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import { Codec, createCodec, metadata, ScaleDecodeError } from "../common/mod.ts"
export function constant<T>(value: T, codec: Pick<Codec<T>, "encode">): Codec<T>export function constant<T>(value: T, pattern?: Uint8Array): Codec<T>export function constant<T>(value: T, c?: Pick<Codec<T>, "encode"> | Uint8Array): Codec<T> {  const pattern = c && (c instanceof Uint8Array ? c : c.encode(value))  return createCodec({    _metadata: metadata("$.constant", constant<T>, value, ...pattern ? [pattern] : []),    // We could set `_staticSize` to `pattern.length`, but in this case it will    // usually more efficient to insert `pattern` dynamically, rather than    // manually copy the bytes.    _staticSize: 0,    _encode(buffer) {      if (pattern) {        buffer.insertArray(pattern)      }    },    _decode(buffer) {      if (pattern) {        const got = buffer.array.subarray(buffer.index, buffer.index += pattern.length)        for (let i = 0; i < pattern.length; i++) {          if (pattern[i] !== got[i]) {            throw new ScaleDecodeError(this, buffer, `Invalid pattern; expected ${hex(pattern)}, got ${hex(got)}`)          }        }      }      return value    },    _assert(assert) {      assert.equals(this, value)    },  })}
function hex(pattern: Uint8Array) {  let str = "0x"  for (let i = 0; i < pattern.length; i++) {    str += pattern[i]!.toString(16).padStart(2, "0")  }  return str}