//! USB class-driver client: the helper a keyboard, mouse, or mass-storage driver
//! uses to reach its device through the xHCI bus driver, so it never hand-rolls
//! the transfer-protocol IPC. Layered over `ipc` and the shared
//! `usb-transfer-protocol` wire format, the way `input.zig` layers over the input
//! service and `device.zig` over the raw device calls.
//!
//! A class driver, spawned with its interface's assigned device id as argv[1]:
//!     if (device_manager.hello(.device, id) == null) return; // meet the spawn deadline
//!     var device = usb.open(id) orelse return;        // open + get its endpoints
//!     _ = device.controlOut(usb_abi.setProtocol(...));// class requests, descriptors
//!     _ = device.subscribeInterrupt(address, length); // reports arrive asynchronously
//!     while (true) { ... ipc.replyWait(device.endpoint, ...) ... }  // its own loop
//!
//! Reports are delivered to `device.endpoint` as asynchronous `interrupt_report`
//! event packets, decoded with `reportOf` (the class driver runs a bare `replyWait`
//! loop to read them, because the service harness drops buffered-message payloads
//! — see service.zig).
//!
//! Every packet this file lays down is an envelope packet: the verb and the
//! device token in the folded `Header`, the transfer's own fields after it, and
//! a control transfer's data stage in the tail.

const std = @import("std");
const channel = @import("channel");
const envelope = @import("envelope");
const ipc = @import("ipc");
const time = @import("time");
const usb_transfer_protocol = @import("usb-transfer-protocol");

const Protocol = usb_transfer_protocol.Protocol;

/// The USB chapter-9 wire ABI and the class taxonomy, re-exported so a class driver reaches
/// the whole USB domain through its one `usb` import (`usb.abi.getDescriptor`, `usb.ids.Class`).
pub const abi = @import("usb-abi");
pub const ids = @import("usb-ids");

pub const Endpoint = usb_transfer_protocol.Endpoint;
pub const InterruptReport = usb_transfer_protocol.InterruptReport;
pub const max_report_data = usb_transfer_protocol.max_report_data;

// Endpoint transfer types (EndpointDescriptor attributes), for `findEndpoint`.
pub const transfer_type_bulk: u8 = 2;
pub const transfer_type_interrupt: u8 = 3;

/// An opened USB device: the bus endpoint to send requests to, this driver's own
/// endpoint that reports arrive on, the device token, and the interface's
/// endpoints (so a driver need not re-read the configuration descriptor).
pub const Device = struct {
    bus: ipc.Handle,
    endpoint: ipc.Handle,
    token: u64,
    class: u8,
    subclass: u8,
    protocol_code: u8,
    interface_number: u8,
    endpoint_count: usize = 0,
    endpoints: [usb_transfer_protocol.max_reported_endpoints]Endpoint = undefined,

    /// The interface's first endpoint of the given transfer type and direction
    /// (`transfer_type_bulk` / `transfer_type_interrupt`), or null.
    pub fn findEndpoint(self: *const Device, transfer_type: u8, direction_in: bool) ?Endpoint {
        for (self.endpoints[0..self.endpoint_count]) |endpoint| {
            if (endpoint.transfer_type == transfer_type and (endpoint.address & 0x80 != 0) == direction_in) return endpoint;
        }
        return null;
    }

    /// One request at the bus driver, addressing this device by its token — the
    /// packet's `Header.target`, so no request body ever names the device again.
    /// Null covers both a failed transport and a refusal: a class driver has the
    /// same recourse either way.
    fn call(
        self: *Device,
        comptime operation: Protocol.Operation,
        request: Protocol.RequestOf(operation),
        tail: []const u8,
        capability: ?ipc.Handle,
        reply: []u8,
    ) ?[]u8 {
        var packet: [usb_transfer_protocol.message_maximum]u8 = undefined;
        const framed = Protocol.encodeRequest(operation, self.token, request, tail, &packet) orelse return null;
        const answer = ipc.callCap(self.bus, framed, reply, capability) catch return null;
        const status = envelope.statusOf(reply[0..answer.len]) orelse return null;
        if (status.status != 0) return null;
        return reply[0..answer.len];
    }

    /// The data stage rides the tail in both directions, so the answer's length
    /// *is* the transferred length — `Status.len`, which the envelope stamps.
    fn controlTransfer(self: *Device, setup: [8]u8, direction_in: bool, data: []u8) ?usize {
        if (data.len > usb_transfer_protocol.max_inline_data) return null;
        const outgoing: []const u8 = if (direction_in) &.{} else data;
        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
        const answered = self.call(.control, .{
            .setup = setup,
            .direction_in = @intFromBool(direction_in),
            .data_length = @intCast(data.len),
        }, outgoing, null, &reply) orelse return null;

        const returned = Protocol.replyTail(.control, answered);
        const actual = @min(returned.len, data.len);
        if (direction_in and actual > 0) @memcpy(data[0..actual], returned[0..actual]);
        return actual;
    }

