/*************************************************************************/
/*  image_saver_tinyexr.cpp                                              */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
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/*************************************************************************/

#include "image_saver_tinyexr.h"
#include "core/math/math_funcs.h"

#include "thirdparty/tinyexr/tinyexr.h"

static bool is_supported_format(Image::Format p_format) {
	// This is checked before anything else.
	// Mostly uncompressed formats are considered.
	switch (p_format) {
		case Image::FORMAT_RF:
		case Image::FORMAT_RGF:
		case Image::FORMAT_RGBF:
		case Image::FORMAT_RGBAF:
		case Image::FORMAT_RH:
		case Image::FORMAT_RGH:
		case Image::FORMAT_RGBH:
		case Image::FORMAT_RGBAH:
		case Image::FORMAT_R8:
		case Image::FORMAT_RG8:
		case Image::FORMAT_RGB8:
		case Image::FORMAT_RGBA8:
			return true;
		default:
			return false;
	}
}

enum SrcPixelType {
	SRC_FLOAT,
	SRC_HALF,
	SRC_BYTE
};

static SrcPixelType get_source_pixel_type(Image::Format p_format) {
	switch (p_format) {
		case Image::FORMAT_RF:
		case Image::FORMAT_RGF:
		case Image::FORMAT_RGBF:
		case Image::FORMAT_RGBAF:
			return SRC_FLOAT;
		case Image::FORMAT_RH:
		case Image::FORMAT_RGH:
		case Image::FORMAT_RGBH:
		case Image::FORMAT_RGBAH:
			return SRC_HALF;
		case Image::FORMAT_R8:
		case Image::FORMAT_RG8:
		case Image::FORMAT_RGB8:
		case Image::FORMAT_RGBA8:
			return SRC_BYTE;
		default:
			CRASH_NOW();
	}
}

static int get_target_pixel_type(Image::Format p_format) {
	switch (p_format) {
		case Image::FORMAT_RF:
		case Image::FORMAT_RGF:
		case Image::FORMAT_RGBF:
		case Image::FORMAT_RGBAF:
			return TINYEXR_PIXELTYPE_FLOAT;
		case Image::FORMAT_RH:
		case Image::FORMAT_RGH:
		case Image::FORMAT_RGBH:
		case Image::FORMAT_RGBAH:
		// EXR doesn't support 8-bit channels so in that case we'll convert
		case Image::FORMAT_R8:
		case Image::FORMAT_RG8:
		case Image::FORMAT_RGB8:
		case Image::FORMAT_RGBA8:
			return TINYEXR_PIXELTYPE_HALF;
		default:
			CRASH_NOW();
	}
}

static int get_pixel_type_size(int p_pixel_type) {
	switch (p_pixel_type) {
		case TINYEXR_PIXELTYPE_HALF:
			return 2;
		case TINYEXR_PIXELTYPE_FLOAT:
			return 4;
	}
	CRASH_NOW();
}

static int get_channel_count(Image::Format p_format) {
	switch (p_format) {
		case Image::FORMAT_RF:
		case Image::FORMAT_RH:
		case Image::FORMAT_R8:
			return 1;
		case Image::FORMAT_RGF:
		case Image::FORMAT_RGH:
		case Image::FORMAT_RG8:
			return 2;
		case Image::FORMAT_RGBF:
		case Image::FORMAT_RGBH:
		case Image::FORMAT_RGB8:
			return 3;
		case Image::FORMAT_RGBAF:
		case Image::FORMAT_RGBAH:
		case Image::FORMAT_RGBA8:
			return 4;
		default:
			CRASH_NOW();
	}
}

Error save_exr(const String &p_path, const Ref<Image> &p_img, bool p_grayscale) {

	Image::Format format = p_img->get_format();

	if (!is_supported_format(format)) {
		// Format not supported
		print_error("Image format not supported for saving as EXR. Consider saving as PNG.");
		return ERR_UNAVAILABLE;
	}

	EXRHeader header;
	InitEXRHeader(&header);

	EXRImage image;
	InitEXRImage(&image);

	const int max_channels = 4;

	// Godot does not support more than 4 channels,
	// so we can preallocate header infos on the stack and use only the subset we need
	PoolByteArray channels[max_channels];
	unsigned char *channels_ptrs[max_channels];
	EXRChannelInfo channel_infos[max_channels];
	int pixel_types[max_channels];
	int requested_pixel_types[max_channels] = { -1 };

