/**
 * Versionless, JSON-lines wire protocol between the Node host and the CPython subprocess. Frames
 * travel on the child's fd 3 (one JSON object per line), leaving stdout/stderr free for the
 * program's own output. Host treats every inbound frame as hostile because model code can post
 * anything through the same fd; the Python bootstrap trusts host replies.
 * @module @deepseek-ai/dsh-code-runtime-python/src/protocol
 */

// The protocol channel is fd 3 from the child's perspective — the host pins it
// positionally via `stdio: ['pipe','pipe','pipe','pipe']` (index.ts), and the
// Python bootstrap reads the same constant from its own protocol.py.

/**
 * What the host sends immediately after spawn, as the first line on fd 3. The
 * Python bootstrap reads this, applies resource limits, then waits for the
 * subsequent run frame. Separated from the run so the run message stays
 * pure model input.
 */
export interface BootMessage {
  type: 'boot'
  /** RLIMIT_CPU seconds; the Python bootstrap sets this on itself before executing model code. */
  cpuSeconds: number
  /** RLIMIT_AS bytes; caps address space so a runaway allocation fails cleanly. */
  addressSpaceBytes: number
  /** Shared byte budget for captured log text (Python-side ledger). */
  maxLogBytes: number
  /** Byte cap for the rendered completion value. */
  maxValueBytes: number
  /**
   * The namespaces to materialize inside the program (globals + names;
   * functions stay host-side). `errorClass` asks the bootstrap to mint a
   * program-visible exception class under that global: rejected calls raise
   * its instances carrying the member name on `memberNameProperty`.
   */
  namespaces: { global: string; names: string[]; errorClass?: { name: string; memberNameProperty: string } }[]
}

// The run request `{ type: 'run', program }` follows BootMessage once the
// child acknowledges with `boot-ack`; the host sends it as an inline literal
// (it carries only the model's program body — caps and bindings crossed on boot).

/** Python → host: acknowledges boot completed and resource limits are in place. */
interface BootAckMessage {
  type: 'boot-ack'
}

/** Python → host: one bridged binding call (`await tools.name(args)` inside the program). */
interface CallMessage {
  type: 'call'
  /** Python-issued correlation id; the host answers each id at most once and ignores duplicates. */
  id: number
  /** The namespace global the call targets. */
  global: string
  /** The function name within the namespace. */
  name: string
  /** The JSON-safe argument the model program passed. */
  args: unknown
}

/**
 * Python → host: captured text, streamed eagerly so output survives a
 * mid-run termination (RLIMIT_CPU, SIGTERM/SIGKILL, host wall-timeout).
 */
interface LogMessage {
  type: 'log'
  text: string
  /**
   * Set when this frame IS the child ledger's truncation marker rather than
   * program output. The two ledgers can exhaust at different points — one
   * child entry larger than `maxLogBytes` sends only the marker while the host
   * ledger is still nearly empty — so the host cannot infer the child's state
   * from its own budget, and comparing the text against the marker string
   * would also honour a program that printed that string itself. Carrying it
   * as a field lets the host stop capturing at the same point the child did
   * and keeps exactly one marker in `logs`.
   */
  truncated?: boolean
}

/**
 * Python → host: the program settled. `error` carries a program exception
 * (traceback text), an `invalid-output` (completion value was not lossless
 * JSON), or an `output-limit` (serialized completion exceeded the configured
 * cap); wall/CPU budgets, aborts, and substrate death are observed host-side.
 * From the honest child `value` is present only on a clean completion that
 * produced one, and crosses as exact lossless JSON — never substituted or
 * truncated. A forged frame CAN carry both `value` and `error`;
 * {@link validateChildFrame} preserves both rather than guessing which to drop,
 * so a consumer MUST check `error` first and ignore `value` when it is set.
 */
interface DoneMessage {
  type: 'done'
  value?: unknown
  error?: { kind: 'exception' | 'invalid-output' | 'output-limit'; message: string }
}

/**
 * Every message the Python side sends. The member interfaces stay module-
 * private: consumers match on the union's discriminant; the host sends the
 * boot and run frames as inline literals.
 */
export type ChildToHost = BootAckMessage | CallMessage | LogMessage | DoneMessage

