/**
 * This CGI program renders the oper.io blog
 * Copyright (C) 2024 Aaron Ball <nullspoon@oper.io>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include "j2.h"


char* j2_strstr(char* line) {
  char* start;
  char* end;

  start = strstr(line, "{{ ");
  if(start == NULL)
    return NULL;
  //start += 3; // Advance past the '{{ '

  // Check for the var close to ensure a complete definition is present
  end = strstr(start, " }}");

  // Incorrectly formatted, early return null
  if(end == NULL)
    return NULL;

  return start;
}


char* j2_readvar(char* line, char* buf, int maxlen) {
  char* start = NULL;
  char* end   = NULL;

  start = j2_strstr(line);
  if(start == NULL)
    return NULL;
  start += 3;

  // Because of how j2_strstr works, this will always work if start is not null
  end = strstr(start, " }}");

  // Only copy up to maxlen to avoid buffer overflows
  if(end - start > maxlen) {
    strncpy(buf, start, maxlen);
    buf[maxlen] = '\0';
  } else {
    strncpy(buf, start, end - start);
    buf[end - start] = '\0';
  }
  return end + 3;
}


/**
 * Reads a jinja file and cats the output, interpolating variables, values from
 * matching environment variables.
 */
int j2_cat(char* path) {
  char line[J2_MAXLINE] = {'\0'};
  char buf[J2_MAXBUF] = {'\0'};
  FILE* fd = fopen(path, "r");
  char* value    = NULL;
  char* varstart = NULL;
  char* varend   = NULL;

  while(fgets(line, J2_MAXLINE, fd) != NULL) {
    varstart = j2_strstr(line);

    if(!varstart) {
      fputs(line, stdout);
      continue;
    }
    varend = j2_readvar(varstart, buf, J2_MAXBUF);

    // Break the beginning of the string and the beginning of the variable
    // (this overwrites the first { that opens the variable def)
    *varstart = '\0';
    // Because of the inserted null byte, this will print from byte 0 to there
    fputs(line, stdout);

    // Execute the variable directive and print the output
    if(strncmp(buf, "shell ", 6) == 0) {
      // Execute the provided shell command and print that
      value = runsh(&buf[6]);
      fputs(value, stdout);
      free(value);
    } else {
      // Print the referenced environment variable
      value = getenv(buf);
      printf("%s", value);
    }

    // varend points to after the final }} of the variable def
    printf("%s", varend);
  }

  fclose(fd);
  return 0;
}