(function(){
function init(){
  var CATS = {
    'pressure': {
      units:{
        'psig':{f:6894.76,name:'psig (gauge)',use:'EPC, USA'},
        'psia':{f:6894.76,name:'psia (abs)',use:'PSV sizing, API 520'},
        'bar':{f:100000,name:'bar (gauge)',use:'Europe, India'},
        'bara':{f:100000,name:'bara (abs)',use:'Process simulation'},
        'kPa':{f:1000,name:'kPa (gauge)',use:'SI / ISO'},
        'kPaa':{f:1000,name:'kPa-a (abs)',use:'Compressor specs'},
        'MPa':{f:1000000,name:'MPa (gauge)',use:'High-pressure ASME VIII'},
        'kgcm2':{f:98066.5,name:'kg/cm² (g)',use:'India, legacy'},
        'atm':{f:101325,name:'atm (abs)',use:'Vapor pressure, lab'},
        'mmHg':{f:133.322,name:'mmHg / Torr',use:'Vacuum service'},
        'inH2O':{f:248.84,name:'inH₂O',use:'Flare / vent draft'},
        'mmH2O':{f:9.80665,name:'mmH₂O',use:'Tank gauging'},
        'inHg':{f:3386.39,name:'inHg',use:'US vacuum'}
      },
      defaults:['psig','bar'],
      chips:[['psig','bar','1000'],['bar','kPa','100'],['psia','bara','100'],['psig','kgcm2','1000'],['MPa','psig','7'],['mmHg','kPa','760']]
    },
    'flow-gas':{
      units:{
        'MMSCFD':{f:1177.17,name:'MMSCFD',use:'Wellhead, US/EPC'},
        'MMSCFh':{f:28252.13,name:'MMSCFH',use:'Hourly metering'},
        'MSCFD':{f:1.17717,name:'MSCFD',use:'Small wells'},
        'SCFM':{f:1.6975,name:'SCFM',use:'Compressed air'},
        'Nm3h':{f:1,name:'Nm³/h',use:'European EPC, ISO'},
        'Nm3d':{f:0.04167,name:'Nm³/d',use:'Pipeline contracts'},
        'Sm3h':{f:1.0549,name:'Sm³/h (15°C)',use:'ISO 13443 standard'},
        'Sm3d':{f:0.04395,name:'Sm³/d',use:'Daily gas accounting'},
        'kgh':{f:1.36,name:'kg/h (CH₄)',use:'Mass flow approx'},
        'kgs':{f:4896,name:'kg/s (CH₄)',use:'Process simulation'},
        'MMscm':{f:42141,name:'MMscm/d',use:'LNG, large pipelines'}
      },
      defaults:['MMSCFD','Nm3h'],
      chips:[['MMSCFD','Nm3h','50'],['MMSCFD','Sm3d','100'],['SCFM','Nm3h','500'],['MSCFD','Nm3d','1000'],['Nm3h','MMSCFD','60000']]
    },
    'flow-liquid':{
      units:{
        'bpd':{f:0.006624,name:'BPD',use:'Crude oil production'},
        'bph':{f:0.158987,name:'BPH',use:'Tankage transfer'},
        'm3h':{f:1,name:'m³/h',use:'Europe, India EPC'},
        'm3d':{f:0.04167,name:'m³/d',use:'Production accounting'},
        'm3s':{f:3600,name:'m³/s',use:'Fire water'},
        'lph':{f:0.001,name:'L/h',use:'Chemical injection'},
        'lpm':{f:0.06,name:'L/min',use:'Pump curves'},
        'gpm':{f:0.227125,name:'GPM (US)',use:'Pump specs, USA'},
        'gpmUK':{f:0.272765,name:'GPM (UK)',use:'UK-spec equipment'},
        'gph':{f:0.003785,name:'GPH (US)',use:'Metering pumps'},
        'cfs':{f:101.94,name:'cfs (ft³/s)',use:'Hydraulics'}
      },
      defaults:['bpd','m3h'],
      chips:[['bpd','m3h','10000'],['bpd','m3d','5000'],['gpm','m3h','100'],['m3h','bph','50']]
    },
    'temp':{
      units:{'C':{name:'°C Celsius',use:'SI, Europe, India'},'F':{name:'°F Fahrenheit',use:'US oil & gas'},'K':{name:'K Kelvin',use:'Process simulation'},'R':{name:'°R Rankine',use:'US thermo'}},
      defaults:['C','F'],
      chips:[['C','F','25'],['F','C','100'],['C','K','100'],['F','R','300']],
      special:'temp'
    },
    'viscosity':{
      units:{
        'cP':{f:1,name:'cP (centipoise)',use:'API datasheets'},
        'mPas':{f:1,name:'mPa·s',use:'SI dynamic = cP'},
        'Pas':{f:1000,name:'Pa·s',use:'SI dynamic'},
        'P':{f:100,name:'P (poise)',use:'CGS, legacy'},
        'lbftsec':{f:1488.16,name:'lb/(ft·s)',use:'US thermal'},
