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/*
 * usage: ./dependencyDiscoverer [-Idir] ... file.c|file.l|file.y ...
 *
 * processes the c/yacc/lex source file arguments, outputting the dependencies
 * between the corresponding .o file, the .c source file, and any included
 * .h files
 *
 * each .h file is also processed to yield a dependency between it and any
 * included .h files
 *
 * these dependencies are written to standard output in a form compatible with
 * make; for example, assume that foo.c includes inc1.h, and inc1.h includes
 * inc2.h and inc3.h; this results in
 *
 *                  foo.o: foo.c inc1.h inc2.h inc3.h
 *
 * note that system includes (i.e. those in angle brackets) are NOT processed
 *
 * dependencyDiscoverer uses the CPATH environment variable, which can contain a
 * set of directories separated by ':' to find included files
 * if any additional directories are specified in the command line,
 * these are prepFound to those in CPATH, left to right
 *
 * for example, if CPATH is "/home/user/include:/usr/local/group/include",
 * and if "-Ifoo/bar/include" is specified on the command line, then when
 * processing
 *           #include "x.h"
 * x.h will be located by searching for the following files in this order
 *
 *      ./x.h
 *      foo/bar/include/x.h
 *      /home/user/include/x.h
 *      /usr/local/group/include/x.h
 */

/*
 * general design of main()
 * ========================
 * There are three globally accessible variables:
 * - dirs: a vector storing the directories to search for headers
 * - theTable: a hash table mapping file names to a list of dependent file names
 * - workQ: a list of file names that have to be processed
 *
 * 1. look up CPATH in environment
 * 2. assemble dirs vector from ".", any -Idir flags, and fields in CPATH
 *    (if it is defined)
 * 3. for each file argument (after -Idir flags)
 *    a. insert mapping from file.o to file.ext (where ext is c, y, or l) into
 *       table
 *    b. insert mapping from file.ext to empty list into table
 *    c. append file.ext on workQ
 * 4. for each file on the workQ
 *    a. lookup list of dependencies
 *    b. invoke process(name, list_of_dependencies)
 * 5. for each file argument (after -Idir flags)
 *    a. create a hash table in which to track file names already printed
 *    b. create a linked list to track dependencies yet to print
 *    c. print "foo.o:", insert "foo.o" into hash table
 *       and append "foo.o" to linked list
 *    d. invoke printDependencies()
 *
 * general design for process()
 * ============================
 *
 * 1. open the file
 * 2. for each line of the file
 *    a. skip leading whitespace
 *    b. if match "#include"
 *       i. skip leading whitespace
 *       ii. if next character is '"'
 *           * collect remaining characters of file name (up to '"')
 *           * append file name to dependency list for this open file
 *           * if file name not already in the master Table
 *             - insert mapping from file name to empty list in master table
 *             - append file name to workQ
 * 3. close file
 *
 * general design for printDependencies()
 * ======================================
 *
 * 1. while there is still a file in the toProcess linked list
 * 2. fetch next file from toProcess
 * 3. lookup up the file in the master table, yielding the linked list of dependencies
 * 4. iterate over dependenceies
 *    a. if the filename is already in the printed hash table, continue
 *    b. print the filename
 *    c. insert into printed
 *    d. append to toProcess
 *
 * Additional helper functions
 * ===========================
 *
 * dirName() - appends trailing '/' if needed
 * parseFile() - breaks up filename into root and extension
 * openFile()  - attempts to open a filename using the search path defined by the dirs vector.
 *
 * Farzwan Mohamed
 * 2553017M
 * SP CW2
 *This is my own work as defined in the Academic Ethics agreement I have signed.
 */

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <string>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <mutex>
#include <thread>

struct Queue {
private:
    std::list <std::string> lst;
    std::mutex mut1;
public:
    void push_back(std::string st) {
        std::unique_lock <std::mutex> lock(mut1);
        lst.push_back(st);
    }

    bool empty() {
        return lst.empty();
    }

    std::string getFront() {
        std::unique_lock <std::mutex> lock(mut1);
        std::string st;
        if (lst.empty())
            st = "";
        else {
            st = lst.front();
            lst.pop_front();
        }
        return st;
    }
};

struct HashTable {
private:
    std::unordered_map <std::string, std::list<std::string>> ht;
    std::mutex mut2;
public:
    bool Found(std::string st) {
        std::unique_lock<std::mutex> lock(mut2);
        return ht.find(st)== ht.end();
    }

    std::list <std::string> &operator[](std::string st) {
        std::unique_lock <std::mutex> lock(mut2);
        return ht[st];
    }

    void insert(std::pair <std::string, std::list<std::string>> p) {
        std::unique_lock <std::mutex> lock(mut2);
        ht.insert(p);
    }

};

std::vector <std::string> dirs;
HashTable theTable;
Queue workQ;


std::string dirName(const char *c_str) {
    std::string s = c_str; // s takes ownership of the string content by allocating memory for it
    if (s.back() != '/') { s += '/'; }
    return s;
}


std::pair <std::string, std::string> parseFile(const char *c_file) {
    std::string file = c_file;
    std::string::size_type pos = file.rfind('.');
    if (pos == std::string::npos) {
        return {file, ""};
    } else {
        return {file.substr(0, pos), file.substr(pos + 1)};
    }
}

// open file using the directory search path constructed in main()
static FILE *openFile(const char *file) {
    FILE *fd;
    for (unsigned int i = 0; i < dirs.size(); i++) {
        std::string path = dirs[i] + file;
        fd = fopen(path.c_str(), "r");
        if (fd != NULL)
            return fd; // return the first file that successfully opens
    }
    return NULL;
}

