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

/* The test file is included into the od source, so we can access
   the internal globals and functions directly. We declare externs only
   for clarity; they are defined above in the included program. */

/* Globals from od.c (visible since this test is included into the TU) */
extern FILE *in_stream;
extern char const *const *file_list;
extern char const *input_filename;
extern bool have_read_stdin;
extern intmax_t end_offset;
extern bool flag_dump_strings;

/* Functions from od.c */
extern bool open_next_file (void);
extern bool check_and_close (int in_errno);
extern bool skip (intmax_t n_skip);

/* Helpers for tests */
static char *create_temp_file_with_size(size_t size) {
    char tmpl[] = "/tmp/od_skip_testXXXXXX";
    int fd = mkstemp(tmpl);
    if (fd < 0) {
        return NULL;
    }

    /* Write 'size' bytes of predictable data */
    size_t remaining = size;
    char buf[4096];
    memset(buf, 'A', sizeof(buf));

    while (remaining > 0) {
        size_t chunk = remaining < sizeof(buf) ? remaining : sizeof(buf);
        ssize_t w = write(fd, buf, chunk);
        if (w < 0) {
            int e = errno;
            close(fd);
            unlink(tmpl);
            errno = e;
            return NULL;
        }
        remaining -= (size_t)w;
    }

    if (fsync(fd) != 0) {
        /* Not fatal for tests, continue */
    }

    if (close(fd) != 0) {
        unlink(tmpl);
        return NULL;
    }

    /* Return a heap-allocated copy of the path so caller can free */
    char *path = strdup(tmpl);
    return path;
}

static long current_offset(FILE *f) {
    off_t off = ftello(f);
    if (off == (off_t)-1) return -1;
    return (long)off;
}

void setUp(void) {
    /* Reset core globals to a safe baseline for each test. */
    in_stream = NULL;
    have_read_stdin = false;
    end_offset = -1;         /* No end limit */
    flag_dump_strings = false;
}

void tearDown(void) {
    /* If a stream is still open, close it safely. Note: in tests, we
       prefer to close via check_and_close within each test before
       local arrays (for file_list) go out of scope. */
    if (in_stream) {
        check_and_close(0);
        in_stream = NULL;
    }
}

/* Test: n_skip == 0 is a no-op and returns true, without requiring an open stream. */
static void test_skip_zero_no_stream(void) {
    in_stream = NULL;
    bool ok = skip(0);
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NULL(in_stream);
}

/* Test: Skip within a single large file using seek optimization. */
static void test_skip_within_single_file_seek(void) {
    char *p1 = create_temp_file_with_size(100000); /* large to trigger seek path */
    TEST_ASSERT_NOT_NULL_MESSAGE(p1, "failed to create temp file");

    /* Set up file list and open first file */
    const char *flist[] = { p1, NULL };
    file_list = flist;

    bool ok = open_next_file();
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NOT_NULL(in_stream);
    TEST_ASSERT_EQUAL_INT(0, current_offset(in_stream));

    ok = skip(12345);
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NOT_NULL(in_stream);
    TEST_ASSERT_EQUAL_INT(12345, current_offset(in_stream));

    /* Cleanup while file_list is still valid */
    check_and_close(0);

    unlink(p1);
    free(p1);
}

/* Test: Skip across two files, requiring skipping past the entire first file
   and partially into the second file. */
static void test_skip_across_two_files_boundary_seek_on_first(void) {
    char *p1 = create_temp_file_with_size(5000);
    char *p2 = create_temp_file_with_size(2000);
    TEST_ASSERT_NOT_NULL(p1);
    TEST_ASSERT_NOT_NULL(p2);

    const char *flist[] = { p1, p2, NULL };
    file_list = flist;

    bool ok = open_next_file();
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NOT_NULL(in_stream);
    TEST_ASSERT_EQUAL_INT(0, current_offset(in_stream));

    /* Skip more than file1, but less than total */
    ok = skip(5200);
    TEST_ASSERT_TRUE(ok);

    /* Expect to be in the second file at offset 200. */
    TEST_ASSERT_NOT_NULL(in_stream);
    long off = current_offset(in_stream);
    TEST_ASSERT_EQUAL_INT(200, off);

    /* Cleanup */
    check_and_close(0);
    unlink(p1); unlink(p2);
    free(p1); free(p2);
}

/* Test: Read-based skipping on a small regular file (size <= block size),
   exercising the fread path. */
static void test_skip_read_based_small_file(void) {
    char *p1 = create_temp_file_with_size(10);
    TEST_ASSERT_NOT_NULL(p1);

    const char *flist[] = { p1, NULL };
    file_list = flist;

    bool ok = open_next_file();
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NOT_NULL(in_stream);
    TEST_ASSERT_EQUAL_INT(0, current_offset(in_stream));

    ok = skip(6);
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_EQUAL_INT(6, current_offset(in_stream));

    /* Cleanup */
    check_and_close(0);
    unlink(p1);
    free(p1);
}

/* Test: Skipping exactly the size of the first file remains at EOF of first file.
   The code seeks within the first file and does not immediately open the next. */
static void test_skip_exact_file_size_stays_on_first_at_eof(void) {
    char *p1 = create_temp_file_with_size(1000);
    char *p2 = create_temp_file_with_size(100);
    TEST_ASSERT_NOT_NULL(p1);
    TEST_ASSERT_NOT_NULL(p2);

    const char *flist[] = { p1, p2, NULL };
    file_list = flist;

    bool ok = open_next_file();
    TEST_ASSERT_TRUE(ok);
    TEST_ASSERT_NOT_NULL(in_stream);

    ok = skip(1000);
    TEST_ASSERT_TRUE(ok);

    /* Expect still on first file at offset 1000 (EOF), not yet transitioned */
    TEST_ASSERT_NOT_NULL(in_stream);
    TEST_ASSERT_EQUAL_INT(1000, current_offset(in_stream));

    /* Cleanup */
    check_and_close(0);
    unlink(p1); unlink(p2);
    free(p1); free(p2);
}

int main(void) {
    UNITY_BEGIN();

    RUN_TEST(test_skip_zero_no_stream);
    RUN_TEST(test_skip_within_single_file_seek);
    RUN_TEST(test_skip_across_two_files_boundary_seek_on_first);
    RUN_TEST(test_skip_read_based_small_file);
    RUN_TEST(test_skip_exact_file_size_stays_on_first_at_eof);

    return UNITY_END();
}