c1be92b2af
Monte Carlo simulation of the 2026 AFL season and 10-team finals series. Elo ratings are backsolved from Squiggle's projected season win totals using the inverse formula: elo = 1500 - 450×log₁₀((1−wins/23)/(wins/23)). - New `afl_bracket` simulator type (schema + migration) - `afl-simulator.ts`: projects remaining regular season via Elo, seeds the AFL_10 finals bracket (Wildcard → QF/EF → SF → PF → Grand Final), and correctly tracks P5/P6 and P7/P8 as separate scoring tiers - `afl.ts` standings sync adapter pulling from Squiggle API (no auth required) - Finals line on standings display set to 10 for AFL seasons - Substring name matching with longest-key-wins to prevent "Port Adelaide" colliding with "Adelaide" when matching "Port Adelaide Power" - 27 unit tests covering bracket logic, column-sum guarantees, and name matching Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
423 lines
18 KiB
TypeScript
423 lines
18 KiB
TypeScript
/**
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* AFL Season + Finals Simulator
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*
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* Monte Carlo simulation of the AFL regular season and finals for 2026.
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*
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* Algorithm:
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* 1. Load all participants for the sports season from DB
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* 2. Load current regular season standings (wins, gamesPlayed) — if available
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* 3. Match participant names to hardcoded team data (Elo ratings)
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* 4. For each simulation:
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* a. For each team, simulate remaining regular season games (TOTAL_GAMES - gamesPlayed)
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* using Elo win probability vs. an average opponent (Elo 1500)
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* → projectedPoints = currentWins*4 + simulatedRemainingWins*4
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* b. Sort all 18 teams by projected points desc + random tiebreaker → final ladder
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* → Top 10 advance to the AFL Finals Series
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* c. Simulate AFL Finals Series (AFL_10 bracket):
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*
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* Wildcard Round: #7 vs #10, #8 vs #9 → losers exit (0 pts)
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* Qualifying Finals: #1 vs #4, #2 vs #3 → winners → Prelim Finals (bye)
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* losers → Semi-Finals (2nd chance)
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* Elimination Finals: #5 vs WC2w, #6 vs WC1w → losers exit (7th/8th)
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* Semi-Finals: QF1L vs EF2w, QF2L vs EF1w → losers exit (5th/6th)
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* Preliminary Finals: QF1w vs SF2w, QF2w vs SF1w → losers exit (3rd/4th)
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* Grand Final: PF1w vs PF2w → winner 1st, loser 2nd
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*
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* 5. Track placement counts per scoring tier
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* 6. Convert counts to probability distributions
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*
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* Win probability (Elo, PARITY_FACTOR = 450):
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* P(A beats B) = 1 / (1 + 10^((eloB - eloA) / 450))
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* A higher parity factor means more randomness per game. AFL uses 450, which is
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* slightly above the NBA (400) — meaning AFL games are marginally less predictable
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* than NBA games but far more predictable than NHL (1000).
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*
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* Regular season projection:
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* Per-game win probability = eloWinProbability(teamElo, 1500) where 1500 = average opponent.
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* If no standings exist in DB, defaults to 0 wins / TOTAL_GAMES remaining (seeding by Elo only).
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*
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* Elo ratings (see TEAMS_DATA below):
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* Backsolved from Squiggle's projected season win totals using the inverse formula:
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* elo = 1500 - 450 × log₁₀((1 − wins/23) / (wins/23))
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* Projected win counts were read from a screenshot of squiggle.com.au's season
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* simulation table (as of Round 2, 2026). Update each round as projections shift.
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* Source: https://squiggle.com.au
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*
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* Placement tiers → SimulationProbabilities mapping:
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* probFirst = Grand Final winner (1 per sim)
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* probSecond = Grand Final loser (1 per sim)
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* probThird/Fourth = Preliminary Finals losers (2 per sim — split evenly)
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* probFifth/Sixth = Semi-Finals losers (2 per sim — split evenly)
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* probSeventh/Eighth = Elimination Finals losers (2 per sim — split evenly)
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* Wildcard losers → all 0 (score 0 points, same as 9th/10th)
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* Missed finals → all 0
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*
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* NOTE: AFL uses the AFL_10 bracket template which splits the 5–8 tier into two
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* separate pairs (5/6 and 7/8). This is already handled by scoring-rules.ts
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* (SPLIT_5678_TEMPLATE_IDS); this simulator outputs the correct probabilities
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* into the appropriate tiers.
