToString("/")

private fun <T> List<T>.replaceFirst(replacement: (T) -> T) = mapIndexed { index, element ->
	if (index == 0) replacement(element) else element
}

private val String.withoutMiddlePathComponents
	get() = split("/").let {
		if (it.size > 2) {
			"${it.first()}/…/${it.last()}"
		} else {
			it.joinToString("/")
		}
	}
private val String.withoutTrailingSlash get() = if (endsWith("/")) substring(0, length - 1) else this
private val SoneTextParserContext.routingKey: ByteArray? get() = postingSone?.routingKey
private val Sone.routingKey: ByteArray get() = id.fromFreenetBase64

private enum class LinkType(private val scheme: String, private val freenetLink: Boolean) {

	KSK("KSK@", true),
	CHK("CHK@", true),
	SSK("SSK@", true),
	USK("USK@", true),
	HTTP("http://", false),
	HTTPS("https://", false),
	SONE("sone://", false) {
		override fun validateLinkLength(length: Int) = length.takeIf { it == 50 }
	},
	POST("post://", false),
	FREEMAIL("", true) {
		override fun findNext(line: String): NextLink? {
			val nextFreemailSuffix = line.indexOf(".freemail").takeIf { it >= 54 } ?: return null
			if (line[nextFreemailSuffix - 53] != '@') return null
			if (!line.substring(nextFreemailSuffix - 52, nextFreemailSuffix).matches(Regex("^[a-z2-7]*\$"))) return null
			val firstCharacterIndex = generateSequence(nextFreemailSuffix - 53) {
				it.minus(1).takeIf { (it >= 0) && line[it].validLocalPart }
			}.lastOrNull() ?: return null
			return NextLink(firstCharacterIndex, this, line.substring(firstCharacterIndex, nextFreemailSuffix + 9), line.substring(nextFreemailSuffix + 9))
		}

		private val Char.validLocalPart get() = (this in ('A'..'Z')) || (this in ('a'..'z')) || (this in ('0'..'9')) || (this == '-') || (this == '_') || (this == '.')
	};

	open fun findNext(line: String): NextLink? {
		val nextLinkPosition = line.indexOf(scheme).takeIf { it != -1 } ?: return null
		val endOfLink = line.substring(nextLinkPosition).findEndOfLink().validate() ?: return null
		val link = line.substring(nextLinkPosition, nextLinkPosition + endOfLink)
		val realNextLinkPosition = if (freenetLink && line.substring(0, nextLinkPosition).endsWith("freenet:")) nextLinkPosition - 8 else nextLinkPosition
		return NextLink(realNextLinkPosition, this, link, line.substring(nextLinkPosition + endOfLink))
	}

	private fun String.findEndOfLink() =
			substring(0, whitespace.find(this)?.range?.start ?: length)
					.dropLastWhile(::isPunctuation)
					.upToFirstUnmatchedParen()

	private fun Int.validate() = validateLinkLength(this)
	protected open fun validateLinkLength(length: Int) = length.takeIf { it > scheme.length }

	private fun String.upToFirstUnmatchedParen() =
			foldIndexed(Pair<Int, Int?>(0, null)) { index, (openParens, firstUnmatchedParen), currentChar ->
				when (currentChar) {
					'(' -> (openParens + 1) to firstUnmatchedParen
					')' -> ((openParens - 1) to (if (openParens == 0) (firstUnmatchedParen ?: index) else firstUnmatchedParen))
					else -> openParens to firstUnmatchedParen
				}
			}.second ?: length

}

private val punctuationChars = listOf('.', ',', '?', '!')
private fun isPunctuation(char: Char) = char in punctuationChars

private val whitespace = Regex("[\\u000a\u0020\u00a0\u1680\u180e\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200a\u200b\u200c\u200d\u202f\u205f\u2060\u2800\u3000]")

private data class NextLink(val position: Int, val linkType: LinkType, val link: String, val remainder: String)