Config: perform basic validation

This just makes sure the parking posture is within the valid range of
motion of the rotator.

src/Config.zig

@@ -8,7 +8,7 @@ const Config = @This();
 var global_internal: Config = undefined;
 pub const global: *const Config = &global_internal;
 
-pub fn load(allocator: std.mem.Allocator, reader: anytype) !void {
+pub fn load(allocator: std.mem.Allocator, reader: anytype, err_writer: anytype) !void {
     var jread = std.json.Reader(1024, @TypeOf(reader)).init(allocator, reader);
     defer jread.deinit();
 
@@ -18,6 +18,8 @@ pub fn load(allocator: std.mem.Allocator, reader: anytype) !void {
         &jread,
         .{},
     );
+
+    try global_internal.validate(err_writer);
 }
 
 pub fn loadDefault(allocator: std.mem.Allocator) void {
@@ -30,6 +32,57 @@ pub fn destroy(allocator: std.mem.Allocator) void {
     _ = allocator;
 }
 
+pub fn validate(self: Config, err_writer: anytype) !void {
+    var valid: bool = true;
+
+    // zig fmt: off
+    if (
+        self.controller.parking_posture.azimuth < (
+            self.labjack.feedback_calibration.azimuth.minimum.angle
+            + self.controller.angle_offset.azimuth
+        ) or self.controller.parking_posture.azimuth > (
+            self.labjack.feedback_calibration.azimuth.maximum.angle
+            + self.controller.angle_offset.azimuth
+        )
+    ) {
+        // zig fmt: on
+        valid = false;
+        try err_writer.print(
+            "Config validation failed: Parking azimuth {d:.1} is outside of the valid azimuth range {d:.1} - {d:.1}\n",
+            .{
+                self.controller.parking_posture.azimuth,
+                self.labjack.feedback_calibration.azimuth.minimum.angle + self.controller.angle_offset.azimuth,
+                self.labjack.feedback_calibration.azimuth.maximum.angle + self.controller.angle_offset.azimuth,
+            },
+        );
+    }
+
+    // zig fmt: off
+    if (
+        self.controller.parking_posture.elevation < (
+            self.labjack.feedback_calibration.elevation.minimum.angle
+            + self.controller.angle_offset.elevation
+        ) or self.controller.parking_posture.elevation > (
+            self.labjack.feedback_calibration.elevation.maximum.angle
+            + self.controller.angle_offset.elevation
+        )
+    ) {
+        // zig fmt: on
+        valid = false;
+        try err_writer.print(
+            "Config validation failed: Parking elevation {d:.1} is outside of the valid elevation range {d:.1} - {d:.1}\n",
+            .{
+                self.controller.parking_posture.elevation,
+                self.labjack.feedback_calibration.elevation.minimum.angle + self.controller.angle_offset.elevation,
+                self.labjack.feedback_calibration.elevation.maximum.angle + self.controller.angle_offset.elevation,
+            },
+        );
+    }
+
+    if (!valid)
+        return error.InvalidConfig;
+}
+
 rotctl: RotControlConfig = .{
     .listen_address = "127.0.0.1",
     .listen_port = 4533,

src/main.zig

@@ -69,7 +69,7 @@ pub fn main() !u8 {
             };
             defer conf_file.close();
 
-            Config.load(allocator, conf_file.reader()) catch |err| {
+            Config.load(allocator, conf_file.reader(), std.io.getStdErr().writer()) catch |err| {
                 log.err("Could not parse config file '{s}': {s}.", .{ confpath, @errorName(err) });
                 return 1;
             };