// Package conditions is the condition store (novox/hq to-be 45 §2, ADR 0227 rules 5 and 6).
//
// **A condition is a durable fact about something the mesh owns that is wrong.** Until this, every
// one of the forty-eight core failures of research 031 was noticed because a person or an agent
// looked: the mesh's own answers carried the fact for whoever asked, and told nobody. A condition is
// raised when an observation says something is wrong past its bound, kept with since-when, evidence
// and who can resolve it, said on the bus as it changes, and cleared when an observation says it is
// resolved — never by hand.
//
// The controller is the store's only writer (to-be 45 §1). Two of its processes may write at once —
// the serving controller's watchdogs, and a command a person runs to silence one — so every write
// is a compare-and-set on the key's revision, and a write that lost the race reads again and redoes
// itself rather than overwriting what the other said.
package conditions

import (
	"fmt"
	"regexp"
	"sort"
	"strings"
	"time"
)

// Severity is how soon the operator is needed: two levels, no more (to-be 45 §2).
type Severity string

const (
	// Urgent needs the operator now.
	Urgent Severity = "urgent"
	// Warning needs the operator when they can.
	Warning Severity = "warning"
)

// The scopes a condition's key starts with: what kind of thing is wrong.
const (
	ScopeMachine  = "machine"
	ScopePlan     = "plan"
	ScopeCall     = "call"
	ScopeBuild    = "build"
	ScopeMerge    = "merge"
	ScopeProvider = "provider"
	ScopeSeat     = "seat"
	ScopeBus      = "bus"
	ScopeCore     = "core"
	ScopeProbe    = "probe"
	ScopeMesh     = "mesh"
)

// Scopes is every scope, in the order a person reads them.
var Scopes = []string{ScopeMachine, ScopePlan, ScopeCall, ScopeBuild, ScopeMerge, ScopeProvider,
	ScopeSeat, ScopeBus, ScopeCore, ScopeProbe, ScopeMesh}

// Who resolves a condition.
const (
	// ResolverSelf clears on observation: the signal returns, the probe passes.
	ResolverSelf = "self"
	// ResolverOperator needs a person: a healer's budget spent, or a repair that could only destroy.
	ResolverOperator = "operator"
	// ResolverAgent is work handed to an agent (research 017; not raised by anything yet).
	ResolverAgent = "agent"
)

// ResolverHealer is the resolver of a condition a registered healer works on (Phase 3).
func ResolverHealer(name string) string { return "healer:" + name }

// Subject is what the condition is about: its scope, its id within the scope, and the machine it
// concerns when there is one.
type Subject struct {
	Scope   string `json:"scope"`
	ID      string `json:"id"`
	Machine string `json:"machine,omitempty"`
	// Also are the other machines it concerns: a consumer's, for a provider failing it.
	Also []string `json:"also,omitempty"`
}

// Evidence is one observation, as it was said.
type Evidence struct {
	At   time.Time `json:"at"`
	Said string    `json:"said"`
}

// Attempt is one healer's try at a condition (to-be 45 §7; written from Phase 3).
type Attempt struct {
	At      time.Time `json:"at"`
	What    string    `json:"what"`
	Outcome string    `json:"outcome"`
}

// Silence is a person saying they know: no messages until it ends (to-be 45 §2). Recorded as a hand
// act; the condition stays open, and `status` still says it.
type Silence struct {
	Until time.Time `json:"until"`
	By    string    `json:"by"`
	Why   string    `json:"why"`
	Since time.Time `json:"since"`
}

// KeptEvidence is how many observations a condition keeps, newest first.
const KeptEvidence = 10

// MaxSilence is the longest a condition may be silenced at once: past it, a person says so again.
const MaxSilence = 7 * 24 * time.Hour

// ReopenWithin is how soon after it cleared a condition raised again is the same one again, with its
// count increased, rather than news (to-be 45 §2).
const ReopenWithin = 10 * time.Minute

