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* @fileoverview Per-MEP voting baseline computation for anomaly detection.
*
* Provides primitives for the `detect_voting_anomalies` MCP tool:
*
* - {@link resolveGroupMajority} — DOCEO group-breakdown → plurality position
* (FOR/AGAINST/ABSTAIN) with deterministic alphabetical tie-breaking.
* - {@link classifyMepVote} — for a given MEP and a single
* {@link LatestVoteRecord}, returns whether the MEP was `aligned` with their
* home group's majority, `defected`, `abstained`, or was `absent`, plus the
* list of *other* groups whose majority matched the MEP's position (used to
* detect cross-party alignment shifts).
* - {@link bucketByWeek} — groups classified votes into ISO-week buckets and
* computes per-week defection / abstention rates.
* - {@link computeBaseline} / {@link zScore} — running mean & standard
* deviation of weekly rates and per-week z-score.
* - {@link findOutlierWeeks} — collects weeks whose rate has a z-score
* ≥ a configurable threshold (default 1.5 per issue spec).
* - {@link findWoWShifts} — collects consecutive-week pairs whose defection
* rate jumped by ≥ a configurable threshold (default 20 percentage points).
* - {@link findCrossPartyAlignmentWindows} — sub-windows where the MEP voted
* with *non-home* group majorities on ≥ a configurable share (default 60%)
* of decisive RCVs.
*
* All helpers are pure and deterministic so they can be exercised with
* synthetic fixtures and the golden-snapshot suite referenced in the
* `detect_voting_anomalies` issue.
*
* ISMS Policy: SC-002 (Input Validation), AC-003 (Least Privilege),
* AU-002 (Audit Logging). GDPR Article 5(1)(d) — accuracy.
*
* @module utils/votingBaseline
* @since 1.4.0
*/
import type { LatestVoteRecord } from '../clients/ep/doceoXmlParser.js';
import { normalizePoliticalGroup } from './politicalGroupNormalization.js';
/** Per-vote MEP alignment classification relative to their home political group. */
export type Alignment = 'aligned' | 'defected' | 'abstained' | 'absent';
/** Per-vote position recorded for an MEP or as a group majority. */
export type VotePosition = 'FOR' | 'AGAINST' | 'ABSTAIN';
/** Default z-score cutoff for outlier-week detection. */
export const DEFAULT_Z_SCORE_THRESHOLD = 1.5;
/** Default week-over-week change (percentage points) flagging a shift. */
export const DEFAULT_WOW_THRESHOLD_PP = 20;
/** Default share of decisive votes with non-home-group majorities flagging a cross-party shift. */
export const DEFAULT_CROSS_PARTY_SHARE = 0.6;
/** Minimum sub-window decisive-vote count before evaluating cross-party share. */
export const MIN_SUBWINDOW_DECISIVE_VOTES = 3;
/**
* Single MEP/RCV-vote classification.
*/
export interface ClassifiedVote {
/**
* DOCEO unique vote identifier (`LatestVoteRecord.id` —
* e.g. `"RCV-10-2026-01-15-001"`). Used to populate
* {@link VotingAnomaly.evidenceVoteIds}.
*/
voteId: string;
/** Sitting date in YYYY-MM-DD (falls back to `vote.date` when sittingDate is absent). */
sittingDate: string;
/** Alignment of the MEP's position with their home-group majority. */
alignment: Alignment;
/** Plurality position of the MEP's home group on this RCV. `null` when undeterminable. */
groupMajority: VotePosition | null;
/** Position cast by the MEP (`null` when absent). */
mepPosition: VotePosition | null;
/**
* Canonical short codes of *other* groups whose majority matched the MEP's
* position on this RCV (excludes the MEP's home group). Empty when the MEP
* was absent or abstained, or when no other group had a determinable
* majority matching their position.
*/
matchingOtherGroups: string[];
}
/**
* Per-week aggregate built by {@link bucketByWeek}.
