// Package config loads the Compass/NHS service configuration from the process
// environment. Every secret comes from the environment (environment.d); nothing
// is compiled into the binary and nothing secret is read from a committed file.
package config

import (
	"errors"
	"fmt"
	"log/slog"
	"os"
	"strconv"
	"strings"
	"time"
	// Embed the IANA time zone database so SCHOOL_TIMEZONE resolves even in a
	// container without tzdata.
	_ "time/tzdata"
)

// Config is the fully resolved runtime configuration.
type Config struct {
	// Addr is the listen address, for example ":8792".
	Addr string
	// DBPath is the SQLite database file, for example "/data/school.db".
	DBPath string
	// SessionSecret signs the session cookie. Required, >= 16 bytes.
	SessionSecret []byte
	// AdminUsername is the single dashboard login name (Sam).
	AdminUsername string
	// AdminPassword is the plaintext password. Optional if AdminPasswordHash is set.
	AdminPassword string
	// AdminPasswordHash is a bcrypt hash. Optional if AdminPassword is set.
	AdminPasswordHash string
	// CookieSecure sets the Secure attribute on cookies. Keep true behind HTTPS.
	CookieSecure bool
	// SessionTTL is how long a session cookie stays valid.
	SessionTTL time.Duration
	// LogLevel is the slog level.
	LogLevel slog.Level
	// AppEnv is a label such as "production" or "development".
	AppEnv string
	// Version is injected at build time.
	Version string
	// Location is the family timezone. Due dates and briefs are wall-clock, so
	// this must be the family's zone, not the container default of UTC.
	Location *time.Location
	// Calendar is the Home Assistant calendar target for important school
	// events (AGENTS.md §4 FR-8).
	Calendar CalendarConfig
}

// CalendarConfig points at Sam's Home Assistant calendar. Every value comes
// from the environment (environment.d); the token never reaches git, the
// database or the logs (AGENTS.md §10 rule 3, AUD-110).
//
// Environment variables:
//
//	SCHOOL_HA_URL                base URL, for example http://192.168.20.30:8123
//	SCHOOL_HA_TOKEN              long-lived access token (secret)
//	SCHOOL_HA_CALENDAR_ENTITY    calendar entity id, for example calendar.school
//	SCHOOL_HA_INSECURE           true to skip TLS verification (internal CA)
//	SCHOOL_HA_TIMEOUT            per-request timeout, default 20s
//
// Calendar writing stays off until all three of URL, token and entity are set,
// so the service still starts before the calendar is configured.
type CalendarConfig struct {
	BaseURL  string
	Token    string
	EntityID string
	Insecure bool
	Timeout  time.Duration
}

// Enabled reports whether the calendar target is fully configured.
func (c CalendarConfig) Enabled() bool {
	return c.BaseURL != "" && c.Token != "" && c.EntityID != ""
}

// Missing lists the environment variables that are still unset, in the order
// the operator should set them. An empty result means the target is usable.
func (c CalendarConfig) Missing() []string {
	var out []string
	if c.BaseURL == "" {
		out = append(out, "SCHOOL_HA_URL")
	}
	if c.Token == "" {
		out = append(out, "SCHOOL_HA_TOKEN")
	}
	if c.EntityID == "" {
		out = append(out, "SCHOOL_HA_CALENDAR_ENTITY")
	}
	return out
}

// DefaultTimezone is the family timezone used when SCHOOL_TIMEZONE is unset.
const DefaultTimezone = "Australia/Sydney"

