package audio

import (
	"io"

	"github.com/zeozeozeo/gomplerate"
)

// resamplingReader 包装 io.Reader 并提供音频重采样
type resamplingReader struct {
	source    io.Reader
	resampler *gomplerate.Resampler
	buffer    []byte // 原始数据缓冲区
	eof       bool
}

// newResamplingReader 创建重采样 reader
// sourceRate: 源采样率（如 16000）
// targetRate: 目标采样率（如 44100）
// channels: 声道数（1=单声道, 2=立体声）
func newResamplingReader(src io.Reader, sourceRate, targetRate, channels int) (io.Reader, error) {
	resampler, err := gomplerate.NewResampler(channels, sourceRate, targetRate)
	if err != nil {
		return nil, err
	}

	return &resamplingReader{
		source:    src,
		resampler: resampler,
		buffer:    make([]byte, 0, 8192),
	}, nil
}

func (r *resamplingReader) Read(p []byte) (n int, err error) {
	const chunkSize = 4096

	// 读取原始数据
	if !r.eof && len(r.buffer) < chunkSize {
		buf := make([]byte, chunkSize)
		rn, readErr := r.source.Read(buf)
		if readErr != nil {
			if readErr == io.EOF {
				r.eof = true
			} else {
				return 0, readErr
			}
		}
		if rn > 0 {
			r.buffer = append(r.buffer, buf[:rn]...)
		}
	}

	// 没有数据了
	if len(r.buffer) == 0 {
		return 0, io.EOF
	}

	// 将字节转换为 int16
	int16Data := bytesToInt16(r.buffer)

	// 重采样
	resampled := r.resampler.ResampleInt16(int16Data)

	// 转回字节
	output := int16ToBytes(resampled)

	// 如果输出太小，继续读取
	if len(output) < len(p) && !r.eof {
		return r.Read(p)
	}

	// 复制到输出
	n = copy(p, output)

	// 更新缓冲区
	remainingSamples := (len(r.buffer) / 2) - len(int16Data)
	if remainingSamples > 0 {
		r.buffer = r.buffer[len(int16Data)*2:]
	} else {
		r.buffer = r.buffer[:0]
	}

	return n, nil
}

// bytesToInt16 将字节切片转换为 int16 切片
func bytesToInt16(b []byte) []int16 {
	result := make([]int16, len(b)/2)
	for i := 0; i < len(result); i++ {
		result[i] = int16(b[i*2]) | int16(b[i*2+1])<<8
	}
	return result
}

// int16ToBytes 将 int16 切片转换为字节切片
func int16ToBytes(i []int16) []byte {
	result := make([]byte, len(i)*2)
	for n, v := range i {
		result[n*2] = byte(v)
		result[n*2+1] = byte(v >> 8)
	}
	return result
}

// needsResample 检查是否需要重采样
func needsResample(sourceRate, targetRate int) bool {
	return sourceRate != targetRate
}