Renamed matchviz -> explain

1 files changed, 171 insertions, 0 deletions

diff --git a/explain.c b/explain.c
new file mode 100644
index 0000000..2d54234
--- /dev/null
+++ b/explain.c
@@ -0,0 +1,171 @@
+//
+// explain.c - Debug visualization of pattern matches.
+//
+
+#include <stdio.h>
+#include <string.h>
+
+#include "types.h"
+#include "utils.h"
+
+typedef struct match_node_s {
+    match_t *m;
+    struct match_node_s *next;
+} match_node_t;
+
+__attribute__((nonnull, pure))
+static int height_of_match(match_t *m);
+__attribute__((nonnull))
+static void _explain_matches(match_node_t *firstmatch, int depth, const char *text, size_t textlen);
+
+//
+// Return the height of a match object (i.e. the number of descendents of the
+// structure).
+//
+static int height_of_match(match_t *m)
+{
+    int height = 0;
+    for (int i = 0; m->children && m->children[i]; i++) {
+        match_t *child = m->children[i];
+        int childheight = height_of_match(child);
+        if (childheight > height) height = childheight;
+    }
+    return 1 + height;
+}
+
+//
+// Print a visual explanation for the as-yet-unprinted matches provided.
+//
+static void _explain_matches(match_node_t *firstmatch, int depth, const char *text, size_t textlen)
+{
+    const char *V = "│"; // Vertical bar
+    const char *H = "─"; // Horizontal bar
+    const char *color = (depth % 2 == 0) ? "34" : "33";
+
+    match_t *viz = firstmatch->m;
+    // This is a heuristic: print matches first if they have more submatches.
+    // In general, this helps reduce the height of the final output by allowing
+    // for more rows that show the same rule matching in multiple places.
+    // TODO: there may be a better heuristic that optimizes for this factor
+    // while also printing earlier matches first when it doesn't affect overall
+    // output height.
+    for (match_node_t *p = firstmatch; p; p = p->next)
+        if (height_of_match(p->m) > height_of_match(viz))
+            viz = p->m;
+    const char *viz_type = viz->pat->start;
+    size_t viz_typelen = (size_t)(viz->pat->end - viz->pat->start);
+
+    // Backrefs use added dim quote marks to indicate that the pattern is a
+    // literal string being matched. (Backrefs have start/end inside the text
+    // input, instead of something the user typed in)
+    if (viz_type >= text && viz_type <= &text[textlen])
+        printf("\033[%luG\033[0;2m\"\033[%s;1m", 2*textlen+3, color);
+    else
+        printf("\033[%luG\033[%s;1m", 2*textlen+3, color);
+
+    for (size_t i = 0; i < viz_typelen; i++) {
+        switch (viz_type[i]) {
+            case '\n': printf("↵"); break;
+            case '\t': printf("⇥"); break;
+            default: printf("%c", viz_type[i]); break;
+        }
+    }
+
+    if (viz_type >= text && viz_type <= &text[textlen])
+        printf("\033[0;2m\"");
+
+    printf("\033[0m");
+
+    match_node_t *children = NULL;
+    match_node_t **nextchild = &children;
+
+#define RIGHT_TYPE(m) (m->m->pat->end == m->m->pat->start + viz_typelen && strncmp(m->m->pat->start, viz_type, viz_typelen) == 0)
+    // Print nonzero-width first:
+    for (match_node_t *m = firstmatch; m; m = m->next) {
+        if (RIGHT_TYPE(m)) {
+            for (int i = 0; m->m->children && m->m->children[i]; i++) {
+                *nextchild = new(match_node_t);
+                (*nextchild)->m = m->m->children[i];
+                nextchild = &((*nextchild)->next);
+            }
+            if (m->m->end == m->m->start) continue;
+            printf("\033[%ldG\033[0;2m%s\033[0;7;%sm", 1+2*(m->m->start - text), V, color);
+            for (const char *c = m->m->start; c < m->m->end; ++c) {
+                // TODO: newline
+                if (c > m->m->start) printf(" ");
+                // TODO: utf8
+                //while ((*c & 0xC0) != 0x80) printf("%c", *(c++));
+                if (*c == '\n')
+                    printf("↵");
+                else if (*c == '\t')
+                    printf("⇥");
+                else
+                    printf("%c", *c);
+            }
+            printf("\033[0;2m%s\033[0m", V);
+        } else {
+            *nextchild = new(match_node_t);
+            (*nextchild)->m = m->m;
+            nextchild = &((*nextchild)->next);
+            printf("\033[%ldG\033[0;2m%s", 1+2*(m->m->start - text), V);
+            for (ssize_t i = (ssize_t)(2*(m->m->end - m->m->start)-1); i > 0; i--)
+                printf(" ");
+            if (m->m->end > m->m->start)
+                printf("\033[0;2m%s", V);
+            printf("\033[0m");
+        }
+    }
+
+    // Print stars for zero-width:
+    for (match_node_t *m = firstmatch; m; m = m->next) {
+        if (m->m->end > m->m->start) continue;
+        if (RIGHT_TYPE(m)) {
+            printf("\033[%ldG\033[7;%sm▒\033[0m", 1+2*(m->m->start - text), color);
+        } else {
+            printf("\033[%ldG\033[0;2m%s\033[0m", 1+2*(m->m->start - text), V);
+        }
+    }
+
+    printf("\n");
+
+    for (match_node_t *m = firstmatch; m; m = m->next) {
+        if (m->m->end == m->m->start) {
+            if (!RIGHT_TYPE(m))
+                printf("\033[%ldG\033[0;2m%s", 1 + 2*(m->m->start - text), V);
+        } else {
+            const char *l = "└";
+            const char *r = "┘";
+            for (match_node_t *c = children; c; c = c->next) {
+                if (c->m->start == m->m->start || c->m->end == m->m->start) l = V;
+                if (c->m->start == m->m->end   || c->m->end == m->m->end) r = V;
+            }
+            printf("\033[%ldG\033[0;2m%s", 1 + 2*(m->m->start - text), l);
+            const char *h = RIGHT_TYPE(m) ? H : " ";
+            for (ssize_t n = (ssize_t)(2*(m->m->end - m->m->start) - 1); n > 0; n--)
+                printf("%s", h);
+            printf("%s\033[0m", r);
+        }
+    }
+#undef RIGHT_TYPE
+
+    printf("\n");
+
+    if (children)
+        _explain_matches(children, depth+1, text, textlen);
+
+    for (match_node_t *c = children, *next = NULL; c; c = next) {
+        next = c->next;
+        delete(&c);
+    }
+}
+
+//
+// Print a visualization of a match object.
+//
+void explain_match(match_t *m)
+{
+    printf("\033[?7l"); // Disable line wrapping
+    match_node_t first = {.m = m};
+    _explain_matches(&first, 0, m->start, (size_t)(m->end - m->start));
+    printf("\033[?7h"); // Re-enable line wrapping
+}