*/
export interface WeekBucket {
/** ISO week start (Monday) in YYYY-MM-DD format. */
weekStart: string;
/** Number of votes (decisive + abstentions, excludes absences). */
voted: number;
/** Number of decisive votes (FOR/AGAINST, excludes abstentions). */
decisive: number;
/** Decisive votes where the MEP defected from the home-group majority. */
defections: number;
/** Votes where the MEP abstained. */
abstentions: number;
/**
* Decisive defections where the MEP's position *also* matched at least one
* non-home group's plurality majority — i.e. a true cross-party signal.
*
* This count is intentionally narrower than "any decisive vote matching a
* non-home majority": when the MEP aligns with their home group, matching
* other groups voting the same way reflects consensus, not cross-party
* realignment. Only counted when the MEP both broke from home AND moved
* toward another bloc.
*/
crossPartyAlignments: number;
/** DOCEO vote IDs in this bucket (preserving DOCEO order). */
voteIds: string[];
/** Defection rate as a percentage of decisive votes, 0 when `decisive === 0`. */
defectionRate: number;
/** Abstention rate as a percentage of voted (decisive + abstain), 0 when `voted === 0`. */
abstentionRate: number;
}
/** Baseline summary statistics for a series of per-week rates. */
export interface BaselineSummary {
mean: number;
/** Sample standard deviation (`ddof=1`). 0 when fewer than two data points. */
stdev: number;
}
/** Resolved outlier week from {@link findOutlierWeeks}. */
export interface OutlierWeek {
weekStart: string;
value: number;
z: number;
/** Baseline mean rate across all weeks (the "expected" value). */
baselineMean: number;
voteIds: string[];
}
/** Resolved week-over-week jump from {@link findWoWShifts}. */
export interface WoWShift {
fromWeek: string;
toWeek: string;
delta: number;
/** Previous week's defection rate (the "expected" value before the shift). */
previousRate: number;
voteIds: string[];
}
/** Resolved cross-party-alignment sub-window from {@link findCrossPartyAlignmentWindows}. */
export interface CrossPartyWindow {
weekStart: string;
/**
* Share of decisive RCVs in this window where the MEP defected toward a
* non-home group's majority, expressed as a **percentage** (0–100).
* The input `share` threshold is a fraction (0–1); the returned value
* is rounded to two decimals.
*/
sharePercent: number;
decisive: number;
voteIds: string[];
}
/**
* Resolve the plurality position of a group-breakdown row.
*
* Ties are broken alphabetically (ABSTAIN < AGAINST < FOR) so the result is
* deterministic and fixture-stable.
*
* @param row - DOCEO group-breakdown counts. `undefined` for groups absent
* from the vote.
* @returns Plurality position or `null` when the row is missing or all zero.
*/
export function resolveGroupMajority(
row: { for: number; against: number; abstain: number } | undefined
): VotePosition | null {
if (row === undefined) return null;
const { for: f, against: a, abstain: ab } = row;
if (f <= 0 && a <= 0 && ab <= 0) return null;
const ranked: [VotePosition, number][] = [
['ABSTAIN', ab],
['AGAINST', a],
['FOR', f],
];
ranked.sort((x, y) => {
if (y[1] !== x[1]) return y[1] - x[1];
return x[0].localeCompare(y[0]);
});
return ranked[0]?.[0] ?? null;
}
/**
* Resolve the breakdown row for a normalized group label, handling the case
* where DOCEO XML uses raw short labels (e.g. `RE`, `Verts/ALE`) while
* `normalizedGroup` is the canonical EP code (`Renew`, `Greens/EFA`).
*
* @internal Exported for testing.
*/
export function resolveGroupBreakdownRow(
breakdown: Record<string, { for: number; against: number; abstain: number }> | undefined,
normalizedGroup: string
): { for: number; against: number; abstain: number } | undefined {
if (breakdown === undefined) return undefined;
if (normalizedGroup in breakdown) return breakdown[normalizedGroup];
for (const [rawKey, row] of Object.entries(breakdown)) {
if (normalizePoliticalGroup(rawKey) === normalizedGroup) return row;
}
return undefined;
}
/**
* Resolve the MEP's home-group majority on a vote.
