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

// Structure defining the content and metadata of a single page
struct Page {
  char title[80];
  char *permalink;
  struct Page *next;
  struct PageList *incoming;
  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 + 1);

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

  fread(buffer, 1, fileLength, file);
  buffer[fileLength] = 0;
  fclose(file);

  return buffer;
}

/*** Hash map implementation ***/
struct PageMap {
  struct Page **pages;
  int capacity;
  int size;
};

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 capacity, char key[]) {
  return helper_hash_polynomial(key, 0, strlen(key), capacity, 0);
}

char * to_lower_case(char str[]) {
  char * lower = malloc((strlen(str) + 1) * sizeof(char));
  int i = 0;
  for (; str[i] != '\0'; i++) {
    lower[i] = tolower(str[i]);
  }
  lower[i] = 0;

  return lower;
}

struct PageMap * map(int capacity) {
  struct PageMap *map = malloc(sizeof(struct PageMap));
  map->pages = calloc(capacity, sizeof(struct Page *));
  map->capacity = capacity;
  map->size = 0;
  return map;
}

void map_free(struct PageMap *map) {
  free(map->pages);
  free(map);
}

void map_put(struct PageMap *map, char title[], struct Page *page) {
  char *lowercased = to_lower_case(title);

  int index = hash_polynomial(map->capacity, lowercased);
  while (map->pages[index] != NULL) index++;
  map->pages[index] = page;
  map->size++;

  // Resize the map if we're running low on space
  if (map->size/map->capacity > 0.75) {
    map->pages = realloc(map->pages, map->capacity * 2);
    for (int i = map->capacity; i < map->capacity * 2; i++) {
      map->pages[i] = 0;
    }
    map->capacity *= 2;
  }

  free(lowercased);
}

struct Page * map_get(struct PageMap *map, char title[]) {
  char *lowercased = to_lower_case(title);

  int index = hash_polynomial(map->capacity, lowercased);
  struct Page *page = map->pages[index];

  char *lowercasedFoundTitle = to_lower_case(page->title);
  while (strcmp(lowercasedFoundTitle, lowercased) != 0) {
    page = map->pages[++index];
    free(lowercasedFoundTitle);
    lowercasedFoundTitle = to_lower_case(page->title);
  }

  free(lowercased);
  free(lowercasedFoundTitle);
  return page;
}

/*** Dynamic Array Implementation ***/
struct PageList {
  struct Page **pages;
  int length;
  int capacity;
};

struct PageList * page_list(int capacity) {
  struct PageList *pageList = malloc(sizeof(struct PageList));
  pageList->pages = malloc(sizeof(struct Page *) * capacity);
  pageList->capacity = capacity;
  pageList->length = 0;

  return pageList;
}

void page_list_insert(struct PageList *list, struct Page *page) {
  // If the page is already present in the list, we don't bother adding it again
  for (int i = 0; i < list->length; i++) {
    if (page == list->pages[i]) {
      return;
    }
  }

  // Increase the length of the array if necessary
  if (list->length >= list->capacity) {
    list->pages = realloc(list->pages, (list->capacity + 1)*sizeof(struct Page *));
  }

  list->pages[list->length] = page;
  list->length++;
}

void page_list_free(struct PageList *list) {
  free(list->pages);
  free(list);
}

/*** Templating ***/
char * concat_strings(int n, ...) {
  va_list list;
  va_start(list, n);

  int length = 0;
  char **strings = malloc(n * sizeof(char *));
  memset(strings, 0, n * sizeof(char *));

  for (int i = 0; i < n; i++) {
    strings[i] = va_arg(list, char *);
    length += strlen(strings[i]);
  }

  char * joinedString = malloc((length + 1) * sizeof(char *));
  memset(joinedString, 0, (length + 1) * sizeof(char *));

  strcpy(joinedString, strings[0]);
  for (int i = 1; i < n; i++) {
    strcat(joinedString, strings[i]);
  }

  free(strings);
  va_end(list);
  return joinedString;
}

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));
  memset(compiled, 0, newLength * sizeof(char));
  strncpy(compiled, dest, startIndex);
  strcat(compiled, sub);
  strcat(compiled, end);

  return compiled;
}

static struct argp_option options[] = {
  { "src", 's', "dir", 0, "Source directory of pages", 0 },
  { "template", 't', "file", 0, "Template file path", 0 },
  { "output", 'o', "dir", 0, "Output directory", 0 },
  { 0 }
};

static char *pagesLocation = "./pages";
static char *templateFileName = "./template.html";
static char *outputDirectoryName = "./build";

static int parse_opt(int key, char *arg, struct argp_state *state) {
  switch (key) {
    case 's': {
      pagesLocation = arg;
      break;
    }
    case 't': {
      templateFileName = arg;
      break;
    }
    case 'o': {
      outputDirectoryName = arg;
      break;
    }
  }

  return 0;
}

int main(int argc, char *argv[]) {
  int initialInboundCapacity = 2;

  struct argp argp = {options, parse_opt, 0, 0 };

  argp_parse(&argp, argc, argv, 0, 0, 0);

