/**
 * OPT Scanner — Optimization Lens / mechanism-fit (v5.7 Fase 1 Chunk 2a)
 *
 * The first detector of the "is the config OPTIMAL?" axis (vs. the existing
 * "is it CORRECT?" scanners). It reads the machine-readable best-practices
 * register (knowledge/best-practices.json) and flags config that works but uses
 * a mechanism a better one would fit — the deterministic half of the hybrid
 * motor (the opus analyzer for prose-judgment cases is Chunk 2b).
 *
 *   CA-OPT-001  A multi-step procedure in CLAUDE.md should be a SKILL (BP-MECH-003).
 *               CLAUDE.md is for facts Claude holds every turn; a procedure there
 *               costs always-loaded tokens whether or not you run it, and a skill's
 *               body loads only on invoke. Detection is deliberately CONSERVATIVE
 *               (a run of >= 6 consecutive numbered steps) to keep precision high —
 *               the negative corpus in the tests proves null false-positives.
 *               Framed as a Missed opportunity (humanizer), severity LOW.
 *
 * Provenance: the recommendation + claim come from the register entry (only a
 * `confirmed` entry is used user-facing — Verifiseringsplikt); an inline default
 * is the graceful fallback if the register is unavailable. Fixture-gated: the
 * marketplace-medium CLAUDE.md has no numbered lists, so it emits nothing (SC-5
 * byte-stable; the additive OPT scanner entry is stripped from frozen baselines).
 *
 * Zero external dependencies.
 */

import { readFile } from 'node:fs/promises';
import { finding, scannerResult } from './lib/output.mjs';
import { SEVERITY } from './lib/severity.mjs';
import { parseFrontmatter } from './lib/yaml-parser.mjs';
import { loadRegister, getEntry } from './lib/best-practices-register.mjs';

const SCANNER = 'OPT';
const STEP_THRESHOLD = 6;
const STEP_RE = /^\s*\d+\.\s+\S/;
const PROCEDURE_TITLE = 'A multi-step procedure in CLAUDE.md belongs in a skill';

// Graceful fallback if the register is missing/unreadable (the register is the
// source of truth; this keeps the scanner working without it).
const DEFAULT_MECH_003 = {
  claim:
    'A multi-step procedure in CLAUDE.md should be a skill — CLAUDE.md is for facts Claude ' +
    'should hold all the time; procedures belong in skills.',
  recommendation:
    'Extract the procedure into .claude/skills/; its body then loads only on invoke instead ' +
    'of every turn.',
};

/** Return the confirmed register entry for `id`, or null (→ caller uses default). */
function confirmedEntry(id) {
  try {
    const e = getEntry(loadRegister(), id);
    return e && e.confidence === 'confirmed' ? e : null;
  } catch {
    return null;
  }
}

/**
 * Longest run of consecutive numbered-list items. Blank lines and indented
 * continuation lines neither extend nor break a run; any other non-step line
 * breaks it. Conservative by design (a wrapped, non-indented step line ends the
 * run → undercount, never overcount).
 * @param {string} text
 * @returns {{count:number, startIndex:number, firstStep:string}}
 */
function longestNumberedRun(text) {
  const lines = String(text).split('\n');
  let maxRun = 0;
  let maxStartIdx = 0;
  let maxFirstStep = '';
  let run = 0;
  let runStartIdx = 0;
  let runFirstStep = '';
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (STEP_RE.test(line)) {
      if (run === 0) {
        runStartIdx = i;
        runFirstStep = line.trim();
      }
      run++;
      if (run > maxRun) {
        maxRun = run;
        maxStartIdx = runStartIdx;
        maxFirstStep = runFirstStep;
      }
    } else if (line.trim() === '' || /^\s+\S/.test(line)) {
      // blank or indented continuation — part of the list, neither step nor break
    } else {
      run = 0;
    }
  }
  return { count: maxRun, startIndex: maxStartIdx, firstStep: maxFirstStep };
}

export async function scan(targetPath, discovery) {
  const start = Date.now();
  const findings = [];
  const claudeMdFiles = ((discovery && discovery.files) || []).filter((f) => f.type === 'claude-md');

  const entry = confirmedEntry('BP-MECH-003');
  const claim = (entry && entry.claim) || DEFAULT_MECH_003.claim;
  const recommendation = (entry && entry.recommendation) || DEFAULT_MECH_003.recommendation;

  let filesScanned = 0;
  for (const file of claudeMdFiles) {
    let content;
    try {
      content = await readFile(file.absPath, 'utf-8');
    } catch {
      continue;
    }
    filesScanned++;

    const parsed = parseFrontmatter(content);
    const body = parsed.body || content;
    const bodyStartLine = parsed.bodyStartLine || 1;
    const run = longestNumberedRun(body);

    if (run.count >= STEP_THRESHOLD) {
      findings.push(
        finding({
          scanner: SCANNER,
          severity: SEVERITY.low,
          title: PROCEDURE_TITLE,
          description: claim,
          file: file.relPath || file.absPath,
          line: bodyStartLine + run.startIndex,
          evidence: run.firstStep,
          recommendation,
          category: 'mechanism-fit',
          details: {
            mechanism: 'skill',
            steps: run.count,
            register: entry ? entry.id : null,
            source: entry ? entry.source.url : null,
            confidence: entry ? entry.confidence : null,
          },
        }),
      );
    }
  }

  return scannerResult(SCANNER, 'ok', findings, filesScanned, Date.now() - start);
}