// Copyright 2019 Joe Drago. All rights reserved.
// SPDX-License-Identifier: BSD-2-Clause

#include "avif/internal.h"

// These are for libaom to deal with
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wduplicate-enum"
#pragma clang diagnostic ignored "-Wextra-semi"
#pragma clang diagnostic ignored "-Wused-but-marked-unused"
#endif

#if defined(AVIF_CODEC_AOM_ENCODE)
#include "aom/aom_encoder.h"
#include "aom/aomcx.h"
#endif

#if defined(AVIF_CODEC_AOM_DECODE)
#include "aom/aom_decoder.h"
#include "aom/aomdx.h"
#endif

#ifdef __clang__
#pragma clang diagnostic pop

// This fixes complaints with aom_codec_control() and aom_img_fmt that are from libaom
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wused-but-marked-unused"
#pragma clang diagnostic ignored "-Wassign-enum"
#endif

#include <limits.h>
#include <stdlib.h>
#include <string.h>

struct avifCodecInternal
{
#if defined(AVIF_CODEC_AOM_DECODE)
    avifBool decoderInitialized;
    aom_codec_ctx_t decoder;
    aom_codec_iter_t iter;
    aom_image_t * image;
#endif

#if defined(AVIF_CODEC_AOM_ENCODE)
    avifBool encoderInitialized;
    aom_codec_ctx_t encoder;
    avifPixelFormatInfo formatInfo;
    aom_img_fmt_t aomFormat;
    avifBool monochromeEnabled;
#endif
};

static void aomCodecDestroyInternal(avifCodec * codec)
{
#if defined(AVIF_CODEC_AOM_DECODE)
    if (codec->internal->decoderInitialized) {
        aom_codec_destroy(&codec->internal->decoder);
    }
#endif

#if defined(AVIF_CODEC_AOM_ENCODE)
    if (codec->internal->encoderInitialized) {
        aom_codec_destroy(&codec->internal->encoder);
    }
    avifFree(codec->internal);
#endif
}

#if defined(AVIF_CODEC_AOM_DECODE)
static avifBool aomCodecOpen(struct avifCodec * codec, avifDecoder * decoder)
{
    aom_codec_dec_cfg_t cfg;
    memset(&cfg, 0, sizeof(aom_codec_dec_cfg_t));
    cfg.threads = decoder->maxThreads;
    cfg.allow_lowbitdepth = 1;

    aom_codec_iface_t * decoder_interface = aom_codec_av1_dx();
    if (aom_codec_dec_init(&codec->internal->decoder, decoder_interface, &cfg, 0)) {
        return AVIF_FALSE;
    }
    codec->internal->decoderInitialized = AVIF_TRUE;

    // Ensure that we only get the "highest spatial layer" as a single frame
    // for each input sample, instead of getting each spatial layer as its own
    // frame one at a time ("all layers").
    if (aom_codec_control(&codec->internal->decoder, AV1D_SET_OUTPUT_ALL_LAYERS, 0)) {
        return AVIF_FALSE;
    }

    codec->internal->iter = NULL;
    return AVIF_TRUE;
}

static avifBool aomCodecGetNextImage(struct avifCodec * codec, const avifDecodeSample * sample, avifBool alpha, avifImage * image)
{
    aom_image_t * nextFrame = NULL;
    for (;;) {
        nextFrame = aom_codec_get_frame(&codec->internal->decoder, &codec->internal->iter);
        if (nextFrame) {
            // Got an image!
            break;
        } else if (sample) {
            codec->internal->iter = NULL;
            if (aom_codec_decode(&codec->internal->decoder, sample->data.data, sample->data.size, NULL)) {
                return AVIF_FALSE;
            }
            sample = NULL;
        } else {
            break;
        }
    }

    if (nextFrame) {
        codec->internal->image = nextFrame;
    } else {
        if (alpha && codec->internal->image) {
            // Special case: reuse last alpha frame
        } else {
            return AVIF_FALSE;
        }
    }

    avifBool isColor = !alpha;
    if (isColor) {
        // Color (YUV) planes - set image to correct size / format, fill color

