picom/src/c2.c

/*
 * Compton - a compositor for X11
 *
 * Based on `xcompmgr` - Copyright (c) 2003, Keith Packard
 *
 * Copyright (c) 2011-2013, Christopher Jeffrey
 * See LICENSE for more information.
 *
 */

#include "c2.h"

/**
 * Parse a condition string.
 */
c2_lptr_t *
c2_parsed(session_t *ps, c2_lptr_t **pcondlst, const char *pattern,
    void *data) {
  if (!pattern)
    return NULL;

  // Parse the pattern
  c2_ptr_t result = C2_PTR_INIT;
  int offset = -1;

  if (strlen(pattern) >= 2 && ':' == pattern[1])
    offset = c2_parse_legacy(ps, pattern, 0, &result);
  else
    offset = c2_parse_grp(ps, pattern, 0, &result, 0);

  if (offset < 0) {
    c2_freep(&result);
    return NULL;
  }

  // Insert to pcondlst
  {
    const static c2_lptr_t lptr_def = C2_LPTR_INIT;
    c2_lptr_t *plptr = malloc(sizeof(c2_lptr_t));
    if (!plptr)
      printf_errfq(1, "(): Failed to allocate memory for new condition linked"
          " list element.");
    memcpy(plptr, &lptr_def, sizeof(c2_lptr_t));
    plptr->ptr = result;
    plptr->data = data;
    if (pcondlst) {
      plptr->next = *pcondlst;
      *pcondlst = plptr;
    }

#ifdef DEBUG_C2
    printf_dbgf("(\"%s\"): ", pattern);
    c2_dump(plptr->ptr);
#endif

    return plptr;
  }
}

#undef c2_error
#define c2_error(format, ...) do { \
  printf_err("Pattern \"%s\" pos %d: " format, pattern, offset, \
      ## __VA_ARGS__); \
  return -1; \
} while(0)

#define C2H_SKIP_SPACES() { while (isspace(pattern[offset])) ++offset; }

/**
 * Parse a group in condition string.
 *
 * @return offset of next character in string
 */
static int
c2_parse_grp(session_t *ps, const char *pattern, int offset, c2_ptr_t *presult, int level) {
  // Check for recursion levels
  if (level > C2_MAX_LEVELS)
    c2_error("Exceeded maximum recursion levels.");

  if (!pattern)
    return -1;

  // Expected end character
  const char endchar = (offset ? ')': '\0');

#undef c2_error
#define c2_error(format, ...) do { \
  printf_err("Pattern \"%s\" pos %d: " format, pattern, offset, \
      ## __VA_ARGS__); \
  goto c2_parse_grp_fail; \
} while(0)

  // We use a system that a maximum of 2 elements are kept. When we find
  // the third element, we combine the elements according to operator
  // precedence. This design limits operators to have at most two-levels
  // of precedence and fixed left-to-right associativity.

  // For storing branch operators. ops[0] is actually unused
  c2_b_op_t ops[3] = { };
  // For storing elements
  c2_ptr_t eles[2] = { C2_PTR_INIT, C2_PTR_INIT };
  // Index of next free element slot in eles
  int elei = 0;
  // Pointer to the position of next element
  c2_ptr_t *pele = eles;
  // Negation flag of next operator
  bool neg = false;
  // Whether we are expecting an element immediately, is true at first, or
  // after encountering a logical operator
  bool next_expected = true;

  // Parse the pattern character-by-character
  for (; pattern[offset]; ++offset) {
    assert(elei <= 2);

    // Jump over spaces
    if (isspace(pattern[offset]))
      continue;

    // Handle end of group
    if (')' == pattern[offset])
      break;

    // Handle "!"
    if ('!' == pattern[offset]) {
      if (!next_expected)
        c2_error("Unexpected \"!\".");

      neg = !neg;
      continue;
    }

    // Handle AND and OR
    if ('&' == pattern[offset] || '|' == pattern[offset]) {
      if (next_expected)
        c2_error("Unexpected logical operator.");

      next_expected = true;
      if (!mstrncmp("&&", pattern + offset)) {
        ops[elei] = C2_B_OAND;
        ++offset;
      }
      else if (!mstrncmp("||", pattern + offset)) {
        ops[elei] = C2_B_OOR;
        ++offset;
      }
      else
        c2_error("Illegal logical operator.");

      continue;
    }

    // Parsing an element
    if (!next_expected)
      c2_error("Unexpected expression.");

    assert(!elei || ops[elei]);

    // If we are out of space
    if (2 == elei) {
      --elei;
      // If the first operator has higher or equal precedence, combine
      // the first two elements
      if (c2h_b_opcmp(ops[1], ops[2]) >= 0) {
        eles[0] = c2h_comb_tree(ops[1], eles[0], eles[1]);
        c2_ptr_reset(&eles[1]);
        pele = &eles[elei];
        ops[1] = ops[2];
      }
      // Otherwise, combine the second and the incoming one
      else {
        eles[1] = c2h_comb_tree(ops[2], eles[1], C2_PTR_NULL);
        assert(eles[1].isbranch);
        pele = &eles[1].b->opr2;
      }
      // The last operator always needs to be reset
      ops[2] = C2_B_OUNDEFINED;
    }

