// Memory store: roots, files, and the compiled indexes.
//
// The layout is deliberately the same at every level, so a project-local
// `.memory/` and the global root are interchangeable:
//
//   ROOT.md              total plan: goals, hard rules, registry, routing table
//   <category>/
//     index.md           one line per file — COMPILED, never hand-edited
//     <slug>.md          the memory itself, with frontmatter
//
// Two rules keep the indexes honest:
//
//  1. `index.md` tables and ROOT's registry/routing tables are generated from
//     frontmatter. A hand-maintained index drifts from reality; a generated
//     one cannot.
//  2. Hand-written regions in ROOT.md live outside `<!-- auto:begin -->`
//     markers and are never touched by the compiler.

import fs from "node:fs"
import path from "node:path"
import { type Frontmatter, parseFrontmatter, stringifyFrontmatter } from "./frontmatter.ts"

export type RootScope = "global" | "project"

export interface MemoryRoot {
  readonly scope: RootScope
  /** Stable identity used in state keys: "global" or "project:<id>". */
  readonly key: string
  /** Human label shown in injected context. */
  readonly label: string
  readonly dir: string
  /** Project wins ties; global is the fallback. */
  readonly rank: number
}

export interface MemoryFile {
  readonly root: MemoryRoot
  /** Path relative to the root, e.g. "pitfalls/sqlite-cjk.md". */
  readonly rel: string
  readonly abs: string
  readonly category: string
  readonly slug: string
  readonly fm: Frontmatter
  readonly body: string
  readonly title: string
  /** One-line description shown in indexes and injected summaries. */
  readonly summary: string
  /** The "重点" column in index.md. */
  readonly highlight: string
  /** Scenarios that should pull this file in. Drives ROOT's routing table. */
  readonly loadWhen: string[]
  readonly pinned: boolean
  readonly created: number
  readonly updated: number
  readonly mtime: number
}

export interface FileState {
  hitCount: number
  lastHitAt: number
}

const AUTO_BEGIN = "<!-- auto:begin"
const AUTO_END = "<!-- auto:end"
const STATE_FILE = ".state.json"

/** Categories whose files are hard rules: always resident, never decayed. */
const HARD_RULES_CATEGORY = "rules"

export function isHardRule(file: MemoryFile): boolean {
  if (file.category === HARD_RULES_CATEGORY) return true
  return String(file.fm.kind ?? "").toLowerCase() === "rule"
}

// ---------------------------------------------------------------------------
// Roots
// ---------------------------------------------------------------------------

export function globalRoot(configDir: string): MemoryRoot {
  return {
    scope: "global",
    key: "global",
    label: "全局",
    dir: path.join(configDir, "memory"),
    rank: 10,
  }
}

export function projectRoot(canonical: string, projectID: string): MemoryRoot {
  return {
    scope: "project",
    key: `project:${projectID}`,
    label: path.basename(canonical) || "项目",
    dir: path.join(canonical, ".memory"),
    rank: 20,
  }
}

/**
 * Walk up from `dir` looking for a `.memory/` directory. This is what makes the
 * feature work in a monorepo or a nested checkout, where the session's
 * canonical project root may be several levels above the file being edited.
 */
export function findNearestRoot(start: string, depth = 4): string | undefined {
  let current = path.resolve(start)
  for (let i = 0; i <= depth; i++) {
    const candidate = path.join(current, ".memory")
    if (fs.existsSync(path.join(candidate, "ROOT.md"))) return candidate
    const parent = path.dirname(current)
    if (parent === current) break
    current = parent
  }
  return undefined
}

