#!/usr/bin/env bun
/**
 * gstack-pr-prep-score — pure collision scorer for the /pr-prep audit.
 *
 * Extracts the Step 4 bucketing rules from pr-prep/SKILL.md into one
 * deterministic, unit-tested place (the v0.2.0 seed the skill flags). The
 * skill's inline bash remains the spec; this is the canonical implementation
 * it points to. No network, no git — pure function of its JSON input.
 *
 * Input (stdin or --file <path>), one commit's candidate set:
 *   {
 *     "commitKeywords": ["reindex", "cli", "fix"],
 *     "changedFiles":   ["src/reindex.ts"],
 *     "candidates": [
 *       { "state": "open_pr",       "titleKeywords": [...], "changedFiles": [...] },
 *       { "state": "open_issue",    "titleKeywords": [...] },
 *       { "state": "merged_recent", "titleKeywords": [...] },
 *       { "state": "closed_issue",  "titleKeywords": [...] }
 *     ]
 *   }
 *
 * Output (stdout): { "bucket", "topScore", "openIssueCount", "reasons": [...] }
 * Buckets: EXACT_DUP | OVERLAP | SIBLING | CLEAN  (precedence in that order).
 * Exit 0 always; the bucket is the signal (the skill maps EXACT_DUP -> exit 1).
 */

export type CandidateState = 'open_pr' | 'open_issue' | 'merged_recent' | 'closed_issue';

export interface Candidate {
  state: CandidateState;
  titleKeywords?: string[];
  changedFiles?: string[];
  ref?: string; // e.g. "#1358" — passed through into reasons
}

export interface ScoreInput {
  commitKeywords?: string[];
  changedFiles?: string[];
  candidates?: Candidate[];
}

export type Bucket = 'EXACT_DUP' | 'OVERLAP' | 'SIBLING' | 'CLEAN';

export interface ScoreResult {
  bucket: Bucket;
  topScore: number;
  openIssueCount: number;
  reasons: string[];
}

// State weighting from SKILL.md Step 4.
const STATE_WEIGHT: Record<CandidateState, number> = {
  open_pr: 1.0,
  open_issue: 0.7,
  merged_recent: 0.6,
  closed_issue: 0.2,
};

function norm(tokens: string[] | undefined): Set<string> {
  return new Set((tokens ?? []).map((t) => t.toLowerCase().trim()).filter(Boolean));
}

export function jaccard(a: string[] | undefined, b: string[] | undefined): number {
  const sa = norm(a);
  const sb = norm(b);
  if (sa.size === 0 || sb.size === 0) return 0;
  let inter = 0;
  for (const x of sa) if (sb.has(x)) inter++;
  const union = sa.size + sb.size - inter;
  return union === 0 ? 0 : inter / union;
}

export function score(input: ScoreInput): ScoreResult {
  const candidates = input.candidates ?? [];
  const reasons: string[] = [];
  let topScore = 0;
  let exactDup = false;
  let overlap = false;
  let sibling = false;
  let openIssueCount = 0;
  let hasOpenPr = false;
  let onlyClosed = candidates.length > 0;

  for (const c of candidates) {
    const titleJ = jaccard(input.commitKeywords, c.titleKeywords);
    // File overlap only meaningful for open PRs (we can read their diff).
    const fileJ =
      c.state === 'open_pr' ? jaccard(input.changedFiles, c.changedFiles) : 0;
    const overlapJ = Math.max(titleJ, fileJ);
    const s = overlapJ * STATE_WEIGHT[c.state];
    if (s > topScore) topScore = s;
    if (c.state !== 'closed_issue') onlyClosed = false;
    if (c.state === 'open_issue') openIssueCount++;
    if (c.state === 'open_pr') hasOpenPr = true;

    const ref = c.ref ? `${c.ref} ` : '';
    // EXACT_DUP: any OPEN PR with title Jaccard >=0.6 OR file overlap >=0.6.
    if (c.state === 'open_pr' && (titleJ >= 0.6 || fileJ >= 0.6)) {
      exactDup = true;
      reasons.push(
        `${ref}EXACT_DUP: open PR titleJ=${titleJ.toFixed(2)} fileJ=${fileJ.toFixed(2)}`,
      );
      continue;
    }
    // OVERLAP: any OPEN PR/issue with score >=0.3.
    if ((c.state === 'open_pr' || c.state === 'open_issue') && s >= 0.3) {
      overlap = true;
      reasons.push(`${ref}OVERLAP: open ${c.state} score=${s.toFixed(2)}`);
      continue;
    }
    // SIBLING: merged-recently with any overlap.
    if (c.state === 'merged_recent' && overlapJ > 0) {
      sibling = true;
      reasons.push(`${ref}SIBLING: merged-recent overlap=${overlapJ.toFixed(2)}`);
    }
  }

  // OVERLAP also triggers on >=3 OPEN issues even when none individually scores high.
  if (openIssueCount >= 3) {
    overlap = true;
    reasons.push(`OVERLAP: ${openIssueCount} open issues`);
  }
  // SIBLING: OPEN issues present but no OPEN PR (and not already EXACT_DUP/OVERLAP).
  if (openIssueCount > 0 && !hasOpenPr) sibling = true;

  let bucket: Bucket;
  if (exactDup) bucket = 'EXACT_DUP';
  else if (overlap) bucket = 'OVERLAP';
  else if (sibling) bucket = 'SIBLING';
  else bucket = 'CLEAN';

  if (bucket === 'CLEAN' && reasons.length === 0) {
    reasons.push(onlyClosed ? 'only closed issues' : 'no hits above threshold');
  }
  return { bucket, topScore: Number(topScore.toFixed(4)), openIssueCount, reasons };
}

// CLI entry — skip when imported by the test.
if (import.meta.main) {
  const fileArg = process.argv.indexOf('--file');
  const raw =
    fileArg !== -1
      ? await Bun.file(process.argv[fileArg + 1]).text()
      : await Bun.stdin.text();
  let input: ScoreInput;
  try {
    input = JSON.parse(raw || '{}');
  } catch {
    console.error('gstack-pr-prep-score: input is not valid JSON');
    process.exit(2);
  }
  process.stdout.write(JSON.stringify(score(input)) + '\n');
}