package juloo.keyboard2;

import java.util.Arrays;

public final class ComposeKey
{
  /** Apply the pending compose sequence to [kv]. Returns [null] if no sequence
      matched. */
  public static KeyValue apply(int state, KeyValue kv)
  {
    switch (kv.getKind())
    {
      case Char:
        return apply(state, kv.getChar());
      case String:
        return apply(state, kv.getString());
    }
    return null;
  }

  /** Apply the pending compose sequence to char [c]. Returns [null] if no
      sequence matched. */
  public static KeyValue apply(int prev, char c)
  {
    char[] states = ComposeKeyData.states;
    char[] edges = ComposeKeyData.edges;
    int prev_length = edges[prev];
    int next = Arrays.binarySearch(states, prev + 1, prev + prev_length, c);
    if (next < 0)
      return null;
    next = edges[next];
    int next_header = states[next];
    if (next_header == 0) // Enter a new intermediate state.
      return KeyValue.makeComposePending(String.valueOf(c), next, 0);
    else if (next_header == 0xFFFF) // String final state
    {
      int next_length = edges[next];
      return KeyValue.getKeyByName(
          new String(states, next + 1, next_length - 1));
    }
    else // Character final state.
      return KeyValue.makeCharKey((char)next_header);
  }

  /** Apply each char of a string to a sequence. Returns [null] if no sequence
      matched. */
  public static KeyValue apply(int prev, String s)
  {
    final int len = s.length();
    int i = 0;
    if (len == 0) return null;
    while (true)
    {
      KeyValue k = apply(prev, s.charAt(i));
      i++;
      if (k == null) return null;
      if (i >= len) return k;
      if (k.getKind() != KeyValue.Kind.Compose_pending)
        return null; // Found a final state before the end of [s].
      prev = k.getPendingCompose();
    }
  }

  /** The state machine is comprised of two arrays.

      The [states] array represents the different states and the associated
      transitions:
      - The first cell is the header cell, [states[s]].
      - If the header is equal to [0],
        The remaining cells are the transitions characters, sorted
        alphabetically.
      - If the header is positive,
        This is a final state, [states[s]] is the result of the sequence.
        In this case, [edges[s]] must be equal to [1].
      - If the header is equal to [-1],
        This is a final state, the remaining cells represent the result string
        which starts at index [s + 1] and has a length of [edges[s] - 1].

      The [edges] array represents the transition state corresponding to each
      accepted inputs.
      - If [states[s]] is a header cell, [edges[s]] is the number of cells
        occupied by the state [s], including the header cell.
      - If [states[s]] is a transition, [edges[s]] is the index of the state to
        jump into.
      - If [states[s]] is a part of a final state, [edges[s]] is not used. */
}