    // It's a subgroup if it starts with '('
    if ('(' == pattern[offset]) {
      if ((offset = c2_parse_grp(ps, pattern, offset + 1, pele, level + 1)) < 0)
        goto c2_parse_grp_fail;
    }
    // Otherwise it's a leaf
    else {
      if ((offset = c2_parse_target(ps, pattern, offset, pele)) < 0)
        goto c2_parse_grp_fail;

      assert(!pele->isbranch && !c2_ptr_isempty(*pele));

      if ((offset = c2_parse_op(pattern, offset, pele)) < 0)
        goto c2_parse_grp_fail;

      if ((offset = c2_parse_pattern(ps, pattern, offset, pele)) < 0)
        goto c2_parse_grp_fail;

      if (!c2_l_postprocess(ps, pele->l))
        goto c2_parse_grp_fail;
    }
    // Decrement offset -- we will increment it in loop update
    --offset;

    // Apply negation
    if (neg) {
      neg = false;
      if (pele->isbranch)
        pele->b->neg = !pele->b->neg;
      else
        pele->l->neg = !pele->l->neg;
    }

    next_expected = false;
    ++elei;
    pele = &eles[elei];
  }

  // Wrong end character?
  if (pattern[offset] && !endchar)
    c2_error("Expected end of string but found '%c'.", pattern[offset]);
  if (!pattern[offset] && endchar)
    c2_error("Expected '%c' but found end of string.", endchar);

  // Handle end of group
  if (!elei) {
    c2_error("Empty group.");
  }
  else if (next_expected) {
    c2_error("Missing rule before end of group.");
  }
  else if (elei > 1) {
    assert(2 == elei);
    assert(ops[1]);
    eles[0] = c2h_comb_tree(ops[1], eles[0], eles[1]);
    c2_ptr_reset(&eles[1]);
  }

  *presult = eles[0];

  if (')' == pattern[offset])
    ++offset;

  return offset;

c2_parse_grp_fail:
  c2_freep(&eles[0]);
  c2_freep(&eles[1]);

  return -1;
}

#undef c2_error
#define c2_error(format, ...) do { \
  printf_err("Pattern \"%s\" pos %d: " format, pattern, offset, \
      ## __VA_ARGS__); \
  return -1; \
} while(0)

/**
 * Parse the target part of a rule.
 */
static int
c2_parse_target(session_t *ps, const char *pattern, int offset, c2_ptr_t *presult) {
  // Initialize leaf
  presult->isbranch = false;
  presult->l = malloc(sizeof(c2_l_t));
  if (!presult->l)
    c2_error("Failed to allocate memory for new leaf.");

  c2_l_t * const pleaf = presult->l;
  memcpy(pleaf, &leaf_def, sizeof(c2_l_t));

  // Parse negation marks
  while ('!' == pattern[offset]) {
    pleaf->neg = !pleaf->neg;
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Copy target name out
  unsigned tgtlen = 0;
  for (; pattern[offset]
      && (isalnum(pattern[offset]) || '_' == pattern[offset]); ++offset) {
    ++tgtlen;
  }
  if (!tgtlen)
    c2_error("Empty target.");
  pleaf->tgt = mstrncpy(&pattern[offset - tgtlen], tgtlen);

  // Check for predefined targets
  for (unsigned i = 1; i < sizeof(C2_PREDEFS) / sizeof(C2_PREDEFS[0]); ++i) {
    if (!strcmp(C2_PREDEFS[i].name, pleaf->tgt)) {
      pleaf->predef = i;
      pleaf->type = C2_PREDEFS[i].type;
      pleaf->format = C2_PREDEFS[i].format;
      break;
    }
  }

  // Alias for predefined targets
  if (!pleaf->predef) {
#define TGTFILL(pdefid) \
  (pleaf->predef = pdefid, \
   pleaf->type = C2_PREDEFS[pdefid].type, \
   pleaf->format = C2_PREDEFS[pdefid].format)

  // if (!strcmp("WM_NAME", tgt) || !strcmp("_NET_WM_NAME", tgt))
  //   TGTFILL(C2_L_PNAME);
#undef TGTFILL

    // Alias for custom properties
#define TGTFILL(target, type, format) \
  (pleaf->target = mstrcpy(target), \
   pleaf->type = type, \
   pleaf->format = format)

    // if (!strcmp("SOME_ALIAS"))
    //   TGTFILL("ALIAS_TEXT", C2_L_TSTRING, 32);
#undef TGTFILL
  }

  C2H_SKIP_SPACES();

  // Parse target-on-frame flag
  if ('@' == pattern[offset]) {
    pleaf->tgt_onframe = true;
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Parse index
  if ('[' == pattern[offset]) {
    offset++;