*
* @internal
*/
function resolveHomeMajority(
vote: LatestVoteRecord,
homeGroup: string | null
): VotePosition | null {
Iif (homeGroup === null) return null;
return resolveGroupMajority(resolveGroupBreakdownRow(vote.groupBreakdown, homeGroup));
}
/**
* Compute the set of non-home groups whose majority matched the MEP's
* decisive position. Returns canonical short codes, alphabetically sorted.
*
* @internal
*/
function collectMatchingOtherGroups(
vote: LatestVoteRecord,
homeGroup: string | null,
mepPosition: VotePosition
): string[] {
Iif (vote.groupBreakdown === undefined) return [];
const matching: string[] = [];
for (const [rawKey, row] of Object.entries(vote.groupBreakdown)) {
const canonical = normalizePoliticalGroup(rawKey);
if (homeGroup !== null && canonical === homeGroup) continue;
const majority = resolveGroupMajority(row);
Eif (majority !== null && majority === mepPosition) matching.push(canonical);
}
matching.sort((a, b) => a.localeCompare(b));
return matching;
}
/**
* Decide alignment between an MEP's decisive position and their home-group
* majority. When the majority is unknown the result is `aligned` (the
* conservative choice — we never report a defection without evidence).
*
* @internal
*/
function alignmentForDecisive(
groupMajority: VotePosition | null,
mepPosition: VotePosition
): Alignment {
if (groupMajority === null) return 'aligned';
return groupMajority === mepPosition ? 'aligned' : 'defected';
}
/**
* Classify an MEP's vote against their home group's majority on a single RCV.
*
* @param vote - DOCEO {@link LatestVoteRecord}.
* @param mepId - EP MEP identifier (e.g. `"197558"`).
* @param homeGroup - The MEP's canonical home group (e.g. `"EPP"`); when
* `null` (group unresolved) the alignment is reported but no defection
* classification is attempted.
* @returns Per-vote classification.
*/
export function classifyMepVote(
vote: LatestVoteRecord,
mepId: string,
homeGroup: string | null
): ClassifiedVote {
const sittingDate = vote.sittingDate ?? vote.date;
const mepPosition = vote.mepVotes?.[mepId];
if (mepPosition === undefined) {
return {
voteId: vote.id, sittingDate, alignment: 'absent',
groupMajority: null, mepPosition: null, matchingOtherGroups: [],
};
}
const groupMajority = resolveHomeMajority(vote, homeGroup);
if (mepPosition === 'ABSTAIN') {
return {
voteId: vote.id, sittingDate, alignment: 'abstained',
groupMajority, mepPosition, matchingOtherGroups: [],
};
}
return {
voteId: vote.id,
sittingDate,
alignment: alignmentForDecisive(groupMajority, mepPosition),
groupMajority,
mepPosition,
matchingOtherGroups: collectMatchingOtherGroups(vote, homeGroup, mepPosition),
};
}
/**
* Resolve the ISO-week Monday for an arbitrary YYYY-MM-DD string.
*
* @internal Exported for testing.
*/
export function isoWeekStart(date: string): string {
if (date === '' || !/^\d{4}-\d{2}-\d{2}$/.test(date)) return date;
const [yearStr, monthStr, dayStr] = date.split('-');
const year = Number(yearStr);
const month = Number(monthStr);
const day = Number(dayStr);
const d = new Date(Date.UTC(year, month - 1, day));
// getUTCDay: 0=Sun..6=Sat → shift so Monday=0.
const dow = (d.getUTCDay() + 6) % 7;
d.setUTCDate(d.getUTCDate() - dow);
const yyyy = String(d.getUTCFullYear()).padStart(4, '0');
const mm = String(d.getUTCMonth() + 1).padStart(2, '0');
const dd = String(d.getUTCDate()).padStart(2, '0');
return `${yyyy}-${mm}-${dd}`;
}
/**
* Bucket classified votes into ISO-week buckets keyed by Monday's date.
