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

/* Access the global program_name used by usage(). */
extern char const *program_name;

/* Forward declaration of the target function. */
void usage (int status);

/* Helper: run usage(status) in a child, capturing either stdout or stderr.
   capture_fd must be STDOUT_FILENO or STDERR_FILENO.
   progname will be assigned to program_name in the child before calling usage.
   On return, *out_buf is a malloc'ed, NUL-terminated buffer with captured output
   (caller must free), and *exit_code is the child's exit code if it exited
   normally (or -1 otherwise). Returns 0 on success, -1 on setup error. */
static int run_usage_and_capture(int status_to_pass, int capture_fd,
                                 const char *progname,
                                 char **out_buf, int *exit_code)
{
    if (!out_buf || !exit_code) return -1;
    *out_buf = NULL;
    *exit_code = -1;

    int p[2];
    if (pipe(p) < 0)
        return -1;

    fflush(stdout);
    fflush(stderr);
    pid_t pid = fork();
    if (pid < 0)
    {
        int saved = errno;
        close(p[0]); close(p[1]);
        errno = saved;
        return -1;
    }

    if (pid == 0)
    {
        /* Child: redirect selected fd to pipe write end. */
        /* Ensure parent's stdout is unaffected; redirection only in child. */
        close(p[0]); /* close read end */

        if (dup2(p[1], capture_fd) < 0)
        {
            /* If dup2 fails, exit with distinctive code. */
            _exit(127);
        }
        /* Close the duplicated fd as pipe write end is now on capture_fd. */
        close(p[1]);

        /* Set the program name to control output. */
        program_name = progname ? progname : "mv";

        /* Call the target; it will call exit(status_to_pass). */
        usage(status_to_pass);

        /* Should not reach here. */
        _exit(126);
    }
    else
    {
        /* Parent: read from pipe and wait for child. */
        close(p[1]); /* close write end */

        size_t cap = 1024;
        size_t len = 0;
        char *buf = (char *)malloc(cap);
        if (!buf)
        {
            close(p[0]);
            /* Best effort: reap child. */
            int st; waitpid(pid, &st, 0);
            return -1;
        }

        ssize_t n;
        while ((n = read(p[0], buf + len, cap - len)) > 0)
        {
            len += (size_t)n;
            if (len == cap)
            {
                size_t newcap = cap * 2;
                char *nb = (char *)realloc(buf, newcap);
                if (!nb)
                {
                    free(buf);
                    close(p[0]);
                    int st; waitpid(pid, &st, 0);
                    return -1;
                }
                buf = nb;
                cap = newcap;
            }
        }
        close(p[0]);

        /* NUL-terminate */
        if (len == cap)
        {
            char *nb = (char *)realloc(buf, cap + 1);
            if (!nb)
            {
                free(buf);
                int st; waitpid(pid, &st, 0);
                return -1;
            }
            buf = nb;
        }
        buf[len] = '\0';

        int st = 0;
        if (waitpid(pid, &st, 0) < 0)
        {
            free(buf);
            return -1;
        }

        *out_buf = buf;
        if (WIFEXITED(st))
            *exit_code = WEXITSTATUS(st);
        else
            *exit_code = -1;

        return 0;
    }
}

/* Utility: check if substring exists. */
static int contains_substr(const char *haystack, const char *needle)
{
    return haystack && needle && strstr(haystack, needle) != NULL;
}

void setUp(void) {
    /* No global setup required. Each test sets program_name in child. */
}

void tearDown(void) {
    /* No global teardown required. */
}

void test_usage_success_writes_help_to_stdout_and_exits_zero(void)
{
    char *out = NULL;
    int code = -1;
    int rc = run_usage_and_capture(0, STDOUT_FILENO, "mv", &out, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_NOT_NULL(out);
    TEST_ASSERT_EQUAL_INT(0, code);

    /* Verify key parts of the help text are present on stdout. */
    TEST_ASSERT_TRUE(contains_substr(out, "Usage:"));
    TEST_ASSERT_TRUE(contains_substr(out, "mv"));
    TEST_ASSERT_TRUE(contains_substr(out, "Rename SOURCE to DEST"));
    TEST_ASSERT_TRUE(contains_substr(out, "--backup"));
    TEST_ASSERT_TRUE(contains_substr(out, "--verbose"));

    free(out);
}

void test_usage_failure_writes_try_help_to_stderr_and_exits_nonzero(void)
{
    char *err = NULL;
    int code = -1;
    int rc = run_usage_and_capture(1, STDERR_FILENO, "mv", &err, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_NOT_NULL(err);
    TEST_ASSERT_EQUAL_INT(1, code);

    /* Typical message: "Try 'mv --help' for more information." */
    TEST_ASSERT_TRUE(contains_substr(err, "Try"));
    TEST_ASSERT_TRUE(contains_substr(err, "mv"));
    TEST_ASSERT_TRUE(contains_substr(err, "--help"));

    free(err);
}

void test_usage_success_does_not_write_to_stderr(void)
{
    char *err = NULL;
    int code = -1;
    int rc = run_usage_and_capture(0, STDERR_FILENO, "mv", &err, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_NOT_NULL(err);
    TEST_ASSERT_EQUAL_INT(0, code);

    /* Expect stderr to be empty for successful usage(status==0). */
    TEST_ASSERT_EQUAL_UINT32(0u, (unsigned)strlen(err));

    free(err);
}

void test_usage_failure_does_not_write_to_stdout(void)
{
    char *out = NULL;
    int code = -1;
    int rc = run_usage_and_capture(1, STDOUT_FILENO, "mv", &out, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_NOT_NULL(out);
    TEST_ASSERT_EQUAL_INT(1, code);

    /* Expect stdout to be empty for failure usage(status!=0). */
    TEST_ASSERT_EQUAL_UINT32(0u, (unsigned)strlen(out));

    free(out);
}

void test_usage_uses_program_name_variable(void)
{
    const char *custom = "my-mv";
    char *out = NULL;
    int code = -1;
    int rc = run_usage_and_capture(0, STDOUT_FILENO, custom, &out, &code);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_NOT_NULL(out);
    TEST_ASSERT_EQUAL_INT(0, code);

    /* Ensure custom program name appears in the usage heading. */
    TEST_ASSERT_TRUE(contains_substr(out, "Usage: my-mv"));

    free(out);
}

int main(void)
{
    UNITY_BEGIN();
    RUN_TEST(test_usage_success_writes_help_to_stdout_and_exits_zero);
    RUN_TEST(test_usage_failure_writes_try_help_to_stderr_and_exits_nonzero);
    RUN_TEST(test_usage_success_does_not_write_to_stderr);
    RUN_TEST(test_usage_failure_does_not_write_to_stdout);
    RUN_TEST(test_usage_uses_program_name_variable);
    return UNITY_END();
}