	// Gimp and Blender are a bit annoying so order of channels isn't straightforward.
	const int channel_mappings[4][4] = {
		{ 0 }, // R
		{ 1, 0 }, // GR
		{ 2, 1, 0 }, // BGR
		{ 2, 1, 0, 3 } // BGRA
	};

	int channel_count = get_channel_count(format);
	ERR_FAIL_COND_V(p_grayscale && channel_count != 1, ERR_INVALID_PARAMETER);

	int target_pixel_type = get_target_pixel_type(format);
	int target_pixel_type_size = get_pixel_type_size(target_pixel_type);
	SrcPixelType src_pixel_type = get_source_pixel_type(format);
	const int pixel_count = p_img->get_width() * p_img->get_height();

	const int *channel_mapping = channel_mappings[channel_count - 1];

	{
		PoolByteArray src_data = p_img->get_data();
		PoolByteArray::Read src_r = src_data.read();

		for (int channel_index = 0; channel_index < channel_count; ++channel_index) {

			// De-interleave channels

			PoolByteArray &dst = channels[channel_index];
			dst.resize(pixel_count * target_pixel_type_size);

			PoolByteArray::Write dst_w = dst.write();

			if (src_pixel_type == SRC_FLOAT && target_pixel_type == TINYEXR_PIXELTYPE_FLOAT) {

				// Note: we don't save mipmaps
				CRASH_COND(src_data.size() < pixel_count * channel_count * target_pixel_type_size);

				const float *src_rp = (float *)src_r.ptr();
				float *dst_wp = (float *)dst_w.ptr();

				for (int i = 0; i < pixel_count; ++i) {
					dst_wp[i] = src_rp[channel_index + i * channel_count];
				}

			} else if (src_pixel_type == SRC_HALF && target_pixel_type == TINYEXR_PIXELTYPE_HALF) {

				CRASH_COND(src_data.size() < pixel_count * channel_count * target_pixel_type_size);

				const uint16_t *src_rp = (uint16_t *)src_r.ptr();
				uint16_t *dst_wp = (uint16_t *)dst_w.ptr();

				for (int i = 0; i < pixel_count; ++i) {
					dst_wp[i] = src_rp[channel_index + i * channel_count];
				}

			} else if (src_pixel_type == SRC_BYTE && target_pixel_type == TINYEXR_PIXELTYPE_HALF) {

				CRASH_COND(src_data.size() < pixel_count * channel_count);

				const uint8_t *src_rp = (uint8_t *)src_r.ptr();
				uint16_t *dst_wp = (uint16_t *)dst_w.ptr();

				for (int i = 0; i < pixel_count; ++i) {
					dst_wp[i] = Math::make_half_float(src_rp[channel_index + i * channel_count] / 255.f);
				}

			} else {
				CRASH_NOW();
			}

			int remapped_index = channel_mapping[channel_index];

			channels_ptrs[remapped_index] = dst_w.ptr();

			// No conversion
			pixel_types[remapped_index] = target_pixel_type;
			requested_pixel_types[remapped_index] = target_pixel_type;

			// Write channel name
			if (p_grayscale) {
				channel_infos[remapped_index].name[0] = 'Y';
				channel_infos[remapped_index].name[1] = '\0';
			} else {
				const char *rgba = "RGBA";
				channel_infos[remapped_index].name[0] = rgba[channel_index];
				channel_infos[remapped_index].name[1] = '\0';
			}
		}
	}

	image.images = channels_ptrs;
	image.num_channels = channel_count;
	image.width = p_img->get_width();
	image.height = p_img->get_height();

	header.num_channels = image.num_channels;
	header.channels = channel_infos;
	header.pixel_types = pixel_types;
	header.requested_pixel_types = requested_pixel_types;

	CharString utf8_filename = p_path.utf8();
	const char *err;
	int ret = SaveEXRImageToFile(&image, &header, utf8_filename.ptr(), &err);
	if (ret != TINYEXR_SUCCESS) {
		print_error(String("Saving EXR failed. Error: {0}").format(varray(err)));
		return ERR_FILE_CANT_WRITE;
	}

	return OK;
}