*
* Buckets are returned in chronological order (oldest first). Votes without
* a valid sittingDate are bucketed under the empty-string key and *placed at
* the tail* (sorting empty-string ahead of real dates would otherwise
* distort week-over-week shift detection and baseline computations).
*
* @param votes - Sequence of classified MEP votes.
* @returns Per-week aggregates with computed defection / abstention rates.
*/
export function bucketByWeek(votes: ClassifiedVote[]): WeekBucket[] {
const byWeek = new Map<string, WeekBucket>();
for (const v of votes) {
if (v.alignment === 'absent') continue;
const week = isoWeekStart(v.sittingDate);
let bucket = byWeek.get(week);
if (bucket === undefined) {
bucket = {
weekStart: week,
voted: 0,
decisive: 0,
defections: 0,
abstentions: 0,
crossPartyAlignments: 0,
voteIds: [],
defectionRate: 0,
abstentionRate: 0,
};
byWeek.set(week, bucket);
}
bucket.voted += 1;
bucket.voteIds.push(v.voteId);
if (v.alignment === 'abstained') {
bucket.abstentions += 1;
} else {
bucket.decisive += 1;
if (v.alignment === 'defected') {
bucket.defections += 1;
// Only true cross-party signals: defections that also matched a
// non-home group's majority. See `WeekBucket.crossPartyAlignments`.
if (v.matchingOtherGroups.length > 0) bucket.crossPartyAlignments += 1;
}
}
}
const buckets = [...byWeek.values()];
// Chronological sort that pushes the "no valid date" bucket (weekStart === '')
// to the tail instead of letting it sort first lexicographically.
buckets.sort((a, b) => {
Iif (a.weekStart === '' && b.weekStart === '') return 0;
Iif (a.weekStart === '') return 1;
Iif (b.weekStart === '') return -1;
return a.weekStart.localeCompare(b.weekStart);
});
for (const b of buckets) {
b.defectionRate = b.decisive > 0
? Math.round((b.defections / b.decisive) * 100 * 100) / 100
: 0;
b.abstentionRate = b.voted > 0
? Math.round((b.abstentions / b.voted) * 100 * 100) / 100
: 0;
}
return buckets;
}
/**
* Compute sample mean & standard deviation (ddof = 1) for a series of
* numbers. Returns `{mean:0, stdev:0}` for empty input.
*/
export function computeBaseline(values: number[]): BaselineSummary {
if (values.length === 0) return { mean: 0, stdev: 0 };
const sum = values.reduce((acc, v) => acc + v, 0);
const mean = sum / values.length;
if (values.length < 2) return { mean, stdev: 0 };
const variance = values.reduce((acc, v) => acc + (v - mean) ** 2, 0) / (values.length - 1);
return { mean, stdev: Math.sqrt(variance) };
}
/**
* Single-sample z-score with a guard for zero variance.
*
* When `stdev` is zero (single data point or constant series) the z-score is
* undefined; this helper returns `0` so callers can treat constant series as
* "no anomaly" without special-casing.
*/
export function zScore(value: number, baseline: BaselineSummary): number {
if (baseline.stdev === 0) return 0;
return (value - baseline.mean) / baseline.stdev;
}
/**
* Find weeks whose `rateKey` value has a z-score ≥ `threshold` against the
* baseline computed across *all* buckets (the MEP's own rolling baseline
* within the period).
*
* @param buckets - Output of {@link bucketByWeek}.
* @param rateKey - Which rate to evaluate (`'defectionRate'` or `'abstentionRate'`).
* @param threshold - Minimum z-score that triggers an anomaly (default {@link DEFAULT_Z_SCORE_THRESHOLD}).
* @returns Outlier weeks (chronological order).
