const GOOGLE_DRIVE_HOST = 'drive.google.com';
const GOOGLE_DRIVE_PLAYER_HOST = 'youtube.googleapis.com';
export const GOOGLE_DRIVE_PLAYER_ORIGIN_PATTERN = 'https://youtube.googleapis.com/*';
export const GOOGLE_DRIVE_PLAYER_ACCESS_REQUIRED = 'google_drive_player_access_required';
export const GOOGLE_DRIVE_PLAYER_AMBIGUOUS = 'google_drive_player_ambiguous';

export function isGoogleDriveUrl(value) {
    try {
        return new URL(value).hostname.toLowerCase() === GOOGLE_DRIVE_HOST;
    } catch {
        return false;
    }
}

export function inspectMediaFrame() {
    const videos = Array.from(document.querySelectorAll('video'));
    const drivePlayerIframes = Array.from(document.querySelectorAll('iframe')).filter((frame) => {
        try {
            const url = new URL(frame.src);
            if (url.hostname.toLowerCase() !== 'youtube.googleapis.com') return false;
            const origin = url.searchParams.get('origin') || url.searchParams.get('post_message_origin');
            return origin === 'https://drive.google.com';
        } catch {
            return false;
        }
    });
    let bestVideoScore = 0;

    for (const video of videos) {
        const width = video.videoWidth || video.offsetWidth || 0;
        const height = video.videoHeight || video.offsetHeight || 0;
        const duration = Number.isFinite(video.duration) ? video.duration : 0;
        bestVideoScore = Math.max(bestVideoScore, (width * height) + (duration * 100));
    }

    return {
        href: window.location.href,
        videoCount: videos.length,
        videoScore: bestVideoScore,
        frameArea: Math.max(0, window.innerWidth) * Math.max(0, window.innerHeight),
        drivePlayerIframeCount: drivePlayerIframes.length,
        parentFrameVisible: window.__koalaParentFrameVisibility?.visible ?? null,
        parentFrameArea: window.__koalaParentFrameVisibility?.area ?? null
    };
}

export function installParentFrameVisibilityProbe(token) {
    const handler = (event) => {
        if (event.source !== window.parent
            || event.data?.type !== 'KOALASYNC_FRAME_VISIBILITY'
            || event.data?.token !== token) {
            return;
        }
        window.__koalaParentFrameVisibility = {
            visible: event.data.visible === true,
            area: Number.isFinite(event.data.area) ? event.data.area : 0
        };
        window.removeEventListener('message', handler);
    };
    window.addEventListener('message', handler);
}

export async function dispatchParentFrameVisibilityProbe(token) {
    let count = 0;
    for (const frame of document.querySelectorAll('iframe')) {
        try {
            const url = new URL(frame.src);
            const origin = url.searchParams.get('origin') || url.searchParams.get('post_message_origin');
            if (url.hostname.toLowerCase() !== 'youtube.googleapis.com'
                || origin !== 'https://drive.google.com') {
                continue;
            }
            const rect = frame.getBoundingClientRect();
            const style = window.getComputedStyle(frame);
            const area = Math.max(0, rect.width) * Math.max(0, rect.height);
            const intersectsViewport = rect.bottom > 0
                && rect.right > 0
                && rect.top < window.innerHeight
                && rect.left < window.innerWidth;
            const browserReportsVisible = typeof frame.checkVisibility === 'function'
                ? frame.checkVisibility({ checkOpacity: true, checkVisibilityCSS: true })
                : true;
            const visible = area > 0
                && intersectsViewport
                && browserReportsVisible
                && style.display !== 'none'
                && style.visibility !== 'hidden'
                && Number(style.opacity) !== 0;
            frame.contentWindow?.postMessage({
                type: 'KOALASYNC_FRAME_VISIBILITY',
                token,
                visible,
                area
            }, 'https://youtube.googleapis.com');
            count++;
        } catch {
            // Ignore unrelated or not-yet-initialized frames.
        }
    }
    await new Promise(resolve => setTimeout(resolve, 100));
    return count;
}

function isGoogleDrivePlayerFrameUrl(value) {
    try {
        const url = new URL(value);
        if (url.hostname.toLowerCase() !== GOOGLE_DRIVE_PLAYER_HOST || url.pathname !== '/embed/') {
            return false;
        }
        const origin = url.searchParams.get('origin') || url.searchParams.get('post_message_origin');
        return origin === 'https://drive.google.com';
    } catch {
        return false;
    }
}

function createGoogleDrivePlayerAccessError() {
    const error = new Error('Google Drive player frame access is required');
    error.code = GOOGLE_DRIVE_PLAYER_ACCESS_REQUIRED;
    error.originPattern = GOOGLE_DRIVE_PLAYER_ORIGIN_PATTERN;
    return error;
}

function createGoogleDrivePlayerAmbiguousError() {
    const error = new Error('Google Drive player frame could not be identified safely');
    error.code = GOOGLE_DRIVE_PLAYER_AMBIGUOUS;
    return error;
}