    C2H_SKIP_SPACES();

    int index = -1;
    char *endptr = NULL;

    index = strtol(pattern + offset, &endptr, 0);

    if (!endptr || pattern + offset == endptr)
      c2_error("No index number found after bracket.");

    if (index < 0)
      c2_error("Index number invalid.");

    if (pleaf->predef)
      c2_error("Predefined targets can't have index.");

    pleaf->index = index;
    offset = endptr - pattern;

    C2H_SKIP_SPACES();

    if (']' != pattern[offset])
      c2_error("Index end marker not found.");

    ++offset;

    C2H_SKIP_SPACES();
  }

  // Parse target type and format
  if (':' == pattern[offset]) {
    ++offset;
    C2H_SKIP_SPACES();

    // Look for format
    bool hasformat = false;
    int format = 0;
    {
      char *endptr = NULL;
      format =  strtol(pattern + offset, &endptr, 0);
      assert(endptr);
      if ((hasformat = (endptr && endptr != pattern + offset)))
        offset = endptr - pattern;
      C2H_SKIP_SPACES();
    }

    // Look for type
    enum c2_l_type type = C2_L_TUNDEFINED;
    {
      switch (pattern[offset]) {
        case 'w': type = C2_L_TWINDOW; break;
        case 'd': type = C2_L_TDRAWABLE; break;
        case 'c': type = C2_L_TCARDINAL; break;
        case 's': type = C2_L_TSTRING; break;
        case 'a': type = C2_L_TATOM; break;
        default:  c2_error("Invalid type character.");
      }

      if (type) {
        if (pleaf->predef) {
          printf_errf("(): Warning: Type specified for a default target will be ignored.");
        }
        else {
          if (pleaf->type && type != pleaf->type)
            printf_errf("(): Warning: Default type overridden on target.");
          pleaf->type = type;
        }
      }

      offset++;
      C2H_SKIP_SPACES();
    }

    // Default format
    if (!pleaf->format) {
      switch (pleaf->type) {
        case C2_L_TWINDOW:
        case C2_L_TDRAWABLE:
        case C2_L_TATOM:
          pleaf->format = 32;  break;
        case C2_L_TSTRING:
          pleaf->format = 8;   break;
        default:
          break;
      }
    }

    // Write format
    if (hasformat) {
      if (pleaf->predef)
        printf_errf("(): Warning: Format \"%d\" specified on a default target will be ignored.", format);
      else if (C2_L_TSTRING == pleaf->type)
        printf_errf("(): Warning: Format \"%d\" specified on a string target will be ignored.", format);
      else {
        if (pleaf->format && pleaf->format != format)
          printf_err("Warning: Default format %d overridden on target.",
              pleaf->format);
        pleaf->format = format;
      }
    }
  }

  if (!pleaf->type)
    c2_error("Target type cannot be determined.");

  // if (!pleaf->predef && !pleaf->format && C2_L_TSTRING != pleaf->type)
  //   c2_error("Target format cannot be determined.");

  if (pleaf->format && 8 != pleaf->format
        && 16 != pleaf->format && 32 != pleaf->format)
    c2_error("Invalid format.");

  return offset;
}

/**
 * Parse the operator part of a leaf.
 */
static int
c2_parse_op(const char *pattern, int offset, c2_ptr_t *presult) {
  c2_l_t * const pleaf = presult->l;

  // Parse negation marks
  C2H_SKIP_SPACES();
  while ('!' == pattern[offset]) {
    pleaf->neg = !pleaf->neg;
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Parse qualifiers
  if ('*' == pattern[offset] || '^' == pattern[offset]
      || '%' == pattern[offset] || '~' == pattern[offset]) {
    switch (pattern[offset]) {
      case '*': pleaf->match = C2_L_MCONTAINS; break;
      case '^': pleaf->match = C2_L_MSTART;    break;
      case '%': pleaf->match = C2_L_MWILDCARD; break;
      case '~': pleaf->match = C2_L_MPCRE;     break;
      default:  assert(0);
    }
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Parse flags
  while ('?' == pattern[offset]) {
    pleaf->match_ignorecase = true;
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Parse operator
  while ('=' == pattern[offset] || '>' == pattern[offset]
      || '<' == pattern[offset]) {
    if ('=' == pattern[offset] && C2_L_OGT == pleaf->op)
      pleaf->op = C2_L_OGTEQ;
    else if ('=' == pattern[offset] && C2_L_OLT == pleaf->op)
      pleaf->op = C2_L_OLTEQ;
    else if (pleaf->op) {
      c2_error("Duplicate operator.");
    }
    else {
      switch (pattern[offset]) {
        case '=': pleaf->op = C2_L_OEQ; break;
        case '>': pleaf->op = C2_L_OGT; break;
        case '<': pleaf->op = C2_L_OLT; break;
        default:  assert(0);
      }
    }
    ++offset;
    C2H_SKIP_SPACES();
  }

