define "Initial Population":
  AgeInYearsAt(date from 
    end of "Measurement Period"
  ) in Interval[18, 85]
    and exists "Essential Hypertension Diagnosis"
    and exists AdultOutpatientEncounters."Qualifying Encounters"

define "Denominator":
  "Initial Population"

define "Denominator Exclusions":
  Hospice."Has Hospice Services"
    or exists ( "Pregnancy or Renal Diagnosis" )
    or exists ( "End Stage Renal Disease Procedures" )
    or exists ( "End Stage Renal Disease Encounter" )
    or AIFrailLTCF."Is Age 66 to 80 with Advanced Illness and Frailty or Is Age 81 or Older with Frailty"
    or AIFrailLTCF."Is Age 66 or Older Living Long Term in a Nursing Home"
    or PalliativeCare."Has Palliative Care in the Measurement Period"

define "Numerator":
  "Has Systolic Blood Pressure Less Than 140"
    and "Has Diastolic Blood Pressure Less Than 90"

// NOTE: The USQualityCore encounter here is not introducing any constraints, and so could be expressed directly using US Core
define "Qualifying Encounters":
  ( ( 
    [USQualityCore.Encounter: "Office Visit"]
      union [USQualityCore.Encounter: "Annual Wellness Visit"]
      union [USQualityCore.Encounter: "Preventive Care Services Established Office Visit, 18 and Up"]
      union [USQualityCore.Encounter: "Preventive Care Services Initial Office Visit, 18 and Up"]
      union [USQualityCore.Encounter: "Home Healthcare Services"]
      union [USQualityCore.Encounter: "Virtual Encounter"]
      union [USQualityCore.Encounter: "Telephone Visits"] 
    ).isEncounterPerformed() 
  ) ValidEncounter
    where ValidEncounter.period during day of "Measurement Period"

define "Has Hospice Services":
  exists ((([USQualityCore.Encounter: "Encounter Inpatient"]).isEncounterPerformed()) InpatientEncounter
      where (InpatientEncounter.hospitalization.dischargeDisposition ~ "Discharge to home for hospice care (procedure)"
          or InpatientEncounter.hospitalization.dischargeDisposition ~ "Discharge to healthcare facility for hospice care (procedure)"
      )
        and InpatientEncounter.period ends during day of "Measurement Period"
  )
    or exists ((([USQualityCore.Encounter: "Hospice Encounter"]).isEncounterPerformed()) HospiceEncounter
        where HospiceEncounter.period overlaps day of "Measurement Period"
    )
    // TODO: Shouldn't need to specify a code path here (see https://jira.hl7.org/browse/FHIR-53941)
    or exists ((([USQualityCore.ObservationScreeningAssessment: code ~ "Hospice care [Minimum Data Set]"]).isAssessmentPerformed()) HospiceAssessment
        where HospiceAssessment.value ~ "Yes (qualifier value)"
          and HospiceAssessment.effective.toInterval() overlaps day of "Measurement Period"
    )
    or exists ((([USQualityCore.ServiceRequest: "Hospice Care Ambulatory"]).isInterventionOrder()) HospiceOrder
        where HospiceOrder.authoredOn during day of "Measurement Period"
    )
    or exists ((([USQualityCore.Procedure: "Hospice Care Ambulatory"]).isInterventionPerformed()) HospicePerformed
        where HospicePerformed.performed.toInterval() overlaps day of "Measurement Period"
    )
    // TODO: Consider whether to keep this as the union of Problems and EncounterDiagnosis
    or exists ((([FHIR.Condition: "Hospice Diagnosis"]).verified()) HospiceCareDiagnosis
        where HospiceCareDiagnosis.prevalenceInterval() overlaps day of "Measurement Period"
    )

