// Font loading code adapted from https://github.com/ocornut/imgui
#include "Font.hpp"

#include "CommonVertexIndex.hpp"
#include "Image.hpp"
#include "Macros.hpp"
#include "String.hpp"
#include "Texture.hpp"
#include "Utils.hpp"
#include "VertexIndex.hpp"

#include <stb_rect_pack.h>
#include <stb_truetype.h>
#include <bit>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <fstream>
#include <iostream>
#include <memory>
#include <string>
#include <string_view>

namespace ProjectBrussel_UNITY_ID {
Font::ErrorCode LoadFile(const char* path, std::unique_ptr<uint8_t[]>& data, stbtt_fontinfo& fontInfo) {
	std::ifstream ifs(path, std::ios::binary | std::ios::ate);
	if (ifs) {
		auto size = static_cast<size_t>(ifs.tellg());
		data = std::make_unique<uint8_t[]>(size);

		ifs.seekg(0, std::ios::beg);
		ifs.read(reinterpret_cast<char*>(data.get()), size);

		auto ptr = static_cast<unsigned char*>(data.get());
		if (!stbtt_InitFont(&fontInfo, ptr, stbtt_GetFontOffsetForIndex(ptr, 0))) {
			return Font::EC_FileIOFailed;
		}

		return Font::EC_Success;
	} else {
		return Font::EC_FontLoadingFailed;
	}
}

const GlyphVariant& GetVariantFor(const GlyphInfo& info, FontType type) {
	switch (type) {
		case FontType::Regular: return info.regular;
		case FontType::Italic: return info.italic;
		case FontType::Bold: return info.bold;
		case FontType::BoldItalic: return info.boldItalic;
		default: UNREACHABLE;
	}
}

GlyphVariant& GetVariantFor(GlyphInfo& info, FontType type) {
	return const_cast<GlyphVariant&>(GetVariantFor(const_cast<const GlyphInfo&>(info), type));
}
} // namespace ProjectBrussel_UNITY_ID

Font::InitResult Font::Init(std::span<LoadingCandidate> candidates, float fontHeight, char32_t fallbackCodepoint, int oversampleH, int oversampleV) {
	using namespace ProjectBrussel_UNITY_ID;

	mFontHeight = fontHeight;

	struct SrcInfo {
		std::vector<int> glyphList; // Need to use vector<int> because stb_true_type use int*
		stbtt_fontinfo fontInfo;
		stbtt_pack_range packRange;
		stbrp_rect* rects; // glyphList.size() long
		stbtt_packedchar* packedChars; // glyphList.size() long
		const char32_t* glyphRange;
		std::unique_ptr<uint8_t[]> data;
		size_t dataSize;
		int glyphHighest = 0; // Highest codepoint in this glyph range
		FontType type;
	};

	// 1. Initialize font loading structure, load ttf from disk
	std::vector<SrcInfo> srcVec(candidates.size());
	int glyphHighest = 0; // Highest codepoint across all given glyph ranges
	for (size_t i = 0; i < candidates.size(); ++i) {
		auto& cand = candidates[i];
		auto& src = srcVec[i];

		src.glyphRange = cand.glyphRange;
		src.type = cand.type;
		auto result = LoadFile(cand.ttfPath, src.data, src.fontInfo);
		if (result != EC_Success) {
			return InitResult{
				.errorCode = result,
				.failedItemIdx = (int)i,
			};
		}

		for (auto range = src.glyphRange; range[0] && range[1]; range += 2) {
			src.glyphHighest = std::max(src.glyphHighest, static_cast<int>(range[1]));
		}
		glyphHighest = std::max(glyphHighest, src.glyphHighest);
	}

	// 2. For every requested codepoint, check for their presence in the font data, and handle redundancy or overlaps between source fonts to avoid unused glyphs
	std::vector<bool> glyphSet(glyphHighest + 1);
	int glyphCount = 0;
	for (auto& src : srcVec) {
		if (src.type != FontType::Regular) {
			continue;
		}

		for (auto range = src.glyphRange; range[0] && range[1]; range += 2) {
			for (char32_t codepoint = range[0]; codepoint <= range[1]; ++codepoint) {
				// Remove duplicates
				if (glyphSet[codepoint]) {
					continue;
				}
				// Font file doesn't have the requested codepoint
				if (!stbtt_FindGlyphIndex(&src.fontInfo, codepoint)) {
					continue;
				}