  // Check for problems
  if (C2_L_OEQ != pleaf->op && (pleaf->match || pleaf->match_ignorecase))
    c2_error("Exists/greater-than/less-than operators cannot have a qualifier.");

  return offset;
}

/**
 * Parse the pattern part of a leaf.
 */
static int
c2_parse_pattern(session_t *ps, const char *pattern, int offset, c2_ptr_t *presult) {
  c2_l_t * const pleaf = presult->l;

  // Exists operator cannot have pattern
  if (!pleaf->op)
    return offset;

  C2H_SKIP_SPACES();

  char *endptr = NULL;
  // Check for boolean patterns
  if (!strcmp_wd("true", &pattern[offset])) {
    pleaf->ptntype = C2_L_PTINT;
    pleaf->ptnint = true;
    offset += strlen("true");
  }
  else if (!strcmp_wd("false", &pattern[offset])) {
    pleaf->ptntype = C2_L_PTINT;
    pleaf->ptnint = false;
    offset += strlen("false");
  }
  // Check for integer patterns
  else if (pleaf->ptnint = strtol(pattern + offset, &endptr, 0),
      pattern + offset != endptr) {
    pleaf->ptntype = C2_L_PTINT;
    offset = endptr - pattern;
    // Make sure we are stopping at the end of a word
    if (isalnum(pattern[offset]))
      c2_error("Trailing characters after a numeric pattern.");
  }
  // Check for string patterns
  else {
    bool raw = false;
    char delim = '\0';

    // String flags
    if ('r' == tolower(pattern[offset])) {
      raw = true;
      ++offset;
      C2H_SKIP_SPACES();
    }

    // Check for delimiters
    if ('\"' == pattern[offset] || '\'' == pattern[offset]) {
      pleaf->ptntype = C2_L_PTSTRING;
      delim = pattern[offset];
      ++offset;
    }

    if (C2_L_PTSTRING != pleaf->ptntype)
      c2_error("Invalid pattern type.");

    // Parse the string now
    // We can't determine the length of the pattern, so we use the length
    // to the end of the pattern string -- currently escape sequences
    // cannot be converted to a string longer than itself.
    char *tptnstr = malloc((strlen(pattern + offset) + 1) * sizeof(char));
    char *ptptnstr = tptnstr;
    pleaf->ptnstr = tptnstr;
    for (; pattern[offset] && delim != pattern[offset]; ++offset) {
      // Handle escape sequences if it's not a raw string
      if ('\\' == pattern[offset] && !raw) {
        switch(pattern[++offset]) {
          case '\\':  *(ptptnstr++) = '\\'; break;
          case '\'':  *(ptptnstr++) = '\''; break;
          case '\"':  *(ptptnstr++) = '\"'; break;
          case 'a':   *(ptptnstr++) = '\a'; break;
          case 'b':   *(ptptnstr++) = '\b'; break;
          case 'f':   *(ptptnstr++) = '\f'; break;
          case 'n':   *(ptptnstr++) = '\n'; break;
          case 'r':   *(ptptnstr++) = '\r'; break;
          case 't':   *(ptptnstr++) = '\t'; break;
          case 'v':   *(ptptnstr++) = '\v'; break;
          case 'o':
          case 'x':
                      {
                        char *tstr = mstrncpy(pattern + offset + 1, 2);
                        char *pstr = NULL;
                        long val = strtol(tstr, &pstr,
                            ('o' == pattern[offset] ? 8: 16));
                        free(tstr);
                        if (pstr != &tstr[2] || val <= 0)
                          c2_error("Invalid octal/hex escape sequence.");
                        assert(val < 256 && val >= 0);
                        *(ptptnstr++) = val;
                        offset += 2;
                        break;
                      }
          default:   c2_error("Invalid escape sequence.");
        }
      }
      else {
        *(ptptnstr++) = pattern[offset];
      }
    }
    if (!pattern[offset])
      c2_error("Premature end of pattern string.");
    ++offset;
    *ptptnstr = '\0';
    pleaf->ptnstr = mstrcpy(tptnstr);
    free(tptnstr);
  }

  C2H_SKIP_SPACES();

  if (!pleaf->ptntype)
    c2_error("Invalid pattern type.");

  // Check if the type is correct
  if (!(((C2_L_TSTRING == pleaf->type
            || C2_L_TATOM == pleaf->type)
          && C2_L_PTSTRING == pleaf->ptntype)
        || ((C2_L_TCARDINAL == pleaf->type
            || C2_L_TWINDOW == pleaf->type
            || C2_L_TDRAWABLE == pleaf->type)
          && C2_L_PTINT == pleaf->ptntype)))
    c2_error("Pattern type incompatible with target type.");

  if (C2_L_PTINT == pleaf->ptntype && pleaf->match)
    c2_error("Integer/boolean pattern cannot have operator qualifiers.");

  if (C2_L_PTINT == pleaf->ptntype && pleaf->match_ignorecase)
    c2_error("Integer/boolean pattern cannot have flags.");

  if (C2_L_PTSTRING == pleaf->ptntype
      && (C2_L_OGT == pleaf->op || C2_L_OGTEQ == pleaf->op
        || C2_L_OLT == pleaf->op || C2_L_OLTEQ == pleaf->op))
    c2_error("String pattern cannot have an arithmetic operator.");

  return offset;
}

/**
 * Parse a condition with legacy syntax.
 */
static int
c2_parse_legacy(session_t *ps, const char *pattern, int offset, c2_ptr_t *presult) {
  unsigned plen = strlen(pattern + offset);

  if (plen < 4 || ':' != pattern[offset + 1]
      || !strchr(pattern + offset + 2, ':'))
    c2_error("Legacy parser: Invalid format.");

