/**
 * cli:derive-uc-coverage — validate.ts
 *
 * Spec validation + prerequisites: the module folder must exist and carry at
 * least one `use-case.md` — an empty report must mean "no UC to cover",
 * never "inputs absent". `pagespecs/` is OPTIONAL (the PRD leg reports
 * `no-pagespecs` loudly instead of failing — SCR-024 runs before the PRD
 * exists).
 */
import { existsSync, readdirSync } from 'node:fs'
import { isAbsolute, join } from 'node:path'
import { DeriveUcCoverageInputSchema, type ValidationResult } from './types.js'

function hasUseCaseDoc(dir: string, depth: number): boolean {
  if (depth > 3) return false
  if (existsSync(join(dir, 'use-case.md'))) return true
  try {
    // Same skip-set as index.ts's collectDocs — the old `/^[a-z]/` filter
    // was the fail-open twin index.ts already removed: an uppercase/digit/
    // accented section folder made the prerequisite claim « no use-case.md »
    // while collectDocs would have read it.
    return readdirSync(dir, { withFileTypes: true }).some(
      (e) =>
        e.isDirectory() &&
        !e.name.startsWith('_') &&
        !e.name.startsWith('.') &&
        e.name !== 'pagespecs' &&
        e.name !== 'node_modules' &&
        hasUseCaseDoc(join(dir, e.name), depth + 1),
    )
  } catch {
    return false
  }
}

export function validateSpec(raw: unknown, workdir?: string): ValidationResult {
  const parsed = DeriveUcCoverageInputSchema.safeParse(raw)
  if (!parsed.success) {
    return {
      valid: false,
      errors: parsed.error.issues.map((i) => `[${i.path.join('.')}] ${i.message}`),
    }
  }
  const spec = parsed.data
  const resolvedBaRoot = isAbsolute(spec.baRoot) ? spec.baRoot : join(workdir ?? process.cwd(), spec.baRoot)
  const errors: string[] = []
  const moduleDir = join(resolvedBaRoot, spec.app, spec.module)
  if (!existsSync(moduleDir)) {
    errors.push(`Module folder not found: ${moduleDir}`)
    return { valid: false, errors, spec, resolvedBaRoot }
  }
  if (!hasUseCaseDoc(moduleDir, 0)) {
    errors.push(
      `${spec.app}/${spec.module} has no use-case.md (module or section) — run /ba-create-use-case (phase 3) first.`,
    )
  }
  return { valid: errors.length === 0, errors, spec, resolvedBaRoot }
}