Canvas.cc

// Copyright (c) 2010 LearnBoost <tj@learnboost.com>

#include "Canvas.h"
#include "InstanceData.h"
#include <algorithm> // std::min
#include <assert.h>
#include <cairo-pdf.h>
#include <cairo-svg.h>
#include "CanvasRenderingContext2d.h"
#include "closure.h"
#include <cstring>
#include <cctype>
#include <ctime>
#include <glib.h>
#include "PNG.h"
#include "register_font.h"
#include <sstream>
#include <stdlib.h>
#include <string>
#include <unordered_set>
#include "Util.h"
#include <vector>
#include "node_buffer.h"

#ifdef HAVE_JPEG
#include "JPEGStream.h"
#endif

#include "backend/ImageBackend.h"
#include "backend/PdfBackend.h"
#include "backend/SvgBackend.h"

#define GENERIC_FACE_ERROR \
  "The second argument to registerFont is required, and should be an object " \
  "with at least a family (string) and optionally weight (string/number) " \
  "and style (string)."

using namespace std;

std::vector<FontFace> font_face_list;

/*
 * Initialize Canvas.
 */

void
Canvas::Initialize(Napi::Env& env, Napi::Object& exports) {
  Napi::HandleScope scope(env);
  InstanceData* data = env.GetInstanceData<InstanceData>();

  // Constructor
  Napi::Function ctor = DefineClass(env, "Canvas", {
    InstanceMethod<&Canvas::ToBuffer>("toBuffer"),
    InstanceMethod<&Canvas::StreamPNGSync>("streamPNGSync"),
    InstanceMethod<&Canvas::StreamPDFSync>("streamPDFSync"),
#ifdef HAVE_JPEG
    InstanceMethod<&Canvas::StreamJPEGSync>("streamJPEGSync"),
#endif
    InstanceAccessor<&Canvas::GetType>("type"),
    InstanceAccessor<&Canvas::GetStride>("stride"),
    InstanceAccessor<&Canvas::GetWidth, &Canvas::SetWidth>("width"),
    InstanceAccessor<&Canvas::GetHeight, &Canvas::SetHeight>("height"),
    InstanceValue("PNG_NO_FILTERS", Napi::Number::New(env, PNG_NO_FILTERS)),
    InstanceValue("PNG_FILTER_NONE", Napi::Number::New(env, PNG_FILTER_NONE)),
    InstanceValue("PNG_FILTER_SUB", Napi::Number::New(env, PNG_FILTER_SUB)),
    InstanceValue("PNG_FILTER_UP", Napi::Number::New(env, PNG_FILTER_UP)),
    InstanceValue("PNG_FILTER_AVG", Napi::Number::New(env, PNG_FILTER_AVG)),
    InstanceValue("PNG_FILTER_PAETH", Napi::Number::New(env, PNG_FILTER_PAETH)),
    InstanceValue("PNG_ALL_FILTERS", Napi::Number::New(env, PNG_ALL_FILTERS)),
    StaticMethod<&Canvas::RegisterFont>("_registerFont"),
    StaticMethod<&Canvas::DeregisterAllFonts>("_deregisterAllFonts")
  });

  data->CanvasCtor = Napi::Persistent(ctor);
  exports.Set("Canvas", ctor);
}

/*
 * Initialize a Canvas with the given width and height.
 */

Canvas::Canvas(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Canvas>(info), env(info.Env()) {
  InstanceData* data = env.GetInstanceData<InstanceData>();
  ctor = Napi::Persistent(data->CanvasCtor.Value());
  Backend* backend = NULL;
  Napi::Object jsBackend;

  if (info[0].IsNumber()) {
    Napi::Number width = info[0].As<Napi::Number>();
    Napi::Number height = Napi::Number::New(env, 0);

    if (info[1].IsNumber()) height = info[1].As<Napi::Number>();

