From 9620ab1990a3c4d219c84e70782032fabc9f97f6 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <github@flamingcow.io>
Date: Sun, 15 Feb 2026 19:34:13 -0800
Subject: [PATCH] Add transitive conflict detection for Must vs Must Not chains

---
 static/trip.html |  2 +
 static/trip.js   | 96 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/static/trip.html b/static/trip.html
index ba46957..c075c0e 100644
--- a/static/trip.html
+++ b/static/trip.html
@@ -63,6 +63,7 @@
         .constraint-add select { font-size: 0.75rem; padding: 0.15rem; border: 1px solid var(--wa-color-neutral-300, #ccc); border-radius: 0.25rem; }
         #conflicts { margin-bottom: 0.5rem; }
         #mismatches { margin-bottom: 0.5rem; }
+        #hard-conflicts { margin-bottom: 0.5rem; }
         .conflict-row { margin-bottom: 0.2rem; }
         .conflict-icon { background: var(--wa-color-danger-50, #dc3545); color: white; border-radius: 0.15rem; padding: 0 0.15rem; font-size: 0.6rem; line-height: 1.2; vertical-align: middle; margin-right: 0.1rem; display: inline-block; }
     </style>
@@ -83,6 +84,7 @@
         </div>
         <div id="conflicts"></div>
         <div id="mismatches"></div>
+        <div id="hard-conflicts"></div>
         <div id="students"></div>
         <wa-details summary="Add Student">
             <div class="add-form">
diff --git a/static/trip.js b/static/trip.js
index 4cb1a34..252ec15 100644
--- a/static/trip.js
+++ b/static/trip.js
@@ -96,6 +96,77 @@ async function loadStudents() {
         }
     }
 
+    const studentName = {};
+    for (const s of students) studentName[s.id] = s.name;
+
+    const mustAdj = {};
+    for (const s of students) {
+        for (const [bId, eff] of Object.entries(allOveralls[s.id])) {
+            if (eff.kind === 'must') {
+                const a = s.id, b = parseInt(bId);
+                if (!mustAdj[a]) mustAdj[a] = [];
+                mustAdj[a].push(b);
+                if (!mustAdj[b]) mustAdj[b] = [];
+                mustAdj[b].push(a);
+            }
+        }
+    }
+
+    const ufParent = {};
+    for (const s of students) ufParent[s.id] = s.id;
+    const ufFind = (x) => {
+        if (ufParent[x] !== x) ufParent[x] = ufFind(ufParent[x]);
+        return ufParent[x];
+    };
+    for (const s of students) {
+        for (const [bId, eff] of Object.entries(allOveralls[s.id])) {
+            if (eff.kind === 'must') {
+                const ra = ufFind(s.id), rb = ufFind(parseInt(bId));
+                if (ra !== rb) ufParent[ra] = rb;
+            }
+        }
+    }
+
+    const findMustPath = (from, to) => {
+        if (from === to) return [from];
+        const visited = new Set([from]);
+        const queue = [[from]];
+        while (queue.length > 0) {
+            const path = queue.shift();
+            const curr = path[path.length - 1];
+            for (const next of (mustAdj[curr] || [])) {
+                if (next === to) return [...path, next];
+                if (!visited.has(next)) {
+                    visited.add(next);
+                    queue.push([...path, next]);
+                }
+            }
+        }
+        return null;
+    };
+
+    const hardConflictList = [];
+    for (const s of students) {
+        for (const [bId, eff] of Object.entries(allOveralls[s.id])) {
+            if (eff.kind !== 'must_not') continue;
+            const b = parseInt(bId);
+            if (ufFind(s.id) !== ufFind(b)) continue;
+            const path = findMustPath(b, s.id);
+            if (!path) continue;
+            const chain = [];
+            for (let i = 0; i < path.length - 1; i++) {
+                const x = path[i], y = path[i + 1];
+                if (allOveralls[x]?.[y]?.kind === 'must') {
+                    chain.push({ from: studentName[x], to: studentName[y], kind: 'must' });
+                } else {
+                    chain.push({ from: studentName[y], to: studentName[x], kind: 'must' });
+                }
+            }
+            chain.push({ from: s.name, to: studentName[b], kind: 'must_not' });
+            hardConflictList.push(chain);
+        }
+    }
+
     const conflictsEl = document.getElementById('conflicts');
     const conflictsWasOpen = conflictsEl.querySelector('wa-details')?.open;
     conflictsEl.innerHTML = '';
@@ -142,6 +213,31 @@ async function loadStudents() {
         mismatchesEl.appendChild(det);
     }
 
+    const hardConflictsEl = document.getElementById('hard-conflicts');
+    const hardConflictsWasOpen = hardConflictsEl.querySelector('wa-details')?.open;
+    hardConflictsEl.innerHTML = '';
+    if (hardConflictList.length > 0) {
+        const det = document.createElement('wa-details');
+        det.summary = '\u26a0 Conflicts (' + hardConflictList.length + ')';
+        if (hardConflictsWasOpen) det.open = true;
+        for (const chain of hardConflictList) {
+            const div = document.createElement('div');
+            div.className = 'conflict-row';
+            chain.forEach((link, i) => {
+                if (i === chain.length - 1 && chain.length > 1) {
+                    div.appendChild(document.createTextNode(', but '));
+                } else if (i > 0) {
+                    div.appendChild(document.createTextNode(', '));
+                }
+                div.appendChild(document.createTextNode(link.from + ' '));
+                div.appendChild(kindSpan(link.kind));
+                div.appendChild(document.createTextNode(' ' + link.to));
+            });
+            det.appendChild(div);
+        }
+        hardConflictsEl.appendChild(det);
+    }
+
     const container = document.getElementById('students');
     const openStates = {};
     for (const card of container.children) {