// Package mqtt is the Control Service's link to the broker (AGENTS.md §10
// rules 5–6, §11 Phase 3; TRANSPORT_DESIGN.md).
//
// The broker is transport only. This package publishes each device's desired
// state, retained, on restrict/<device>/config, and consumes the reports that
// devices write back. SQLite stays the source of truth (SYSTEM_MAP.md): nothing
// here is authoritative, and a report is handed straight to the store.
//
// Topics (TRANSPORT_DESIGN.md "Topic design"):
//
//	restrict/<device>/config     service → device, retained
//	restrict/<device>/status     device → service, retained (presence)
//	restrict/<device>/telemetry  device → service, not retained
//
// "config" keeps the exact topic the device table already stores, so a device's
// identity never changes when it is renamed.
package mqtt

import (
	"encoding/json"
	"fmt"
	"strings"
	"time"

	"gitea.lab.audasmedia.com.au/sam/internet_use_control/internal/store"
)

// TopicPrefix is the first topic level for every message this service touches.
const TopicPrefix = "restrict"

// Topic suffixes, appended to "restrict/<device>".
const (
	SuffixConfig    = "/config"
	SuffixStatus    = "/status"
	SuffixTelemetry = "/telemetry"
)

// StatusSubscription and TelemetrySubscription are the wildcard topics the
// Control Service reads. A device may write only its own status and telemetry
// (AGENTS.md §10 rule 6).
const (
	StatusSubscription    = TopicPrefix + "/+/status"
	TelemetrySubscription = TopicPrefix + "/+/telemetry"
)

// StatusTopic returns the status topic for a device's config topic.
func StatusTopic(configTopic string) string {
	return withSuffix(configTopic, SuffixStatus)
}

// TelemetryTopic returns the telemetry topic for a device's config topic.
func TelemetryTopic(configTopic string) string {
	return withSuffix(configTopic, SuffixTelemetry)
}

func withSuffix(configTopic, suffix string) string {
	return strings.TrimSuffix(configTopic, SuffixConfig) + suffix
}

// deviceFromTopic turns "restrict/harry_phone_2/status" back into the config
// topic "restrict/harry_phone_2/config" so the store can find the device.
func deviceFromTopic(topic, suffix string) (string, bool) {
	if !strings.HasPrefix(topic, TopicPrefix+"/") || !strings.HasSuffix(topic, suffix) {
		return "", false
	}
	base := strings.TrimSuffix(topic, suffix)
	if strings.Count(base, "/") != 1 || len(base) <= len(TopicPrefix)+1 {
		return "", false
	}
	return base + SuffixConfig, true
}

// Config is the desired state for one device. It is published retained on
// restrict/<device>/config: a device that reconnects is configured at once,
// with no poll and no waiting (TRANSPORT_DESIGN.md).
//
// The shape is versioned with "v" and is consumed by the kids' clients in
// Phases 4 and 5. Add fields; do not repurpose them.
type Config struct {
	V        int        `json:"v"`
	DeviceID int64      `json:"device_id"`
	Name     string     `json:"name"`
	Platform string     `json:"platform"`
	Locked   bool       `json:"locked"`
	Until    *time.Time `json:"until"`
	Allow    []string   `json:"allow"`
	Block    []string   `json:"block"`
	// Reason is why the device is locked: "schedule" for an active weekly
	// window, "manual" for a lock from the dashboard or the admin API. It is
	// omitted when the device is not locked. It is additive (Phase 6), so v
	// stays 1.
	Reason string `json:"reason,omitempty"`
	// GrantUntil is set when a time-limited exemption is active (Phase 8): the
	// device is unlocked and must not re-lock before this instant. It is omitted
	// when there is no grant. Additive, so v stays 1.
	GrantUntil *time.Time `json:"grant_until,omitempty"`

	GeneratedAt time.Time `json:"generated_at"`
}

// ConfigVersion is the current schema version of Config.
const ConfigVersion = 1

// Marshal renders the payload. Lists are always present, never null, so a
// client can parse without null checks.
func (c Config) Marshal() ([]byte, error) {
	if c.Allow == nil {
		c.Allow = []string{}
	}
	if c.Block == nil {
		c.Block = []string{}
	}
	b, err := json.Marshal(c)
	if err != nil {
		return nil, fmt.Errorf("marshal config: %w", err)
	}
	return b, nil
}