// ---------------------------------------------------------------------------
// Scanning
// ---------------------------------------------------------------------------

export function scanRoot(root: MemoryRoot): MemoryFile[] {
  const out: MemoryFile[] = []
  let entries: fs.Dirent[]
  try {
    entries = fs.readdirSync(root.dir, { withFileTypes: true })
  } catch {
    return out
  }

  for (const entry of entries) {
    if (!entry.isDirectory() || entry.name.startsWith(".")) continue
    const category = entry.name
    const dir = path.join(root.dir, category)
    let files: fs.Dirent[]
    try {
      files = fs.readdirSync(dir, { withFileTypes: true })
    } catch {
      continue
    }
    for (const file of files) {
      // `index.md` is compiled output; ROOT.md lives at the root, not here.
      if (!file.isFile() || !file.name.endsWith(".md")) continue
      if (file.name === "index.md" || file.name === "ROOT.md") continue
      const abs = path.join(dir, file.name)
      const parsed = readMemoryFile(root, abs, category, file.name)
      if (parsed) out.push(parsed)
    }
  }
  return out
}

function readMemoryFile(root: MemoryRoot, abs: string, category: string, name: string): MemoryFile | undefined {
  let raw: string
  let stat: fs.Stats
  try {
    raw = fs.readFileSync(abs, "utf8")
    stat = fs.statSync(abs)
  } catch {
    return undefined
  }
  const { data, body } = parseFrontmatter(raw)
  const slug = name.replace(/\.md$/, "")
  return {
    root,
    rel: path.posix.join(category, name),
    abs,
    category,
    slug,
    fm: data,
    body,
    title: String(data.title ?? firstHeading(body) ?? slug),
    summary: String(data.summary ?? deriveSummary(body, slug)),
    highlight: String(data.highlight ?? ""),
    loadWhen: toStringArray(data.load_when ?? data.loadWhen),
    pinned: data.pinned === true || data.pinned === "true",
    created: toNumber(data.created) ?? stat.mtimeMs,
    updated: toNumber(data.updated) ?? stat.mtimeMs,
    mtime: stat.mtimeMs,
  }
}

function firstHeading(body: string): string | undefined {
  const m = /^#{1,3}\s+(.+)$/m.exec(body)
  return m?.[1]?.trim()
}

/**
 * Fallback summary when frontmatter omits one: the first real paragraph,
 * flattened to a single line and clipped. Falls back to the slug so the index
 * never has an empty cell.
 */
function deriveSummary(body: string, slug: string): string {
  const lines = body.split(/\r?\n/)
  const buf: string[] = []
  for (const line of lines) {
    const text = line.trim()
    if (!text || text.startsWith("#") || text.startsWith("```")) continue
    buf.push(text)
    if (buf.join(" ").length > 90) break
  }
  const text = buf.join(" ").replace(/\s+/g, " ").trim()
  if (!text) return slug
  return text.length > 140 ? `${text.slice(0, 139)}…` : text
}

function toStringArray(value: unknown): string[] {
  if (Array.isArray(value)) return value.map((v) => String(v)).filter(Boolean)
  if (typeof value === "string" && value.trim()) {
    return value
      .split(/[,，]/)
      .map((s) => s.trim())
      .filter(Boolean)
  }
  return []
}

function toNumber(value: unknown): number | undefined {
  if (typeof value === "number" && Number.isFinite(value)) return value
  if (typeof value === "string") {
    const n = Number(value)
    if (Number.isFinite(n)) return n
    const parsed = Date.parse(value)
    if (Number.isFinite(parsed)) return parsed
  }
  return undefined
}

// ---------------------------------------------------------------------------
// State (hit counts) — derived, never the source of truth
// ---------------------------------------------------------------------------

export function readState(root: MemoryRoot): Record<string, FileState> {
  try {
    const raw = fs.readFileSync(path.join(root.dir, STATE_FILE), "utf8")
    const parsed = JSON.parse(raw)
    return typeof parsed === "object" && parsed ? (parsed as Record<string, FileState>) : {}
  } catch {
    return {}
  }
}

