# All files / src/utils votingBaseline.ts

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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';
    }