add assertions about seek state and seek position

src/image.zig

@@ -45,6 +45,15 @@ fn sopen(
         return ImageError.OpenFail;
     }
 
+    const frames_on_end = c.sf_seek(file, 0, c.SEEK_END);
+    _ = c.sf_seek(file, 0, c.SEEK_SET);
+    std.testing.expectEqual(fmt.frames, frames_on_end);
+
+    const frames_on_end_by_end = c.sf_seek(file, frames_on_end, c.SEEK_SET);
+    std.testing.expectEqual(frames_on_end, frames_on_end_by_end);
+
+    std.debug.warn("frames on end: {}, frame on end (2): {}\n", frames_on_end, frames_on_end_by_end);
+
     return file.?;
 }
 
@@ -52,22 +61,20 @@ fn swrite(file: *c.SNDFILE, buf: [*]f32, frames: i64) !void {
     const count = c.sf_writef_float(file, buf, frames);
 
     if (count != frames) {
-        std.debug.warn("Wanted to read {}, got {}\n", frames, count);
+        std.debug.warn("Wanted to write {}, got {}\n", frames, count);
         return ImageError.WriteFail;
     }
 }
 
 fn sseek(file: *c.SNDFILE, offset: usize) void {
-    const frames = c.sf_seek(file, @intCast(i64, offset), c.SEEK_SET);
-    if (frames != @intCast(i64, offset)) {
-        std.debug.warn("failed to seek to {}\n", offset);
-    }
-}
+    const offset_i64 = @intCast(i64, offset);
+    const frames = c.sf_seek(file, offset_i64, c.SEEK_SET);
+    const frames_current = c.sf_seek(file, 0, c.SEEK_CUR);
+    std.testing.expectEqual(frames, frames_current);
 
-fn sf_tell(file: *c.SNDFILE) i64 {
-    var frames = c.sf_seek(file, 0, c.SEEK_CUR);
-    std.debug.warn("\t\t{} frames\n", frames);
-    return -frames;
+    if (frames != offset_i64) {
+        std.debug.warn("failed to seek to {} (seeked {} frames, offset_i64={})\n", offset, frames, offset_i64);
+    }
 }
 
 /// Caller owns the returned memory.
@@ -132,6 +139,7 @@ pub const Image = struct {
     pub fn open(allocator: *std.mem.Allocator, path: []const u8) !*Image {
         var in_fmt = mkSfInfo();
         var sndfile = try sopen(allocator, path, c.SFM_READ, &in_fmt);
+
         var image = try allocator.create(Image);
 
         std.debug.assert(in_fmt.frames > i64(0));
@@ -152,6 +160,8 @@ pub const Image = struct {
         var in_fmt = mkSfInfo();
         // clone sndfile
         var sndfile = try sopen(self.allocator, self.curpath, c.SFM_READ, &in_fmt);
+        std.testing.expectEqual(self.frames, @intCast(usize, in_fmt.frames));
+
         var image = try self.allocator.create(Image);
 
         std.debug.assert(in_fmt.frames > i64(0));
@@ -249,10 +259,17 @@ pub const Image = struct {
         var in_fmt = mkSfInfo();
 
         self.sndfile = try sopen(self.allocator, path, c.SFM_READ, &in_fmt);
+        std.testing.expectEqual(self.frames, @intCast(usize, in_fmt.frames));
+
         self.curpath = path;
         self.frames = @intCast(usize, in_fmt.frames);
 
-        std.debug.warn("\timage: reopened on '{}'\n", self.curpath);
+        std.debug.warn(
+            "\timage: reopened on '{}' (frames={}, fmt.frames={})\n",
+            self.curpath,
+            self.frames,
+            in_fmt.frames,
+        );
     }
 
     pub fn checkValid(self: *Image) !void {

src/main.zig

@@ -65,7 +65,7 @@ pub fn doRepl(allocator: *std.mem.Allocator, args_it: var) !void {
     defer runqs_args.deinit();
 
     // TODO change the runqs command to something given in an env var
-    try runqs_args.append("feh");
+    try runqs_args.append("ristretto");
 
     while (true) {
         lang.reset();

src/plugin.zig

@@ -34,6 +34,7 @@ pub const Position = struct {
     index: usize,
 
     pub fn seekPos(self: Position, total_size: usize) SeekPos {
+        std.debug.assert(self.index <= self.split);
         var tot = total_size / self.split;
 
         return SeekPos{