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import { AnyCodec, Codec, CodecVisitor, createCodec, Expand, Input, metadata, Output, U2I } from "../common/mod.ts"import { constant } from "./constant.ts"import { option } from "./option.ts"
export function field<K extends keyof any, VI, VO>(key: K, $value: Codec<VI, VO>): Codec<  Expand<Readonly<Record<K, VI>>>,  Expand<Record<K, VO>>> {  return createCodec({    _metadata: metadata("$.field", field, key, $value),    _staticSize: $value._staticSize,    _encode(buffer, value) {      $value._encode(buffer, value[key])    },    _decode(buffer) {      return { [key]: $value._decode(buffer) } as any    },    _assert(assert) {      $value._assert(assert.key(this, key))    },  })}
export function optionalField<K extends keyof any, VI, VO>(key: K, $value: Codec<VI, VO>): Codec<  Expand<Readonly<Partial<Record<K, VI>>>>,  Expand<Partial<Record<K, VO>>>> {  const $option = option($value)  return createCodec({    _metadata: metadata("$.optionalField", optionalField, key, $value),    _staticSize: $value._staticSize,    _encode(buffer, value) {      $option._encode(buffer, value[key])    },    _decode(buffer) {      if (buffer.array[buffer.index++]) {        return { [key]: $value._decode(buffer) } as any      } else {        return {}      }    },    _assert(assert) {      assert.typeof(this, "object")      assert.nonNull(this)      if (key in (assert.value as any)) {        $option._assert(assert.key(this, key))      }    },  })}
export type InputObject<T extends AnyCodec[]> = Expand<  U2I<    | { x: {} }    | {      [K in keyof T]: { x: Input<T[K]> }    }[number]  >["x"]>export type OutputObject<T extends AnyCodec[]> = Expand<  U2I<    | { x: {} }    | {      [K in keyof T]: { x: Output<T[K]> }    }[number]  >["x"]>
type UnionKeys<T> = T extends T ? keyof T : neverexport type ObjectMembers<T extends AnyCodec[]> = [  ...never extends T ? {      [K in keyof T]: AnyCodec extends T[K] ? AnyCodec        :           & UnionKeys<Input<T[K]>>          & {            [L in keyof T]: K extends L ? never : UnionKeys<Input<T[L]>>          }[number] extends (infer O extends keyof any)          ? [O] extends [never] ? Codec<Input<T[K]> & {}> : Codec<{ [_ in O]?: never }>        : never    }    : T,]
export function object<T extends AnyCodec[]>(...members: ObjectMembers<T>): Codec<InputObject<T>, OutputObject<T>> {  return createCodec({    _metadata: metadata("$.object", object<T>, ...members),    _staticSize: members.map((x) => x._staticSize).reduce((a, b) => a + b, 0),    _encode: generateEncode(members as Codec<any>[]),    _decode: generateDecode(members as Codec<any>[]),    _assert(assert) {      assert.typeof(this, "object")      assert.nonNull(this)      for (const member of members as T) {        member._assert(assert)      }    },  })}
function generateEncode(members: Codec<any>[]) {  const vars: string[] = []  const args: unknown[] = []
  const valueVisitor = new CodecVisitor<(v: string) => string>()  valueVisitor.add(constant, (codec, value, pattern) => (v) => {    if (pattern) {      return `${addVar(codec)}._encode(buffer, ${v})`    }    return addVar(value)  })  valueVisitor.fallback((codec) => (v) => {    return `${addVar(codec)}._encode(buffer, ${v})`  })
  const fieldVisitor = new CodecVisitor<string>()  fieldVisitor.add(field, (_, key, value) => {    return valueVisitor.visit(value)(`value[${typeof key === "symbol" ? addVar(key) : JSON.stringify(key)}]`)  })  fieldVisitor.add(optionalField, (_, key, value) => {    return fieldVisitor.visit(field(key, option(value)))  })  fieldVisitor.add(object, (_, ...members) => {    return members.map((x) => fieldVisitor.visit(x)).join(";")  })  fieldVisitor.fallback((codec) => {    return `${addVar(codec)}._encode(buffer, value)`  })
  const content = members.map((x) => fieldVisitor.visit(x)).join(";")
  return (new Function(...vars, `return function objectEncode(buffer,value){${content}}`))(...args)
  function addVar(value: unknown) {    const v = "v" + vars.length    vars.push(v)    args.push(value)    return v  }}
function generateDecode(members: Codec<any>[]) {  const vars: string[] = []  const args: unknown[] = []
  const valueVisitor = new CodecVisitor<string>()  valueVisitor.add(constant, (codec, value, pattern) => {    if (pattern) {      return `${addVar(codec)}._decode(buffer)`    }    return addVar(value)  })  valueVisitor.fallback((codec) => {    return `${addVar(codec)}._decode(buffer)`  })  const fieldVisitor = new CodecVisitor<string>()  fieldVisitor.add(field, (_, key, value) => {    return `[${typeof key === "symbol" ? addVar(key) : JSON.stringify(key)}]: ${valueVisitor.visit(value)}`  })  fieldVisitor.add(optionalField, (_, key, value) => {    return `...buffer.array[buffer.index++] ? {${fieldVisitor.visit(field(key, value))} } : undefined`  })  fieldVisitor.add(object, (_, ...members) => {    return members.map((x) => fieldVisitor.visit(x)).join(",")  })  fieldVisitor.fallback((codec) => {    return `...${addVar(codec)}._decode(buffer)`  })
  const content = members.map((x) => fieldVisitor.visit(x)).join(",")
  return (new Function(...vars, `return function objectDecode(buffer){return{${content}}}`))(...args)
  function addVar(value: unknown) {    const v = "v" + vars.length    vars.push(v)    args.push(value)    return v  }}