package identity

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"strings"
	"time"

	customer "git.sendico.io/tech/sxchnge/product/customers/model"
	merrors "git.sendico.io/tech/sxchnge/shared/errors"
	"go.uber.org/zap"
)

// Profile holds unverified customer assertions. Email and customer reference are
// always supplied by the authenticated backend, never accepted from the browser.
type Profile struct {
	FullName         string
	DateOfBirth      string
	ResidenceCountry string
}

func (p Profile) Validate() error {
	birth, err := time.Parse("2006-01-02", p.DateOfBirth)
	if strings.TrimSpace(p.FullName) == "" || len(p.FullName) > 800 || err != nil || !birth.Before(time.Now()) || len(p.ResidenceCountry) != 2 || p.ResidenceCountry[0] < 'A' || p.ResidenceCountry[0] > 'Z' || p.ResidenceCountry[1] < 'A' || p.ResidenceCountry[1] > 'Z' {
		return merrors.InvalidArgument("complete identity profile required")
	}
	return nil
}

type Verification struct {
	Status         string
	UpgradePending bool
	Reason         string
	SubmissionID   string
	Profile        Profile
}

// VerificationProvider consumes reviewed state through the platform public API.
// It cannot accept a browser-selected subject, policy profile or approval.
type VerificationProvider interface {
	Verification(context.Context, string) (Verification, error)
	SubmitVerification(context.Context, string, string, Profile, Facts, []byte, []byte) (Verification, error)
}

// Decimal amounts are transported losslessly in their currency's major unit.
// No fiat scale or illustrative client caps are applied to provider policy.
type Limit struct {
	Operation string
	Period    string
	Currency  string
	Cap       string
	Remaining string
	Used      string
	Reserved  string
}
type Limits struct {
	Tier       string
	ProfileRef string
	Entries    []Limit
}
type LimitsProvider interface {
	Limits(context.Context, string) (Limits, error)
}

func (s *Service) Limits(ctx context.Context, a *customer.Account) (Limits, error) {
	b, err := s.binding(ctx, a)
	if err != nil {
		return Limits{}, err
	}
	p, ok := s.Provider.(LimitsProvider)
	if !ok {
		return Limits{}, unavailable()
	}
	return p.Limits(ctx, b.SubjectRef)
}

func (s *Service) binding(ctx context.Context, a *customer.Account) (*Binding, error) {
	if s == nil || s.Provider == nil || s.Store == nil {
		return nil, merrors.ServiceUnavailable("identity verification unavailable")
	}
	if a == nil || a.ID.IsZero() {
		return nil, merrors.InvalidArgument("customer required")
	}
	b, err := s.Store.Get(ctx, a.ID)
	if errors.Is(err, merrors.ErrNoData) || err == nil && b.Receipt == nil {
		if err = s.Ensure(ctx, a); err != nil {
			return nil, err
		}
		b, err = s.Store.Get(ctx, a.ID)
	}
	if err != nil {
		return nil, err
	}
	if b.Namespace != s.Provider.Namespace() || b.SubjectRef == "" || b.Receipt == nil || b.Receipt.SubjectRef != b.SubjectRef {
		return nil, merrors.FailedPrecondition("identity binding requires reconciliation")
	}
	return b, nil
}

func (s *Service) Verification(ctx context.Context, a *customer.Account) (Verification, error) {
	b, err := s.binding(ctx, a)
	if err != nil {
		return Verification{}, err
	}
	provider, ok := s.Provider.(VerificationProvider)
	if !ok {
		return Verification{}, unavailable()
	}
	v, err := provider.Verification(ctx, b.SubjectRef)
	if err == nil && v.Profile.FullName == "" {
		v.Profile.FullName = a.Name
	}
	return v, err
}

func (s *Service) SubmitVerification(ctx context.Context, a *customer.Account, key string, p Profile, document, selfie []byte) (Verification, error) {
	if len(key) < 16 || len(key) > 128 {
		return Verification{}, merrors.InvalidArgument("valid idempotency key required")
	}
	if err := p.Validate(); err != nil {
		return Verification{}, err
	}
	for _, photo := range [][]byte{document, selfie} {
		if err := ValidatePhoto(photo); err != nil {
			return Verification{}, err
		}
	}
	b, err := s.binding(ctx, a)
	if err != nil {
		return Verification{}, err
	}
	provider, ok := s.Provider.(VerificationProvider)
	if !ok {
		return Verification{}, unavailable()
	}
	digest := sha256.Sum256([]byte(a.ID.Hex() + "\x00" + key))
	facts := b.Facts
	facts.Email = a.Login
	facts.CustomerRef = a.ID.Hex()
	v, err := provider.SubmitVerification(ctx, b.SubjectRef, "sxchnge:identity:"+hex.EncodeToString(digest[:]), p, facts, document, selfie)
	if err != nil {
		s.Logger.Warn("Identity proof submission incomplete", zap.String("account_ref", a.ID.Hex()))
		return Verification{}, err
	}
	s.Logger.Info("Identity proofs accepted for review", zap.String("account_ref", a.ID.Hex()), zap.String("submission_ref", v.SubmissionID))
	return v, nil
}