kotlin/com.example.android.contentproviderpaging/ImageProvider.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.contentproviderpaging

import android.content.*
import android.database.Cursor
import android.database.MatrixCursor
import android.net.Uri
import android.os.Bundle
import android.os.CancellationSignal
import android.util.Log
import java.io.File
import java.io.IOException

/**
 * ContentProvider that demonstrates how the paging support works introduced in Android O.
 * This class fetches the images from the local storage but the storage could be
 * other locations such as a remote server.
 */
class ImageProvider : ContentProvider() {

    private var mBaseDir: File? = null

    override fun onCreate(): Boolean {
        Log.d(TAG, "onCreate")

        val context = context ?: return false
        mBaseDir = context.filesDir
        writeDummyFilesToStorage(context)

        return true
    }

    override fun query(uri: Uri, strings: Array<String>?, s: String?,
                       strings1: Array<String>?, s1: String?): Cursor? {
        throw UnsupportedOperationException()
    }

    override fun query(uri: Uri, projection: Array<String>?, queryArgs: Bundle,
                       cancellationSignal: CancellationSignal?): Cursor? {
        val match = sUriMatcher.match(uri)
        // We only support a query for multiple images, return null for other form of queries
        // including a query for a single image.
        when (match) {
            IMAGES -> {
            }
            else -> return null
        }
        val result = MatrixCursor(resolveDocumentProjection(projection))

        val files = mBaseDir!!.listFiles()
        val offset = queryArgs.getInt(ContentResolver.QUERY_ARG_OFFSET, 0)
        val limit = queryArgs.getInt(ContentResolver.QUERY_ARG_LIMIT, Integer.MAX_VALUE)
        Log.d(TAG, "queryChildDocuments with Bundle, Uri: " +
                uri + ", offset: " + offset + ", limit: " + limit)
        if (offset < 0) {
            throw IllegalArgumentException("Offset must not be less than 0")
        }
        if (limit < 0) {
            throw IllegalArgumentException("Limit must not be less than 0")
        }

        if (offset >= files.size) {
            return result
        }

        val maxIndex = Math.min(offset + limit, files.size)
        for (i in offset..maxIndex) {
            includeFile(result, files[i])
        }

        val bundle = constructExtras(queryArgs, files)
        result.extras = bundle
        return result
    }

    private fun constructExtras(queryArgs: Bundle, files: Array<File>): Bundle {
        val bundle = Bundle()
        bundle.putInt(ContentResolver.EXTRA_TOTAL_SIZE, files.size)
        var size = 0
        if (queryArgs.containsKey(ContentResolver.QUERY_ARG_OFFSET)) {
            size++
        }
        if (queryArgs.containsKey(ContentResolver.QUERY_ARG_LIMIT)) {
            size++
        }
        if (size > 0) {
            val honoredArgs = arrayOfNulls<String>(size)
            var index = 0
            if (queryArgs.containsKey(ContentResolver.QUERY_ARG_OFFSET)) {
                honoredArgs[index++] = ContentResolver.QUERY_ARG_OFFSET
            }
            if (queryArgs.containsKey(ContentResolver.QUERY_ARG_LIMIT)) {
                honoredArgs[index++] = ContentResolver.QUERY_ARG_LIMIT
            }
            bundle.putStringArray(ContentResolver.EXTRA_HONORED_ARGS, honoredArgs)
        }
        return bundle
    }

    override fun getType(uri: Uri): String? {
        val match = sUriMatcher.match(uri)
        when (match) {
            IMAGES -> return "vnd.android.cursor.dir/images"
            IMAGE_ID -> return "vnd.android.cursor.item/images"
            else -> throw IllegalArgumentException(String.format("Unknown URI: %s", uri))
        }
    }

    override fun insert(uri: Uri, contentValues: ContentValues?): Uri? {
        throw UnsupportedOperationException()
    }

    override fun delete(uri: Uri, s: String?, strings: Array<String>?): Int {
        throw UnsupportedOperationException()
    }

    override fun update(uri: Uri, contentValues: ContentValues?, s: String?,
                        strings: Array<String>?): Int {
        throw UnsupportedOperationException()
    }

    /**
     * Add a representation of a file to a cursor.

     * @param result the cursor to modify
     * *
     * @param file   the File object representing the desired file (may be null if given docID)
     */
    private fun includeFile(result: MatrixCursor, file: File) {
        val row = result.newRow()
        row.add(ImageContract.Columns.DISPLAY_NAME, file.name)
        row.add(ImageContract.Columns.SIZE, file.length())
        row.add(ImageContract.Columns.ABSOLUTE_PATH, file.absolutePath)
    }

    /**
     * Preload sample files packaged in the apk into the internal storage directory.  This is a
     * dummy function specific to this demo.  The MyCloud mock cloud service doesn't actually
     * have a backend, so it simulates by reading content from the device's internal storage.
     */
    private fun writeDummyFilesToStorage(context: Context) {
        if (mBaseDir!!.list().isNotEmpty()) {
            return
        }

        val imageResIds = getResourceIdArray(context, R.array.image_res_ids)
        for (i in 0..REPEAT_COUNT_WRITE_FILES - 1) {
            for (resId in imageResIds) {
                writeFileToInternalStorage(context, resId, "-$i.jpeg")
            }
        }
    }

    /**
     * Write a file to internal storage.  Used to set up our dummy "cloud server".

     * @param context   the Context
     * *
     * @param resId     the resource ID of the file to write to internal storage
     * *
     * @param extension the file extension (ex. .png, .mp3)
     */
    private fun writeFileToInternalStorage(context: Context, resId: Int, extension: String) {
        val ins = context.resources.openRawResource(resId)
        val buffer = ByteArray(1024)
        try {
            val filename = context.resources.getResourceEntryName(resId) + extension
            val fos = context.openFileOutput(filename, Context.MODE_PRIVATE)
            while (true) {
                val size = ins.read(buffer, 0, 1024)
                if (size < 0) break
                fos.write(buffer, 0, size)
            }
            ins.close()
            fos.write(buffer)
            fos.close()
        } catch (e: IOException) {
            throw RuntimeException(e)
        }

    }

    private fun getResourceIdArray(context: Context, arrayResId: Int): IntArray {
        val ar = context.resources.obtainTypedArray(arrayResId)
        val len = ar.length()
        val resIds = IntArray(len)
        for (i in 0..len - 1) {
            resIds[i] = ar.getResourceId(i, 0)
        }
        ar.recycle()
        return resIds
    }

    companion object {

        private val TAG = "ImageDocumentsProvider"

        private val IMAGES = 1

        private val IMAGE_ID = 2

        private val sUriMatcher = UriMatcher(UriMatcher.NO_MATCH)

        init {
            sUriMatcher.addURI(ImageContract.AUTHORITY, "images", IMAGES)
            sUriMatcher.addURI(ImageContract.AUTHORITY, "images/#", IMAGE_ID)
        }

        // Indicated how many same images are going to be written as dummy images
        private val REPEAT_COUNT_WRITE_FILES = 10

        private fun resolveDocumentProjection(projection: Array<String>?): Array<String> {
            return projection ?: ImageContract.PROJECTION_ALL
        }
    }
}