// Resizes a BMP file

#include <stdio.h>
#include <stdlib.h>

#include "bmp.h"

int main(int argc, char *argv[])
{

    char *p;
    if (!argv[1])
    {
        fprintf(stderr, "Usage: resize n infile outfile\n");
        return 1;
    }
    int n = strtol(argv[1], &p, 10);
    if (*p != '\0')
    {
        fprintf(stderr, "Usage: resize n infile outfile\n");
        return 1;
    }
    // ensure proper usage
    if (argc != 4 || n > 100)
    {
        fprintf(stderr, "Usage: resize n infile outfile\n");
        return 1;
    }

    // remember filenames
    char *infile = argv[2];
    char *outfile = argv[3];

    // open input file
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 2;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 3;
    }

    // read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bfSmall;
    fread(&bfSmall, sizeof(BITMAPFILEHEADER), 1, inptr);

    // read infile's BITMAPINFOHEADER
    BITMAPINFOHEADER biSmall;
    fread(&biSmall, sizeof(BITMAPINFOHEADER), 1, inptr);

    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bfSmall.bfType != 0x4d42 || bfSmall.bfOffBits != 54 || biSmall.biSize != 40 ||
        biSmall.biBitCount != 24 || biSmall.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }

    BITMAPFILEHEADER bfLarge = bfSmall;
    BITMAPINFOHEADER biLarge = biSmall;

    // determine padding for scanlines
    int paddingSmall = (4 - (biSmall.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int paddingLarge = (4 - (biLarge.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //update the header files
    if(n != 1)
    {
        biLarge.biWidth *= n;
        paddingLarge = (4 - (biLarge.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
        biLarge.biHeight *= n;
        biLarge.biSizeImage = ((sizeof(RGBTRIPLE) * biLarge.biWidth) + paddingLarge) * abs(biLarge.biHeight);
        bfLarge.bfSize = biLarge.biSizeImage + sizeof(BITMAPINFOHEADER) + sizeof(BITMAPFILEHEADER);
    }
    // write outfile's BITMAPFILEHEADER
    fwrite(&bfLarge, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER
    fwrite(&biLarge, sizeof(BITMAPINFOHEADER), 1, outptr);
    RGBTRIPLE secLine[biSmall.biWidth];

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(biLarge.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline
        for (int j = 0; j < biSmall.biWidth; j++)
        {
            if (i % n == 0)
            {
                // temporary storage
                RGBTRIPLE triple;

                // read RGB triple from infile
                fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
                secLine[j] = triple;

                // write RGB triple to outfile n times
                for(int k = 0; k < n; k++)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }
            else
            {
                for (int k = 0; k < n; k++)
                {
                    fwrite(&secLine[j], sizeof(RGBTRIPLE), 1, outptr);
                }
            }
        }

        // skip over padding, if any
        fseek(inptr, paddingSmall, SEEK_CUR);


        // then add it back (to demonstrate how)
        for (int z = 0; z < paddingLarge; z++)
        {
            fputc(0x00, outptr);
        }
    }
    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}