define "Has Criteria Indicating Frailty":
  exists ( (([USQualityCore.DeviceRequest: "Frailty Device"]).isDeviceOrderPersonalUseDevices()) FrailtyDeviceOrder
      where FrailtyDeviceOrder.authoredOn.toInterval() during day of "Measurement Period"
  )
    or exists ( (([ObservationScreeningAssessment: "Medical equipment used"]).isAssessmentPerformed()) EquipmentUsed
        where EquipmentUsed.value as CodeableConcept in "Frailty Device" 
        and EquipmentUsed.effective.toInterval() ends during day of "Measurement Period"
    )
    // TODO: Consider whether to keep this as the union of problems and encounter diagnoses
    or exists ( (([FHIR.Condition: "Frailty Diagnosis"]).verified()) FrailtyDiagnosis
        where FrailtyDiagnosis.prevalenceInterval() overlaps day of "Measurement Period"
    )
    or exists ( (([USQualityCore.Encounter: "Frailty Encounter"]).isEncounterPerformed()) FrailtyEncounter
        where FrailtyEncounter.period overlaps day of "Measurement Period"
    )
    or exists ( (([USQualityCore.SimpleObservation: "Frailty Symptom"]).isSymptom()) FrailtySymptom
        where FrailtySymptom.effective.toInterval() overlaps day of "Measurement Period"
    )

define "Has Advanced Illness in Year Before or During Measurement Period":
// TODO: Consider whether to keep this as the union of problems and encounter diagnoses
exists ((([Condition: "Advanced Illness"]).verified()) AdvancedIllnessDiagnosis
where AdvancedIllnessDiagnosis.prevalenceInterval() starts during day of Interval[start of "Measurement Period" - 1 year, end of "Measurement Period"])

define "Has Dementia Medications in Year Before or During Measurement Period":
  exists (( ([FHIR.MedicationRequest: "Dementia Medications"]).isMedicationActive()) DementiaMedication
      where DementiaMedication.medicationRequestPeriod() overlaps day of Interval[start of "Measurement Period" - 1 year, 
        end of "Measurement Period"]
  )

define "Is Age 66 to 80 with Advanced Illness and Frailty or Is Age 81 or Older with Frailty":
  ( AgeInYearsAt(date from end of "Measurement Period") in Interval[66, 80]
      and "Has Criteria Indicating Frailty"
      and ( "Has Advanced Illness in Year Before or During Measurement Period"
          or "Has Dementia Medications in Year Before or During Measurement Period"
      )
  )
    or ( AgeInYearsAt(date from end of "Measurement Period")>= 81
        and "Has Criteria Indicating Frailty"
    )

define "Is Age 66 or Older Living Long Term in a Nursing Home":
  AgeInYearsAt(date from end of "Measurement Period") >= 66
    and ( ( Last( (([ObservationScreeningAssessment: "Housing status"]).isAssessmentPerformed()) HousingStatus    
          where HousingStatus.effective.toInterval() ends on or before 
          day of end of "Measurement Period"
          sort by 
          end of effective.toInterval() asc
      )) LastHousingStatus
        where LastHousingStatus.value ~ "Lives in nursing home (finding)"
    ) is not null

define "Has Palliative Care in the Measurement Period":
  // TODO: Shouldn't need to specify a code path here (see https://jira.hl7.org/browse/FHIR-53941)
  exists ((([USQualityCore.ObservationScreeningAssessment: code ~ "Functional Assessment of Chronic Illness Therapy - Palliative Care Questionnaire (FACIT-Pal)"]).isAssessmentPerformed()) PalliativeAssessment
      where PalliativeAssessment.effective.toInterval() overlaps day of "Measurement Period"
  )
    // TODO: Consider whether to keep this as the union of the problems and encounter diagnosis list? Anything enforced by the profiles that is expected but isn't stated here?
    or exists ((([FHIR.Condition: "Palliative Care Diagnosis"]).verified()) PalliativeDiagnosis
        where PalliativeDiagnosis.prevalenceInterval() overlaps day of "Measurement Period"
    )
    or exists ((([USQualityCore.Encounter: "Palliative Care Encounter"]).isEncounterPerformed()) PalliativeEncounter
        where PalliativeEncounter.period overlaps day of "Measurement Period"
    )
    or exists ((([USQualityCore.Procedure: "Palliative Care Intervention"]).isInterventionPerformed()) PalliativeIntervention
        where PalliativeIntervention.performed.toInterval() overlaps day of "Measurement Period"
    )

define "SDE Sex":
  case
    when Patient.sex() = '248153007' then "Male (finding)"
    when Patient.sex() = '248152002' then "Female (finding)"
    else null
  end

define "SDE Payer":
  [USQualityCore.Coverage: type in "Payer Type"] Payer
    return {
      code: Payer.type,
      period: Payer.period
    }

define "SDE Ethnicity":
  (Patient.ethnicity()) E
    return Tuple {
      codes: { E.ombCategory } union E.detailed,
      display: E.text
    }