    if (info[2].IsString()) {
      std::string str = info[2].As<Napi::String>();
      if (str == "pdf") {
        Napi::Maybe<Napi::Object> instance = data->PdfBackendCtor.New({ width, height });
        if (instance.IsJust()) backend = PdfBackend::Unwrap(jsBackend = instance.Unwrap());
      } else if (str == "svg") {
        Napi::Maybe<Napi::Object> instance = data->SvgBackendCtor.New({ width, height });
        if (instance.IsJust()) backend = SvgBackend::Unwrap(jsBackend = instance.Unwrap());
      } else {
        Napi::Maybe<Napi::Object> instance = data->ImageBackendCtor.New({ width, height });
        if (instance.IsJust()) backend = ImageBackend::Unwrap(jsBackend = instance.Unwrap());
      }
    } else {
      Napi::Maybe<Napi::Object> instance = data->ImageBackendCtor.New({ width, height });
      if (instance.IsJust()) backend = ImageBackend::Unwrap(jsBackend = instance.Unwrap());
    }
  } else if (info[0].IsObject()) {
    jsBackend = info[0].As<Napi::Object>();
    if (jsBackend.InstanceOf(data->ImageBackendCtor.Value()).UnwrapOr(false)) {
      backend = ImageBackend::Unwrap(jsBackend);
    } else if (jsBackend.InstanceOf(data->PdfBackendCtor.Value()).UnwrapOr(false)) {
      backend = PdfBackend::Unwrap(jsBackend);
    } else if (jsBackend.InstanceOf(data->SvgBackendCtor.Value()).UnwrapOr(false)) {
      backend = SvgBackend::Unwrap(jsBackend);
    } else {
      Napi::TypeError::New(env, "Invalid arguments").ThrowAsJavaScriptException();
      return;
    }
  } else {
    Napi::Number width = Napi::Number::New(env, 0);
    Napi::Number height = Napi::Number::New(env, 0);
    Napi::Maybe<Napi::Object> instance = data->ImageBackendCtor.New({ width, height });
    if (instance.IsJust()) backend = ImageBackend::Unwrap(jsBackend = instance.Unwrap());
  }

  if (!backend->isSurfaceValid()) {
    Napi::Error::New(env, backend->getError()).ThrowAsJavaScriptException();
    return;
  }

  backend->setCanvas(this);

  // Note: the backend gets destroyed when the jsBackend is GC'd. The cleaner
  // way would be to only store the jsBackend and unwrap it when the c++ ref is
  // needed, but that's slower and a burden. The _backend might be null if we
  // returned early, but since an exception was thrown it gets destroyed soon.
  _backend = backend;
  _jsBackend = Napi::Persistent(jsBackend);
}

/*
 * Get type string.
 */

Napi::Value
Canvas::GetType(const Napi::CallbackInfo& info) {
  return Napi::String::New(env, backend()->getName());
}

/*
 * Get stride.
 */
Napi::Value
Canvas::GetStride(const Napi::CallbackInfo& info) {
  return Napi::Number::New(env, stride());
}

/*
 * Get width.
 */

Napi::Value
Canvas::GetWidth(const Napi::CallbackInfo& info) {
  return Napi::Number::New(env, getWidth());
}

/*
 * Set width.
 */

void
Canvas::SetWidth(const Napi::CallbackInfo& info, const Napi::Value& value) {
  if (value.IsNumber()) {
    backend()->setWidth(value.As<Napi::Number>().Uint32Value());
    resurface(info.This().As<Napi::Object>());
  }
}

/*
 * Get height.
 */

Napi::Value
Canvas::GetHeight(const Napi::CallbackInfo& info) {
  return Napi::Number::New(env, getHeight());
}

/*
 * Set height.
 */

void
Canvas::SetHeight(const Napi::CallbackInfo& info, const Napi::Value& value) {
  if (value.IsNumber()) {
    backend()->setHeight(value.As<Napi::Number>().Uint32Value());
    resurface(info.This().As<Napi::Object>());
  }
}

/*
 * EIO toBuffer callback.
 */

void
Canvas::ToPngBufferAsync(Closure* base) {
  PngClosure* closure = static_cast<PngClosure*>(base);

  closure->status = canvas_write_to_png_stream(
    closure->canvas->surface(),
    PngClosure::writeVec,
    closure);
}

