content: import React from 'react';
  import { makeStyles } from '@material-ui/core/styles';
  import Stepper from '@material-ui/core/Stepper';
  import Step from '@material-ui/core/Step';
  import StepButton from '@material-ui/core/StepButton';
  import Button from '@material-ui/core/Button';
  import Typography from '@material-ui/core/Typography';
  
  const useStyles = makeStyles((theme) => ({
    root: {
      width: '100%',
    },
    button: {
      marginRight: theme.spacing(1),
    },
    backButton: {
      marginRight: theme.spacing(1),
    },
    completed: {
      display: 'inline-block',
    },
    instructions: {
      marginTop: theme.spacing(1),
      marginBottom: theme.spacing(1),
    },
  }));
  
  function getSteps() {
    return ['Select campaign settings', 'Create an ad group', 'Create an ad'];
  }
  
  function getStepContent(step) {
    switch (step) {
      case 0:
        return 'Step 1: Select campaign settings...';
      case 1:
        return 'Step 2: What is an ad group anyways?';
      case 2:
        return 'Step 3: This is the bit I really care about!';
      default:
        return 'Unknown step';
    }
  }
  
  export default function HorizontalNonLinearAlternativeLabelStepper() {
    const classes = useStyles();
    const [activeStep, setActiveStep] = React.useState(0);
    const [completed, setCompleted] = React.useState(new Set());
    const [skipped, setSkipped] = React.useState(new Set());
    const steps = getSteps();
  
    const totalSteps = () => {
      return getSteps().length;
    };
  
    const isStepOptional = (step) => {
      return step === 1;
    };
  
    const handleSkip = () => {
      if (!isStepOptional(activeStep)) {
        // You probably want to guard against something like this
        // it should never occur unless someone's actively trying to break something.
        throw new Error("You can't skip a step that isn't optional.");
      }
  
      setActiveStep((prevActiveStep) => prevActiveStep + 1);
      setSkipped((prevSkipped) => {
        const newSkipped = new Set(prevSkipped.values());
        newSkipped.add(activeStep);
        return newSkipped;
      });
    };
  
    const skippedSteps = () => {
      return skipped.size;
    };
  
    const completedSteps = () => {
      return completed.size;
    };
  
    const allStepsCompleted = () => {
      return completedSteps() === totalSteps() - skippedSteps();
    };
  
    const isLastStep = () => {
      return activeStep === totalSteps() - 1;
    };
  
    const handleNext = () => {
      const newActiveStep =
        isLastStep() && !allStepsCompleted()
          ? // It's the last step, but not all steps have been completed
            // find the first step that has been completed
            steps.findIndex((step, i) => !completed.has(i))
          : activeStep + 1;
  
      setActiveStep(newActiveStep);
    };
  
    const handleBack = () => {
      setActiveStep((prevActiveStep) => prevActiveStep - 1);
    };
  
    const handleStep = (step) => () => {
      setActiveStep(step);
    };
  
    const handleComplete = () => {
      const newCompleted = new Set(completed);
      newCompleted.add(activeStep);
      setCompleted(newCompleted);
  
      /**
       * Sigh... it would be much nicer to replace the following if conditional with
       * `if (!this.allStepsComplete())` however state is not set when we do this,
       * thus we have to resort to not being very DRY.
       */
      if (completed.size !== totalSteps() - skippedSteps()) {
        handleNext();
      }
    };
  
    const handleReset = () => {
      setActiveStep(0);
      setCompleted(new Set());
      setSkipped(new Set());
    };
  
    const isStepSkipped = (step) => {
      return skipped.has(step);
    };
  
    function isStepComplete(step) {
      return completed.has(step);
    }
  
    return (
      <div className={classes.root}>
        <Stepper alternativeLabel nonLinear activeStep={activeStep}>
          {steps.map((label, index) => {
            const stepProps = {};
            const buttonProps = {};
            if (isStepOptional(index)) {
              buttonProps.optional = <Typography variant="caption">Optional</Typography>;
            }
            if (isStepSkipped(index)) {
              stepProps.completed = false;
            }
            return (
              <Step key={label} {...stepProps}>
                <StepButton
                  onClick={handleStep(index)}
                  completed={isStepComplete(index)}
                  {...buttonProps}
                >
                  {label}
                </StepButton>
              </Step>
            );
          })}
        </Stepper>
        <div>
          {allStepsCompleted() ? (
            <div>
              <Typography className={classes.instructions}>
                All steps completed - you&apos;re finished
              </Typography>
              <Button onClick={handleReset}>Reset</Button>
            </div>
          ) : (
            <div>
              <Typography className={classes.instructions}>{getStepContent(activeStep)}</Typography>
              <div>
                <Button disabled={activeStep === 0} onClick={handleBack} className={classes.button}>
                  Back
                </Button>
                <Button
                  variant="contained"
                  color="primary"
                  onClick={handleNext}
                  className={classes.button}
                >
                  Next
                </Button>
                {isStepOptional(activeStep) && !completed.has(activeStep) && (
                  <Button
                    variant="contained"
                    color="primary"
                    onClick={handleSkip}
                    className={classes.button}
                  >
                    Skip
                  </Button>
                )}
  
                {activeStep !== steps.length &&
                  (completed.has(activeStep) ? (
                    <Typography variant="caption" className={classes.completed}>
                      Step {activeStep + 1} already completed
                    </Typography>
                  ) : (
                    <Button variant="contained" color="primary" onClick={handleComplete}>
                      {completedSteps() === totalSteps() - 1 ? 'Finish' : 'Complete Step'}
                    </Button>
                  ))}
              </div>
            </div>
          )}
        </div>
      </div>
    );
  }
  