*/
export function findOutlierWeeks(
buckets: WeekBucket[],
rateKey: 'defectionRate' | 'abstentionRate',
threshold: number = DEFAULT_Z_SCORE_THRESHOLD
): OutlierWeek[] {
if (buckets.length < 2) return [];
const values = buckets.map(b => b[rateKey]);
const baseline = computeBaseline(values);
if (baseline.stdev === 0) return [];
const outliers: OutlierWeek[] = [];
for (const b of buckets) {
const z = zScore(b[rateKey], baseline);
if (z >= threshold) {
outliers.push({
weekStart: b.weekStart,
value: b[rateKey],
z: Math.round(z * 100) / 100,
baselineMean: Math.round(baseline.mean * 100) / 100,
voteIds: [...b.voteIds],
});
}
}
return outliers;
}
/**
* Find consecutive-week pairs where the defection rate jumped by `≥ threshold`
* percentage points.
*
* Only positive jumps are reported (the MEP becoming *more* defection-prone).
*
* @param buckets - Output of {@link bucketByWeek}.
* @param threshold - Minimum percentage-point delta (default {@link DEFAULT_WOW_THRESHOLD_PP}).
* @returns Detected shifts in chronological order.
*/
export function findWoWShifts(
buckets: WeekBucket[],
threshold: number = DEFAULT_WOW_THRESHOLD_PP
): WoWShift[] {
const shifts: WoWShift[] = [];
for (let i = 1; i < buckets.length; i += 1) {
const prev = buckets[i - 1];
const curr = buckets[i];
Iif (prev === undefined || curr === undefined) continue;
const delta = curr.defectionRate - prev.defectionRate;
if (delta >= threshold) {
shifts.push({
fromWeek: prev.weekStart,
toWeek: curr.weekStart,
delta: Math.round(delta * 100) / 100,
previousRate: Math.round(prev.defectionRate * 100) / 100,
voteIds: [...prev.voteIds, ...curr.voteIds],
});
}
}
return shifts;
}
/**
* Find sub-windows (weeks) where the MEP defected toward non-home-group
* majorities on ≥ `share` of decisive RCVs.
*
* Skips weeks with fewer than {@link MIN_SUBWINDOW_DECISIVE_VOTES} decisive
* votes to avoid spurious 100% windows on tiny samples.
*
* Units: the `share` parameter is a **fraction** (0–1). The returned
* {@link CrossPartyWindow.sharePercent} field is converted to a
* **percentage** (0–100) for consumer ergonomics — keep this distinction in
* mind when wiring severity classifiers (e.g. `severityFromShare` expects
* percent input).
*
* @param buckets - Output of {@link bucketByWeek}.
* @param share - Minimum share (0–1) of decisive RCVs where the MEP
* defected toward non-home group majorities (default
* {@link DEFAULT_CROSS_PARTY_SHARE}).
* @returns Windows in chronological order.
*/
export function findCrossPartyAlignmentWindows(
buckets: WeekBucket[],
share: number = DEFAULT_CROSS_PARTY_SHARE
): CrossPartyWindow[] {
const windows: CrossPartyWindow[] = [];
for (const b of buckets) {
if (b.decisive < MIN_SUBWINDOW_DECISIVE_VOTES) continue;
const observed = b.crossPartyAlignments / b.decisive;
if (observed >= share) {
windows.push({
weekStart: b.weekStart,
sharePercent: Math.round(observed * 100 * 100) / 100,
decisive: b.decisive,
voteIds: [...b.voteIds],
});
}
}
return windows;
}
/**
* Resolve confidence based on the number of RCV votes inspected for the MEP.
*
* - `HIGH` when `≥50` votes,
* - `MEDIUM` when `10–49` votes,
* - `LOW` when `<10` votes.
*/
export function coverageConfidence(rcvVotesInspected: number): 'HIGH' | 'MEDIUM' | 'LOW' {
if (rcvVotesInspected >= 50) return 'HIGH';
if (rcvVotesInspected >= 10) return 'MEDIUM';
return 'LOW';
}
/**
* Hard cap on the number of plenary weeks enumerated by {@link iteratePlenaryWeeks}
* — ~6 months of weekly fan-out per request. The {@link MAX_PLENARY_WEEKS}th
* week is the last one returned. Truncation is not implied by length alone:
* callers should combine `length === MAX_PLENARY_WEEKS` with an input-window
* overflow check (for example, {@link detectWindowTruncation} in
* `detectVotingAnomalies`).
