From ed613db39eefa111141b49581fc22fbed5803d2c Mon Sep 17 00:00:00 2001
From: William Miles <wmpmiles@gmail.com>
Date: Mon, 5 Sep 2022 21:01:26 +1000
Subject: [PATCH] Half implemented decompression. Need to figure out how to
 handle group size adjustment on decompressed data.

---
 NavmeshList/main.c    | 13 ++++++++--
 espReader/ESPReader.h |  6 +++++
 espReader/Reader.c    | 59 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/NavmeshList/main.c b/NavmeshList/main.c
index c9602b6..ede5f43 100644
--- a/NavmeshList/main.c
+++ b/NavmeshList/main.c
@@ -23,8 +23,17 @@ int main(void) {
 	size_t read = fread(buffer, sizeof(char), size, fp);
 	assert(read == size);
 
-	size_t formids = espr_formid_count(buffer, size);
-	printf("FormID Count: %zu\n", formids);
+	size_t dc_size = espr_decompressed_size(buffer, size);
+	
+	char *decompressed = malloc(dc_size);
+	if (!decompressed)
+		return errno;
+
+	espr_decompress(buffer, size, decompressed, dc_size);
+
+	size_t formid_count = espr_formid_count(decompressed, dc_size);
+
+	printf("FormID Count: %zu\n", formid_count);
 
 	return 0;
 }
diff --git a/espReader/ESPReader.h b/espReader/ESPReader.h
index 17a1240..3f41784 100644
--- a/espReader/ESPReader.h
+++ b/espReader/ESPReader.h
@@ -277,6 +277,12 @@ extern "C" {
 	 */
 	size_t espr_formid_count(char *data, size_t size);
 
+	/* Copies the data from `data` to `buf` decompressing compressed fields as
+	 * it does so. buf_size should be the value returned from `espr_decompressed_size`,
+	 * and `buf` should be at least of that size.
+	 */
+	void espr_decompress(char *data, size_t size, char *buf, size_t buf_size);
+
 // End C++ guard
 #ifdef __cplusplus
 }
diff --git a/espReader/Reader.c b/espReader/Reader.c
index 36b00bb..bbc99dc 100644
--- a/espReader/Reader.c
+++ b/espReader/Reader.c
@@ -1,6 +1,7 @@
 #include <assert.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <string.h>
 #include <intrin.h>
 
 #include "zlib.h"
@@ -45,6 +46,7 @@ Timestamp convert_ts(uint16_t ts);
 void print_callback(Node n, void *_);
 void dc_size_cb(Node n, void *dc_size_ptr);
 void formid_count_cb(Node n, void *count_ptr);
+void decompress_cb(Node n, void *decom_ptr);
 
 //
 // === FUNCTIONS ===
@@ -135,6 +137,63 @@ void formid_count_cb(Node n, void *count_ptr) {
 	}
 }
 
+struct decom {
+	char *buf;
+	char *start;
+	size_t remaining;
+};
+
+void espr_decompress(char *data, size_t size, char *buf, size_t buf_size) {
+	struct decom s = { .buf = buf, .start = data, .remaining = buf_size };
+	espr_walk(data, size, decompress_cb, &s);
+
+	// handle final segment
+	size_t remaining = buf_size - (s.buf - buf);
+	assert(remaining == s.remaining);
+	memcpy(s.buf, s.start, remaining);
+}
+
+void decompress_cb(Node n, void *decom_ptr) {
+	struct decom *d = decom_ptr;
+
+	// only need to do anything when we find a compressed flag
+	if (n.type == NT_RECORD && n.header.record->flags & COMPRESSED_FLAG) {
+		// uncompressed segment copy
+		size_t size = n.data - d->start;
+		assert(size < d->remaining);
+		memcpy(d->buf, d->start, size);
+
+		// update decom struct
+		d->remaining -= size;
+		d->buf += size;
+
+		// copied header
+		Record *header = (Record *)(d->buf) - 1;
+
+		// decompress directly into buffer
+		const size_t dc_size = *((uint32_t *)n.data);
+		size_t to_copy = dc_size;
+		size_t cur_size = n.header.record->size - sizeof(uint32_t);
+		char *data_start = n.data + sizeof(uint32_t);
+		int ret = uncompress(d->buf, &to_copy, data_start, cur_size);
+		assert(ret == Z_OK);
+		assert(to_copy == dc_size);
+		
+		// update decom struct
+		d->remaining -= dc_size;
+		d->buf += dc_size;
+
+		// update start to start of next record/group
+		d->start = n.data + n.header.record->size;
+
+		// update header data size
+		header->size = dc_size;
+
+		// unset compressed flag
+		header->flags &= ~COMPRESSED_FLAG;
+	}
+}
+
 /* Unknown data will be some concatenation of groups and records.
  *
  * `walk_concat` will call the appropriate walking function