/*
Copyright 2021 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import posthog, { PostHog } from 'posthog-js';
import PlatformPeg from './PlatformPeg';
import SdkConfig from './SdkConfig';
import SettingsStore from './settings/SettingsStore';
import { MatrixClientPeg } from "./MatrixClientPeg";
import { MatrixClient } from "../../matrix-js-sdk";

/* Posthog analytics tracking.
 *
 * Anonymity behaviour is as follows:
 *
 * - If Posthog isn't configured in `config.json`, events are not sent.
 * - If [Do Not Track](https://developer.mozilla.org/en-US/docs/Web/API/Navigator/doNotTrack) is
 *   enabled, events are not sent (this detection is built into posthog and turned on via the
 *   `respect_dnt` flag being passed to `posthog.init`).
 * - If the `feature_pseudonymous_analytics_opt_in` labs flag is `true`, track pseudonomously, i.e.
 *   hash all matrix identifiers in tracking events (user IDs, room IDs etc) using SHA-256.
 * - Otherwise, if the existing `analyticsOptIn` flag is `true`, track anonymously, i.e.
 *   redact all matrix identifiers in tracking events.
 * - If both flags are false or not set, events are not sent.
 */

interface IEvent {
    // The event name that will be used by PostHog. Event names should use snake_case.
    eventName: string;

    // The properties of the event that will be stored in PostHog. This is just a placeholder,
    // extending interfaces must override this with a concrete definition to do type validation.
    properties: {};
}

export enum Anonymity {
    Disabled,
    Anonymous,
    Pseudonymous
}

// If an event extends IPseudonymousEvent, the event contains pseudonymous data
// that won't be sent unless the user has explicitly consented to pseudonymous tracking.
// For example, it might contain hashed user IDs or room IDs.
// Such events will be automatically dropped if PosthogAnalytics.anonymity isn't set to Pseudonymous.
export interface IPseudonymousEvent extends IEvent {}

// If an event extends IAnonymousEvent, the event strictly contains *only* anonymous data;
// i.e. no identifiers that can be associated with the user.
export interface IAnonymousEvent extends IEvent {}

export interface IRoomEvent extends IPseudonymousEvent {
    hashedRoomId: string;
}

interface IPageView extends IAnonymousEvent {
    eventName: "$pageview";
    properties: {
        durationMs?: number;
        screen?: string;
    };
}

const hashHex = async (input: string): Promise<string> => {
    const buf = new TextEncoder().encode(input);
    const digestBuf = await window.crypto.subtle.digest("sha-256", buf);
    return [...new Uint8Array(digestBuf)].map((b: number) => b.toString(16).padStart(2, "0")).join("");
};

const whitelistedScreens = new Set([
    "register", "login", "forgot_password", "soft_logout", "new", "settings", "welcome", "home", "start", "directory",
    "start_sso", "start_cas", "groups", "complete_security", "post_registration", "room", "user", "group",
]);

export async function getRedactedCurrentLocation(
    origin: string,
    hash: string,
    pathname: string,
    anonymity: Anonymity,
): Promise<string> {
    // Redact PII from the current location.
    // If anonymous is true, redact entirely, if false, substitute it with a hash.
    // For known screens, assumes a URL structure of /<screen name>/might/be/pii
    if (origin.startsWith('file://')) {
        pathname = "/<redacted_file_scheme_url>/";
    }

    let hashStr;
    if (hash == "") {
        hashStr = "";
    } else {
        let [beforeFirstSlash, screen, ...parts] = hash.split("/");

        if (!whitelistedScreens.has(screen)) {
            screen = "<redacted_screen_name>";
        }

        for (let i = 0; i < parts.length; i++) {
            parts[i] = anonymity === Anonymity.Anonymous ? `<redacted>` : await hashHex(parts[i]);
        }

        hashStr = `${beforeFirstSlash}/${screen}/${parts.join("/")}`;
    }
    return origin + pathname + hashStr;
}

interface PlatformProperties {
    appVersion: string;
    appPlatform: string;
}

export class PosthogAnalytics {
    /* Wrapper for Posthog analytics.
     * 3 modes of anonymity are supported, governed by this.anonymity
     * - Anonymity.Disabled means *no data* is passed to posthog
     * - Anonymity.Anonymous means all identifers will be redacted before being passed to posthog
     * - Anonymity.Pseudonymous means all identifiers will be hashed via SHA-256 before being passed
     *   to Posthog
     *
     * To update anonymity, call updateAnonymityFromSettings() or you can set it directly via setAnonymity().
     *
     * To pass an event to Posthog:
     *
     * 1. Declare a type for the event, extending IAnonymousEvent, IPseudonymousEvent or IRoomEvent.
     * 2. Call the appropriate track*() method. Pseudonymous events will be dropped when anonymity is
     *    Anonymous or Disabled; Anonymous events will be dropped when anonymity is Disabled.
     */

