#include <cassert>
#include <charconv>
#include <cmath>
#include <cstdint>
#include <ranges>
#include <string>
#include <fstream>
#include <sstream>

#include "doctest.h"

namespace day2 {
  const std::string sample =
	"11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,"
	"446443-446449,38593856-38593862,565653-565659,824824821-824824827,"
	"2121212118-2121212124";

  struct Range {
	uint64_t start;
	uint64_t end;
  };
} // namespace day2

template<>
struct std::formatter<day2::Range> : std::formatter<std::string_view> {
  static auto format(const day2::Range &i, std::format_context &ctx) {
	return std::format_to(ctx.out(), "Range[start: {}, end: {}]", i.start,i.end);
  }
};

namespace day2 {
  Range parse_range(std::string_view s) {
	std::string_view start;
	std::string_view end;

	for (size_t i = 0; i < s.size(); i++) {
	  const char c = s[i];
	  if (c == '-') {
		start = {s.data(), i};
		end = {s.data() + i + 1, s.size() - start.size()};
	  }
	}

	Range range;
	uint64_t parsed;
	std::from_chars(start.data(), start.end(), parsed);
	range.start = parsed;
	std::from_chars(end.data(), end.end(), parsed);
	range.end = parsed;
	return range;
  }

  size_t find_divisor(uint64_t n) {
    for (size_t i = 1;; i++) {
      size_t div = n / std::pow(10, i);
      if (div == 0) {
		return std::pow(10, (i / 2));
      }
    }
	assert(0 && "Unreachable");
  }

  uint64_t count_repetitions(const Range range) {
	uint64_t total = 0;
    for (uint64_t n = range.start; n <= range.end; n++) {
      auto div = find_divisor(n);
      auto left = n / div;
	  auto right = n % div;
	  if (left == right) total++;
    }

	return total;
  }

  uint64_t sum_repetitions(const Range range) {
	uint64_t total = 0;
    for (uint64_t n = range.start; n <= range.end; n++) {
      auto div = find_divisor(n);
      auto left = n / div;
	  auto right = n % div;
	  if (left == right) total += n;
    }

	return total;
  }

  uint64_t solve_first(std::string_view input) {
    uint64_t result = 0;
    for (const auto range :
         std::views::split(input, ',') | std::views::transform([](auto s) {
           return parse_range(std::string_view(s));
         })) {
	  result += sum_repetitions(range);
    }

	return result;
  }

  uint64_t sum_repetitions_2(const Range range, std::string& buf) {
	uint64_t total = 0;
	for (uint64_t n = range.start; n <= range.end; n++) {
	  std::format_to(buf, "{}", n);
    }

	return total;
  }

  uint64_t solve_second(std::string_view input) {
    std::string buf;
	buf.reserve(100);
    uint64_t result = 0;
    for (const auto range :
         std::views::split(input, ',') | std::views::transform([](auto s) {
           return parse_range(std::string_view(s));
         })) {
      result += sum_repetitions_2(range, buf);
	  buf.clear();
    }

	return result;
  }


  TEST_CASE("Can parse input") {
	auto range = parse_range("11-22");
	CHECK(range.start == 11);
	CHECK(range.end == 22);
  }

  TEST_CASE("Solve first sample") {
	CHECK(solve_first(sample) == 1227775554);
  }

  TEST_CASE("Solve first input") {
    std::ifstream fs("day2input.txt");
    std::stringstream ss{};
	ss << fs.rdbuf();
	CHECK(solve_first(ss.str()) == 1227775554);
  }

  TEST_CASE("Find divisor works") {
	CHECK(find_divisor(11) == 10);
	CHECK(find_divisor(1221) == 100);
	CHECK(find_divisor(222222) == 1000);
  }

  TEST_CASE("Count repetition works") {
	CHECK(count_repetitions({.start = 11, .end = 22}) == 2);
	CHECK(count_repetitions({.start = 1188511880, .end = 1188511890}) == 1);
  }

} // namespace day2