#ifdef HAVE_JPEG
void
Canvas::ToJpegBufferAsync(Closure* base) {
  JpegClosure* closure = static_cast<JpegClosure*>(base);
  write_to_jpeg_buffer(closure->canvas->surface(), closure);
}
#endif

static void
parsePNGArgs(Napi::Value arg, PngClosure& pngargs) {
  if (arg.IsObject()) {
    Napi::Object obj = arg.As<Napi::Object>();
    Napi::Value cLevel;

    if (obj.Get("compressionLevel").UnwrapTo(&cLevel) && cLevel.IsNumber()) {
      uint32_t val = cLevel.As<Napi::Number>().Uint32Value();
      // See quote below from spec section 4.12.5.5.
      if (val <= 9) pngargs.compressionLevel = val;
    }

    Napi::Value rez;
    if (obj.Get("resolution").UnwrapTo(&rez) && rez.IsNumber()) {
      uint32_t val = rez.As<Napi::Number>().Uint32Value();
      if (val > 0) pngargs.resolution = val;
    }

    Napi::Value filters;
    if (obj.Get("filters").UnwrapTo(&filters) && filters.IsNumber()) {
      pngargs.filters = filters.As<Napi::Number>().Uint32Value();
    }

    Napi::Value palette;
    if (obj.Get("palette").UnwrapTo(&palette) && palette.IsTypedArray()) {
      Napi::TypedArray palette_ta = palette.As<Napi::TypedArray>();
      if (palette_ta.TypedArrayType() == napi_uint8_clamped_array) {
        pngargs.nPaletteColors = palette_ta.ElementLength();
        if (pngargs.nPaletteColors % 4 != 0) {
          throw "Palette length must be a multiple of 4.";
        }
        pngargs.palette = palette_ta.As<Napi::Uint8Array>().Data();
        pngargs.nPaletteColors /= 4;
        // Optional background color index:
        Napi::Value backgroundIndexVal;
        if (obj.Get("backgroundIndex").UnwrapTo(&backgroundIndexVal) && backgroundIndexVal.IsNumber()) {
          pngargs.backgroundIndex = backgroundIndexVal.As<Napi::Number>().Uint32Value();
        }
      }
    }
  }
}

#ifdef HAVE_JPEG
static void parseJPEGArgs(Napi::Value arg, JpegClosure& jpegargs) {
  // "If Type(quality) is not Number, or if quality is outside that range, the
  // user agent must use its default quality value, as if the quality argument
  // had not been given." - 4.12.5.5
  if (arg.IsObject()) {
    Napi::Object obj = arg.As<Napi::Object>();

    Napi::Value qual;
    if (obj.Get("quality").UnwrapTo(&qual) && qual.IsNumber()) {
      double quality = qual.As<Napi::Number>().DoubleValue();
      if (quality >= 0.0 && quality <= 1.0) {
        jpegargs.quality = static_cast<uint32_t>(100.0 * quality);
      }
    }

    Napi::Value chroma;
    if (obj.Get("chromaSubsampling").UnwrapTo(&chroma)) {
      if (chroma.IsBoolean()) {
        bool subsample = chroma.As<Napi::Boolean>().Value();
        jpegargs.chromaSubsampling = subsample ? 2 : 1;
      } else if (chroma.IsNumber()) {
        jpegargs.chromaSubsampling = chroma.As<Napi::Number>().Uint32Value();
      }
    }

    Napi::Value progressive;
    if (obj.Get("progressive").UnwrapTo(&progressive) && progressive.IsBoolean()) {
      jpegargs.progressive = progressive.As<Napi::Boolean>().Value();
    }
  }
}
#endif

#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 16, 0)

static inline void setPdfMetaStr(cairo_surface_t* surf, Napi::Object opts,
  cairo_pdf_metadata_t t, const char* propName) {
  Napi::Value propValue;
  if (opts.Get(propName).UnwrapTo(&propValue) && propValue.IsString()) {
    // (copies char data)
    cairo_pdf_surface_set_metadata(surf, t, propValue.As<Napi::String>().Utf8Value().c_str());
  }
}