// Condition is one open condition, as the store keeps it and its events carry it.
type Condition struct {
	Key string `json:"key"`
	// Kind is the condition kind: from the signals table, the probe registry or an event kind.
	Kind     string   `json:"kind"`
	Subject  Subject  `json:"subject"`
	Severity Severity `json:"severity"`
	// Summary is one line in the mesh's words.
	Summary string `json:"summary"`
	// Evidence is the newest observations, at most KeptEvidence, newest first.
	Evidence []Evidence `json:"evidence"`
	// Source is the signals-table row, probe or event that raised it: `S1`, `D3`, `provisioner.failing`.
	Source string `json:"source"`
	// Raised is when it was first observed this time; LastObserved the newest observation.
	Raised       time.Time `json:"raised"`
	LastObserved time.Time `json:"last-observed"`
	// Observations is how many times it was observed since raised.
	Observations int `json:"observations"`
	// Count is how many times it has been raised, a reopening within ReopenWithin counted.
	Count    int       `json:"count"`
	Tried    []Attempt `json:"tried,omitempty"`
	Resolver string    `json:"resolver"`
	// Silenced is null when no silence is in force: said, not left out, so a reader need not guess.
	Silenced *Silence `json:"silenced"`
	// Epoch is the controller lease epoch that last wrote it (to-be 45 §6). Zero where it was written
	// by a controller serving without the lease, or before the lease existed.
	Epoch uint64 `json:"epoch"`
}

// SilencedAt says whether a person's silence is in force at a moment.
func (c Condition) SilencedAt(now time.Time) bool {
	return c.Silenced != nil && now.Before(c.Silenced.Until)
}

// Show is the verb that shows more about a condition, as a message carries it.
func (c Condition) Show() string { return "mesh-controller.conditions key=" + c.Key }

// Observation is one watchdog, probe or event saying something is wrong now.
type Observation struct {
	Scope string
	// ID is the thing within the scope; several tokens joined by dots where the thing is named by
	// several (a provider's module, its machine and the consumer).
	ID string
	// Token is the last part of the key, short for the kind: `silent` for a machine, `failing` for a
	// provider. Kind's own word when empty.
	Token   string
	Kind    string
	Machine string
	// Also are the other machines it concerns.
	Also     []string
	Severity Severity
	Summary  string
	// Said is this observation's evidence, in the mesh's words; Summary when empty.
	Said     string
	Source   string
	Resolver string
}

// Key is where the observation's condition is kept: `<scope>.<id>.<kind>`, so the same fault said
// again is the same condition.
func (o Observation) Key() string {
	token := o.Token
	if token == "" {
		token = o.Kind
	}
	return Key(o.Scope, o.ID, token)
}

// unsafeKey is anything a key may not hold: the bus takes letters, digits and `-_/=` in a key's
// tokens, and a `*` or `>` would make one a wildcard.
var unsafeKey = regexp.MustCompile(`[^A-Za-z0-9_=/-]`)

// Key composes a condition's key from its parts, each token made safe for the bus: a character the
// bus would refuse becomes `_`, so a key is never refused for the name of the thing it is about.
func Key(scope, id, token string) string {
	var parts []string
	for _, p := range append(append([]string{scope}, strings.Split(id, ".")...), token) {
		p = unsafeKey.ReplaceAllString(strings.TrimSpace(p), "_")
		if p == "" {
			p = "_"
		}
		parts = append(parts, p)
	}
	return strings.Join(parts, ".")
}

// check refuses an observation that could not be said: a condition with no kind, no scope the mesh
// knows, or no severity is one nobody could route.
func (o Observation) check() error {
	known := false
	for _, s := range Scopes {
		if s == o.Scope {
			known = true
		}
	}
	switch {
	case !known:
		return fmt.Errorf("a condition's scope is one of %s, not %q", strings.Join(Scopes, ", "), o.Scope)
	case strings.TrimSpace(o.ID) == "":
		return fmt.Errorf("a %s condition names what it is about", o.Scope)
	case strings.TrimSpace(o.Kind) == "":
		return fmt.Errorf("the condition %s has no kind", o.Key())
	case o.Severity != Urgent && o.Severity != Warning:
		return fmt.Errorf("the condition %s is urgent or a warning, not %q", o.Key(), o.Severity)
	case strings.TrimSpace(o.Summary) == "":
		return fmt.Errorf("the condition %s says nothing", o.Key())
	case strings.TrimSpace(o.Source) == "":
		return fmt.Errorf("the condition %s does not say what raised it", o.Key())
	}
	return nil
}

// Order sorts conditions as `status` says them: urgent before warning, then oldest first.
func Order(list []Condition) {
	sort.SliceStable(list, func(i, j int) bool {
		if list[i].Severity != list[j].Severity {
			return list[i].Severity == Urgent
		}
		if !list[i].Raised.Equal(list[j].Raised) {
			return list[i].Raised.Before(list[j].Raised)
		}
		return list[i].Key < list[j].Key
	})
}