  // Allocate memory for new leaf
  c2_l_t *pleaf = malloc(sizeof(c2_l_t));
  if (!pleaf)
    printf_errfq(1, "(): Failed to allocate memory for new leaf.");
  presult->isbranch = false;
  presult->l = pleaf;
  memcpy(pleaf, &leaf_def, sizeof(c2_l_t));
  pleaf->type = C2_L_TSTRING;
  pleaf->op = C2_L_OEQ;
  pleaf->ptntype = C2_L_PTSTRING;

  // Determine the pattern target
#define TGTFILL(pdefid) \
  (pleaf->predef = pdefid, \
   pleaf->type = C2_PREDEFS[pdefid].type, \
   pleaf->format = C2_PREDEFS[pdefid].format)
  switch (pattern[offset]) {
    case 'n': TGTFILL(C2_L_PNAME);    break;
    case 'i': TGTFILL(C2_L_PCLASSI);  break;
    case 'g': TGTFILL(C2_L_PCLASSG);  break;
    case 'r': TGTFILL(C2_L_PROLE);    break;
    default:  c2_error("Target \"%c\" invalid.\n", pattern[offset]);
  }
#undef TGTFILL

  offset += 2;

  // Determine the match type
  switch (pattern[offset]) {
    case 'e': pleaf->match = C2_L_MEXACT;       break;
    case 'a': pleaf->match = C2_L_MCONTAINS;    break;
    case 's': pleaf->match = C2_L_MSTART;       break;
    case 'w': pleaf->match = C2_L_MWILDCARD;    break;
    case 'p': pleaf->match = C2_L_MPCRE;        break;
    default:  c2_error("Type \"%c\" invalid.\n", pattern[offset]);
  }
  ++offset;

  // Determine the pattern flags
  while (':' != pattern[offset]) {
    switch (pattern[offset]) {
      case 'i': pleaf->match_ignorecase = true;  break;
      default:  c2_error("Flag \"%c\" invalid.", pattern[offset]);
    }
    ++offset;
  }
  ++offset;

  // Copy the pattern
  pleaf->ptnstr = mstrcpy(pattern + offset);

  if (!c2_l_postprocess(ps, pleaf))
    return -1;

  return offset;
}

#undef c2_error
#define c2_error(format, ...) { \
  printf_err(format, ## __VA_ARGS__); \
  return false; }

/**
 * Do postprocessing on a condition leaf.
 */
static bool
c2_l_postprocess(session_t *ps, c2_l_t *pleaf) {
  // Give a pattern type to a leaf with exists operator, if needed
  if (C2_L_OEXISTS == pleaf->op && !pleaf->ptntype) {
    pleaf->ptntype =
      (C2_L_TSTRING == pleaf->type ? C2_L_PTSTRING: C2_L_PTINT);
  }

  // Get target atom if it's not a predefined one
  if (!pleaf->predef) {
    pleaf->tgtatom = get_atom(ps, pleaf->tgt);
    if (!pleaf->tgtatom)
      c2_error("Failed to get atom for target \"%s\".", pleaf->tgt);
  }

  // Insert target Atom into atom track list
  if (pleaf->tgtatom) {
    bool found = false;
    for (latom_t *platom = ps->track_atom_lst; platom;
        platom = platom->next) {
      if (pleaf->tgtatom == platom->atom) {
        found = true;
        break;
      }
    }
    if (!found) {
      latom_t *pnew = malloc(sizeof(latom_t));
      if (!pnew)
        printf_errfq(1, "(): Failed to allocate memory for new track atom.");
      pnew->next = ps->track_atom_lst;
      pnew->atom = pleaf->tgtatom;
      ps->track_atom_lst = pnew;
    }
  }

  // Enable specific tracking options in compton if needed by the condition
  // TODO: Add track_leader
  if (pleaf->predef) {
    switch (pleaf->predef) {
      case C2_L_PFOCUSED: ps->o.track_focus = true; break;
      case C2_L_PNAME:
      case C2_L_PCLASSG:
      case C2_L_PCLASSI:
      case C2_L_PROLE:    ps->o.track_wdata = true; break;
      default:            break;
    }
  }

  // Warn about lower case characters in target name
  if (!pleaf->predef) {
    for (const char *pc = pleaf->tgt; *pc; ++pc) {
      if (islower(*pc)) {
        printf_errf("(): Warning: Lowercase character in target name \"%s\".", pleaf->tgt);
        break;
      }
    }
  }

