// Copyright 2026 International Digital Economy Academy
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

///|
#borrow(input, out_meta)
extern "C" fn flac_decode_all_i16le(
  input : Bytes,
  input_len : Int,
  out_meta : FixedArray[UInt],
  out_meta_len : Int,
) -> Bytes = "moon_rodio_flac_decode_all_i16le"

///|
fn flac_read_i16_le(bytes : Bytes, offset : Int) -> Int {
  let u = bytes[offset].to_int() | (bytes[offset + 1].to_int() << 8)
  if u >= 0x8000 {
    u - 0x10000
  } else {
    u
  }
}

///|
pub fn decode_flac_bytes(bytes : Bytes) -> DecodedSamples raise DecoderError {
  guard bytes.length() > 0 else { raise InvalidFormat("flac bytes are empty") }

  let out_meta = FixedArray::make(3, (0 : UInt))
  let pcm = flac_decode_all_i16le(
    bytes,
    bytes.length(),
    out_meta,
    out_meta.length(),
  )

  let status = out_meta[0].reinterpret_as_int()
  guard status == 0 else {
    raise InvalidFormat("flac decode failed (dr_flac status \{status})")
  }

  let channels = out_meta[1].reinterpret_as_int()
  let sample_rate = out_meta[2].reinterpret_as_int()
  guard channels > 0 && sample_rate > 0 else {
    raise InvalidFormat("invalid decoded flac stream metadata")
  }

  guard pcm.length() % 2 == 0 else {
    raise InvalidFormat("decoded flac pcm bytes must be i16-aligned")
  }

  let sample_count = pcm.length() / 2
  let samples : Array[Double] = []
  for i in 0..