/**
 * TOK Scanner — Token Hotspots / Opus 4.7 patterns
 *
 * Detects three structural Opus 4.7-era token-efficiency patterns:
 *   CA-TOK-001  cache-breaking volatile top in CLAUDE.md (medium)
 *   CA-TOK-002  redundant tool/permission declarations (low)
 *   CA-TOK-003  deep @import chain (>2 hops) (medium)
 *
 * Note: the v4 sonnet-era signature pattern was removed in v5 F5 — too noisy
 * and not actionable; live token costs are better surfaced by the hotspots
 * ranking and per-pattern findings.
 *
 * Also ranks every discovered config source by estimated tokens and exposes
 * a `hotspots` array (≤10 entries, possibly fewer for tiny projects) on the
 * scanner result.
 *
 * Pattern catalogue: knowledge/opus-4.7-patterns.md
 * Token heuristic:   estimateTokens() in scanners/lib/active-config-reader.mjs
 *
 * Zero external dependencies.
 */

import { resolve, dirname, isAbsolute } from 'node:path';
import { stat } from 'node:fs/promises';
import { readTextFile } from './lib/file-discovery.mjs';
import { finding, scannerResult } from './lib/output.mjs';
import { SEVERITY } from './lib/severity.mjs';
import { findImports, parseJson } from './lib/yaml-parser.mjs';
import { estimateTokens, readActiveConfig } from './lib/active-config-reader.mjs';

const SCANNER = 'TOK';

const VOLATILE_TOP_LINES = 30;
const VOLATILE_PATTERNS = [
  /\{timestamp\}/i,
  /\{uuid\}/i,
  /\{date\}/i,
  /\{session(?:_id)?\}/i,
  /\bactivity log\b/i,
  /^\s*\d{4}-\d{2}-\d{2}T\d{2}:\d{2}/m, // ISO timestamps at line start
  /^\s*\[\d{4}-\d{2}-\d{2}/m,            // [YYYY-MM-DD ...] log lines
];

const MAX_IMPORT_DEPTH = 2;

const HOTSPOTS_MAX = 10;

/**
 * Classify a discovered config file into a token-estimation kind.
 */
function tokenKind(type) {
  if (type === 'claude-md' || type === 'agent-md' || type === 'command-md' || type === 'skill-md' || type === 'rule') {
    return 'markdown';
  }
  if (type === 'settings-json' || type === 'mcp-json' || type === 'hooks-json' ||
      type === 'plugin-json' || type === 'claude-json' || type === 'keybindings-json') {
    return 'json';
  }
  return 'markdown';
}

async function fileExists(absPath) {
  try { await stat(absPath); return true; } catch { return false; }
}

function resolveImportPath(importPath, fromFile) {
  let p = importPath.trim();
  if (!p) return null;
  if (p.startsWith('~/')) {
    const home = process.env.HOME || process.env.USERPROFILE || '';
    p = resolve(home, p.slice(2));
  } else if (p.startsWith('~')) {
    const home = process.env.HOME || process.env.USERPROFILE || '';
    p = resolve(home, p.slice(1));
  } else if (!isAbsolute(p)) {
    p = resolve(dirname(fromFile), p);
  }
  return p;
}

/**
 * Compute the deepest @import chain reachable from `startFile`.
 * Returns max depth observed (0 = no imports, 1 = direct import, etc.).
 */
async function maxImportDepth(startFile, contentCache) {
  let maxDepth = 0;
  async function walk(file, depth, visited) {
    if (depth > 20 || visited.has(file)) return;
    visited.add(file);
    if (depth > maxDepth) maxDepth = depth;
    let content = contentCache.get(file);
    if (content === undefined) {
      content = await readTextFile(file);
      contentCache.set(file, content);
    }
    if (!content) return;
    const imports = findImports(content);
    for (const imp of imports) {
      const target = resolveImportPath(imp.path, file);
      if (!target) continue;
      if (!(await fileExists(target))) continue;
      await walk(target, depth + 1, new Set(visited));
    }
  }
  await walk(startFile, 0, new Set());
  return maxDepth;
}

/**
 * Detect cache-breaking volatile content in the first VOLATILE_TOP_LINES
 * lines of a CLAUDE.md file.
 */
function detectVolatileTop(content) {
  if (!content) return false;
  const top = content.split('\n').slice(0, VOLATILE_TOP_LINES).join('\n');
  return VOLATILE_PATTERNS.some(rx => rx.test(top));
}

