From 35586a37128df60a71044132e409ccaede29c5b9 Mon Sep 17 00:00:00 2001
From: Adrian Cochrane <adrian@openwork.nz>
Date: Wed, 31 Jan 2024 17:58:35 +1300
Subject: [PATCH] Encode & decode charsets on C side (fix Haskell side)

---
 cbits/transcode.c                        | 42 ++++++++++++++++++++++++
 fontconfig-pure.cabal                    |  2 +-
 lib/Graphics/Text/Font/Choose/CharSet.hs |  2 +-
 3 files changed, 44 insertions(+), 2 deletions(-)
 create mode 100644 cbits/transcode.c

diff --git a/cbits/transcode.c b/cbits/transcode.c
new file mode 100644
index 0000000..52469fb
--- /dev/null
+++ b/cbits/transcode.c
@@ -0,0 +1,42 @@
+#include "cmp.h"
+#include <fontconfig/fontconfig.h>
+#include <assert.h>
+
+FcCharSet *decodeCharSet(cmp_ctx_t *bytes) {
+    uint32_t size;
+    if (!cmp_read_array(bytes, &size)) return NULL;
+
+    FcCharSet *ret = FcCharSetCreate();
+    if (ret == NULL) return NULL;
+
+    FcChar32 prev = 0;
+    for (uint32_t i = 0; i < size; i++) {
+        uint32_t x;
+        if (!cmp_read_uint(bytes, &x)) goto fail;
+        prev += x;
+        if (!FcCharSetAddChar(ret, prev)) goto fail;
+    }
+    return ret;
+fail:
+    FcCharSetDestroy(ret);
+    return NULL;
+}
+
+bool encodeCharSet(cmp_ctx_t *bytes, FcCharSet *data) {
+    FcChar32 size = FcCharSetCount(data);
+    FcChar32 count = 0; // For validation
+    if (!cmp_write_array(bytes, size)) return false;
+
+    FcChar32 map[FC_CHARSET_MAP_SIZE];
+    FcChar32 next;
+    FcChar32 c = FcCharSetFirstPage(data, map, &next);
+    FcChar32 prev = 0;
+    while (c != FC_CHARSET_DONE) {
+        if (!cmp_write_uinteger(bytes, c - prev)) return false;
+        prev = c;
+        count++;
+        c = FcCharSetNextPage(data, map, &next);
+    }
+    assert(size == count);
+    return true;
+}
diff --git a/fontconfig-pure.cabal b/fontconfig-pure.cabal
index a44fefe..2b6ec4f 100644
--- a/fontconfig-pure.cabal
+++ b/fontconfig-pure.cabal
@@ -68,7 +68,7 @@ library
             Graphics.Text.Font.Choose.StrSet, Graphics.Text.Font.Choose.Value,
             Graphics.Text.Font.Choose.Pattern, Graphics.Text.Font.Choose.FontSet
 
-    c-sources: cbits/cmp.c
+    c-sources: cbits/cmp.c, cbits/transcode.c
 
     -- Modules included in this library but not exported.
     -- other-modules:
diff --git a/lib/Graphics/Text/Font/Choose/CharSet.hs b/lib/Graphics/Text/Font/Choose/CharSet.hs
index c6f94dd..78c6ffd 100644
--- a/lib/Graphics/Text/Font/Choose/CharSet.hs
+++ b/lib/Graphics/Text/Font/Choose/CharSet.hs
@@ -47,7 +47,7 @@ diffCompress :: Int -> [Int] -> [Int]
 diffCompress prev (x:xs) = x - prev:diffCompress x xs
 diffCompress _ [] = []
 diffDecompress :: Int -> [Int] -> [Int]
-diffDecompress prev (x:xs) = prev + x:diffDecompress x xs
+diffDecompress prev (x:xs) = let y = prev + x in y:diffDecompress y xs
 diffDecompress _ [] = []
 
 newtype CharSet' = CharSet' { unCharSet :: CharSet }
-- 
2.30.2