*/
export const MAX_PLENARY_WEEKS = 26;
/**
* Parse and validate a `[from, to]` window for {@link iteratePlenaryWeeks}.
* Returns the parsed millisecond bounds, or `null` for empty/malformed/
* reversed inputs. Extracted to keep `iteratePlenaryWeeks` below the
* cyclomatic-complexity ceiling.
*
* @internal
*/
function parseIsoDateWindow(from: string, to: string): { fromMs: number; toMs: number } | null {
if (from === '' || to === '') return null;
if (!/^\d{4}-\d{2}-\d{2}$/.test(from) || !/^\d{4}-\d{2}-\d{2}$/.test(to)) return null;
const fromMs = Date.parse(`${from}T00:00:00Z`);
const toMs = Date.parse(`${to}T00:00:00Z`);
Iif (Number.isNaN(fromMs) || Number.isNaN(toMs)) return null;
if (fromMs > toMs) return null;
return { fromMs, toMs };
}
/**
* Enumerate the Monday (ISO-week start, UTC) of every plenary week whose
* Mon–Fri span intersects the inclusive `[from, to]` date range.
*
* Used by `detect_voting_anomalies` to drive the multi-week DOCEO fetch loop
* so the per-MEP rolling baseline reflects every plenary week in the requested
* window rather than the single week containing `to`.
*
* Behaviour:
*
* - Returns an empty array when either bound is missing/empty or unparsable.
* - Returns an empty array when `from > to`.
* - A week is included only when its Mon–Fri span intersects `[from, to]`
* (i.e. `weekStart + 4d >= from`). This prevents `from` on Sat/Sun from
* pulling in the prior week, whose Friday ended before `from`.
* - Weeks are ordered chronologically (oldest first) for stable iteration.
* - Capped at {@link MAX_PLENARY_WEEKS} (≈6 months) per request, retaining
* the *most recent* in-scope weeks (enumeration walks backward from `to`
* and is then reversed). Callers should treat `result.length ===
* MAX_PLENARY_WEEKS` AND a wider input window as truncation and surface a
* `weeksTruncated` warning.
*
* @param from - Inclusive period start (YYYY-MM-DD).
* @param to - Inclusive period end (YYYY-MM-DD).
* @returns Mondays of intersecting plenary weeks, oldest first.
*/
export function iteratePlenaryWeeks(from: string, to: string): string[] {
const bounds = parseIsoDateWindow(from, to);
if (bounds === null) return [];
const { fromMs, toMs } = bounds;
const DAY_MS = 24 * 3_600_000;
const WEEK_MS = 7 * DAY_MS;
// Plenary weeks run Mon–Fri; intersection with `[from, to]` requires
// `weekStart <= to` AND `weekStart + 4d >= from`.
const FRIDAY_OFFSET_MS = 4 * DAY_MS;
// Walk backward from the ISO-week containing `to` so the
// MAX_PLENARY_WEEKS cap retains the *most recent* in-scope weeks.
const endMonday = isoWeekStart(to);
let cursorMs = Date.parse(`${endMonday}T00:00:00Z`);
const weeks: string[] = [];
while (weeks.length < MAX_PLENARY_WEEKS) {
if (cursorMs + FRIDAY_OFFSET_MS < fromMs) break;
Eif (cursorMs <= toMs) {
const d = new Date(cursorMs);
const yyyy = String(d.getUTCFullYear()).padStart(4, '0');
const mm = String(d.getUTCMonth() + 1).padStart(2, '0');
const dd = String(d.getUTCDate()).padStart(2, '0');
weeks.push(`${yyyy}-${mm}-${dd}`);
}
cursorMs -= WEEK_MS;
}
weeks.reverse();
return weeks;
}
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