package media

import "encoding/binary"

func validateAudio(codec string, declaredDurationMS int, prefix []byte) string {
	if codec != "wav_pcm_s16le" {
		return "CODEC_VALIDATION_UNAVAILABLE"
	}
	if len(prefix) < 44 || string(prefix[:4]) != "RIFF" || string(prefix[8:12]) != "WAVE" {
		return "INVALID_AUDIO_CONTAINER"
	}
	var byteRate, dataSize uint32
	var audioFormat, bitsPerSample uint16
	for offset := 12; offset+8 <= len(prefix); {
		chunkID := string(prefix[offset : offset+4])
		chunkSize := int(binary.LittleEndian.Uint32(prefix[offset+4 : offset+8]))
		dataStart := offset + 8
		if chunkID == "data" {
			dataSize = uint32(chunkSize)
			break
		}
		if chunkSize < 0 || dataStart+chunkSize > len(prefix) {
			break
		}
		switch chunkID {
		case "fmt ":
			if chunkSize < 16 {
				return "INVALID_AUDIO_CONTAINER"
			}
			audioFormat = binary.LittleEndian.Uint16(prefix[dataStart : dataStart+2])
			byteRate = binary.LittleEndian.Uint32(prefix[dataStart+8 : dataStart+12])
			bitsPerSample = binary.LittleEndian.Uint16(prefix[dataStart+14 : dataStart+16])
		}
		offset = dataStart + chunkSize
		if offset%2 != 0 {
			offset++
		}
	}
	if audioFormat != 1 || bitsPerSample != 16 || byteRate == 0 || dataSize == 0 {
		return "UNSUPPORTED_AUDIO_ENCODING"
	}
	actualDurationMS := int((uint64(dataSize) * 1000) / uint64(byteRate))
	if actualDurationMS != declaredDurationMS {
		return "DURATION_MISMATCH"
	}
	return ""
}