package io.ktor.http.content

import io.ktor.application.*
import io.ktor.http.*
import io.ktor.util.*
import java.io.*
import java.nio.file.*

/**
 * @param path is a relative path to the resource
 * @param resourcePackage is a base package the path to be appended to
 * @param mimeResolve is a function that resolves content type by file extension, optional
 *
 * @return [LocalFileContent] or [JarFileContent] or `null`
 */
fun ApplicationCall.resolveResource(
    path: String,
    resourcePackage: String? = null,
    classLoader: ClassLoader = application.environment.classLoader,
    mimeResolve: (String) -> ContentType = { ContentType.defaultForFileExtension(it) }
): OutgoingContent? {
    val packagePath = (resourcePackage?.replace('.', '/') ?: "").appendPathPart(path)
    val normalizedPath = Paths.get(packagePath).normalizeAndRelativize()
    val normalizedResource = normalizedPath.toString().replace(File.separatorChar, '/')

    // note: we don't need to check for .. in the normalizedPath because all .. get replaced with //

    for (url in classLoader.getResources(normalizedResource).asSequence()) {
        when (url.protocol) {
            "file" -> {
                val file = File(url.path.decodeURLPart())
                return if (file.isFile) LocalFileContent(file, mimeResolve(file.extension)) else null
            }
            "jar" -> {
                return if (packagePath.endsWith("/")) {
                    null
                } else {
                    val zipFile = findContainingJarFile(url.toString())
                    JarFileContent(zipFile, normalizedResource, mimeResolve(url.path.extension()))
                }
            }
            "jrt" -> {
                return URIFileContent(url, mimeResolve(url.path.extension()))
            }
            else -> {
            }
        }
    }

    return null
}

internal fun findContainingJarFile(url: String): File {
    if (url.startsWith("jar:file:")) {
        val jarPathSeparator = url.indexOf("!", startIndex = 9)
        require(jarPathSeparator != -1) { "Jar path requires !/ separator but it is: $url" }

        return File(url.substring(9, jarPathSeparator).decodeURLPart())
    }

    throw IllegalArgumentException("Only local jars are supported (jar:file:)")
}

private fun String.extension(): String {
    val indexOfName = lastIndexOf('/').takeIf { it != -1 } ?: lastIndexOf('\\').takeIf { it != -1 } ?: 0
    val indexOfDot = indexOf('.', indexOfName)
    return if (indexOfDot >= 0) substring(indexOfDot) else ""
}

private fun String.appendPathPart(part: String): String {
    val count = (if (isNotEmpty() && this[length - 1] == '/') 1 else 0) +
        (if (part.isNotEmpty() && part[0] == '/') 1 else 0)

    return when (count) {
        2 -> this + part.removePrefix("/")
        1 -> this + part
        else -> StringBuilder(length + part.length + 1).apply { append(this@appendPathPart); append('/'); append(part) }.toString()
    }
}
