export interface StringBuilder {
    byteLength: number
    appendChar: (char: number) => void
    appendBuf: (buf: Uint8Array, start?: number, end?: number) => void
    reset: () => void
    toString: () => string
}

export class NonBufferedString implements StringBuilder {
    private decoder = new TextDecoder('utf-8')
    private string = ''
    public byteLength = 0

    public appendChar(char: number): void {
        this.string += String.fromCharCode(char)
        this.byteLength += 1
    }

    public appendBuf(buf: Uint8Array, start = 0, end: number = buf.length): void {
        this.string += this.decoder.decode(buf.subarray(start, end))
        this.byteLength += end - start
    }

    public reset(): void {
        this.string = ''
        this.byteLength = 0
    }

    public toString(): string {
        return this.string
    }
}

export class BufferedString implements StringBuilder {
    private decoder = new TextDecoder('utf-8')
    private buffer: Uint8Array
    private bufferOffset = 0
    private string = ''
    public byteLength = 0

    public constructor(bufferSize: number) {
        this.buffer = new Uint8Array(bufferSize)
    }

    public appendChar(char: number): void {
        if (this.bufferOffset >= this.buffer.length) this.flushStringBuffer()
        this.buffer[this.bufferOffset++] = char
        this.byteLength += 1
    }

    public appendBuf(buf: Uint8Array, start = 0, end: number = buf.length): void {
        const size = end - start
        if (this.bufferOffset + size > this.buffer.length) this.flushStringBuffer()
        this.buffer.set(buf.subarray(start, end), this.bufferOffset)
        this.bufferOffset += size
        this.byteLength += size
    }

    private flushStringBuffer(): void {
        this.string += this.decoder.decode(this.buffer.subarray(0, this.bufferOffset))
        this.bufferOffset = 0
    }

    public reset(): void {
        this.string = ''
        this.bufferOffset = 0
        this.byteLength = 0
    }
    public toString(): string {
        this.flushStringBuffer()
        return this.string
    }
}