{
  "schemaVersion": 1,
  "slug": "birthday-calculator",
  "category": "date-time",
  "kind": "implementation",
  "independentValidation": false,
  "implementationHash": "692863845d135f7ed620a3f7d17d8bd663bf6535f82224cc2fdc137787539163",
  "provenance": "Generated from the calculation contract used by the published page. Publication is not external validation.",
  "sourceFiles": [
    "data/calculators/birthday-calculator.json",
    "src/engine.js"
  ],
  "runtimeSource": "/sources/engine.txt",
  "runtimeHash": "5c888d8898afbdee36267bb9977829e1e2ac568f6677c8ee87469c139864645c",
  "scope": "The compute function records implemented equations, constants, lookup tables and custom rules. Inputs record defaults and allowed values; outputs record precision and units. Defaults are examples, not recommendations. General background references are not evidence for this specific algorithm.",
  "publishedFormula": {
    "formula": "d = (t_next − t_today) ÷ 86 400 000 ms; age = year(t_next) − y_b",
    "vars": [
      [
        "t_next",
        "Next birthday on/after today"
      ],
      [
        "t_today",
        "Today at UTC midnight"
      ],
      [
        "d",
        "Days until birthday"
      ],
      [
        "age",
        "Age reached on that birthday"
      ],
      [
        "y_b",
        "Birth year"
      ]
    ],
    "note": "All dates use UTC midnight; a February 29 birthday falls back to March 1 in non-leap years."
  },
  "externalEvidence": null,
  "contract": {
    "compute": "const valid=s=>{const m=/^(\\d{4})-(\\d{2})-(\\d{2})$/.exec(String(s));if(!m)return false;const x=new Date(s+'T00:00:00Z');return Number.isFinite(x.getTime())&&x.getUTCFullYear()===+m[1]&&x.getUTCMonth()+1===+m[2]&&x.getUTCDate()===+m[3]};const bad={daysUntil:null,ageTurning:null,nextBirthdayDate:null,nextBirthdayWeekday:null,birthdaysCelebrated:null,__error:'inputError'};if(!valid(birthDate))return bad;const b=new Date(birthDate+'T00:00:00Z'),now=new Date();now.setUTCHours(0,0,0,0);if(b>now)return bad;const birthday=y=>b.getUTCMonth()===1&&b.getUTCDate()===29&&new Date(Date.UTC(y,1,29)).getUTCMonth()!==1?new Date(Date.UTC(y,2,1)):new Date(Date.UTC(y,b.getUTCMonth(),b.getUTCDate()));let y=now.getUTCFullYear(),next=birthday(y);if(next<now){y++;next=birthday(y)}const age=y-b.getUTCFullYear(),daysUntil=Math.round((next-now)/86400000),thisYear=birthday(now.getUTCFullYear()),birthdaysCelebrated=Math.max(0,now.getUTCFullYear()-b.getUTCFullYear()-(thisYear>now?1:0)),wd=['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];return{daysUntil,ageTurning:age,nextBirthdayDate:next.toISOString().slice(0,10),nextBirthdayWeekday:wd[next.getUTCDay()],birthdaysCelebrated};",
    "inputs": [
      {
        "name": "birthDate",
        "type": "date",
        "default": "1990-06-15",
        "step": 1
      }
    ],
    "outputs": [
      {
        "name": "daysUntil",
        "precision": 0,
        "unit": "days"
      },
      {
        "name": "ageTurning",
        "precision": 0,
        "unit": "years"
      },
      {
        "name": "nextBirthdayDate",
        "precision": 0,
        "unit": "",
        "type": "text"
      },
      {
        "name": "nextBirthdayWeekday",
        "precision": 0,
        "unit": "",
        "type": "text"
      },
      {
        "name": "birthdaysCelebrated",
        "precision": 0,
        "unit": ""
      }
    ],
    "interpret": null
  }
}