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

#define FILE_HEADER_STRING "__info2_image_file_format__"
#define FILE_HEADER_LENGTH (sizeof(FILE_HEADER_STRING) - 1U)

// Reads an entire image series file and returns a heap-allocated descriptor.
GrayScaleImageSeries *readImages(const char *path)
{
    FILE *file = fopen(path, "rb");
    if(file == NULL)
    {
        return NULL;
    }

    if(!checkFileHeader(file))
    {
        fclose(file);
        return NULL;
    }

    unsigned int numberOfImages = readDimension(file);
    unsigned short width = readDimension(file);
    unsigned short height = readDimension(file);

    GrayScaleImageSeries *series = (GrayScaleImageSeries *)malloc(sizeof(GrayScaleImageSeries));
    if(series == NULL)
    {
        fclose(file);
        return NULL;
    }

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

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

    for(unsigned int i = 0; i < numberOfImages; i++)
    {
        series->images[i] = readImage(file, width, height);
        series->labels[i] = readLabel(file);
    }

    fclose(file);
    return series;
}


// Validates and consumes the file header tag that identifies the custom format.
bool checkFileHeader(FILE *file)
{
    char buffer[FILE_HEADER_LENGTH + 1] = {0};
    size_t bytesRead = fread(buffer, sizeof(char), FILE_HEADER_LENGTH, file);
    if(bytesRead != FILE_HEADER_LENGTH)
    {
        return false;
    }

    return strncmp(buffer, FILE_HEADER_STRING, FILE_HEADER_LENGTH) == 0;
}

// Reads a single 16-bit dimension (width, height or count of Images) from the file.
unsigned short int readDimension(FILE *file)
{
    unsigned short int dimension = 0;
    fread(&dimension, sizeof(unsigned short int), 1, file);
    return dimension;
}

// Reads a single grayscale image of the provided dimensions from the file.
GrayScaleImage readImage(FILE *file, unsigned short width, unsigned short height)
{
    GrayScaleImage image = {0};
    image.width = width;
    image.height = height;

    unsigned int pixelCount = (unsigned int)width * (unsigned int)height;
    image.buffer = (GrayScalePixelType *)malloc(pixelCount * sizeof(GrayScalePixelType));
    if(image.buffer != NULL)
    {
        fread(image.buffer, sizeof(GrayScalePixelType), pixelCount, file);
    }

    return image;
}

// Reads one byte label that belongs to the preceding image.
unsigned char readLabel(FILE *file)
{
    unsigned char label = 0;
    fread(&label, sizeof(unsigned char), 1, file);
    return label;
}

// Releases all heap allocations associated with a GrayScaleImageSeries.
void clearSeries(GrayScaleImageSeries *series)
{
    if (series != NULL)
    {
        if (series->images != NULL)
        {
            // Free each image's buffer
            for (unsigned int i = 0; i < series->count; i++)
            {
                if (series->images[i].buffer != NULL)
                    free(series->images[i].buffer);
            }
            free(series->images);
        }
        
        if (series->labels != NULL)
            free(series->labels);
        
        free(series);
    }
}