define "SDE Race":
  (Patient.race()) R
    return Tuple {
      codes: R.ombCategory union R.detailed,
      display: R.text
    }

define "SDE Sex":
  SDE."SDE Sex"

define "Qualifying Blood Pressure Reading":
  ( ( ( [USCore.BloodPressureProfile] ).isObservationBP ( ) ) BloodPressure
      without ( ( [Encounter: "Encounter Inpatient"]
          union [Encounter: "Emergency Department Evaluation and Management Visit"]
      ).isEncounterPerformed ( ) ) DisqualifyingEncounter
        such that BloodPressure.effective.latest ( ) during day of DisqualifyingEncounter.period
      where BloodPressure.effective.latest ( ) during day of "Measurement Period"
  )
    union ( ( ( [USCore.BloodPressureProfile] ).isObservationBP ( ) ) BloodPressure
        where ( not ( ( BloodPressure.encounter.getEncounter ( ) ).class.code in { 'EMER', 'IMP', 'ACUTE', 'NONAC', 'PRENC', 'SS' } ) )
          and BloodPressure.effective.latest ( ) during day of "Measurement Period"
    )

define "Blood Pressure Days":
  "Qualifying Blood Pressure Reading" BPExam
    return date from BPExam.effective.latest ( )

define "Most Recent Blood Pressure Day":
  Last("Blood Pressure Days" BPDays
      sort asc
  )

define "Lowest Systolic Reading on Most Recent Blood Pressure Day":
  First("Qualifying Blood Pressure Reading" BPReading
      where BPReading.effective.latest() same day as "Most Recent Blood Pressure Day"
      return singleton from(BPReading.component BPComponent
          where BPComponent.code ~ "Systolic blood pressure"
          return BPComponent.value as Quantity
      )
      sort asc
  )

define "Has Systolic Blood Pressure Less Than 140":
  "Lowest Systolic Reading on Most Recent Blood Pressure Day" < 140 'mm[Hg]'

define "Lowest Diastolic Reading on Most Recent Blood Pressure Day":
  First("Qualifying Blood Pressure Reading" BPReading
      where BPReading.effective.latest() same day as "Most Recent Blood Pressure Day"
      return singleton from(BPReading.component BPComponent
          where BPComponent.code ~ "Diastolic blood pressure"
          return BPComponent.value as Quantity
      )
      sort asc
  )

define "Has Diastolic Blood Pressure Less Than 90":
  "Lowest Diastolic Reading on Most Recent Blood Pressure Day" < 90 'mm[Hg]'

define "Numerator":
  "Has Systolic Blood Pressure Less Than 140"
    and "Has Diastolic Blood Pressure Less Than 90"

define "Essential Hypertension Diagnosis":
  ( ( [Condition: "Essential Hypertension"] ).verified ( ) ) Hypertension
    where Hypertension.prevalenceInterval ( ) overlaps Interval[start of "Measurement Period", start of "Measurement Period" + 6 months )

define "Initial Population":
  AgeInYearsAt(date from 
    end of "Measurement Period"
  ) in Interval[18, 85]
    and exists "Essential Hypertension Diagnosis"
    and exists AdultOutpatientEncounters."Qualifying Encounters"

define "Denominator":
  "Initial Population"

define "SDE Payer":
  SDE."SDE Payer"

define "SDE Ethnicity":
  SDE."SDE Ethnicity"

define "Pregnancy or Renal Diagnosis":
  ( ( [Condition: "Pregnancy"]
      union [Condition: "End Stage Renal Disease"]
      union [Condition: "Kidney Transplant Recipient"]
      union [Condition: "Chronic Kidney Disease, Stage 5"]
  ).verified ( ) ) PregnancyESRDDiagnosis
    where PregnancyESRDDiagnosis.prevalenceInterval ( ) overlaps "Measurement Period"

define "End Stage Renal Disease Procedures":
  ( ( [Procedure: "Kidney Transplant"]
      union [Procedure: "Dialysis Services"]
  ).isProcedurePerformed ( ) ) ESRDProcedure
    where ESRDProcedure.performed.toInterval ( ) ends on or before end of "Measurement Period"

define "End Stage Renal Disease Encounter":
  ( ( [Encounter: "ESRD Monthly Outpatient Services"] ).isEncounterPerformed ( ) ) ESRDEncounter
    where ESRDEncounter.period starts on or before end of "Measurement Period"

