abspath2relpath.cpp

#include <iostream>
#include <regex>
#include <string>
#include <sstream>
#include <vector>

std::vector<std::string> split(std::string const& target, std::regex const& pattern)
{
    std::sregex_token_iterator first{target.begin(), target.end(), pattern, -1};
    std::sregex_token_iterator last;
    return std::vector<std::string>(first, last);
}

std::string resolve(std::string const& base, std::string const& target)
{
    auto base_token = split(base, std::regex{"/"});
    auto target_token = split(target, std::regex{"/"});
    auto base_it = base_token.begin();
    auto target_it = target_token.begin();
    while (*base_it == *target_it && base_it != base_token.end() && target_it != target_token.end()) {
        ++base_it;
        ++target_it;
    }
    base_token.erase(base_token.begin(), base_it);
    target_token.erase(target_token.begin(), target_it);
    for (auto i = 0U; i < base_token.size() -1; ++i) {
        target_token.insert(target_token.begin(), "..");
    }
    std::ostringstream oss;
    bool is_first = true;
    for (auto const path : target_token) {
        if (!std::exchange(is_first, false)) {
            oss << "/";
        }
        oss << path;
    }
    return oss.str();
}


int main()
{
    std::cout << resolve("a/b/c/d.js", "a/e/f/g.js") << std::endl;
    std::cout << resolve("a.js", "b/c/d/e.js") << std::endl;
    std::cout << resolve("a/b/c/d.js", "e.js") << std::endl;
    std::cout << resolve("a.js", "b.js") << std::endl;
    std::cout << resolve("a/b/c.js", "d/e/f.js") << std::endl;
    std::cout << resolve("a/b/c/d.js", "a/b/c/e.js") << std::endl;
    std::cout << resolve("a/b/c/d.js", "a/b/e/f.js") << std::endl;
    std::cout << resolve("a/b/c/d.js", "a/b/f.js") << std::endl;
    std::cout << resolve("a/b/c.js", "a/b/d/e.js") << std::endl;
}