/** JSON string-prefix accounting for the outer-output ledger. @module @deepseek-ai/dsh-code-runtime-worker/output-json */

import type { CodeJsonValue } from '@deepseek-ai/dsh-code-runtime'

type IntrinsicCallable = (this: unknown, ...args: unknown[]) => unknown

const intrinsicReflectApply = Reflect.apply as (
  target: IntrinsicCallable,
  thisArgument: unknown,
  argumentsList: readonly unknown[],
) => unknown
const intrinsicArrayIsArray = Array.isArray
const IntrinsicBuffer = Buffer
const intrinsicBufferByteLength = Reflect.get(Buffer, 'byteLength') as IntrinsicCallable
const intrinsicObjectDefineProperty = Object.defineProperty
const intrinsicObjectKeys = Object.keys
const intrinsicString = String
const intrinsicStringCharCodeAt = Reflect.get(String.prototype, 'charCodeAt') as IntrinsicCallable
const intrinsicStringCodePointAt = Reflect.get(String.prototype, 'codePointAt') as IntrinsicCallable
const intrinsicStringSlice = Reflect.get(String.prototype, 'slice') as IntrinsicCallable

/** UTF-8 byte length through the module-captured Node intrinsic. */
function byteLength(text: string): number {
  return intrinsicReflectApply(intrinsicBufferByteLength, IntrinsicBuffer, [text, 'utf8']) as number
}

/** Append without consulting a model-mutated `Array.prototype`. */
function append<T>(target: T[], value: T): void {
  intrinsicObjectDefineProperty(target, target.length, {
    value,
    enumerable: true,
    configurable: true,
    writable: true,
  })
}

/** Pop without consulting a model-mutated `Array.prototype`. */
function takeLast<T>(target: T[]): T | undefined {
  if (target.length === 0) return undefined
  const index = target.length - 1
  const value = target[index]
  intrinsicObjectDefineProperty(target, 'length', { value: index })
  return value
}

/** One code-point-aligned character from a string. */
function characterAt(text: string, index: number): string {
  const codePoint = intrinsicReflectApply(intrinsicStringCodePointAt, text, [index]) as number
  const width = codePoint > 0xffff ? 2 : 1
  return intrinsicReflectApply(intrinsicStringSlice, text, [index, index + width]) as string
}

/** Serialized bytes contributed by one complete Unicode code point inside JSON quotes. */
function serializedCharacterBytes(character: string): number {
  if (character.length === 2) return 4
  if (character === '"' || character === '\\') return 2
  const code = intrinsicReflectApply(intrinsicStringCharCodeAt, character, [0]) as number
  if (code >= 0xd800 && code <= 0xdfff) return 6
  if (code < 0x20) return code === 0x08 || code === 0x09 || code === 0x0a || code === 0x0c || code === 0x0d ? 2 : 6
  return byteLength(character)
}

/**
 * Measure one JSON string without materializing its complete escaped form.
 * @param text - the candidate string.
 * @param maxBytes - largest serialized size the caller can admit.
 * @returns Exact serialized bytes, or `undefined` as soon as the cap is crossed.
 */
export function jsonStringBytesUpTo(text: string, maxBytes: number): number | undefined {
  if (maxBytes < 2) return undefined
  let bytes = 2
  for (let index = 0; index < text.length;) {
    const character = characterAt(text, index)
    bytes += serializedCharacterBytes(character)
    if (bytes > maxBytes) return undefined
    index += character.length
  }
  return bytes
}

/**
 * Measure one lossless JSON value without allocating its serialized form.
 * @param value - already validated lossless JSON.
 * @param maxBytes - largest serialized size the caller can admit.
 * @returns Exact serialized bytes, or `undefined` as soon as the cap is crossed.
 */
export function jsonValueBytesUpTo(value: CodeJsonValue, maxBytes: number): number | undefined {
  type Task =
    | { kind: 'value'; value: CodeJsonValue }
    | { kind: 'array'; value: CodeJsonValue[]; index: number }
    | { kind: 'object'; value: Record<string, CodeJsonValue>; keys: string[]; index: number }

  let bytes = 0
  const add = (cost: number): boolean => {
    bytes += cost
    return bytes <= maxBytes
  }
  const tasks: Task[] = [{ kind: 'value', value }]
  for (let task = takeLast(tasks); task !== undefined; task = takeLast(tasks)) {
    if (task.kind === 'value') {
      const current = task.value
      if (current === null) {
        if (!add(4)) return undefined
      } else if (typeof current === 'string') {
        const stringBytes = jsonStringBytesUpTo(current, maxBytes - bytes)
        if (stringBytes === undefined) return undefined
        bytes += stringBytes
      } else if (typeof current === 'number') {
        if (!add(byteLength(intrinsicString(current)))) return undefined
      } else if (typeof current === 'boolean') {
        if (!add(current ? 4 : 5)) return undefined
      } else if (intrinsicArrayIsArray(current)) {
        if (!add(2)) return undefined
        if (current.length > 0) append(tasks, { kind: 'array', value: current, index: 0 })
      } else {
        if (!add(2)) return undefined
        const keys = intrinsicObjectKeys(current)
        if (keys.length > 0) append(tasks, { kind: 'object', value: current, keys, index: 0 })
      }
      continue
    }

    if (task.index > 0 && !add(1)) return undefined
    if (task.kind === 'array') {
      const item = task.value[task.index]
      if (item === undefined) return undefined
      if (task.index + 1 < task.value.length) append(tasks, { ...task, index: task.index + 1 })
      append(tasks, { kind: 'value', value: item })
      continue
    }

    const key = task.keys[task.index]
    /* v8 ignore next -- an object frame is created and advanced only for an existing Object.keys entry. */
    if (key === undefined) return undefined
    const keyBytes = jsonStringBytesUpTo(key, maxBytes - bytes)
    if (keyBytes === undefined) return undefined
    if (!add(keyBytes + 1)) return undefined
    const item = task.value[key]
    if (item === undefined) return undefined
    if (task.index + 1 < task.keys.length) append(tasks, { ...task, index: task.index + 1 })
    append(tasks, { kind: 'value', value: item })
  }
  return bytes
}

/**
 * Return the longest code-point-aligned prefix whose JSON string encoding,
 * including its surrounding quotes, fits `maxBytes`.
 *
 * @param text - the candidate string.
 * @param maxBytes - serialized JSON-string bytes available.
 * @returns the fitting prefix, or an empty string when even useful content cannot fit.
 */
export function truncateJsonStringBytes(text: string, maxBytes: number): string {
  if (maxBytes < 2) return ''
  let bytes = 2
  let end = 0
  for (let index = 0; index < text.length;) {
    const character = characterAt(text, index)
    const cost = serializedCharacterBytes(character)
    if (bytes + cost > maxBytes) break
    bytes += cost
    end += character.length
    index += character.length
  }
  return end === text.length ? text : intrinsicReflectApply(intrinsicStringSlice, text, [0, end]) as string
}