static inline void setPdfMetaDate(cairo_surface_t* surf, Napi::Object opts,
  cairo_pdf_metadata_t t, const char* propName) {
  Napi::Value propValue;
  if (opts.Get(propName).UnwrapTo(&propValue) && propValue.IsDate()) {
    auto date = static_cast<time_t>(propValue.As<Napi::Date>().ValueOf() / 1000); // ms -> s
    char buf[sizeof "2011-10-08T07:07:09Z"];
    strftime(buf, sizeof buf, "%FT%TZ", gmtime(&date));
    cairo_pdf_surface_set_metadata(surf, t, buf);
  }
}

static void setPdfMetadata(Canvas* canvas, Napi::Object opts) {
  cairo_surface_t* surf = canvas->surface();

  setPdfMetaStr(surf, opts, CAIRO_PDF_METADATA_TITLE, "title");
  setPdfMetaStr(surf, opts, CAIRO_PDF_METADATA_AUTHOR, "author");
  setPdfMetaStr(surf, opts, CAIRO_PDF_METADATA_SUBJECT, "subject");
  setPdfMetaStr(surf, opts, CAIRO_PDF_METADATA_KEYWORDS, "keywords");
  setPdfMetaStr(surf, opts, CAIRO_PDF_METADATA_CREATOR, "creator");
  setPdfMetaDate(surf, opts, CAIRO_PDF_METADATA_CREATE_DATE, "creationDate");
  setPdfMetaDate(surf, opts, CAIRO_PDF_METADATA_MOD_DATE, "modDate");
}

#endif // CAIRO 16+

/*
 * Converts/encodes data to a Buffer. Async when a callback function is passed.

 * PDF canvases:
    (any) => Buffer
    ("application/pdf", config) => Buffer

 * SVG canvases:
    (any) => Buffer

 * ARGB data:
    ("raw") => Buffer

 * PNG-encoded
    () => Buffer
    (undefined|"image/png", {compressionLevel?: number, filter?: number}) => Buffer
    ((err: null|Error, buffer) => any)
    ((err: null|Error, buffer) => any, undefined|"image/png", {compressionLevel?: number, filter?: number})

 * JPEG-encoded
    ("image/jpeg") => Buffer
    ("image/jpeg", {quality?: number, progressive?: Boolean, chromaSubsampling?: Boolean|number}) => Buffer
    ((err: null|Error, buffer) => any, "image/jpeg")
    ((err: null|Error, buffer) => any, "image/jpeg", {quality?: number, progressive?: Boolean, chromaSubsampling?: Boolean|number})
 */

Napi::Value
Canvas::ToBuffer(const Napi::CallbackInfo& info) {
  EncodingWorker *worker = new EncodingWorker(info.Env());
  cairo_status_t status;

  // Vector canvases, sync only
  const std::string name = backend()->getName();
  if (name == "pdf" || name == "svg") {
    // mime type may be present, but it's not checked
    PdfSvgClosure* closure;
    if (name == "pdf") {
      closure = static_cast<PdfBackend*>(backend())->closure();
#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 16, 0)
      if (info[1].IsObject()) { // toBuffer("application/pdf", config)
        setPdfMetadata(this, info[1].As<Napi::Object>());
      }
#endif // CAIRO 16+
    } else {
      closure = static_cast<SvgBackend*>(backend())->closure();
    }

    cairo_surface_finish(surface());
    return Napi::Buffer<uint8_t>::Copy(env, &closure->vec[0], closure->vec.size());
  }

  // Raw ARGB data -- just a memcpy()
  if (info[0].StrictEquals(Napi::String::New(env, "raw"))) {
    cairo_surface_t *surface = this->surface();
    cairo_surface_flush(surface);
    if (nBytes() > node::Buffer::kMaxLength) {
      Napi::Error::New(env, "Data exceeds maximum buffer length.").ThrowAsJavaScriptException();
      return env.Undefined();
    }
    return Napi::Buffer<uint8_t>::Copy(env, cairo_image_surface_get_data(surface), nBytes());
  }