define "Denominator Exclusions":
  Hospice."Has Hospice Services"
    or exists ( "Pregnancy or Renal Diagnosis" )
    or exists ( "End Stage Renal Disease Procedures" )
    or exists ( "End Stage Renal Disease Encounter" )
    or AIFrailLTCF."Is Age 66 to 80 with Advanced Illness and Frailty or Is Age 81 or Older with Frailty"
    or AIFrailLTCF."Is Age 66 or Older Living Long Term in a Nursing Home"
    or PalliativeCare."Has Palliative Care in the Measurement Period"

define "SDE Race":
  SDE."SDE Race"

define fluent function getEncounter(reference Reference):
  singleton from ( [Encounter] E
    where reference.references(E)
  )

/*
@description: Returns the single extension (if present) on the given resource with the specified url.
@comment: This function uses singleton from to ensure that a run-time exception is thrown if there
is more than one extension on the given resource with the specified url.
*/
define fluent function ext(domainResource DomainResource, url String):
  singleton from domainResource.exts(url)

/*
@description: Returns any extensions defined on the given resource with the specified url
*/
define fluent function exts(domainResource DomainResource, url String):
  domainResource.extension E
    where E.url = url
    return E

/*
@description: Given an interval, returns the ending point if the interval has an ending boundary specified,
otherwise, returns the starting point
*/
define fluent function latest(choice Choice<FHIR.dateTime, FHIR.Period, FHIR.Age, FHIR.Range>):
  (choice.toInterval()) period
    return
      if (period.hasEnd()) then end of period
      else start of period

/*
@description: Normalizes a value that is a choice of timing-valued types to an equivalent interval
@comment: Normalizes a choice type of FHIR.dateTime, FHIR.Period, FHIR.Timing, FHIR.instance, FHIR.string, FHIR.Age, or FHIR.Range types
to an equivalent interval. This selection of choice types is a superset of the majority of choice types that are used as possible
representations for timing-valued elements in FHIR, allowing this function to be used across any resource.

The input can be provided as a dateTime, Period, Timing, instant, string, Age, or Range.
The intent of this function is to provide a clear and concise mechanism to treat single
elements that have multiple possible representations as intervals so that logic doesn't have to account
for the variability. More complex calculations (such as medication request period or dispense period
calculation) need specific guidance and consideration. That guidance may make use of this function, but
the focus of this function is on single element calculations where the semantics are unambiguous.
If the input is a dateTime, the result a DateTime Interval beginning and ending on that dateTime.
If the input is a Period, the result is a DateTime Interval.
If the input is a Timing, an error is raised indicating a single interval cannot be computed from a Timing.
If the input is an instant, the result is a DateTime Interval beginning and ending on that instant.
If the input is a string, an error is raised indicating a single interval cannot be computed from a string.
If the input is an Age, the result is a DateTime Interval beginning when the patient was the given Age,
and ending immediately prior to when the patient was the given Age plus one year.
If the input is a Range, the result is a DateTime Interval beginning when the patient was the Age given
by the low end of the Range, and ending immediately prior to when the patient was the Age given by the
high end of the Range plus one year.

NOTE: Due to the
complexity of determining a single interval from a Timing or String type, this function will throw a run-time exception if it is used
with a Timing or String.
*/
define fluent function toInterval(choice Choice<FHIR.dateTime, FHIR.Period, FHIR.Timing, FHIR.instant, FHIR.string, FHIR.Age, FHIR.Range>):
  case
    when choice is FHIR.dateTime then
      Interval[FHIRHelpers.ToDateTime(choice as FHIR.dateTime), FHIRHelpers.ToDateTime(choice as FHIR.dateTime)]
    when choice is FHIR.Period then
      FHIRHelpers.ToInterval(choice as FHIR.Period)
    when choice is FHIR.instant then
      Interval[FHIRHelpers.ToDateTime(choice as FHIR.instant), FHIRHelpers.ToDateTime(choice as FHIR.instant)]
    when choice is FHIR.Age then
      Interval[FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity(choice as FHIR.Age),
        FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity(choice as FHIR.Age) + 1 year)
    when choice is FHIR.Range then
      Interval[FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity((choice as FHIR.Range).low),
        FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity((choice as FHIR.Range).high) + 1 year)
    when choice is FHIR.Timing then
      Message(null as Interval<DateTime>, true, 'NOT_IMPLEMENTED', 'Error', 'Calculation of an interval from a Timing value is not supported')
    when choice is FHIR.string then
      Message(null as Interval<DateTime>, true, 'NOT_IMPLEMENTED', 'Error', 'Calculation of an interval from a String value is not supported')
    else
      null as Interval<DateTime>
  end

