/**
 * 全站渠道首次归因。
 * 与落地页约定一致，按 dc、ch、pc 顺序识别，并同步到 localStorage 与 cookie。
 */
(function (global) {
    "use strict";

    var STORAGE_KEY = "channel";
    var QUERY_KEYS = ["dc", "ch", "pc"];

    function clean(value) {
        return String(value == null ? "" : value).trim();
    }

    function readStorage() {
        try {
            return clean(global.localStorage.getItem(STORAGE_KEY));
        } catch (e) {
            return "";
        }
    }

    function writeStorage(channel) {
        try {
            global.localStorage.setItem(STORAGE_KEY, channel);
        } catch (e) {}
    }

    function readCookie() {
        try {
            var match = document.cookie.match(/(?:^|;\s*)channel=([^;]*)/);
            return match ? clean(decodeURIComponent(match[1])) : "";
        } catch (e) {
            return "";
        }
    }

    function writeCookie(channel) {
        try {
            var secure = global.location && global.location.protocol === "https:" ? "; Secure" : "";
            document.cookie =
                STORAGE_KEY +
                "=" +
                encodeURIComponent(channel) +
                "; Path=/; Max-Age=31536000; SameSite=Lax" +
                secure;
        } catch (e) {}
    }

    function readQuery() {
        try {
            var params = new URLSearchParams(global.location.search || "");
            for (var i = 0; i < QUERY_KEYS.length; i += 1) {
                var channel = clean(params.get(QUERY_KEYS[i]));
                if (channel) return channel;
            }
        } catch (e) {}
        return "";
    }

    function syncTracker(channel) {
        try {
            if (global.tracker && typeof global.tracker.setChannel === "function") {
                global.tracker.setChannel(channel);
            }
        } catch (e) {}
    }

    function capture() {
        // localStorage 与服务端 cookie 都属于已归因结果，必须先于当前 URL。
        var channel = readStorage() || readCookie() || readQuery();
        if (!channel) return "";

        writeStorage(channel);
        writeCookie(channel);
        global.__CHANNEL_CODE__ = channel;
        syncTracker(channel);
        return channel;
    }

    global.ChannelAttribution = {
        get: capture,
        capture: capture,
    };

    var channel = capture();
    try {
        document.dispatchEvent(
            new CustomEvent("channel:ready", { detail: { channel: channel } })
        );
    } catch (e) {}
})(window);