import { existsSync, readFileSync } from 'node:fs'
import { basename, dirname, join } from 'node:path'
import { stripFrontmatter } from '@/frontmatter'

const INDEX_TOPIC = 'index'

/**
 * The two roots a topic resolves against, in precedence order. `docs/` holds
 * consumer-facing reference and `.claude/context/` holds per-domain internal
 * narrative, so a name present in both resolves to the consumer-facing copy.
 */
const ROOTS: readonly string[] = ['docs', join('.claude', 'context')]

export interface ResolvedTopic {
  readonly path: string
  readonly rel: string
}

/**
 * A domain too large for one file splits into `<domain>/` with a generated
 * `index.md`, so a topic names either a sibling file or such a folder. Both
 * spellings resolve to the same name a caller types.
 */
export function resolveTopic(
  root: string,
  topic: string,
): ResolvedTopic | undefined {
  for (const dir of ROOTS) {
    const candidates = [
      join(dir, `${topic}.md`),
      join(dir, topic, `${INDEX_TOPIC}.md`),
    ]

    for (const rel of candidates) {
      const path = join(root, rel)
      if (existsSync(path)) return { path, rel }
    }
  }

  return undefined
}

/**
 * Names every topic a `get` could resolve, listed per root in the order the
 * roots are searched. Shown when a topic misses, so it doubles as the answer to
 * what the caller should have typed.
 */
export function listTopics(root: string): string[] {
  const topics: string[] = []

  for (const dir of ROOTS) {
    const cwd = join(root, dir)
    if (!existsSync(cwd)) continue

    const files = [
      ...new Bun.Glob('*.md').scanSync({ cwd, onlyFiles: true, dot: true }),
    ]
      .map((name) => basename(name, '.md'))
      .filter((name) => name !== INDEX_TOPIC)

    const folders = [
      ...new Bun.Glob(`*/${INDEX_TOPIC}.md`).scanSync({
        cwd,
        onlyFiles: true,
        dot: true,
      }),
    ].map((name) => dirname(name))

    topics.push(...[...files, ...folders].sort())
  }

  return topics
}

export function readTopic(topic: ResolvedTopic): string {
  return stripFrontmatter(readFileSync(topic.path, 'utf8'))
}