/*
@description: Given an interval, returns true if the interval has an ending boundary specified
(i.e. the end of the interval is not null and not the maximum DateTime value)
*/
define fluent function hasEnd(period Interval<DateTime>):
  not (
    end of period is null
      or end of period = maximum DateTime
  )

/*
@description: Returns true if the given reference is to the given resource
@comment: Returns true if the `id` element of the given resource exactly equals the tail of the given reference.
NOTE: This function assumes resources from the same source server.
*/
define fluent function references(reference FHIR.Reference, resource FHIR.Resource):
  resource.id = Last(Split(reference.reference, '/'))

/*
@description: Returns conditions in the given list that either have no verification status or have a verification status of confirmed, unconfirmed, provisional, or differential
*/
define fluent function verified(conditions List<FHIR.Condition>):
  conditions C
    where C.verificationStatus is not null implies
      (C.verificationStatus ~ "confirmed"
        or C.verificationStatus ~ "unconfirmed"
        or C.verificationStatus ~ "provisional"
        or C.verificationStatus ~ "differential"
      )

/*
@description: Returns an interval representing the normalized prevalence period of a given Condition resource.
@comment: Uses the toInterval and toAbatementInterval functions to determine the widest potential interval from
onset to abatement as specified in the given Condition.
*/
define fluent function prevalenceInterval(condition Condition):
if condition.clinicalStatus ~ "active"
  or condition.clinicalStatus ~ "recurrence"
  or condition.clinicalStatus ~ "relapse" then
  Interval[start of condition.onset.toInterval(), end of condition.abatementInterval()]
else
  (end of condition.abatementInterval()) abatementDate
    return 
	  if abatementDate is null then
        Interval[start of condition.onset.toInterval(), abatementDate)
      else
        Interval[start of condition.onset.toInterval(), abatementDate]

/*
@description: Returns an interval representing the normalized Abatement of a given Condition resource.
@comment: @comment: If the abatement element of the Condition is represented as a DateTime, the result
is an interval beginning and ending on that DateTime.
If the abatement is represented as a Quantity, the quantity is expected to be a calendar-duration and is interpreted as the age of the patient. The
result is an interval from the date the patient turned that age to immediately before one year later.
If the abatement is represented as a Quantity Interval, the quantities are expected to be calendar-durations and are interpreted as an age range during
which the abatement occurred. The result is an interval from the date the patient turned the starting age of the quantity interval, and ending immediately
before one year later than the date the patient turned the ending age of the quantity interval.

NOTE: Due to the complexity of determining an interval from a String, this function will throw
a run-time exception if used with a Condition instance that has a String as the abatement value.
*/
define fluent function abatementInterval(condition Condition):
  if condition.abatement is FHIR.dateTime then
    Interval[FHIRHelpers.ToDateTime(condition.abatement as FHIR.dateTime), FHIRHelpers.ToDateTime(condition.abatement as FHIR.dateTime)]
  else if condition.abatement is FHIR.Period then
    FHIRHelpers.ToInterval(condition.abatement as FHIR.Period)
  else if condition.abatement is FHIR.string then
    Message(null as Interval<DateTime>, true, 'NOT_IMPLEMENTED', 'Error', 'Calculation of an interval from a String value is not supported')
  else if condition.abatement is FHIR.Age then
    Interval[FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity(condition.abatement as FHIR.Age),
      FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity(condition.abatement as FHIR.Age) + 1 year)
  else if condition.abatement is FHIR.Range then
    Interval[FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity((condition.abatement as FHIR.Range).low),
      FHIRHelpers.ToDate(Patient.birthDate) + FHIRHelpers.ToQuantity((condition.abatement as FHIR.Range).high) + 1 year)
  else if condition.abatement is FHIR.boolean then
    Interval[end of condition.onset.toInterval(), condition.recordedDate)
  else 
    null

/*
@description: Returns the single extension (if present) on the given element with the specified url.
@comment: This function uses singleton from to ensure that a run-time exception is thrown if there
is more than one extension on the given element with the specified url.
*/
define fluent function ext(element Element, url String):
  singleton from element.exts(url)

