Initial Release

app.js

@@ -0,0 +1,181 @@
+const isoAEl = document.getElementById("isoA");
+const fAEl = document.getElementById("fA");
+const tAEl = document.getElementById("tA");
+
+const isoBEl = document.getElementById("isoB");
+const fBEl = document.getElementById("fB");
+const tBEl = document.getElementById("tB");
+
+const resultEl = document.getElementById("result");
+
+document.getElementById("calcBtn").addEventListener("click", calculate);
+document.getElementById("resetBtn").addEventListener("click", reset);
+
+document.addEventListener("keydown", (e) => {
+  if (e.key === "Enter") calculate();
+});
+
+function parseShutter(value) {
+  const raw = String(value ?? "").trim();
+  if (!raw) return NaN;
+
+  if (raw.includes("/")) {
+    const parts = raw.split("/");
+    if (parts.length !== 2) return NaN;
+    const num = parseFloat(parts[0]);
+    const den = parseFloat(parts[1]);
+    if (!isFinite(num) || !isFinite(den) || den === 0) return NaN;
+    return num / den;
+  }
+
+  const v = parseFloat(raw);
+  if (!isFinite(v)) return NaN;
+  return v;
+}
+
+function parsePositiveOrEmpty(value, parser = parseFloat) {
+  const raw = String(value ?? "").trim();
+  if (raw === "") return { empty: true, value: null };
+  const parsed = parser(raw);
+  if (!isFinite(parsed) || parsed <= 0) return { empty: false, value: NaN };
+  return { empty: false, value: parsed };
+}
+
+function prettyShutter(seconds) {
+  if (!(seconds > 0) || !isFinite(seconds)) return "Invalid";
+
+  // exact decimal seconds (up to 8 decimals, trimmed)
+  const exactSeconds = seconds.toFixed(8).replace(/0+$/, "").replace(/\.$/, "");
+
+  if (seconds < 1) {
+    // exact reciprocal (not snapped to common shutter values)
+    const reciprocal = 1 / seconds;
+    const reciprocalStr = reciprocal
+      .toFixed(6)
+      .replace(/0+$/, "")
+      .replace(/\.$/, "");
+
+    return `1/${reciprocalStr} s (${exactSeconds} s)`;
+  }
+
+  return `${exactSeconds} s`;
+}
+
+function formatAperture(n) {
+  if (!(n > 0) || !isFinite(n)) return "Invalid";
+  return `f/${n.toFixed(2).replace(/0+$/, "").replace(/\.$/, "")}`;
+}
+
+function formatISO(iso) {
+  if (!(iso > 0) || !isFinite(iso)) return "Invalid";
+  return `ISO ${Math.round(iso)}`;
+}
+
+function calculate() {
+  // Reference (must all be present)
+  const isoA = parseFloat(isoAEl.value);
+  const fA = parseFloat(fAEl.value);
+  const tA = parseShutter(tAEl.value);
+
+  if (
+    !(isoA > 0) ||
+    !(fA > 0) ||
+    !(tA > 0) ||
+    !isFinite(isoA) ||
+    !isFinite(fA) ||
+    !isFinite(tA)
+  ) {
+    resultEl.innerHTML = `<span class="error">Camera A must have valid positive ISO, f-stop, and shutter speed.</span>`;
+    return;
+  }
+
+  // Camera B: exactly one missing
+  const isoBParsed = parsePositiveOrEmpty(isoBEl.value, parseFloat);
+  const fBParsed = parsePositiveOrEmpty(fBEl.value, parseFloat);
+  const tBParsed = parsePositiveOrEmpty(tBEl.value, parseShutter);
+
+  const fields = [
+    { key: "iso", ...isoBParsed },
+    { key: "f", ...fBParsed },
+    { key: "t", ...tBParsed },
+  ];
+
+  const emptyFields = fields.filter((f) => f.empty);
+  if (emptyFields.length !== 1) {
+    resultEl.innerHTML = `<span class="error">For Camera B, leave exactly one field empty (the one to calculate).</span>`;
+    return;
+  }
+
+  if (fields.some((f) => !f.empty && (!isFinite(f.value) || f.value <= 0))) {
+    resultEl.innerHTML = `<span class="error">Camera B has invalid values. Use positive numbers, and shutter like 1/250 or 0.004.</span>`;
+    return;
+  }
+
+  const missing = emptyFields[0].key;
+  let isoB = isoBParsed.value;
+  let fB = fBParsed.value;
+  let tB = tBParsed.value;
+
+  // From:
+  // tB = tA * (fB^2 / fA^2) * (isoA / isoB)
+  // Rearranged for each missing variable:
+  if (missing === "t") {
+    tB = tA * ((fB * fB) / (fA * fA)) * (isoA / isoB);
+    if (!(tB > 0) || !isFinite(tB)) {
+      resultEl.innerHTML = `<span class="error">Could not compute shutter speed from given values.</span>`;
+      return;
+    }
+    tBEl.value = tB.toPrecision(6);
+
+    resultEl.innerHTML = `
+  <div class="ok">Calculated shutter speed for Camera B: <span class="mono">${prettyShutter(tB)}</span></div>
+  <div style="margin-top:8px;">B now: <span class="mono">${formatISO(isoB)}, ${formatAperture(fB)}, ${prettyShutter(tB)}</span></div>
+`;
+    return;
+  }
+
+  if (missing === "iso") {
+    // isoB = isoA * tA * fB^2 / ( tB * fA^2 )
+    isoB = (isoA * tA * (fB * fB)) / (tB * (fA * fA));
+    if (!(isoB > 0) || !isFinite(isoB)) {
+      resultEl.innerHTML = `<span class="error">Could not compute ISO from given values.</span>`;
+      return;
+    }
+    isoBEl.value = Math.round(isoB).toString();
+
+    resultEl.innerHTML = `
+  <div class="ok">Calculated ISO for Camera B: <span class="mono">${formatISO(isoB)}</span></div>
+  <div style="margin-top:8px;">B now: <span class="mono">${formatISO(isoB)}, ${formatAperture(fB)}, ${prettyShutter(tB)}</span></div>
+`;
+    return;
+  }
+
+  if (missing === "f") {
+    // fB^2 = (tB * fA^2 * isoB) / (tA * isoA)
+    // fB = sqrt(...)
+    const inside = (tB * (fA * fA) * isoB) / (tA * isoA);
+    fB = Math.sqrt(inside);
+    if (!(fB > 0) || !isFinite(fB)) {
+      resultEl.innerHTML = `<span class="error">Could not compute aperture from given values.</span>`;
+      return;
+    }
+    fBEl.value = fB.toFixed(2);
+
+    resultEl.innerHTML = `
+  <div class="ok">Calculated aperture for Camera B: <span class="mono">${formatAperture(fB)}</span></div>
+  <div style="margin-top:8px;">B now: <span class="mono">${formatISO(isoB)}, ${formatAperture(fB)}, ${prettyShutter(tB)}</span></div>
+`;
+  }
+}
+
+function reset() {
+  isoAEl.value = "100";
+  fAEl.value = "2.0";
+  tAEl.value = "1/1000";
+
+  isoBEl.value = "";
+  fBEl.value = "";
+  tBEl.value = "";
+
+  resultEl.textContent = "Result will appear here.";
+}