        avifPixelFormat yuvFormat = AVIF_PIXEL_FORMAT_NONE;
        switch (codec->internal->image->fmt) {
            case AOM_IMG_FMT_I420:
            case AOM_IMG_FMT_AOMI420:
            case AOM_IMG_FMT_I42016:
                yuvFormat = AVIF_PIXEL_FORMAT_YUV420;
                break;
            case AOM_IMG_FMT_I422:
            case AOM_IMG_FMT_I42216:
                yuvFormat = AVIF_PIXEL_FORMAT_YUV422;
                break;
            case AOM_IMG_FMT_I444:
            case AOM_IMG_FMT_I44416:
                yuvFormat = AVIF_PIXEL_FORMAT_YUV444;
                break;
            case AOM_IMG_FMT_NONE:
            case AOM_IMG_FMT_YV12:
            case AOM_IMG_FMT_AOMYV12:
            case AOM_IMG_FMT_YV1216:
            default:
                return AVIF_FALSE;
        }
        if (codec->internal->image->monochrome) {
            yuvFormat = AVIF_PIXEL_FORMAT_YUV400;
        }

        if (image->width && image->height) {
            if ((image->width != codec->internal->image->d_w) || (image->height != codec->internal->image->d_h) ||
                (image->depth != codec->internal->image->bit_depth) || (image->yuvFormat != yuvFormat)) {
                // Throw it all out
                avifImageFreePlanes(image, AVIF_PLANES_ALL);
            }
        }
        image->width = codec->internal->image->d_w;
        image->height = codec->internal->image->d_h;
        image->depth = codec->internal->image->bit_depth;

        image->yuvFormat = yuvFormat;
        image->yuvRange = (codec->internal->image->range == AOM_CR_STUDIO_RANGE) ? AVIF_RANGE_LIMITED : AVIF_RANGE_FULL;
        image->yuvChromaSamplePosition = (avifChromaSamplePosition)codec->internal->image->csp;

        image->colorPrimaries = (avifColorPrimaries)codec->internal->image->cp;
        image->transferCharacteristics = (avifTransferCharacteristics)codec->internal->image->tc;
        image->matrixCoefficients = (avifMatrixCoefficients)codec->internal->image->mc;

        avifPixelFormatInfo formatInfo;
        avifGetPixelFormatInfo(yuvFormat, &formatInfo);

        // Steal the pointers from the decoder's image directly
        avifImageFreePlanes(image, AVIF_PLANES_YUV);
        int yuvPlaneCount = (yuvFormat == AVIF_PIXEL_FORMAT_YUV400) ? 1 : 3;
        for (int yuvPlane = 0; yuvPlane < yuvPlaneCount; ++yuvPlane) {
            image->yuvPlanes[yuvPlane] = codec->internal->image->planes[yuvPlane];
            image->yuvRowBytes[yuvPlane] = codec->internal->image->stride[yuvPlane];
        }
        image->imageOwnsYUVPlanes = AVIF_FALSE;
    } else {
        // Alpha plane - ensure image is correct size, fill color

        if (image->width && image->height) {
            if ((image->width != codec->internal->image->d_w) || (image->height != codec->internal->image->d_h) ||
                (image->depth != codec->internal->image->bit_depth)) {
                // Alpha plane doesn't match previous alpha plane decode, bail out
                return AVIF_FALSE;
            }
        }
        image->width = codec->internal->image->d_w;
        image->height = codec->internal->image->d_h;
        image->depth = codec->internal->image->bit_depth;

        avifImageFreePlanes(image, AVIF_PLANES_A);
        image->alphaPlane = codec->internal->image->planes[0];
        image->alphaRowBytes = codec->internal->image->stride[0];
        image->alphaRange = (codec->internal->image->range == AOM_CR_STUDIO_RANGE) ? AVIF_RANGE_LIMITED : AVIF_RANGE_FULL;
        image->imageOwnsAlphaPlane = AVIF_FALSE;
    }

    return AVIF_TRUE;
}
#endif // defined(AVIF_CODEC_AOM_DECODE)

