//! User-space display client: talk to the display service (query the mode, and — from D3
//! — create layers, draw, and present) without hand-rolling the IPC. The `runtime.block`
//! shape: a cached `.display` lookup with a boot-race retry, then extern-struct request/
//! reply marshalling. See system/services/display/ and docs/display.md.

const std = @import("std");
const ipc = @import("ipc.zig");
const system = @import("system.zig");
const protocol = @import("display-protocol");

/// The display's current mode, as `info()` reports it.
pub const Info = struct {
    width: u32,
    height: u32,
    pitch: u32, // bytes per row (may exceed width*4; see docs/framebuffer.md)
    format: u32, // a device-abi DisplayFormat value (0 = rgbx, 1 = bgrx)
};

/// The service endpoint, looked up once and cached.
var handle: ?ipc.Handle = null;

/// Look up the display service, retrying while it comes up (a client races its
/// registration at boot). Returns the endpoint, or null if it never appears.
fn service() ?ipc.Handle {
    if (handle) |h| return h;
    var attempts: usize = 0;
    while (attempts < 100) : (attempts += 1) {
        if (ipc.lookup(.display)) |h| {
            handle = h;
            return h;
        }
        system.sleep(50);
    }
    return null;
}

/// Send one request, receive its reply; true on a zero status. `out` receives the reply
/// so callers can read `info`/`layer` fields on success.
fn transact(request: protocol.Request, out: *protocol.Reply) bool {
    const h = service() orelse return false;
    var req = request;
    var reply: [protocol.reply_size]u8 = undefined;
    const len = ipc.call(h, std.mem.asBytes(&req), &reply) catch return false;
    if (len < protocol.reply_size) return false;
    out.* = std.mem.bytesToValue(protocol.Reply, reply[0..protocol.reply_size]);
    return out.status == 0;
}

/// The display's current mode, or null if the service never came up.
pub fn info() ?Info {
    var reply: protocol.Reply = undefined;
    if (!transact(.{ .operation = @intFromEnum(protocol.Operation.info) }, &reply)) return null;
    return .{ .width = reply.width, .height = reply.height, .pitch = reply.pitch, .format = reply.format };
}

/// Composite the dirty layers and flush the frame to the screen.
pub fn present() bool {
    var reply: protocol.Reply = undefined;
    return transact(.{ .operation = @intFromEnum(protocol.Operation.present) }, &reply);
}