/*
DESCRIPTION
  decode.go provides slice decoding functionality.

AUTHORS
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  Copyright (C) 2019 the Australian Ocean Lab (AusOcean).

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package h264dec

// picOrderCntType0 is used to return topFieldOrderCnt and bottomFieldOrderCnt
// when pic_order_cnt_type i.e vid.PicOrderCntType == 0, using the process
// defined in section 8.2.1.1 of the specifications. If topFieldOrderCnt or
// bottomFieldOrderCnt are -1 they are unset.
func picOrderCntType0(vid *VideoStream, ctx SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
	prevPicOrderCntMsb, prevPicOrderCntLsb := 0, 0
	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1

	// NB: We're currently only handling IDRs so panic.
	if !vid.idrPicFlag {
		panic("not implemented")
	}

	switch {
	case (ctx.PicOrderCntLsb < prevPicOrderCntLsb) && ((prevPicOrderCntLsb - ctx.PicOrderCntLsb) >= (vid.maxPicOrderCntLsb / 2)):
		vid.picOrderCntMsb = prevPicOrderCntMsb + vid.maxPicOrderCntLsb
	case (ctx.PicOrderCntLsb > prevPicOrderCntLsb) && ((ctx.PicOrderCntLsb - prevPicOrderCntLsb) > (vid.maxPicOrderCntLsb / 2)):
		vid.picOrderCntMsb = prevPicOrderCntMsb - vid.maxPicOrderCntLsb
	default:
		vid.picOrderCntMsb = prevPicOrderCntMsb
	}

	if !ctx.BottomField {
		topFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
	} else {
		if !ctx.FieldPic {
			bottomFieldOrderCnt = topFieldOrderCnt + ctx.DeltaPicOrderCntBottom
		} else {
			bottomFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
		}
	}
	return
}

// picOrderCntType1 is used to return topFieldOrderCnt and bottomFieldOrderCnt
// when vic.PicOrderCntType == 1 according to logic defined in section 8.2.1.2
// of the specifications. If topFieldOrderCnt or bottomFieldOrderCnt are -1,
// then they are considered unset.
func picOrderCntType1(vid VideoStream, ctx SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1

	// TODO: this will be prevFrameNum when we do frames other than IDR.
	_ = vid.priorPic.FrameNum

	if vid.idrPicFlag {
		vid.frameNumOffset = 0
	} else {
		panic("not implemented")
	}

	absFrameNum := 0
	if ctx.NumRefFramesInPicOrderCntCycle != 0 {
		absFrameNum = vid.frameNumOffset + ctx.FrameNum
	}

	if ctx.RefIdc == 0 && absFrameNum > 0 {
		absFrameNum = absFrameNum - 1
	}

	var expectedPicOrderCnt int
	if absFrameNum > 0 {
		picOrderCntCycleCnt := (absFrameNum - 1) / int(ctx.NumRefFramesInPicOrderCntCycle)
		frameNumInPicOrderCntCycle := (absFrameNum - 1) % int(ctx.NumRefFramesInPicOrderCntCycle)
		expectedPicOrderCnt = picOrderCntCycleCnt * vid.expectedDeltaPerPicOrderCntCycle
		for i := 0; i <= frameNumInPicOrderCntCycle; i++ {
			expectedPicOrderCnt = expectedPicOrderCnt + ctx.OffsetForRefFrameList[i]
		}
	}

	if ctx.RefIdc == 0 {
		expectedPicOrderCnt = expectedPicOrderCnt + int(ctx.OffsetForNonRefPic)
	}

	switch {
	case !ctx.FieldPic:
		topFieldOrderCnt = expectedPicOrderCnt + ctx.DeltaPicOrderCnt[0]
		bottomFieldOrderCnt = topFieldOrderCnt + int(ctx.OffsetForTopToBottomField) + ctx.DeltaPicOrderCnt[1]
	case !ctx.BottomField:
		topFieldOrderCnt = expectedPicOrderCnt + ctx.DeltaPicOrderCnt[0]
	default:
		bottomFieldOrderCnt = expectedPicOrderCnt + int(ctx.OffsetForTopToBottomField) + ctx.DeltaPicOrderCnt[0]
	}
	return
}