const MAX_U6 = Math.pow(2, 6) - 1
const MAX_U14 = Math.pow(2, 14) - 1
const MAX_U30 = Math.pow(2, 30) - 1
const MAX_U31 = Math.pow(2, 31) - 1
const MAX_U53 = Number.MAX_SAFE_INTEGER
const MAX_U62: bigint = 2n ** 62n - 1n

// Reader wraps a stream and provides convience methods for reading pieces from a stream
// Unfortunately we can't use a BYOB reader because it's not supported with WebTransport+WebWorkers yet.
export class Reader {
	#buffer: Uint8Array
	#stream: ReadableStream<Uint8Array>
	#reader: ReadableStreamDefaultReader<Uint8Array>

	constructor(buffer: Uint8Array, stream: ReadableStream<Uint8Array>) {
		this.#buffer = buffer
		this.#stream = stream
		this.#reader = this.#stream.getReader()
	}

	// Adds more data to the buffer, returning true if more data was added.
	async #fill(): Promise<boolean> {
		const result = await this.#reader.read()
		if (result.done) {
			return false
		}

		const buffer = new Uint8Array(result.value)

		if (this.#buffer.byteLength == 0) {
			this.#buffer = buffer
		} else {
			const temp = new Uint8Array(this.#buffer.byteLength + buffer.byteLength)
			temp.set(this.#buffer)
			temp.set(buffer, this.#buffer.byteLength)
			this.#buffer = temp
		}

		return true
	}

	// Add more data to the buffer until it's at least size bytes.
	async #fillTo(size: number) {
		while (this.#buffer.byteLength < size) {
			if (!(await this.#fill())) {
				throw new Error("unexpected end of stream")
			}
		}
	}

	// Consumes the first size bytes of the buffer.
	#slice(size: number): Uint8Array {
		const result = new Uint8Array(this.#buffer.buffer, this.#buffer.byteOffset, size)
		this.#buffer = new Uint8Array(this.#buffer.buffer, this.#buffer.byteOffset + size)

		return result
	}

	async read(size: number): Promise<Uint8Array> {
		if (size == 0) return new Uint8Array()

		await this.#fillTo(size)
		return this.#slice(size)
	}

	async readAll(): Promise<Uint8Array> {
		// eslint-disable-next-line no-empty
		while (await this.#fill()) {}
		return this.#slice(this.#buffer.byteLength)
	}

	async string(maxLength?: number): Promise<string> {
		const length = await this.u53()
		if (maxLength !== undefined && length > maxLength) {
			throw new Error(`string length ${length} exceeds max length ${maxLength}`)
		}

		const buffer = await this.read(length)
		return new TextDecoder().decode(buffer)
	}

	async u8(): Promise<number> {
		await this.#fillTo(1)
		return this.#slice(1)[0]
	}

	// Returns a Number using 53-bits, the max Javascript can use for integer math
	async u53(): Promise<number> {
		const v = await this.u62()
		if (v > MAX_U53) {
			throw new Error("value larger than 53-bits; use v62 instead")
		}

		return Number(v)
	}

	// NOTE: Returns a bigint instead of a number since it may be larger than 53-bits
	async u62(): Promise<bigint> {
		await this.#fillTo(1)
		const size = (this.#buffer[0] & 0xc0) >> 6

		if (size == 0) {
			const first = this.#slice(1)[0]
			return BigInt(first) & 0x3fn
		} else if (size == 1) {
			await this.#fillTo(2)
			const slice = this.#slice(2)
			const view = new DataView(slice.buffer, slice.byteOffset, slice.byteLength)

			return BigInt(view.getInt16(0)) & 0x3fffn
		} else if (size == 2) {
			await this.#fillTo(4)
			const slice = this.#slice(4)
			const view = new DataView(slice.buffer, slice.byteOffset, slice.byteLength)

			return BigInt(view.getUint32(0)) & 0x3fffffffn
		} else if (size == 3) {
			await this.#fillTo(8)
			const slice = this.#slice(8)
			const view = new DataView(slice.buffer, slice.byteOffset, slice.byteLength)

			return view.getBigUint64(0) & 0x3fffffffffffffffn
		} else {
			throw new Error("impossible")
		}
	}

	async done(): Promise<boolean> {
		if (this.#buffer.byteLength > 0) return false
		return !(await this.#fill())
	}

	async close() {
		this.#reader.releaseLock()
		await this.#stream.cancel()
	}

	release(): [Uint8Array, ReadableStream<Uint8Array>] {
		this.#reader.releaseLock()
		return [this.#buffer, this.#stream]
	}
}

