// Package service is pansy's business-logic seam: all permission checks and
// invariants live here rather than in the HTTP handlers. Resource operations
// take (ctx, actor, args) so every rule is enforced regardless of caller; the
// auth operations here are the exception — they establish the actor, so they
// take credentials rather than one. REST handlers (internal/api) and, later,
// agent tools (internal/agent) are thin adapters over these methods, so both
// inherit the same rules. This file holds the shared plumbing; feature methods
// live alongside it (auth.go, and gardens/objects/… in later issues).
package service

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"time"

	"gitea.stevedudenhoeffer.com/steve/pansy/internal/config"
	"gitea.stevedudenhoeffer.com/steve/pansy/internal/store"
)

// timeLayout is the ISO-8601 UTC format used for every full timestamp pansy
// stores (created_at/updated_at/expires_at). It matches the schema's
// strftime('%Y-%m-%dT%H:%M:%SZ') so string comparison (e.g. session expiry) is
// equivalent to time comparison. Date-only fields (planting planted_at/
// removed_at) use dateLayout instead.
const timeLayout = "2006-01-02T15:04:05Z"

// sessionTTL is how long a session lives from its last use (sliding expiry).
const sessionTTL = 30 * 24 * time.Hour

// Service holds the dependencies shared by every operation.
type Service struct {
	store *store.DB
	cfg   *config.Config
	// now is the clock, injectable so tests can advance time (session expiry).
	now func() time.Time
	// dummyHash is a valid argon2id hash Login verifies against when an email is
	// unknown, so response time doesn't reveal whether an account exists. It is
	// produced by timingHash (fixed salt, no RNG) so it is always present — an
	// empty one would silently re-open account enumeration.
	dummyHash string
}

// New constructs a Service.
func New(st *store.DB, cfg *config.Config) *Service {
	return &Service{
		store:     st,
		cfg:       cfg,
		now:       time.Now,
		dummyHash: timingHash(),
	}
}

// formatTime renders a time as pansy's canonical UTC string.
func formatTime(t time.Time) string { return t.UTC().Format(timeLayout) }

// parseTime parses a canonical pansy timestamp.
func parseTime(s string) (time.Time, error) { return time.Parse(timeLayout, s) }

// newSessionToken returns a fresh URL-safe random bearer token (32 bytes of
// entropy). The raw token goes in the cookie; only its hash is persisted.
func newSessionToken() (string, error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", fmt.Errorf("service: generate session token: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(b), nil
}

// hashToken maps a raw bearer token to the hex sha256 stored as the session's
// primary key.
func hashToken(raw string) string {
	sum := sha256.Sum256([]byte(raw))
	return hex.EncodeToString(sum[:])
}