import { Codec, createCodec, metadata } from "../common/mod.js"
import { compact } from "./compact.js"
import { u32 } from "./int.js"

const compactU32 = compact(u32)

export function lenPrefixed<I, O>($inner: Codec<I, O>): Codec<I, O> {
  return createCodec({
    _metadata: metadata("$.lenPrefixed", lenPrefixed, $inner),
    _staticSize: compactU32._staticSize + $inner._staticSize,
    _encode(buffer, extrinsic) {
      const lengthCursor = buffer.createCursor(compactU32._staticSize)
      const contentCursor = buffer.createCursor($inner._staticSize)
      $inner._encode(contentCursor, extrinsic)
      buffer.waitForBuffer(contentCursor, () => {
        const length = contentCursor.finishedSize + contentCursor.index
        compactU32._encode(lengthCursor, length)
        lengthCursor.close()
        contentCursor.close()
      })
    },
    _decode(buffer) {
      const length = compactU32._decode(buffer)
      return $inner.decode(buffer.array.subarray(buffer.index, buffer.index += length))
    },
    _assert(assert) {
      $inner._assert(assert)
    },
  })
}