#define _CRT_SECURE_NO_WARNINGS
#define _CRT_NONSTDC_NO_DEPRECATE
#include <string>
#include <vector>
#include <stdio.h>
#include <io.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>

using std::string, std::string_view, std::vector;

struct Config {
    const char *markdownLabel = "markdown";
    const char *codeLabel = "cpp";
    const char *markdownExt = ".md";
    const char *codeExt = ".cpp";
    const char *openCodeBlock = "```";
    const char *closeCodeBlock = "````\n";
    const char *openCommentBlock = "/***";
    const char *closeCommentBlock = "****/\n";
};

string readFile(const string &path) {
    string result;
    if (int fileDescriptor; (fileDescriptor = open(path.data(), _O_RDONLY | _O_TEXT)) != -1) {
        if (struct stat fileStat; fstat(fileDescriptor, &fileStat) == 0) {
            result.resize(fileStat.st_size);
            result.resize(read(fileDescriptor, &result[0], (int)result.size()));
        }
        close(fileDescriptor);
    }
    return result;
}

bool writeFile(const string &path, const string &text) {
    int fileDescriptor = open(path.data(), O_WRONLY | O_CREAT | O_TRUNC | _O_TEXT, 0640);
    if (fileDescriptor == -1)
        return false;
    int written = write(fileDescriptor, &text[0], (int)text.size());
    int closeResult = close(fileDescriptor);
    return written == text.size() && closeResult != -1;
}

string join(const vector<string_view> &spans, const char *openBlock, const char *sourceLanguage, const char *closeBlock) {
    auto joinInto = [](char *dest, const vector<string_view> &spans, const char *openBlock, const char *sourceLanguage, const char *closeBlock) {
        size_t totalSize = 0;
        char *cursor = dest;
        size_t maxSize = dest == nullptr ? 0 : size_t(-1);
        bool comment = true;
        for (auto span : spans) {
            if (dest != nullptr)
                cursor = dest + totalSize;
            if (span.size() > 0) {
                if (comment)
                    totalSize += snprintf(cursor, maxSize, "%s %s\n%.*s%s", openBlock, sourceLanguage, (int)span.size(), span.data(), closeBlock);
                else
                    totalSize += snprintf(cursor, maxSize, "%.*s", (int)span.size(), span.data());
            }
            comment = !comment;
        }
        return totalSize;
    };
    size_t totalSize = joinInto(nullptr, spans, openBlock, sourceLanguage, closeBlock);
    string result(totalSize, '\0');
    joinInto(&result[0], spans, openBlock, sourceLanguage, closeBlock);
    return result;
}

string convert(const string &source,
               const char *destLanguage,  const char *sourceLanguage,
               const char *destOpenBlock, const char *destCloseBlock,
               const char *srcOpenBlock,  const char *srcCloseBlock) {
    vector<string_view> spans;
    const char *token = srcOpenBlock;
    const string::size_type strlenSrcCloseBlock = strlen(srcCloseBlock);
    const string::size_type sourceSize = source.size();
    for (string::size_type spanStart = 0, spanEnd = 0; spanEnd < sourceSize;) {
        spanEnd = source.find(token, spanStart);
        if (spanEnd == string::npos)
            spanEnd = sourceSize;
        if (token == srcCloseBlock)
            spanStart = source.find('\n', spanStart) + 1;
        string_view span = string_view(&source[spanStart], spanEnd - spanStart);
        spans.push_back(span);

        if (token == srcCloseBlock)
            spanEnd += strlenSrcCloseBlock;
        token = token == srcOpenBlock ? srcCloseBlock : srcOpenBlock;
        spanStart = spanEnd;
    }
    string result = join(spans, destOpenBlock, sourceLanguage, destCloseBlock);
    return result;
}

string codeFromMarkdown(const string &markdown, const Config &config) {
    return convert(markdown,
        config.codeLabel, config.markdownLabel,
        config.openCommentBlock, config.closeCommentBlock,
        config.openCodeBlock, config.closeCodeBlock);
}

string markdownFromCode(const string &code, const Config &config) {
    return convert(code,
        config.markdownLabel, config.codeLabel,
        config.openCodeBlock, config.closeCodeBlock,
        config.openCommentBlock, config.closeCommentBlock);
}

bool endsWith(const string s, const char *x) { return s.rfind(x) == (s.size() - strlen(x)); }

int main(int argc, char *argv[]) {
    Config config;
    int errors = 0;
    for (int arg = 1; arg < argc; arg++) {
        string srcPath(argv[arg]);
        const char *mdExt = config.markdownExt, *codeExt = config.codeExt;
        const char *srcExt = endsWith(srcPath, mdExt) ? mdExt : codeExt;
        const char *dstExt = srcExt == mdExt ? codeExt : mdExt;
        string srcText = readFile(srcPath.data());
        string dstText = dstExt == mdExt ? markdownFromCode(srcText, config)
                                         : codeFromMarkdown(srcText, config);
        if (dstText.empty()) {
            errors++;
            fprintf(stderr, "Failed to convert %.*s\n", (int)srcPath.size(), srcPath.data());
        }
        else {
            string dstPath = srcPath.replace(srcPath.rfind(srcExt), strlen(srcExt), dstExt);
            if (!writeFile(dstPath.data(), dstText)) {
                errors++;
                fprintf(stderr, "Failed to write %.*s\n", (int)dstPath.size(), dstPath.data());
            }
        }
    }
    return errors;
}