/** Duplicate-install-safe JSON and immutable-value helpers. @module @deepseek-ai/dsh-util-values */

/** A value that round-trips through JSON without loss. */
export type JsonValue = null | boolean | number | string | JsonValue[] | { [key: string]: JsonValue }

/**
 * Mark an unreachable closed-union branch.
 * @param value - impossible value; an unhandled typed variant fails at the call site.
 * @param context - optional switch-site label included in the failure message.
 * @returns never; a runtime value that escaped its type always throws.
 */
export function assertNever(value: never, context?: string): never {
  const rendered = (JSON.stringify(value) as string | undefined) ?? String(value)
  throw new Error(`unreachable variant${context ? ` in ${context}` : ''}: ${rendered}`)
}

/** Whether a realm-owned intrinsic prototype has a native constructor matching this engine's representation. */
function hasIntrinsicConstructor(prototype: object, name: 'Array' | 'Object'): boolean {
  const descriptor = Object.getOwnPropertyDescriptor(prototype, 'constructor')
  const constructor: unknown = descriptor?.value
  if (typeof constructor !== 'function') return false
  try {
    return constructor.name === name
      && constructor.prototype === prototype
      && Function.prototype.toString.call(constructor) === Function.prototype.toString.call(name === 'Array' ? Array : Object)
  } catch {
    return false
  }
}

/** Whether a candidate is one realm's intrinsic `Object.prototype`. */
function isIntrinsicObjectPrototype(value: object): boolean {
  return Object.getPrototypeOf(value) === null && hasIntrinsicConstructor(value, 'Object')
}

/** Whether an array uses one realm's intrinsic `Array.prototype`, not a subclass or forged prototype. */
function hasPlainArrayPrototype(value: unknown[]): boolean {
  const prototype: unknown = Object.getPrototypeOf(value)
  if (!Array.isArray(prototype) || !hasIntrinsicConstructor(prototype, 'Array')) return false
  const objectPrototype: unknown = Object.getPrototypeOf(prototype)
  return typeof objectPrototype === 'object'
    && objectPrototype !== null
    && isIntrinsicObjectPrototype(objectPrototype)
}

/** Whether an object is a plain or null-prototype record from any JavaScript realm. */
function hasPlainObjectPrototype(value: object): boolean {
  const prototype: unknown = Object.getPrototypeOf(value)
  return prototype === null
    || typeof prototype === 'object' && isIntrinsicObjectPrototype(prototype)
}

/** Return every JSON-visible object key, or reject own data JSON would discard. */
function enumerableStringKeys(value: object): string[] | undefined {
  const keys = Reflect.ownKeys(value)
  if (keys.some(key => typeof key !== 'string' || !Object.prototype.propertyIsEnumerable.call(value, key))) return undefined
  return keys as string[]
}

/** One active container, with child reads in its captured key or index order. */
type JsonWalkFrame =
  | { kind: 'array'; source: unknown[]; length: number; index: number; key: number; indices: number[] | undefined; target: JsonValue[] | undefined }
  | { kind: 'object'; source: Record<string, unknown>; keys: string[]; index: number; key: string; target: { [key: string]: JsonValue } | undefined }

/** Validate lossless JSON iteratively, optionally materializing a detached snapshot. */
function walkJsonValue(value: unknown, detach: boolean): JsonValue | true | undefined {
  const ancestors = new Set<object>()
  let root: JsonValue | undefined
  let parent: JsonWalkFrame | undefined
  const assign = (item: JsonValue): void => {
    if (parent === undefined) {
      if (detach) root = item
    } else if (parent.kind === 'array') {
      if (parent.target !== undefined) parent.target[parent.key] = item
    } else if (parent.target !== undefined) {
      Object.defineProperty(parent.target, parent.key, {
        value: item,
        enumerable: true,
        configurable: true,
        writable: true,
      })
    }
  }

  const frames: JsonWalkFrame[] = []
  let current: unknown = value
  for (;;) {
    if (current === null) {
      assign(null)
    } else if (typeof current === 'boolean' || typeof current === 'string') {
      assign(current)
    } else if (typeof current === 'number') {
      if (!Number.isFinite(current) || Object.is(current, -0)) return undefined
      assign(current)
    } else {
      if (typeof current !== 'object') return undefined
      if (ancestors.has(current)) return undefined
      if (Array.isArray(current)) {
        if (!hasPlainArrayPrototype(current)) return undefined
        const length = current.length
        if (Reflect.ownKeys(current).length !== length + 1) return undefined
        const target = detach ? [] as JsonValue[] : undefined
        if (target !== undefined) assign(target)
        let indices: number[] | undefined
        if (!Number.isInteger(length)) {
          // Capture indices with one subtraction for fractional or coercible Proxy lengths.
          indices = []
          for (let index = length - 1; index >= 0; index--) indices.push(index)
        }
        frames.push({ kind: 'array', source: current, length: indices?.length ?? length, index: 0, key: 0, indices, target })
      } else {
        if (!hasPlainObjectPrototype(current)) return undefined
        const keys = enumerableStringKeys(current)
        if (keys === undefined) return undefined
        const target = detach ? {} as { [key: string]: JsonValue } : undefined
        if (target !== undefined) assign(target)
        frames.push({ kind: 'object', source: current as Record<string, unknown>, keys, index: 0, key: '', target })
      }
      ancestors.add(current)
    }

