#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "imageInput.h"

#define BUFFER_SIZE 100
#define FILE_HEADER_STRING "__info2_image_file_format__"


/// @brief Reads a value in little-endian format from file
/// @param openedFile stream FILE, from which to read
/// @param bytes how many bytes to read
static unsigned int readLittleEndian(FILE* openedFile, int bytes) {
    unsigned int value = 0;

    if (openedFile == NULL) return 0;

    for (int i = 0; i < bytes; i++) {
        int tmp = fgetc(openedFile);
        if (tmp == EOF) return 0;
        
        value |= ((unsigned int)tmp) << (i * 8);
    }

    return value;
}

// TODO Vervollständigen Sie die Funktion readImages unter Benutzung Ihrer Hilfsfunktionen
GrayScaleImageSeries *readImages(const char *path)
{
    FILE* openFile = fopen(path, "rb");

    // file Could not be opened/does not exist
    if (openFile == NULL) {
        return NULL;
    }

    char actualFileTag[strlen(FILE_HEADER_STRING) + 1];
    
    size_t tagLength = strlen(FILE_HEADER_STRING);
    if (fread(actualFileTag, 1, tagLength, openFile) != tagLength) {
        fclose(openFile);
        return NULL;
    }
    actualFileTag[tagLength] = '\0';

    // checks if the files are equal
    if (strcmp(actualFileTag, FILE_HEADER_STRING) != 0) {
        fclose(openFile);
        return NULL;
    }

    unsigned int numberOfImages = readLittleEndian(openFile, 2);

    // no Images in series -> No image-series
    if (numberOfImages == 0) {
        fclose(openFile);
        return NULL;
    }

    unsigned int width  = readLittleEndian(openFile, 2);
    unsigned int height = readLittleEndian(openFile, 2);

    // no height/width --> impossible file 
    if(height == 0 || width == 0) {
        fclose(openFile);
        return NULL;
    }

    //all the starting parameters are set --> the images can be read and stored
    GrayScaleImageSeries* series = malloc(sizeof(GrayScaleImageSeries));
    if (series == NULL) {
        fclose(openFile);
        return NULL;
    }

    GrayScaleImage* images = malloc(numberOfImages * sizeof(GrayScaleImage));
    unsigned char* labels = malloc(numberOfImages * sizeof(unsigned char));

    if (images == NULL || labels == NULL) {
        free(images);
        free(labels);
        free(series);
        fclose(openFile);
        return NULL;
    }

    series->count = 0;
    series->images = images;
    series->labels = labels;

    for (unsigned int i = 0; i < numberOfImages; i++) {
        // allocating the actual matrix image for each image
        images[i].buffer = malloc(width * height);
        
        if (images[i].buffer == NULL) {
            for (unsigned int k = 0; k < i; k++) {
                free(images[k].buffer);
            }
            free(images);
            free(labels);
            free(series);
            fclose(openFile);
            return NULL;
        }

        images[i].height = height;
        images[i].width = width;

        if (fread(images[i].buffer, 1, width * height, openFile) != width * height) {
            for (unsigned int k = 0; k <= i; k++) {
                free(images[k].buffer);
            }
            free(images);
            free(labels);
            free(series);
            fclose(openFile);
            return NULL;
        }
        
        //rest of the values that only affect the image itself
        int label = fgetc(openFile);
        if (label == EOF) {
            for (unsigned int k = 0; k <= i; k++) {
                free(images[k].buffer);
            }
            free(images);
            free(labels);
            free(series);
            fclose(openFile);
            return NULL;
        }
        series->labels[i] = (unsigned char)label;
        series->count++;
    }

    fclose(openFile);
    return series;
}

// TODO Vervollständigen Sie die Funktion clearSeries, welche eine Bildserie vollständig aus dem Speicher freigibt
void clearSeries(GrayScaleImageSeries *series)
{
    if (series == NULL) return;

    for (int i = 0; i < series->count; i++) {
        free(series->images[i].buffer);
    }

    free(series->images);
    free(series->labels);
    free(series);
}