main: treat elevation offset as offset from horizon

Rather than having somewhat confusing flipped logic when the rotator is
operating in the 180-90 degree elevation regime, this internally
performs sign flipping. This means that a 3 degree elevation offset
means "point an additional 3 degrees up from the horizon" regardless
of whether the rotator is operating in the 0-90 or 180-90 elevation
ranges.

src/Config.zig

@@ -0,0 +1,47 @@
+const std = @import("std");
+
+const Config = @This();
+
+elevation_mask: f64 = 19,
+rotctld: AddressPort = .{ .address = "127.0.0.1", .port = 4533 },
+listen: AddressPort = .{ .address = "127.0.0.1", .port = 42069 },
+
+const confdir = "rotint";
+const conffile = "config.json";
+
+pub fn default() Config {
+    return .{};
+}
+
+pub fn load(allocator: std.mem.Allocator, env: *const std.process.EnvMap) !Config {
+    if (env.get("XDG_CONFIG_HOME")) |cfg|
+        if (cfg.len > 0) {
+            return try loadPath(allocator, try std.fs.path.join(
+                allocator,
+                &.{ cfg, confdir, conffile },
+            ));
+        };
+
+    if (env.get("HOME")) |home|
+        if (home.len > 0) {
+            return try loadPath(allocator, try std.fs.path.join(
+                allocator,
+                &.{ home, ".config", confdir, conffile },
+            ));
+        };
+
+    return error.ConfigHomeMissing;
+}
+
+fn loadPath(allocator: std.mem.Allocator, path: []const u8) !Config {
+    defer allocator.free(path);
+    const data = try std.fs.cwd().readFileAlloc(allocator, path, 1024);
+    defer allocator.free(data);
+
+    return try std.json.parseFromSliceLeaky(Config, allocator, data, .{});
+}
+
+const AddressPort = struct {
+    address: []const u8,
+    port: u16,
+};

src/main.zig

@@ -6,6 +6,7 @@ const xev = @import("xev");
 
 const networking = @import("./networking.zig");
 const rotctl = @import("./rotctl.zig");
+const Config = @import("./Config.zig");
 
 const log = std.log.scoped(.rotint);
 
@@ -84,6 +85,7 @@ pub const RotInt = struct {
     command_freq: u8 = 4,
     pollcount: u9 = 0,
     state: State = .initial,
+    conf: Config,
 
     termbuffer: std.io.BufferedWriter(4096, std.io.AnyWriter),
     vx: *vaxis.Vaxis,
@@ -110,8 +112,18 @@ pub const RotInt = struct {
         self.rotator.rotint = self;
         self.log = try Log.init();
 
-        const connect_addr = try std.net.Address.parseIp("127.0.0.1", 4533);
-        try self.rotator.connect(self.loop, connect_addr);
+        const rotctld_addr = std.net.Address.parseIp(
+            self.conf.rotctld.address,
+            self.conf.rotctld.port,
+        ) catch |err| {
+            log.err("could not parse rotctld address {s}:{d}: {s}", .{
+                self.conf.rotctld.address,
+                self.conf.rotctld.port,
+                @errorName(err),
+            });
+            return err;
+        };
+        try self.rotator.connect(self.loop, rotctld_addr);
     }
 
     pub fn stateEvent(self: *RotInt, event: State) void {
@@ -126,12 +138,15 @@ pub const RotInt = struct {
             },
             .rotator_ready => if (self.state == .rotator_connected) {
                 self.warn("rotator ready", .{});
-                const listen_addr = std.net.Address.parseIp("127.0.0.1", 42069) catch {
-                    self.warn("bogus listen address", .{});
+                const listen_addr = std.net.Address.parseIp(
+                    self.conf.listen.address,
+                    self.conf.listen.port,
+                ) catch |err| {
+                    self.showError("bogus listen address: {s}", .{@errorName(err)});
                     return;
                 };
-                self.server.listen(self.loop, listen_addr) catch {
-                    self.warn("listen problem", .{});
+                self.server.listen(self.loop, listen_addr) catch |err| {
+                    self.showError("listen problem: {s}", .{@errorName(err)});
                     return;
                 };
                 // demangle here to avoid causing initial moves
@@ -165,10 +180,15 @@ pub const RotInt = struct {
         self.pollcount = (self.pollcount + 1) % self.command_freq;
 
         if (self.pollcount == 0) {
-            const mangled: AzEl = .{
+            var mangled: AzEl = .{
                 .az = self.requested_posture.az + self.offsets.az,
-                .el = self.requested_posture.el + self.offsets.el,
+                .el = self.requested_posture.el + if (self.requested_posture.el > 90) -self.offsets.el else self.offsets.el,
             };
+            mangled.el = if (mangled.el > 90)
+                @min(mangled.el, 180 - self.conf.elevation_mask)
+            else
+                @max(mangled.el, self.conf.elevation_mask);
+
             self.sendRotatorCommand(.{ .set_position = mangled });
         } else {
             self.sendRotatorCommand(.get_position);
@@ -209,6 +229,10 @@ pub const RotInt = struct {
         log.warn(fmt, args);
     }
 
+    pub fn showError(_: *RotInt, comptime fmt: []const u8, args: anytype) void {
+        log.err(fmt, args);
+    }
+
     pub fn handleControlRequest(self: *RotInt, req: []const u8) void {
         const command = self.parser.parseCommand(req) catch |err| switch (err) {
             error.Incomplete => return,
@@ -387,8 +411,15 @@ pub fn main() !void {
     });
     defer loop.deinit();
 
+    var env = try std.process.getEnvMap(alloc);
+    defer env.deinit();
+
     var app: RotInt = .{
         .allocator = alloc,
+        .conf = Config.load(alloc, &env) catch cfg: {
+            log.warn("Could not load config file. Using defaults.", .{});
+            break :cfg Config.default();
+        },
         .termbuffer = tty.bufferedWriter(),
         .vx = &vx,
         .loop = &loop,