// Writer wraps a stream and writes chunks of data
export class Writer {
	#scratch: Uint8Array
	#writer: WritableStreamDefaultWriter<Uint8Array>
	#stream: WritableStream<Uint8Array>

	constructor(stream: WritableStream<Uint8Array>) {
		this.#stream = stream
		this.#scratch = new Uint8Array(8)
		this.#writer = this.#stream.getWriter()
	}

	async u8(v: number) {
		await this.write(setUint8(this.#scratch, v))
	}

	async i32(v: number) {
		if (Math.abs(v) > MAX_U31) {
			throw new Error(`overflow, value larger than 32-bits: ${v}`)
		}

		// We don't use a VarInt, so it always takes 4 bytes.
		// This could be improved but nothing is standardized yet.
		await this.write(setInt32(this.#scratch, v))
	}

	async u53(v: number) {
		if (v < 0) {
			throw new Error(`underflow, value is negative: ${v}`)
		} else if (v > MAX_U53) {
			throw new Error(`overflow, value larger than 53-bits: ${v}`)
		}

		await this.write(setVint53(this.#scratch, v))
	}

	async u62(v: bigint) {
		if (v < 0) {
			throw new Error(`underflow, value is negative: ${v}`)
		} else if (v >= MAX_U62) {
			throw new Error(`overflow, value larger than 62-bits: ${v}`)
		}

		await this.write(setVint62(this.#scratch, v))
	}

	async write(v: Uint8Array) {
		await this.#writer.write(v)
	}

	async string(str: string) {
		const data = new TextEncoder().encode(str)
		await this.u53(data.byteLength)
		await this.write(data)
	}

	async close() {
		this.#writer.releaseLock()
		await this.#stream.close()
	}

	release(): WritableStream<Uint8Array> {
		this.#writer.releaseLock()
		return this.#stream
	}
}

function setUint8(dst: Uint8Array, v: number): Uint8Array {
	dst[0] = v
	return dst.slice(0, 1)
}

function setUint16(dst: Uint8Array, v: number): Uint8Array {
	const view = new DataView(dst.buffer, dst.byteOffset, 2)
	view.setUint16(0, v)

	return new Uint8Array(view.buffer, view.byteOffset, view.byteLength)
}

function setInt32(dst: Uint8Array, v: number): Uint8Array {
	const view = new DataView(dst.buffer, dst.byteOffset, 4)
	view.setInt32(0, v)

	return new Uint8Array(view.buffer, view.byteOffset, view.byteLength)
}

function setUint32(dst: Uint8Array, v: number): Uint8Array {
	const view = new DataView(dst.buffer, dst.byteOffset, 4)
	view.setUint32(0, v)

	return new Uint8Array(view.buffer, view.byteOffset, view.byteLength)
}

function setVint53(dst: Uint8Array, v: number): Uint8Array {
	if (v <= MAX_U6) {
		return setUint8(dst, v)
	} else if (v <= MAX_U14) {
		return setUint16(dst, v | 0x4000)
	} else if (v <= MAX_U30) {
		return setUint32(dst, v | 0x80000000)
	} else if (v <= MAX_U53) {
		return setUint64(dst, BigInt(v) | 0xc000000000000000n)
	} else {
		throw new Error(`overflow, value larger than 53-bits: ${v}`)
	}
}

function setVint62(dst: Uint8Array, v: bigint): Uint8Array {
	if (v < MAX_U6) {
		return setUint8(dst, Number(v))
	} else if (v < MAX_U14) {
		return setUint16(dst, Number(v) | 0x4000)
	} else if (v <= MAX_U30) {
		return setUint32(dst, Number(v) | 0x80000000)
	} else if (v <= MAX_U62) {
		return setUint64(dst, BigInt(v) | 0xc000000000000000n)
	} else {
		throw new Error(`overflow, value larger than 62-bits: ${v}`)
	}
}

function setUint64(dst: Uint8Array, v: bigint): Uint8Array {
	const view = new DataView(dst.buffer, dst.byteOffset, 8)
	view.setBigUint64(0, v)

	return new Uint8Array(view.buffer, view.byteOffset, view.byteLength)
}