package service

import (
	"context"
	"errors"
	"fmt"

	"github.com/google/uuid"

	"github.com/vasyakrg/dns-autoresolver/internal/crypto"
	"github.com/vasyakrg/dns-autoresolver/internal/diff"
	"github.com/vasyakrg/dns-autoresolver/internal/model"
	"github.com/vasyakrg/dns-autoresolver/internal/provider"
	"github.com/vasyakrg/dns-autoresolver/internal/provider/registry"
	"github.com/vasyakrg/dns-autoresolver/internal/store/dto"
	"github.com/vasyakrg/dns-autoresolver/internal/tmpl"
)

// ErrProviderUnavailable marks failures that happened while talking to the
// DNS provider itself (network, auth, rate limit, ...), as opposed to
// failures resolving the domain/zone locally (not found, bad credentials
// stored, unknown provider name). Callers use errors.Is against this to
// pick 502 vs 404 without leaking provider error details as "not found".
var ErrProviderUnavailable = errors.New("service: provider unavailable")

// DomainRef is the minimal data the service needs about a domain.
type DomainRef struct {
	ZoneID    string
	ZoneName  string
	Provider  string
	SecretEnc string
	Template  dto.TemplateDoc
}

// ZoneRef is the provider-access subset of a domain, without a template —
// enough to read a zone's live records.
type ZoneRef struct {
	ZoneID    string
	Provider  string
	SecretEnc string
}

type Loader interface {
	LoadDomain(ctx context.Context, projectID, domainID uuid.UUID) (DomainRef, error)
	LoadZone(ctx context.Context, projectID, domainID uuid.UUID) (ZoneRef, error)
}

type Recorder interface {
	SaveCheckRun(ctx context.Context, domainID uuid.UUID, cs diff.Changeset) error
}

type ApplyRequest struct {
	Updates []string // record keys (RecordDiff.Key) to add/update
	Prunes  []string // record keys to delete
}

type DomainService struct {
	loader Loader
	rec    Recorder
	reg    *registry.Registry
	cipher *crypto.Cipher
}

func New(loader Loader, rec Recorder, reg *registry.Registry, cipher *crypto.Cipher) *DomainService {
	return &DomainService{loader: loader, rec: rec, reg: reg, cipher: cipher}
}

// resolve loads the domain, its provider and decrypted credentials, and computes the diff.
// projectID scopes the lookup so a domainID belonging to another tenant's
// project can never be resolved here (closes IDOR).
func (s *DomainService) resolve(ctx context.Context, projectID, domainID uuid.UUID) (provider.Provider, provider.Credentials, DomainRef, diff.Changeset, error) {
	ref, err := s.loader.LoadDomain(ctx, projectID, domainID)
	if err != nil {
		return nil, provider.Credentials{}, ref, diff.Changeset{}, err
	}
	p, err := s.reg.ByName(ref.Provider)
	if err != nil {
		return nil, provider.Credentials{}, ref, diff.Changeset{}, err
	}
	secret, err := s.cipher.Decrypt(ref.SecretEnc)
	if err != nil {
		return nil, provider.Credentials{}, ref, diff.Changeset{}, err
	}
	creds := provider.Credentials{Secret: string(secret)}
	actual, err := p.GetRecords(ctx, creds, ref.ZoneID)
	if err != nil {
		return nil, provider.Credentials{}, ref, diff.Changeset{}, err
	}
	cs := diff.Diff(tmpl.Materialize(ref.Template, ref.ZoneName), actual)
	return p, creds, ref, cs, nil
}

// Check computes and records the diff between template and zone.
func (s *DomainService) Check(ctx context.Context, projectID, domainID uuid.UUID) (diff.Changeset, error) {
	_, _, _, cs, err := s.resolve(ctx, projectID, domainID)
	if err != nil {
		return diff.Changeset{}, err
	}
	if err := s.rec.SaveCheckRun(ctx, domainID, cs); err != nil {
		return diff.Changeset{}, err
	}
	return cs, nil
}

// ZoneRecords reads a zone's current records straight from the provider,
// with no diff and no template required. Used for read-only zone viewing and
// as the source for a snapshot template.
func (s *DomainService) ZoneRecords(ctx context.Context, projectID, domainID uuid.UUID) ([]model.Record, error) {
	ref, err := s.loader.LoadZone(ctx, projectID, domainID)
	if err != nil {
		return nil, err
	}
	p, err := s.reg.ByName(ref.Provider)
	if err != nil {
		return nil, err
	}
	secret, err := s.cipher.Decrypt(ref.SecretEnc)
	if err != nil {
		return nil, err
	}
	recs, err := p.GetRecords(ctx, provider.Credentials{Secret: string(secret)}, ref.ZoneID)
	if err != nil {
		// Only a failure of the provider call itself is "provider unavailable" —
		// LoadZone/ByName/Decrypt errors above are local resolution failures
		// (e.g. domain not found) and must not be conflated with it.
		return nil, fmt.Errorf("%w: %v", ErrProviderUnavailable, err)
	}
	return recs, nil
}

// Apply applies exactly the diffs whose keys are selected in req.Updates and
// req.Prunes. Selected prunes are added to the applied set BEFORE selected
// updates: deletes first is an invariant, not an option — the provider
// rejects an Add/Update whose name still has a conflicting record (e.g. a
// CNAME cannot be created while an A on the same name exists), so pruning the
// old records before applying updates avoids that.
func (s *DomainService) Apply(ctx context.Context, projectID, domainID uuid.UUID, req ApplyRequest) (diff.Changeset, error) {
	p, creds, ref, cs, err := s.resolve(ctx, projectID, domainID)
	if err != nil {
		return diff.Changeset{}, err
	}
	selPrunes := toSet(req.Prunes)
	selUpdates := toSet(req.Updates)
	var toApply []diff.RecordDiff
	for _, d := range cs.Prunes() {
		if selPrunes[d.Key()] {
			toApply = append(toApply, d)
		}
	}
	for _, d := range cs.Updates() {
		if selUpdates[d.Key()] {
			toApply = append(toApply, d)
		}
	}
	applied := diff.Changeset{Diffs: toApply}
	if len(toApply) > 0 {
		if err := p.ApplyChanges(ctx, creds, ref.ZoneID, applied); err != nil {
			return diff.Changeset{}, err
		}
	}
	return applied, nil
}

func toSet(keys []string) map[string]bool {
	m := make(map[string]bool, len(keys))
	for _, k := range keys {
		m[k] = true
	}
	return m
}