/** Write state atomically so a crash mid-write cannot truncate the file. */
export function writeState(root: MemoryRoot, state: Record<string, FileState>): void {
  fs.mkdirSync(root.dir, { recursive: true })
  const target = path.join(root.dir, STATE_FILE)
  const tmp = `${target}.tmp-${process.pid}`
  fs.writeFileSync(tmp, `${JSON.stringify(state, null, 2)}\n`, "utf8")
  fs.renameSync(tmp, target)
}

// ---------------------------------------------------------------------------
// Writing memories
// ---------------------------------------------------------------------------

export interface WriteInput {
  category: string
  slug: string
  title?: string
  summary?: string
  highlight?: string
  body: string
  kind?: string
  loadWhen?: string[]
  pinned?: boolean
  supersedes?: string
}

const CATEGORY_RE = /^[a-z0-9][a-z0-9._-]{0,31}$/
const SLUG_RE = /^[A-Za-z0-9][A-Za-z0-9._-]{0,63}$/

export function validateCategory(category: string): string | undefined {
  if (!CATEGORY_RE.test(category)) {
    return `category must be lowercase [a-z0-9._-] (got ${JSON.stringify(category)})`
  }
  return undefined
}

export function validateSlug(slug: string): string | undefined {
  if (!SLUG_RE.test(slug)) {
    return `slug must match [A-Za-z0-9][A-Za-z0-9._-]* (got ${JSON.stringify(slug)})`
  }
  return undefined
}

export function writeMemory(root: MemoryRoot, input: WriteInput, now = Date.now()): MemoryFile {
  const dir = path.join(root.dir, input.category)
  fs.mkdirSync(dir, { recursive: true })
  const abs = path.join(dir, `${input.slug}.md`)
  const rel = path.posix.join(input.category, `${input.slug}.md`)

  const existing = fs.existsSync(abs) ? readMemoryFile(root, abs, input.category, `${input.slug}.md`) : undefined
  const data: Frontmatter = {
    id: rel,
    // A file under `rules/` is a hard rule regardless of what it was labelled
    // before, so the category-derived value wins over a stale stored one. An
    // explicit `kind` from the caller still wins over both.
    kind: input.kind ?? (input.category === "rules" ? "rule" : String(existing?.fm.kind ?? "fact")),
    summary: input.summary ?? String(existing?.fm.summary ?? ""),
    highlight: input.highlight ?? String(existing?.fm.highlight ?? ""),
    created: existing?.created ?? now,
    updated: now,
  }
  if (input.loadWhen?.length) data.load_when = input.loadWhen
  else if (existing?.loadWhen.length) data.load_when = existing.loadWhen
  if (input.pinned ?? existing?.pinned) data.pinned = true
  if (input.supersedes) data.supersedes = input.supersedes

  const body = input.body.trim() || String(existing?.body ?? "")
  fs.writeFileSync(abs, stringifyFrontmatter(data, body), "utf8")
  return readMemoryFile(root, abs, input.category, `${input.slug}.md`)!
}

/** Mark `supersedes` (a rel path) as replaced, keeping the row for audit. */
export function markSuperseded(root: MemoryRoot, target: string, byRel: string, now = Date.now()): void {
  const abs = path.join(root.dir, target)
  if (!fs.existsSync(abs) || !target.endsWith(".md")) return
  const { data, body } = parseFrontmatter(fs.readFileSync(abs, "utf8"))
  data.superseded_by = byRel
  data.updated = now
  fs.writeFileSync(abs, stringifyFrontmatter(data, body), "utf8")
}

// ---------------------------------------------------------------------------
// Compiled indexes
// ---------------------------------------------------------------------------