/*
@description: Returns any extensions defined on the given element with the specified url.
*/
define fluent function exts(element Element, url String):
  element.extension E
    where E.url = url
    return E

//Observation Vital Signs
define fluent function isObservationBP(Obs List<BloodPressureProfile>):
  Obs O
    where O.status in { 'final', 'amended', 'corrected' }

//Encounter, Performed
//General usage unless required otherwise by measure intent (e.g., follow-up encounters)
define fluent function isEncounterPerformed(Enc List<FHIR.Encounter>):
  Enc E
    where E.status = 'finished'

//Assessment, Performed
define fluent function isAssessmentPerformed(Obs List<ObservationScreeningAssessment>):
  Obs O
    where O.status in { 'final', 'amended', 'corrected' }

//Intervention, Order
define fluent function isInterventionOrder(ServiceRequest List<FHIR.ServiceRequest>):
  ServiceRequest S
    where S.status in { 'active', 'completed' }
      and S.intent in {'order', 'original-order', 'reflex-order', 'filler-order', 'instance-order'}

//Intervention, Performed
define fluent function isInterventionPerformed(Proc List<FHIR.Procedure>):
  Proc P
    where P.status ~ 'completed'

//Procedure, Performed
define fluent function isProcedurePerformed(Proc List<FHIR.Procedure>):
  Proc P
    where P.status ~ 'completed'

//Device, Order - Personal Use Devices
define fluent function isDeviceOrderPersonalUseDevices(DeviceRequest List<FHIR.DeviceRequest>):
  DeviceRequest D
    where D.status in { 'active', 'completed' }
      and D.intent in {'order', 'original-order', 'reflex-order', 'filler-order', 'instance-order'}

//Symptom
define fluent function isSymptom(Obs List<SimpleObservation>):
  Obs O
    where O.status in { 'preliminary', 'final', 'amended', 'corrected' }

//Medication, Active
define fluent function isMedicationActive(MedicationRequest List<FHIR.MedicationRequest>):
  MedicationRequest M
    where M.status = 'active'
      and M.intent in {'order', 'original-order', 'reflex-order', 'filler-order', 'instance-order'}

/*
Calculates the Medication Period for a single MedicationRequest.
MedicationRequest instances provided to this function are expected
to conform to the [MMEMedicationRequest](http://build.fhir.org/ig/cqframework/opioid-mme-r4/StructureDefinition-mmemedicationrequest.html)
profile, which expects:
* 1 and only 1 dosageInstruction, multiple dosageInstruction elements will result in an error
* 1 and only 1 doseAndRate, multiple doseAndRate elements will result in an error
* 1 timing with 1 repeat, missing timing or repeat elements will result in a null
* frequency, frequencyMax, defaulting to 1
* period, periodUnit, defaulting to 1 'd'
* timeOfDay
* doseQuantity or doseRange, missing doseQuantity and doseRange will result in a null
Note that MedicationRequest status is not considered by this calculation, as the
list of MedicationRequest instances provided to this function should already have
considered appropriate statuses, depending on the use case, typically `completed`.

NOTE: Updated return to use "date from end of boundsPeriod" to ensure result is Interval<Date>
*/
define fluent function medicationRequestPeriod(Request MedicationRequest):
  Request R
    let
      dosage: singleton from R.dosageInstruction,
      doseAndRate: singleton from dosage.doseAndRate,
      timing: dosage.timing,
      frequency: Coalesce(timing.repeat.frequencyMax, timing.repeat.frequency),
      period: Quantity(timing.repeat.period, timing.repeat.periodUnit),
      doseRange: doseAndRate.dose as FHIR.Range,
      doseQuantity: doseAndRate.dose as FHIR.SimpleQuantity,

      dose: Coalesce(end of doseRange, doseQuantity),
      dosesPerDay: Coalesce(ToDaily(frequency, period), Count(timing.repeat.timeOfDay), 1.0),
      boundsPeriod: timing.repeat.bounds as Period,
      // TODO: this isn't working as expected, convert results in null
      //daysSupply: (convert(R.dispenseRequest.expectedSupplyDuration) to days).value,
      daysSupply: (R.dispenseRequest.expectedSupplyDuration).value,
      quantity: R.dispenseRequest.quantity,
      refills: Coalesce(R.dispenseRequest.numberOfRepeatsAllowed, 0),
      startDate:
        Coalesce(
          date from start of boundsPeriod,
          date from R.authoredOn,
          date from start of R.dispenseRequest.validityPeriod
        ),
      totalDaysSupplied: Coalesce(daysSupply, quantity.value / (dose.value * dosesPerDay)) * (1 + refills)
    return
      if startDate is not null and totalDaysSupplied is not null then
        Interval[startDate, startDate + Quantity(totalDaysSupplied - 1, 'day') ]
      else if startDate is not null and boundsPeriod."end" is not null then
        Interval[startDate, date from end of boundsPeriod]
      else
        null