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*/
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import { database } from "~/database/context";
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import { eq } from "drizzle-orm";
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import * as schema from "~/database/schema";
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import type { Simulator, SimulationResult } from "./types";
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import { normalizeTeamName } from "~/lib/normalize-team-name";
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import { logger } from "~/lib/logger";
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import { getRegularSeasonStandings } from "~/models/regular-season-standings";
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// ─── Simulation parameters ────────────────────────────────────────────────────
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const NUM_SIMULATIONS = 10_000;
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/**
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* Elo parity factor for AFL single-game win probability.
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* 450 reflects moderate variance — lower than NHL (1000) to account for
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* AFL's relatively predictable results vs. basketball's coin-flip tendencies.
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*/
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const PARITY_FACTOR = 450;
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/** Approximate total regular season games per AFL team (2026 season). */
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const AFL_REGULAR_SEASON_GAMES = 23;
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/** Average opponent Elo used for regular season projections. */
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const AVERAGE_OPPONENT_ELO = 1500;
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// ─── Team data (2026 AFL season, as of end of Round 2) ───────────────────────
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//
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// Elo ratings are backsolved from Squiggle's projected season win totals.
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// Process: we screenshotted squiggle.com.au's season simulation table (Round 2,
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// 2026), read each team's projected wins, then applied the inverse formula:
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// elo = 1500 - 450 × log₁₀((1 − wins/23) / (wins/23))
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// This calibrates each team so the simulator reproduces Squiggle's ladder
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// projection when every game is played against an average opponent (Elo 1500).
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// Update each round by re-reading the projected wins from Squiggle and recalculating.
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// Source: https://squiggle.com.au
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interface AflTeamData {
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elo: number;
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}
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const TEAMS_DATA: Record<string, AflTeamData> = {
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"Western Bulldogs": { elo: 1646 }, // 15.6 projected wins
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"Hawthorn": { elo: 1604 }, // 14.5
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"Gold Coast": { elo: 1601 }, // 14.5 (3rd by %)
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"Sydney": { elo: 1579 }, // 13.8
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"Adelaide": { elo: 1576 }, // 13.7
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"Geelong": { elo: 1572 }, // 13.6
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"Brisbane Lions": { elo: 1541 }, // 12.7
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"Fremantle": { elo: 1524 }, // 12.2
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"Collingwood": { elo: 1517 }, // 12.0
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"Greater Western Sydney":{ elo: 1500 }, // 11.5
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"GWS Giants": { elo: 1500 }, // alias
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"Melbourne": { elo: 1473 }, // 10.7
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"St Kilda": { elo: 1466 }, // 10.5
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"North Melbourne": { elo: 1459 }, // 10.3
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"Carlton": { elo: 1449 }, // 10.0
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"Port Adelaide": { elo: 1435 }, // 9.6
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"Richmond": { elo: 1366 }, // 7.7
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"West Coast": { elo: 1362 }, // 7.6
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"Essendon": { elo: 1342 }, // 7.1
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};
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// ─── Public helpers (exported for unit testing) ───────────────────────────────
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/**
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* Look up team data by participant name.
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*
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* Uses a two-step match so "Gold Coast Suns" → "Gold Coast", "Hawthorn Hawks" → "Hawthorn", etc.
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* When multiple keys substring-match (e.g. "Adelaide" AND "Port Adelaide" both appear in
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* "Port Adelaide Power"), the longest key wins — giving the more specific match priority.
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* "GWS Giants" is an explicit alias since it won't substring-match "Greater Western Sydney".
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*/
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export function getTeamData(name: string): AflTeamData | undefined {
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const normalized = normalizeTeamName(name);
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const keys = Object.keys(TEAMS_DATA);
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// 1. Exact match (fast path)
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for (const key of keys) {
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if (normalizeTeamName(key) === normalized) return TEAMS_DATA[key];
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}
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// 2. Substring match — collect all candidates then pick the longest key so that
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// "Port Adelaide" (13) beats "Adelaide" (8) for "Port Adelaide Power".