/**
 * Detect redundant or overlapping permission entries in a settings JSON object.
 * Returns array of `{list, entry, reason}` for reporting.
 */
function detectRedundantPermissions(settings) {
  const issues = [];
  if (!settings || typeof settings !== 'object') return issues;
  const perms = settings.permissions;
  if (!perms || typeof perms !== 'object') return issues;
  for (const list of ['allow', 'deny', 'ask']) {
    const arr = perms[list];
    if (!Array.isArray(arr)) continue;
    const seen = new Set();
    for (const entry of arr) {
      if (typeof entry !== 'string') continue;
      // Exact duplicate
      if (seen.has(entry)) {
        issues.push({ list, entry, reason: 'duplicate entry' });
        continue;
      }
      seen.add(entry);
    }
    // Subset detection: an entry like `Read(src/**)` is redundant if `Read(**)`
    // or bare `Read` is also present in the same list.
    for (const entry of arr) {
      if (typeof entry !== 'string') continue;
      const tool = entry.replace(/\(.*\)$/, '').trim();
      const hasBare = arr.includes(tool);
      const hasWildcard = arr.includes(`${tool}(**)`) || arr.includes(`${tool}(*)`);
      const isBare = entry === tool;
      const isWildcard = entry === `${tool}(**)` || entry === `${tool}(*)`;
      if (!isBare && !isWildcard && (hasBare || hasWildcard)) {
        issues.push({ list, entry, reason: `overlapped by ${hasBare ? tool : `${tool}(**)`}` });
      }
    }
  }
  return issues;
}

/**
 * Build the ranked hotspots array.
 *
 * v5 F1: when activeConfig is available, expand each MCP server into its own
 * hotspot entry (richer signal than the parent .mcp.json file). Discovery
 * files remain the primary source for CLAUDE.md / settings / skills.
 */
async function buildHotspots(discovery, targetPath, activeConfig) {
  const ranked = [];
  for (const f of discovery.files) {
    const kind = tokenKind(f.type);
    const tokens = estimateTokens(f.size, kind);
    if (tokens <= 0) continue;
    ranked.push({
      absPath: f.absPath,
      relPath: f.relPath || f.absPath.replace(targetPath + '/', ''),
      type: f.type,
      scope: f.scope,
      size: f.size,
      estimated_tokens: tokens,
    });
  }
  // Per-MCP-server entries from activeConfig (each ~500+ tokens at runtime,
  // not represented by the parent .mcp.json file size alone).
  if (activeConfig && Array.isArray(activeConfig.mcpServers)) {
    for (const m of activeConfig.mcpServers) {
      if (!m || !m.enabled) continue;
      ranked.push({
        absPath: m.source || `mcp:${m.name}`,
        relPath: `mcp:${m.name} (${m.source})`,
        type: 'mcp-server',
        scope: m.source,
        size: 0,
        estimated_tokens: m.estimatedTokens || 0,
      });
    }
  }
  ranked.sort((a, b) => b.estimated_tokens - a.estimated_tokens);

  const top = ranked.slice(0, HOTSPOTS_MAX);
  const out = [];
  for (let i = 0; i < top.length; i++) {
    const h = top[i];
    out.push({
      source: h.relPath || h.absPath,
      estimated_tokens: h.estimated_tokens,
      rank: i + 1,
      recommendations: hotspotRecommendations(h),
    });
  }

  return out;
}

function hotspotRecommendations(h) {
  const recs = [];
  if (h.type === 'claude-md') {
    recs.push('Move volatile top-of-file content to the bottom or extract to an @import-ed file.');
    recs.push('Split overlong CLAUDE.md into focused @imports (≤200 lines each).');
  } else if (h.type === 'settings-json' || h.type === 'mcp-json' || h.type === 'hooks-json') {
    recs.push('Deduplicate overlapping entries — each duplicate inflates the per-turn schema payload.');
    recs.push('Move rarely-used permissions to a project-local override.');
  } else if (h.type === 'skill-md' || h.type === 'agent-md' || h.type === 'command-md') {
    recs.push('Tighten the description field — it loads on every turn even when the body does not.');
  } else {
    recs.push('Review whether this source needs to load on every turn.');
  }
  // Always cap to 1–3 recommendations
  return recs.slice(0, 3);
}

/**
 * Main scanner entry point.
 * @param {string} targetPath
 * @param {{files: Array<{absPath:string, relPath:string, type:string, scope:string, size:number}>, skipped?:number}} discovery
 */
export async function scan(targetPath, discovery) {
  const start = Date.now();
  const findings = [];
  let filesScanned = 0;
  const contentCache = new Map();