  // PCRE patterns
  if (C2_L_PTSTRING == pleaf->ptntype && C2_L_MPCRE == pleaf->match) {
#ifdef CONFIG_REGEX_PCRE
    const char *error = NULL;
    int erroffset = 0;
    int options = 0;

    // Ignore case flag
    if (pleaf->match_ignorecase)
      options |= PCRE_CASELESS;

    // Compile PCRE expression
    pleaf->regex_pcre = pcre_compile(pleaf->ptnstr, options,
        &error, &erroffset, NULL);
    if (!pleaf->regex_pcre)
      c2_error("Pattern \"%s\": PCRE regular expression parsing failed on "
          "offset %d: %s", pleaf->ptnstr, erroffset, error);
#ifdef CONFIG_REGEX_PCRE_JIT
    pleaf->regex_pcre_extra = pcre_study(pleaf->regex_pcre,
        PCRE_STUDY_JIT_COMPILE, &error);
    if (!pleaf->regex_pcre_extra) {
      printf("Pattern \"%s\": PCRE regular expression study failed: %s",
          pleaf->ptnstr, error);
    }
#endif

    // Free the target string
    // free(pleaf->tgt);
    // pleaf->tgt = NULL;
#else
    c2_error("PCRE regular expression support not compiled in.");
#endif
  }

  return true;
}
/**
 * Free a condition tree.
 */
static void
c2_free(c2_ptr_t p) {
  // For a branch element
  if (p.isbranch) {
    c2_b_t * const pbranch = p.b;

    if (!pbranch)
      return;

    c2_free(pbranch->opr1);
    c2_free(pbranch->opr2);
    free(pbranch);
  }
  // For a leaf element
  else {
    c2_l_t * const pleaf = p.l;

    if (!pleaf)
      return;

    free(pleaf->tgt);
    free(pleaf->ptnstr);
#ifdef CONFIG_REGEX_PCRE
    pcre_free(pleaf->regex_pcre);
    LPCRE_FREE_STUDY(pleaf->regex_pcre_extra);
#endif
    free(pleaf);
  }
}

/**
 * Free a condition tree in c2_lptr_t.
 */
c2_lptr_t *
c2_free_lptr(c2_lptr_t *lp) {
  if (!lp)
    return NULL;

  c2_lptr_t *pnext = lp->next;
  c2_free(lp->ptr);
  free(lp);

  return pnext;
}

/**
 * Get a string representation of a rule target.
 */
static const char *
c2h_dump_str_tgt(const c2_l_t *pleaf) {
  if (pleaf->predef)
    return C2_PREDEFS[pleaf->predef].name;
  else
    return pleaf->tgt;
}

/**
 * Get a string representation of a target.
 */
static const char *
c2h_dump_str_type(const c2_l_t *pleaf) {
  switch (pleaf->type) {
    case C2_L_TWINDOW:    return "w";
    case C2_L_TDRAWABLE:  return "d";
    case C2_L_TCARDINAL:  return "c";
    case C2_L_TSTRING:    return "s";
    case C2_L_TATOM:      return "a";
    case C2_L_TUNDEFINED: break;
  }

  return NULL;
}

/**
 * Dump a condition tree.
 */
static void
c2_dump_raw(c2_ptr_t p) {
  // For a branch
  if (p.isbranch) {
    const c2_b_t * const pbranch = p.b;

    if (!pbranch)
      return;

    if (pbranch->neg)
      putchar('!');

    printf("(");
    c2_dump_raw(pbranch->opr1);

    switch (pbranch->op) {
      case C2_B_OAND: printf(" && ");   break;
      case C2_B_OOR:  printf(" || ");   break;
      case C2_B_OXOR: printf(" XOR ");  break;
      default:        assert(0);        break;
    }

    c2_dump_raw(pbranch->opr2);
    printf(")");
  }
  // For a leaf
  else {
    const c2_l_t * const pleaf = p.l;

    if (!pleaf)
      return;

    if (C2_L_OEXISTS == pleaf->op && pleaf->neg)
      putchar('!');

    // Print target name, type, and format
    {
      printf("%s", c2h_dump_str_tgt(pleaf));
      if (pleaf->tgt_onframe)
        putchar('@');
      if (pleaf->index >= 0)
        printf("[%d]", pleaf->index);
      printf(":%d%s", pleaf->format, c2h_dump_str_type(pleaf));
    }

    // Print operator
    putchar(' ');

    if (C2_L_OEXISTS != pleaf->op && pleaf->neg)
      putchar('!');

    switch (pleaf->match) {
      case C2_L_MEXACT:     break;
      case C2_L_MCONTAINS:  putchar('*');   break;
      case C2_L_MSTART:     putchar('^');   break;
      case C2_L_MPCRE:      putchar('~');   break;
      case C2_L_MWILDCARD:  putchar('%');   break;
    }

    if (pleaf->match_ignorecase)
      putchar('?');

    switch (pleaf->op) {
      case C2_L_OEXISTS:                        break;
      case C2_L_OEQ:      fputs("=",  stdout);  break;
      case C2_L_OGT:      fputs(">",  stdout);  break;
      case C2_L_OGTEQ:    fputs(">=", stdout);  break;
      case C2_L_OLT:      fputs("<",  stdout);  break;
      case C2_L_OLTEQ:    fputs("<=",  stdout); break;
    }

    if (C2_L_OEXISTS == pleaf->op)
      return;