				src.glyphList.push_back(codepoint);
				glyphSet[codepoint] = true;
				glyphCount++;
			}
		}
	}
	for (auto& src : srcVec) {
		if (src.type == FontType::Regular) {
			continue;
		}

		for (auto range = src.glyphRange; range[0] && range[1]; range += 2) {
			for (char32_t codepoint = range[0]; codepoint <= range[1]; ++codepoint) {
				// Ignore any formatted (italic, bold, bolditalic) glyph that doesn't have a regular variant
				if (!glyphSet[codepoint]) {
					continue;
				}
				// Font file doesn't have the requested codepoint
				if (!stbtt_FindGlyphIndex(&src.fontInfo, codepoint)) {
					continue;
				}

				src.glyphList.push_back(codepoint);
				glyphCount++;
			}
		}
	}
	glyphSet.clear();

	// 3. Reserve memory for packing
	mGlyphs.reserve(glyphCount);
	std::vector<stbrp_rect> rects(glyphCount); // This type them as non-packed (zero initialization)
	std::vector<stbtt_packedchar> packedChars(glyphCount);

	// 4. Gather glyphs sizes so we can pack them in our virtual canvas
	constexpr int kTexGlyphPadding = 1; // Prevent texture sampler from accidentally getting neighbor glyph's pixel data
	float totalSurface = 0;
	int rectCount = 0;
	int packedCharCount = 0;
	for (auto& src : srcVec) {
		int glyphCount = static_cast<int>(src.glyphList.size());

		src.rects = &rects[rectCount];
		src.packedChars = &packedChars[packedCharCount];
		rectCount += glyphCount;
		packedCharCount += glyphCount;

		src.packRange.font_size = mFontHeight;
		src.packRange.first_unicode_codepoint_in_range = 0;
		src.packRange.array_of_unicode_codepoints = src.glyphList.data();
		src.packRange.num_chars = glyphCount;
		src.packRange.chardata_for_range = src.packedChars;
		src.packRange.h_oversample = oversampleH;
		src.packRange.v_oversample = oversampleV;

		float scale = stbtt_ScaleForPixelHeight(&src.fontInfo, mFontHeight);
		for (int i = 0; i < glyphCount; ++i) {
			int glyphIndex = stbtt_FindGlyphIndex(&src.fontInfo, src.glyphList[i]);
			int x0, y0, x1, y1;
			stbtt_GetGlyphBitmapBoxSubpixel(&src.fontInfo, glyphIndex, scale * oversampleH, scale * oversampleV, 0, 0, &x0, &y0, &x1, &y1);
			src.rects[i].w = (stbrp_coord)(x1 - x0 + kTexGlyphPadding + oversampleH - 1);
			src.rects[i].h = (stbrp_coord)(y1 - y0 + kTexGlyphPadding + oversampleV - 1);
			totalSurface += static_cast<float>(src.rects[i].w * src.rects[i].h);
		}
	}

	// We need a width for the skyline algorithm, any width
	// The exact width doesn't really matter much, but some API/GPU have texture size limitations and increasing width can decrease height
	auto surfaceSqrt = static_cast<int>(std::sqrt(totalSurface)) + 1;
	int atlasWidth =
		(surfaceSqrt >= 4096 * 0.7f)   ? 4096
		: (surfaceSqrt >= 2048 * 0.7f) ? 2048
		: (surfaceSqrt >= 1024 * 0.7f) ? 1024
									   : 512;
	int atlasHeight = 0; // Calculate later in 6

	// 5. Start packing
	constexpr int kMaxAtlasHeight = 1024 * 32;
	stbtt_pack_context spc;
	stbtt_PackBegin(&spc, nullptr, atlasWidth, kMaxAtlasHeight, 0, kTexGlyphPadding, nullptr);

	// 6. Pack each source font. No rendering yet, we are working with rectangles in an infinitely tall texture at this point
	auto context = reinterpret_cast<stbrp_context*>(spc.pack_info);
	for (auto& src : srcVec) {
		int glyphCount = static_cast<int>(src.glyphList.size());
		stbrp_pack_rects(context, src.rects, glyphCount);

		for (int i = 0; i < glyphCount; i++) {
			if (src.rects[i].was_packed) {
				atlasHeight = std::max(atlasHeight, src.rects[i].y + src.rects[i].h);
			}
		}
	}

