semGrid.js Core logic

Generates the ordered list of semesters for a student's cohort window and computes fast lookup maps. Called whenever entry or graduation dates change.

Parent

core/

Called by

PlannerContext.jsx (useMemo on entry/grad dates)

Output consumed by

SemRow, SummerRow, prereqEval, planModel

Semester ID format

Semester IDs are human-readable strings. They're used as stable keys across the whole app.

"fall2026"    → Fall 2026 (regular semester)
"spring2027"  → Spring 2027
"sumA2027"    → Summer I 2027
"sumB2027"    → Summer II 2027
"incoming"    → Pre-matriculation (placed-out / AP credit)

Exported functions

buildCohortSemesters(entSem, entYear, gradSem, gradYear) → Semester[]

Main entry point. Generates the full ordered list of semesters between entry and graduation (inclusive). Prepends the special "incoming" slot. Calls generateSemesters() internally and trims to the cohort window.

Returns: Semester[] — each is {id, label, type, year}

generateSemesters(startYear, numYears) → Semester[]

Creates the raw full grid: 4 semesters per year (fall, spring, sumA, sumB) × numYears. Used internally by buildCohortSemesters().

deriveSemMaps(semesters) → { SEM_INDEX, SEM_NEXT, SEM_PREV }

Computes three O(1) lookup maps from the semester array. All are plain objects:

SEM_INDEX: { semId → ordinal } — used to compare "is A before B?"
SEM_NEXT: { semId → nextSemId } — used to advance one semester
SEM_PREV: { semId → prevSemId } — used to go back one semester

Returns: { SEM_INDEX, SEM_NEXT, SEM_PREV }

Example: 5-year CS cohort (Fall 2026 → Spring 2031)

graph LR A["incoming\n(ordinal 0)"] --> B["fall2026\n(1)"] --> C["spring2027\n(2)"] --> D["sumA2027\n(3)"] --> E["sumB2027\n(4)"] --> F["fall2027\n(5)"] --> G["...\n..."] --> Z["spring2031\n(last)"] style A fill:#f6f8fa,stroke:#d0d7de

SEMESTERS array for a Fall 2026 entry, Spring 2031 graduation. Ordinals assigned left-to-right.

Sticky courses: remapping on cohort change

When the user adjusts entry/graduation dates, all placed courses need to stay in their "relative" semester position if stickyCourses = true. PlannerContext handles this: it reads SEM_INDEX for the old grid, then maps each course to the same ordinal position in the new grid.