// Status is a presence report from a device.
//
// The device publishes a retained {"online": true} when it comes up and
// registers the will {"online": false} on the same topic, so the broker
// publishes "offline" the moment the connection drops without a clean
// goodbye. That is the whole of presence detection (FR-6).
type Status struct {
	Online *bool  `json:"online"`
	App    string `json:"app"`
	Locked *bool  `json:"locked"`
	At     string `json:"at"`
}

// ParseStatus reads a status payload. A report with no "online" field means the
// device is talking, so it counts as online.
func ParseStatus(payload []byte) (Status, error) {
	var st Status
	if err := json.Unmarshal(payload, &st); err != nil {
		return Status{}, fmt.Errorf("parse status: %w", err)
	}
	if len(payload) == 0 {
		return Status{}, fmt.Errorf("parse status: empty payload")
	}
	return st, nil
}

// IsOnline reports the presence the payload asserts.
func (s Status) IsOnline() bool { return s.Online == nil || *s.Online }

// At parses the report timestamp, falling back to the current time.
func (s Status) Timestamp(now time.Time) time.Time {
	if s.At == "" {
		return now
	}
	for _, layout := range []string{time.RFC3339, time.RFC3339Nano} {
		if t, err := time.Parse(layout, s.At); err == nil {
			return t
		}
	}
	return now
}

// UsageEntry is one app or domain total.
type UsageEntry struct {
	Name    string `json:"name"`
	Seconds int    `json:"seconds"`
}

// Telemetry is a rolling daily usage report from a device. Devices report
// totals for the day, not deltas, so a repeated report replaces the row
// (migration 002).
//
// Two shapes are accepted: the list form
//
//	{"day":"2026-10-13","apps":[{"name":"com.spotify.music","seconds":600}],
//	 "domains":[{"name":"youtube.com","seconds":120}]}
//
// and the flat single-row form
//
//	{"app":"com.spotify.music","seconds":600}
type Telemetry struct {
	Day     string       `json:"day"`
	Apps    []UsageEntry `json:"apps"`
	Domains []UsageEntry `json:"domains"`
	App     string       `json:"app"`
	Domain  string       `json:"domain"`
	Seconds int          `json:"seconds"`
}

// ParseTelemetry reads a telemetry payload.
func ParseTelemetry(payload []byte) (Telemetry, error) {
	var t Telemetry
	if len(payload) == 0 {
		return Telemetry{}, fmt.Errorf("parse telemetry: empty payload")
	}
	if err := json.Unmarshal(payload, &t); err != nil {
		return Telemetry{}, fmt.Errorf("parse telemetry: %w", err)
	}
	return t, nil
}

// DayOrDefault returns the day the report belongs to, in the given location. A
// device may send its own local day; anything that is not YYYY-MM-DD is
// ignored and today's date is used instead.
func (t Telemetry) DayOrDefault(now time.Time) string {
	if t.Day != "" {
		if d, err := time.Parse("2006-01-02", t.Day); err == nil {
			return d.Format("2006-01-02")
		}
	}
	return now.Format("2006-01-02")
}

// Rows flattens the payload into telemetry rows. The app and the domain are
// kept in separate columns; a row with neither is dropped.
func (t Telemetry) Rows() []store.TelemetryEntry {
	out := make([]store.TelemetryEntry, 0, len(t.Apps)+len(t.Domains)+1)
	for _, e := range t.Apps {
		if e.Name == "" || e.Seconds < 0 {
			continue
		}
		out = append(out, store.TelemetryEntry{App: e.Name, Seconds: e.Seconds})
	}
	for _, e := range t.Domains {
		if e.Name == "" || e.Seconds < 0 {
			continue
		}
		out = append(out, store.TelemetryEntry{Domain: e.Name, Seconds: e.Seconds})
	}
	if (t.App != "" || t.Domain != "") && t.Seconds >= 0 {
		out = append(out, store.TelemetryEntry{App: t.App, Domain: t.Domain, Seconds: t.Seconds})
	}
	return out
}