1 files changed, 148 insertions, 0 deletions
diff --git a/include/mbgl/style/expression/parsing_context.hpp b/include/mbgl/style/expression/parsing_context.hpp
new file mode 100644
index 0000000000..a983789cbd
--- /dev/null
+++ b/include/mbgl/style/expression/parsing_context.hpp
@@ -0,0 +1,148 @@
+#pragma once
+
+#include <mbgl/util/optional.hpp>
+#include <mbgl/util/string.hpp>
+#include <mbgl/style/expression/type.hpp>
+#include <mbgl/style/conversion.hpp>
+
+#include <map>
+#include <string>
+#include <vector>
+#include <memory>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+class Expression;
+
+struct ParsingError {
+    std::string message;
+    std::string key;
+    bool operator==(const ParsingError& rhs) const { return message == rhs.message && key == rhs.key; }
+};
+
+using ParseResult = optional<std::unique_ptr<Expression>>;
+
+namespace detail {
+
+class Scope {
+public:
+    Scope(const std::map<std::string, std::shared_ptr<Expression>>& bindings_, std::shared_ptr<Scope> parent_ = nullptr) :
+        bindings(bindings_),
+        parent(std::move(parent_))
+    {}
+
+    const std::map<std::string, std::shared_ptr<Expression>>& bindings;
+    std::shared_ptr<Scope> parent;
+    
+    optional<std::shared_ptr<Expression>> get(const std::string& name) {
+        auto it = bindings.find(name);
+        if (it != bindings.end()) {
+            return {it->second};
+        } else if (parent) {
+            return parent->get(name);
+        } else {
+            return optional<std::shared_ptr<Expression>>();
+        }
+    }
+};
+
+} // namespace detail
+
+class ParsingContext {
+public:
+    ParsingContext() : errors(std::make_shared<std::vector<ParsingError>>()) {}
+    ParsingContext(std::string key_) : key(std::move(key_)), errors(std::make_shared<std::vector<ParsingError>>()) {}
+    explicit ParsingContext(optional<type::Type> expected_)
+        : expected(std::move(expected_)),
+          errors(std::make_shared<std::vector<ParsingError>>())
+    {}
+    ParsingContext(ParsingContext&&) = default;
+    
+    ParsingContext(const ParsingContext&) = delete;
+    ParsingContext& operator=(const ParsingContext&) = delete;
+
+    std::string getKey() const { return key; }
+    optional<type::Type> getExpected() const { return expected; }
+    const std::vector<ParsingError>& getErrors() const { return *errors; }
+
+    /*
+        Parse the given style-spec JSON value into an Expression object.
+        Specifically, this function is responsible for determining the expression
+        type (either Literal, or the one named in value[0]) and dispatching to the
+        appropriate ParseXxxx::parse(const V&, ParsingContext) method.
+    */
+    ParseResult parse(const mbgl::style::conversion::Convertible& value);
+    
+    /*
+        Parse a child expression.
+    */
+    ParseResult parse(const mbgl::style::conversion::Convertible&,
+                      std::size_t,
+                      optional<type::Type> = {});
+    
+    /*
+        Parse a child expression.
+    */
+    ParseResult parse(const mbgl::style::conversion::Convertible&,
+                      std::size_t index,
+                      optional<type::Type>,
+                      const std::map<std::string, std::shared_ptr<Expression>>&);
+
+    /*
+        Check whether `t` is a subtype of `expected`, collecting an error if not.
+     */
+    optional<std::string> checkType(const type::Type& t);
+    
+    optional<std::shared_ptr<Expression>> getBinding(const std::string name) {
+        if (!scope) return optional<std::shared_ptr<Expression>>();
+        return scope->get(name);
+    }
+
+    void error(std::string message) {
+        errors->push_back({message, key});
+    }
+    
+    void error(std::string message, std::size_t child) {
+        errors->push_back({message, key + "[" + util::toString(child) + "]"});
+    }
+    
+    void error(std::string message, std::size_t child, std::size_t grandchild) {
+        errors->push_back({message, key + "[" + util::toString(child) + "][" + util::toString(grandchild) + "]"});
+    }
+    
+    void appendErrors(ParsingContext&& ctx) {
+        errors->reserve(errors->size() + ctx.errors->size());
+        std::move(ctx.errors->begin(), ctx.errors->end(), std::inserter(*errors, errors->end()));
+        ctx.errors->clear();
+    }
+    
+    void clearErrors() {
+        errors->clear();
+    }
+    
+private:
+    ParsingContext(std::string key_,
+                   std::shared_ptr<std::vector<ParsingError>> errors_,
+                   optional<type::Type> expected_,
+                   std::shared_ptr<detail::Scope> scope_)
+        : key(std::move(key_)),
+          expected(std::move(expected_)),
+          scope(std::move(scope_)),
+        errors(std::move(errors_))
+    {}
+    
+    std::string key;
+    optional<type::Type> expected;
+    std::shared_ptr<detail::Scope> scope;
+    std::shared_ptr<std::vector<ParsingError>> errors;
+};
+
+using ParseFunction = ParseResult (*)(const conversion::Convertible&, ParsingContext&);
+using ExpressionRegistry = std::unordered_map<std::string, ParseFunction>;
+const ExpressionRegistry& getExpressionRegistry();
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl