// Package sensors is the one standard way anything reads what Ham Lab measures.
//
// Every measurable thing is a Sensor: a stable dotted ID ("cpu.core.3.usage",
// "fan.nct6775.fan2", "fs.root.used_pct"), a little metadata, and a current value. A
// consumer discovers them from the catalog, then asks for exactly the ones it wants —
// one by ID, many by glob, or as a shaped query where the client sends the object it
// wants and gets it back with the values filled in. See SENSORS.md.
//
// Sources of sensors are Providers. The registry only joins them; it measures nothing.
package sensors

import (
	"encoding/json"
	"errors"
	"fmt"
	"path"
	"sort"
	"strings"
)

// Sensor is one measurable thing and its reading. Value is a float64, bool or string.
type Sensor struct {
	ID     string            `json:"id"`
	Name   string            `json:"name"`           // human label
	Kind   string            `json:"kind"`           // usage | load | temperature | fan | rate | bytes | duration | voltage | power | state
	Unit   string            `json:"unit,omitempty"` // % · °C · rpm · B/s · B · s · min · V · W · MHz
	Value  any               `json:"value"`
	T      int64             `json:"t"` // unix ms the value was read — slow sensors are older than the tick
	Min    *float64          `json:"min,omitempty"`
	Max    *float64          `json:"max,omitempty"`
	Warn   *float64          `json:"warn,omitempty"` // the hardware's own thresholds, where it states them
	Crit   *float64          `json:"crit,omitempty"`
	Labels map[string]string `json:"labels,omitempty"` // the real names behind the ID: chip, iface, mount…
}

// Series is a numeric sensor's recent past.
type Series struct {
	ID   string    `json:"id"`
	Unit string    `json:"unit,omitempty"`
	T    []int64   `json:"t"`
	V    []float64 `json:"v"`
}

// Provider is a source of sensors. Sensors returns every sensor it has, with current values.
type Provider interface {
	Sensors() []Sensor
}

// Historian is a Provider that also remembers. ok is false for an ID it doesn't hold.
type Historian interface {
	SensorHistory(id string) (s Series, ok bool)
}

// Ticker is a Provider that can say when its values have changed.
type Ticker interface {
	Subscribe() (tick <-chan struct{}, cancel func())
}

// Subscribe follows the first provider that ticks. ok is false when none does.
func (r *Registry) Subscribe() (tick <-chan struct{}, cancel func(), ok bool) {
	for _, p := range r.providers {
		if t, is := p.(Ticker); is {
			tick, cancel = t.Subscribe()
			return tick, cancel, true
		}
	}
	return nil, nil, false
}

// F is a pointer to a float, for the optional bounds.
func F(v float64) *float64 { return &v }

// Seg makes one ID segment from a real-world name: lower case, [a-z0-9_-] only, so IDs
// survive URLs, query strings and templating languages untouched. "Package id 0" →
// "package_id_0", "/mnt/tank" → "mnt_tank", "/" → "root".
func Seg(name string) string {
	if name == "/" {
		return "root"
	}
	var b strings.Builder
	gap := false
	for _, r := range strings.ToLower(strings.TrimSpace(name)) {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9', r == '-':
			if gap && b.Len() > 0 {
				b.WriteByte('_')
			}
			gap = false
			b.WriteRune(r)
		default:
			gap = true
		}
	}
	if b.Len() == 0 {
		return "unnamed"
	}
	return b.String()
}

// ID joins already-safe segments.
func ID(segs ...string) string { return strings.Join(segs, ".") }

// Registry joins providers into one namespace.
type Registry struct{ providers []Provider }

func NewRegistry(p ...Provider) *Registry { return &Registry{providers: p} }

func (r *Registry) Add(p Provider) { r.providers = append(r.providers, p) }

// All returns every sensor, sorted by ID. Two sensors that would share an ID (two
// identical chips) get "_2", "_3" on the colliding one, in the provider's order.
func (r *Registry) All() []Sensor {
	var out []Sensor
	seen := map[string]int{}
	for _, p := range r.providers {
		for _, s := range p.Sensors() {
			seen[s.ID]++
			if n := seen[s.ID]; n > 1 {
				s.ID = fmt.Sprintf("%s_%d", s.ID, n)
			}
			out = append(out, s)
		}
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].ID < out[j].ID })
	return out
}

// History finds the provider that remembers id.
func (r *Registry) History(id string) (Series, bool) {
	for _, p := range r.providers {
		if h, ok := p.(Historian); ok {
			if s, ok := h.SensorHistory(id); ok {
				return s, true
			}
		}
	}
	return Series{}, false
}

// IsGlob reports whether a selector names many sensors rather than one.
func IsGlob(sel string) bool { return strings.ContainsAny(sel, "*?[") }

// Select returns the sensors a selector names: an exact ID, or a glob where * crosses
// dots ("fan.*" is every fan, "cpu.core.*.usage" every core).
func Select(all []Sensor, sel string) ([]Sensor, error) {
	if !IsGlob(sel) {
		for _, s := range all {
			if s.ID == sel {
				return []Sensor{s}, nil
			}
		}
		return nil, nil
	}
	if _, err := path.Match(sel, ""); err != nil {
		return nil, fmt.Errorf("bad pattern %q", sel)
	}
	var out []Sensor
	for _, s := range all {
		if ok, _ := path.Match(sel, s.ID); ok {
			out = append(out, s)
		}
	}
	return out, nil
}

// Shape answers a shaped query: the client sends the object it wants, with selectors
// where the values go, and gets the same object back with them filled in.
//
//	{"cpu": "cpu.usage", "fans": "fan.*", "box": {"up": "uptime"}}
//	→ {"cpu": 12.4, "fans": {"fan.nct6775.fan1": 820}, "box": {"up": 80520}}
//
// An exact ID becomes its value (null if there is no such sensor here — machines differ,
// and a dashboard shouldn't fail because one has no fans). A glob becomes an object keyed
// by ID. Objects and arrays are walked. With full, every value is the whole Sensor.
func Shape(all []Sensor, query json.RawMessage, full bool) (any, error) {
	var q any
	if err := json.Unmarshal(query, &q); err != nil {
		return nil, errors.New("query is not valid JSON")
	}
	return shape(all, q, full, 0)
}

func shape(all []Sensor, q any, full bool, depth int) (any, error) {
	if depth > 16 {
		return nil, errors.New("query nested too deep")
	}
	leaf := func(s Sensor) any {
		if full {
			return s
		}
		return s.Value
	}
	switch v := q.(type) {
	case string:
		got, err := Select(all, v)
		if err != nil {
			return nil, err
		}
		if !IsGlob(v) {
			if len(got) == 0 {
				return nil, nil
			}
			return leaf(got[0]), nil
		}
		m := make(map[string]any, len(got))
		for _, s := range got {
			m[s.ID] = leaf(s)
		}
		return m, nil
	case map[string]any:
		m := make(map[string]any, len(v))
		for k, sub := range v {
			r, err := shape(all, sub, full, depth+1)
			if err != nil {
				return nil, err
			}
			m[k] = r
		}
		return m, nil
	case []any:
		a := make([]any, len(v))
		for i, sub := range v {
			r, err := shape(all, sub, full, depth+1)
			if err != nil {
				return nil, err
			}
			a[i] = r
		}
		return a, nil
	default:
		return nil, fmt.Errorf("a query holds sensor IDs, objects and arrays; got %v", v)
	}
}