package main

import (
	"context"
	"fmt"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"
)

// The module's long-running code (novox/hq ADR 0198): the profile switcher, launched with the tools
// by the node's runtime and running beside them in the same process.
//
// It replaces the predecessor's `auto-profile`, a user unit that woke every five seconds for ever —
// read the adapters, read /proc/stat, maybe call asusctl — on battery too, where its only possible
// answer was the one it had already given. Here the kernel's power-supply event is the trigger; the
// CPU is sampled only on mains, where the answer depends on it; and on battery the process sleeps
// until the adapter comes back.
//
// **It acts on a change of its decision, never to restore one.** A profile chosen by hand — the
// vendor's profile key, asusctl in a terminal, the profile tool — stays until the power source
// changes or the load crosses a line. The predecessor re-asserted its choice every five seconds and so
// made the profile key useless on battery.

// Emitter publishes an event as the module; nil when the process is not under the runtime.
type Emitter func(eventType string, body any) error

// Switcher is the switcher's state, shared with the tools that report it.
type Switcher struct {
	m    *Machine
	now  func() time.Time
	emit Emitter

	mu        sync.Mutex
	policy    Policy
	source    *Source
	decision  *Decision
	applied   string
	appliedAt time.Time
	lastError string
	holdUntil time.Time
	holdOf    string
	watching  string
	cpuPrev   *CPUTimes
	disabled  string
	asserted  []string
}

func NewSwitcher(m *Machine, emit Emitter) *Switcher {
	return &Switcher{m: m, now: time.Now, emit: emit}
}

// Model is the machine's product family as its firmware reports it.
func (m *Machine) Model() string { return m.read("/sys/class/dmi/id/product_family") }

// ModelFamily is the family this module is written for.
const ModelFamily = "ROG Zephyrus G14"

// ThisModel says whether the machine is the model this module is written for.
func (m *Machine) ThisModel() bool { return strings.EqualFold(m.Model(), ModelFamily) }

// sampleCPU reads /proc/stat and answers the busy percentage since the previous reading.
func (s *Switcher) sampleCPU() (float64, bool) {
	t, err := ParseProcStat(s.m.read("/proc/stat"))
	if err != nil {
		return 0, false
	}
	prev := s.cpuPrev
	s.cpuPrev = &t
	if prev == nil {
		return 0, false
	}
	return Busy(*prev, t)
}

// Evaluate reads the power source, takes a CPU sample when asked and on mains, decides, and applies
// the decision when it changed. It is the whole of one wake-up and what the tests drive.
func (s *Switcher) Evaluate(ctx context.Context, sample bool) {
	if body := s.evaluate(ctx, sample); body != nil && s.emit != nil {
		// Outside the lock: publishing waits for the bus, and the tools that report the switcher
		// must not wait with it.
		if err := s.emit("profile.switched", body); err != nil {
			fmt.Fprintf(os.Stderr, "profile.switched not published: %v\n", err)
		}
	}
}

// evaluate is Evaluate under the lock; it answers the event to publish when it switched.
func (s *Switcher) evaluate(ctx context.Context, sample bool) map[string]any {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.disabled != "" {
		return nil
	}
	src := PowerSource(s.m.Supplies())
	now := s.now()
	first := s.source == nil
	if first || s.source.OnAC != src.OnAC {
		// A new power source: what was learnt about load on the other one says nothing here, and a
		// hold was for the source it was asked on.
		s.policy.Reset()
		s.cpuPrev = nil
		s.holdUntil = time.Time{}
		s.holdOf = ""
		s.sampleCPU() // the first reading on this source, so the next sample is a difference
	} else if sample && src.OnAC {
		if busy, ok := s.sampleCPU(); ok {
			s.policy.Observe(busy, now)
		}
	}
	s.source = &src
	d := s.policy.Decide(src)
	s.decision = &d
	// **Starting is not a reason to switch.** The runtime starts this process on every push that
	// changes a bundle; at boot and at every change of power source asusd has already applied its own
	// profile for the source, which AssertVendorSettings made the policy's. So the first decision is
	// taken as applied, and a profile someone chose by hand survives a push.
	if first {
		s.applied = d.Profile
		return nil
	}
	// Compared with what the switcher itself last applied, never with the profile in force: a profile
	// someone chose by hand is not a reason to act, a new decision is.
	if d.Profile == s.applied || now.Before(s.holdUntil) {
		return nil
	}
	from := s.applied
	if err := s.m.SetProfile(ctx, d.Profile); err != nil {
		s.lastError = err.Error() // and tried again at the next wake-up, since applied did not move
		return nil
	}
	s.lastError = ""
	s.applied, s.appliedAt = d.Profile, now
	body := map[string]any{"profile": d.Profile, "reason": d.Reason, "source": src.Source}
	if from != "" {
		body["from"] = from
	}
	return body
}

// Hold keeps a profile chosen through the tool for a while: the switcher does not move it until the
// hold ends or the power source changes.
func (s *Switcher) Hold(profile string, d time.Duration) time.Time {
	s.mu.Lock()
	defer s.mu.Unlock()
	if d <= 0 {
		s.holdUntil, s.holdOf = time.Time{}, ""
		return time.Time{}
	}
	s.holdUntil, s.holdOf = s.now().Add(d), profile
	return s.holdUntil
}

