import { RLP } from '@ethereumjs/rlp'
import { EthereumJSErrorWithoutCode, bitsToBytes, bytesToBits } from '@ethereumjs/util'

import { BinaryNodeType } from './types.ts'

import type { BinaryNodeOptions, ChildBinaryNode } from './types.ts'

/** Binary tree internal (branch) node with two child references. */
export class InternalBinaryNode {
  public children: Array<ChildBinaryNode | null>

  public type = BinaryNodeType.Internal

  constructor(options: BinaryNodeOptions[typeof BinaryNodeType.Internal]) {
    this.children = options.children ?? Array(2).fill(null)
  }

  static fromRawNode(rawNode: Uint8Array[]): InternalBinaryNode {
    const nodeType = rawNode[0][0]
    if (nodeType !== BinaryNodeType.Internal) {
      throw EthereumJSErrorWithoutCode('Invalid node type')
    }

    // The length of the rawNode should be the # of children * 2 (for hash and path) + 1 for the node type

    if (rawNode.length !== 2 * 2 + 1) {
      throw EthereumJSErrorWithoutCode('Invalid node length')
    }
    const [, leftChildHash, rightChildHash, leftChildRawPath, rightChildRawPath] = rawNode

    const decodeChild = (hash: Uint8Array, rawPath: Uint8Array): ChildBinaryNode | null => {
      if (hash.length === 0) return null
      const decoded = RLP.decode(rawPath)

      if (!Array.isArray(decoded) || decoded.length !== 2) {
        throw EthereumJSErrorWithoutCode('Invalid RLP encoding for child path')
      }

      const [encodedLength, encodedPath] = decoded as Uint8Array[]

      if (encodedLength.length !== 1) {
        throw EthereumJSErrorWithoutCode('Invalid path length encoding')
      }

      const pathLength = encodedLength[0]
      const path = bytesToBits(encodedPath, pathLength)

      return { hash, path }
    }

    const children = [
      decodeChild(leftChildHash, leftChildRawPath),
      decodeChild(rightChildHash, rightChildRawPath),
    ]

    return new InternalBinaryNode({ children })
  }

  /**
   * Generates a new Internal node
   * @param children the children nodes
   * @returns a new Internal node
   */
  static create(children?: (ChildBinaryNode | null)[]): InternalBinaryNode {
    if (children !== undefined && children.length !== 2) {
      throw EthereumJSErrorWithoutCode('Internal node must have 2 children')
    }
    return new InternalBinaryNode({ children })
  }

  getChild(index: number): ChildBinaryNode | null {
    return this.children[index]
  }

  setChild(index: number, child: ChildBinaryNode | null): void {
    this.children[index] = child
  }

  /**
   * @returns the RLP serialized node
   */
  serialize(): Uint8Array {
    return RLP.encode(this.raw())
  }

  /**
   * Returns the raw serialized representation of this internal node as an array of Uint8Arrays.
   *
   * The returned array contains:
   * 1. A single-byte Uint8Array indicating the node type (BinaryNodeType.Internal).
   * 2. For each child (left then right):
   *    - The child’s hash, or an empty Uint8Array if the child is null.
   * 3. For each child (left then right):
   *    - An RLP-encoded tuple [pathLength, packedPathBytes] where:
   *         - `pathLength` is a one-byte Uint8Array representing the number of meaningful bits in the child’s path.
   *         - `packedPathBytes` is the packed byte representation of the child's bit path (as produced by `bitsToBytes`).
   *
   * @returns Raw RLP array: type byte, child hashes, then RLP-encoded child paths
   */

  raw(): Uint8Array[] {
    return [
      new Uint8Array([BinaryNodeType.Internal]),
      ...this.children.map((child) => (child !== null ? child.hash : new Uint8Array())),
      ...this.children.map((child) =>
        child !== null
          ? RLP.encode([new Uint8Array([child.path.length]), bitsToBytes(child.path)])
          : new Uint8Array(),
      ),
    ]
  }
}