#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "compressor.h"

#define BUFSIZE 1024

// Huffman Tree Node
struct MinHeapNode {
    char data;
    unsigned freq;
    struct MinHeapNode *left, *right;
};

// MinHeap
struct MinHeap {
    unsigned size;
    unsigned capacity;
    struct MinHeapNode** array;
};

// Create a new node
struct MinHeapNode* newNode(char data, unsigned freq) {
    struct MinHeapNode* temp = (struct MinHeapNode*)malloc(sizeof(struct MinHeapNode));
    temp->data = data;
    temp->freq = freq;
    temp->left = temp->right = NULL;
    return temp;
}

// Create a MinHeap
struct MinHeap* createMinHeap(unsigned capacity) {
    struct MinHeap* minHeap = (struct MinHeap*)malloc(sizeof(struct MinHeap));
    minHeap->size = 0;
    minHeap->capacity = capacity;
    minHeap->array = (struct MinHeapNode**)malloc(minHeap->capacity * sizeof(struct MinHeapNode*));
    return minHeap;
}

// Swap two min heap nodes
void swapMinHeapNode(struct MinHeapNode** a, struct MinHeapNode** b) {
    struct MinHeapNode* t = *a;
    *a = *b;
    *b = t;
}

// MinHeapify a node
void minHeapify(struct MinHeap* minHeap, int idx) {
    int smallest = idx;
    int left = 2 * idx + 1;
    int right = 2 * idx + 2;

    if (left < minHeap->size && minHeap->array[left]->freq < minHeap->array[smallest]->freq)
        smallest = left;

    if (right < minHeap->size && minHeap->array[right]->freq < minHeap->array[smallest]->freq)
        smallest = right;

    if (smallest != idx) {
        swapMinHeapNode(&minHeap->array[smallest], &minHeap->array[idx]);
        minHeapify(minHeap, smallest);
    }
}

// Extract the minimum value node
struct MinHeapNode* extractMin(struct MinHeap* minHeap) {
    struct MinHeapNode* temp = minHeap->array[0];
    minHeap->array[0] = minHeap->array[minHeap->size - 1];
    --minHeap->size;
    minHeapify(minHeap, 0);
    return temp;
}

// Insert a node into the MinHeap
void insertMinHeap(struct MinHeap* minHeap, struct MinHeapNode* minHeapNode) {
    ++minHeap->size;
    int i = minHeap->size - 1;

    while (i && minHeapNode->freq < minHeap->array[(i - 1) / 2]->freq) {
        minHeap->array[i] = minHeap->array[(i - 1) / 2];
        i = (i - 1) / 2;
    }
    minHeap->array[i] = minHeapNode;
}

// Build a MinHeap
struct MinHeap* buildMinHeap(char data[], int freq[], int size) {
    struct MinHeap* minHeap = createMinHeap(size);
    for (int i = 0; i < size; ++i)
        minHeap->array[i] = newNode(data[i], freq[i]);
    minHeap->size = size;
    for (int i = (minHeap->size - 2) / 2; i >= 0; --i)
        minHeapify(minHeap, i);
    return minHeap;
}

// Build Huffman Tree
struct MinHeapNode* buildHuffmanTree(char data[], int freq[], int size) {
    struct MinHeapNode *left, *right, *top;
    struct MinHeap* minHeap = buildMinHeap(data, freq, size);

    while (minHeap->size != 1) {
        left = extractMin(minHeap);
        right = extractMin(minHeap);

        top = newNode('$', left->freq + right->freq);
        top->left = left;
        top->right = right;

        insertMinHeap(minHeap, top);
    }

    return extractMin(minHeap);
}

// Generate Huffman Codes
void generateCodes(struct MinHeapNode* root, char** codes, char* buffer, int top) {
    if (root->left) {
        buffer[top] = '0';
        generateCodes(root->left, codes, buffer, top + 1);
    }
    if (root->right) {
        buffer[top] = '1';
        generateCodes(root->right, codes, buffer, top + 1);
    }
    if (!root->left && !root->right) {
        buffer[top] = '\0';
        codes[(unsigned char)root->data] = strdup(buffer);
    }
}