  // v5 F1: pull active-config snapshot once. Failures are non-fatal — the
  // scanner falls back to the discovery-only path used in v4.
  let activeConfig = null;
  try {
    activeConfig = await readActiveConfig(targetPath, {});
  } catch {
    activeConfig = null;
  }

  // ── Pattern A: cache-breaking volatile top in CLAUDE.md ──
  for (const f of discovery.files) {
    if (f.type !== 'claude-md') continue;
    filesScanned++;
    const content = await readTextFile(f.absPath);
    contentCache.set(f.absPath, content);
    if (detectVolatileTop(content)) {
      findings.push(finding({
        scanner: SCANNER,
        severity: SEVERITY.medium,
        title: 'Cache-breaking volatile content at top of CLAUDE.md',
        description:
          `The first ${VOLATILE_TOP_LINES} lines of ${f.relPath || f.absPath} contain volatile ` +
          'tokens (timestamps, session ids, or activity logs). Volatile content above stable ' +
          'content defeats Opus 4.7 prompt-cache reuse on every turn.',
        file: f.absPath,
        recommendation:
          'Move volatile sections to the bottom of the file, or extract them to an @import-ed ' +
          'file outside the cached prefix. Keep the first 30 lines stable across turns.',
        category: 'token-efficiency',
      }));
    }
  }

  // ── Pattern B: redundant tool/permission declarations ──
  for (const f of discovery.files) {
    if (f.type !== 'settings-json') continue;
    filesScanned++;
    const content = await readTextFile(f.absPath);
    if (!content) continue;
    const parsed = parseJson(content);
    if (!parsed) continue;
    const issues = detectRedundantPermissions(parsed);
    if (issues.length === 0) continue;
    findings.push(finding({
      scanner: SCANNER,
      severity: SEVERITY.low,
      title: 'Redundant permission declarations',
      description:
        `${f.relPath || f.absPath} contains ${issues.length} redundant or overlapping ` +
        `permission entr${issues.length === 1 ? 'y' : 'ies'}. Each duplicate inflates the ` +
        'tool-schema payload sent on every turn.',
      file: f.absPath,
      evidence: issues.slice(0, 5).map(i => `${i.list}: "${i.entry}" (${i.reason})`).join('; '),
      recommendation:
        'Deduplicate the permissions.allow / permissions.deny arrays. Prefer the most ' +
        'specific entry that still grants the intended access.',
      category: 'token-efficiency',
    }));
  }

  // ── Pattern C: deep @import chain (>2 hops) ──
  for (const f of discovery.files) {
    if (f.type !== 'claude-md') continue;
    const depth = await maxImportDepth(f.absPath, contentCache);
    if (depth > MAX_IMPORT_DEPTH) {
      findings.push(finding({
        scanner: SCANNER,
        severity: SEVERITY.medium,
        title: 'Deep @import chain defeats prompt-cache reuse',
        description:
          `${f.relPath || f.absPath} reaches @import depth ${depth} (>${MAX_IMPORT_DEPTH} hops). ` +
          'Each @import boundary fragments the prompt-cache prefix; deeply chained imports ' +
          'defeat caching for the deepest content even when it never changes.',
        file: f.absPath,
        evidence: `Max chain depth: ${depth}`,
        recommendation:
          'Flatten the @import chain to ≤2 hops. Inline the deepest layer back into its parent.',
        category: 'token-efficiency',
      }));
    }
  }

  // ── Hotspots ranking ──
  const hotspots = await buildHotspots(discovery, targetPath, activeConfig);

  // ── Total estimated tokens (sum of every discovered source + activeConfig MCP) ──
  let totalTokens = 0;
  for (const f of discovery.files) {
    totalTokens += estimateTokens(f.size, tokenKind(f.type));
  }
  if (activeConfig && Array.isArray(activeConfig.mcpServers)) {
    for (const m of activeConfig.mcpServers) {
      if (m && m.enabled) totalTokens += m.estimatedTokens || 0;
    }
  }

  const result = scannerResult(SCANNER, 'ok', findings, filesScanned, Date.now() - start);
  result.hotspots = hotspots;
  result.total_estimated_tokens = totalTokens;
  if (activeConfig) {
    result.activeConfig = {
      claudeMdEstimatedTokens: activeConfig.claudeMd?.estimatedTokens ?? 0,
      mcpServerCount: activeConfig.mcpServers?.length ?? 0,
      pluginCount: activeConfig.plugins?.length ?? 0,
      skillCount: activeConfig.skills?.length ?? 0,
    };
  }
  return result;
}