/** Host → Python: the answer to one {@link CallMessage}. */
export type ReplyMessage =
  | { type: 'reply'; id: number; ok: true; value: unknown }
  | { type: 'reply'; id: number; ok: false; message: string }

/**
 * The in-band marker text announcing that log capture stopped at the byte
 * budget. Shared wire vocabulary: the Python-side LogBuffer emits it when ITS
 * ledger exhausts, and the host emits identical text when its own ledger drops
 * a frame first (forged fd-3 traffic, stray stdout bytes) — a truncated run
 * reads the same however the cap was hit.
 * @param maxBytes - the configured `maxLogBytes` the marker names.
 * @returns the marker line.
 */
export function logTruncationMarker(maxBytes: number): string {
  return `[dsh-code-runtime-python] log capture truncated at ${maxBytes} bytes`
}

/**
 * Serialize one JSON-parse-produced value without recursion. `JSON.stringify`
 * recurses per nesting level and throws `RangeError` a few thousand levels
 * deep, but the seam's `CodeJsonValue` has no depth limit — an honest deep
 * completion or binding resolution below the byte budget must cross intact
 * (the worker backend's wire is equally stack-safe). Callers must pass a value
 * produced by `JSON.parse` (or equally JSON-plain): only `null`, finite
 * numbers, booleans, strings, dense arrays, and plain objects — this encoder
 * validates nothing. Output matches compact `JSON.stringify` byte for byte
 * EXCEPT on an integral double beyond the safe range, where {@link scalarJson}
 * emits the exact integer's BigInt digits rather than `JSON.stringify`'s rounded
 * spelling (`1152921504606846976`, not `...847000`) so the seam's lossless-JSON
 * promise holds across the wire.
 * @param value - a JSON-plain value (e.g. straight from `JSON.parse`).
 * @returns the compact JSON encoding.
 */
export function encodeJsonPlain(value: unknown): string {
  type Task = { text: string } | { value: unknown }
  const chunks: string[] = []
  const tasks: Task[] = [{ value }]
  for (let task = tasks.pop(); task !== undefined; task = tasks.pop()) {
    if ('text' in task) {
      chunks.push(task.text)
      continue
    }
    const current = task.value
    if (typeof current === 'string') {
      chunks.push(JSON.stringify(current))
    } else if (Array.isArray(current)) {
      chunks.push('[')
      tasks.push({ text: ']' })
      for (let index = current.length - 1; index >= 0; index--) {
        if (index < current.length - 1) tasks.push({ text: ',' })
        tasks.push({ value: current[index] })
      }
    } else if (typeof current === 'object' && current !== null) {
      const record = current as Record<string, unknown>
      chunks.push('{')
      tasks.push({ text: '}' })
      const keys = Object.keys(record)
      for (let index = keys.length - 1; index >= 0; index--) {
        const key = keys[index] as string
        if (index < keys.length - 1) tasks.push({ text: ',' })
        tasks.push({ value: record[key] })
        tasks.push({ text: `${JSON.stringify(key)}:` })
      }
    } else {
      chunks.push(scalarJson(current))
    }
  }
  return chunks.join('')
}

/**
 * One scalar (null, boolean, finite number) as JSON text. A beyond-safe-range
 * integral double needs BigInt digits: `String(2 ** 60)` emits the ROUNDED
 * `...847000` form, and echoing that to the child would silently change the
 * integer the seam promised to carry losslessly — `BigInt(2 ** 60)` prints the
 * exact `...846976` the double actually holds.
 * @param current - a JSON-plain scalar (JSON.parse emits nothing else).
 * @returns its JSON encoding.
 */
function scalarJson(current: unknown): string {
  if (typeof current === 'number' && Number.isInteger(current) && !Number.isSafeInteger(current)) {
    return BigInt(current).toString()
  }
  return String(current)
}