// Compress using Huffman encoding
void compress_1(const char* input_file_name, const char* output_file_name) {
    FILE* input = fopen(input_file_name, "rb");
    FILE* output = fopen(output_file_name, "wb");
    if (!input || !output) {
        perror("File error");
        exit(EXIT_FAILURE);
    }

    int freq[256] = {0};
    char buffer[BUFSIZE];
    size_t bytes_read;

    while ((bytes_read = fread(buffer, 1, BUFSIZE, input)) > 0) {
        for (size_t i = 0; i < bytes_read; i++) {
            freq[(unsigned char)buffer[i]]++;
        }
    }

    char data[256];
    int freq_array[256];
    int size = 0;

    for (int i = 0; i < 256; i++) {
        if (freq[i] > 0) {
            data[size] = (char)i;
            freq_array[size] = freq[i];
            size++;
        }
    }

    struct MinHeapNode* root = buildHuffmanTree(data, freq_array, size);
    char* codes[256] = {NULL};
    char code_buffer[256];
    generateCodes(root, codes, code_buffer, 0);

    rewind(input);

    fwrite(&size, sizeof(int), 1, output);
    for (int i = 0; i < size; i++) {
        fputc(data[i], output);
        fwrite(&freq_array[i], sizeof(int), 1, output);
    }

    unsigned char bit_buffer = 0;
    int bit_count = 0;

    while ((bytes_read = fread(buffer, 1, BUFSIZE, input)) > 0) {
        for (size_t i = 0; i < bytes_read; i++) {
            char* code = codes[(unsigned char)buffer[i]];
            for (char* p = code; *p; p++) {
                bit_buffer = (bit_buffer << 1) | (*p - '0');
                bit_count++;
                if (bit_count == 8) {
                    fputc(bit_buffer, output);
                    bit_buffer = 0;
                    bit_count = 0;
                }
            }
        }
    }

    if (bit_count > 0) {
        bit_buffer <<= (8 - bit_count);
        fputc(bit_buffer, output);
    }

    fclose(input);
    fclose(output);
    for (int i = 0; i < 256; i++) {
        free(codes[i]);
    }
}

// Decompress using Huffman encoding
void decompress_1(const char* input_file_name, const char* output_file_name) {
    FILE* input = fopen(input_file_name, "rb");
    FILE* output = fopen(output_file_name, "wb");
    if (!input || !output) {
        perror("File error");
        exit(EXIT_FAILURE);
    }

    int size;
    fread(&size, sizeof(int), 1, input);
    char data[256];
    int freq[256];

    for (int i = 0; i < size; i++) {
        data[i] = fgetc(input);
        fread(&freq[i], sizeof(int), 1, input);
    }

    struct MinHeapNode* root = buildHuffmanTree(data, freq, size);
    struct MinHeapNode* current = root;

    int bit_buffer;
    int bit_count = 0;
    int byte;

    while ((byte = fgetc(input)) != EOF) {
        for (int i = 7; i >= 0; i--) {
            int bit = (byte >> i) & 1;
            if (bit == 0) {
                current = current->left;
            } else {
                current = current->right;
            }

            if (!current->left && !current->right) {
                fputc(current->data, output);
                current = root;
            }
        }
    }

    fclose(input);
    fclose(output);
}

// Compress using RLE
void compress_2(const char* input_file_name, const char* output_file_name) {
    FILE* input = fopen(input_file_name, "rb");
    FILE* output = fopen(output_file_name, "wb");
    if (!input || !output) {
        perror("File error");
        exit(EXIT_FAILURE);
    }

    unsigned char buffer[BUFSIZE];
    size_t bytes_read;

    while ((bytes_read = fread(buffer, 1, BUFSIZE, input)) > 0) {
        for (size_t i = 0; i < bytes_read; i++) {
            unsigned char current = buffer[i];
            size_t count = 1;
            while (i + 1 < bytes_read && buffer[i + 1] == current) {
                count++;
                i++;
            }

            fputc(current, output);
            fputc(count, output);
        }
    }

    fclose(input);
    fclose(output);
}

// Decompress using RLE
void decompress_2(const char* input_file_name, const char* output_file_name) {
    FILE* input = fopen(input_file_name, "rb");
    FILE* output = fopen(output_file_name, "wb");
    if (!input || !output) {
        perror("File error");
        exit(EXIT_FAILURE);
    }

    int current;
    int count;

    while ((current = fgetc(input)) != EOF) {
        count = fgetc(input);
        for (int i = 0; i < count; i++) {
            fputc(current, output);
        }
    }

    fclose(input);
    fclose(output);
}