  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 PageMap *pageMap = map(100);

  // 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;
      }
    }

    currentPage->incoming = page_list(initialInboundCapacity);

    // Build the page's permalink
    currentPage->permalink = concat_strings(2, fileBasename, ".html");

    // Construct the relative path
    // The two accounts for the slash and the terminal zero
    char *relativePath = concat_strings(3, pagesLocation, "/", fileEntry->d_name);

    char *buffer = read_file(relativePath);
    free(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 = calloc(strlen(buffer), sizeof(char));
    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, 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 = concat_strings(3, "mkdir ", outputDirectoryName, " 2> /dev/null");
  system(createOutputDir);
  free(createOutputDir);

  /*** Link 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;

      char *nextVerticalBar = strchr(nextLinkStart, '|');

      char *linkTitle = calloc(linkLength - 3, sizeof(char));
      char *linkPageTitle = NULL;

      if (nextVerticalBar != NULL && nextVerticalBar < nextLinkEnd) {
        // The link is in the from [[link title|page title]]
        strncpy(linkTitle, nextLinkStart + 2, (nextVerticalBar - 1) - (nextLinkStart + 1));
        linkPageTitle = calloc((nextLinkEnd - 2) - nextVerticalBar, sizeof(char));
        strncpy(linkPageTitle, nextVerticalBar + 1, (nextLinkEnd - 1) - nextVerticalBar);
      } else {
        // The link is of the form [[page title]]
        linkPageTitle = linkTitle;
        strncpy(linkTitle, nextLinkStart + 2, (linkLength - 2)*sizeof(char));
      }

      struct Page *linkedPage = map_get(pageMap, linkPageTitle);

      char *compiledLink = NULL;

      if (linkedPage == NULL) {
        // i.e. the page does not exist
        compiledLink = concat_strings(3,
          "<a class=\"calathea-404\" href=\"#\">",
          linkTitle,
          "</a>"
        );
      } else {
        page_list_insert(linkedPage->incoming, currentPage);
        compiledLink = concat_strings(5, "[", linkTitle, "](", linkedPage->permalink, ")");
      }

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

      free(compiledLink);
      if (linkTitle != linkPageTitle) {
        free(linkPageTitle);
      }
      free(linkTitle);

      // 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, "[[");
    }

    currentPage = currentPage->next;
  }

  /*** Rendering ***/
  currentPage = firstPage;
  while (currentPage != NULL) {
    // Compile the markdown
    currentPage->content = cmark_markdown_to_html(
        currentPage->content,
        strlen(currentPage->content),
        (1 << 17) // Disables safe mode, allowing raw HTML
    );

    // Insert the content into the template
    char *renderedPage = NULL;
    char *templateTagStart = strstr(templateContent, "{{content}}");
    char *renderedWithContent = substitute_string(
      templateContent,
      currentPage->content,
      templateTagStart,
      templateTagStart + 11
    );

    renderedPage = renderedWithContent;

    char *incomingTagStart = strstr(renderedPage, "{{incoming}}");
    if (incomingTagStart != NULL) {
      // Build the incoming links list
      int incomingListSize = 37;   // <ul class="calathea-incoming">\n</ul>\n
      for (int i = 0; i < currentPage->incoming->length; i++) {
        // `  <li><a href=\"[permalink]\">[title]</a></li>\n`
        struct Page *page = currentPage->incoming->pages[i];
        incomingListSize += 27 + strlen(page->title) + strlen(page->permalink);
      }

      char *incomingLinksList = malloc((incomingListSize + 1) * sizeof(char));
      memset(incomingLinksList, 0, (incomingListSize + 1) * sizeof(char));

      strcpy(incomingLinksList, "<ul class=\"calathea-incoming\">\n");
      for (int i = 0; i < currentPage->incoming->length; i++) {
        struct Page *page = currentPage->incoming->pages[i];
        char *link = concat_strings(5,
            "  <li><a href=\"",
            page->permalink,
            "\">",
            page->title,
            "</a></li>\n"
        );
        strcat(incomingLinksList, link);
        free(link);
      }
      strcat(incomingLinksList, "</ul>\n");

      char *renderedWithInbound = substitute_string(
        renderedPage,
        incomingLinksList,
        incomingTagStart,
        incomingTagStart + 12
      );

      renderedPage = renderedWithInbound;
      free(renderedWithContent);
    }

    // Output the page to the file
    char *outputFileName = concat_strings(3,
        outputDirectoryName, "/", currentPage->permalink);

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

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

    free(outputFileName);
    free(renderedPage);

    currentPage = currentPage->next;
  }

  printf("Pages built successfully in %s\n", outputDirectoryName);

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

  return 0;
}