/**
 * Meter a forged done value's compact-JSON byte length AND its number
 * losslessness in one bounded traversal, stopping the instant `maxBytes` is
 * crossed. A forged `done.value` arrives straight off fd 3 and can sit anywhere
 * below the 256 MiB frame ceiling while `maxValueBytes` defaults to 32 KiB. The
 * previous split — an unbounded `hasNonLosslessNumber` scan in
 * {@link validateChildFrame} followed by a separate byte meter — pushed every
 * member of a wide flat payload onto a scan stack before any cap check ran, so
 * a below-ceiling forgery could still force a hundreds-of-megabytes host
 * allocation. Folding both jobs here rejects over-budget BEFORE enqueuing an
 * array's or object's children, keeping the traversal O(cap). A non-lossless
 * number (non-finite, negative zero) is caught only when the value fits the
 * budget — an over-budget value is rejected regardless, so the distinction is
 * moot. Same JSON-plain precondition and traversal shape as
 * {@link encodeJsonPlain}; per-scalar byte length is measured through
 * {@link scalarJson} (matching the encoder, so a beyond-safe-range integer
 * meters its exact BigInt digits, not `JSON.stringify`'s rounded spelling) and
 * `JSON.stringify` for strings.
 * @param value - a JSON-plain value (e.g. straight from `JSON.parse`).
 * @param maxBytes - the completion-value budget in bytes.
 * @returns `{ ok: true, bytes }` with the exact serialized size, or
 * `{ ok: false, reason }` — `over-budget` once the size exceeds `maxBytes`,
 * `non-lossless` on a non-finite or negative-zero number.
 */
export function checkDoneValue(value: unknown, maxBytes: number): { ok: true; bytes: number } | { ok: false; reason: 'over-budget' | 'non-lossless' } {
  let bytes = 0
  const stack: unknown[] = [value]
  while (stack.length > 0) {
    const current = stack.pop()
    if (typeof current === 'number') {
      if (!Number.isFinite(current) || Object.is(current, -0)) return { ok: false, reason: 'non-lossless' }
      bytes += Buffer.byteLength(scalarJson(current), 'utf8')
    } else if (typeof current === 'string') {
      // Lower-bound BEFORE materializing the escaped form: every UTF-16 code
      // unit is at least one UTF-8 byte plus the two quotes, so a huge or
      // control-heavy forged string (whose escaped copy expands severalfold)
      // is rejected without allocating that copy.
      if (bytes + current.length + 2 > maxBytes) return { ok: false, reason: 'over-budget' }
      bytes += Buffer.byteLength(JSON.stringify(current), 'utf8')
    } else if (Array.isArray(current)) {
      // Brackets plus one comma per gap; elements add themselves. Reject
      // BEFORE enqueuing children: every element serializes to at least one
      // byte, so a forged flat array below the frame ceiling but far above
      // the budget fails here without growing the host stack by millions of
      // entries first.
      bytes += 2 + (current.length > 1 ? current.length - 1 : 0)
      if (bytes + current.length > maxBytes) return { ok: false, reason: 'over-budget' }
      for (const item of current) stack.push(item)
    } else if (typeof current === 'object' && current !== null) {
      const record = current as Record<string, unknown>
      // Count own keys WITHOUT Object.entries/Object.keys (either allocates one
      // slot per member up front), AND bail mid-count the instant the minimum
      // encoding exceeds the budget: braces (+2), each entry a quoted key
      // (>= 2 bytes) + colon + >= 1-byte value (>= 4 bytes), and a comma per
      // gap. A forged wide object with millions of keys and a small cap must
      // fail in O(cap), not walk its whole breadth first. `bytes` still holds
      // the pre-object total throughout this loop.
      let count = 0
      for (const key in record) {
        if (!Object.hasOwn(record, key)) continue
        count += 1
        if (bytes + 2 + count * 4 + (count - 1) > maxBytes) return { ok: false, reason: 'over-budget' }
      }
      // The loop's final iteration already proved the whole object's lower
      // bound fits, so no separate post-count check is needed here.
      bytes += 2 + (count > 1 ? count - 1 : 0)
      for (const key in record) {
        if (!Object.hasOwn(record, key)) continue
        // The same string lower bound, before escaping the key.
        if (bytes + key.length + 3 > maxBytes) return { ok: false, reason: 'over-budget' }
        bytes += Buffer.byteLength(JSON.stringify(key), 'utf8') + 1
        stack.push(record[key])
      }
    } else {
      bytes += Buffer.byteLength(scalarJson(current), 'utf8')
    }
    if (bytes > maxBytes) return { ok: false, reason: 'over-budget' }
  }
  return { ok: true, bytes }
}