    private anonymity = Anonymity.Disabled;
    // set true during the constructor if posthog config is present, otherwise false
    private enabled = false;
    private static _instance = null;
    private platformSuperProperties = {};

    public static get instance(): PosthogAnalytics {
        if (!this._instance) {
            this._instance = new PosthogAnalytics(posthog);
        }
        return this._instance;
    }

    constructor(private readonly posthog: PostHog) {
        const posthogConfig = SdkConfig.get()["posthog"];
        if (posthogConfig) {
            this.posthog.init(posthogConfig.projectApiKey, {
                api_host: posthogConfig.apiHost,
                autocapture: false,
                mask_all_text: true,
                mask_all_element_attributes: true,
                // This only triggers on page load, which for our SPA isn't particularly useful.
                // Plus, the .capture call originating from somewhere in posthog makes it hard
                // to redact URLs, which requires async code.
                //
                // To raise this manually, just call .capture("$pageview") or posthog.capture_pageview.
                capture_pageview: false,
                sanitize_properties: this.sanitizeProperties,
                respect_dnt: true,
            });
            this.enabled = true;
        } else {
            this.enabled = false;
        }
    }

    private sanitizeProperties = (properties: posthog.Properties): posthog.Properties => {
        // Callback from posthog to sanitize properties before sending them to the server.
        //
        // Here we sanitize posthog's built in properties which leak PII e.g. url reporting.
        // See utils.js _.info.properties in posthog-js.

        // Replace the $current_url with a redacted version.
        // $redacted_current_url is injected by this class earlier in capture(), as its generation
        // is async and can't be done in this non-async callback.
        if (!properties['$redacted_current_url']) {
            console.log("$redacted_current_url not set in sanitizeProperties, will drop $current_url entirely");
        }
        properties['$current_url'] = properties['$redacted_current_url'];
        delete properties['$redacted_current_url'];

        if (this.anonymity == Anonymity.Anonymous) {
            // drop referrer information for anonymous users
            properties['$referrer'] = null;
            properties['$referring_domain'] = null;
            properties['$initial_referrer'] = null;
            properties['$initial_referring_domain'] = null;

            // drop device ID, which is a UUID persisted in local storage
            properties['$device_id'] = null;
        }

        return properties;
    };

    private static getAnonymityFromSettings(): Anonymity {
        // determine the current anonymity level based on current user settings

        // "Send anonymous usage data which helps us improve Element. This will use a cookie."
        const analyticsOptIn = SettingsStore.getValue("analyticsOptIn", null, true);

        // (proposed wording) "Send pseudonymous usage data which helps us improve Element. This will use a cookie."
        //
        // TODO: Currently, this is only a labs flag, for testing purposes.
        const pseudonumousOptIn = SettingsStore.getValue("feature_pseudonymous_analytics_opt_in", null, true);

        let anonymity;
        if (pseudonumousOptIn) {
            anonymity = Anonymity.Pseudonymous;
        } else if (analyticsOptIn) {
            anonymity = Anonymity.Anonymous;
        } else {
            anonymity = Anonymity.Disabled;
        }

        return anonymity;
    }

    private registerSuperProperties(properties: posthog.Properties) {
        if (this.enabled) {
            this.posthog.register(properties);
        }
    }

    private static async getPlatformProperties(): Promise<PlatformProperties> {
        const platform = PlatformPeg.get();
        let appVersion;
        try {
            appVersion = await platform.getAppVersion();
        } catch (e) {
            // this happens if no version is set i.e. in dev
            appVersion = "unknown";
        }

        return {
            appVersion,
            appPlatform: platform.getHumanReadableName(),
        };
    }

    private async capture(eventName: string, properties: posthog.Properties) {
        if (!this.enabled) {
            return;
        }
        const { origin, hash, pathname } = window.location;
        properties['$redacted_current_url'] = await getRedactedCurrentLocation(
            origin, hash, pathname, this.anonymity);
        this.posthog.capture(eventName, properties);
    }

