#include "ExternalEditor.h"

#include <cstdlib>
#include <filesystem>
#include <fstream>
#include <iterator>
#include <sstream>
#include <stdexcept>

#if defined(__unix__) || defined(__APPLE__)
#include <unistd.h>
#endif

namespace fs = std::filesystem;

namespace {

#ifdef _WIN32
const char kPathSeparator = ';';
#else
const char kPathSeparator = ':';
#endif

bool isExecutableFile(const fs::path& path) {
    std::error_code error;
    if (!fs::is_regular_file(path, error)) {
        return false;
    }
#if defined(__unix__) || defined(__APPLE__)
    return access(path.c_str(), X_OK) == 0;
#else
    return true;
#endif
}

bool findInPath(const std::string& program) {
    if (program.find('/') != std::string::npos || program.find('\\') != std::string::npos) {
        return isExecutableFile(program);
    }

    const char* pathVariable = std::getenv("PATH");
    if (!pathVariable) {
        return false;
    }

    std::stringstream paths(pathVariable);
    std::string directory;
    while (std::getline(paths, directory, kPathSeparator)) {
        if (directory.empty()) {
            continue;
        }
        if (isExecutableFile(fs::path(directory) / program)) {
            return true;
        }
#ifdef _WIN32
        if (isExecutableFile(fs::path(directory) / (program + ".exe"))) {
            return true;
        }
#endif
    }
    return false;
}

std::string firstWord(const std::string& command) {
    std::istringstream in(command);
    std::string word;
    in >> word;
    return word;
}

std::string quotePath(const std::string& path) {
#ifdef _WIN32
    return "\"" + path + "\"";
#else
    std::string quoted = "'";
    for (char c : path) {
        if (c == '\'') {
            quoted += "'\\''";
        } else {
            quoted.push_back(c);
        }
    }
    return quoted + "'";
#endif
}

std::string makeTempFile(const std::string& content) {
#if defined(__unix__) || defined(__APPLE__)
    std::string pattern = (fs::temp_directory_path() / "task-tracker-XXXXXX.txt").string();
    std::vector<char> buffer(pattern.begin(), pattern.end());
    buffer.push_back('\0');

    int fd = mkstemps(buffer.data(), 4);
    if (fd < 0) {
        throw std::runtime_error("Cannot create a temporary file for the editor.");
    }
    std::size_t written = 0;
    while (written < content.size()) {
        ssize_t n = ::write(fd, content.data() + written, content.size() - written);
        if (n <= 0) {
            ::close(fd);
            throw std::runtime_error("Cannot write the temporary file for the editor.");
        }
        written += static_cast<std::size_t>(n);
    }
    ::close(fd);
    return std::string(buffer.data());
#else
    fs::path path = fs::temp_directory_path() / ("task-tracker-" + std::to_string(std::rand()) + ".txt");
    std::ofstream out(path, std::ios::binary);
    out << content;
    if (!out) {
        throw std::runtime_error("Cannot write the temporary file for the editor.");
    }
    return path.string();
#endif
}

}  // namespace

namespace ExternalEditor {

std::string defaultCommand() {
    for (const char* variable : {"VISUAL", "EDITOR"}) {
        const char* value = std::getenv(variable);
        if (value && *value) {
            return value;
        }
    }
    for (const char* candidate : {"nano", "vim", "vi"}) {
        if (findInPath(candidate)) {
            return candidate;
        }
    }
    return "";
}

bool commandExists(const std::string& command) {
    const std::string program = firstWord(command);
    return !program.empty() && findInPath(program);
}

std::vector<std::string> installedEditors() {
    std::vector<std::string> found;
    for (const char* candidate : {"nano", "vim", "nvim", "vi", "emacs", "micro", "helix", "hx", "code", "kate", "gedit"}) {
        if (findInPath(candidate)) {
            found.push_back(candidate);
        }
    }
    return found;
}

std::string edit(const std::string& command, const std::string& initialText) {
    const std::string path = makeTempFile(initialText);
    const std::string commandLine = command + " " + quotePath(path);
    const int status = std::system(commandLine.c_str());

    std::ifstream in(path, std::ios::binary);
    std::string content((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
    in.close();
    std::error_code error;
    fs::remove(path, error);

    if (status != 0) {
        throw std::runtime_error("The editor exited with an error; nothing was changed.");
    }
    return content;
}

}  // namespace ExternalEditor