Convert newpipe/util/image/ImageStrategy to kotlin

Author: Yevhen Babiichuk (DustDFG)

app/src/main/java/org/schabi/newpipe/util/image/ImageStrategy.java

@@ -0,0 +1,182 @@
+package org.schabi.newpipe.util.image
+
+import org.schabi.newpipe.extractor.Image
+import org.schabi.newpipe.extractor.Image.ResolutionLevel
+import kotlin.math.abs
+
+object ImageStrategy {
+    // when preferredImageQuality is LOW or MEDIUM, images are sorted by how close their preferred
+    // image quality is to these values (H stands for "Height")
+    private const val BEST_LOW_H = 75
+    private const val BEST_MEDIUM_H = 250
+
+    private var preferredImageQuality = PreferredImageQuality.MEDIUM
+
+    @JvmStatic
+    fun setPreferredImageQuality(preferredImageQuality: PreferredImageQuality) {
+        ImageStrategy.preferredImageQuality = preferredImageQuality
+    }
+
+    @JvmStatic
+    fun shouldLoadImages(): Boolean {
+        return preferredImageQuality != PreferredImageQuality.NONE
+    }
+
+    @JvmStatic
+    fun estimatePixelCount(image: Image, widthOverHeight: Double): Double {
+        if (image.height == Image.HEIGHT_UNKNOWN) {
+            if (image.width == Image.WIDTH_UNKNOWN) {
+                // images whose size is completely unknown will be in their own subgroups, so
+                // any one of them will do, hence returning the same value for all of them
+                return 0.0
+            } else {
+                return image.width * image.width / widthOverHeight
+            }
+        } else if (image.width == Image.WIDTH_UNKNOWN) {
+            return image.height * image.height * widthOverHeight
+        } else {
+            return (image.height * image.width).toDouble()
+        }
+    }
+
+    /**
+     * [choosePreferredImage] contains the description for this function's logic.
+     *
+     * @param images the images from which to choose
+     * @param nonNoneQuality the preferred quality (must NOT be [PreferredImageQuality.NONE])
+     * @return the chosen preferred image, or `null` if the list is empty
+     * @see [choosePreferredImage]
+     */
+    @JvmStatic
+    fun choosePreferredImage(images: List<Image>, nonNoneQuality: PreferredImageQuality): String? {
+        // this will be used to estimate the pixel count for images where only one of height or
+        // width are known
+        val widthOverHeight = images
+            .filter { image ->
+                image.height != Image.HEIGHT_UNKNOWN && image.width != Image.WIDTH_UNKNOWN
+            }
+            .map { image -> (image.width.toDouble()) / image.height }
+            .elementAtOrNull(0) ?: 1.0
+
+        val preferredLevel = nonNoneQuality.toResolutionLevel()
+        // TODO: rewrite using kotlin collections API `groupBy` will be handy
+        val initialComparator =
+            Comparator // the first step splits the images into groups of resolution levels
+                .comparingInt { i: Image ->
+                    if (i.estimatedResolutionLevel == ResolutionLevel.UNKNOWN) {
+                        return@comparingInt 3 // avoid unknowns as much as possible
+                    } else if (i.estimatedResolutionLevel == preferredLevel) {
+                        return@comparingInt 0 // prefer a matching resolution level
+                    } else if (i.estimatedResolutionLevel == ResolutionLevel.MEDIUM) {
+                        return@comparingInt 1 // the preferredLevel is only 1 "step" away (either HIGH or LOW)
+                    } else {
+                        return@comparingInt 2 // the preferredLevel is the furthest away possible (2 "steps")
+                    }
+                }
+                // then each level's group is further split into two subgroups, one with known image
+                // size (which is also the preferred subgroup) and the other without
+                .thenComparing { image -> image.height == Image.HEIGHT_UNKNOWN && image.width == Image.WIDTH_UNKNOWN }
+
+        // The third step chooses, within each subgroup with known image size, the best image based
+        // on how close its size is to BEST_LOW_H or BEST_MEDIUM_H (with proper units). Subgroups
+        // without known image size will be left untouched since estimatePixelCount always returns
+        // the same number for those.
+        val finalComparator = when (nonNoneQuality) {
+            PreferredImageQuality.NONE -> initialComparator