  // Sync PNG, default
  if (info[0].IsUndefined() || info[0].StrictEquals(Napi::String::New(env, "image/png"))) {
    try {
      PngClosure closure(this);
      parsePNGArgs(info[1], closure);
      if (closure.nPaletteColors == 0xFFFFFFFF) {
        Napi::Error::New(env, "Palette length must be a multiple of 4.").ThrowAsJavaScriptException();
        return env.Undefined();
      }

      status = canvas_write_to_png_stream(surface(), PngClosure::writeVec, &closure);

      if (!env.IsExceptionPending()) {
        if (status) {
          throw status; // TODO: throw in js?
        } else {
          // TODO it's possible to avoid this copy
          return Napi::Buffer<uint8_t>::Copy(env, &closure.vec[0], closure.vec.size());
        }
      }
    } catch (cairo_status_t ex) {
      CairoError(ex).ThrowAsJavaScriptException();
    } catch (const char* ex) {
      Napi::Error::New(env, ex).ThrowAsJavaScriptException();

    }

    return env.Undefined();
  }

  // Async PNG
  if (info[0].IsFunction() &&
    (info[1].IsUndefined() || info[1].StrictEquals(Napi::String::New(env, "image/png")))) {

    PngClosure* closure;
    try {
      closure = new PngClosure(this);
      parsePNGArgs(info[2], *closure);
    } catch (cairo_status_t ex) {
      CairoError(ex).ThrowAsJavaScriptException();
      return env.Undefined();
    } catch (const char* ex) {
      Napi::Error::New(env, ex).ThrowAsJavaScriptException();
      return env.Undefined();
    }

    Ref();
    closure->cb = Napi::Persistent(info[0].As<Napi::Function>());

    // Make sure the surface exists since we won't have an isolate context in the async block:
    surface();
    worker->Init(&ToPngBufferAsync, closure);
    worker->Queue();

    return env.Undefined();
  }

#ifdef HAVE_JPEG
  // Sync JPEG
  Napi::Value jpegStr = Napi::String::New(env, "image/jpeg");
  if (info[0].StrictEquals(jpegStr)) {
    try {
      JpegClosure closure(this);
      parseJPEGArgs(info[1], closure);

      write_to_jpeg_buffer(surface(), &closure);

      if (!env.IsExceptionPending()) {
        // TODO it's possible to avoid this copy.
        return Napi::Buffer<uint8_t>::Copy(env, &closure.vec[0], closure.vec.size());
      }
    } catch (cairo_status_t ex) {
      CairoError(ex).ThrowAsJavaScriptException();
      return env.Undefined();
    }
    return env.Undefined();
  }

  // Async JPEG
  if (info[0].IsFunction() && info[1].StrictEquals(jpegStr)) {
    JpegClosure* closure = new JpegClosure(this);
    parseJPEGArgs(info[2], *closure);

    Ref();
    closure->cb = Napi::Persistent(info[0].As<Napi::Function>());

    // Make sure the surface exists since we won't have an isolate context in the async block:
    surface();
    worker->Init(&ToJpegBufferAsync, closure);
    worker->Queue();
    return env.Undefined();
  }
#endif

  return env.Undefined();
}

/*
 * Canvas::StreamPNG callback.
 */

static cairo_status_t
streamPNG(void *c, const uint8_t *data, unsigned len) {
  PngClosure* closure = (PngClosure*) c;
  Napi::Env env = closure->canvas->env;
  Napi::HandleScope scope(env);
  Napi::AsyncContext async(env, "canvas:StreamPNG");
  Napi::Value buf = Napi::Buffer<uint8_t>::Copy(env, data, len);
  closure->cb.MakeCallback(env.Global(), { env.Null(), buf, Napi::Number::New(env, len) }, async);
  return CAIRO_STATUS_SUCCESS;
}

/*
 * Stream PNG data synchronously. TODO async
 * StreamPngSync(this, options: {palette?: Uint8ClampedArray, backgroundIndex?: uint32, compressionLevel: uint32, filters: uint32})
 */

void
Canvas::StreamPNGSync(const Napi::CallbackInfo& info) {
  if (!info[0].IsFunction()) {
    Napi::TypeError::New(env, "callback function required").ThrowAsJavaScriptException();
    return;
  }

  PngClosure closure(this);
  parsePNGArgs(info[1], closure);

  closure.cb = Napi::Persistent(info[0].As<Napi::Function>());

  cairo_status_t status = canvas_write_to_png_stream(surface(), streamPNG, &closure);

  if (!env.IsExceptionPending()) {
    if (status) {
      closure.cb.Call(env.Global(), { CairoError(status).Value() });
    } else {
      closure.cb.Call(env.Global(), { env.Null(), env.Null(), Napi::Number::New(env, 0) });
    }
  }
}


struct PdfStreamInfo {
  Napi::Function fn;
  uint32_t len;
  uint8_t* data;
};

