#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <math.h>
#include <ctype.h>
#include <cmark.h>

// Structure defining the content and metadata of a single page
struct Page {
  char title[80];
  char *permalink;
  struct Page *next;
  char *content;
};

/*** Helper functions ***/
int min(int x, int y) {
  return x > y ? y : x;
}

char * read_file(char *filename) {
  FILE *file = fopen(filename, "rb");

  if (file == NULL) {
    printf("Warning: Failed to open %s\n", filename);
    return NULL;
  }

  // First, we calculate the length of the file
  fseek(file, 0, SEEK_END);     // Traverse to the end of the file
  int fileLength = ftell(file); // Get the current position in the file
  rewind(file);                 // Go back to the beginning of the file

  // Allocate enough space in our buffer to hold the entire file.
  char *buffer = malloc(fileLength);

  if (buffer == NULL) {
    printf("Warning: Failed to allocate enough memory for %s\n", filename);
    fclose(file);
    return NULL;
  }

  fread(buffer, 1, fileLength, file);
  fclose(file);

  return buffer;
}

/*** Hash map implementation ***/
int helper_hash_polynomial(
    char string[],
    int i,
    int length,
    int tableSize,
    unsigned long long acc
) {
  if (i == length) {
    return acc % tableSize;
  } else {
    return helper_hash_polynomial(string, i + 1, length, tableSize,
        acc + string[i] * pow(33, length-i-1));
  }
}

int hash_polynomial(int mapSize, char key[]) {
  return helper_hash_polynomial(key, 0, strlen(key), mapSize, 0);
}

void to_lower_case(char dest[], char str[]) {
  int i = 0;
  for (; str[i] != '\0'; i++) {
    dest[i] = tolower(str[i]);
  }
  dest[i] = 0;
}

void map_put(struct Page **map, int mapSize, char title[], struct Page *page) {
  char lowercased[80];
  to_lower_case(lowercased, title);

  int index = hash_polynomial(mapSize, lowercased);
  map[index] = page;
}

struct Page * map_get(struct Page **map, int mapSize, char title[]) {
  char lowercased[80];
  to_lower_case(lowercased, title);

  int index = hash_polynomial(mapSize, lowercased);
  struct Page *page = map[index];

  return page;
}

/*** Templating ***/
char * substitute_string(char dest[], char sub[], char *start, char *end) {
  int startIndex = start - dest;

  int newLength = strlen(dest) - (end - start) + strlen(sub) + 1;

  char * compiled = malloc(newLength * sizeof(char));
  compiled[0] = 0;
  strncpy(compiled, dest, startIndex);
  strcat(compiled, sub);
  strcat(compiled, end);

  return compiled;
}

int main(int argc, char *argv[]) {
  char pagesLocation[256] = "./pages";
  int mapSize = 1000;
  char templateFileName[256] = "./template.html";
  char outputDirectoryName[256] = "./build";

  /*** Argument Parsing ***/
  for (int i = 1; i < argc; i++) {
    if (strcmp(argv[i], "--pages") == 0) {
      // We only want to do this if a directory was actually supplied
      if (i + 1 < argc) {
        i++;
        strcpy(pagesLocation, argv[i]);
      }
    } else if (strcmp(argv[i], "--table-size") == 0) {
      if (i + 1 < argc) {
        i++;
        mapSize = atoi(argv[i]);
      }
    } else if (strcmp(argv[i], "--template") == 0) {
      if (i + 1 < argc) {
        i++;
        strcpy(templateFileName, argv[i]);
      }
    } else if (strcmp(argv[i], "--output-dir") == 0) {
      if (i + 1 < argc) {
        i++;
        strcpy(outputDirectoryName, argv[i]);
      }
    } else {
      printf("Unknown argument: %s\n", argv[i]);
    }
  }

  char *templateContent = read_file(templateFileName);

  if (templateContent == NULL) {
    // If no template is given, we'll just dump the rendered markdown into a
    // plaintext file
    templateContent = malloc(sizeof(char) * 12);
    strcpy(templateContent, "{{content}}\0");
  }

  DIR *pagesDir = opendir(pagesLocation);

  if (pagesDir == NULL) {
    fprintf(stderr, "Unable to open directory: %s\n", pagesLocation);
    return 1;
  }

  struct Page ** pageMap = malloc(mapSize * sizeof(struct Page *));
  memset(pageMap, 0, mapSize * sizeof(struct Page *));

  // Contains some information about the current file picked from pagesDir
  struct dirent *fileEntry = readdir(pagesDir);
  struct Page *currentPage = malloc(sizeof(struct Page));
  struct Page *firstPage = currentPage;

  while (fileEntry != NULL) {
    // Ignore hidden files, ".", and ".." on Unix
    if (fileEntry->d_name[0] == '.') {
      fileEntry = readdir(pagesDir);
      continue;
    }

    // Determine the base name of the file
    int filenameLength = strlen(fileEntry->d_name);

    char fileBasename[filenameLength];
    memset(fileBasename, 0, filenameLength);

    unsigned char foundPoint = 0;

    for (int i = filenameLength - 1; i >= 0; i--) {
      if (foundPoint) {
        // Start writing the base name into the string
        fileBasename[i] = fileEntry->d_name[i];
      } else if (fileEntry->d_name[i] == '.') {
        // Start writing on the next iteration
        foundPoint = 1;
      } else {
        // Write zeros where the extension would have been
        fileBasename[i] = 0;
      }
    }

    // Build the page's permalink
    currentPage->permalink = malloc(strlen(fileBasename) + 6);

    strcpy(currentPage->permalink, fileBasename);
    strcat(currentPage->permalink, ".html");

