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// Formatting library for C++ - scanning API proof of concept
//
// Copyright (c) 2019 - present, Victor Zverovich
// All rights reserved.
//
// For the license information refer to format.h.
#include <array>
#include <cassert>
#include <climits>
#include "fmt/format.h"
FMT_BEGIN_NAMESPACE
template <typename T, typename Char = char> struct scanner {
// A deleted default constructor indicates a disabled scanner.
scanner() = delete;
};
class scan_parse_context {
private:
string_view format_;
public:
using iterator = string_view::iterator;
explicit FMT_CONSTEXPR scan_parse_context(string_view format)
: format_(format) {}
FMT_CONSTEXPR iterator begin() const { return format_.begin(); }
FMT_CONSTEXPR iterator end() const { return format_.end(); }
void advance_to(iterator it) {
format_.remove_prefix(detail::to_unsigned(it - begin()));
}
};
struct scan_context {
private:
string_view input_;
public:
using iterator = const char*;
explicit scan_context(string_view input) : input_(input) {}
iterator begin() const { return input_.data(); }
iterator end() const { return begin() + input_.size(); }
void advance_to(iterator it) {
input_.remove_prefix(detail::to_unsigned(it - begin()));
}
};
namespace detail {
enum class scan_type {
none_type,
int_type,
uint_type,
long_long_type,
ulong_long_type,
string_type,
string_view_type,
custom_type
};
struct custom_scan_arg {
void* value;
void (*scan)(void* arg, scan_parse_context& parse_ctx, scan_context& ctx);
};
class scan_arg {
public:
scan_type type;
union {
int* int_value;
unsigned* uint_value;
long long* long_long_value;
unsigned long long* ulong_long_value;
std::string* string;
fmt::string_view* string_view;
custom_scan_arg custom;
// TODO: more types
};
scan_arg() : type(scan_type::none_type) {}
scan_arg(int& value) : type(scan_type::int_type), int_value(&value) {}
scan_arg(unsigned& value) : type(scan_type::uint_type), uint_value(&value) {}
scan_arg(long long& value)
: type(scan_type::long_long_type), long_long_value(&value) {}
scan_arg(unsigned long long& value)
: type(scan_type::ulong_long_type), ulong_long_value(&value) {}
scan_arg(std::string& value) : type(scan_type::string_type), string(&value) {}
scan_arg(fmt::string_view& value)
: type(scan_type::string_view_type), string_view(&value) {}
template <typename T> scan_arg(T& value) : type(scan_type::custom_type) {
custom.value = &value;
custom.scan = scan_custom_arg<T>;
}
private:
template <typename T>
static void scan_custom_arg(void* arg, scan_parse_context& parse_ctx,
scan_context& ctx) {
scanner<T> s;
parse_ctx.advance_to(s.parse(parse_ctx));
ctx.advance_to(s.scan(*static_cast<T*>(arg), ctx));
}
};
} // namespace detail
struct scan_args {
int size;
const detail::scan_arg* data;
template <size_t N>
scan_args(const std::array<detail::scan_arg, N>& store)
: size(N), data(store.data()) {
static_assert(N < INT_MAX, "too many arguments");
}
};
namespace detail {
struct scan_handler : error_handler {
private:
scan_parse_context parse_ctx_;
scan_context scan_ctx_;
scan_args args_;
int next_arg_id_;
scan_arg arg_;
template <typename T = unsigned> T read_uint() {
T value = 0;
auto it = scan_ctx_.begin(), end = scan_ctx_.end();
while (it != end) {
char c = *it++;
if (c < '0' || c > '9') on_error("invalid input");
// TODO: check overflow
value = value * 10 + static_cast<unsigned>(c - '0');
}
scan_ctx_.advance_to(it);
return value;
}
template <typename T = int> T read_int() {
auto it = scan_ctx_.begin(), end = scan_ctx_.end();
bool negative = it != end && *it == '-';
if (negative) ++it;
scan_ctx_.advance_to(it);
const auto value = read_uint<typename std::make_unsigned<T>::type>();
if (negative) return -static_cast<T>(value);
return static_cast<T>(value);
}
public:
scan_handler(string_view format, string_view input, scan_args args)
: parse_ctx_(format), scan_ctx_(input), args_(args), next_arg_id_(0) {}
const char* pos() const { return scan_ctx_.begin(); }
void on_text(const char* begin, const char* end) {
auto size = to_unsigned(end - begin);
auto it = scan_ctx_.begin();
if (it + size > scan_ctx_.end() ||
!std::equal(begin, end, make_checked(it, size))) {
on_error("invalid input");
}
scan_ctx_.advance_to(it + size);
}
FMT_CONSTEXPR int on_arg_id() { return on_arg_id(next_arg_id_++); }
FMT_CONSTEXPR int on_arg_id(int id) {
if (id >= args_.size) on_error("argument index out of range");
arg_ = args_.data[id];
return id;
}
FMT_CONSTEXPR int on_arg_id(string_view id) {
if (id.data()) on_error("invalid format");
return 0;
}
void on_replacement_field(int, const char*) {
auto it = scan_ctx_.begin(), end = scan_ctx_.end();
switch (arg_.type) {
case scan_type::int_type:
*arg_.int_value = read_int();
break;
case scan_type::uint_type:
*arg_.uint_value = read_uint();
break;
case scan_type::long_long_type:
*arg_.long_long_value = read_int<long long>();
break;
case scan_type::ulong_long_type:
*arg_.ulong_long_value = read_uint<unsigned long long>();
break;
case scan_type::string_type:
while (it != end && *it != ' ') arg_.string->push_back(*it++);
scan_ctx_.advance_to(it);
break;
case scan_type::string_view_type: {
auto s = it;
while (it != end && *it != ' ') ++it;
*arg_.string_view = fmt::string_view(s, to_unsigned(it - s));
scan_ctx_.advance_to(it);
break;
}
case scan_type::none_type:
case scan_type::custom_type:
assert(false);
}
}
const char* on_format_specs(int, const char* begin, const char*) {
if (arg_.type != scan_type::custom_type) return begin;
parse_ctx_.advance_to(begin);
arg_.custom.scan(arg_.custom.value, parse_ctx_, scan_ctx_);
return parse_ctx_.begin();
}
};
} // namespace detail
template <typename... Args>
std::array<detail::scan_arg, sizeof...(Args)> make_scan_args(Args&... args) {
return {{args...}};
}
string_view::iterator vscan(string_view input, string_view format_str,
scan_args args) {
detail::scan_handler h(format_str, input, args);
detail::parse_format_string<false>(format_str, h);
return input.begin() + (h.pos() - &*input.begin());
}
template <typename... Args>
string_view::iterator scan(string_view input, string_view format_str,
Args&... args) {
return vscan(input, format_str, make_scan_args(args...));
}
FMT_END_NAMESPACE
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