Local manga in zip/cbz/folder format (#648)

* add local source

* small fixes

* change Chapter to SChapter and and Manga to SManga in ChapterRecognition.
Use ChapterRecognition.parseChapterNumber() to recognize chapter numbers.

* use thread poll

* update isImage()

* add isImage() function to DiskUtil

* improve cover handling

* Support external SD cards

* use R.string.app_name as root folder name

app/src/main/java/eu/kanade/tachiyomi/util/DiskUtil.kt

@@ -1,11 +1,53 @@
 package eu.kanade.tachiyomi.util
 
+import android.content.Context
+import android.os.Environment
+import android.support.v4.content.ContextCompat
+import android.support.v4.os.EnvironmentCompat
 import java.io.File
+import java.io.InputStream
+import java.net.URLConnection
 import java.security.MessageDigest
 import java.security.NoSuchAlgorithmException
 
 object DiskUtil {
 
+    fun isImage(name: String, openStream: (() -> InputStream)? = null): Boolean {
+        val contentType = URLConnection.guessContentTypeFromName(name)
+        if (contentType != null)
+            return contentType.startsWith("image/")
+
+        if (openStream != null) try {
+            openStream.invoke().buffered().use {
+                var bytes = ByteArray(11)
+                it.mark(bytes.size)
+                var length = it.read(bytes, 0, bytes.size)
+                it.reset()
+                if (length == -1)
+                    return false
+                if (bytes[0] == 'G'.toByte() && bytes[1] == 'I'.toByte() && bytes[2] == 'F'.toByte() && bytes[3] == '8'.toByte()) {
+                    return true // image/gif
+                } else if (bytes[0] == 0x89.toByte() && bytes[1] == 0x50.toByte() && bytes[2] == 0x4E.toByte()
+                        && bytes[3] == 0x47.toByte() && bytes[4] == 0x0D.toByte() && bytes[5] == 0x0A.toByte()
+                        && bytes[6] == 0x1A.toByte() && bytes[7] == 0x0A.toByte()) {
+                    return true // image/png
+                } else if (bytes[0] == 0xFF.toByte() && bytes[1] == 0xD8.toByte() && bytes[2] == 0xFF.toByte()) {
+                    if (bytes[3] == 0xE0.toByte() || bytes[3] == 0xE1.toByte() && bytes[6] == 'E'.toByte()
+                            && bytes[7] == 'x'.toByte() && bytes[8] == 'i'.toByte()
+                            && bytes[9] == 'f'.toByte() && bytes[10] == 0.toByte()) {
+                        return true // image/jpeg
+                    } else if (bytes[3] == 0xEE.toByte()) {
+                        return true // image/jpg
+                    }
+                } else if (bytes[0] == 'W'.toByte() && bytes[1] == 'E'.toByte() && bytes[2] == 'B'.toByte() && bytes[3] == 'P'.toByte()) {
+                    return true // image/webp
+                }
+            }
+        } catch(e: Exception) {
+        }
+        return false
+    }
+
     fun hashKeyForDisk(key: String): String {
         return try {
             val bytes = MessageDigest.getInstance("MD5").digest(key.toByteArray())
@@ -31,9 +73,26 @@ object DiskUtil {
         return size
     }
 
+    /**
+     * Returns the root folders of all the available external storages.
+     */
+    fun getExternalStorages(context: Context): List<File> {
+        return ContextCompat.getExternalFilesDirs(context, null)
+                .filterNotNull()
+                .mapNotNull {
+                    val file = File(it.absolutePath.substringBefore("/Android/"))
+                    val state = EnvironmentCompat.getStorageState(file)
+                    if (state == Environment.MEDIA_MOUNTED || state == Environment.MEDIA_MOUNTED_READ_ONLY) {
+                        file
+                    } else {
+                        null
+                    }
+                }
+    }
+
     /**
      * Mutate the given filename to make it valid for a FAT filesystem,
-     * replacing any invalid characters with "_". This method doesn't allow private files (starting
+     * replacing any invalid characters with "_". This method doesn't allow hidden files (starting
      * with a dot), but you can manually add it later.
      */
     fun buildValidFilename(origName: String): String {