frontend: add a line editor for shell input

frontend/line-ed/history.c

@@ -0,0 +1,67 @@
+#include "line-ed.h"
+
+#include <blue/object/array.h>
+#include <blue/object/string.h>
+
+void alloc_empty_history_entry(struct line_ed *ed)
+{
+	b_string *str = (b_string *)b_array_at(
+		ed->l_history, b_array_size(ed->l_history) - 1);
+	if (!str || !b_string_get_size(str, B_STRLEN_NORMAL)) {
+		str = b_string_create();
+		b_array_append(ed->l_history, (b_object *)str);
+	}
+
+	ed->l_history_pos = b_array_size(ed->l_history) - 1;
+}
+
+void save_buf_to_history(struct line_ed *ed)
+{
+	b_string *cur = (b_string *)b_array_get(ed->l_history, ed->l_history_pos);
+	b_string_replace_all(cur, ed->l_buf);
+}
+
+void append_buf_to_history(struct line_ed *ed)
+{
+	b_string *cur = (b_string *)b_array_get(ed->l_history, ed->l_history_pos);
+	char s[] = {'\n', 0};
+	b_string_append_cstr(cur, s);
+	b_string_append_cstr(cur, ed->l_buf);
+}
+
+void load_buf_from_history(struct line_ed *ed)
+{
+	b_string *cur = (b_string *)b_array_at(ed->l_history, ed->l_history_pos);
+	size_t len
+		= MIN(ed->l_buf_end - ed->l_buf - 1,
+	              b_string_get_size(cur, B_STRLEN_NORMAL));
+
+	memcpy(ed->l_buf, b_string_ptr(cur), len);
+	ed->l_buf[len] = '\0';
+
+	unsigned int x = 0, y = 0;
+	for (size_t i = 0; ed->l_buf[i]; i++) {
+		if (ed->l_buf[i] == '\n') {
+			x = 0;
+			y++;
+		} else {
+			x++;
+		}
+	}
+
+	ed->l_buf_ptr = ed->l_buf + len;
+	ed->l_line_end = ed->l_buf_ptr;
+	ed->l_cursor_x = x;
+	ed->l_cursor_y = y;
+}
+
+const char *last_history_line(struct line_ed *ed)
+{
+	unsigned long nlines = b_array_size(ed->l_history);
+	if (nlines < 2) {
+		return NULL;
+	}
+
+	b_string *last = (b_string *)b_array_at(ed->l_history, nlines - 2);
+	return b_string_ptr(last);
+}