From 6f644cb24e580c9dce94ed032f2fcf7c0c6a4438 Mon Sep 17 00:00:00 2001
From: Kyle Bowman <kylebowman14@gmail.com>
Date: Sun, 6 Oct 2024 14:46:41 -0400
Subject: [PATCH] fix: add rule to build whole directories

---
 Makefile | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 04a35bc..1c3d035 100644
--- a/Makefile
+++ b/Makefile
@@ -1,17 +1,39 @@
 SRC_DIR := src
 BUILD_DIR := build
 
-MARKDOWN_FILES := $(wildcard $(SRC_DIR)/**/*.md)
-HTML_FILES := $(patsubst $(SRC_DIR)/%.md, $(BUILD_DIR)/%, $(MARKDOWN_FILES))
+IGNORE_VCS=*.git*
 
 .PHONY: all clean index
 
-all: $(HTML_FILES)
-
-index: 
+# Pro/con - this builds *everything* due to recursion
+# Pro - simple
+# Con - I can't do make build/demo; make index to get a partial build.
+# Idea -
+#   I think I could use mindepth/maxdepth in the subdirs find.
+#   Then, make index wouldn't recurse. 
+index: $(BUILD_DIR)
 	scripts/index.sh > build/index.html
 
-# Build HTML file from Markdown
+# This pattern defines a multi-target rule; it defines a target 
+# build/DIR for each DIR in src/DIR.
+subdirs := $(shell find -L $(SRC_DIR) -type d -not -path $(IGNORE_VCS)) 
+builddirs := $(patsubst $(SRC_DIR)%, $(BUILD_DIR)%, $(subdirs))
+
+# USAGE: `make $(BUILD_DIR)/arbitary-dir`
+# BEHAVIOR: For each file in the build dir, invoke the markdown rule.
+# UNDERSTANDING THE APPROACH:
+#   1. From build target $@,
+#   2. Get a list of corresponding md files in SRC_DIR $(shell find ...), and
+#   3. Rewrite the result as a build target $(patsubstr $(SRC_DIR)%.md, ...)
+# WHY $$ and .SECONDEXPANSION?
+#   To let users specify arbitrary directories, I wanted to use the target $@ 
+#   in the prerequisites. To get scoping to work for $@ in the prerequisites, 
+#   you must go through a second phase of expansion. The $$ defers expansion 
+#   until the second phase. Single $ can be expanded on the first phase.
+.SECONDEXPANSION:
+$(builddirs): $$(patsubst $(SRC_DIR)%.md, $(BUILD_DIR)%, $$(shell find -L $$(patsubst $(BUILD_DIR)%, $(SRC_DIR)%, $$@) -name '*.md'))
+
+# For a given md file in src, make the corresponding html in build.
 $(BUILD_DIR)/%: $(SRC_DIR)/%.md 
 	@mkdir -p $(dir $@)
 	@pandoc \
@@ -19,7 +41,7 @@ $(BUILD_DIR)/%: $(SRC_DIR)/%.md
 		--standalone \
 		--defaults=./defaults.yml \
 		--output=$@ $<
-	@echo "Building $@ from $<"
+	@echo "Building $@ from $<..."
 
 # Clean up generated HTML files
 clean:
-- 
2.39.5