#ifndef LIBLEX_PATTERN_H
#define LIBLEX_PATTERN_H

#include "liblex.h"

/**
 * Enum that represents the type
 * of a NFA node / state.
 */
enum pattern_node_type_e {
  /**
   * Represents a clear, un-configured node.
   */
  PNODE_CLEAR,
  /**
   * Represents a single value to be matched.
   */
  PNODE_VALUE,
  /**
   * Represents a range of values, inclusive.
   */
  PNODE_RANGE,
  /**
   * Represents any character other than the NULL terminator.
   */
  PNODE_ANY,
  /**
   * Represents a "connection" between nodes, does not 
   * match any value.
   * */
  PNODE_CONNECT,
  /**
   * Represents a fork / divide in possible "next" states.
   */
  PNODE_FORK,
  /**
   * Represents a succesfully matched pattern.
   */
  PNODE_END
};

/**
 * Struct representing a single NFA node / state.
 */
struct pattern_node_s {
  /**
   * The type of this node.
   */
  enum pattern_node_type_e type;
  /**
   * The id of this node.
   * The id is unique within the pattern.
   */
  int id;
  /**
   * The id of the pattern that this node belongs to.
   */
  int pattern_id;

  /**
   * The node's data that varies based on type.
   */
  union {
    /**
     * Data for a "value" node.
     */
    struct {
      /**
       * The value this node matches.
       */
      char value;
      /**
       * The next state in the pattern.
       */
      struct pattern_node_s* next;
    } value_s;

    /**
     * Data for a "range" node.
     */
    struct {
      /**
       * The beginning of the range, inclusive, of matched values.
       */
      char from;
      /**
       * The end of the range, inclusive, of matched values.
       */
      char to;
      /**
       * The next state in the pattern.
       */
      struct pattern_node_s* next;
    } range_s;

    /**
     * Data for an "any" node.
     */
    struct {
      /**
       * The next state in the pattern.
       */
      struct pattern_node_s* next;
    } any_s;

    /**
     * Data for a "connect" node.
     */
    struct {
      /**
       * The next node in the pattern.
       */
      struct pattern_node_s* next;
    } connect_s;

    /**
     * Data for a "fork" node.
     */
    struct {
      /**
       * The left node in the fork.
       */
      struct pattern_node_s* left;
      /**
       * The right node in the fork.
       */
      struct pattern_node_s* right;
    } fork_s;
  } data_u;
};

/**
 * A chain of pattern nodes.
 */
struct pattern_chain_s {
  /**
   * The beginning of the chain, its first state.
   */
  struct pattern_node_s* head;
  /**
   * The end of the chain, its last state.
   */
  struct pattern_node_s* tail;
};

/**
 * Represents a single compiled pattern.
 */
struct pattern_s {
  /**
   * The first NFA state of the pattern.
   */
  struct pattern_node_s* head;
  /**
   * The number of NFA nodes in this pattern.
   */
  int size;
};

typedef enum pattern_node_type_e pattern_node_type;
typedef struct pattern_node_s pattern_node;
typedef struct pattern_chain_s pattern_chain;
typedef struct pattern_s pattern;

/**
 * Compiles a string representation of a pattern into a pattern NFA,
 * and stores the first node of the new NFA in root.
 * @param root the node to store the resulting pattern into.
 * @param expression the pattern represented as a string.
 * @param id the id of the pattern.
 * @return LIBLEX_SUCCESS if all goes well, otherwise some other liblex_result.
 */
liblex_result pattern_compile(pattern* ptrn, const char* expression, int id);
/**
 * Frees a pattern NFA allocated by pattern_compile.
 * @param root the root node to start freeing from.
 * @return LIBLEX_SUCCESS if all goes well, otherwise some other liblex_result.
 */
liblex_result pattern_free(pattern* ptrn);

#endif