Step1Coder.c

/*
************************************************************
* COMPILERS COURSE - Algonquin College
* Code version: Fall, 2025
* Author: Alex Vu and Yassine Amraoui
* Professors: Paulo Sousa
************************************************************

        "\t=-------------------------------------------------------------------=\n",
        "\t|               COMPILERS - ALGONQUIN COLLEGE (S25)                 |\n",
        "\t=-------------------------------------------------------------------=\n",
        "\t    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@    \n",
        "\t    @@                                                        @@    \n",
        "\t    @@           %&@@@@@@@@@@@         @@@@@@@@@@@@@@@@@@     @@    \n",
        "\t    @@       @%% (@@@@@@@@@  @                  @             @@    \n",
        "\t    @@      @& @   @ @       @                  @             @@    \n",
        "\t    @@     @ @ %  / /   @@@@@@                  @             @@    \n",
        "\t    @@      & @ @  @@                           @             @@    \n",
        "\t    @@       @/ @*@ @ @   @                     @             @@    \n",
        "\t    @@           @@@@  @@ @ @                   @             @@    \n",
        "\t    @@            /@@    @@@ @                  @             @@    \n",
        "\t    @@     @      / /     @@ @                  @             @@    \n",
        "\t    @@     @ @@   /@/   @@@ @                   @             @@    \n",
        "\t    @@     @@@@@@@@@@@@@@@                      @             @@    \n",
        "\t    @@                                                        @@    \n",
        "\t    @@                 S T R U C T U R A L                    @@    \n",
        "\t    @@           By Alex Vu and Yassine Amraoui               @@    \n",
        "\t    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@    \n",
        "\t                                                                    \n",
        "\t[COMPILER SCRIPT ..................................................]\n",*/

/*
***********************************************************
* File name: Reader.c
* Compiler: MS Visual Studio 2022
* Course: CST 8152 � Compilers, Lab Section: [011, 012, 013]
* Assignment: A12.
* Date: Sep 01 2025
* Professor: Paulo Sousa
* Purpose: This file is the main code for Buffer/Reader (A12)
************************************************************
*/

/*
 *.............................................................................
 * MAIN ADVICE:
 * - Please check the "TODO" labels to develop your activity.
 * - Review the functions to use "Defensive Programming".
 *.............................................................................
 */

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

#ifndef COMPILERS_H_
#include "Compilers.h"
#endif

#ifndef CODER_H_
#include "Step1Coder.h"
#endif

void vigenereFile(const struct_strg inputFileName, const struct_strg outputFileName, const struct_strg key, struct_int encode) {
    
    FILE* inputFile = fopen(inputFileName, "r");
    if (!inputFile) {
        fprintf(stderr, "ERROR: Cannot open input file: %s\n", inputFileName);
        return;
    }

    FILE* outputFile = fopen(outputFileName, "w");
    if (!outputFile) {
        fprintf(stderr, "ERROR: Cannot open output file: %s\n", outputFileName);
        fclose(inputFile);
        return;
    }

    if (!key || strlen(key) == 0) {
        fprintf(stderr, "ERROR: Key cannot be empty.\n");
        fclose(inputFile);
        fclose(outputFile);
        return;
    }

    struct_int ch;
    size_t keyLen = strlen(key);
    size_t keyIndex = 0;

    struct_char prevChar = '\0';
    struct_char nextChar = '\0';
    struct_int peekCh;

    while ((ch = fgetc(inputFile)) != EOF) {
        struct_char currentChar = (struct_char)ch;
        struct_char processedChar;

        // Peek ahead for next character
        peekCh = fgetc(inputFile);
        nextChar = (peekCh != EOF) ? (struct_char)peekCh : '\0';
        if (peekCh != EOF) {
            ungetc(peekCh, inputFile);
        }

        // Only process visible characters (ASCII 32 to 126)
        if (currentChar >= 32 && currentChar <= 126) {
            // Check if it's a letter
            if (isalpha(currentChar)) {
                // Don't encode single uppercase letters (variables) if they're isolated
                // A letter is a variable if: uppercase AND (prev is not letter) AND (next is not letter)
                struct_int isSingleUppercase = isupper(currentChar) &&
                                               !isalpha(prevChar) &&
                                               !isalpha(nextChar);

                if (isSingleUppercase) {
                    // Keep variable as-is for consistency
                    processedChar = currentChar;
                } else {
                    struct_char keyCh = key[keyIndex % keyLen];
                    struct_char base = isupper(currentChar) ? 'A' : 'a';
                    struct_char keyBase = isupper(keyCh) ? 'A' : 'a';

                    struct_int c = currentChar - base;
                    struct_int k = keyCh - keyBase;