/**
 * Replace the region belonging to one specific `<!-- auto:begin <label> -->`.
 *
 * The label must be part of the match. Matching on a bare `auto:begin` pairs
 * the first marker with the *next* marker regardless of which region was meant,
 * which silently swaps two unrelated tables.
 */
export function replaceAutoRegion(text: string, label: string, generated: string): string {
  const re = new RegExp(
    `(${escapeRe(`${AUTO_BEGIN} ${label}`)}[^\\n]*\\n)[\\s\\S]*?(${escapeRe(AUTO_END)})`,
  )
  if (!re.test(text)) return text
  return text.replace(re, (_m, open: string, close: string) => `${open}${generated}${close}`)
}

function escapeRe(value: string): string {
  return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&")
}

function cell(value: string): string {
  return value.replace(/\|/g, "\\|").replace(/\r?\n/g, " ").trim() || "—"
}

export interface CategoryIndex {
  category: string
  files: MemoryFile[]
}

export function groupByCategory(files: MemoryFile[]): CategoryIndex[] {
  const map = new Map<string, MemoryFile[]>()
  for (const file of files) {
    const list = map.get(file.category) ?? []
    list.push(file)
    map.set(file.category, list)
  }
  return [...map.entries()]
    .map(([category, list]) => ({
      category,
      files: list.sort((a, b) => a.slug.localeCompare(b.slug)),
    }))
    .sort((a, b) => a.category.localeCompare(b.category))
}

/** Rewrite `<root>/<category>/index.md` for every category that has files. */
export function compileCategoryIndexes(root: MemoryRoot, files: MemoryFile[]): string[] {
  const written: string[] = []
  for (const { category, files: list } of groupByCategory(files)) {
    const heading = `# ${category} 索引`
    const rows = list.map((f) => `| ${cell(f.slug + ".md")} | ${cell(f.summary)} | ${cell(f.highlight)} |`)
    const table = [
      "| 文件 | 概述 | 重点 |",
      "|---|---|---|",
      ...rows,
      "",
    ].join("\n")
    const generated = `\n| 文件 | 概述 | 重点 |\n|---|---|---|\n${rows.join("\n")}\n`
    // Create the directory before writing: a root can be compiled before anything
  // was ever written into it (e.g. the global root was seeded but the project
  // root has no memories yet), and the compiler must not depend on that.
  fs.mkdirSync(path.join(root.dir, category), { recursive: true })
    const target = path.join(root.dir, category, "index.md")

    let existing = ""
    try {
      existing = fs.readFileSync(target, "utf8")
    } catch {
      /* first build */
    }
    const next = existing.includes(AUTO_BEGIN)
      ? replaceAutoRegion(existing, category, generated)
      : `${heading}\n\n${AUTO_BEGIN} ${category}\n${generated}${AUTO_END}\n`

    // Skip the write when nothing changed: index.md is regenerated often and a
    // stable mtime keeps file watchers (and git) quiet.
    if (existing !== next) fs.writeFileSync(target, next, "utf8")
    written.push(path.join(category, "index.md"))
  }

  // Prune indexes whose category lost every memory. A stale index listing
  // deleted files is exactly the drift this whole design exists to prevent, so
  // it must not be left behind.
  pruneEmptyIndexes(root, files)
  return written
}

function pruneEmptyIndexes(root: MemoryRoot, files: MemoryFile[]): void {
  const populated = new Set(files.map((f) => f.category))
  let entries: fs.Dirent[]
  try {
    entries = fs.readdirSync(root.dir, { withFileTypes: true })
  } catch {
    return
  }
  for (const entry of entries) {
    if (!entry.isDirectory() || entry.name.startsWith(".")) continue
    if (populated.has(entry.name)) continue
    // A hand-written index in an empty category is the user's content; only
    // remove one this compiler produced.
    const target = path.join(root.dir, entry.name, "index.md")
    try {
      const text = fs.readFileSync(target, "utf8")
      if (text.includes(AUTO_BEGIN)) fs.rmSync(target)
    } catch {
      /* nothing to prune */
    }
  }
}

export interface CompiledRoot {
  registry: string
  routing: string
}

export function compileRootTables(root: MemoryRoot, files: MemoryFile[]): CompiledRoot {
  const categories = groupByCategory(files)

  const registryRows = categories.map(({ category, files: list }) => {
    const pinned = list.filter((f) => f.pinned).length
    const desc = describeCategory(category, list)
    return `| ${cell(category + "/")} | ${cell(desc)} | ${list.length}${pinned ? ` (${pinned} 钉住)` : ""} |`
  })
  const registry = `\n| 目录 | 概述 | 条目 |\n|---|---|---|\n${registryRows.join("\n")}\n`

