package service

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"

	"github.com/google/uuid"

	"apskel-pos-be/internal/appcontext"
	"apskel-pos-be/internal/constants"
	"apskel-pos-be/internal/contract"
	"apskel-pos-be/internal/models"
	"apskel-pos-be/internal/processor"
	"apskel-pos-be/internal/repository"
)

// LoyaltySettingsService is the dashboard's access to loyalty settings
// (docs/prd-point-coin.md F1, F2). Every call is scoped to the caller's organization.
type LoyaltySettingsService interface {
	GetOutletSettings(ctx context.Context, apctx *appcontext.ContextInfo, outletID uuid.UUID) *contract.Response
	// UpdateOutletSettings applies a JSON body on top of the current settings: fields
	// left out keep their value, and null clears an optional limit.
	UpdateOutletSettings(ctx context.Context, apctx *appcontext.ContextInfo, outletID uuid.UUID, body []byte) *contract.Response

	GetOrganizationSettings(ctx context.Context, apctx *appcontext.ContextInfo) *contract.Response
	// UpdateOrganizationSettings applies a JSON body like UpdateOutletSettings. With
	// dryRun it only validates and reports what would change and its impact.
	UpdateOrganizationSettings(ctx context.Context, apctx *appcontext.ContextInfo, body []byte, dryRun bool) *contract.Response
	// ListHistory returns the settings history of the organization, or of one outlet.
	ListHistory(ctx context.Context, apctx *appcontext.ContextInfo, outletID *uuid.UUID, page, limit int) *contract.Response
}

type outstandingBalanceReader interface {
	OrganizationOutstanding(ctx context.Context, organizationID uuid.UUID) (points, coins int64, err error)
}

type LoyaltySettingsServiceImpl struct {
	settings    *processor.LoyaltySettingsProcessor
	outstanding outstandingBalanceReader
}

func NewLoyaltySettingsService(settings *processor.LoyaltySettingsProcessor, outstanding outstandingBalanceReader) *LoyaltySettingsServiceImpl {
	return &LoyaltySettingsServiceImpl{settings: settings, outstanding: outstanding}
}

func (s *LoyaltySettingsServiceImpl) GetOutletSettings(ctx context.Context, apctx *appcontext.ContextInfo, outletID uuid.UUID) *contract.Response {
	current, err := s.settings.OutletForOrganization(ctx, apctx.OrganizationID, outletID)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	view, err := s.outletView(ctx, apctx.OrganizationID, outletID, *current, nil)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	return contract.BuildSuccessResponse(view)
}

// outletSettingsInput is what PUT accepts: the settings, plus the read-only fields of
// the GET response so a client can send back what it received. Those are ignored.
type outletSettingsInput struct {
	*models.OutletLoyaltySettings
	OutletID             json.RawMessage `json:"outlet_id"`
	PointValue           json.RawMessage `json:"point_value"`
	PointCashbackPercent json.RawMessage `json:"point_cashback_percent"`
	Changes              json.RawMessage `json:"changes"`
}

func (s *LoyaltySettingsServiceImpl) UpdateOutletSettings(ctx context.Context, apctx *appcontext.ContextInfo, outletID uuid.UUID, body []byte) *contract.Response {
	current, err := s.settings.OutletForOrganization(ctx, apctx.OrganizationID, outletID)
	if err != nil {
		return loyaltyErrorResponse(err)
	}

	next := *current
	decoder := json.NewDecoder(bytes.NewReader(body))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&outletSettingsInput{OutletLoyaltySettings: &next}); err != nil {
		return contract.BuildErrorResponse([]*contract.ResponseError{
			contract.NewResponseError(constants.MalformedFieldErrorCode, constants.LoyaltySettingsServiceEntity, fmt.Sprintf("invalid request body: %v", err)),
		})
	}

	changes, err := s.settings.UpdateOutlet(ctx, apctx.OrganizationID, outletID, apctx.UserID, next)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	saved, err := s.settings.Outlet(ctx, outletID)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	view, err := s.outletView(ctx, apctx.OrganizationID, outletID, *saved, changes)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	return contract.BuildSuccessResponse(view)
}

