import React from "react";

const ACTIONS = {
  UPDATE_FIELD: 'updateField',
  RESET_FORM: 'resetForm',
}

const FORM_FIELDS = {
  USERNAME: 'username',
  EMAIL: 'email',
  EMPLOYEE_ID: 'employeeId',
  JOINED_DATE: 'joinedDate',
}

const initialArgs = {
  username: '',
  email: '',
  employeeId: '',
  joinedDate: '',
  errors: {
    username: 'initial',
    email: 'initial',
    employeeId: 'initial',
    joinedDate: 'initial',
  },
}

// getting current year
const getCurrentDate = () => {
  const date = new Date()

  return date.getFullYear()
}

const validateInput = (formField, value) => {
  switch(formField) {
    case FORM_FIELDS.USERNAME: {
      const alphabetSpacesRegex = /^[A-Za-z\s]*$/
      if (alphabetSpacesRegex.test(value) && value.length > 3) {
        return ''
      } else {
        return 'Name must be at least 4 characters long and only contain letters and spaces.'
      }
    }
    case FORM_FIELDS.EMAIL: {
      const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/

      if (emailRegex.test(value)) {
        return ''
      } else {
        return 'Email must be a valid email address'
      }
    }
    case FORM_FIELDS.EMPLOYEE_ID: {
      if (typeof value === "number" && `${value}`.length === 6) {
        return ''
      } else {
        return 'Employee ID must be exactly 6 digits.'
      }
    }
    case FORM_FIELDS.JOINED_DATE: {
      const currentYear = getCurrentDate()
      const [yearValue, _m, _d] = value.split("-")

      if (parseInt(yearValue) < parseInt(currentYear, 10)) {
        return ''
      } else {
        return 'Joining Date cannot be in the future'
      }
      
    }

    default: {
      return ''
    }
  }
}

const reducer = (state, action) => {
  try {
    if (!Object.hasOwn(action, 'type')) {
      throw Error('"type" not found');
    }

    switch(action.type) {
      case ACTIONS.UPDATE_FIELD: {
        // Expecting action to have field and value prop
        if (!Object.hasOwn(action, 'field')) {
          throw Error('"field" is required to update a form field')
        }

        const error = validateInput(action.field, action.value)

        return {
          ...state,
          [action.field]: action?.value || "",
          errors: {
            ...state.errors,
            [action.field]: error
          },
          formStates: {
            ...state.formStates,
            isDirty: true
          }
        }
      }

      case ACTIONS.RESET_FORM: {
        return initialArgs
      }

      default: {
        throw Error('Unknown action.');
      }
    }
  } catch(e) {
    console.log(`ERROR: ${e}`)
    return state
  }
  
}

const isAllInputValid = (state) => {
  try {
    const inputFieldsErrors = Object.values(state.errors)

    return inputFieldsErrors.every(value => !value)
  } catch(e) {
    console.log("Validation: Type ERROR")
  }
  
}


function EmployeeValidationForm() {
  const [employeeForm, dispatch] = React.useReducer(reducer, initialArgs)
  const isFormValid = isAllInputValid(employeeForm)

  const updateInput = (formField, event, transformInput) => {
    let inputValue = event.target.value
    if (transformInput) {
      inputValue = transformInput(inputValue)
    }
    dispatch({type: ACTIONS.UPDATE_FIELD, field: formField, value: inputValue})
  }

  return (
    <div className="layout-column align-items-center mt-20 ">
      <div className="layout-column align-items-start mb-10 w-50" data-testid="input-name">
        <input
          className="w-100"
          type="text"
          name="name"
          value={employeeForm.username}
          onChange={(e) => updateInput(FORM_FIELDS.USERNAME, e)}
          placeholder="Name"
          data-testid="input-name-test"
        />
        {
          employeeForm.errors.username ? <p className="error mt-2">
            Name must be at least 4 characters long and only contain letters and spaces
          </p> : null
        }

      </div>
      <div className="layout-column align-items-start mb-10 w-50" data-testid="input-email">
        <input
          className="w-100"
          type="text"
          name="email"
          value={employeeForm.email}
          onChange={(e) => updateInput(FORM_FIELDS.EMAIL, e)}
          placeholder="Email"
        />
        {employeeForm.errors.email ? <p className="error mt-2">Email must be a valid email address</p> : null}
        
      </div>
      <div className="layout-column align-items-start mb-10 w-50" data-testid="input-employee-id">
        <input
          className="w-100"
          type="text"
          name="employeeId"
          value={employeeForm.employeeId}
          onChange={(e) => updateInput(FORM_FIELDS.EMPLOYEE_ID, e, (v) => parseInt(v, 10))}
          placeholder="Employee ID"
        />
        {employeeForm.errors.employeeId ? <p className="error mt-2">Employee ID must be exactly 6 digits</p> : null}
      
      </div>
      <div className="layout-column align-items-start mb-10 w-50" data-testid="input-joining-date">
        <input
          className="w-100"
          type="date"
          name="joiningDate"
          value={employeeForm.joinedDate}
          onChange={(e) => updateInput(FORM_FIELDS.JOINED_DATE, e)}
          placeholder="Joining Date"
        />
        {
          employeeForm.errors.joinedDate ? <p className="error mt-2">Joining Date cannot be in the future</p> : null
        }
      </div>
      <button data-testid="submit-btn" type="button" onClick={() => dispatch({type: ACTIONS.RESET_FORM})} disabled={!isFormValid}>
        Submit
      </button>
    </div>
  );
}

export default EmployeeValidationForm;