chrome.runtime.onMessage.addListener(
    function (request, sender, sendResponse) {
        // console.log(request);
        switch (request.from) {
            case "DataExtracter:Extract":
                let data = extractTabData(request.itemsSelector, request.fieldSelectors);
                if (sendResponse) sendResponse(data);
                break;
            case "DataExtracter:GotoUrl":
                window.location.replace(request.url);
                if (sendResponse) sendResponse(request.url);
                break;
            case "DataExtracter:ReportIn":
                if (sendResponse) sendResponse(request.from);
                break;
            case "DataExtracter:QueryUrl":
                if (sendResponse) sendResponse(window.location.href);
                break;
            default:
                break;
        }
    }
);

function extractTabData(itemsSelector, fieldSelectors) {
    return $(itemsSelector).toArray().map(
        item => fieldSelectors.map(
            selector => {
                let [cls, attr] = selector.split('@').slice(0, 2);
                return $(item).find(cls).toArray().map(find => attr ? find[attr] : find.textContent.trim()).join('\n')
            }
        )
    );
}

function extract(...args) {
    let sig = `
# DataExtracter Help
----------------------------

## Signitures:
----------------------------

function extract(itemsSelector:string, fieldSelectors:string[])
function extract(itemsSelector:string, fieldSelectors:string[], url:string, from:number, to:number, interval:number)
function extract(itemsSelector:string, fieldSelectors:string, url:string, pages:number[])
function extract(itemsSelector:string, fieldSelectors:string[], urls:string[])

## Examples:
----------------------------

### Extract current page
extract(".list-item", ["a.title", "p.content"])

### Extract multiple pages (1-10, interval 1)
extract(".list-item", ["a.title", "p.content"],"http://sample.com/?pn=\${page}", 1, 10, 1)

### Extract multiple urls (list)
extract(".list-item", ["a.title", "p.content"],["http://sample.com/abc","http://sample.com/xyz"])

### Extract specified pages (1,3,5)
extract(".list-item", ["a.title", "p.content"], "http://sample.com/?pn=\${page}", [1, 3, 5])

## Advanced Examples:
----------------------------

### Extract link text and target (use 'selector@attribute')
extract('.list-item', ['a.title', 'a.title@href'])
`.trim();
    if (!testArgs(...args)) {
        console.log(sig);
        return;
    }
    if (args.length == 2) {
        let data = extractTabData(args[0], args[1]);
        data.unshift(args[1]);
        saveFileAsk(data);
        return;
    }
    let message = {
        from: "DataExtracter:Extract",
        args: args
    }
    chrome.runtime.sendMessage(message, r => {
        if (r) {
            console.log(r);
            alert(r);
        }
    });
}

function testArgs(...args) {
    if (args.length < 2) return false;
    if (args.length == 2)
        return (args[0] && args[1] && (typeof args[0] == "string") && (args[1] instanceof Array))
    let urls = [];
    if (args.length > 2) return (typeof args[2] == "string") && (
        (args[3] instanceof Array) ||
        (!isNaN(args[3]) && !isNaN(args[4]) && !isNaN(args[5]))
    )
}