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const candidates = keys.filter((key) => {
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const normKey = normalizeTeamName(key);
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return (
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normKey.length >= 4 &&
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normalized.length >= 4 &&
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(normalized.includes(normKey) || normKey.includes(normalized))
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);
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});
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if (candidates.length === 0) return undefined;
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candidates.sort((a, b) => b.length - a.length);
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return TEAMS_DATA[candidates[0]];
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}
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/**
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* Elo win probability for team A in a single game against team B.
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* P(A) = 1 / (1 + 10^((eloB - eloA) / PARITY_FACTOR))
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* Exported for unit testing.
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*/
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export function eloWinProbability(eloA: number, eloB: number): number {
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return 1 / (1 + Math.pow(10, (eloB - eloA) / PARITY_FACTOR));
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}
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// ─── Internal types ───────────────────────────────────────────────────────────
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interface TeamEntry {
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id: string;
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name: string;
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data: AflTeamData | undefined;
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/** Actual wins from the standings table (0 if no standings loaded). */
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currentWins: number;
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/** Remaining regular season games = TOTAL_GAMES - gamesPlayed (0 if season is complete). */
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remainingGames: number;
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/** Elo win probability vs. average opponent — constant per team. */
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winProb: number;
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}
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/** Get Elo for a team entry.
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* Fallback 1400 = conservative below-average estimate for unknown/unrecognized teams. */
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function elo(entry: TeamEntry): number {
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return entry.data?.elo ?? 1400;
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}
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/** Simulate remaining regular season games for a team.
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* Returns projected total wins for the season. */
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function simulateProjectedWins(entry: TeamEntry): number {
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let extra = 0;
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for (let g = 0; g < entry.remainingGames; g++) {
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if (Math.random() < entry.winProb) extra++;
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}
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return entry.currentWins + extra;
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}
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// ─── Simulator ────────────────────────────────────────────────────────────────
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export class AFLSimulator implements Simulator {
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async simulate(sportsSeasonId: string): Promise<SimulationResult[]> {
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const db = database();
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// 1. Load participants and standings in parallel.
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const [participantRows, standings] = await Promise.all([
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db
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.select({ id: schema.participants.id, name: schema.participants.name })
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.from(schema.participants)
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.where(eq(schema.participants.sportsSeasonId, sportsSeasonId)),
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getRegularSeasonStandings(sportsSeasonId),
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]);
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if (participantRows.length === 0) {
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throw new Error(
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`No participants found for sports season ${sportsSeasonId}. ` +
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`Add all 18 AFL clubs as participants before running simulation.`
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);
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}
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if (participantRows.length < 10) {
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throw new Error(
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`AFL simulation requires at least 10 participants to fill the finals bracket ` +
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`(got ${participantRows.length}). Add all 18 AFL clubs before running simulation.`
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);
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}
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// 2. Build standings lookup and construct team entries.
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// currentWins, remainingGames, and per-game winProb are all resolved once
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// here so nothing is recomputed inside the hot simulation loop.
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const standingsMap = new Map(standings.map((s) => [s.participantId, s]));
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const participantIds = participantRows.map((r) => r.id);
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const teams: TeamEntry[] = participantRows.map((r) => {
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const standing = standingsMap.get(r.id);
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const data = getTeamData(r.name);
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if (!data) {
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logger.warn(
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{ participantName: r.name, sportsSeasonId },
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`AFL simulator: no Elo found for participant "${r.name}" — falling back to 1400. ` +
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`Add an entry to TEAMS_DATA or rename the participant to match an existing key.`
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);
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}
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const gamesPlayed = standing?.gamesPlayed ?? 0;
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return {
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id: r.id,
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name: r.name,
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data,
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currentWins: standing?.wins ?? 0,
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remainingGames: Math.max(0, AFL_REGULAR_SEASON_GAMES - gamesPlayed),
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winProb: eloWinProbability(data?.elo ?? 1400, AVERAGE_OPPONENT_ELO),
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};
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});
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// ─── Helpers (defined once, outside the hot loop) ─────────────────────────
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/** Simulate a single AFL game. Returns the winner. */
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const simGame = (a: TeamEntry, b: TeamEntry): TeamEntry =>
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Math.random() < eloWinProbability(elo(a), elo(b)) ? a : b;
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/**
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* Project end-of-season ladder and return the top 10 finalists seeded 1–10.
