#include <dirent.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>

#include <pagemap/pagemap.h>

struct proc_info {
    pid_t pid;
    pm_memusage_t usage;
    unsigned long wss;
};

static void usage(char *myname);
static int getprocname(pid_t pid, char *buf, int len);
static int numcmp(long long a, long long b);

#define declare_sort(field) \
    static int sort_by_ ## field (const void *a, const void *b)

declare_sort(vss);
declare_sort(rss);
declare_sort(pss);
declare_sort(uss);

int (*compfn)(const void *a, const void *b);
static int order;

void print_mem_info() {
    char buffer[1024];
    int numFound = 0;

    int fd = open("/proc/meminfo", O_RDONLY);

    if (fd < 0) {
        printf("Unable to open /proc/meminfo: %s\n", strerror(errno));
        return;
    }

    const int len = read(fd, buffer, sizeof(buffer)-1);
    close(fd);

    if (len < 0) {
        printf("Empty /proc/meminfo");
        return;
    }
    buffer[len] = 0;

    static const char* const tags[] = {
            "MemTotal:",
            "MemFree:",
            "Buffers:",
            "Cached:",
            "Shmem:",
            "Slab:",
            NULL
    };
    static const int tagsLen[] = {
            9,
            8,
            8,
            7,
            6,
            5,
            0
    };
    long mem[] = { 0, 0, 0, 0, 0, 0 };

    char* p = buffer;
    while (*p && numFound < 6) {
        int i = 0;
        while (tags[i]) {
            if (strncmp(p, tags[i], tagsLen[i]) == 0) {
                p += tagsLen[i];
                while (*p == ' ') p++;
                char* num = p;
                while (*p >= '0' && *p <= '9') p++;
                if (*p != 0) {
                    *p = 0;
                    p++;
                }
                mem[i] = atoll(num);
                numFound++;
                break;
            }
            i++;
        }
        while (*p && *p != '\n') {
            p++;
        }
        if (*p) p++;
    }

    printf("RAM: %ldK total, %ldK free, %ldK buffers, %ldK cached, %ldK shmem, %ldK slab\n",
            mem[0], mem[1], mem[2], mem[3], mem[4], mem[5]);
}

int main(int argc, char *argv[]) {
    pm_kernel_t *ker;
    pm_process_t *proc;
    pid_t *pids;
    struct proc_info **procs;
    size_t num_procs;
    unsigned long total_pss;
    unsigned long total_uss;
    char cmdline[256]; // this must be within the range of int
    int error;

    #define WS_OFF   0
    #define WS_ONLY  1
    #define WS_RESET 2
    int ws;

    int arg;
    size_t i, j;

    compfn = &sort_by_pss;
    order = -1;
    ws = WS_OFF;

    for (arg = 1; arg < argc; arg++) {
        if (!strcmp(argv[arg], "-v")) { compfn = &sort_by_vss; continue; }
        if (!strcmp(argv[arg], "-r")) { compfn = &sort_by_rss; continue; }
        if (!strcmp(argv[arg], "-p")) { compfn = &sort_by_pss; continue; }
        if (!strcmp(argv[arg], "-u")) { compfn = &sort_by_uss; continue; }
        if (!strcmp(argv[arg], "-w")) { ws = WS_ONLY; continue; }
        if (!strcmp(argv[arg], "-W")) { ws = WS_RESET; continue; }
        if (!strcmp(argv[arg], "-R")) { order *= -1; continue; }
        if (!strcmp(argv[arg], "-h")) { usage(argv[0]); exit(0); }
        fprintf(stderr, "Invalid argument \"%s\".\n", argv[arg]);
        usage(argv[0]);
        exit(EXIT_FAILURE);
    }

    error = pm_kernel_create(&ker);
    if (error) {
        fprintf(stderr, "Error creating kernel interface -- "
                        "does this kernel have pagemap?\n");
        exit(EXIT_FAILURE);
    }

    error = pm_kernel_pids(ker, &pids, &num_procs);
    if (error) {
        fprintf(stderr, "Error listing processes.\n");
        exit(EXIT_FAILURE);
    }

    procs = calloc(num_procs, sizeof(struct proc_info*));
    if (procs == NULL) {
        fprintf(stderr, "calloc: %s", strerror(errno));
        exit(EXIT_FAILURE);
    }

    for (i = 0; i < num_procs; i++) {
        procs[i] = malloc(sizeof(struct proc_info));
        if (procs[i] == NULL) {
            fprintf(stderr, "malloc: %s\n", strerror(errno));
            exit(EXIT_FAILURE);
        }
        procs[i]->pid = pids[i];
        pm_memusage_zero(&procs[i]->usage);
        error = pm_process_create(ker, pids[i], &proc);
        if (error) {
            fprintf(stderr, "warning: could not create process interface for %d\n", pids[i]);
            continue;
        }

        switch (ws) {
        case WS_OFF:
            error = pm_process_usage(proc, &procs[i]->usage);
            break;
        case WS_ONLY:
            error = pm_process_workingset(proc, &procs[i]->usage, 0);
            break;
        case WS_RESET:
            error = pm_process_workingset(proc, NULL, 1);
            break;
        }

