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#pragma once
#include <mbgl/style/types.hpp>
#include <mbgl/style/property_value.hpp>
#include <mbgl/style/transition_options.hpp>
#include <mbgl/util/variant.hpp>
#include <mbgl/util/optional.hpp>
#include <mbgl/util/color.hpp>
#include <mbgl/util/enum.hpp>
#include <array>
#include <string>
#include <vector>
namespace mbgl {
namespace style {
namespace conversion {
/*
This namespace defines a generic conversion from a templated type `V` representing a JSON object conforming
to a style property from the Mapbox Style Specification, to `PropertyValue<T>`:
template <class T, class V>
Result<PropertyValue<T>> convertPropertyValue(const V& value);
This is used concretely for conversions from RapidJSON types in mbgl core, and from v8 types in
the node bindings.
The requirements are that the following are legal expressions for a value `v` of type `const V&`:
* `isArray(v)` -- returns a boolean indicating whether `v` represents a JSON array
* `arrayLength(v)` -- called only if `isArray(v)`; returns a size_t length
* `arrayMember(v)` -- called only if `isArray(v)`; returns `V` or `V&`
* `isObject(v)` -- returns a boolean indicating whether `v` represents a JSON object
* `objectMember(v, name)` -- called only if `isObject(v)`; `name` is `const char *`; return value:
* is true when evaluated in a boolean context iff the named member exists
* is convertable to a `V` or `V&` when dereferenced
* `toBool(v)` -- returns `optional<bool>`, absence indicating `v` is not a JSON boolean
* `toNumber(v)` -- returns `optional<float>`, absence indicating `v` is not a JSON number
* `toString(v)` -- returns `optional<std::string>`, absence indicating `v` is not a JSON string
If for any reason the conversion fails, the result of `convertPropertyValue` will be the `Error` variant,
which includes explanatory text.
*/
struct Error { const char * message; };
template <class V>
using Result = variant<V, Error>;
template <class V, class T, class Enable = void>
struct ConstantConverter {};
template <class V>
struct ConstantConverter<V, bool> {
Result<bool> operator()(const V& value) const {
optional<bool> converted = toBool(value);
if (!converted) {
return Error { "value must be a boolean" };
}
return *converted;
}
};
template <class V>
struct ConstantConverter<V, float> {
Result<float> operator()(const V& value) const {
optional<float> converted = toNumber(value);
if (!converted) {
return Error { "value must be a number" };
}
return *converted;
}
};
template <class V>
struct ConstantConverter<V, std::string> {
Result<std::string> operator()(const V& value) const {
optional<std::string> converted = toString(value);
if (!converted) {
return Error { "value must be a string" };
}
return *converted;
}
};
template <class V, class T>
struct ConstantConverter<V, T, typename std::enable_if_t<std::is_enum<T>::value>> {
Result<T> operator()(const V& value) const {
optional<std::string> string = toString(value);
if (!string) {
return Error { "value must be a string" };
}
const auto result = Enum<T>::toEnum(*string);
if (!result) {
return Error { "value must be a valid enumeration value" };
}
return *result;
}
};
template <class V>
struct ConstantConverter<V, Color> {
Result<Color> operator()(const V& value) const {
optional<std::string> string = toString(value);
if (!string) {
return Error { "value must be a string" };
}
optional<Color> color = Color::parse(*string);
if (!color) {
return Error { "value must be a valid color" };
}
return *color;
}
};
template <class V>
struct ConstantConverter<V, std::array<float, 2>> {
Result<std::array<float, 2>> operator()(const V& value) const {
if (!isArray(value) || arrayLength(value) != 2) {
return Error { "value must be an array of two numbers" };
}
optional<float> first = toNumber(arrayMember(value, 0));
optional<float> second = toNumber(arrayMember(value, 1));
if (!first || !second) {
return Error { "value must be an array of two numbers" };
}
return std::array<float, 2> {{ *first, *second }};
}
};
template <class V>
struct ConstantConverter<V, std::array<float, 4>> {
Result<std::array<float, 4>> operator()(const V& value) const {
if (!isArray(value) || arrayLength(value) != 4) {
return Error { "value must be an array of four numbers" };
}
optional<float> first = toNumber(arrayMember(value, 0));
optional<float> second = toNumber(arrayMember(value, 1));
optional<float> third = toNumber(arrayMember(value, 2));
optional<float> fourth = toNumber(arrayMember(value, 3));
if (!first || !second) {
return Error { "value must be an array of four numbers" };
}
return std::array<float, 4> {{ *first, *second, *third, *fourth }};
}
};
template <class V>
struct ConstantConverter<V, std::vector<float>> {
Result<std::vector<float>> operator()(const V& value) const {
if (!isArray(value)) {
return Error { "value must be an array" };
}
std::vector<float> result;
result.reserve(arrayLength(value));
for (std::size_t i = 0; i < arrayLength(value); ++i) {
optional<float> number = toNumber(arrayMember(value, i));
if (!number) {
return Error { "value must be an array of numbers" };
}
result.push_back(*number);
}
return result;
}
};
template <class V>
struct ConstantConverter<V, std::vector<std::string>> {
Result<std::vector<std::string>> operator()(const V& value) const {
if (!isArray(value)) {
return Error { "value must be an array" };
}
std::vector<std::string> result;
result.reserve(arrayLength(value));
for (std::size_t i = 0; i < arrayLength(value); ++i) {
optional<std::string> string = toString(arrayMember(value, i));
if (!string) {
return Error { "value must be an array of strings" };
}
result.push_back(*string);
}
return result;
}
};
template <class T, class V>
Result<PropertyValue<T>> convertPropertyValue(const V& value) {
if (!isObject(value)) {
Result<T> constant = ConstantConverter<V, T>()(value);
if (constant.template is<Error>()) {
return constant.template get<Error>();
}
return constant.template get<T>();
}
auto stopsValue = objectMember(value, "stops");
if (!stopsValue) {
return Error { "function value must specify stops" };
}
if (!isArray(*stopsValue)) {
return Error { "function stops must be an array" };
}
std::vector<std::pair<float, T>> stops;
for (std::size_t i = 0; i < arrayLength(*stopsValue); ++i) {
const auto& stopValue = arrayMember(*stopsValue, i);
if (!isArray(stopValue)) {
return Error { "function stop must be an array" };
}
if (arrayLength(stopValue) != 2) {
return Error { "function stop must have two elements" };
}
optional<float> z = toNumber(arrayMember(stopValue, 0));
if (!z) {
return Error { "function stop zoom level must be a number" };
}
Result<T> v = ConstantConverter<V, T>()(arrayMember(stopValue, 1));
if (v.template is<Error>()) {
return v.template get<Error>();
}
stops.emplace_back(*z, v.template get<T>());
}
auto baseValue = objectMember(value, "base");
if (!baseValue) {
return Function<T>(stops, 1.0f);
}
optional<float> base = toNumber(*baseValue);
if (!base) {
return Error { "function base must be a number"};
}
return Function<T>(stops, *base);
}
} // namespace conversion
} // namespace style
} // namespace mbgl
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