// process file, looking for #include "foo.h" lines
static void process(const char *file, std::list <std::string> *ll) {
    char buf[4096], name[4096];
    // 1. open the file
    FILE *fd = openFile(file);
    if (fd == NULL) {
        fprintf(stderr, "Error opening %s\n", file);
        exit(-1);
    }
    while (fgets(buf, sizeof(buf), fd) != NULL) {
        char *p = buf;
        // 2a. skip leading whitespace
        while (isspace((int) *p)) { p++; }
        // 2b. if match #include
        if (strncmp(p, "#include", 8) != 0) { continue; }
        p += 8; // point to first character past #include
        // 2bi. skip leading whitespace
        while (isspace((int) *p)) { p++; }
        if (*p != '"') { continue; }
        // 2bii. next character is a "
        p++; // skip "
        // 2bii. collect remaining characters of file name
        char *q = name;
        while (*p != '\0') {
            if (*p == '"') { break; }
            *q++ = *p++;
        }
        *q = '\0';
        // 2bii. append file name to dependency list
        ll->push_back({name});
        // 2bii. if file name not already in table ...
        if (!theTable.Found(name)) { continue; }
        // ... insert mapping from file name to empty list in table ...
        theTable.insert({name, {}});
        // ... append file name to workQ
        workQ.push_back(name);
    }
    // 3. close file
    fclose(fd);
}

// iteratively print dependencies
static void printDependencies(std::unordered_set <std::string> *printed,
                              std::list <std::string> *toProcess,
                              FILE *fd) {
    if (!printed || !toProcess || !fd) return;

    // 1. while there is still a file in the toProcess list
    while (toProcess->size() > 0) {
        // 2. fetch next file to process
        std::string name = toProcess->front();
        toProcess->pop_front();
        // 3. lookup file in the table, yielding list of dependencies
        std::list <std::string> *ll = &theTable[name];
        // 4. iterate over dependencies
        for (auto iter = ll->begin(); iter != ll->end(); iter++) {
            // 4a. if filename is already in the printed table, continue
            if (printed->find(*iter) != printed->end()) { continue; }
            // 4b. print filename
            fprintf(fd, " %s", iter->c_str());
            // 4c. insert into printed
            printed->insert(*iter);
            // 4d. append to toProcess
            toProcess->push_back(*iter);
        }
    }
}

void workerThread() {
    while (!workQ.empty()) {
        std::string fname = workQ.getFront();
        if (fname.empty())
            break;
        if (theTable.Found(fname)) {
            fprintf(stderr, "Hashmap and queue discrepant\n");
            exit(-1);
        }
        process(fname.c_str(), &theTable[fname]);
    }
}

int main(int argc, char *argv[]) {
    // 1. look up CPATH in environment
    char *cpath = getenv("CPATH");

    // determine the number of -Idir arguments
    int i;
    for (i = 1; i < argc; i++) {
        if (strncmp(argv[i], "-I", 2) != 0)
            break;
    }
    int start = i;

    // 2. start assembling dirs vector
    dirs.push_back(dirName("./")); // always search current directory first
    for (i = 1; i < start; i++) {
        dirs.push_back(dirName(argv[i] + 2 /* skip -I */));
    }
    if (cpath != NULL) {
        std::string str(cpath);
        std::string::size_type last = 0;
        std::string::size_type next = 0;
        while ((next = str.find(":", last)) != std::string::npos) {
            dirs.push_back(str.substr(last, next - last));
            last = next + 1;
        }
        dirs.push_back(str.substr(last));
    }
    // 2. finished assembling dirs vector

    // 3. for each file argument ...
    for (i = start; i < argc; i++) {
        std::pair <std::string, std::string> pair = parseFile(argv[i]);
        if (pair.second != "c" && pair.second != "y" && pair.second != "l") {
            fprintf(stderr, "Illegal extension: %s - must be .c, .y or .l\n",
                    pair.second.c_str());
            return -1;
        }

        std::string obj = pair.first + ".o";

        // 3a. insert mapping from file.o to file.ext
        theTable.insert({obj, {argv[i]}});

        // 3b. insert mapping from file.ext to empty list
        theTable.insert({argv[i], {}});

        // 3c. append file.ext on workQ
        workQ.push_back(argv[i]);
    }
    char* crawler_threads = getenv("CRAWLER_THREADS");
    int crawl = 2;
    if (crawler_threads != NULL) {
        crawl = atoi(crawler_threads);
    }

    std::vector <std::thread> threads;
    for (int i = 0; i < crawl; i++) {
        threads.emplace_back([](){workerThread(); });
    }
    for (int i = 0; i < crawl; i++) {
        threads[i].join();
    }


        // 5. for each file argument
        for (i = start; i < argc; i++) {
            // 5a. create hash table in which to track file names already printed
            std::unordered_set <std::string> printed;
            // 5b. create list to track dependencies yet to print
            std::list <std::string> toProcess;

            std::pair <std::string, std::string> pair = parseFile(argv[i]);

            std::string obj = pair.first + ".o";
            // 5c. print "foo.o:" ...
            printf("%s:", obj.c_str());
            // 5c. ... insert "foo.o" into hash table and append to list
            printed.insert(obj);
            toProcess.push_back(obj);
            // 5d. invoke
            printDependencies(&printed, &toProcess, stdout);

            printf("\n");
        }

    return 0;
}