#include "../../unity/unity.h"
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <errno.h>

/* usage(int) is defined in the included program source. We also rely on
   set_program_name() and program_name being available via earlier includes
   in the translation unit (system.h/progname.h). */

/* Helper: read all from fd into a NUL-terminated buffer. Caller must free. */
static char *read_all_fd(int fd) {
    size_t cap = 4096;
    size_t len = 0;
    char *buf = (char *)malloc(cap + 1);
    if (!buf) return NULL;

    for (;;) {
        if (len + 2048 > cap) {
            size_t new_cap = cap * 2;
            char *new_buf = (char *)realloc(buf, new_cap + 1);
            if (!new_buf) {
                free(buf);
                return NULL;
            }
            buf = new_buf;
            cap = new_cap;
        }
        ssize_t r = read(fd, buf + len, cap - len);
        if (r > 0) {
            len += (size_t)r;
        } else if (r == 0) {
            break; /* EOF */
        } else {
            if (errno == EINTR) continue;
            /* On error, stop and return what we have so far */
            break;
        }
    }
    buf[len] = '\0';
    return buf;
}

/* Run usage(status) in a child, capturing stdout/stderr and exit status.
   Returns 0 on success (child ran and exited), -1 on error.
   On success, out_str and err_str are malloc'd NUL-terminated strings. */
static int run_usage_and_capture(int status_code, char **out_str, char **err_str, int *exit_status) {
    int out_pipe[2];
    int err_pipe[2];
    if (pipe(out_pipe) != 0) return -1;
    if (pipe(err_pipe) != 0) {
        close(out_pipe[0]); close(out_pipe[1]);
        return -1;
    }

    fflush(stdout);
    fflush(stderr);
    pid_t pid = fork();
    if (pid < 0) {
        close(out_pipe[0]); close(out_pipe[1]);
        close(err_pipe[0]); close(err_pipe[1]);
        return -1;
    } else if (pid == 0) {
        /* Child: redirect stdout/stderr and call usage. */
        /* Ensure English messages for deterministic tests. */
        setenv("LC_ALL", "C", 1);

        /* Ensure program_name is set properly for output formatting. */
        /* Prototype is available from earlier includes in the TU. */
        set_program_name("expr");

        /* Redirect to pipes. */
        dup2(out_pipe[1], STDOUT_FILENO);
        dup2(err_pipe[1], STDERR_FILENO);

        /* Close all pipe fds we don't need. */
        close(out_pipe[0]); close(out_pipe[1]);
        close(err_pipe[0]); close(err_pipe[1]);

        /* Call the function under test; it will call exit(). */
        usage(status_code);

        /* Should not reach here, but be safe. */
        _exit(255);
    } else {
        /* Parent: close write ends, read outputs, wait for child. */
        close(out_pipe[1]);
        close(err_pipe[1]);

        char *out_buf = read_all_fd(out_pipe[0]);
        char *err_buf = read_all_fd(err_pipe[0]);

        close(out_pipe[0]);
        close(err_pipe[0]);

        int wstatus = 0;
        if (waitpid(pid, &wstatus, 0) < 0) {
            if (out_buf) free(out_buf);
            if (err_buf) free(err_buf);
            return -1;
        }

        if (WIFEXITED(wstatus)) {
            *exit_status = WEXITSTATUS(wstatus);
        } else if (WIFSIGNALED(wstatus)) {
            /* Child terminated by signal; emulate a nonzero code. */
            *exit_status = 128 + WTERMSIG(wstatus);
        } else {
            *exit_status = -1;
        }

        *out_str = out_buf ? out_buf : strdup("");
        *err_str = err_buf ? err_buf : strdup("");
        return 0;
    }
}

/* Unity fixtures */
void setUp(void) {
    /* No global setup needed */
}

void tearDown(void) {
    /* No global cleanup needed */
}

/* Tests */

static void assert_contains(const char *haystack, const char *needle, const char *context) {
    if (!haystack || !needle) {
        TEST_FAIL_MESSAGE("Null pointer passed to assert_contains");
    }
    if (strstr(haystack, needle) == NULL) {
        char msg[512];
        snprintf(msg, sizeof(msg), "Expected to find substring \"%s\" in %s output, but did not.", needle, context);
        TEST_FAIL_MESSAGE(msg);
    }
}

void test_usage_success_prints_full_help_and_exits_zero(void) {
    char *out = NULL;
    char *err = NULL;
    int code = -1;

    int rc = run_usage_and_capture(0, &out, &err, &code);
    TEST_ASSERT_EQUAL_INT_MESSAGE(0, rc, "Failed to execute usage() in child process");
    TEST_ASSERT_EQUAL_INT_MESSAGE(0, code, "usage(EXIT_SUCCESS) did not exit with code 0");

    /* stdout should contain the main usage lines with program name */
    assert_contains(out, "Usage: expr EXPRESSION", "stdout");
    assert_contains(out, "or:  expr OPTION", "stdout");

    /* stderr should be empty for full help */
    TEST_ASSERT_TRUE_MESSAGE(err != NULL, "err buffer is NULL");
    TEST_ASSERT_EQUAL_UINT_MESSAGE(0u, (unsigned)strlen(err), "stderr should be empty for full help");

    free(out);
    free(err);
}

void test_usage_nonzero_prints_try_help_on_stderr_and_exits_with_status(void) {
    char *out = NULL;
    char *err = NULL;
    int code = -1;

    int rc = run_usage_and_capture(7, &out, &err, &code);
    TEST_ASSERT_EQUAL_INT_MESSAGE(0, rc, "Failed to execute usage() in child process");
    TEST_ASSERT_EQUAL_INT_MESSAGE(7, code, "usage(nonzero) did not exit with the given status");

    /* stdout should be empty or minimal for nonzero status */
    TEST_ASSERT_TRUE_MESSAGE(out != NULL, "out buffer is NULL");
    TEST_ASSERT_EQUAL_UINT_MESSAGE(0u, (unsigned)strlen(out), "stdout should be empty for nonzero status");

    /* stderr should contain a prompt to use --help and program name */
    assert_contains(err, "--help", "stderr");
    assert_contains(err, "expr", "stderr");

    free(out);
    free(err);
}

void test_usage_success_includes_exit_status_explanation(void) {
    char *out = NULL;
    char *err = NULL;
    int code = -1;

    int rc = run_usage_and_capture(0, &out, &err, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_EQUAL_INT(0, code);

    /* Check that the full help text includes the exit status explanation line */
    assert_contains(out, "Exit status is 0 if EXPRESSION is neither null nor 0", "stdout");

    free(out);
    free(err);
}

int main(void) {
    UNITY_BEGIN();
    RUN_TEST(test_usage_success_prints_full_help_and_exits_zero);
    RUN_TEST(test_usage_nonzero_prints_try_help_on_stderr_and_exits_with_status);
    RUN_TEST(test_usage_success_includes_exit_status_explanation);
    return UNITY_END();
}