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*
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* Teams are sorted by projected ladder points (4 per win) descending.
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* A small random tiebreaker simulates the percentage-based AFL tiebreaker
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* without requiring actual scores.
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*/
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const buildFinalsList = (): TeamEntry[] => {
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const projected = teams.map((t) => ({
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team: t,
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points: simulateProjectedWins(t) * 4,
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tiebreaker: Math.random(),
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}));
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projected.sort((a, b) => b.points - a.points || b.tiebreaker - a.tiebreaker);
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return projected.slice(0, 10).map((x) => x.team);
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};
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/**
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* Simulate the AFL Finals Series from a seeded list of 10 teams.
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*
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* Returns the placement for each team:
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* "gf_winner" → 1st
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* "gf_loser" → 2nd
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* "pf_loser" → 3rd/4th (two teams per sim)
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* "sf_loser" → 5th/6th (two teams per sim)
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* "ef_loser" → 7th/8th (two teams per sim)
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* "wc_loser" → 9th/10th (zero scoring points)
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*/
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const simAFLFinals = (
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finalists: TeamEntry[]
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): {
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gfWinner: TeamEntry;
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gfLoser: TeamEntry;
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pfLosers: [TeamEntry, TeamEntry];
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sfLosers: [TeamEntry, TeamEntry];
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efLosers: [TeamEntry, TeamEntry];
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} => {
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const [s1, s2, s3, s4, s5, s6, s7, s8, s9, s10] = finalists;
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// Wildcard Round: #7 vs #10, #8 vs #9
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const wc1Winner = simGame(s7, s10);
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const wc2Winner = simGame(s8, s9);
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// Qualifying Finals: #1 vs #4, #2 vs #3 (double-chance: winners get bye to PF)
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const qf1Winner = simGame(s1, s4);
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const qf1Loser = qf1Winner === s1 ? s4 : s1;
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const qf2Winner = simGame(s2, s3);
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const qf2Loser = qf2Winner === s2 ? s3 : s2;
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// Elimination Finals: #5 vs WC2 winner, #6 vs WC1 winner
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const ef1Winner = simGame(s5, wc2Winner);
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const ef1Loser = ef1Winner === s5 ? wc2Winner : s5;
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const ef2Winner = simGame(s6, wc1Winner);
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const ef2Loser = ef2Winner === s6 ? wc1Winner : s6;
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// Semi-Finals: QF losers (2nd chance) vs EF winners
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const sf1Winner = simGame(qf1Loser, ef2Winner);
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const sf1Loser = sf1Winner === qf1Loser ? ef2Winner : qf1Loser;
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const sf2Winner = simGame(qf2Loser, ef1Winner);
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const sf2Loser = sf2Winner === qf2Loser ? ef1Winner : qf2Loser;
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// Preliminary Finals: QF winners vs SF winners
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const pf1Winner = simGame(qf1Winner, sf2Winner);
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const pf1Loser = pf1Winner === qf1Winner ? sf2Winner : qf1Winner;
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const pf2Winner = simGame(qf2Winner, sf1Winner);
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const pf2Loser = pf2Winner === qf2Winner ? sf1Winner : qf2Winner;
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// Grand Final
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const gfWinner = simGame(pf1Winner, pf2Winner);
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const gfLoser = gfWinner === pf1Winner ? pf2Winner : pf1Winner;
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return {
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gfWinner,
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gfLoser,
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pfLosers: [pf1Loser, pf2Loser ],
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sfLosers: [sf1Loser, sf2Loser ],
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efLosers: [ef1Loser, ef2Loser ],
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};
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};
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// 3. Integer placement count maps — initialized to 0 for all participants.
