1 files changed, 99 insertions, 0 deletions
diff --git a/plugins/base/src/main/kotlin/resolvers/ExternalLocationProvider.kt b/plugins/base/src/main/kotlin/resolvers/ExternalLocationProvider.kt
new file mode 100644
index 00000000..7c0e9952
--- /dev/null
+++ b/plugins/base/src/main/kotlin/resolvers/ExternalLocationProvider.kt
@@ -0,0 +1,99 @@
+package org.jetbrains.dokka.base.resolvers
+
+import org.jetbrains.dokka.DokkaConfiguration.ExternalDocumentationLink
+import org.jetbrains.dokka.links.DRI
+import java.net.HttpURLConnection
+import java.net.URL
+import java.net.URLConnection
+
+object ExternalLocationProvider { // TODO: Refactor this!!!
+    private const val DOKKA_PARAM_PREFIX = "\$dokka."
+
+    private val cache: MutableMap<URL, LocationInfo> = mutableMapOf()
+
+    fun getLocation(dri: DRI, externalDocumentationLinks: List<ExternalDocumentationLink>): String {
+        val toResolve: MutableList<ExternalDocumentationLink> = mutableListOf()
+        for(link in externalDocumentationLinks){
+            val info = cache[link.packageListUrl]
+            if(info == null) {
+                toResolve.add(link)
+            } else if(info.packages.contains(dri.packageName)) {
+                return link.url.toExternalForm() + getLink(dri, info)
+            }
+        }
+        // Not in cache, resolve packageLists
+        while (toResolve.isNotEmpty()){
+            val link = toResolve.first().also { toResolve.remove(it) }
+            val locationInfo = loadPackageList(link.packageListUrl)
+            if(locationInfo.packages.contains(dri.packageName)) {
+                return link.url.toExternalForm() + getLink(dri, locationInfo)
+            }
+        }
+        return ""
+    }
+
+    private fun getLink(dri: DRI, locationInfo: LocationInfo): String = when(locationInfo.format) {
+        "javadoc" ->  dri.toJavadocLocation(8)
+        "kotlin-website-html", "html" -> locationInfo.locations[dri.packageName + "." + dri.classNames] ?: dri.toDokkaLocation(".html")
+        "markdown" -> locationInfo.locations[dri.packageName + "." + dri.classNames] ?: dri.toDokkaLocation(".md")
+        // TODO: rework this
+        else -> throw RuntimeException("Unrecognized format")
+    }
+
+
+    private fun loadPackageList(url: URL): LocationInfo {
+        val packageListStream = url.doOpenConnectionToReadContent().getInputStream()
+        val (params, packages) =
+            packageListStream
+                .bufferedReader()
+                .useLines { lines -> lines.partition { it.startsWith(DOKKA_PARAM_PREFIX) } }
+
+        val paramsMap = params.asSequence()
+            .map { it.removePrefix(DOKKA_PARAM_PREFIX).split(":", limit = 2) }
+            .groupBy({ (key, _) -> key }, { (_, value) -> value })
+
+        val format = paramsMap["format"]?.singleOrNull() ?: "javadoc"
+
+        val locations = paramsMap["location"].orEmpty()
+            .map { it.split("\u001f", limit = 2) }
+            .map { (key, value) -> key to value }
+            .toMap()
+
+        val info = LocationInfo(format, packages.toSet(), locations)
+        cache[url] = info
+        return info
+    }
+
+    private fun URL.doOpenConnectionToReadContent(timeout: Int = 10000, redirectsAllowed: Int = 16): URLConnection {
+        val connection = this.openConnection().apply {
+            connectTimeout = timeout
+            readTimeout = timeout
+        }
+
+        when (connection) {
+            is HttpURLConnection -> {
+                return when (connection.responseCode) {
+                    in 200..299 -> {
+                        connection
+                    }
+                    HttpURLConnection.HTTP_MOVED_PERM,
+                    HttpURLConnection.HTTP_MOVED_TEMP,
+                    HttpURLConnection.HTTP_SEE_OTHER -> {
+                        if (redirectsAllowed > 0) {
+                            val newUrl = connection.getHeaderField("Location")
+                            URL(newUrl).doOpenConnectionToReadContent(timeout, redirectsAllowed - 1)
+                        } else {
+                            throw RuntimeException("Too many redirects")
+                        }
+                    }
+                    else -> {
+                        throw RuntimeException("Unhandled http code: ${connection.responseCode}")
+                    }
+                }
+            }
+            else -> return connection
+        }
+    }
+    data class LocationInfo(val format: String, val packages: Set<String>, val locations: Map<String, String>)
+
+}