	// 7. Allocate bitmap
	atlasHeight = std::bit_ceil<unsigned int>(atlasHeight);
	auto bitmap = std::make_unique<uint8_t[]>(atlasWidth * atlasHeight);
	std::memset(bitmap.get(), 0, atlasWidth * atlasHeight * sizeof(uint8_t));
	spc.pixels = bitmap.get();
	spc.height = atlasHeight;

	// 8. Render/rasterize font characters into the texture
	for (auto& src : srcVec) {
		stbtt_PackFontRangesRenderIntoRects(&spc, &src.fontInfo, &src.packRange, 1, src.rects);
		src.rects = nullptr;
	}

	// 9. End packing
	stbtt_PackEnd(&spc);
	rects.clear();

	// Lambda for code reuse for step 10 and 12
	auto SetupGlyphInfoVariant = [&](SrcInfo& src) -> void {
		float scale = stbtt_ScaleForPixelHeight(&src.fontInfo, mFontHeight);
		int unscaledAscent, unscaledDescent, unscaledLineGap;
		stbtt_GetFontVMetrics(&src.fontInfo, &unscaledAscent, &unscaledDescent, &unscaledLineGap);

		float ascent = std::floor(unscaledAscent * scale + ((unscaledAscent > 0.0f) ? +1 : -1));
		float descent = std::floor(unscaledDescent * scale + ((unscaledDescent > 0.0f) ? +1 : -1));
		float fontOffsetX = 0;
		float fontOffsetY = std::round(ascent);

		UNUSED(descent);

		int glyphCount = static_cast<int>(src.glyphList.size());
		for (int i = 0; i < glyphCount; ++i) {
			int codepoint = src.glyphList[i];
			auto& packedChar = src.packedChars[i];

			float x = 0;
			float y = 0;
			UNUSED(x);
			UNUSED(y);

			stbtt_aligned_quad quad;
			stbtt_GetPackedQuad(src.packedChars, atlasWidth, atlasHeight, i, &x, &y, &quad, 0);

			GlyphInfo* info;
			if (src.type == FontType::Regular) {
				mGlyphs.emplace_back();
				info = &mGlyphs.back();
				info->codepoint = codepoint;
			} else {
				info = &mGlyphs[mGlyphLookup[codepoint]];
			}

			auto& variant = ProjectBrussel_UNITY_ID::GetVariantFor(*info, src.type);
			variant.x0 = quad.x0 + fontOffsetX;
			variant.y0 = quad.y0 + fontOffsetY;
			variant.x1 = quad.x1 + fontOffsetX;
			variant.y1 = quad.y1 + fontOffsetY;
			variant.u0 = quad.s0;
			variant.v0 = quad.t0;
			variant.u1 = quad.s1;
			variant.v1 = quad.t1;
			variant.horizontalAdvance = std::lrint(packedChar.xadvance);

			// For step 12 to override
			// If some glyph doesn't have a particular variant, it will remain as Regular in the final product
			if (src.type == FontType::Regular) {
				info->italic = info->regular;
				info->bold = info->regular;
				info->boldItalic = info->regular;
			}
		}
	};

	// 10. Setup glyph infos
	for (auto& src : srcVec) {
		if (src.type == FontType::Regular) {
			SetupGlyphInfoVariant(src);
		}
	}

	// 11. Setup glyph lookup table
	mGlyphLookup.resize(glyphHighest + 1, -1);
	for (int i = 0, size = (int)mGlyphs.size(); i < size; ++i) {
		auto& info = mGlyphs[i];
		mGlyphLookup[info.codepoint] = i;
	}

	// Provided fallback codepoint doesn't exist, use the first glyph present
	if (fallbackCodepoint >= static_cast<char32_t>(glyphHighest) ||
		mGlyphLookup[fallbackCodepoint] == -1)
	{
		mFallbackGlyphIdx = 0;
	} else {
		mFallbackGlyphIdx = mGlyphLookup[fallbackCodepoint];
	}
	for (size_t i = 0; i < mGlyphLookup.size(); ++i) {
		if (mGlyphLookup[i] == -1) {
			mGlyphLookup[i] = mFallbackGlyphIdx;
		}
	}

	// 12. Setup glyph info for non-regular variants
	// This step won't cause any new glyph infos to be added, so it's fine (and we need the lookup table here) to do it after building lookup table
	for (auto& src : srcVec) {
		if (src.type != FontType::Regular) {
			SetupGlyphInfoVariant(src);
		}
	}

	// 13. Upload our rasterized bitmap into a Texture
	Image image;
	image.InitFromPixels(std::move(bitmap), glm::ivec2(atlasWidth, atlasHeight), 1);

