//! Machine power control: enter ACPI mode, reboot, and power off (ACPI S5).
//!
//! Built entirely on the register map `acpi` extracted from the FADT plus the
//! sleep-state (`_Sx`) types the AML submodule pulled from the DSDT, driven through the
//! injected `Hal` (port I/O and MMIO). Nothing here is x86-specific beyond the
//! well-known legacy reset fallbacks, which are guarded behind the ACPI methods.
//!
//! S3 (suspend-to-RAM) is stubbed: it needs a wake trampoline and device
//! re-initialisation, a milestone of its own.

const acpi = @import("acpi.zig");
const device_model = @import("device-model.zig");
const Hal = device_model.Hal;

const slp_en: u32 = 1 << 13; // SLP_EN: writing 1 triggers the sleep transition
const sci_en: u32 = 1 << 0; // SCI_EN in PM1 control: set once ACPI mode is active

/// Switch the platform into ACPI mode if it isn't already, so the PM1 control
/// register is live. A no-op when the firmware exposes no SMI command port (ACPI
/// already enabled, as under QEMU/OVMF) — we still verify SCI_EN first.
pub fn enable(hal: Hal) void {
    const pi = acpi.power_information;
    if (!pi.pm1a_cnt.present()) return;
    if (readRegister(hal, pi.pm1a_cnt) & sci_en != 0) return; // already in ACPI mode
    if (pi.smi_cmd == 0 or pi.acpi_enable == 0) return; // no way to switch; assume fine

    hal.pioWrite(1, pi.smi_cmd, pi.acpi_enable);
    var spins: usize = 0;
    while (readRegister(hal, pi.pm1a_cnt) & sci_en == 0 and spins < 1_000_000) : (spins += 1) {}
}

/// Restart the machine. Tries the ACPI reset register first, then the two legacy
/// fallbacks. Returns only if every method failed (very unlikely).
pub fn reboot(hal: Hal) void {
    const pi = acpi.power_information;

    // 1. The FADT reset register, when the firmware advertises support.
    if (pi.reset_supported and pi.reset.present()) {
        writeRegister(hal, pi.reset, pi.reset_value);
        delay();
    }
    // 2. The PCI reset-control register at port 0xCF9 (RST_CPU | SYSTEM_RST).
    hal.pioWrite(1, 0xCF9, 0x0E);
    hal.pioWrite(1, 0xCF9, 0x06);
    delay();
    // 3. Pulse the 8042 keyboard controller's reset line.
    hal.pioWrite(1, 0x64, 0xFE);
    delay();
}

/// Power the machine off via ACPI S5. Requires the soft-off (`_S5`) sleep type; if
/// it wasn't found in the AML, there is nothing safe to do and this returns.
pub fn shutdown(hal: Hal) void {
    enable(hal);
    const pi = acpi.power_information;
    const s5 = pi.s5 orelse return;

    if (pi.pm1a_cnt.present()) {
        writeRegister(hal, pi.pm1a_cnt, sleepValue(s5.slp_typ_a));
    }
    if (pi.pm1b_cnt.present()) {
        writeRegister(hal, pi.pm1b_cnt, sleepValue(s5.slp_typ_b));
    }
    delay();
}

/// S3 suspend-to-RAM — not implemented (needs a wake path + device re-init).
pub fn sleepS3(hal: Hal) error{Unsupported}!void {
    _ = hal;
    return error.Unsupported;
}

/// The PM1 control write that requests sleep type `slp_typ`: SLP_TYP in bits
/// [12:10], SLP_EN in bit 13.
fn sleepValue(slp_typ: u8) u32 {
    return (@as(u32, slp_typ & 0x7) << 10) | slp_en;
}

fn readRegister(hal: Hal, register: acpi.RegisterAccess) u32 {
    if (register.mmio) {
        const p: *align(1) volatile u32 = @ptrFromInt(hal.mapMmio(register.address, 4, true));
        return p.*;
    }
    return hal.pioRead(register.width, @intCast(register.address));
}

fn writeRegister(hal: Hal, register: acpi.RegisterAccess, value: u32) void {
    if (register.mmio) {
        const p: *align(1) volatile u32 = @ptrFromInt(hal.mapMmio(register.address, 4, true));
        p.* = value;
    } else {
        hal.pioWrite(register.width, @intCast(register.address), value);
    }
}

/// A short busy-wait so a reset/power-off takes effect before we fall through to
/// the next method. The empty asm is an architecture-neutral barrier that keeps the loop
/// from being optimised away.
fn delay() void {
    var i: usize = 0;
    while (i < 50_000_000) : (i += 1) {
        asm volatile ("" ::: .{ .memory = true });
    }
}