package app.softwork.markdowncompose

import androidx.compose.runtime.*
import org.jetbrains.compose.web.attributes.*
import org.jetbrains.compose.web.dom.*

@Composable
public fun renderMarkdown(markdown: String) {
    val iterator = markdown.getTokens().iterator()
    while (iterator.hasNext()) {
        val (rawText, htmlTag) = iterator.next()
        val htmlValue = htmlTag?.groups?.get(1)?.value
        val markdownLink = htmlTag?.groups?.get(2)?.value
        when {
            markdownLink != null -> renderLink(markdownLink)
            htmlValue == null -> Text(rawText)
            htmlValue == "br" -> Br()
            htmlValue.startsWith("a") -> renderA(htmlValue, iterator)
        }
    }
}

private const val markdownLink = """!\[([^\]]*)\]\(([^\)*])\)"""
private val markdownLinkRegex = markdownLink.toRegex()
private val regex = """<([^>]*)>|($markdownLink)""".toRegex()

private fun String.getTokens(): Sequence<Pair<String, MatchResult?>> = sequence {
    var last = 0
    for (match in regex.findAll(this@getTokens)) {
        yield(substring(last until match.range.first) to null)
        last = match.range.last + 1
        yield(substring(match.range) to match)
    }
    if (last != length) {
        yield(substring(last) to null)
    }
}

@Composable
private fun renderA(htmlValue: String, iterator: Iterator<Pair<String, MatchResult?>>) {
    val attrs = htmlValue.split(" ")
    val content = iterator.next()
    A(
        attrs = {
            for (attr in attrs) {
                when {
                    attr.startsWith("href") -> href(attr.removePrefix("href=\"").dropLast(1))
                }
            }
        }) {
        Text(content.first)
    }
    iterator.next()
}

@Composable
private fun renderLink(markdown: String) {
    val link = markdownLinkRegex.matchEntire(markdown)!!.groups
    val content = link[1]!!.value
    val href = link[2]!!.value
    A(href = href) {
        Text(content)
    }
}