  // The routing table is the union of every file's `load_when`, so it stays
  // correct without anyone maintaining it.
  const routingRows: string[] = []
  for (const { category, files: list } of categories) {
    for (const file of list) {
      for (const trigger of file.loadWhen) {
        routingRows.push(`| ${cell(trigger)} | ${cell(file.rel)} | ${cell(file.kind ?? "fact")} |`)
      }
    }
  }
  routingRows.sort((a, b) => a.localeCompare(b))
  const routing = routingRows.length
    ? `\n| 场景 / 触发 | 读哪个文件 | 类型 |\n|---|---|---|\n${routingRows.join("\n")}\n`
    : `\n_暂无 load_when 标记的记忆。给文件加 frontmatter 的 \`load_when:\` 即可自动进入路由表。_\n`

  return { registry, routing }
}

function describeCategory(category: string, files: MemoryFile[]): string {
  const pinned = files.find((f) => isHardRule(f))
  if (pinned && category === HARD_RULES_CATEGORY) return "不可违反的硬规则，常驻"
  const first = files[0]
  if (first?.fm.category_desc) return String(first.fm.category_desc)
  return first ? first.summary.slice(0, 40) : "（空）"
}

/** Recompile ROOT.md's generated regions and write it if it does not exist. */
export function compileRoot(root: MemoryRoot, files: MemoryFile[]): string {
  // Same reason as the category index: ROOT.md may be the first thing written
  // into a root that does not exist yet.
  fs.mkdirSync(root.dir, { recursive: true })
  const target = path.join(root.dir, "ROOT.md")
  const { registry, routing } = compileRootTables(root, files)

  let existing: string | undefined
  try {
    existing = fs.readFileSync(target, "utf8")
  } catch {
    /* first build */
  }

  const text = existing ?? defaultRootTemplate(root)
  // Labeled regions, replaced in order. Each call is independent because the
  // label is part of the match — see replaceAutoRegion.
  let next = replaceAutoRegion(text, "registry", registry)
  next = replaceAutoRegion(next, "routing", routing)

  if (next !== existing) fs.writeFileSync(target, next, "utf8")
  return next
}

export function defaultRootTemplate(root: MemoryRoot): string {
  const where =
    root.scope === "global"
      ? "跨项目通用记忆：你的偏好、技术决策、通用约定、踩过的坑。"
      : "本项目专属记忆：项目目标、事实、决策、坑。优先级高于全局根。"

  return `# 记忆总纲 — ${root.label}

> ${where}
> 由 memory 插件维护。\`auto:begin\` / \`auto:end\` 之间的表格是编译产物，不要手改；
> 其余区域随便写。

## 当前目标

<!-- 手写：现在在做什么。插件不会碰这里。 -->

## 铁规则（常驻，永不衰减）

<!-- 手写：只写硬性要求。rules/ 目录下的文件会被自动常驻注入。 -->

## 目录登记

${AUTO_BEGIN} registry
${AUTO_END}

## 加载路由表

${AUTO_BEGIN} routing
${AUTO_END}
`
}

/** Create the skeleton (ROOT.md + category dirs) for a root that does not exist. */
export function ensureRoot(root: MemoryRoot, categories: string[]): void {
  fs.mkdirSync(root.dir, { recursive: true })
  for (const category of categories) fs.mkdirSync(path.join(root.dir, category), { recursive: true })
  if (!fs.existsSync(path.join(root.dir, "ROOT.md"))) {
    fs.writeFileSync(path.join(root.dir, "ROOT.md"), defaultRootTemplate(root), "utf8")
  }
}