template-parser: renderer: implemented 'else' support in templates

yeah, this is stupid. after more than 320 commits and 26 releases, we
finally support the 'else' statement in the template engine. I don't
know if I'm dumb or what, but it took me that long to find a "simple"
solution to this basic issue. yep, no more
`{% ifdef FOO %}...{% endif %}{% ifndef FOO %}...{% endif %}` blocks.
but seriously, who cares?! :/

4 files changed, 80 insertions, 4 deletions

diff --git a/src/debug.c b/src/debug.c
index 767e1a5..7039608 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -55,6 +55,9 @@ blogc_debug_template(sb_slist_t *stmts)
                 fprintf(stderr, "IF: %s %s %s", data->value,
                     get_operator(data->op), data->value2);
                 break;
+            case BLOGC_TEMPLATE_ELSE_STMT:
+                fprintf(stderr, "ELSE");
+                break;
             case BLOGC_TEMPLATE_ENDIF_STMT:
                 fprintf(stderr, "ENDIF");
                 break;
diff --git a/src/renderer.c b/src/renderer.c
index 0f71ba7..351dfb1 100644
--- a/src/renderer.c
+++ b/src/renderer.c
@@ -188,6 +188,7 @@ blogc_render(sb_slist_t *tmpl, sb_slist_t *sources, sb_trie_t *config, bool list
     bool if_not = false;
     bool inside_block = false;
     bool evaluate = false;
+    bool valid_else = false;
 
     int cmp = 0;
 
@@ -343,13 +344,23 @@ blogc_render(sb_slist_t *tmpl, sb_slist_t *sources, sb_trie_t *config, bool list
                             if_count++;
                             continue;
                         }
+                        if ((stmt->type == BLOGC_TEMPLATE_ELSE_STMT) &&
+                            (if_count == 0))
+                        {
+                            // this is somewhat complex. only an else statement
+                            // right after a non evaluated block should be considered
+                            // valid, because all the inner conditionals were just
+                            // skipped, and all the outter conditionals evaluated
+                            // to true.
+                            valid_else = true;
+                            break;
+                        }
                         if (stmt->type == BLOGC_TEMPLATE_ENDIF_STMT) {
                             if (if_count > 0) {
                                 if_count--;
                                 continue;
                             }
-                            if (if_count == 0)
-                                break;
+                            break;
                         }
                     }
                 }
@@ -358,7 +369,41 @@ blogc_render(sb_slist_t *tmpl, sb_slist_t *sources, sb_trie_t *config, bool list
                 if_not = false;
                 break;
 
+            case BLOGC_TEMPLATE_ELSE_STMT:
+                if_count = 0;
+                if (!valid_else) {
+
+                    // at this point we can just skip anything, counting the
+                    // number of 'if's, to know how many 'endif's we need to
+                    // skip as well.
+                    while (1) {
+                        tmp = tmp->next;
+                        stmt = tmp->data;
+                        if ((stmt->type == BLOGC_TEMPLATE_IF_STMT) ||
+                            (stmt->type == BLOGC_TEMPLATE_IFDEF_STMT) ||
+                            (stmt->type == BLOGC_TEMPLATE_IFNDEF_STMT))
+                        {
+                            if_count++;
+                            continue;
+                        }
+                        // no need to handle else statements here, because every
+                        // if should have an endif.
+                        if (stmt->type == BLOGC_TEMPLATE_ENDIF_STMT) {
+                            if (if_count > 0) {
+                                if_count--;
+                                continue;
+                            }
+                            break;
+                        }
+                    }
+                }
+                valid_else = false;
+                break;
+
             case BLOGC_TEMPLATE_ENDIF_STMT:
+                // any endif statement should invalidate valid_else, to avoid
+                // propagation to outter conditionals.
+                valid_else = false;
                 if (if_count > 0)
                     if_count--;
                 break;
diff --git a/src/template-parser.c b/src/template-parser.c
index 525f5f5..344e398 100644
--- a/src/template-parser.c
+++ b/src/template-parser.c
@@ -69,6 +69,7 @@ blogc_template_parse(const char *src, size_t src_len, blogc_error_t **err)
     blogc_template_stmt_operator_t tmp_op = 0;
 
     unsigned int if_count = 0;
+    bool else_open = false;
     bool foreach_open = false;
 
     sb_slist_t *stmts = NULL;
@@ -224,6 +225,7 @@ blogc_template_parse(const char *src, size_t src_len, blogc_error_t **err)
                         type = BLOGC_TEMPLATE_IFDEF_STMT;
                         start = current;
                         if_count++;
+                        else_open = false;
                         break;
                     }
                     else if ((current - start == 6) &&
@@ -233,6 +235,7 @@ blogc_template_parse(const char *src, size_t src_len, blogc_error_t **err)
                         type = BLOGC_TEMPLATE_IFNDEF_STMT;
                         start = current;
                         if_count++;
+                        else_open = false;
                         break;
                     }
                     else if ((current - start == 2) &&
@@ -242,6 +245,29 @@ blogc_template_parse(const char *src, size_t src_len, blogc_error_t **err)
                         type = BLOGC_TEMPLATE_IF_STMT;
                         start = current;
                         if_count++;
+                        else_open = false;
+                        break;
+                    }
+                    else if ((current - start == 4) &&
+                        (0 == strncmp("else", src + start, 4)))
+                    {
+                        if (if_count > 0) {
+                            if (!else_open) {
+                                state = TEMPLATE_BLOCK_END_WHITESPACE_CLEANER;
+                                type = BLOGC_TEMPLATE_ELSE_STMT;
+                                else_open = true;
+                                break;
+                            }
+                            *err = blogc_error_parser(BLOGC_ERROR_TEMPLATE_PARSER,
+                                src, src_len, current,
+                                "More than one 'else' statement for an open 'if', "
+                                "'ifdef' or 'ifndef' statement.");
+                            break;
+                        }
+                        *err = blogc_error_parser(BLOGC_ERROR_TEMPLATE_PARSER,
+                            src, src_len, current,
+                            "'else' statement without an open 'if', 'ifdef' or "
+                            "'ifndef' statement.");
                         break;
                     }
                     else if ((current - start == 5) &&
@@ -251,12 +277,13 @@ blogc_template_parse(const char *src, size_t src_len, blogc_error_t **err)
                             state = TEMPLATE_BLOCK_END_WHITESPACE_CLEANER;
                             type = BLOGC_TEMPLATE_ENDIF_STMT;
                             if_count--;
+                            else_open = false;
                             break;
                         }
                         *err = blogc_error_parser(BLOGC_ERROR_TEMPLATE_PARSER,
                             src, src_len, current,
-                            "'endif' statement without an open 'ifdef' or 'ifndef' "
-                            "statement.");
+                            "'endif' statement without an open 'if', 'ifdef' or "
+                            "'ifndef' statement.");
                         break;
                     }
                     else if ((current - start == 7) &&
diff --git a/src/template-parser.h b/src/template-parser.h
index 46223ec..fe2721e 100644
--- a/src/template-parser.h
+++ b/src/template-parser.h
@@ -21,6 +21,7 @@ typedef enum {
     BLOGC_TEMPLATE_IFDEF_STMT = 1,
     BLOGC_TEMPLATE_IFNDEF_STMT,
     BLOGC_TEMPLATE_IF_STMT,
+    BLOGC_TEMPLATE_ELSE_STMT,
     BLOGC_TEMPLATE_ENDIF_STMT,
     BLOGC_TEMPLATE_FOREACH_STMT,
     BLOGC_TEMPLATE_ENDFOREACH_STMT,