        'lbfthr':{f:0.4134,name:'lb/(ft·hr)',use:'US datasheets'}
      },
      defaults:['cP','mPas'],
      chips:[['cP','mPas','100'],['cP','Pas','1'],['cP','P','100']]
    },
    'density':{
      units:{
        'kgm3':{f:1,name:'kg/m³',use:'SI density'},
        'gcm3':{f:1000,name:'g/cm³',use:'Lab samples'},
        'lbft3':{f:16.0185,name:'lb/ft³',use:'US engineering'},
        'lbgal':{f:119.826,name:'lb/US gal',use:'Drilling muds'},
        'SG':{f:1000,name:'SG (water=1)',use:'Crude oil char.'},
        'API':{f:0,name:'°API gravity',use:'Crude oil sales'}
      },
      defaults:['SG','API'],
      chips:[['SG','API','0.85'],['API','SG','35'],['lbft3','kgm3','50'],['kgm3','SG','850']]
    },
    'power':{
      units:{
        'W':{f:1,name:'W',use:'SI base'},
        'kW':{f:1000,name:'kW',use:'Pumps, compressors'},
        'MW':{f:1000000,name:'MW',use:'Power generation'},
        'hp':{f:745.7,name:'hp (mech)',use:'US pumps/motors'},
        'hpMet':{f:735.499,name:'hp (metric)',use:'European motors'},
        'BTUh':{f:0.293071,name:'BTU/h',use:'US heat duty'},
        'MMBTUh':{f:293071,name:'MMBTU/h',use:'Fired heater duty'},
        'kcalh':{f:1.16222,name:'kcal/h',use:'Legacy heat duty'},
        'MJh':{f:277.78,name:'MJ/h',use:'SI heat duty'},
        'GJd':{f:11574,name:'GJ/d',use:'LNG energy'}
      },
      defaults:['kW','hp'],
      chips:[['kW','hp','100'],['MMBTUh','kW','5'],['kW','BTUh','1000'],['hp','kW','500']]
    },
    'length':{
      units:{
        'mm':{f:0.001,name:'mm',use:'Pipe wall thickness'},
        'cm':{f:0.01,name:'cm',use:'Drawings'},
        'm':{f:1,name:'m',use:'SI base'},
        'km':{f:1000,name:'km',use:'Pipeline length'},
        'in':{f:0.0254,name:'inch',use:'Pipe NPS, USA'},
        'ft':{f:0.3048,name:'ft',use:'Vessel dimensions'},
        'mile':{f:1609.34,name:'mile',use:'US pipeline'},
        'mil':{f:0.0000254,name:'mil (0.001 in)',use:'Coating thickness'}
      },
      defaults:['in','mm'],
      chips:[['in','mm','6'],['ft','m','100'],['mil','mm','30'],['mile','km','100']]
    },
    'gor':{
      units:{
        'scfbbl':{f:0.1781,name:'SCF/bbl',use:'GOR US oil'},
        'scfstb':{f:0.1781,name:'SCF/STB',use:'Reservoir eng.'},
        'm3m3':{f:1,name:'m³/m³',use:'SI GOR'},
        'Sm3Sm3':{f:1,name:'Sm³/Sm³',use:'European reservoir'},
        'm3bbl':{f:6.2898,name:'m³/bbl',use:'Cross-unit'},
        'BscfMM':{f:178.107,name:'Bscf/MMbbl',use:'Field production'}
      },
      defaults:['scfbbl','m3m3'],
      chips:[['scfbbl','m3m3','500'],['scfbbl','m3m3','1000'],['m3m3','scfbbl','100']]
    }
  };

  var elFrom=document.getElementById('ucFrom'),elFromU=document.getElementById('ucFromUnit'),
      elTo=document.getElementById('ucTo'),elToU=document.getElementById('ucToUnit'),
      elSwap=document.getElementById('ucSwap'),elChips=document.getElementById('ucChips'),
      elForm=document.getElementById('ucFormula'),
      tableEl=document.getElementById('ucTable'),
      elTBody=tableEl?tableEl.querySelector('tbody'):null,
      tabs=document.querySelectorAll('.dh-uc-tab'),current='pressure';

  if(!elFrom||!elFromU||!elToU){console.log('DH-UC: required elements missing');return;}

  function toCan(v,k,c){
    if(c.special==='temp'){
      if(k==='C')return v;if(k==='F')return (v-32)*5/9;
      if(k==='K')return v-273.15;if(k==='R')return (v-491.67)*5/9;
    }
    if(k==='API')return (141.5/(v+131.5))*1000;
    return v*c.units[k].f;
  }
  function fromCan(cv,k,c){
    if(c.special==='temp'){
      if(k==='C')return cv;if(k==='F')return cv*9/5+32;