#if defined(AVIF_CODEC_AOM_ENCODE)

static aom_img_fmt_t avifImageCalcAOMFmt(const avifImage * image, avifBool alpha)
{
    aom_img_fmt_t fmt;
    if (alpha) {
        // We're going monochrome, who cares about chroma quality
        fmt = AOM_IMG_FMT_I420;
    } else {
        switch (image->yuvFormat) {
            case AVIF_PIXEL_FORMAT_YUV444:
                fmt = AOM_IMG_FMT_I444;
                break;
            case AVIF_PIXEL_FORMAT_YUV422:
                fmt = AOM_IMG_FMT_I422;
                break;
            case AVIF_PIXEL_FORMAT_YUV420:
            case AVIF_PIXEL_FORMAT_YUV400:
                fmt = AOM_IMG_FMT_I420;
                break;
            case AVIF_PIXEL_FORMAT_NONE:
            default:
                return AOM_IMG_FMT_NONE;
        }
    }

    if (image->depth > 8) {
        fmt |= AOM_IMG_FMT_HIGHBITDEPTH;
    }

    return fmt;
}

static avifBool aomOptionParseInt(const char * str, int * val)
{
    char * endptr;
    const long rawval = strtol(str, &endptr, 10);

    if (str[0] != '\0' && endptr[0] == '\0' && rawval >= INT_MIN && rawval <= INT_MAX) {
        *val = (int)rawval;
        return AVIF_TRUE;
    }

    return AVIF_FALSE;
}

struct aomOptionEnumList
{
    const char * name;
    int val;
};

static avifBool aomOptionParseEnum(const char * str, const struct aomOptionEnumList * enums, int * val)
{
    const struct aomOptionEnumList * listptr;
    long int rawval;
    char * endptr;

    // First see if the value can be parsed as a raw value.
    rawval = strtol(str, &endptr, 10);
    if (str[0] != '\0' && endptr[0] == '\0') {
        // Got a raw value, make sure it's valid.
        for (listptr = enums; listptr->name; listptr++)
            if (listptr->val == rawval) {
                *val = (int)rawval;
                return AVIF_TRUE;
            }
    }

    // Next see if it can be parsed as a string.
    for (listptr = enums; listptr->name; listptr++) {
        if (!strcmp(str, listptr->name)) {
            *val = listptr->val;
            return AVIF_TRUE;
        }
    }

    return AVIF_FALSE;
}

static const struct aomOptionEnumList endUsageEnum[] = { //
    { "vbr", AOM_VBR },                                  // Variable Bit Rate (VBR) mode
    { "cbr", AOM_CBR },                                  // Constant Bit Rate (CBR) mode
    { "cq", AOM_CQ },                                    // Constrained Quality (CQ)  mode
    { "q", AOM_Q },                                      // Constrained Quality (CQ)  mode
    { NULL, 0 }
};

static avifBool avifProcessAOMOptionsPreInit(avifCodec * codec, struct aom_codec_enc_cfg * cfg)
{
    for (uint32_t i = 0; i < codec->csOptions->count; ++i) {
        avifCodecSpecificOption * entry = &codec->csOptions->entries[i];
        int val;
        if (!strcmp(entry->key, "end-usage")) { // Rate control mode
            if (!aomOptionParseEnum(entry->value, endUsageEnum, &val)) {
                return AVIF_FALSE;
            }
            cfg->rc_end_usage = val;
        }
    }
    return AVIF_TRUE;
}

struct aomOptionDef
{
    const char * name;
    int controlId;
    const struct aomOptionEnumList * enums;
};

static const struct aomOptionEnumList tuningEnum[] = { //
    { "psnr", AOM_TUNE_PSNR },                         //
    { "ssim", AOM_TUNE_SSIM },                         //
    { NULL, 0 }
};

static const struct aomOptionDef aomOptionDefs[] = {                 //
    { "aq-mode", AV1E_SET_AQ_MODE, NULL },                           // Adaptive quantization mode
    { "cq-level", AOME_SET_CQ_LEVEL, NULL },                         // Constant/Constrained Quality level
    { "enable-chroma-deltaq", AV1E_SET_ENABLE_CHROMA_DELTAQ, NULL }, // Enable delta quantization in chroma planes
    { "sharpness", AOME_SET_SHARPNESS, NULL },                       // Loop filter sharpness
    { "tune", AOME_SET_TUNING, tuningEnum },                         // Tune distortion metric
    { NULL, 0, NULL }
};