// Load reads and validates the configuration.
func Load() (*Config, error) {
	cfg := &Config{
		Addr:              env("SCHOOL_ADDR", ":8792"),
		DBPath:            env("SCHOOL_DB_PATH", "/data/school.db"),
		AdminUsername:     env("SCHOOL_ADMIN_USERNAME", "sam"),
		AdminPassword:     os.Getenv("SCHOOL_ADMIN_PASSWORD"),
		AdminPasswordHash: os.Getenv("SCHOOL_ADMIN_PASSWORD_HASH"),
		CookieSecure:      envBool("SCHOOL_COOKIE_SECURE", true),
		AppEnv:            env("SCHOOL_APP_ENV", "production"),
	}

	secret := os.Getenv("SCHOOL_SESSION_SECRET")
	if len(secret) < 16 {
		return nil, errors.New("SCHOOL_SESSION_SECRET must be set and at least 16 characters")
	}
	cfg.SessionSecret = []byte(secret)

	if cfg.AdminPassword == "" && cfg.AdminPasswordHash == "" {
		return nil, errors.New("set SCHOOL_ADMIN_PASSWORD or SCHOOL_ADMIN_PASSWORD_HASH")
	}
	if cfg.AdminUsername == "" {
		return nil, errors.New("SCHOOL_ADMIN_USERNAME must not be empty")
	}

	ttl, err := time.ParseDuration(env("SCHOOL_SESSION_TTL", "12h"))
	if err != nil {
		return nil, fmt.Errorf("SCHOOL_SESSION_TTL: %w", err)
	}
	cfg.SessionTTL = ttl

	lvl, err := parseLevel(env("SCHOOL_LOG_LEVEL", "info"))
	if err != nil {
		return nil, err
	}
	cfg.LogLevel = lvl

	loc, err := time.LoadLocation(env("SCHOOL_TIMEZONE", DefaultTimezone))
	if err != nil {
		return nil, fmt.Errorf("SCHOOL_TIMEZONE: %w", err)
	}
	cfg.Location = loc
	cfg.Calendar = loadCalendar()

	return cfg, nil
}

// DBConfig is the minimum a database-only command needs. The parse subcommand
// opens the same SQLite file as the service without requiring the service's
// session secret or login.
type DBConfig struct {
	DBPath   string
	Location *time.Location
	Calendar CalendarConfig
}

// LoadDB reads the database path and the family timezone only.
func LoadDB() (*DBConfig, error) {
	loc, err := time.LoadLocation(env("SCHOOL_TIMEZONE", DefaultTimezone))
	if err != nil {
		return nil, fmt.Errorf("SCHOOL_TIMEZONE: %w", err)
	}
	return &DBConfig{
		DBPath:   env("SCHOOL_DB_PATH", "/data/school.db"),
		Location: loc,
		Calendar: loadCalendar(),
	}, nil
}

// loadCalendar reads the Home Assistant calendar target. It never fails: an
// empty value simply leaves the target disabled, so the service boots before
// the calendar is configured and the calendar commands fail loudly instead.
func loadCalendar() CalendarConfig {
	timeout := 20 * time.Second
	if v := strings.TrimSpace(os.Getenv("SCHOOL_HA_TIMEOUT")); v != "" {
		if d, err := time.ParseDuration(v); err == nil && d > 0 {
			timeout = d
		}
	}
	return CalendarConfig{
		BaseURL:  strings.TrimRight(strings.TrimSpace(os.Getenv("SCHOOL_HA_URL")), "/"),
		Token:    strings.TrimSpace(os.Getenv("SCHOOL_HA_TOKEN")),
		EntityID: strings.TrimSpace(os.Getenv("SCHOOL_HA_CALENDAR_ENTITY")),
		Insecure: envBool("SCHOOL_HA_INSECURE", false),
		Timeout:  timeout,
	}
}

func env(key, fallback string) string {
	if v := strings.TrimSpace(os.Getenv(key)); v != "" {
		return v
	}
	return fallback
}

func envBool(key string, fallback bool) bool {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	b, err := strconv.ParseBool(v)
	if err != nil {
		return fallback
	}
	return b
}

func parseLevel(s string) (slog.Level, error) {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "debug":
		return slog.LevelDebug, nil
	case "info", "":
		return slog.LevelInfo, nil
	case "warn", "warning":
		return slog.LevelWarn, nil
	case "error":
		return slog.LevelError, nil
	default:
		return 0, fmt.Errorf("SCHOOL_LOG_LEVEL: unknown level %q", s)
	}
}