/**
 * Generic buffered writer.
 * Writes data to an auto-expanding ArrayBuffer.
 *
 * @import {Writer} from '../src/types.js'
 * @returns {Writer}
 */
export function ByteWriter() {
  this.buffer = new ArrayBuffer(1024)
  this.view = new DataView(this.buffer)
  this.offset = 0 // bytes written
  this.index = 0 // index in buffer
  return this
}

/**
 * @param {number} size
 */
ByteWriter.prototype.ensure = function(size) {
  // auto-expanding buffer
  if (this.index + size > this.buffer.byteLength) {
    const newSize = Math.max(this.buffer.byteLength * 2, this.index + size)
    const newBuffer = new ArrayBuffer(newSize)
    // TODO: save buffers until later and merge once?
    new Uint8Array(newBuffer).set(new Uint8Array(this.buffer))
    this.buffer = newBuffer
    this.view = new DataView(this.buffer)
  }
}

ByteWriter.prototype.finish = function() {
}

ByteWriter.prototype.getBuffer = function() {
  return this.buffer.slice(0, this.index)
}

/**
 * @param {number} value
 */
ByteWriter.prototype.appendUint8 = function(value) {
  this.ensure(this.index + 1)
  this.view.setUint8(this.index, value)
  this.offset++
  this.index++
}

/**
 * @param {number} value
 */
ByteWriter.prototype.appendUint32 = function(value) {
  this.ensure(this.index + 4)
  this.view.setUint32(this.index, value, true)
  this.offset += 4
  this.index += 4
}

/**
 * @param {number} value
 */
ByteWriter.prototype.appendInt32 = function(value) {
  this.ensure(this.index + 4)
  this.view.setInt32(this.index, value, true)
  this.offset += 4
  this.index += 4
}

/**
 * @param {bigint} value
 */
ByteWriter.prototype.appendInt64 = function(value) {
  this.ensure(this.index + 8)
  this.view.setBigInt64(this.index, BigInt(value), true)
  this.offset += 8
  this.index += 8
}

/**
 * @param {number} value
 */
ByteWriter.prototype.appendFloat32 = function(value) {
  this.ensure(this.index + 8)
  this.view.setFloat32(this.index, value, true)
  this.offset += 4
  this.index += 4
}

/**
 * @param {number} value
 */
ByteWriter.prototype.appendFloat64 = function(value) {
  this.ensure(this.index + 8)
  this.view.setFloat64(this.index, value, true)
  this.offset += 8
  this.index += 8
}

/**
 * @param {ArrayBuffer} value
 */
ByteWriter.prototype.appendBuffer = function(value) {
  this.appendBytes(new Uint8Array(value))
}

/**
 * @param {Uint8Array} value
 */
ByteWriter.prototype.appendBytes = function(value) {
  this.ensure(this.index + value.length)
  new Uint8Array(this.buffer, this.index, value.length).set(value)
  this.offset += value.length
  this.index += value.length
}

/**
 * Convert a 32-bit signed integer to varint (1-5 bytes).
 * Writes out groups of 7 bits at a time, setting high bit if more to come.
 *
 * @param {number} value
 */
ByteWriter.prototype.appendVarInt = function(value) {
  while (true) {
    if ((value & ~0x7f) === 0) {
      // fits in 7 bits
      this.appendUint8(value)
      return
    } else {
      // write 7 bits and set high bit
      this.appendUint8(value & 0x7f | 0x80)
      value >>>= 7
    }
  }
}

/**
 * Convert a bigint to varint (1-10 bytes for 64-bit range).
 *
 * @param {bigint} value
 */
ByteWriter.prototype.appendVarBigInt = function(value) {
  while (true) {
    if ((value & ~0x7fn) === 0n) {
      // fits in 7 bits
      this.appendUint8(Number(value))
      return
    } else {
      // write 7 bits and set high bit
      this.appendUint8(Number(value & 0x7fn | 0x80n))
      value >>= 7n
    }
  }
}