/*
 * Canvas::StreamPDF callback.
 */

static cairo_status_t
streamPDF(void *c, const uint8_t *data, unsigned len) {
  PdfStreamInfo* streaminfo = static_cast<PdfStreamInfo*>(c);
  Napi::Env env = streaminfo->fn.Env();
  Napi::HandleScope scope(env);
  Napi::AsyncContext async(env, "canvas:StreamPDF");
  // TODO this is technically wrong, we're returning a pointer to the data in a
  // vector in a class with automatic storage duration. If the canvas goes out
  // of scope while we're in the handler, a use-after-free could happen.
  Napi::Value buf = Napi::Buffer<uint8_t>::New(env, (uint8_t *)(data), len);
  streaminfo->fn.MakeCallback(env.Global(), { env.Null(), buf, Napi::Number::New(env, len) }, async);
  return CAIRO_STATUS_SUCCESS;
}


cairo_status_t canvas_write_to_pdf_stream(cairo_surface_t *surface, cairo_write_func_t write_func, PdfStreamInfo* streaminfo) {
  size_t whole_chunks = streaminfo->len / PAGE_SIZE;
  size_t remainder = streaminfo->len - whole_chunks * PAGE_SIZE;

  for (size_t i = 0; i < whole_chunks; ++i) {
    write_func(streaminfo, &streaminfo->data[i * PAGE_SIZE], PAGE_SIZE);
  }

  if (remainder) {
    write_func(streaminfo, &streaminfo->data[whole_chunks * PAGE_SIZE], remainder);
  }

  return CAIRO_STATUS_SUCCESS;
}

/*
 * Stream PDF data synchronously.
 */

void
Canvas::StreamPDFSync(const Napi::CallbackInfo& info) {
  if (!info[0].IsFunction()) {
    Napi::TypeError::New(env, "callback function required").ThrowAsJavaScriptException();
    return;
  }

  if (backend()->getName() != "pdf") {
    Napi::TypeError::New(env, "wrong canvas type").ThrowAsJavaScriptException();
    return;
  }

#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 16, 0)
  if (info[1].IsObject()) {
    setPdfMetadata(this, info[1].As<Napi::Object>());
  }
#endif

  cairo_surface_finish(surface());

  PdfSvgClosure* closure = static_cast<PdfBackend*>(backend())->closure();
  Napi::Function fn = info[0].As<Napi::Function>();
  PdfStreamInfo streaminfo;
  streaminfo.fn = fn;
  streaminfo.data = &closure->vec[0];
  streaminfo.len = closure->vec.size();

  cairo_status_t status = canvas_write_to_pdf_stream(surface(), streamPDF, &streaminfo);

  if (!env.IsExceptionPending()) {
    if (status) {
      fn.Call(env.Global(), { CairoError(status).Value() });
    } else {
      fn.Call(env.Global(), { env.Null(), env.Null(), Napi::Number::New(env, 0) });
    }
  }
}

/*
 * Stream JPEG data synchronously.
 */

#ifdef HAVE_JPEG
static uint32_t getSafeBufSize(Canvas* canvas) {
  // Don't allow the buffer size to exceed the size of the canvas (#674)
  // TODO not sure if this is really correct, but it fixed #674
  return (std::min)(canvas->getWidth() * canvas->getHeight() * 4, static_cast<int>(PAGE_SIZE));
}

void
Canvas::StreamJPEGSync(const Napi::CallbackInfo& info) {
  if (!info[1].IsFunction()) {
    Napi::TypeError::New(env, "callback function required").ThrowAsJavaScriptException();
    return;
  }