    // Construct the relative path
    // The two accounts for the slash and the terminal zero
    char relativePath[strlen(pagesLocation) + filenameLength + 2];
    memset(relativePath, 0, strlen(pagesLocation) + filenameLength + 2);

    strcpy(relativePath, pagesLocation);
    strcat(relativePath, "/");
    strcat(relativePath,fileEntry->d_name);
    relativePath[strlen(pagesLocation) + filenameLength + 1] = 0;

    char *buffer = read_file(relativePath);

    if (buffer == NULL) {
      fileEntry = readdir(pagesDir);
      continue;
    }

    // Get a pointer to the start of the content part of the page
    char *endOfFirstLine = strchr(buffer, '\n');

    if (endOfFirstLine == NULL) {
      printf("Warning: First line in %s/%s must be the title\n",
          pagesLocation, fileEntry->d_name);
      free(buffer);
      fileEntry = readdir(pagesDir);
      continue;
    }

    // We subtract the buffer pointer from the pointer to the end of the
    // first line to get the length of the title
    int titleLength = (endOfFirstLine - buffer)/sizeof(char);

    // Save the content string for later by mallocing it
    char *contentBuffer = endOfFirstLine;
    currentPage->content = malloc(
        sizeof(char) * (strlen(buffer) - titleLength + 1)
    );
    strcpy(currentPage->content, contentBuffer);

    // Copy the first line (title) into its respective field
    strncpy(currentPage->title, buffer, min(titleLength, 80));
    currentPage->title[min(titleLength, 80)] = 0;

    // Insert it into the hash map for lookup later
    map_put(pageMap, mapSize, currentPage->title, currentPage);

    // Get ready to process the next page
    fileEntry = readdir(pagesDir);

    if (fileEntry != NULL) {
      struct Page *nextPage = malloc(sizeof(struct Page));

      // Swap the pages
      currentPage->next = nextPage;
      currentPage = nextPage;
    } else {
      currentPage->next = NULL;
    }

    free(buffer);
  }

  // Create the directory if it doesn't exist
  char *createOutputDir = malloc(
      (7 + strlen(outputDirectoryName)) * sizeof(char)
  );

  strcpy(createOutputDir, "mkdir \0");
  strcat(createOutputDir, outputDirectoryName);

  system(createOutputDir);

  free(createOutputDir);

  /*** Page Processing ***/
  currentPage = firstPage;
  while (currentPage != NULL) {
    // Scan the file for links
    // This pointer is updated upon each iteration
    char *nextLinkStart = strstr(currentPage->content, "[[");
    while (nextLinkStart != NULL) {
      char *nextLinkEnd = strstr(nextLinkStart, "]]");

      if (nextLinkEnd == NULL) {
        // This link is broken
        printf("Warning: \"%s\" contains a broken link", currentPage->title);
        break;
      }

      int linkLength = nextLinkEnd - nextLinkStart;

      // Determine the exact title of the link
      char title[linkLength - 3];

      strncpy(title, nextLinkStart + 2, (linkLength - 2)*sizeof(char));
      title[linkLength - 2] = 0;

      struct Page *linkedPage = map_get(pageMap, mapSize, title);
      char *compiledLink;

      if (linkedPage == NULL) {
        // i.e. the page does not exist
        compiledLink = malloc(strlen(title) + 38);
        strcpy(compiledLink, "<a class=\"calathea-404\" href=\"#\">");
        strcat(compiledLink, title);
        strcat(compiledLink, "</a>\0");
      } else {
        compiledLink = malloc(strlen(title) + strlen(linkedPage->permalink) + 5);
        strcpy(compiledLink, "[");
        strcat(compiledLink, title);
        strcat(compiledLink, "](");
        strcat(compiledLink, linkedPage->permalink);
        strcat(compiledLink, ")\0");
      }

      char *newContent = substitute_string(
          currentPage->content, compiledLink, nextLinkStart, nextLinkEnd + 2);
      free(currentPage->content);
      currentPage->content = newContent;

      free(compiledLink);

      // Move to the next chunk of the file
      // NOTE: This is suboptimal, because we search for "[[" from the
      // beginning of the content at each iteration. We could start from
      // the nextLinkEnd pointer, but since the memory is reallocated, we'd
      // need to take into account that this pointer now points to a chunk
      // of deallocated memory
      nextLinkStart = strstr(currentPage->content, "[[");
    }

    // Compile the markdown
    currentPage->content = cmark_markdown_to_html(
        currentPage->content,
        strlen(currentPage->content),
        (1 << 17) // Disables safe mode, allowing raw HTML
    );

    char *templateTagStart = strstr(templateContent, "{{content}}");
    char *renderedPageContent = substitute_string(
        templateContent,
        currentPage->content,
        templateTagStart,
        templateTagStart + 11
    );

    // Output the page to the file
    char *outputFileName = malloc(
        (strlen(outputDirectoryName)
         + strlen(currentPage->permalink)
         + 2));
    strcpy(outputFileName, outputDirectoryName);
    strcat(outputFileName, "/\0");
    strcat(outputFileName, currentPage->permalink);

    FILE *outputFile = fopen(outputFileName, "w");

    if (outputFile != NULL) {
      fputs(renderedPageContent, outputFile);
      fclose(outputFile);
    } else {
      printf("Warning: failed to create %s\n", outputFileName);
    }

    free(outputFileName);
    free(renderedPageContent);

    currentPage = currentPage->next;
  }

  /*** Deallocation and whatnot ***/
  currentPage = firstPage;
  while (currentPage != NULL) {
    free(currentPage->content);
    free(currentPage->permalink);
    struct Page *next = currentPage->next;
    free(currentPage);
    currentPage = next;
  }
  closedir(pagesDir);
  free(templateContent);

  // Deallocate all the pages

  return 0;
}