static avifBool avifProcessAOMOptionsPostInit(avifCodec * codec)
{
    for (uint32_t i = 0; i < codec->csOptions->count; ++i) {
        avifCodecSpecificOption * entry = &codec->csOptions->entries[i];
        // Skip options processed by avifProcessAOMOptionsPreInit.
        if (!strcmp(entry->key, "end-usage")) {
            continue;
        }

        avifBool match = AVIF_FALSE;
        for (int j = 0; aomOptionDefs[j].name; ++j) {
            if (!strcmp(entry->key, aomOptionDefs[j].name)) {
                match = AVIF_TRUE;
                int val;
                avifBool parsed;
                if (aomOptionDefs[j].enums) {
                    parsed = aomOptionParseEnum(entry->value, aomOptionDefs[j].enums, &val);
                } else {
                    parsed = aomOptionParseInt(entry->value, &val);
                }
                if (!parsed) {
                    return AVIF_FALSE;
                }
                if (aom_codec_control(&codec->internal->encoder, aomOptionDefs[j].controlId, val) != AOM_CODEC_OK) {
                    return AVIF_FALSE;
                }
                break;
            }
        }
        if (!match) {
            return AVIF_FALSE;
        }
    }
    return AVIF_TRUE;
}

static avifResult aomCodecEncodeImage(avifCodec * codec,
                                      avifEncoder * encoder,
                                      const avifImage * image,
                                      avifBool alpha,
                                      uint32_t addImageFlags,
                                      avifCodecEncodeOutput * output)
{
    if (!codec->internal->encoderInitialized) {
        // Map encoder speed to AOM usage + CpuUsed:
        // Speed  0: GoodQuality CpuUsed 0
        // Speed  1: GoodQuality CpuUsed 1
        // Speed  2: GoodQuality CpuUsed 2
        // Speed  3: GoodQuality CpuUsed 3
        // Speed  4: GoodQuality CpuUsed 4
        // Speed  5: GoodQuality CpuUsed 5
        // Speed  6: GoodQuality CpuUsed 6
        // Speed  7: GoodQuality CpuUsed 6
        // Speed  8: RealTime    CpuUsed 6
        // Speed  9: RealTime    CpuUsed 7
        // Speed 10: RealTime    CpuUsed 8
        unsigned int aomUsage = AOM_USAGE_GOOD_QUALITY;
        int aomCpuUsed = -1;
        if (encoder->speed != AVIF_SPEED_DEFAULT) {
            if (encoder->speed < 8) {
                aomUsage = AOM_USAGE_GOOD_QUALITY;
                aomCpuUsed = AVIF_CLAMP(encoder->speed, 0, 6);
            } else {
                aomUsage = AOM_USAGE_REALTIME;
                aomCpuUsed = AVIF_CLAMP(encoder->speed - 2, 6, 8);
            }
        }

        // aom_codec.h says: aom_codec_version() == (major<<16 | minor<<8 | patch)
        static const int aomVersion_2_0_0 = (2 << 16);
        const int aomVersion = aom_codec_version();
        if ((aomVersion < aomVersion_2_0_0) && (image->depth > 8)) {
            // Due to a known issue with libavif v1.0.0-errata1-avif, 10bpc and
            // 12bpc image encodes will call the wrong variant of
            // aom_subtract_block when cpu-used is 7 or 8, and crash. Until we get
            // a new tagged release from libaom with the fix and can verify we're
            // running with that version of libaom, we must avoid using
            // cpu-used=7/8 on any >8bpc image encodes.
            //
            // Context:
            //   * https://github.com/AOMediaCodec/libavif/issues/49
            //   * https://bugs.chromium.org/p/aomedia/issues/detail?id=2587
            //
            // Continued bug tracking here:
            //   * https://github.com/AOMediaCodec/libavif/issues/56

            if (aomCpuUsed > 6) {
                aomCpuUsed = 6;
            }
        }

        codec->internal->aomFormat = avifImageCalcAOMFmt(image, alpha);
        if (codec->internal->aomFormat == AOM_IMG_FMT_NONE) {
            return AVIF_RESULT_UNKNOWN_ERROR;
        }

        avifGetPixelFormatInfo(image->yuvFormat, &codec->internal->formatInfo);

        aom_codec_iface_t * encoderInterface = aom_codec_av1_cx();
        struct aom_codec_enc_cfg cfg;
        aom_codec_enc_config_default(encoderInterface, &cfg, aomUsage);