    /// A control transfer with no data stage (SET_PROTOCOL, SET_IDLE, ...). The
    /// `setup` is a bit-cast `usb_abi.Request`.
    pub fn controlOut(self: *Device, setup: [8]u8) bool {
        return self.controlTransfer(setup, false, &.{}) != null;
    }

    /// A device-to-host control transfer, returning the bytes read into `out`.
    pub fn controlIn(self: *Device, setup: [8]u8, out: []u8) ?usize {
        return self.controlTransfer(setup, true, out);
    }

    /// Begin periodic IN polling of an interrupt endpoint; reports flow back to
    /// `self.endpoint` as asynchronous `InterruptReport` messages.
    pub fn subscribeInterrupt(self: *Device, endpoint_address: u8, max_length: u16) bool {
        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
        return self.call(.interrupt_subscribe, .{
            .endpoint_address = endpoint_address,
            .max_length = max_length,
        }, &.{}, null, &reply) != null;
    }

    /// Hand the controller a DMA-region capability (`handle` — from a `shareable`
    /// dma_alloc, or forwarded from another process) so it binds that buffer into its
    /// IOMMU domain. Must be called for every buffer whose physical address this device
    /// will name in a `bulk` transfer, before the transfer. Harmless (and a no-op
    /// success) when no IOMMU is enforcing. Returns false on failure.
    pub fn attachDma(self: *Device, handle: ipc.Handle) bool {
        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
        return self.call(.dma_attach, {}, &.{}, handle, &reply) != null;
    }

    /// One bulk transfer (IN or OUT per `endpoint_address`'s direction bit) to or
    /// from the caller's own DMA buffer at `physical`. Returns the bytes moved.
    pub fn bulk(self: *Device, endpoint_address: u8, physical: u64, length: u32) ?u32 {
        var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
        const answered = self.call(.bulk, .{
            .physical_address = physical,
            .length = length,
            .endpoint_address = endpoint_address,
        }, &.{}, null, &reply) orelse return null;
        return (Protocol.decodeReply(.bulk, answered) orelse return null).actual_length;
    }
};

/// Decode one asynchronous interrupt report out of a packet that arrived on the
/// class driver's own endpoint. Null when it is not one — a stray message, or a
/// packet too short to carry the report it names. The device it came from is the
/// packet's `Header.target`, which a single-device class driver never has to read.
pub fn reportOf(packet: []const u8) ?InterruptReport {
    const event = Protocol.eventOf(packet) orelse return null;
    if (event != .interrupt_report) return null;
    return Protocol.decodeEvent(.interrupt_report, packet);
}

/// Open `/protocol/usb-transfer` and, on that channel, open the device with the
/// assigned id, handing over a freshly created endpoint for asynchronous interrupt
/// reports. Retries while the bus is still coming up (a class driver races the bus
/// driver at boot). Two opens, deliberately: the first names the contract, the
/// second names an object within it.
pub fn open(device_id: u64) ?Device {
    var attempts: usize = 0;
    const bus = while (attempts < 100) : (attempts += 1) {
        if (channel.openEndpoint("usb-transfer")) |handle| break handle;
        time.sleepMillis(20);
    } else return null;

    const endpoint = ipc.createIpcEndpoint() orelse return null;
    // The assigned device id is the target: it is what the caller has before a
    // token exists, and the token the reply hands back addresses every packet
    // after this one.
    var packet: [usb_transfer_protocol.message_maximum]u8 = undefined;
    const framed = Protocol.encodeRequest(.open, device_id, {}, &.{}, &packet) orelse return null;
    var reply: [usb_transfer_protocol.message_maximum]u8 = undefined;
    const result = ipc.callCap(bus, framed, &reply, endpoint) catch return null;
    const answered = reply[0..result.len];
    const status = envelope.statusOf(answered) orelse return null;
    if (status.status != 0) return null;
    const open_reply = Protocol.decodeReply(.open, answered) orelse return null;

    var device = Device{
        .bus = bus,
        .endpoint = endpoint,
        .token = open_reply.device_token,
        .class = open_reply.interface_class,
        .subclass = open_reply.interface_subclass,
        .protocol_code = open_reply.interface_protocol,
        .interface_number = open_reply.interface_number,
        .endpoint_count = @min(open_reply.endpoint_count, usb_transfer_protocol.max_reported_endpoints),
    };
    for (0..device.endpoint_count) |index| device.endpoints[index] = open_reply.endpoints[index];
    return device;
}