import type { Observation } from 'fhir/r4';

const LOINC = 'http://loinc.org';
const UCUM = 'http://unitsofmeasure.org';
const VITAL_SIGNS_CATEGORY = [{
  coding: [{ system: 'http://terminology.hl7.org/CodeSystem/observation-category', code: 'vital-signs', display: 'Vital Signs' }],
}];

export interface VitalsInput {
  systolic?: number; diastolic?: number; heartRate?: number; respRate?: number;
  temperature?: number; spo2?: number; height?: number; weight?: number;
}

// The simple (single-value) vitals that drive the form grid - US customary units.
export const SIMPLE_VITALS: { key: keyof VitalsInput; label: string; loinc: string; loincDisplay: string; unitCode: string; unitDisplay: string }[] = [
  { key: 'heartRate',   label: 'Heart rate',    loinc: '8867-4', loincDisplay: 'Heart rate',          unitCode: '/min',    unitDisplay: '/min' },
  { key: 'respRate',    label: 'Resp. rate',    loinc: '9279-1', loincDisplay: 'Respiratory rate',    unitCode: '/min',    unitDisplay: '/min' },
  { key: 'temperature', label: 'Temp',          loinc: '8310-5', loincDisplay: 'Body temperature',    unitCode: '[degF]',  unitDisplay: '°F' },
  { key: 'spo2',        label: 'SpO₂',          loinc: '2708-6', loincDisplay: 'Oxygen saturation',   unitCode: '%',       unitDisplay: '%' },
  { key: 'height',      label: 'Height',        loinc: '8302-2', loincDisplay: 'Body height',         unitCode: '[in_i]',  unitDisplay: 'in' },
  { key: 'weight',      label: 'Weight',        loinc: '29463-7', loincDisplay: 'Body weight',        unitCode: '[lb_av]', unitDisplay: 'lb' },
];

const isNum = (v?: number): v is number => typeof v === 'number' && !Number.isNaN(v);

export const computeBmi = (heightIn?: number, weightLb?: number): number | undefined => {
  if (!isNum(heightIn) || !isNum(weightLb) || heightIn <= 0) return undefined;
  return Math.round((703 * weightLb / (heightIn * heightIn)) * 10) / 10;
};

const base = (loinc: string, display: string, patientId: string, encounterId: string | undefined, nowIso: string): Observation => ({
  resourceType: 'Observation',
  status: 'final',
  category: VITAL_SIGNS_CATEGORY,
  code: { coding: [{ system: LOINC, code: loinc, display }] },
  subject: { reference: `Patient/${patientId}` },
  ...(encounterId && { encounter: { reference: `Encounter/${encounterId}` } }),
  effectiveDateTime: nowIso,
});

const qty = (value: number, unitDisplay: string, unitCode: string) => ({ value, unit: unitDisplay, system: UCUM, code: unitCode });

export const buildVitalObservations = (values: VitalsInput, patientId: string, encounterId: string | undefined, nowIso: string): Observation[] => {
  const out: Observation[] = [];

  // Blood pressure panel - only when both sides entered.
  if (isNum(values.systolic) && isNum(values.diastolic)) {
    out.push({
      ...base('85354-9', 'Blood pressure panel', patientId, encounterId, nowIso),
      component: [
        { code: { coding: [{ system: LOINC, code: '8480-6', display: 'Systolic blood pressure' }] }, valueQuantity: qty(values.systolic, 'mmHg', 'mm[Hg]') },
        { code: { coding: [{ system: LOINC, code: '8462-4', display: 'Diastolic blood pressure' }] }, valueQuantity: qty(values.diastolic, 'mmHg', 'mm[Hg]') },
      ],
    });
  }

  for (const v of SIMPLE_VITALS) {
    const value = values[v.key];
    if (isNum(value)) out.push({ ...base(v.loinc, v.loincDisplay, patientId, encounterId, nowIso), valueQuantity: qty(value, v.unitDisplay, v.unitCode) });
  }

  const bmi = computeBmi(values.height, values.weight);
  if (isNum(bmi)) out.push({ ...base('39156-5', 'Body mass index (BMI)', patientId, encounterId, nowIso), valueQuantity: qty(bmi, 'kg/m²', 'kg/m2') });

  return out;
};

/** Where the person entering readings says they came from. Only "measured here" can make them this practice's own. */
export type VitalSource = 'measured-here' | 'from-another-record';

/** One reading as the native vital route takes it: typed fields only; the server owns codes, units and the record. */
export interface NativeVitalEntry {
  kind: 'blood-pressure' | 'heart-rate' | 'resp-rate' | 'temperature' | 'spo2' | 'height' | 'weight';
  value?: number;
  systolic?: number;
  diastolic?: number;
  effectiveDateTime: string;
  encounterId?: string;
  source: VitalSource;
}

const NATIVE_KIND: Record<(typeof SIMPLE_VITALS)[number]['key'], NativeVitalEntry['kind'] | undefined> = {
  heartRate: 'heart-rate', respRate: 'resp-rate', temperature: 'temperature', spo2: 'spo2', height: 'height', weight: 'weight',
  systolic: undefined, diastolic: undefined,
};

/** The entries to send, one per reading. A blood pressure needs both halves; BMI is shown, never sent. */
export const buildNativeVitalEntries = (
  values: VitalsInput, encounterId: string | undefined, nowIso: string, source: VitalSource,
): { field: keyof VitalsInput | 'bloodPressure'; entry: NativeVitalEntry }[] => {
  const common = { effectiveDateTime: nowIso, source, ...(encounterId ? { encounterId } : {}) };
  const out: { field: keyof VitalsInput | 'bloodPressure'; entry: NativeVitalEntry }[] = [];
  if (isNum(values.systolic) && isNum(values.diastolic)) {
    out.push({ field: 'bloodPressure', entry: { kind: 'blood-pressure', systolic: values.systolic, diastolic: values.diastolic, ...common } });
  }
  for (const v of SIMPLE_VITALS) {
    const value = values[v.key];
    const kind = NATIVE_KIND[v.key];
    if (kind && isNum(value)) out.push({ field: v.key, entry: { kind, value, ...common } });
  }
  return out;
};