  JpegClosure closure(this);
  parseJPEGArgs(info[0], closure);
  closure.cb = Napi::Persistent(info[1].As<Napi::Function>());

  uint32_t bufsize = getSafeBufSize(this);
  write_to_jpeg_stream(surface(), bufsize, &closure);
}
#endif

char *
str_value(Napi::Maybe<Napi::Value> maybe, const char *fallback, bool can_be_number) {
  Napi::Value val;
  if (maybe.UnwrapTo(&val)) {
    if (val.IsString() || (can_be_number && val.IsNumber())) {
      Napi::String strVal;
      if (val.ToString().UnwrapTo(&strVal)) return strdup(strVal.Utf8Value().c_str());
    } else if (fallback) {
      return strdup(fallback);
    }
  }
  
  return NULL;
}

void
Canvas::RegisterFont(const Napi::CallbackInfo& info) {
  Napi::Env env = info.Env();
  if (!info[0].IsString()) {
    Napi::Error::New(env, "Wrong argument type").ThrowAsJavaScriptException();
    return;
  } else if (!info[1].IsObject()) {
    Napi::Error::New(env, GENERIC_FACE_ERROR).ThrowAsJavaScriptException();
    return;
  }

  std::string filePath = info[0].As<Napi::String>();
  PangoFontDescription *sys_desc = get_pango_font_description((unsigned char *)(filePath.c_str()));

  if (!sys_desc) {
    Napi::Error::New(env, "Could not parse font file").ThrowAsJavaScriptException();
    return;
  }

  PangoFontDescription *user_desc = pango_font_description_new();

  // now check the attrs, there are many ways to be wrong
  Napi::Object js_user_desc = info[1].As<Napi::Object>();

  char *family = str_value(js_user_desc.Get("family"), NULL, false);
  char *weight = str_value(js_user_desc.Get("weight"), "normal", true);
  char *style = str_value(js_user_desc.Get("style"), "normal", false);

  if (family && weight && style) {
    pango_font_description_set_weight(user_desc, Canvas::GetWeightFromCSSString(weight));
    pango_font_description_set_style(user_desc, Canvas::GetStyleFromCSSString(style));
    pango_font_description_set_family(user_desc, family);

    auto found = std::find_if(font_face_list.begin(), font_face_list.end(), [&](FontFace& f) {
      return pango_font_description_equal(f.sys_desc, sys_desc);
    });

    if (found != font_face_list.end()) {
      pango_font_description_free(found->user_desc);
      found->user_desc = user_desc;
    } else if (register_font((unsigned char *) filePath.c_str())) {
      FontFace face;
      face.user_desc = user_desc;
      face.sys_desc = sys_desc;
      strncpy((char *)face.file_path, (char *) filePath.c_str(), 1023);
      font_face_list.push_back(face);
    } else {
      pango_font_description_free(user_desc);
      Napi::Error::New(env, "Could not load font to the system's font host").ThrowAsJavaScriptException();

    }
  } else {
    pango_font_description_free(user_desc);
    if (!env.IsExceptionPending()) {
      Napi::Error::New(env, GENERIC_FACE_ERROR).ThrowAsJavaScriptException();
    }
  }

  free(family);
  free(weight);
  free(style);
}

void
Canvas::DeregisterAllFonts(const Napi::CallbackInfo& info) {
  Napi::Env env = info.Env();
  // Unload all fonts from pango to free up memory
  bool success = true;

  std::for_each(font_face_list.begin(), font_face_list.end(), [&](FontFace& f) {
    if (!deregister_font( (unsigned char *)f.file_path )) success = false;
    pango_font_description_free(f.user_desc);
    pango_font_description_free(f.sys_desc);
  });

  font_face_list.clear();
  if (!success) Napi::Error::New(env, "Could not deregister one or more fonts").ThrowAsJavaScriptException();
}

/*
 * Get a PangoStyle from a CSS string (like "italic")
 */

PangoStyle
Canvas::GetStyleFromCSSString(const char *style) {
  PangoStyle s = PANGO_STYLE_NORMAL;

  if (strlen(style) > 0) {
    if (0 == strcmp("italic", style)) {
      s = PANGO_STYLE_ITALIC;
    } else if (0 == strcmp("oblique", style)) {
      s = PANGO_STYLE_OBLIQUE;
    }
  }

  return s;
}

/*
 * Get a PangoWeight from a CSS string ("bold", "100", etc)
 */

PangoWeight
Canvas::GetWeightFromCSSString(const char *weight) {
  PangoWeight w = PANGO_WEIGHT_NORMAL;