/**********************************************************************/
/* Functions in this region are copied from opioid-mme-r4             */
/**********************************************************************/

define function Quantity(value Decimal, unit String):
  if value is not null then
    System.Quantity { value: value, unit: unit }
  else
    null

/*
 Goal is to get to number of days
 Two broad approaches to the calculation:
  1) Based on supply and frequency, calculate the number of expected days the medication will cover/has covered
  2) Based on relevant period, determine a covered interval and calculate the length of that interval in days

This topic covers several use cases and illustrates how to calculate Cumulative
Medication Duration for each type of medication resource using the supply and
frequency approach.
*/

/*
  For the first approach, we need to get from frequency to a frequency/day
  So we define ToDaily
*/

/*
  Calculates daily frequency given frequency within a period
*/
define function ToDaily(frequency System.Integer, period System.Quantity):
  case period.unit
    when 'h' then frequency * (24.0 / period.value)
    when 'min' then frequency * (24.0 / period.value) * 60
    when 's' then frequency * (24.0 / period.value) * 60 * 60
    when 'd' then frequency * (24.0 / period.value) / 24
    when 'wk' then frequency * (24.0 / period.value) / (24 * 7)
    when 'mo' then frequency * (24.0 / period.value) / (24 * 30) /* assuming 30 days in month */
    when 'a' then frequency * (24.0 / period.value) / (24 * 365) /* assuming 365 days in year */
    when 'hour' then frequency * (24.0 / period.value)
    when 'minute' then frequency * (24.0 / period.value) * 60
    when 'second' then frequency * (24.0 / period.value) * 60 * 60
    when 'day' then frequency * (24.0 / period.value) / 24
    when 'week' then frequency * (24.0 / period.value) / (24 * 7)
    when 'month' then frequency * (24.0 / period.value) / (24 * 30) /* assuming 30 days in month */
    when 'year' then frequency * (24.0 / period.value) / (24 * 365) /* assuming 365 days in year */
    when 'hours' then frequency * (24.0 / period.value)
    when 'minutes' then frequency * (24.0 / period.value) * 60
    when 'seconds' then frequency * (24.0 / period.value) * 60 * 60
    when 'days' then frequency * (24.0 / period.value) / 24
    when 'weeks' then frequency * (24.0 / period.value) / (24 * 7)
    when 'months' then frequency * (24.0 / period.value) / (24 * 30) /* assuming 30 days in month */
    when 'years' then frequency * (24.0 / period.value) / (24 * 365) /* assuming 365 days in year */
    else Message(null, true, 'CMDLogic.ToDaily.UnknownUnit', ErrorLevel, 'Unknown unit ' & period.unit)
  end

define function ToString(value string): value.value

define function ToString(value uri): value.value

/*
@description: Converts the given FHIR [Quantity](https://hl7.org/fhir/datatypes.html#Quantity) 
value to a CQL Quantity
@comment: If the given quantity has a comparator specified, a runtime error is raised. If the given quantity
has a system other than UCUM (i.e. `http://unitsofmeasure.org`) or CQL calendar units (i.e. `http://hl7.org/fhirpath/CodeSystem/calendar-units`)
an error is raised. For UCUM to calendar units, the `ToCalendarUnit` function is used.
@seealso: ToCalendarUnit
*/
define function ToQuantity(quantity FHIR.Quantity):
    case
        when quantity is null then null
        when quantity.value is null then null
        when quantity.comparator is not null then
            Message(null, true, 'FHIRHelpers.ToQuantity.ComparatorQuantityNotSupported', 'Error', 'FHIR Quantity value has a comparator and cannot be converted to a System.Quantity value.')
        when quantity.system is null or quantity.system.value = 'http://unitsofmeasure.org'
              or quantity.system.value = 'http://hl7.org/fhirpath/CodeSystem/calendar-units' then
            System.Quantity { value: quantity.value.value, unit: ToCalendarUnit(Coalesce(quantity.code.value, quantity.unit.value, '1')) }
        else
            Message(null, true, 'FHIRHelpers.ToQuantity.InvalidFHIRQuantity', 'Error', 'Invalid FHIR Quantity code: ' & quantity.unit.value & ' (' & quantity.system.value & '|' & quantity.code.value & ')')
    end

