pragma ComponentBehavior: Bound

import QtQuick
import qs.Common
import qs.Services
import "../../Common/WidgetPlacement.js" as Placement
import "../../Common/LockScrollAtlas.js" as Atlas

Item {
    id: root

    required property var screen

    readonly property string screenName: screen.name
    readonly property string source: {
        const path = SessionData.getMonitorWallpaper(screenName);
        return path && !path.startsWith("#") ? "file://" + path.split('/').map(s => encodeURIComponent(s)).join('/') : "";
    }
    readonly property string backgroundKey: LockPlacementService.backgroundKey(screenName, screen.width, screen.height)
    readonly property bool needed: !IdleService.isShellLocked && LockPlacementService.usesScrollAtlas(screenName) && LockPlacementService.neededFor(screen) && !LockPlacementService.hasSample(screenName, backgroundKey)
    readonly property real sampleScale: LockPlacementService.sampleSize / Math.max(1, screen.width, screen.height)
    readonly property int sampleWidth: Math.max(1, Math.round(screen.width * sampleScale))
    readonly property int sampleHeight: Math.max(1, Math.round(screen.height * sampleScale))
    readonly property string atlasKey: JSON.stringify([source, screen.width, screen.height, Theme.lockScreenScrimAlpha, Theme.screenOffColor.toString(), SettingsData.effectiveWallpaperBackgroundColor.toString()])
    property var atlas: null
    readonly property bool busy: builder.active

    onNeededChanged: sample()
    onBackgroundKeyChanged: sample()
    Component.onCompleted: LockPlacementService.setScrollSampler(screenName, true)
    Component.onDestruction: LockPlacementService.setScrollSampler(screenName, false)

    function sample() {
        if (!needed || busy)
            return;
        if (atlas?.key !== atlasKey) {
            builder.active = true;
            return;
        }
        if (atlas.failed)
            return;
        const scroll = SessionData.getMonitorScrollPosition(screenName);
        const view = Atlas.scrollWindow(atlas.imageWidth, atlas.imageHeight, screen.width, screen.height, scroll.scrollX, scroll.scrollY);
        LockPlacementService.storeSample(screenName, backgroundKey, Atlas.crop(atlas.luminances, atlas.width, atlas.height, view, sampleWidth, sampleHeight), sampleWidth, sampleHeight);
    }

    function finish(result) {
        atlas = result;
        Qt.callLater(() => {
            builder.active = false;
            sample();
        });
    }

    Loader {
        id: builder
        active: false

        sourceComponent: Item {
            property string key
            property string url

            Component.onCompleted: {
                key = root.atlasKey;
                url = root.source;
            }

            Image {
                id: probe
                visible: false
                asynchronous: true
                cache: false
                source: parent.url
                sourceSize: Qt.size(LockPlacementService.sampleSize * 8, LockPlacementService.sampleSize * 8)

                onStatusChanged: {
                    if (status === Image.Error) {
                        root.finish({
                            key: parent.key,
                            failed: true
                        });
                        return;
                    }
                    if (status !== Image.Ready)
                        return;
                    const size = Atlas.atlasSize(implicitWidth, implicitHeight, root.screen.width, root.screen.height, root.sampleWidth, root.sampleHeight);
                    canvas.width = size.width;
                    canvas.height = size.height;
                    canvas.load();
                }
            }

            Canvas {
                id: canvas
                readonly property string key: parent.key
                readonly property string imageUrl: parent.url

                opacity: 0

                function load() {
                    if (available && width > 0)
                        loadImage(imageUrl, Qt.size(width, height));
                }

                onAvailableChanged: load()
                onImageLoaded: requestPaint()
                onPaint: {
                    if (isImageError(imageUrl)) {
                        root.finish({
                            key,
                            failed: true
                        });
                        return;
                    }
                    if (!isImageLoaded(imageUrl))
                        return;
                    const context = getContext("2d");
                    context.fillStyle = SettingsData.effectiveWallpaperBackgroundColor;
                    context.fillRect(0, 0, width, height);
                    context.drawImage(imageUrl, 0, 0, width, height);
                    const pixels = context.getImageData(0, 0, width, height).data;
                    unloadImage(imageUrl);
                    const scrim = Theme.screenOffColor;
                    const alpha = Theme.lockScreenScrimAlpha;
                    const blend = (value, over) => value / 255 * (1 - alpha) + over * alpha;
                    const luminances = new Array(width * height);
                    for (let i = 0; i < luminances.length; i++)
                        luminances[i] = Placement.luminance(blend(pixels[i * 4], scrim.r), blend(pixels[i * 4 + 1], scrim.g), blend(pixels[i * 4 + 2], scrim.b));
                    root.finish({
                        key,
                        imageWidth: probe.implicitWidth,
                        imageHeight: probe.implicitHeight,
                        width,
                        height,
                        luminances
                    });
                }
            }
        }
    }
}