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//
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// AFL scoring uses the AFL_10 bracket template which splits 5–8 into two
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// separate pairs: Semi-Finals losers share 5th/6th (higher value), and
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// Elimination Finals losers share 7th/8th (lower value). Both pairs get
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// distinct point values so we track them in separate count maps.
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const championCounts = new Map<string, number>(participantIds.map((id) => [id, 0]));
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const finalistCounts = new Map<string, number>(participantIds.map((id) => [id, 0]));
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const pfLoserCounts = new Map<string, number>(participantIds.map((id) => [id, 0]));
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const sfLoserCounts = new Map<string, number>(participantIds.map((id) => [id, 0]));
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const efLoserCounts = new Map<string, number>(participantIds.map((id) => [id, 0]));
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// 4. Monte Carlo simulation loop.
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for (let s = 0; s < NUM_SIMULATIONS; s++) {
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const finalists = buildFinalsList();
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const { gfWinner, gfLoser, pfLosers, sfLosers, efLosers } = simAFLFinals(finalists);
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championCounts.set(gfWinner.id, (championCounts.get(gfWinner.id) ?? 0) + 1);
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finalistCounts.set(gfLoser.id, (finalistCounts.get(gfLoser.id) ?? 0) + 1);
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for (const loser of pfLosers) {
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pfLoserCounts.set(loser.id, (pfLoserCounts.get(loser.id) ?? 0) + 1);
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}
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for (const loser of sfLosers) {
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sfLoserCounts.set(loser.id, (sfLoserCounts.get(loser.id) ?? 0) + 1);
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}
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for (const loser of efLosers) {
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efLoserCounts.set(loser.id, (efLoserCounts.get(loser.id) ?? 0) + 1);
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}
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// Wildcard losers and non-finalists are not counted (0 points per scoring rules).
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}
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// 5. Convert integer counts to probability distributions.
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//
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// Exact denominators guarantee column sums of 1.0 by construction:
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// probFirst/Second → / NUM_SIMULATIONS (1 per sim)
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// probThird/Fourth → / (2 * NUM_SIMULATIONS) (2 PF losers per sim)
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// probFifth/Sixth → / (2 * NUM_SIMULATIONS) (2 SF losers per sim)
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// probSeventh/Eighth → / (2 * NUM_SIMULATIONS) (2 EF losers per sim)
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//
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// Within each pair (3rd/4th, 5th/6th, 7th/8th), both positions receive the
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// same probability — matching the AFL_10 bracket's averaged point values.
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const N = NUM_SIMULATIONS;
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const results: SimulationResult[] = participantIds.map((participantId) => {
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const c = championCounts.get(participantId) ?? 0;
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const f = finalistCounts.get(participantId) ?? 0;
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const pf = pfLoserCounts.get(participantId) ?? 0;
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const sf = sfLoserCounts.get(participantId) ?? 0;
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const ef = efLoserCounts.get(participantId) ?? 0;
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return {
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participantId,
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probabilities: {
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probFirst: c / N,
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probSecond: f / N,
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probThird: pf / (2 * N),
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probFourth: pf / (2 * N),
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probFifth: sf / (2 * N),
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probSixth: sf / (2 * N),
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probSeventh: ef / (2 * N),
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probEighth: ef / (2 * N),
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},
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source: "afl_bracket_monte_carlo",
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};
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});
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// 6. Per-position normalization — belt-and-suspenders guard against floating-point
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// division residuals. Columns are already near-exactly 1.0 after step 5.
|
||
const positionKeys: Array<keyof (typeof results)[0]["probabilities"]> = [
|
||
"probFirst", "probSecond", "probThird", "probFourth",
|
||
"probFifth", "probSixth", "probSeventh", "probEighth",
|
||
];
|
||
for (const key of positionKeys) {
|
||
const colSum = results.reduce((s, r) => s + r.probabilities[key], 0);
|
||
const residual = 1.0 - colSum;
|
||
if (residual !== 0) {
|
||
const maxResult = results.reduce((best, r) =>
|
||
r.probabilities[key] > best.probabilities[key] ? r : best
|
||
);
|
||
maxResult.probabilities[key] += residual;
|
||
}
|
||
}
|
||
|
||
return results;
|
||
}
|
||
}
|