        // Profile 0.  8-bit and 10-bit 4:2:0 and 4:0:0 only.
        // Profile 1.  8-bit and 10-bit 4:4:4
        // Profile 2.  8-bit and 10-bit 4:2:2
        //            12-bit 4:0:0, 4:2:0, 4:2:2 and 4:4:4
        uint8_t seqProfile = 0;
        if (image->depth == 12) {
            // Only seqProfile 2 can handle 12 bit
            seqProfile = 2;
        } else {
            // 8-bit or 10-bit

            if (alpha) {
                seqProfile = 0;
            } else {
                switch (image->yuvFormat) {
                    case AVIF_PIXEL_FORMAT_YUV444:
                        seqProfile = 1;
                        break;
                    case AVIF_PIXEL_FORMAT_YUV422:
                        seqProfile = 2;
                        break;
                    case AVIF_PIXEL_FORMAT_YUV420:
                        seqProfile = 0;
                        break;
                    case AVIF_PIXEL_FORMAT_YUV400:
                        seqProfile = 0;
                        break;
                    case AVIF_PIXEL_FORMAT_NONE:
                    default:
                        break;
                }
            }
        }

        cfg.g_profile = seqProfile;
        cfg.g_bit_depth = image->depth;
        cfg.g_input_bit_depth = image->depth;
        cfg.g_w = image->width;
        cfg.g_h = image->height;
        if (addImageFlags & AVIF_ADD_IMAGE_FLAG_SINGLE) {
            // Set the maximum number of frames to encode to 1. This instructs
            // libaom to set still_picture and reduced_still_picture_header to
            // 1 in AV1 sequence headers.
            cfg.g_limit = 1;
            // Set g_lag_in_frames to 1 to reduce the number of frame buffers
            // (from 20 to 2) in libaom's lookahead structure. This reduces
            // memory consumption when encoding a single image.
            cfg.g_lag_in_frames = 1;
        }
        if (encoder->maxThreads > 1) {
            cfg.g_threads = encoder->maxThreads;
        }

        int minQuantizer = AVIF_CLAMP(encoder->minQuantizer, 0, 63);
        int maxQuantizer = AVIF_CLAMP(encoder->maxQuantizer, 0, 63);
        if (alpha) {
            minQuantizer = AVIF_CLAMP(encoder->minQuantizerAlpha, 0, 63);
            maxQuantizer = AVIF_CLAMP(encoder->maxQuantizerAlpha, 0, 63);
        }
        avifBool lossless = ((minQuantizer == AVIF_QUANTIZER_LOSSLESS) && (maxQuantizer == AVIF_QUANTIZER_LOSSLESS));
        cfg.rc_min_quantizer = minQuantizer;
        cfg.rc_max_quantizer = maxQuantizer;

        codec->internal->monochromeEnabled = AVIF_FALSE;
        if (aomVersion > aomVersion_2_0_0) {
            // There exists a bug in libaom's chroma_check() function where it will attempt to
            // access nonexistent UV planes when encoding monochrome at faster libavif "speeds". It
            // was fixed shortly after the 2.0.0 libaom release, and the fix exists in both the
            // master and applejack branches. This ensures that the next version *after* 2.0.0 will
            // have the fix, and we must avoid cfg.monochrome until then.
            //
            // Bugfix Change-Id: https://aomedia-review.googlesource.com/q/I26a39791f820b4d4e1d63ff7141f594c3c7181f5

            if (alpha || (image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400)) {
                codec->internal->monochromeEnabled = AVIF_TRUE;
                cfg.monochrome = 1;
            }
        }

        if (!avifProcessAOMOptionsPreInit(codec, &cfg)) {
            return AVIF_RESULT_INVALID_CODEC_SPECIFIC_OPTION;
        }

        aom_codec_flags_t encoderFlags = 0;
        if (image->depth > 8) {
            encoderFlags |= AOM_CODEC_USE_HIGHBITDEPTH;
        }
        aom_codec_enc_init(&codec->internal->encoder, encoderInterface, &cfg, encoderFlags);
        codec->internal->encoderInitialized = AVIF_TRUE;