+            PreferredImageQuality.LOW -> initialComparator.thenComparingDouble { image ->
+                val pixelCount = estimatePixelCount(image, widthOverHeight)
+                abs(pixelCount - BEST_LOW_H * BEST_LOW_H * widthOverHeight)
+            }
+
+            PreferredImageQuality.MEDIUM -> initialComparator.thenComparingDouble { image ->
+                val pixelCount = estimatePixelCount(image, widthOverHeight)
+                abs(pixelCount - BEST_MEDIUM_H * BEST_MEDIUM_H * widthOverHeight)
+            }
+
+            PreferredImageQuality.HIGH -> initialComparator.thenComparingDouble { image ->
+                // this is reversed with a - so that the highest resolution is chosen
+                -estimatePixelCount(image, widthOverHeight)
+            }
+        }
+
+        return images.stream() // using "min" basically means "take the first group, then take the first subgroup,
+            // then choose the best image, while ignoring all other groups and subgroups"
+            .min(finalComparator)
+            .map(Image::getUrl)
+            .orElse(null)
+    }
+
+    /**
+     * Chooses an image amongst the provided list based on the user preference previously set with
+     * [setPreferredImageQuality]. `null` will be returned in
+     * case the list is empty or the user preference is to not show images.
+     * <br>
+     * These properties will be preferred, from most to least important:
+     *
+     * 1. The image's [Image.estimatedResolutionLevel] is not unknown and is close to [preferredImageQuality]
+     * 2. At least one of the image's width or height are known
+     * 3. The highest resolution image is finally chosen if the user's preference is
+     * [PreferredImageQuality.HIGH], otherwise the chosen image is the one that has the height
+     * closest to [BEST_LOW_H] or [BEST_MEDIUM_H]
+     *
+     * <br>
+     * Use [imageListToDbUrl] if the URL is going to be saved to the database, to avoid
+     * saving nothing in case at the moment of saving the user preference is to not show images.
+     *
+     * @param images the images from which to choose
+     * @return the chosen preferred image, or `null` if the list is empty or the user disabled
+     * images
+     * @see [imageListToDbUrl]
+     */
+    @JvmStatic
+    fun choosePreferredImage(images: List<Image>): String? {
+        if (preferredImageQuality == PreferredImageQuality.NONE) {
+            return null // do not load images
+        }
+
+        return choosePreferredImage(images, preferredImageQuality)
+    }
+
+    /**
+     * Like [choosePreferredImage], except that if [preferredImageQuality] is
+     * [PreferredImageQuality.NONE] an image will be chosen anyway (with preferred quality
+     * [PreferredImageQuality.MEDIUM].
+     * <br></br>
+     * To go back to a list of images (obviously with just the one chosen image) from a URL saved in
+     * the database use [dbUrlToImageList].
+     *
+     * @param images the images from which to choose
+     * @return the chosen preferred image, or `null` if the list is empty
+     * @see [choosePreferredImage]
+     * @see [dbUrlToImageList]
+     */
+    @JvmStatic
+    fun imageListToDbUrl(images: List<Image>): String? {
+        val quality = when (preferredImageQuality) {
+            PreferredImageQuality.NONE -> PreferredImageQuality.MEDIUM
+            else -> preferredImageQuality
+        }
+
+        return choosePreferredImage(images, quality)
+    }
+
+    /**
+     * Wraps the URL (coming from the database) in a `List<Image>` so that it is usable
+     * seamlessly in all of the places where the extractor would return a list of images, including
+     * allowing to build info objects based on database objects.
+     * <br></br>
+     * To obtain a url to save to the database from a list of images use [imageListToDbUrl].
+     *
+     * @param url the URL to wrap coming from the database, or `null` to get an empty list
+     * @return a list containing just one [Image] wrapping the provided URL, with unknown
+     * image size fields, or an empty list if the URL is `null`
+     * @see [imageListToDbUrl]
+     */
+    @JvmStatic
+    fun dbUrlToImageList(url: String?): List<Image> {
+        return when (url) {
+            null -> listOf()
+            else -> listOf(Image(url, -1, -1, ResolutionLevel.UNKNOWN))
+        }
+    }
+}