/*
 * Copyright 2010, Axel Dörfler, axeld@pinc-software.de.
 * This file may be used under the terms of the MIT License.
 */


#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include <algorithm>


void
test_for_content(int fd, off_t start, const char* contents, size_t length)
{
        char buffer[4096];
        while (length > 0) {
                size_t toRead = std::min(length, sizeof(buffer));

                if (pread(fd, buffer, toRead, start) != (ssize_t)toRead) {
                        perror("reading failed");
                        exit(1);
                }
                
                if (memcmp(contents, buffer, toRead)) {
                        fprintf(stderr, "Contents at %lld differ!\n", start);
                        exit(1);
                }

                contents += toRead;
                start += toRead;
                length -= toRead;
        }
}


void
test_for_zero(int fd, off_t start, off_t end)
{
        while (start < end) {
                char buffer[4096];
                size_t length = std::min((size_t)(end - start), sizeof(buffer));
                
                if (pread(fd, buffer, length, start) != (ssize_t)length) {
                        perror("reading failed");
                        exit(1);
                }

                for (size_t i = 0; i < length; i++) {
                        if (buffer[i] != 0) {
                                fprintf(stderr, "Buffer at %lld is not empty (%#x)!\n",
                                        start + i, buffer[i]);
                                exit(1);
                        }
                }

                start += length;
        }
}


int
main(int argc, char** argv)
{
        const char* name = "/tmp/seek_and_write";
        bool prefill = true;

        for (int i = 1; i < argc; i++) {
                if (argv[i][0] == '-') {
                        if (argv[i][1] == 'n')
                                prefill = false;
                        else {
                                fprintf(stderr, "Unknown option\n");
                                return 1;
                        }

                        continue;
                }

                name = argv[i];
        }

        int fd = open(name, O_RDWR | O_TRUNC | O_CREAT, 0644);
        if (fd < 0) {
                perror("failed to open file");
                return 1;
        }

        char buffer[256];
        for (size_t i = 0; i < 256; i++)
                buffer[i] = i;

        if (prefill) {
                // Write test data to file to make sure it's not empty

                for (size_t i = 0; i < 100; i++) {
                        if (write(fd, buffer, sizeof(buffer)) != (ssize_t)sizeof(buffer)) {
                                perror("writing failed");
                                return 1;
                        }
                }
        }

        // Truncate it again in order to remove its contents

        ftruncate(fd, 0);

        // Seek past its end, and write something

        pwrite(fd, "---", 3, 100 * 1024);
        pwrite(fd, "+++", 3, 200 * 1024);

        // Test contents
        
        test_for_zero(fd, 0, 100 * 1024);
        test_for_content(fd, 100 * 1024, "---", 3);
        test_for_zero(fd, 100 * 1024 + 256, 200 * 1024);
        test_for_content(fd, 200 * 1024, "+++", 3);

        return 0;
}