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

#define BUFFER_SIZE 100
#define FILE_HEADER_STRING "__info2_image_file_format__"


/*
 * Diese Hilfsfunktionen kümmern sich um:
 * - Das Öffnen der Datei und Überprüfen des Dateinamens
 * - Das Überprüfen des Headers, um sicherzustellen, dass es sich um die richtige Datei handelt
 * - Das Einlesen der Metadaten (Anzahl der Bilder, Bildbreite und -höhe)
 *  -> Die Hilfsfunktionen garantieren, dass die Datei gültig ist, bevor mit dem Einlesen der Bilddaten fortgefahren wird.
 */


static FILE *openImageFile(const char *path) // Checks if the given filename pointer is valid (not NULL).
{  
    if (path == NULL)
    {
        return NULL;
    }

    return fopen(path, "rb");  //opening document in binear 
}

static int readAndCheckHeader(FILE *file) // gets the length of the header text
{
    size_t headerLength = strlen(FILE_HEADER_STRING);
    char buffer[BUFFER_SIZE];

    if (headerLength + 1 > BUFFER_SIZE) //checks if buffer is big enough for header size
    {
        return 0;
    }

    if (fread(buffer, 1, headerLength, file) != headerLength) // Checks if reading the expected number of header bytes from the file succeeded
    {
        return 0;
    }

    buffer[headerLength] = '\0'; // add string terminator so the header becomes a valid C-string

    if (strcmp(buffer, FILE_HEADER_STRING) != 0) // checks if the expected header matches the header read from the file
    {
        return 0;
    }

    return 1; /* Header ok */
}


static int readImageMetaData(FILE *file, // reads the metadata (count, width, height) from the file and stores them in the provided pointers
                             unsigned short *count,
                             unsigned short *width,
                             unsigned short *height)
{
    if (fread(count, sizeof(unsigned short), 1, file) != 1) // read the number of images from the file
    {    
        return 0;
    }
    if (fread(width, sizeof(unsigned short), 1, file) != 1) // reads the image width
    {
        return 0;
    }
    if (fread(height, sizeof(unsigned short), 1, file) != 1) //reads the image height
    {
        return 0;
    }

    if (*count == 0 || *width == 0 || *height == 0)  // check for invalid metadata (count, width or height cannot be zero)
    {
        return 0;
    }

    return 1;
}


/*
    Hauptfunktion
*/
GrayScaleImageSeries *readImages(const char *path)
{
    // 1. Open the file
    FILE *file = openImageFile(path);
    if (file == NULL)
    {
        return NULL;
    }

    // 2. Check the header
    if (!readAndCheckHeader(file))
    {
        fclose(file);
        return NULL;
    }

    // 3. Read image metadata
    unsigned short count = 0;
    unsigned short width = 0;
    unsigned short height = 0;

    if (!readImageMetaData(file, &count, &width, &height))
    {
        fclose(file);
        return NULL;
    }

    // 4. Allocate memory for image series
    GrayScaleImageSeries *series = (GrayScaleImageSeries *)malloc(sizeof(GrayScaleImageSeries)); // Allocate memory for the image series, images, and labels. Return NULL if allocation fails.
    if (series == NULL)
    {
        fclose(file);
        return NULL;
    }

    series->count  = count;
    series->images = (GrayScaleImage *)calloc(count, sizeof(GrayScaleImage));
    series->labels = (unsigned char *)malloc(count * sizeof(unsigned char));

    if (series->images == NULL || series->labels == NULL)
    {
        free(series->images);
        free(series->labels);
        free(series);
        fclose(file);
        return NULL;
    }

    // 5. Read the images and labels 
    for (unsigned int i = 0; i < count; i++)
    {
        GrayScaleImage *image = &series->images[i];

        image->width  = (unsigned int)width;
        image->height = (unsigned int)height;

        size_t numPixels = (size_t)width * (size_t)height;

        image->buffer = (GrayScalePixelType *)malloc(numPixels * sizeof(GrayScalePixelType));
        if (image->buffer == NULL)
        {
            for (unsigned int j = 0; j < i; j++)
            {
                free(series->images[j].buffer);
            }
            free(series->images);
            free(series->labels);
            free(series);
            fclose(file);
            return NULL;
        }

        if (fread(image->buffer, sizeof(GrayScalePixelType), numPixels, file) != numPixels) // Check if the correct number of pixel values (width * height) were read for the image
        {
            for (unsigned int j = 0; j <= i; j++)
            {
                free(series->images[j].buffer);
            }
            free(series->images);
            free(series->labels);
            free(series);
            fclose(file);
            return NULL;
        }

        if (fread(&series->labels[i], sizeof(unsigned char), 1, file) != 1) // Check if the label for the image was successfully read (1 byte)
        {
            for (unsigned int j = 0; j <= i; j++)
            {
                free(series->images[j].buffer);
            }
            free(series->images);
            free(series->labels);
            free(series);
            fclose(file);
            return NULL;
        }
    }

    fclose(file);
    return series;
}

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

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

    if (series->labels != NULL)
    {
        free(series->labels);
        series->labels = NULL;
    }

    free(series);
}
