From 09206ddc5c2681c3e5cad503920bb5e8497f2773 Mon Sep 17 00:00:00 2001
From: Robin Linden <dev@robinlinden.eu>
Date: Tue, 14 Jan 2025 02:28:04 +0100
Subject: [PATCH] json: Support parsing numbers

---
 json/json.h        | 98 ++++++++++++++++++++++++++++++++++++++++++++++
 json/json_test.cpp | 18 +++++++++
 2 files changed, 116 insertions(+)

diff --git a/json/json.h b/json/json.h
index 2508e61a..e526deac 100644
--- a/json/json.h
+++ b/json/json.h
@@ -114,6 +114,10 @@ class Parser {
             return std::nullopt;
         }
 
+        if (*c == '-' || (*c >= '0' && *c <= '9')) {
+            return parse_number();
+        }
+
         switch (*c) {
             case '"':
                 return parse_string();
@@ -132,6 +136,100 @@ class Parser {
         }
     }
 
+    constexpr std::optional<Value> parse_number() {
+        std::string number;
+        if (auto c = peek(); c == '-') {
+            number.push_back('-');
+            std::ignore = consume();
+        }
+
+        if (auto c = peek(); c == '0') {
+            number.push_back('0');
+            std::ignore = consume();
+        } else if (c >= '1' && c <= '9') {
+            number.push_back(*c);
+            std::ignore = consume();
+
+            for (c = peek(); c && *c >= '0' && *c <= '9'; c = peek()) {
+                number.push_back(*c);
+                std::ignore = consume();
+            }
+        } else {
+            return std::nullopt;
+        }
+
+        bool is_floating_point = false;
+        if (peek() == '.') {
+            number.push_back('.');
+            std::ignore = consume();
+            is_floating_point = true;
+
+            auto c = peek();
+            if (!c || *c < '0' || *c > '9') {
+                return std::nullopt;
+            }
+
+            number.push_back(*c);
+            std::ignore = consume();
+
+            while ((c = peek())) {
+                if (*c >= '0' && *c <= '9') {
+                    number.push_back(*c);
+                    std::ignore = consume();
+                    continue;
+                }
+
+                break;
+            }
+        }
+
+        if (auto c = peek(); c == 'e' || c == 'E') {
+            number.push_back(*c);
+            std::ignore = consume();
+            is_floating_point = true;
+
+            if (c = peek(); c == '+' || c == '-') {
+                number.push_back(*c);
+                std::ignore = consume();
+            }
+
+            if (c = peek(); !c || *c < '0' || *c > '9') {
+                return std::nullopt;
+            }
+
+            number.push_back(*c);
+            std::ignore = consume();
+
+            while ((c = peek())) {
+                if (*c >= '0' && *c <= '9') {
+                    number.push_back(*c);
+                    std::ignore = consume();
+                    continue;
+                }
+
+                break;
+            }
+        }
+
+        if (!is_floating_point) {
+            std::int64_t value{};
+            if (auto [p, ec] = std::from_chars(number.data(), number.data() + number.size(), value);
+                    ec != std::errc{} || p != number.data() + number.size()) {
+                return std::nullopt;
+            }
+
+            return Value{value};
+        }
+
+        double value{};
+        if (auto [p, ec] = std::from_chars(number.data(), number.data() + number.size(), value);
+                ec != std::errc{} || p != number.data() + number.size()) {
+            return std::nullopt;
+        }
+
+        return Value{value};
+    }
+
     // NOLINTNEXTLINE(misc-no-recursion)
     constexpr std::optional<Value> parse_object() {
         std::ignore = consume(); // '{'
diff --git a/json/json_test.cpp b/json/json_test.cpp
index 485bde3e..7d571ac4 100644
--- a/json/json_test.cpp
+++ b/json/json_test.cpp
@@ -107,5 +107,23 @@ int main() {
         a.expect_eq(json::parse(R"({"key":true})"), Value{json::Object{{{"key", Value{true}}}}});
     });
 
+    s.add_test("numbers", [](etest::IActions &a) {
+        a.expect_eq(json::parse("0"), Value{0});
+        a.expect_eq(json::parse("1"), Value{1});
+        a.expect_eq(json::parse("123"), Value{123});
+        a.expect_eq(json::parse("123.456"), Value{123.456});
+        a.expect_eq(json::parse("-0"), Value{-0});
+        a.expect_eq(json::parse("-1"), Value{-1});
+        a.expect_eq(json::parse("-123"), Value{-123});
+        a.expect_eq(json::parse("-123.456"), Value{-123.456});
+        a.expect_eq(json::parse("0.123"), Value{0.123});
+        a.expect_eq(json::parse("0.123e4"), Value{0.123e4});
+        a.expect_eq(json::parse("0.123e-4"), Value{0.123e-4});
+        a.expect_eq(json::parse("0.123e+4"), Value{0.123e+4});
+
+        a.expect_eq(json::parse("0.123e456"), std::nullopt); // out-of-range
+        a.expect_eq(json::parse("123."), std::nullopt);
+    });
+
     return s.run();
 }