        if (lossless) {
            aom_codec_control(&codec->internal->encoder, AV1E_SET_LOSSLESS, 1);
        }
        if (encoder->maxThreads > 1) {
            aom_codec_control(&codec->internal->encoder, AV1E_SET_ROW_MT, 1);
        }
        if (encoder->tileRowsLog2 != 0) {
            int tileRowsLog2 = AVIF_CLAMP(encoder->tileRowsLog2, 0, 6);
            aom_codec_control(&codec->internal->encoder, AV1E_SET_TILE_ROWS, tileRowsLog2);
        }
        if (encoder->tileColsLog2 != 0) {
            int tileColsLog2 = AVIF_CLAMP(encoder->tileColsLog2, 0, 6);
            aom_codec_control(&codec->internal->encoder, AV1E_SET_TILE_COLUMNS, tileColsLog2);
        }
        if (aomCpuUsed != -1) {
            aom_codec_control(&codec->internal->encoder, AOME_SET_CPUUSED, aomCpuUsed);
        }
        if (!avifProcessAOMOptionsPostInit(codec)) {
            return AVIF_RESULT_INVALID_CODEC_SPECIFIC_OPTION;
        }
    }

    int yShift = codec->internal->formatInfo.chromaShiftY;
    uint32_t uvHeight = (image->height + yShift) >> yShift;
    aom_image_t * aomImage = aom_img_alloc(NULL, codec->internal->aomFormat, image->width, image->height, 16);
    avifBool monochromeRequested = AVIF_FALSE;

    if (alpha) {
        aomImage->range = (image->alphaRange == AVIF_RANGE_FULL) ? AOM_CR_FULL_RANGE : AOM_CR_STUDIO_RANGE;
        aom_codec_control(&codec->internal->encoder, AV1E_SET_COLOR_RANGE, aomImage->range);
        monochromeRequested = AVIF_TRUE;
        for (uint32_t j = 0; j < image->height; ++j) {
            uint8_t * srcAlphaRow = &image->alphaPlane[j * image->alphaRowBytes];
            uint8_t * dstAlphaRow = &aomImage->planes[0][j * aomImage->stride[0]];
            memcpy(dstAlphaRow, srcAlphaRow, image->alphaRowBytes);
        }

        // Ignore UV planes when monochrome
    } else {
        aomImage->range = (image->yuvRange == AVIF_RANGE_FULL) ? AOM_CR_FULL_RANGE : AOM_CR_STUDIO_RANGE;
        aom_codec_control(&codec->internal->encoder, AV1E_SET_COLOR_RANGE, aomImage->range);
        int yuvPlaneCount = 3;
        if (image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400) {
            yuvPlaneCount = 1; // Ignore UV planes when monochrome
            monochromeRequested = AVIF_TRUE;
        }
        for (int yuvPlane = 0; yuvPlane < yuvPlaneCount; ++yuvPlane) {
            uint32_t planeHeight = (yuvPlane == AVIF_CHAN_Y) ? image->height : uvHeight;

            for (uint32_t j = 0; j < planeHeight; ++j) {
                uint8_t * srcRow = &image->yuvPlanes[yuvPlane][j * image->yuvRowBytes[yuvPlane]];
                uint8_t * dstRow = &aomImage->planes[yuvPlane][j * aomImage->stride[yuvPlane]];
                memcpy(dstRow, srcRow, image->yuvRowBytes[yuvPlane]);
            }
        }

        aomImage->cp = (aom_color_primaries_t)image->colorPrimaries;
        aomImage->tc = (aom_transfer_characteristics_t)image->transferCharacteristics;
        aomImage->mc = (aom_matrix_coefficients_t)image->matrixCoefficients;
        aomImage->csp = (aom_chroma_sample_position_t)image->yuvChromaSamplePosition;
        aom_codec_control(&codec->internal->encoder, AV1E_SET_COLOR_PRIMARIES, aomImage->cp);
        aom_codec_control(&codec->internal->encoder, AV1E_SET_TRANSFER_CHARACTERISTICS, aomImage->tc);
        aom_codec_control(&codec->internal->encoder, AV1E_SET_MATRIX_COEFFICIENTS, aomImage->mc);
        aom_codec_control(&codec->internal->encoder, AV1E_SET_CHROMA_SAMPLE_POSITION, aomImage->csp);
    }

    if (monochromeRequested && !codec->internal->monochromeEnabled) {
        // The user requested monochrome (via alpha or YUV400) but libaom cannot currently support
        // monochrome (see chroma_check comment above). Manually set UV planes to 0.5.