    for (;;) {
      const frame = frames.at(-1)
      if (frame === undefined) return detach ? root : true
      const length = frame.kind === 'array' ? frame.length : frame.keys.length
      if (frame.index >= length) {
        ancestors.delete(frame.source)
        frames.pop()
        continue
      }
      const index = frame.index++
      parent = frame
      if (frame.kind === 'array') {
        const key = frame.indices === undefined ? index : frame.indices[frame.indices.length - index - 1]
        /* v8 ignore next -- the loop is bounded by the captured index count. */
        if (key === undefined) return undefined
        if (!Object.prototype.hasOwnProperty.call(frame.source, key)) return undefined
        frame.key = key
        current = frame.source[key]
      } else {
        const key = frame.keys[index]
        /* v8 ignore next -- the loop is bounded by the captured key count. */
        if (key === undefined) return undefined
        frame.key = key
        current = frame.source[key]
      }
      break
    }
  }
}

/**
 * Validate and detach lossless JSON in one read per property.
 * @param value - candidate value to validate and detach.
 * @returns the detached snapshot, or `undefined` when the value is not losslessly JSON-serializable.
 */
export function snapshotJsonValue<T>(value: T): T | undefined {
  return walkJsonValue(value, true) as T | undefined
}

/**
 * Test the same lossless JSON rules as {@link snapshotJsonValue} without detaching the value.
 * @param value - candidate value to test.
 * @returns whether the value survives a JSON round trip without loss.
 */
export function isJsonValue(value: unknown): boolean {
  return walkJsonValue(value, false) === true
}

/**
 * Compare JSON-compatible values structurally.
 * @param a - one JSON-compatible value.
 * @param b - the other JSON-compatible value.
 * @returns whether both values contain the same JSON data.
 */
export function deepEqualJson(a: unknown, b: unknown): boolean {
  if (a === b) return true
  if (typeof a !== 'object' || typeof b !== 'object' || a === null || b === null) return false
  if (Array.isArray(a) || Array.isArray(b)) {
    if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) return false
    return a.every((entry, index) => deepEqualJson(entry, b[index]))
  }
  const left = a as Record<string, unknown>
  const right = b as Record<string, unknown>
  const keys = Object.keys(left)
  if (keys.length !== Object.keys(right).length) return false
  return keys.every(key => key in right && deepEqualJson(left[key], right[key]))
}

/**
 * Deep-freeze an object graph in place while leaving live AbortSignal objects mutable.
 * @param value - value to freeze.
 * @returns the same value after every reachable enumerable child is frozen.
 */
export function deepFreeze<T>(value: T): T {
  const seen = new WeakSet<object>()
  const pending: (
    | { kind: 'visit'; node: unknown }
    | { kind: 'property'; source: Record<string, unknown>; key: string }
  )[] = [{ kind: 'visit', node: value }]
  while (pending.length > 0) {
    const task = pending.pop()
    /* v8 ignore next -- the loop condition guarantees one pending task. */
    if (task === undefined) continue
    if (task.kind === 'property') {
      pending.push({ kind: 'visit', node: task.source[task.key] })
      continue
    }
    const node = task.node
    if (node === null || typeof node !== 'object') continue
    if (node instanceof AbortSignal) continue
    if (seen.has(node)) continue
    seen.add(node)
    Object.freeze(node)
    const keys = Object.keys(node)
    for (let index = keys.length - 1; index >= 0; index--) {
      const key = keys[index]
      /* v8 ignore next -- the loop is bounded by the captured key count. */
      if (key === undefined) continue
      pending.push({ kind: 'property', source: node as Record<string, unknown>, key })
    }
  }
  return value
}

/**
 * Weak-key lookup with a strongly retained iterable set of associated values.
 *
 * Each value must belong to only one key. The container performs no automatic
 * cleanup; owners delete associations or clear the container at lifecycle end.
 */
export class WeakMapWithValues<Key extends object, Value> {
  private keys = new WeakMap<Key, Value>()
  private readonly valueSet = new Set<Value>()
  /** Live strongly retained values in insertion order. */
  readonly values: ReadonlySet<Value> = this.valueSet

  /**
   * Read the value associated with a key.
   * @param key - weakly held lookup key.
   * @returns the associated value, or absence.
   */
  get(key: Key): Value | undefined {
    return this.keys.get(key)
  }

  /**
   * Test whether a key has an association.
   * @param key - weakly held lookup key.
   * @returns whether the key is present.
   */
  has(key: Key): boolean {
    return this.keys.has(key)
  }

  /**
   * Associate one key with one caller-unique value.
   * @param key - weakly held lookup key.
   * @param value - strongly retained value that belongs to no other key.
   * @returns this container.
   */
  set(key: Key, value: Value): this {
    if (this.keys.has(key)) {
      const previous = this.keys.get(key) as Value
      if (previous === value) return this
      this.valueSet.delete(previous)
    }
    this.keys.set(key, value)
    this.valueSet.add(value)
    return this
  }

  /**
   * Remove one association and its strongly retained value.
   * @param key - weakly held lookup key.
   * @returns whether an association was removed.
   */
  delete(key: Key): boolean {
    if (!this.keys.has(key)) return false
    const value = this.keys.get(key) as Value
    const deleted = this.keys.delete(key)
    this.valueSet.delete(value)
    return deleted
  }

  /** Remove every association and strongly retained value. */
  clear(): void {
    this.keys = new WeakMap()
    this.valueSet.clear()
  }
}

export { PartialArguments, type LengthReadOptions } from './partial-json.ts'