// Package asks is the contract of asking a person and answering on a channel (novox/hq ADR 0259): the
// shapes an asker, the router and a channel exchange on the bus, and the subjects they travel on. No
// transport and no channel's service: an asker publishes an Ask under its own name and acts on the Warrant
// it hears; the router holds the ask, sends channels a Message, and judges the Choice a channel says; a
// channel shows a Message and says what was chosen and by whom, as its service authenticated it.
package asks

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

// The seats (novox/hq ADR 0259 §3).
const (
	// Seat is held by the router: an ask and its cancel are its accepts, a warrant its event, each named by
	// the asker.
	Seat = "operator-channel"
	// ChannelSeat is the kinded bench a channel holds to show and say: its accepts carry the kind.
	ChannelSeat = "channel"
	// IntakeSeat is the kinded bench a channel holds to say what was chosen: its events and proofs carry
	// the kind.
	IntakeSeat = "intake"
)

// AskSubject is where an asker publishes an ask, CancelSubject its cancel, and DecidedSubject where it
// hears the warrant, or the ask's end without one.
func AskSubject(asker string) string     { return "mesh.seat." + Seat + ".accept.ask." + asker }
func CancelSubject(asker string) string  { return "mesh.seat." + Seat + ".accept.cancel." + asker }
func DecidedSubject(asker string) string { return "mesh.seat." + Seat + ".event.decided." + asker }

// The work a channel takes, on ChannelSubject.
const (
	Show = "show" // a message offering answers
	Edit = "edit" // a message shown before, replaced
	Send = "send" // a message offering nothing
)

// ChannelSubject is where the router sends a channel of a kind its work.
func ChannelSubject(verb, kind string) string {
	return "mesh.seat." + ChannelSeat + ".accept." + verb + "." + kind
}

// What a channel says, on IntakeSubject.
const (
	Chosen = "choice" // a button tapped
	Link   = "link"   // somebody asked to be linked as the operator
)

// IntakeSubject is where a channel of a kind says what arrived.
func IntakeSubject(what, kind string) string {
	return "mesh.seat." + IntakeSeat + ".event." + what + "." + kind
}

// CodeProof is the one proof verb: a code the operator typed, carried by request and reply, never kept.
const CodeProof = "code"

// ProofSubject is where a channel of a kind asks a proof.
func ProofSubject(verb, kind string) string {
	return "mesh.seat." + IntakeSeat + ".proof." + verb + "." + kind
}

// A Level is how much proof an option's answer needs (novox/hq ADR 0234 §8, the glossary's assurance level).
type Level string

const (
	// Acknowledge performs only what any granted principal may already do: silencing, details. No proof.
	Acknowledge Level = "acknowledge"
	// Approve needs one proof: a verified sender (a linked account, linked an hour or more) or a code.
	Approve Level = "approve"
	// Destroy needs two proofs, one of them a code.
	Destroy Level = "destroy"
)

// Rank orders the levels; an unknown level ranks above every known one, so it is never taken as less.
func (l Level) Rank() int {
	switch l {
	case Acknowledge:
		return 0
	case Approve:
		return 1
	case Destroy:
		return 2
	}
	return 3
}

// Operator is the one role an ask may be answered by today.
const Operator = "operator"

// Option is one answer an ask offers: a label for the button, what it does in plain words, its level.
type Option struct {
	ID    string `json:"id"`
	Label string `json:"label"`
	Does  string `json:"does"`
	Level Level  `json:"level"`
}

// Ask is a request for a person's word (novox/hq ADR 0259 §4).
type Ask struct {
	// ID is the asker's own, unique to it.
	ID string `json:"id"`
	// Headline names the thing and what is wrong, in a few plain words; Explanation is what happened and
	// what it means. Both are held to the plain rule and the content rule by the router.
	Headline    string   `json:"headline"`
	Explanation string   `json:"explanation"`
	Options     []Option `json:"options"`
	// Who may answer: Operator.
	Who string `json:"who"`
	// Expires is when the ask ends unanswered; OnExpiry is what the asker then does, in words the person
	// is shown ("the delivery stays held"). An ask that authorises never defaults.
	Expires  time.Time `json:"expires"`
	OnExpiry string    `json:"on-expiry"`
	// About is what the ask is about (a condition's key): a newer ask about it replaces the older.
	About  string `json:"about,omitempty"`
	Urgent bool   `json:"urgent,omitempty"`
}