      if(k==='K')return cv+273.15;if(k==='R')return (cv+273.15)*9/5;
    }
    if(k==='API')return (141.5/(cv/1000))-131.5;
    return cv/c.units[k].f;
  }
  function fmt(n){
    if(!isFinite(n))return '—';
    if(n===0)return '0';
    var a=Math.abs(n);
    if(a>=1e6||a<0.001)return n.toExponential(4);
    if(a>=1000)return n.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g,',');
    if(a>=10)return n.toFixed(3);
    if(a>=1)return n.toFixed(4);
    return n.toFixed(6).replace(/0+$/,'').replace(/\.$/,'');
  }
  function build(catKey){
    var c=CATS[catKey];
    elFromU.innerHTML='';elToU.innerHTML='';
    Object.keys(c.units).forEach(function(k){
      elFromU.add(new Option(c.units[k].name,k));
      elToU.add(new Option(c.units[k].name,k));
    });
    elFromU.value=c.defaults[0];elToU.value=c.defaults[1];
    if(elChips){
      elChips.innerHTML='';
      (c.chips||[]).forEach(function(p){
        var b=document.createElement('button');
        b.className='dh-uc-chip';
        var fu=c.units[p[0]],tu=c.units[p[1]];
        if(!fu||!tu)return;
        b.textContent=p[2]+' '+fu.name.split(' ')[0]+' to '+tu.name.split(' ')[0];
        b.onclick=function(){elFromU.value=p[0];elToU.value=p[1];elFrom.value=p[2];conv();};
        elChips.appendChild(b);
      });
    }
  }
  function conv(){
    var c=CATS[current],v=parseFloat(elFrom.value);
    if(isNaN(v)){if(elTo)elTo.value='';return;}
    var can=toCan(v,elFromU.value,c),res=fromCan(can,elToU.value,c);
    if(elTo)elTo.value=fmt(res);
    var fu=c.units[elFromU.value],tu=c.units[elToU.value];
    if(elForm){
      var f='<span style="color:#FFB347">METHOD</span> <span style="color:#7B9BC4">to</span> ';
      if(c.special==='temp'){
        f+='<span style="color:#E8F4F8;font-weight:700">'+v+' '+fu.name.split(' ')[0]+' = '+fmt(res)+' '+tu.name.split(' ')[0]+'</span>';
      }else if(elFromU.value==='API'||elToU.value==='API'){
        f+='<span style="color:#E8F4F8;font-weight:700">SG = 141.5 / (API + 131.5) - API formula ASTM D1298</span>';
      }else{
        var factor=(tu.f&&fu.f)?(fu.f/tu.f):1;
        f+='<span style="color:#E8F4F8;font-weight:700">'+v+' x '+fmt(factor)+' = '+fmt(res)+'</span>';
      }
      f+=' <span style="color:#A8C0D8">Ref: NIST SP 811, API 14E</span>';
      elForm.innerHTML=f;
    }
    if(elTBody){
      elTBody.innerHTML='';
      Object.keys(c.units).forEach(function(k){
        if(k===elFromU.value)return;
        var u=c.units[k],val=fromCan(can,k,c);
        var tr=document.createElement('tr');
        tr.innerHTML='<td>'+u.name+'</td><td>'+fmt(val)+'</td><td>'+u.use+'</td>';
        elTBody.appendChild(tr);
      });
    }
  }
  tabs.forEach(function(tab){
    tab.addEventListener('click',function(){
      tabs.forEach(function(t){t.classList.remove('active');});
      tab.classList.add('active');
      current=tab.dataset.cat;
      build(current);
      var defs={'pressure':1000,'flow-gas':50,'flow-liquid':10000,'temp':25,'viscosity':100,'density':0.85,'power':100,'length':6,'gor':500};
      elFrom.value=defs[current]||1;
      conv();
    });
  });
  elFrom.addEventListener('input',conv);
  elFromU.addEventListener('change',conv);
  elToU.addEventListener('change',conv);
  if(elSwap){
    elSwap.addEventListener('click',function(){
      var t=elFromU.value;elFromU.value=elToU.value;elToU.value=t;
      elFrom.value=elTo.value;conv();
    });
  }
  build(current);conv();
  console.log('DH-UC: initialized successfully');
}
if(document.readyState==='loading'){
  document.addEventListener('DOMContentLoaded',init);
}else{
  init();
}
})();