    public isEnabled(): boolean {
        return this.enabled;
    }

    public setAnonymity(anonymity: Anonymity): void {
        // Update this.anonymity.
        // This is public for testing purposes, typically you want to call updateAnonymityFromSettings
        // to ensure this value is in step with the user's settings.
        if (this.enabled && (anonymity == Anonymity.Disabled || anonymity == Anonymity.Anonymous)) {
            // when transitioning to Disabled or Anonymous ensure we clear out any prior state
            // set in posthog e.g. distinct ID
            this.posthog.reset();
            // Restore any previously set platform super properties
            this.registerSuperProperties(this.platformSuperProperties);
        }
        this.anonymity = anonymity;
    }

    private static getUUIDv4(): string {
        // https://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid
        return ([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g, c =>
            (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16),
        );
    }

    public async identifyUser(client: MatrixClientPeg, analyticsIdGenerator: () => string): Promise<void> {
        if (this.anonymity == Anonymity.Pseudonymous) {
            // Check the user's account_data for an analytics ID to use. Storing the ID in account_data allows
            // different devices to send the same ID.
            try {
                const accountData = await client.getAccountDataFromServer("im.vector.web.analytics_id");
                let analyticsID = accountData?.id;
                if (!analyticsID) {
                    // Couldn't retrieve an analytics ID from user settings, so create one and set it on the server.
                    // Note there's a race condition here - if two devices do these steps at the same time, last write
                    // wins, and the first writer will send tracking with an ID that doesn't match the one on the server
                    // until the next time account data is refreshed and this function is called (most likely on next
                    // page load). This will happen pretty infrequently, so we can tolerate the possibility.
                    analyticsID = analyticsIdGenerator();
                    await client.setAccountData("im.vector.web.analytics_id", { id: analyticsID });
                }
                this.posthog.identify(analyticsID);
            } catch (e) {
                // The above could fail due to network requests, but not essential to starting the application,
                // so swallow it.
                console.log("Unable to identify user for tracking" + e.toString());
            }
        }
    }

    public getAnonymity(): Anonymity {
        return this.anonymity;
    }

    public logout(): void {
        if (this.enabled) {
            this.posthog.reset();
        }
        this.setAnonymity(Anonymity.Anonymous);
    }

    public async trackPseudonymousEvent<E extends IPseudonymousEvent>(
        eventName: E["eventName"],
        properties: E["properties"] = {},
    ) {
        if (this.anonymity == Anonymity.Anonymous || this.anonymity == Anonymity.Disabled) return;
        await this.capture(eventName, properties);
    }

    public async trackAnonymousEvent<E extends IAnonymousEvent>(
        eventName: E["eventName"],
        properties: E["properties"] = {},
    ): Promise<void> {
        if (this.anonymity == Anonymity.Disabled) return;
        await this.capture(eventName, properties);
    }

    public async trackRoomEvent<E extends IRoomEvent>(
        eventName: E["eventName"],
        roomId: string,
        properties: Omit<E["properties"], "roomId">,
    ): Promise<void> {
        const updatedProperties = {
            ...properties,
            hashedRoomId: roomId ? await hashHex(roomId) : null,
        };
        await this.trackPseudonymousEvent(eventName, updatedProperties);
    }

    public async trackPageView(durationMs: number): Promise<void> {
        const hash = window.location.hash;

        let screen = null;
        const split = hash.split("/");
        if (split.length >= 2) {
            screen = split[1];
        }

        await this.trackAnonymousEvent<IPageView>("$pageview", {
            durationMs,
            screen,
        });
    }

    public async updatePlatformSuperProperties(): Promise<void> {
        // Update super properties in posthog with our platform (app version, platform).
        // These properties will be subsequently passed in every event.
        //
        // This only needs to be done once per page lifetime. Note that getPlatformProperties
        // is async and can involve a network request if we are running in a browser.
        this.platformSuperProperties = await PosthogAnalytics.getPlatformProperties();
        this.registerSuperProperties(this.platformSuperProperties);
    }

    public async updateAnonymityFromSettings(userId?: string): Promise<void> {
        // Update this.anonymity based on the user's analytics opt-in settings
        // Identify the user (via hashed user ID) to posthog if anonymity is pseudonmyous
        this.setAnonymity(PosthogAnalytics.getAnonymityFromSettings());
        if (userId && this.getAnonymity() == Anonymity.Pseudonymous) {
            await this.identifyUser(MatrixClientPeg.get(), PosthogAnalytics.getUUIDv4);
        }
    }
}