#include <errno.h>
#include <fcntl.h>
#include <luna.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

FILE* stderr;
FILE* stdout;
FILE* stdin;

void file_read_buf(FILE* stream)
{
    if (!stream->f_buf)
    {
        stream->f_buf = (char*)malloc(BUFSIZ); // FIXME: Handle errors.
        stream->f_bufrsize = BUFSIZ;
    }
    stream->f_bufoff = 0;
    ssize_t nread = read(stream->f_fd, stream->f_buf, stream->f_bufrsize);
    if (nread < 0)
    {
        stream->f_err = 1;
        return;
    }
    if (nread == 0)
    {
        stream->f_eof = 1;
        return;
    }
    stream->f_bufsize = nread;
}

extern "C"
{
    int fclose(FILE* stream)
    {
        if (stream->f_buf) free(stream->f_buf);
        int status = close(stream->f_fd);
        if (status < 0)
        {
            int savederr = errno;
            free(stream); // We do not want to leak memory. man fclose(3) says that whether fclose() fails or not, any
                          // further operation on the stream results in undefined behavior. So we are free to free the
                          // stream.
            errno = savederr; // free might reset errno. We don't want that.
        }
        else { free(stream); }
        return status;
    }

    int fflush(FILE*)
    {
        return 0; // FIXME: Implement buffered IO.
    }

    FILE* fopen(const char* pathname, const char* mode)
    {
        int fd = open(pathname, O_RDWR); // FIXME: Use the mode string.
        if (fd < 0) { return 0; }
        return fdopen(fd, mode);
    }

    FILE* fdopen(int fd, const char*)
    {
        if (fd < 0) // FIXME: Also check if the mode string is compatible with how fd was opened.
        {
            errno = EBADF;
            return 0;
        }
        FILE* stream = (FILE*)malloc(sizeof(FILE));
        if (!stream) { return 0; }
        stream->f_fd = fd;
        clearerr(stream);
        stream->f_buf = 0;
        stream->f_bufoff = 0;
        stream->f_bufsize = 0;
        return stream;
    }

    FILE* freopen(const char* pathname, const char*,
                  FILE* stream) // FIXME: If pathname is NULL, open the original file with the new mode.
    {
        int fd = open(pathname, O_RDWR); // FIXME: Use the mode string.
        if (fd < 0) { return 0; }

        fflush(stream); // To make it future-proof.
        fclose(stream);

        stream->f_fd = fd;
        clearerr(stream);
        return stream;
    }

    int fileno(FILE* stream)
    {
        return stream->f_fd;
    }

    size_t fread(void* buf, size_t size, size_t nmemb, FILE* stream)
    {
        ssize_t status =
            read(stream->f_fd, buf,
                 size * nmemb); // FIXME: This function should use file_read_buf() to not conflict with fgets().
        if (status < 0)
        {
            stream->f_err = 1;
            return 0;
        }
        if (status == 0) stream->f_eof = 1;
        return (size_t)status;
    }

    char* fgets(char* buf, int size, FILE* stream)
    {
        char* s = buf;
        int original_size = size;
        while (size > 1)
        {
            if (stream->f_bufoff < stream->f_bufsize)
            {
                *buf = *(stream->f_buf + stream->f_bufoff);
                stream->f_bufoff++;
                if (*buf == '\n')
                {
                    buf++;
                    break;
                }
                buf++;
                size--;
            }
            else
            {
                file_read_buf(stream);
                if (ferror(stream)) return NULL;
                if (feof(stream)) break;
            }
        }
        if (size == original_size && feof(stream)) return NULL; // EOF while reading the first character
        *buf = 0;
        return s;
    }

    int fgetc(FILE* stream)
    {
        char result;
    read:
        if (stream->f_bufoff < stream->f_bufsize)
        {
            result = *(stream->f_buf + stream->f_bufoff);
            stream->f_bufoff++;
        }
        else
        {
            file_read_buf(stream);
            if (ferror(stream)) return EOF;
            if (feof(stream)) return EOF;
            goto read;
        }
        return (int)result;
    }

    int getc(FILE* stream)
    {
        return fgetc(stream);
    }

    int getchar()
    {
        return fgetc(stdin);
    }

    int ungetc(int c, FILE* stream)
    {
        if (stream->f_bufoff > 0)
        {
            stream->f_bufoff--;
            stream->f_buf[stream->f_bufoff] = (char)c;
            return c;
        }
        else
        {
            return EOF; // FIXME: Handle this case properly.
        }
    }

    int ferror(FILE* stream)
    {
        return stream->f_err;
    }

    int feof(FILE* stream)
    {
        return stream->f_eof;
    }

    void clearerr(FILE* stream)
    {
        stream->f_err = stream->f_eof = 0;
    }

    int fseek(FILE* stream, long offset, int whence)
    {
        long result = lseek(stream->f_fd, offset, whence);
        if (result < 0) { return -1; }
        return 0;
    }

    int fseeko(FILE* stream, off_t offset, int whence)
    {
        return fseek(stream, offset, whence);
    }

    int fsetpos(FILE* stream, const fpos_t* pos)
    {
        return fseek(stream, *pos, SEEK_SET);
    }

    long ftell(FILE* stream)
    {
        return lseek(stream->f_fd, 0,
                     SEEK_CUR); // FIXME: Store the last seeked position in the file struct to avoid redundant syscalls
                                // maybe? We'd have to update this value in fread() and fwrite() as well...
    }

    off_t ftello(FILE* stream)
    {
        return ftell(stream);
    }

    int fgetpos(FILE* stream, fpos_t* pos)
    {
        long result = ftell(stream);
        if (result < 0) { return -1; }
        *pos = result;
        return 0;
    }

    void rewind(FILE* stream)
    {
        lseek(stream->f_fd, 0, SEEK_SET);
        clearerr(stream);
    }

    size_t fwrite(const void* buf, size_t size, size_t nmemb, FILE* stream)
    {
        ssize_t status = write(stream->f_fd, buf, size * nmemb);
        if (status < 0)
        {
            stream->f_err = 1;
            return 0;
        }
        if (status == 0) stream->f_eof = 1;
        return (size_t)status;
    }

    void setbuf(FILE*, char*)
    {
        NOT_IMPLEMENTED("setbuf");
    }

    int setvbuf(FILE*, char*, int, size_t)
    {
        NOT_IMPLEMENTED("setvbuf");
    }
}