    // Print pattern
    putchar(' ');
    switch (pleaf->ptntype) {
      case C2_L_PTINT:
        printf("%ld", pleaf->ptnint);
        break;
      case C2_L_PTSTRING:
        // TODO: Escape string before printing out?
        printf("\"%s\"", pleaf->ptnstr);
        break;
      default:
        assert(0);
        break;
    }
  }
}

/**
 * Get the type atom of a condition.
 */
static Atom
c2_get_atom_type(const c2_l_t *pleaf) {
  switch (pleaf->type) {
    case C2_L_TCARDINAL:
      return XA_CARDINAL;
    case C2_L_TWINDOW:
      return XA_WINDOW;
    case C2_L_TSTRING:
      return XA_STRING;
    case C2_L_TATOM:
      return XA_ATOM;
    case C2_L_TDRAWABLE:
      return XA_DRAWABLE;
    default:
      assert(0);
      break;
  }

  assert(0);
  return AnyPropertyType;
}

/**
 * Match a window against a single leaf window condition.
 *
 * For internal use.
 */
static inline void
c2_match_once_leaf(session_t *ps, win *w, const c2_l_t *pleaf,
    bool *pres, bool *perr) {
  assert(pleaf);

  const Window wid = (pleaf->tgt_onframe ? w->client_win: w->id);

  // Return if wid is missing
  if (!pleaf->predef && !wid)
    return;

  const int idx = (pleaf->index < 0 ? 0: pleaf->index);

  switch (pleaf->ptntype) {
    // Deal with integer patterns
    case C2_L_PTINT:
      {
        long tgt = 0;

        // Get the value
        // A predefined target
        if (pleaf->predef) {
          *perr = false;
          switch (pleaf->predef) {
            case C2_L_PID:      tgt = wid;                      break;
            case C2_L_POVREDIR: tgt = w->a.override_redirect;   break;
            case C2_L_PARGB:    tgt = (WMODE_ARGB == w->mode);  break;
            case C2_L_PFOCUSED: tgt = w->focused_real;          break;
            case C2_L_PWMWIN:   tgt = w->wmwin;                 break;
            case C2_L_PCLIENT:  tgt = w->client_win;            break;
            case C2_L_PLEADER:  tgt = w->leader;                break;
            default:            *perr = true; assert(0);        break;
          }
        }
        // A raw window property
        else {
          winprop_t prop = wid_get_prop_adv(ps, wid, pleaf->tgtatom,
              idx, 1L, c2_get_atom_type(pleaf), pleaf->format);
          if (prop.nitems) {
            *perr = false;
            tgt = winprop_get_int(prop);
          }
          free_winprop(&prop);
        }

        if (*perr)
          return;

        // Do comparison
        switch (pleaf->op) {
          case C2_L_OEXISTS:
            *pres = (pleaf->predef ? tgt: true);
            break;
          case C2_L_OEQ:   *pres = (tgt == pleaf->ptnint);  break;
          case C2_L_OGT:   *pres = (tgt > pleaf->ptnint);   break;
          case C2_L_OGTEQ: *pres = (tgt >= pleaf->ptnint);  break;
          case C2_L_OLT:   *pres = (tgt < pleaf->ptnint);   break;
          case C2_L_OLTEQ: *pres = (tgt <= pleaf->ptnint);  break;
          default:         *perr = true; assert(0);         break;
        }
      }
      break;
    // String patterns
    case C2_L_PTSTRING:
      {
        const char *tgt = NULL;
        char *tgt_free = NULL;

        // A predefined target
        if (pleaf->predef) {
          switch (pleaf->predef) {
            case C2_L_PWINDOWTYPE:  tgt = WINTYPES[w->window_type];
                                    break;
            case C2_L_PNAME:        tgt = w->name;            break;
            case C2_L_PCLASSG:      tgt = w->class_general;   break;
            case C2_L_PCLASSI:      tgt = w->class_instance;  break;
            case C2_L_PROLE:        tgt = w->role;            break;
            default:                assert(0);                break;
          }
        }
        // If it's an atom type property, convert atom to string
        else if (C2_L_TATOM == pleaf->type) {
          winprop_t prop = wid_get_prop_adv(ps, wid, pleaf->tgtatom,
              idx, 1L, c2_get_atom_type(pleaf), pleaf->format);
          Atom atom = winprop_get_int(prop);
          if (atom) {
            tgt_free = XGetAtomName(ps->dpy, atom);
          }
          if (tgt_free) {
            tgt = tgt_free;
          }
          free_winprop(&prop);
        }
        // Otherwise, just fetch the string list
        else {
          char **strlst = NULL;
          int nstr;
          if (wid_get_text_prop(ps, wid, pleaf->tgtatom, &strlst,
              &nstr) && nstr > idx) {
            tgt_free = mstrcpy(strlst[idx]);
            tgt = tgt_free;
          }
          if (strlst)
            XFreeStringList(strlst);
        }

        if (tgt) {
          *perr = false;
        }
        else {
          return;
        }

