chrome.runtime.onMessage.addListener(
    function (request, sender, sendResponse) {
        if (!request.from) return;
        let [ext, act] = request.from.split(":");
        if (ext.toLowerCase() !== 'dataextracter') return;
        // console.log(request);
        switch (act.toLowerCase()) {
            case "extract":
                let data = extractTabData(request.itemsSelector, request.fieldSelectors);
                if (sendResponse) sendResponse(data);
                break;
            case "gotourl":
                window.location.replace(request.url);
                if (sendResponse) sendResponse(request.url);
                break;
            case "reportin":
                if (sendResponse) sendResponse(request.from);
                break;
            case "queryurl":
                if (sendResponse) sendResponse(window.location.href);
                break;
            default:
                break;
        }
    }
);

const 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'])

### Collect links from page(s) & Extract data of each link (only available in console of extension background page)

extract('body',["a.title", "p.content"], await getData('.list-item', ['.item a@href'],["http://sample.com/abc"]))
`.trim();

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) {
    if (!testArgs(...args)) {
        console.log(sig);
        return;
    }

    let message = {
        from: "DataExtracter:Extract",
        args: args
    }
    chrome.runtime.sendMessage(message, r => {
        if (r) {
            console.log(r);
            alert(r);
        }
    });
}

function testArgs(...args) {
    switch (args.length) {
        case 0, 1:
            return false;
        case 2:
            return args[0] && args[1] &&
                (typeof args[0] == "string") &&
                (args[1] instanceof Array) &&
                testArrayVals(args[1], v => typeof v == "string");
        case 3:
            return args[0] && args[1] &&
                typeof args[0] == "string" &&
                args[1] instanceof Array &&
                testArrayVals(args[1], v => typeof v == "string") &&
                args[2] instanceof Array &&
                testArrayVals(args[2], v => typeof v == "string");
        case 4:
            return args[0] && args[1] &&
                typeof args[0] == "string" &&
                args[1] instanceof Array &&
                testArrayVals(args[1], v => typeof v == "string") &&
                typeof args[2] == "string" &&
                args[3] instanceof Array &&
                testArrayVals(args[3], v => typeof v == "number");
        case 5:
            return args[0] && args[1] &&
                typeof args[0] == "string" &&
                args[1] instanceof Array &&
                testArrayVals(args[1], v => typeof v == "string") &&
                typeof args[2] == "string" &&
                !isNaN(args[3]) && !isNaN(args[4]) && !isNaN(args[5]);
        default:
            return false;
    }

    function testArrayVals(arr, tester) {
        return arr.reduce((p, c) => p && tester(c), true);
    }
}