export function selectGoogleDrivePlayerFrame(injectionResults) {
    let candidates = (Array.isArray(injectionResults) ? injectionResults : [])
        .filter(entry => Number.isInteger(entry?.frameId) && entry?.result)
        .filter(entry => isGoogleDrivePlayerFrameUrl(entry.result.href));

    if (candidates.length > 1) {
        const confirmedVisible = candidates.filter(entry => entry.result.parentFrameVisible === true);
        if (confirmedVisible.length > 0) {
            candidates = confirmedVisible;
        } else {
            const notConfirmedHidden = candidates.filter(entry =>
                entry.result.parentFrameVisible !== false
            );
            if (notConfirmedHidden.length !== 1) return null;
            candidates = notConfirmedHidden;
        }
    }

    candidates.sort((left, right) => {
            const visibilityRank = result => result.parentFrameVisible === true
                ? 2
                : result.parentFrameVisible === false
                    ? 0
                    : 1;
            const leftVisible = visibilityRank(left.result);
            const rightVisible = visibilityRank(right.result);
            if (leftVisible !== rightVisible) return rightVisible - leftVisible;
            const leftParentArea = Number.isFinite(left.result.parentFrameArea)
                ? left.result.parentFrameArea
                : left.result.frameArea;
            const rightParentArea = Number.isFinite(right.result.parentFrameArea)
                ? right.result.parentFrameArea
                : right.result.frameArea;
            if (leftParentArea !== rightParentArea) return rightParentArea - leftParentArea;
            const leftHasVideo = left.result.videoCount > 0 ? 1 : 0;
            const rightHasVideo = right.result.videoCount > 0 ? 1 : 0;
            if (leftHasVideo !== rightHasVideo) return rightHasVideo - leftHasVideo;
            if (left.result.videoScore !== right.result.videoScore) {
                return right.result.videoScore - left.result.videoScore;
            }
            return right.result.frameArea - left.result.frameArea;
    });

    return candidates[0] || null;
}

export async function resolveMediaScriptTarget(chromeApi, tabId, tabUrl, {
    attempts = 8,
    retryDelayMs = 200
} = {}) {
    const topFrameTarget = { tabId };
    if (!isGoogleDriveUrl(tabUrl)) return topFrameTarget;

    let fallbackFrame = null;
    let drivePlayerIframeDetected = false;
    let ambiguousPlayerFramesDetected = false;
    for (let attempt = 0; attempt < attempts; attempt++) {
        let results;
        try {
            results = await chromeApi.scripting.executeScript({
                target: { tabId, allFrames: true },
                func: inspectMediaFrame
            });
        } catch {
            let topFrameResult = null;
            try {
                const topResults = await chromeApi.scripting.executeScript({
                    target: { tabId },
                    func: inspectMediaFrame
                });
                topFrameResult = Array.isArray(topResults) ? topResults[0]?.result : null;
            } catch {
                // The generic injection path below remains the final source of truth.
            }
            if (topFrameResult?.drivePlayerIframeCount > 0) {
                throw createGoogleDrivePlayerAccessError();
            }
            return topFrameTarget;
        }

        const topFrame = results.find(entry => entry?.frameId === 0);
        if (topFrame?.result?.drivePlayerIframeCount > 0) {
            drivePlayerIframeDetected = true;
        }
        const playerFrameCount = results.filter(entry =>
            isGoogleDrivePlayerFrameUrl(entry?.result?.href)
        ).length;
        if (playerFrameCount > 1) {
            const token = `${tabId}:${attempt}:${Date.now()}:${Math.random()}`;
            try {
                await chromeApi.scripting.executeScript({
                    target: { tabId, allFrames: true },
                    func: installParentFrameVisibilityProbe,
                    args: [token]
                });
                await chromeApi.scripting.executeScript({
                    target: { tabId },
                    func: dispatchParentFrameVisibilityProbe,
                    args: [token]
                });
                results = await chromeApi.scripting.executeScript({
                    target: { tabId, allFrames: true },
                    func: inspectMediaFrame
                });
            } catch {
                // Ambiguous frames are retried below; never guess a stale player.
            }
        }
        const selectedFrame = selectGoogleDrivePlayerFrame(results);
        if (!selectedFrame && playerFrameCount > 1) {
            ambiguousPlayerFramesDetected = true;
        }
        if (selectedFrame?.result?.videoCount > 0) {
            return { tabId, frameIds: [selectedFrame.frameId] };
        }
        if (selectedFrame) fallbackFrame = selectedFrame;

        if (attempt < attempts - 1) {
            await new Promise(resolve => setTimeout(resolve, retryDelayMs));
        }
    }

    if (!fallbackFrame && ambiguousPlayerFramesDetected) {
        throw createGoogleDrivePlayerAmbiguousError();
    }
    if (!fallbackFrame && drivePlayerIframeDetected) {
        throw createGoogleDrivePlayerAccessError();
    }

    return fallbackFrame
        ? { tabId, frameIds: [fallbackFrame.frameId] }
        : topFrameTarget;
}