        // Actual matching
        switch (pleaf->op) {
          case C2_L_OEXISTS:
            *pres = true;
            break;
          case C2_L_OEQ:
            switch (pleaf->match) {
              case C2_L_MEXACT:
                if (pleaf->match_ignorecase)
                  *pres = !strcasecmp(tgt, pleaf->ptnstr);
                else
                  *pres = !strcmp(tgt, pleaf->ptnstr);
                break;
              case C2_L_MCONTAINS:
                if (pleaf->match_ignorecase)
                  *pres = strcasestr(tgt, pleaf->ptnstr);
                else
                  *pres = strstr(tgt, pleaf->ptnstr);
                break;
              case C2_L_MSTART:
                if (pleaf->match_ignorecase)
                  *pres = !strncasecmp(tgt, pleaf->ptnstr,
                      strlen(pleaf->ptnstr));
                else
                  *pres = !strncmp(tgt, pleaf->ptnstr,
                      strlen(pleaf->ptnstr));
                break;
              case C2_L_MWILDCARD:
                {
                  int flags = 0;
                  if (pleaf->match_ignorecase)
                    flags |= FNM_CASEFOLD;
                  *pres = !fnmatch(pleaf->ptnstr, tgt, flags);
                }
                break;
              case C2_L_MPCRE:
#ifdef CONFIG_REGEX_PCRE
                *pres = (pcre_exec(pleaf->regex_pcre,
                      pleaf->regex_pcre_extra,
                      tgt, strlen(tgt), 0, 0, NULL, 0) >= 0);
#else
                assert(0);
#endif
                break;
            }
            break;
          default:
            *perr = true;
            assert(0);
        }

        // Free the string after usage, if necessary
        if (tgt_free) {
          if (C2_L_TATOM == pleaf->type)
            cxfree(tgt_free);
          else
            free(tgt_free);
        }
      }
      break;
    default:
      assert(0);
      break;
  }
}

/**
 * Match a window against a single window condition.
 *
 * @return true if matched, false otherwise.
 */
static bool
c2_match_once(session_t *ps, win *w, const c2_ptr_t cond) {
  bool result = false;
  bool error = true;

  // Handle a branch
  if (cond.isbranch) {
    const c2_b_t *pb = cond.b;

    if (!pb)
      return false;

    error = false;

    switch (pb->op) {
      case C2_B_OAND:
        result = (c2_match_once(ps, w, pb->opr1)
            && c2_match_once(ps, w, pb->opr2));
        break;
      case C2_B_OOR:
        result = (c2_match_once(ps, w, pb->opr1)
            || c2_match_once(ps, w, pb->opr2));
        break;
      case C2_B_OXOR:
        result = (c2_match_once(ps, w, pb->opr1)
            != c2_match_once(ps, w, pb->opr2));
        break;
      default:
        error = true;
        assert(0);
    }

#ifdef DEBUG_WINMATCH
    printf_dbgf("(%#010lx): branch: result = %d, pattern = ", w->id, result);
    c2_dump(cond);
#endif
  }
  // Handle a leaf
  else {
    const c2_l_t *pleaf = cond.l;

    if (!pleaf)
      return false;

    c2_match_once_leaf(ps, w, pleaf, &result, &error);

    // For EXISTS operator, no errors are fatal
    if (C2_L_OEXISTS == pleaf->op && error) {
      result = false;
      error = false;
    }

#ifdef DEBUG_WINMATCH
    printf_dbgf("(%#010lx): leaf: result = %d, error = %d, "
        "client = %#010lx,  pattern = ",
        w->id, result, error, w->client_win);
    c2_dump(cond);
#endif
  }

  // Postprocess the result
  if (error)
    result = false;

  if (cond.isbranch ? cond.b->neg: cond.l->neg)
    result = !result;

  return result;
}

/**
 * Match a window against a condition linked list.
 *
 * @param cache a place to cache the last matched condition
 * @param pdata a place to return the data
 * @return true if matched, false otherwise.
 */
bool
c2_matchd(session_t *ps, win *w, const c2_lptr_t *condlst,
    const c2_lptr_t **cache, void **pdata) {
  // Check if the cached entry matches firstly
  if (cache && *cache && c2_match_once(ps, w, (*cache)->ptr)) {
    if (pdata)
      *pdata = (*cache)->data;
    return true;
  }

  // Then go through the whole linked list
  for (; condlst; condlst = condlst->next) {
    if (c2_match_once(ps, w, condlst->ptr)) {
      if (cache)
        *cache = condlst;
      if (pdata)
        *pdata = condlst->data;
      return true;
    }
  }

  return false;
}