// The bounds of an ask (novox/hq ADR 0234 §8, ADR 0259 §4).
const (
	MostOptions    = 4
	MostOpen       = 3
	ApproveLasts   = 24 * time.Hour
	DestroyLasts   = 10 * time.Minute
	HeadlineLength = 60
	LabelLength    = 24
)

var usableID = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_-]{0,63}$`)

// UsableID says whether a name can be an ask's or an option's id: a key and a subject token both.
func UsableID(id string) bool { return usableID.MatchString(id) }

// Highest is the highest level among the ask's options.
func (a Ask) Highest() Level {
	high := Acknowledge
	for _, o := range a.Options {
		if o.Level.Rank() > high.Rank() {
			high = o.Level
		}
	}
	return high
}

// Option is the option of this id, or false.
func (a Ask) Option(id string) (Option, bool) {
	for _, o := range a.Options {
		if o.ID == id {
			return o, true
		}
	}
	return Option{}, false
}

// Check is what an ask is held to before anything is shown: every refusal, in words its asker can act on.
func (a Ask) Check(now time.Time) error {
	var problems []string
	say := func(format string, args ...any) { problems = append(problems, fmt.Sprintf(format, args...)) }
	if !UsableID(a.ID) {
		say("its id %q is not letters, digits, - and _, at most 64", a.ID)
	}
	if strings.TrimSpace(a.Headline) == "" || len([]rune(a.Headline)) > HeadlineLength {
		say("its headline is empty or longer than %d characters", HeadlineLength)
	}
	if strings.TrimSpace(a.Explanation) == "" {
		say("it explains nothing")
	}
	if a.Who != Operator {
		say("it is answered by %q, and only the operator answers today", a.Who)
	}
	if len(a.Options) == 0 || len(a.Options) > MostOptions {
		say("it offers %d options, and an ask offers one to %d", len(a.Options), MostOptions)
	}
	seen := map[string]bool{}
	for _, o := range a.Options {
		switch {
		case !UsableID(o.ID):
			say("an option's id %q is not letters, digits, - and _", o.ID)
		case seen[o.ID]:
			say("the option %s is offered twice", o.ID)
		}
		seen[o.ID] = true
		if strings.TrimSpace(o.Label) == "" || len([]rune(o.Label)) > LabelLength {
			say("the option %s's label is empty or longer than %d characters", o.ID, LabelLength)
		}
		if strings.TrimSpace(o.Does) == "" {
			say("the option %s does not say what it does", o.ID)
		}
		if o.Level.Rank() > Destroy.Rank() {
			say("the option %s has the level %q, which is none of acknowledge, approve, destroy", o.ID, o.Level)
		}
	}
	if !a.Expires.After(now) {
		say("it expires before it is asked")
	}
	switch a.Highest() {
	case Approve:
		if a.Expires.After(now.Add(ApproveLasts)) {
			say("an ask that approves lasts at most %s", ApproveLasts)
		}
	case Destroy:
		if a.Expires.After(now.Add(DestroyLasts)) {
			say("an ask that destroys lasts at most %s", DestroyLasts)
		}
	}
	if a.Highest() != Acknowledge && strings.TrimSpace(a.OnExpiry) == "" {
		say("it does not say what happens when nobody answers, and an ask that authorises never defaults")
	}
	if a.About != "" && strings.ContainsAny(a.About, " \n") {
		say("what it is about is a key, without spaces")
	}
	if len(problems) > 0 {
		return errors.New("the ask is refused: " + strings.Join(problems, "; "))
	}
	return nil
}

// Outcome is how an ask ended.
type Outcome string

const (
	OutcomeChosen    Outcome = "chosen"    // a person chose an option: a warrant
	OutcomeExpired   Outcome = "expired"   // nobody answered in time
	OutcomeCancelled Outcome = "cancelled" // its asker took it back
	OutcomeReplaced  Outcome = "replaced"  // a newer ask about the same thing replaced it
	OutcomeRefused   Outcome = "refused"   // it was never shown: Words says why
)

// Person is who chose, as the router verified them.
type Person struct {
	// Who is the role: Operator.
	Who string `json:"who"`
	// Kind is the channel kind they answered on, Identity their account on that service, Display the name
	// the service shows, and Verified how the router knew it was them.
	Kind     string `json:"kind"`
	Identity string `json:"identity"`
	Display  string `json:"display,omitempty"`
	Verified string `json:"verified"`
}