// Run is the switcher's life: assert asusd's settings once, then wake on each power-supply event, on
// each CPU sample while on mains, and at SafetyRecheck otherwise.
func (s *Switcher) Run(ctx context.Context) {
	defer func() {
		if r := recover(); r != nil {
			s.mu.Lock()
			s.disabled = fmt.Sprintf("the switcher stopped on a fault: %v", r)
			s.mu.Unlock()
			fmt.Fprintln(os.Stderr, s.disabled)
		}
	}()
	if !s.m.ThisModel() {
		s.mu.Lock()
		s.disabled = fmt.Sprintf("this machine reports %q, not %q: the switcher does not act on another model",
			s.m.Model(), ModelFamily)
		s.mu.Unlock()
		fmt.Fprintln(os.Stderr, s.disabled)
		return
	}
	s.AssertVendorSettings(ctx)

	events, err := listenPowerSupply(ctx)
	s.mu.Lock()
	if err != nil {
		s.watching = "polling every " + SampleEvery.String() + ": " + err.Error()
	} else {
		s.watching = "the kernel's power-supply events"
	}
	s.mu.Unlock()

	s.Evaluate(ctx, false)
	timer := time.NewTimer(s.interval(err != nil))
	defer timer.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case _, open := <-events:
			if !open {
				events = nil
				s.mu.Lock()
				s.watching = "polling every " + SampleEvery.String() + ": the uevent socket closed"
				s.mu.Unlock()
				err = fmt.Errorf("closed")
				continue
			}
			// Settle: an adapter change arrives as several events within a moment.
			time.Sleep(time.Second)
			s.Evaluate(ctx, false)
		case <-timer.C:
			s.Evaluate(ctx, true)
			timer.Reset(s.interval(err != nil))
		}
	}
}

// interval is how long to sleep: a CPU sample's period on mains (or with no events to wake on), the
// safety recheck on battery.
func (s *Switcher) interval(polling bool) time.Duration {
	s.mu.Lock()
	defer s.mu.Unlock()
	if polling || s.source == nil || s.source.OnAC {
		return SampleEvery
	}
	return SafetyRecheck
}

// AssertVendorSettings puts asusd's own settings where the module wants them, once at start: the
// battery charge limit, and the profiles asusd itself switches to on mains and on battery, so that the
// vendor daemon's own switching and this module's never disagree. Each is read first and set only if
// it differs. A value changed later with a tool stands until the next start.
func (s *Switcher) AssertVendorSettings(ctx context.Context) []string {
	var said []string
	if limit, err := s.m.ChargeLimit(ctx); err != nil {
		said = append(said, "charge limit not read: "+err.Error())
	} else if limit != ChargeLimitPercent {
		if _, err := s.m.Run(ctx, "asusctl", "battery", "limit", strconv.Itoa(ChargeLimitPercent)); err != nil {
			said = append(said, "charge limit not set: "+vendor("asusctl", err).Error())
		} else {
			said = append(said, fmt.Sprintf("charge limit %d%% → %d%%", limit, ChargeLimitPercent))
		}
	} else {
		said = append(said, fmt.Sprintf("charge limit already %d%%", ChargeLimitPercent))
	}
	p, err := s.m.Profile(ctx)
	if err != nil {
		said = append(said, "asusd's profiles not read: "+err.Error())
	} else {
		for _, want := range []struct{ flag, have, want, what string }{
			{"-a", p.OnAC, ProfileOnAC, "on mains"},
			{"-b", p.Battery, ProfileOnBattery, "on battery"},
		} {
			if want.have == "" || strings.EqualFold(want.have, want.want) {
				continue
			}
			if _, err := s.m.Run(ctx, "asusctl", "profile", "set", want.flag, want.want); err != nil {
				said = append(said, "asusd's profile "+want.what+" not set: "+err.Error())
			} else {
				said = append(said, fmt.Sprintf("asusd's profile %s %s → %s", want.what, want.have, want.want))
			}
		}
	}
	s.mu.Lock()
	s.asserted = said
	s.mu.Unlock()
	for _, line := range said {
		fmt.Fprintln(os.Stderr, line)
	}
	return said
}

// SwitcherReport is the switcher's state as the profile-policy tool shows it.
type SwitcherReport struct {
	Running         bool       `json:"running"`
	Disabled        string     `json:"disabled,omitempty"`
	Watching        string     `json:"woken_by,omitempty"`
	Source          *Source    `json:"source,omitempty"`
	Decision        *Decision  `json:"decision,omitempty"`
	Load            Policy     `json:"load"`
	LastApplied     string     `json:"last_applied,omitempty"`
	LastAppliedAt   *time.Time `json:"last_applied_at,omitempty"`
	LastError       string     `json:"last_error,omitempty"`
	HeldUntil       *time.Time `json:"held_until,omitempty"`
	Held            string     `json:"held_profile,omitempty"`
	AssertedAtStart []string   `json:"asserted_at_start,omitempty"`
}

func (s *Switcher) Report() SwitcherReport {
	s.mu.Lock()
	defer s.mu.Unlock()
	r := SwitcherReport{
		Running: s.watching != "" && s.disabled == "", Disabled: s.disabled, Watching: s.watching,
		Source: s.source, Decision: s.decision, Load: s.policy, LastApplied: s.applied,
		LastAppliedAt: when(s.appliedAt), LastError: s.lastError, AssertedAtStart: s.asserted,
	}
	if s.now().Before(s.holdUntil) {
		r.HeldUntil, r.Held = when(s.holdUntil), s.holdOf
	}
	return r
}

// when is a time for a report: absent rather than the zero time.
func when(t time.Time) *time.Time {
	if t.IsZero() {
		return nil
	}
	return &t
}