  if (strlen(weight) > 0) {
    if (0 == strcmp("bold", weight)) {
      w = PANGO_WEIGHT_BOLD;
    } else if (0 == strcmp("100", weight)) {
      w = PANGO_WEIGHT_THIN;
    } else if (0 == strcmp("200", weight)) {
      w = PANGO_WEIGHT_ULTRALIGHT;
    } else if (0 == strcmp("300", weight)) {
      w = PANGO_WEIGHT_LIGHT;
    } else if (0 == strcmp("400", weight)) {
      w = PANGO_WEIGHT_NORMAL;
    } else if (0 == strcmp("500", weight)) {
      w = PANGO_WEIGHT_MEDIUM;
    } else if (0 == strcmp("600", weight)) {
      w = PANGO_WEIGHT_SEMIBOLD;
    } else if (0 == strcmp("700", weight)) {
      w = PANGO_WEIGHT_BOLD;
    } else if (0 == strcmp("800", weight)) {
      w = PANGO_WEIGHT_ULTRABOLD;
    } else if (0 == strcmp("900", weight)) {
      w = PANGO_WEIGHT_HEAVY;
    }
  }

  return w;
}

/*
 * Given a user description, return a description that will select the
 * font either from the system or @font-face
 */

PangoFontDescription *
Canvas::ResolveFontDescription(const PangoFontDescription *desc) {
  // One of the user-specified families could map to multiple SFNT family names
  // if someone registered two different fonts under the same family name.
  // https://drafts.csswg.org/css-fonts-3/#font-style-matching
  FontFace best;
  istringstream families(pango_font_description_get_family(desc));
  unordered_set<string> seen_families;
  string resolved_families;
  bool first = true;

  for (string family; getline(families, family, ','); ) {
    string renamed_families;
    for (auto& ff : font_face_list) {
      string pangofamily = string(pango_font_description_get_family(ff.user_desc));
      if (streq_casein(family, pangofamily)) {
        const char* sys_desc_family_name = pango_font_description_get_family(ff.sys_desc);
        bool unseen = seen_families.find(sys_desc_family_name) == seen_families.end();
        bool better = best.user_desc == nullptr || pango_font_description_better_match(desc, best.user_desc, ff.user_desc);

        // Avoid sending duplicate SFNT font names due to a bug in Pango for macOS:
        // https://bugzilla.gnome.org/show_bug.cgi?id=762873
        if (unseen) {
          seen_families.insert(sys_desc_family_name);

          if (better) {
            renamed_families = string(sys_desc_family_name) + (renamed_families.size() ? "," : "") + renamed_families;
          } else {
            renamed_families = renamed_families + (renamed_families.size() ? "," : "") + sys_desc_family_name;
          }
        }

        if (first && better) best = ff;
      }
    }

    if (resolved_families.size()) resolved_families += ',';
    resolved_families += renamed_families.size() ? renamed_families : family;
    first = false;
  }

  PangoFontDescription* ret = pango_font_description_copy(best.sys_desc ? best.sys_desc : desc);
  pango_font_description_set_family(ret, resolved_families.c_str());

  return ret;
}

/*
 * Re-alloc the surface, destroying the previous.
 */

void
Canvas::resurface(Napi::Object This) {
  Napi::HandleScope scope(env);
  Napi::Value context;

  if (This.Get("context").UnwrapTo(&context) && context.IsObject()) {
    backend()->recreateSurface();
    // Reset context
    Context2d *context2d = Context2d::Unwrap(context.As<Napi::Object>());
    cairo_t *prev = context2d->context();
    context2d->setContext(createCairoContext());
    context2d->resetState();
    cairo_destroy(prev);
  }
}

/**
 * Wrapper around cairo_create()
 * (do not call cairo_create directly, call this instead)
 */
cairo_t*
Canvas::createCairoContext() {
  cairo_t* ret = cairo_create(surface());
  cairo_set_line_width(ret, 1); // Cairo defaults to 2
  return ret;
}

/*
 * Construct an Error from the given cairo status.
 */

Napi::Error
Canvas::CairoError(cairo_status_t status) {
  return Napi::Error::New(env, cairo_status_to_string(status));
}