/**
 * Whether a raw JSON line contains an integer token that would lose precision
 * as a JavaScript number. `JSON.parse` silently rounds such a token
 * (`9007199254740993` becomes `...992`) BEFORE any validation can see it, so
 * the check must read the source text; a beyond-safe-range token whose double
 * parse round-trips exactly (`2**53`, `2**60`) is lossless and passes. The scan walks the line skipping string literals (a digit run
 * inside a string is data, not a number token) and tests every number token
 * in plain integer form — no fraction or exponent, which parse as doubles by
 * intent. A reviver cannot do this job: the reviver walk recurses per nesting
 * level and would reintroduce the depth limit `encodeJsonPlain` removes.
 * @param line - the raw UTF-8 text of one JSON-lines frame.
 * @returns true when an unsafe integer token is present outside strings.
 */
export function hasUnsafeIntegerToken(line: string): boolean {
  for (let index = 0; index < line.length; index++) {
    const char = line[index]
    if (char === '"') {
      // Skip the string literal, honoring backslash escapes.
      for (index++; index < line.length; index++) {
        if (line[index] === '\\') index++
        else if (line[index] === '"') break
      }
      continue
    }
    if (char === '-' || (char !== undefined && char >= '0' && char <= '9')) {
      let end = index + 1
      while (end < line.length) {
        const c = line[end] as string
        if ((c >= '0' && c <= '9') || c === '.' || c === 'e' || c === 'E' || c === '+' || c === '-') end++
        else break
      }
      const token = line.slice(index, end)
      // Beyond the safe range an integer token is still lossless IFF the
      // double parse round-trips exactly (2**53 does; 2**53+1 rounds) — the
      // canonical boundary accepts every JS-double-exact value, so only a
      // genuinely rounding token marks the frame as forged.
      if (/^-?\d+$/.test(token)) {
        const parsed = Number(token)
        // A token that parses to Infinity is trivially lossy; a finite
        // beyond-safe-range one is lossy only when the BigInt round-trip
        // disagrees.
        if (!Number.isFinite(parsed)) return true
        if (!Number.isSafeInteger(parsed) && BigInt(token) !== BigInt(parsed)) return true
      }
      index = end - 1
    }
  }
  return false
}

/**
 * Lazily yield one plain object's own enumerable property values. A generator
 * (not `Object.values`/`Object.entries`) because {@link hasNonLosslessNumber}
 * traverses breadth it cannot bound: those helpers copy the whole member list
 * up front, so a wide forged object would cost a second full-breadth
 * allocation before a single value is examined.
 * @param record - a JSON-parse-produced object.
 * @yields each own enumerable property value, in key order.
 */
function* ownValues(record: object): Generator {
  for (const key in record) {
    if (Object.hasOwn(record, key)) yield (record as Record<string, unknown>)[key]
  }
}

/**
 * Whether a JSON.parse-produced value contains a number outside lossless
 * JSON: non-finite (`1e400` parses to `Infinity`) or negative zero (`-0.0`
 * parses to JS `-0`, whose sign bit a re-serialization drops). The honest
 * child's validator rejects these before sending, so a frame carrying one is
 * forged.
 *
 * Runs on `call.args`, which — unlike a completion value — has NO seam byte
 * cap, so there is no budget to reject a wide payload against the way
 * {@link checkDoneValue} does. The traversal therefore holds ONE cursor per
 * NESTING LEVEL (an array or {@link ownValues} iterator) instead of one entry
 * per member: a forged flat `args` just below the 256 MiB frame ceiling would
 * otherwise push tens of millions of stack entries — and `Object.values` would
 * copy each object's full breadth — allocating hundreds of megabytes beyond
 * what `JSON.parse` already holds. Iterative either way, so a deep frame
 * cannot overflow the host stack.
 * @param value - a JSON-parse-produced value from an fd-3 frame.
 * @returns true when any contained number is non-finite or negative zero.
 */
export function hasNonLosslessNumber(value: unknown): boolean {
  const cursors: Iterator<unknown>[] = [[value].values()]
  while (cursors.length > 0) {
    // The loop condition guarantees a top cursor.
    const cursor = cursors.at(-1) as Iterator<unknown>
    const step = cursor.next()
    if (step.done === true) {
      cursors.pop()
      continue
    }
    const current = step.value
    if (typeof current === 'number') {
      if (!Number.isFinite(current) || Object.is(current, -0)) return true
    } else if (Array.isArray(current)) {
      cursors.push((current as unknown[]).values())
    } else if (typeof current === 'object' && current !== null) {
      cursors.push(ownValues(current))
    }
  }
  return false
}