/*
@description: Converts a UCUM definite duration unit to a CQL calendar duration
unit using conversions specified in the [quantities](https://cql.hl7.org/02-authorsguide.html#quantities) 
topic of the CQL specification.
@comment: Note that for durations above days (or weeks), the conversion is understood to be approximate
*/
define function ToCalendarUnit(unit System.String):
    case unit
        when 'ms' then 'millisecond'
        when 's' then 'second'
        when 'min' then 'minute'
        when 'h' then 'hour'
        when 'd' then 'day'
        when 'wk' then 'week'
        when 'mo' then 'month'
        when 'a' then 'year'
        else unit
    end

define function ToString(value ObservationStatus): value.value

define function ToString(value EncounterStatus): value.value

define function ToDateTime(value dateTime): value.value

/*
@description: Converts the given [Period](https://hl7.org/fhir/datatypes.html#Period)
value to a CQL DateTime Interval
@comment: If the start value of the given period is unspecified, the starting
boundary of the resulting interval will be open (meaning the start of the interval
is unknown, as opposed to interpreted as the beginning of time).
*/
define function ToInterval(period FHIR.Period):
    if period is null then
        null
    else
        if period."start" is null then
            Interval(period."start".value, period."end".value]
        else
            Interval[period."start".value, period."end".value]

define function ToDateTime(value instant): value.value

define function ToDate(value date): value.value

/*
@description: Converts the given FHIR [CodeableConcept](https://hl7.org/fhir/datatypes.html#CodeableConcept) value to a CQL Concept.
*/
define function ToConcept(concept FHIR.CodeableConcept):
    if concept is null then
        null
    else
        System.Concept {
            codes: concept.coding C return ToCode(C),
            display: concept.text.value
        }

/*
@description: Converts the given FHIR [Coding](https://hl7.org/fhir/datatypes.html#Coding) value to a CQL Code.
*/
define function ToCode(coding FHIR.Coding):
    if coding is null then
        null
    else
        System.Code {
          code: coding.code.value,
          system: coding.system.value,
          version: coding.version.value,
          display: coding.display.value
        }

define function ToString(value ServiceRequestStatus): value.value

define function ToString(value ServiceRequestIntent): value.value

define function ToString(value ProcedureStatus): value.value

define function ToString(value DeviceRequestStatus): value.value

define function ToString(value RequestIntent): value.value

define function ToString(value MedicationRequestStatus): value.value

define function ToString(value MedicationRequestIntent): value.value

define function ToDecimal(value decimal): value.value

define function ToString(value UnitsOfTime): value.value

/*
@description: Converts the given FHIR [Range](https://hl7.org/fhir/datatypes.html#Range) value to a CQL Interval of Quantity
*/
define function ToInterval(range FHIR.Range):
    if range is null then
        null
    else
        Interval[ToQuantity(range.low), ToQuantity(range.high)]

define function ToInteger(value integer): value.value

/*
@description: Returns the sex element as defined for the USCore patient profile
*/
define fluent function sex(patient Patient):
  patient.ext('http://hl7.org/fhir/us/core/StructureDefinition/us-core-sex').value as FHIR.code

define fluent function ethnicity(patient Patient):
  (patient.ext('http://hl7.org/fhir/us/core/StructureDefinition/us-core-ethnicity')) E
    return {
      ombCategory: E.ext('ombCategory').value as FHIR.Coding,
      detailed: (E.exts('detailed')) d return d.value as FHIR.Coding,
      text: E.ext('text').value as FHIR.string
    }

define fluent function race(patient Patient):
  (patient.ext('http://hl7.org/fhir/us/core/StructureDefinition/us-core-race')) E
    return {
      ombCategory: (E.exts('ombCategory')) o return o.value as FHIR.Coding,
      detailed: (E.exts('detailed')) d return d.value as FHIR.Coding,
      text: E.ext('text').value as FHIR.string
    }