// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.

type RawBaseTypes = "int8" | "int16" | "int32" | "uint8" | "uint16" | "uint32";
type RawNumberTypes = RawBaseTypes | "float32" | "float64";
type RawBigTypes = RawBaseTypes | "int64" | "uint64";
type RawTypes = RawNumberTypes | RawBigTypes;

/** How encoded binary data is ordered. */
export type Endianness = "little" | "big";

/** Options for working with the `number` type. */
export interface VarnumOptions {
  /** The binary format used. */
  dataType?: RawNumberTypes;
  /** The binary encoding order used. */
  endian?: Endianness;
}

/** Options for working with the `bigint` type. */
export interface VarbigOptions {
  /** The binary format used. */
  dataType?: RawBigTypes;
  /** The binary encoding order used. */
  endian?: Endianness;
}

const rawTypeSizes = {
  int8: 1,
  uint8: 1,
  int16: 2,
  uint16: 2,
  int32: 4,
  uint32: 4,
  int64: 8,
  uint64: 8,
  float32: 4,
  float64: 8
};

/** Returns the number of bytes required to store the given data-type. */
export function sizeof(dataType: RawTypes): number {
  return rawTypeSizes[dataType];
}

/** Reads `n` bytes from `r`.
 *
 * Returns it in a `Uint8Array`, or throws `Deno.errors.UnexpectedEof` if `n` bytes cannot be read. */
export async function getNBytes(
  r: Deno.Reader,
  n: number
): Promise<Uint8Array> {
  const scratch = new Uint8Array(n);
  const nRead = await r.read(scratch);
  if (nRead === Deno.EOF || nRead < n) throw new Deno.errors.UnexpectedEof();
  return scratch;
}

/** Decode a number from `b`, and return it as a `number`. Data-type defaults to `int32`.
 * Returns `EOF` if `b` is too short for the data-type given in `o`. */
export function varnum(
  b: Uint8Array,
  o: VarnumOptions = {}
): number | Deno.EOF {
  o.dataType = o.dataType ?? "int32";
  const littleEndian = (o.endian ?? "big") === "little" ? true : false;
  if (b.length < sizeof(o.dataType)) return Deno.EOF;
  const view = new DataView(b.buffer);
  switch (o.dataType) {
    case "int8":
      return view.getInt8(0);
    case "uint8":
      return view.getUint8(0);
    case "int16":
      return view.getInt16(0, littleEndian);
    case "uint16":
      return view.getUint16(0, littleEndian);
    case "int32":
      return view.getInt32(0, littleEndian);
    case "uint32":
      return view.getUint32(0, littleEndian);
    case "float32":
      return view.getFloat32(0, littleEndian);
    case "float64":
      return view.getFloat64(0, littleEndian);
  }
}

/** Decode an integer from `b`, and return it as a `bigint`. Data-type defaults to `int64`.
 * Returns `EOF` if `b` is too short for the data-type given in `o`. */
export function varbig(
  b: Uint8Array,
  o: VarbigOptions = {}
): bigint | Deno.EOF {
  o.dataType = o.dataType ?? "int64";
  const littleEndian = (o.endian ?? "big") === "little" ? true : false;
  if (b.length < sizeof(o.dataType)) return Deno.EOF;
  const view = new DataView(b.buffer);
  switch (o.dataType) {
    case "int8":
      return BigInt(view.getInt8(0));
    case "uint8":
      return BigInt(view.getUint8(0));
    case "int16":
      return BigInt(view.getInt16(0, littleEndian));
    case "uint16":
      return BigInt(view.getUint16(0, littleEndian));
    case "int32":
      return BigInt(view.getInt32(0, littleEndian));
    case "uint32":
      return BigInt(view.getUint32(0, littleEndian));
    case "int64":
      return view.getBigInt64(0, littleEndian);
    case "uint64":
      return view.getBigUint64(0, littleEndian);
  }
}