                    struct_int result = encode ? (c + k) % 26 : (c - k + 26) % 26;
                    processedChar = (struct_char)(result + base);

                    keyIndex++;
                }
            } else {
                // Non-letter visible characters are not encoded
                processedChar = currentChar;
            }
        } else {
            // Non-visible characters are not encoded
            processedChar = currentChar;
        }

        fputc(processedChar, outputFile);
        prevChar = currentChar;
    }

    fclose(inputFile);
    fclose(outputFile);
}



struct_strg vigenereMem(const struct_strg inputFileName, const struct_strg key, struct_int encode) {
    // Defensive programming: check inputs
    if (!inputFileName || !key || strlen(key) == 0) {
        fprintf(stderr, "ERROR: Invalid input file name or key.\n");
        return NULL;
    }

    // Open file for reading in BINARY mode to preserve exact byte count
    FILE* inputFile = fopen(inputFileName, "rb");
    if (!inputFile) {
        fprintf(stderr, "ERROR: Cannot open input file: %s\n", inputFileName);
        return NULL;
    }

    // Determine size of the file
    fseek(inputFile, 0, SEEK_END);
    struct_long fileSize = ftell(inputFile);
    rewind(inputFile);

    if (fileSize <= 0) {
        fprintf(stderr, "ERROR: Input file is empty or unreadable.\n");
        fclose(inputFile);
        return NULL;
    }

    // Allocate memory to read input file content
    struct_strg inputBuffer = (struct_strg)malloc((fileSize + 1) * sizeof(struct_char));
    if (!inputBuffer) {
        fprintf(stderr, "ERROR: Memory allocation failed.\n");
        fclose(inputFile);
        return NULL;
    }

    fread(inputBuffer, sizeof(struct_char), fileSize, inputFile);
    inputBuffer[fileSize] = '\0'; // Null-terminate
    fclose(inputFile);

    // Prepare output buffer
    struct_strg output = (struct_strg)calloc(fileSize + 1, sizeof(struct_char));
    if (!output) {
        fprintf(stderr, "ERROR: Memory allocation failed for output.\n");
        free(inputBuffer);
        return NULL;
    }

    size_t keyLen = strlen(key);
    size_t keyIndex = 0;

    for (size_t i = 0; i < fileSize; ++i) {
        struct_char ch = inputBuffer[i];
        struct_char processedChar;

        // Get prev and next characters for context
        struct_char prevChar = (i > 0) ? inputBuffer[i - 1] : '\0';
        struct_char nextChar = (i < fileSize - 1) ? inputBuffer[i + 1] : '\0';

        if (ch >= 32 && ch <= 126) {
            if (isalpha(ch)) {
                // Don't encode single uppercase letters (variables) if they're isolated
                struct_int isSingleUppercase = isupper(ch) &&
                                               !isalpha(prevChar) &&
                                               !isalpha(nextChar);

                if (isSingleUppercase) {
                    // Keep variable as-is for consistency
                    processedChar = ch;
                } else {
                    struct_char keyCh = key[keyIndex % keyLen];
                    struct_char base = isupper(ch) ? 'A' : 'a';
                    struct_char keyBase = isupper(keyCh) ? 'A' : 'a';

                    struct_int c = ch - base;
                    struct_int k = keyCh - keyBase;

                    struct_int result = encode ? (c + k) % 26 : (c - k + 26) % 26;
                    processedChar = (struct_char)(result + base);

                    keyIndex++;
                }
            }
            else {
                // Non-alpha visible character – copy as-is
                processedChar = ch;
            }
        }
        else {
            // Non-visible character – copy as-is
            processedChar = ch;
        }

        output[i] = processedChar;
    }

    output[fileSize] = '\0'; // Explicitly null-terminate output
    free(inputBuffer);
    return output;
}



// Function to encode (cypher)
void cypher(const struct_strg inputFileName, const struct_strg outputFileName, const struct_strg key) {
    vigenereFile(inputFileName, outputFileName, key, CYPHER);
}

// Function to decode (decypher)
void decypher(const struct_strg inputFileName, const struct_strg outputFileName, const struct_strg key) {
    vigenereFile(inputFileName, outputFileName, key, DECYPHER);
}

struct_int getSizeOfFile(const struct_strg filename) {
    struct_int size = 0;
    FILE* file = fopen(filename, "rb");
    if (!file) {
        fprintf(stderr, "ERROR: Cannot open file for size check: %s\n", filename);
        return -1; // or any error code you prefer
    }

    fseek(file, 0, SEEK_END);
    size = (struct_int)ftell(file);
    fclose(file);
    return size;
}