// Warrant is the router's record that a person chose one option of one ask, or the ask's end without one
// (novox/hq ADR 0259 §6). It carries no secret.
type Warrant struct {
	Ask     string  `json:"ask"`
	Asker   string  `json:"asker"`
	About   string  `json:"about,omitempty"`
	Outcome Outcome `json:"outcome"`
	// Option, Label and Level are the option chosen; By who chose it, Channel the module it came through,
	// Proofs which proofs were present (P1, P2, P3).
	Option  string    `json:"option,omitempty"`
	Label   string    `json:"label,omitempty"`
	Level   Level     `json:"level,omitempty"`
	By      *Person   `json:"by,omitempty"`
	Channel string    `json:"channel,omitempty"`
	Proofs  []string  `json:"proofs,omitempty"`
	At      time.Time `json:"at"`
	// Words are why an ask ended without a choice, or what refused it.
	Words string `json:"words,omitempty"`
}

// Says is the warrant in the words an asker records with its act: "the operator, via telegram (user id
// verified), chose Release".
func (w Warrant) Says() string {
	if w.Outcome != OutcomeChosen || w.By == nil {
		return fmt.Sprintf("no person chose: the ask %s %s", w.Ask, w.Outcome)
	}
	via := w.By.Kind
	if w.By.Verified != "" {
		via += " (" + w.By.Verified + ")"
	}
	return fmt.Sprintf("the %s, via %s, chose %s", w.By.Who, via, w.Label)
}

// For checks a warrant against the ask its asker made: the same asker and ask, a choice, an option the ask
// offered, at that option's level. An asker acts on nothing else.
func (w Warrant) For(asker string, a Ask) (Option, error) {
	if w.Asker != asker || w.Ask != a.ID {
		return Option{}, fmt.Errorf("the warrant is for %s's ask %s, not %s's %s", w.Asker, w.Ask, asker, a.ID)
	}
	if w.Outcome != OutcomeChosen || w.By == nil || w.By.Who != a.Who {
		return Option{}, fmt.Errorf("the ask %s ended %s; no person chose", a.ID, w.Outcome)
	}
	o, offered := a.Option(w.Option)
	if !offered {
		return Option{}, fmt.Errorf("the ask %s offered no option %s", a.ID, w.Option)
	}
	if w.Level != o.Level {
		return Option{}, fmt.Errorf("the option %s is %s, and the warrant says %s", o.ID, o.Level, w.Level)
	}
	return o, nil
}

// Button is one answer a channel offers: its label and the router's one-time ticket for it.
type Button struct {
	Label  string `json:"label"`
	Ticket string `json:"ticket"`
}

// Message is the work a channel takes: shown with buttons (Show), shown again in place (Edit), or said
// (Send). Handle is the router's name for it, the same across a show and its edits; the channel keeps
// which of its own messages that is. The words are the router's, shown as given.
type Message struct {
	Handle  string   `json:"handle"`
	Title   string   `json:"title"`
	Body    string   `json:"body"`
	Buttons []Button `json:"buttons,omitempty"`
	Urgent  bool     `json:"urgent,omitempty"`
	Silent  bool     `json:"silent,omitempty"`
}

// Sender is who a channel's service says sent something: the account, the name it shows, and whether the
// service authenticated it. The router alone judges whether that is the operator.
type Sender struct {
	Identity      string `json:"identity"`
	Display       string `json:"display,omitempty"`
	Authenticated bool   `json:"authenticated"`
}

// Choice is a button chosen on a channel.
type Choice struct {
	// ID is the channel's own for this arrival, unique, so the router acts on it once.
	ID     string    `json:"id"`
	Ticket string    `json:"ticket"`
	Handle string    `json:"handle,omitempty"`
	Sender Sender    `json:"sender"`
	At     time.Time `json:"at"`
}

// LinkAsked is somebody on a channel asking to be linked as the operator.
type LinkAsked struct {
	ID     string    `json:"id"`
	Sender Sender    `json:"sender"`
	At     time.Time `json:"at"`
}

// Code is a code a person typed on a channel, asked as a proof: never in an event, never kept.
type Code struct {
	Sender  Sender `json:"sender"`
	Code    string `json:"code"`
	Purpose string `json:"purpose"`
}

// ProofAnswer is the router's answer to a proof: whether it was taken, and words to say to the person.
type ProofAnswer struct {
	Accepted bool   `json:"accepted"`
	Words    string `json:"words"`
}