/** Encode a number `x` into `b`, and return the number of bytes used. Data-type defaults to `int32`.
 * Returns 0 if `b` is too short for the data-type given in `o`. */
export function putVarnum(
  b: Uint8Array,
  x: number,
  o: VarnumOptions = {}
): number {
  o.dataType = o.dataType ?? "int32";
  const littleEndian = (o.endian ?? "big") === "little" ? true : false;
  if (b.length < sizeof(o.dataType)) return 0;
  const view = new DataView(b.buffer);
  switch (o.dataType) {
    case "int8":
      view.setInt8(0, x);
      break;
    case "uint8":
      view.setUint8(0, x);
      break;
    case "int16":
      view.setInt16(0, x, littleEndian);
      break;
    case "uint16":
      view.setUint16(0, x, littleEndian);
      break;
    case "int32":
      view.setInt32(0, x, littleEndian);
      break;
    case "uint32":
      view.setUint32(0, x, littleEndian);
      break;
    case "float32":
      view.setFloat32(0, x, littleEndian);
      break;
    case "float64":
      view.setFloat64(0, x, littleEndian);
      break;
  }
  return sizeof(o.dataType);
}

/** Encode an integer `x` into `b`, and return the number of bytes used. Data-type defaults to `int64`.
 * Returns 0 if `b` is too short for the data-type given in `o`. */
export function putVarbig(
  b: Uint8Array,
  x: bigint,
  o: VarbigOptions = {}
): number {
  o.dataType = o.dataType ?? "int64";
  const littleEndian = (o.endian ?? "big") === "little" ? true : false;
  if (b.length < sizeof(o.dataType)) return 0;
  const view = new DataView(b.buffer);
  switch (o.dataType) {
    case "int8":
      view.setInt8(0, Number(x));
      break;
    case "uint8":
      view.setUint8(0, Number(x));
      break;
    case "int16":
      view.setInt16(0, Number(x), littleEndian);
      break;
    case "uint16":
      view.setUint16(0, Number(x), littleEndian);
      break;
    case "int32":
      view.setInt32(0, Number(x), littleEndian);
      break;
    case "uint32":
      view.setUint32(0, Number(x), littleEndian);
      break;
    case "int64":
      view.setBigInt64(0, x, littleEndian);
      break;
    case "uint64":
      view.setBigUint64(0, x, littleEndian);
      break;
  }
  return sizeof(o.dataType);
}

/** Reads a number from `r`, comsuming `sizeof(o.dataType)` bytes. Data-type defaults to `int32`.
 *
 * Returns it as `number`, or throws `Deno.errors.UnexpectedEof` if not enough bytes can be read. */
export async function readVarnum(
  r: Deno.Reader,
  o: VarnumOptions = {}
): Promise<number> {
  o.dataType = o.dataType ?? "int32";
  const scratch = await getNBytes(r, sizeof(o.dataType));
  return varnum(scratch, o) as number;
}

/** Reads an integer from `r`, comsuming `sizeof(o.dataType)` bytes. Data-type defaults to `int64`.
 *
 * Returns it as `bigint`, or throws `Deno.errors.UnexpectedEof` if not enough bytes can be read. */
export async function readVarbig(
  r: Deno.Reader,
  o: VarbigOptions = {}
): Promise<bigint> {
  o.dataType = o.dataType ?? "int64";
  const scratch = await getNBytes(r, sizeof(o.dataType));
  return varbig(scratch, o) as bigint;
}

/** Writes a number `x` to `w`. Data-type defaults to `int32`.
 *
 * Returns the number of bytes written. */
export function writeVarnum(
  w: Deno.Writer,
  x: number,
  o: VarnumOptions = {}
): Promise<number> {
  o.dataType = o.dataType ?? "int32";
  const scratch = new Uint8Array(sizeof(o.dataType));
  putVarnum(scratch, x, o);
  return w.write(scratch);
}

/** Writes an integer `x` to `w`. Data-type defaults to `int64`.
 *
 * Returns the number of bytes written. */
export function writeVarbig(
  w: Deno.Writer,
  x: bigint,
  o: VarbigOptions = {}
): Promise<number> {
  o.dataType = o.dataType ?? "int64";
  const scratch = new Uint8Array(sizeof(o.dataType));
  putVarbig(scratch, x, o);
  return w.write(scratch);
}