        // aomImage is always 420 when we're monochrome
        uint32_t monoUVWidth = (image->width + 1) >> 1;
        uint32_t monoUVHeight = (image->height + 1) >> 1;

        for (int yuvPlane = 1; yuvPlane < 3; ++yuvPlane) {
            if (image->depth > 8) {
                const uint16_t half = 1 << (image->depth - 1);
                for (uint32_t j = 0; j < monoUVHeight; ++j) {
                    uint16_t * dstRow = (uint16_t *)&aomImage->planes[yuvPlane][j * aomImage->stride[yuvPlane]];
                    for (uint32_t i = 0; i < monoUVWidth; ++i) {
                        dstRow[i] = half;
                    }
                }
            } else {
                const uint8_t half = 128;
                size_t planeSize = (size_t)monoUVHeight * aomImage->stride[yuvPlane];
                memset(aomImage->planes[yuvPlane], half, planeSize);
            }
        }
    }

    aom_enc_frame_flags_t encodeFlags = 0;
    if (addImageFlags & AVIF_ADD_IMAGE_FLAG_FORCE_KEYFRAME) {
        encodeFlags |= AOM_EFLAG_FORCE_KF;
    }
    aom_codec_encode(&codec->internal->encoder, aomImage, 0, 1, encodeFlags);

    aom_codec_iter_t iter = NULL;
    for (;;) {
        const aom_codec_cx_pkt_t * pkt = aom_codec_get_cx_data(&codec->internal->encoder, &iter);
        if (pkt == NULL) {
            break;
        }
        if (pkt->kind == AOM_CODEC_CX_FRAME_PKT) {
            avifCodecEncodeOutputAddSample(output, pkt->data.frame.buf, pkt->data.frame.sz, (pkt->data.frame.flags & AOM_FRAME_IS_KEY));
        }
    }

    aom_img_free(aomImage);
    return AVIF_RESULT_OK;
}

static avifBool aomCodecEncodeFinish(avifCodec * codec, avifCodecEncodeOutput * output)
{
    for (;;) {
        // flush encoder
        aom_codec_encode(&codec->internal->encoder, NULL, 0, 1, 0);

        avifBool gotPacket = AVIF_FALSE;
        aom_codec_iter_t iter = NULL;
        for (;;) {
            const aom_codec_cx_pkt_t * pkt = aom_codec_get_cx_data(&codec->internal->encoder, &iter);
            if (pkt == NULL) {
                break;
            }
            if (pkt->kind == AOM_CODEC_CX_FRAME_PKT) {
                gotPacket = AVIF_TRUE;
                avifCodecEncodeOutputAddSample(
                    output, pkt->data.frame.buf, pkt->data.frame.sz, (pkt->data.frame.flags & AOM_FRAME_IS_KEY));
            }
        }

        if (!gotPacket) {
            break;
        }
    }
    return AVIF_TRUE;
}

#endif // defined(AVIF_CODEC_AOM_ENCODE)

const char * avifCodecVersionAOM(void)
{
    return aom_codec_version_str();
}

avifCodec * avifCodecCreateAOM(void)
{
    avifCodec * codec = (avifCodec *)avifAlloc(sizeof(avifCodec));
    memset(codec, 0, sizeof(struct avifCodec));

#if defined(AVIF_CODEC_AOM_DECODE)
    codec->open = aomCodecOpen;
    codec->getNextImage = aomCodecGetNextImage;
#endif

#if defined(AVIF_CODEC_AOM_ENCODE)
    codec->encodeImage = aomCodecEncodeImage;
    codec->encodeFinish = aomCodecEncodeFinish;
#endif

    codec->destroyInternal = aomCodecDestroyInternal;
    codec->internal = (struct avifCodecInternal *)avifAlloc(sizeof(struct avifCodecInternal));
    memset(codec->internal, 0, sizeof(struct avifCodecInternal));
    return codec;
}

#ifdef __clang__
#pragma clang diagnostic pop
#endif