	// Leave the texture upside down, we flip the UV in the text shader
	mAtlas.Attach(new Texture());
	mAtlas->InitFromImage(
		image,
		TextureProperties{
			// When down sampling, 'linear' help reduce flicker when scale changes
			.minifyingFilter = Tags::TF_Linear,
			// When up sampling, 'nearest' make the text look sharp (though pixelated)
			.magnifyingFilter = Tags::TF_Nearest,
		});

	return InitResult{
		.errorCode = EC_Success,
		.failedItemIdx = 0,
	};
}

float Font::GetFontHeight() const {
	return mFontHeight;
}

int Font::HorizontalAdvance(char32_t c, FontType type) const {
	auto info = FindGlyphFallback(c);
	return ProjectBrussel_UNITY_ID::GetVariantFor(info, type).horizontalAdvance;
}

int Font::HorizontalAdvance(std::string_view str, FontType type) const {
	int width = 0;
	for (auto c : Utf8IterableString(str)) {
		width += HorizontalAdvance(c, type);
	}
	return width;
}

int Font::GetGlyphCount() const {
	return mGlyphs.size();
}

const GlyphInfo& Font::GetFallbackGlyph() const {
	return mGlyphs[mFallbackGlyphIdx];
}

const GlyphInfo& Font::FindGlyphFallback(char32_t codepoint) const {
	auto codepointInt = static_cast<uint32_t>(codepoint);
	if (codepointInt < mGlyphLookup.size()) {
		return mGlyphs[mGlyphLookup[codepointInt]];
	} else {
		return mGlyphs[mFallbackGlyphIdx];
	}
}

const GlyphInfo* Font::FindGlyph(char32_t codepoint) const {
	auto codepointInt = static_cast<uint32_t>(codepoint);
	if (codepointInt < mGlyphLookup.size()) {
		return &mGlyphs[mGlyphLookup[codepointInt]];
	} else {
		return nullptr;
	}
}

namespace ProjectBrussel_UNITY_ID {
void GenQuad(Vertex_PTC* vertices, glm::vec3 pos, const GlyphVariant& variant) {
	// Top left
	vertices[0].x = pos.x + variant.x0;
	vertices[0].y = pos.y + variant.y0;
	vertices[0].u = variant.u0;
	vertices[0].v = variant.v0;
	// Top right
	vertices[1].x = pos.x + variant.x1;
	vertices[1].y = pos.y + variant.y0;
	vertices[1].u = variant.u1;
	vertices[1].v = variant.v0;
	// Bottom right
	vertices[2].x = pos.x + variant.x1;
	vertices[2].y = pos.y + variant.y1;
	vertices[2].u = variant.u1;
	vertices[2].v = variant.v1;
	// Bottom left
	vertices[3].x = pos.x + variant.x0;
	vertices[3].y = pos.y + variant.y1;
	vertices[3].u = variant.u0;
	vertices[3].v = variant.v1;
}

template <class TStringIterable>
void DrawString(const Font& font, TStringIterable text, Font::DrawTargetPointer& t) {
	auto pos = t.pos;
	auto vertices = t.vertices;
	auto indices = t.indices;
	auto initialVertexIdx = t.initialVertexIdx;

	for (char32_t codepoint : text) {
		auto& info = font.FindGlyphFallback(codepoint);
		auto& variant = ProjectBrussel_UNITY_ID::GetVariantFor(info, t.type);
		GenQuad(vertices, pos, variant);
		Vertex_PTC::Assign(vertices, pos.z);
		Vertex_PTC::Assign(vertices, t.color);
		Index_U32::Assign(indices, initialVertexIdx);

		pos.x += variant.horizontalAdvance;
		t.glyphsRendered++;
		t.horizontalAdvance += variant.horizontalAdvance;

		vertices += 4;
		indices += 6;
		initialVertexIdx += 4;
	}
}
} // namespace ProjectBrussel_UNITY_ID

void Font::DrawTo(std::string_view text, DrawTargetPointer& t) const {
	ProjectBrussel_UNITY_ID::DrawString(*this, Utf8IterableString(text), t);
}

void Font::DrawTo(std::u32string_view text, DrawTargetPointer& t) const {
	ProjectBrussel_UNITY_ID::DrawString(*this, text, t);
}

const Texture& Font::GetGlyphAtlas() const {
	return *mAtlas;
}