        if (error) {
            fprintf(stderr, "warning: could not read usage for %d\n", pids[i]);
        }

        pm_process_destroy(proc);
    }

    free(pids);

    if (ws == WS_RESET) exit(0);

    j = 0;
    for (i = 0; i < num_procs; i++) {
        if (procs[i]->usage.vss) {
            procs[j++] = procs[i];
        } else {
            free(procs[i]);
        }
    }
    num_procs = j;

    qsort(procs, num_procs, sizeof(procs[0]), compfn);

    if (ws)
        printf("%5s  %7s  %7s  %7s  %s\n", "PID", "WRss", "WPss", "WUss", "cmdline");
    else
        printf("%5s  %7s  %7s  %7s  %7s  %s\n", "PID", "Vss", "Rss", "Pss", "Uss", "cmdline");

    total_pss = 0;
    total_uss = 0;

    for (i = 0; i < num_procs; i++) {
        if (getprocname(procs[i]->pid, cmdline, (int)sizeof(cmdline)) < 0) {
            /*
             * Something is probably seriously wrong if writing to the stack
             * failed.
             */
            free(procs[i]);
            continue;
        }

        total_pss += procs[i]->usage.pss;
        total_uss += procs[i]->usage.uss;

        if (ws)
            printf("%5d  %6dK  %6dK  %6dK  %s\n",
                procs[i]->pid,
                procs[i]->usage.rss / 1024,
                procs[i]->usage.pss / 1024,
                procs[i]->usage.uss / 1024,
                cmdline
            );
        else
            printf("%5d  %6dK  %6dK  %6dK  %6dK  %s\n",
                procs[i]->pid,
                procs[i]->usage.vss / 1024,
                procs[i]->usage.rss / 1024,
                procs[i]->usage.pss / 1024,
                procs[i]->usage.uss / 1024,
                cmdline
            );

        free(procs[i]);
    }

    free(procs);

    if (ws) {
        printf("%5s  %7s  %7s  %7s  %s\n",
            "", "", "------", "------", "------");
        printf("%5s  %7s  %6ldK  %6ldK  %s\n",
            "", "", total_pss / 1024, total_uss / 1024, "TOTAL");
    } else {
        printf("%5s  %7s  %7s  %7s  %7s  %s\n",
            "", "", "", "------", "------", "------");
        printf("%5s  %7s  %7s  %6ldK  %6ldK  %s\n",
            "", "", "", total_pss / 1024, total_uss / 1024, "TOTAL");
    }

    printf("\n");
    print_mem_info();

    return 0;
}

static void usage(char *myname) {
    fprintf(stderr, "Usage: %s [ -W ] [ -v | -r | -p | -u | -h ]\n"
                    "    -v  Sort by VSS.\n"
                    "    -r  Sort by RSS.\n"
                    "    -p  Sort by PSS.\n"
                    "    -u  Sort by USS.\n"
                    "        (Default sort order is PSS.)\n"
                    "    -R  Reverse sort order (default is descending).\n"
                    "    -w  Display statistics for working set only.\n"
                    "    -W  Reset working set of all processes.\n"
                    "    -h  Display this help screen.\n",
    myname);
}

/*
 * Get the process name for a given PID. Inserts the process name into buffer
 * buf of length len. The size of the buffer must be greater than zero to get
 * any useful output.
 *
 * Note that fgets(3) only declares length as an int, so our buffer size is
 * also declared as an int.
 *
 * Returns 0 on success, a positive value on partial success, and -1 on
 * failure. Other interesting values:
 *   1 on failure to create string to examine proc cmdline entry
 *   2 on failure to open proc cmdline entry
 *   3 on failure to read proc cmdline entry
 */
static int getprocname(pid_t pid, char *buf, int len) {
    char *filename;
    FILE *f;
    int rc = 0;
    static const char* unknown_cmdline = "<unknown>";

    if (len <= 0) {
        return -1;
    }

    if (asprintf(&filename, "/proc/%zd/cmdline", pid) < 0) {
        rc = 1;
        goto exit;
    }

    f = fopen(filename, "r");
    if (f == NULL) {
        rc = 2;
        goto releasefilename;
    }

    if (fgets(buf, len, f) == NULL) {
        rc = 3;
        goto closefile;
    }

closefile:
    (void) fclose(f);
releasefilename:
    free(filename);
exit:
    if (rc != 0) {
        /*
         * The process went away before we could read its process name. Try
         * to give the user "<unknown>" here, but otherwise they get to look
         * at a blank.
         */
        if (strlcpy(buf, unknown_cmdline, (size_t)len) >= (size_t)len) {
            rc = 4;
        }
    }

    return rc;
}

static int numcmp(long long a, long long b) {
    if (a < b) return -1;
    if (a > b) return 1;
    return 0;
}

#define create_sort(field, compfn) \
    static int sort_by_ ## field (const void *a, const void *b) { \
        return order * compfn( \
            (*((struct proc_info**)a))->usage.field, \
            (*((struct proc_info**)b))->usage.field \
        ); \
    }

create_sort(vss, numcmp)
create_sort(rss, numcmp)
create_sort(pss, numcmp)
create_sort(uss, numcmp)