/**
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* @fileoverview
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* State handler.
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*
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* @author mebjas <minhazav@gmail.com>
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*/
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/** Different states of scanner */
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export enum Html5QrcodeScannerState {
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// Invalid internal state, do not set to this state.
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UNKNOWN = 0,
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// Indicates the scanning is not running or user is using file based
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// scanning.
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NOT_STARTED = 1,
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// Camera scan is running.
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SCANNING,
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// Camera scan is paused but camera is running.
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PAUSED,
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}
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/** Transaction for state transition. */
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export interface StateManagerTransaction {
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/**
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* Executes the current transaction.
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*/
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execute(): void;
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/**
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* Cancels the current transaction.
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*/
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cancel(): void;
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}
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/** Manager class for states. */
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export interface StateManager {
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/**
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* Start a transition to a new state. No other transitions will be allowed
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* till this one is executed.
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*
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* @param newState new state to transition to.
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*
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* @returns transaction of type {@interface StateManagerTransaction}.
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*
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* @throws error if the new state is not a valid transition from current
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* state.
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*/
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startTransition(newState: Html5QrcodeScannerState): StateManagerTransaction;
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/**
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* Directly execute a transition.
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*
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* @param newState new state to transition to.
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*
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* @throws error if the new state is not a valid transition from current
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* state.
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*/
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directTransition(newState: Html5QrcodeScannerState): void;
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/**
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* Get current state.
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*/
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getState(): Html5QrcodeScannerState;
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}
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/**
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* Implementation of {@interface StateManager} and
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* {@interface StateManagerTransaction}.
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*/
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class StateManagerImpl implements StateManager, StateManagerTransaction {
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private state: Html5QrcodeScannerState = Html5QrcodeScannerState.NOT_STARTED;
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private onGoingTransactionNewState: Html5QrcodeScannerState
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= Html5QrcodeScannerState.UNKNOWN;
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public directTransition(newState: Html5QrcodeScannerState) {
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this.failIfTransitionOngoing();
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this.validateTransition(newState);
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this.state = newState;
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}
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public startTransition(newState: Html5QrcodeScannerState): StateManagerTransaction {
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this.failIfTransitionOngoing();
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this.validateTransition(newState);
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this.onGoingTransactionNewState = newState;
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return this;
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}
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public execute() {
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if (this.onGoingTransactionNewState
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=== Html5QrcodeScannerState.UNKNOWN) {
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throw "Transaction is already cancelled, cannot execute().";
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}
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const tempNewState = this.onGoingTransactionNewState;
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this.onGoingTransactionNewState = Html5QrcodeScannerState.UNKNOWN;
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this.directTransition(tempNewState);
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}
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public cancel() {
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if (this.onGoingTransactionNewState
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=== Html5QrcodeScannerState.UNKNOWN) {
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throw "Transaction is already cancelled, cannot cancel().";
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}
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this.onGoingTransactionNewState = Html5QrcodeScannerState.UNKNOWN;
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}
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public getState(): Html5QrcodeScannerState {
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return this.state;
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}
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//#region private methods
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private failIfTransitionOngoing() {
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if (this.onGoingTransactionNewState
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!== Html5QrcodeScannerState.UNKNOWN) {
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throw "Cannot transition to a new state, already under transition";
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}
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}
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private validateTransition(newState: Html5QrcodeScannerState) {
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switch(this.state) {
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case Html5QrcodeScannerState.UNKNOWN:
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throw "Transition from unknown is not allowed";
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case Html5QrcodeScannerState.NOT_STARTED:
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this.failIfNewStateIs(newState, [Html5QrcodeScannerState.PAUSED]);
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break;
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case Html5QrcodeScannerState.SCANNING:
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// Both state transitions legal from here.
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break;
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case Html5QrcodeScannerState.PAUSED:
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// Both state transitions legal from here.
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break;
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}
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}
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private failIfNewStateIs(
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newState: Html5QrcodeScannerState,
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disallowedStatesToTransition: Array<Html5QrcodeScannerState>) {
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for (const disallowedState of disallowedStatesToTransition) {
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if (newState === disallowedState) {
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throw `Cannot transition from ${this.state} to ${newState}`;
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}
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}
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}
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//#endregion
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}
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export class StateManagerProxy {
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private stateManager: StateManager;
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constructor(stateManager: StateManager) {
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this.stateManager = stateManager;
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}
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startTransition(newState: Html5QrcodeScannerState): StateManagerTransaction {
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return this.stateManager.startTransition(newState);
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}
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directTransition(newState: Html5QrcodeScannerState) {
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this.stateManager.directTransition(newState);
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}
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getState(): Html5QrcodeScannerState {
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return this.stateManager.getState();
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}
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canScanFile(): boolean {
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return this.stateManager.getState() === Html5QrcodeScannerState.NOT_STARTED;
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}
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isScanning(): boolean {
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return this.stateManager.getState() !== Html5QrcodeScannerState.NOT_STARTED;
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}
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isStrictlyScanning(): boolean {
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return this.stateManager.getState() === Html5QrcodeScannerState.SCANNING;
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}
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isPaused(): boolean {
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return this.stateManager.getState() === Html5QrcodeScannerState.PAUSED;
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}
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}
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/**
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* Factory for creating instance of {@class StateManagerProxy}.
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*/
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export class StateManagerFactory {
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public static create(): StateManagerProxy {
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return new StateManagerProxy(new StateManagerImpl());
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}
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}
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