/**
 * Runtime shape gate for inbound fd-3 traffic. Model code has full access to
 * fd 3 and can post anything — `null`, primitives, poisoned fields — so the
 * compile-time union means nothing here: every field is validated and REBUILT
 * before the host reads it (forged extras never ride along; a non-number id
 * can never be echoed into a reply). Junk returns `undefined` and is dropped
 * so a throw in the host's `message` handler cannot crash the host process.
 * @param raw - one JSON-parsed frame from fd 3.
 * @returns the rebuilt frame, or `undefined` to drop it silently.
 */
export function validateChildFrame(raw: unknown): ChildToHost | undefined {
  if (typeof raw !== 'object' || raw === null) return undefined
  const m = raw as Record<string, unknown>
  switch (m.type) {
    case 'boot-ack':
      return { type: 'boot-ack' }
    case 'log':
      if (typeof m.text !== 'string') return undefined
      // Rebuilt, not passed through: a forged `truncated` of any other type
      // would reach the host as a truthy value and silence capture for the
      // rest of the run. Only the literal `true` counts.
      return { type: 'log', text: m.text, ...m.truncated === true ? { truncated: true } : {} }
    case 'call': {
      // The id must be a finite number: it is echoed verbatim into the reply
      // frame, and a forged `1e400` id (Infinity after JSON.parse) would make
      // the reply unencodable as strict JSON. Negative zero is rejected too:
      // it passes `Number.isFinite`, but the reply re-serializes it as `0`
      // (`JSON.stringify({id:-0})` is `{"id":0}`), colliding with a real call
      // whose id is `0` — the honest child never issues `-0`.
      if (typeof m.id !== 'number' || !Number.isFinite(m.id) || Object.is(m.id, -0) || typeof m.global !== 'string' || typeof m.name !== 'string') return undefined
      // A forged frame can omit `args` entirely; rebuilding it as `undefined`
      // would invoke the binding with a non-JSON value, bypassing the
      // lossless-JSON argument boundary. Any PRESENT value is JSON-plain by
      // construction (the frame came from JSON.parse), so presence is the
      // whole check.
      if (!Object.hasOwn(m, 'args')) return undefined
      // JSON.parse yields Infinity for 1e400 and preserves -0; both are
      // outside lossless JSON, and the honest child never sends them.
      if (hasNonLosslessNumber(m.args)) return undefined
      return { type: 'call', id: m.id, global: m.global, name: m.name, args: m.args }
    }
    case 'done': {
      // The value passes through untouched here: scanning it for non-lossless
      // numbers would push every member of a wide forged payload before any
      // byte cap runs. The done handler's bounded `checkDoneValue` folds the
      // losslessness check into the metered traversal, rejecting over-budget
      // before it enqueues children.
      const err = m.error
      if (err === undefined) {
        return m.value === undefined ? { type: 'done' } : { type: 'done', value: m.value }
      }
      if (typeof err !== 'object' || err === null) return undefined
      const { kind, message } = err as Record<string, unknown>
      if (typeof message !== 'string') return undefined
      if (kind !== 'exception' && kind !== 'invalid-output' && kind !== 'output-limit') return undefined
      return m.value === undefined
        ? { type: 'done', error: { kind, message } }
        : { type: 'done', value: m.value, error: { kind, message } }
    }
    default:
      return undefined
  }
}