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Spec — Tournament Calculator dual-meet fixes

Status: implemented. Built and in use.

Two changes to dual-meet mode in tools/tournament-calculator.html: collapse the two club-pair inputs into one, and give dual meets their own bracket default.

Independent of calculator-pwa-spec.md — same file, unrelated concern. Either can ship first.

1. Current state

Default category object (line ~692):

{id:nextId++, code:free[0], name:free[1], teams:16, group:4, adv:2, fill:'bye',
 teamsA:8, teamsB:8, poFormat:'semis'}

The dual-meet card renders three inputs: Club A pairs (teamsA, default 8), Club B pairs (teamsB, default 8), and Number of brackets (group).

group is shared with standard mode. The dual card's value="${c.group||1}" only falls back to 1 when group is falsy — and the default is 4, so a new dual category opens showing 4 brackets, not 1.

The maths in calcDualCategory / dualGroupStage already handles unequal club sizes correctly and clamps the bracket count:

const kEff = Math.max(1, Math.min(30, Math.round(k)||1, a, b));

That clamp is correct — a bracket needs at least one pair from each club — and is not in scope to change.

2. One pairs input, default 5

Replace the two club-pair fields with a single Pairs per club input, default 5.

2.1 UI

In catCard()'s dual branch, the grid3 becomes:

<label class="f"><span class="lab">Pairs per club</span>
  <input type="number" data-k="pairsPerClub" min="1" max="50" value="${c.teamsA||5}"></label>
<label class="f"><span class="lab">Number of brackets</span>
  <input type="number" data-k="groupDual" min="1" max="30" value="${c.groupDual||1}"></label>

Two fields now, not three — adjust the wrapper from grid3 to grid2.

2.2 Keep teamsA / teamsB internally

Do not collapse the model to a single field. The pairsPerClub handler writes the same value to both:

else if(k==='pairsPerClub'){
  const v = Math.min(50, Math.max(1, +e.target.value||1));
  c.teamsA = v; c.teamsB = v;
}

Reasons to keep both:

  • calcDualCategory, dualGroupStage, and splitEven are already written and correct for asymmetric inputs. Collapsing the model means rewriting working maths for no gain.
  • The CSV schema's teams_a / teams_b columns stay stable, so previously exported plans still import.
  • Asymmetry remains reachable via CSV import (§2.3), so the code paths are not dead.

Change the default to teamsA: 5, teamsB: 5.

2.3 Keep the unequal-pairs note

if(a!==b) notes.push(`Club pair counts differ (${a} v ${b}) — pairs play unequal numbers of matches this category.`);

Keep this. It can no longer be triggered from the UI, but importing a CSV written before this change can still produce teamsA !== teamsB, and the note is exactly what tells the user why their imported numbers look odd. Removing it would make that case silent.

On import, populate the single input from teamsA (falling back to teamsB). Do not silently equalise them — let the note fire, and let the user correct it by typing in the field, which then writes both.

3. Dual meets default to 1 bracket

Add a separate groupDual field rather than reusing group:

{... teams:16, group:4, adv:2, groupDual:1, teamsA:5, teamsB:5, poFormat:'semis'}
  • Dual card binds to groupDual (§2.1).
  • calcDualCategory reads c.groupDual instead of c.group: 
    const wantedK = Math.min(30, Math.max(1, Math.round(c.groupDual)||1));
  • Standard mode keeps using group (default 4), untouched.

Why a separate field rather than resetting group on mode switch: the format toggle is global and flips every category at once. Overwriting group would destroy a carefully set standard-mode bracket layout the moment someone peeks at dual mode, with no undo. Two fields means toggling back and forth is lossless.

CSV: the existing brackets column carries whichever field is active for the current format setting — group when format=standard, groupDual when format=dual. The format setting row already appears earlier in the file, so the importer knows which field to populate. This keeps the column count unchanged.

4. Acceptance checklist

  • A new dual-meet category opens with Pairs per club = 5 and Number of brackets = 1, and two inputs, not three.
  • Typing in Pairs per club updates both clubs; the summary line reads 1 bracket (5 v 5).
  • Switching format standard → dual → standard leaves the standard-mode bracket count untouched (not reset to 1).
  • Setting brackets above the pair count still clamps, and still shows the "Only N brackets possible" note.
  • Export CSV → Import CSV round-trips a dual plan with the right bracket count landing in groupDual, not group.
  • The exported Breakdown sheet still opens and its Brackets column matches the on-screen bracket count — this spec does not change that sheet, so it is a regression check, not a new behaviour.
  • Importing a pre-change CSV with teams_a=8, teams_b=3 loads, shows 8 in the single input, and still emits the "Club pair counts differ" note.

5. Out of scope

  • The min(k, a, b) bracket clamp and the dual-meet match maths generally — both are correct.
  • Re-introducing asymmetric club sizes as a UI feature.
  • Any change to standard-mode defaults (teams: 16, group: 4, adv: 2).
  • The PWA work in calculator-pwa-spec.md.
  • The exported Breakdown sheet's bracket columns. Deliberately deferred, not overlooked. For the record, so it isn't rediscovered as a fresh bug: the Brackets column (p.groups) is correct — it reports the effective count after the clamp, and §3's default fix is what stops it opening at 4. The adjacent Bracket sizes column is the questionable one: bracketShorthand() renders p.sizes, which for dual meets is the combined A+B per bracket, so 5 pairs a side over 2 brackets prints 5-5 rather than 3v2, 2v3. Real, but cosmetic and export-only.