func (s *LoyaltySettingsServiceImpl) outletView(ctx context.Context, organizationID, outletID uuid.UUID, settings models.OutletLoyaltySettings, changes []models.LoyaltySettingChange) (*models.OutletLoyaltySettingsView, error) {
	pointValue, err := s.settings.PointValue(ctx, organizationID)
	if err != nil {
		return nil, err
	}
	if changes == nil {
		changes = []models.LoyaltySettingChange{}
	}
	return &models.OutletLoyaltySettingsView{
		OutletID:              outletID,
		OutletLoyaltySettings: settings,
		PointValue:            pointValue,
		PointCashbackPercent:  models.LoyaltyCashbackPercent(settings.Point.EarnValue, pointValue, settings.Point.EarnPerAmount),
		Changes:               changes,
	}, nil
}

func loyaltyErrorResponse(err error) *contract.Response {
	code, message := constants.InternalServerErrorCode, err.Error()
	switch {
	case errors.Is(err, repository.ErrLoyaltyOutletNotFound):
		code, message = constants.NotFoundErrorCode, "outlet not found"
	case errors.Is(err, processor.ErrInvalidLoyaltySettings):
		code = constants.ValidationErrorCode
	}
	return contract.BuildErrorResponse([]*contract.ResponseError{
		contract.NewResponseError(code, constants.LoyaltySettingsServiceEntity, message),
	})
}

func (s *LoyaltySettingsServiceImpl) GetOrganizationSettings(ctx context.Context, apctx *appcontext.ContextInfo) *contract.Response {
	current, err := s.settings.Organization(ctx, apctx.OrganizationID)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	view, err := s.organizationView(ctx, apctx.OrganizationID, *current, *current, nil, false)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	return contract.BuildSuccessResponse(view)
}

// organizationSettingsInput is what PUT accepts: the settings plus the read-only fields
// of the GET response, which are ignored.
type organizationSettingsInput struct {
	*models.OrganizationLoyaltySettings
	Impact  json.RawMessage `json:"impact"`
	Changes json.RawMessage `json:"changes"`
	DryRun  json.RawMessage `json:"dry_run"`
}

func (s *LoyaltySettingsServiceImpl) UpdateOrganizationSettings(ctx context.Context, apctx *appcontext.ContextInfo, body []byte, dryRun bool) *contract.Response {
	current, err := s.settings.Organization(ctx, apctx.OrganizationID)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	next := *current
	decoder := json.NewDecoder(bytes.NewReader(body))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&organizationSettingsInput{OrganizationLoyaltySettings: &next}); err != nil {
		return contract.BuildErrorResponse([]*contract.ResponseError{
			contract.NewResponseError(constants.MalformedFieldErrorCode, constants.LoyaltySettingsServiceEntity, fmt.Sprintf("invalid request body: %v", err)),
		})
	}

	var changes []models.LoyaltySettingChange
	if dryRun {
		changes, err = s.settings.PreviewOrganization(ctx, apctx.OrganizationID, next)
	} else {
		changes, err = s.settings.UpdateOrganization(ctx, apctx.OrganizationID, apctx.UserID, next)
	}
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	after := next
	if !dryRun {
		saved, err := s.settings.Organization(ctx, apctx.OrganizationID)
		if err != nil {
			return loyaltyErrorResponse(err)
		}
		after = *saved
	}
	view, err := s.organizationView(ctx, apctx.OrganizationID, *current, after, changes, dryRun)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	return contract.BuildSuccessResponse(view)
}

func (s *LoyaltySettingsServiceImpl) ListHistory(ctx context.Context, apctx *appcontext.ContextInfo, outletID *uuid.UUID, page, limit int) *contract.Response {
	history, err := s.settings.ListChanges(ctx, apctx.OrganizationID, outletID, page, limit)
	if err != nil {
		return loyaltyErrorResponse(err)
	}
	return contract.BuildSuccessResponse(history)
}

func (s *LoyaltySettingsServiceImpl) organizationView(ctx context.Context, organizationID uuid.UUID, before, after models.OrganizationLoyaltySettings, changes []models.LoyaltySettingChange, dryRun bool) (*models.OrganizationLoyaltySettingsView, error) {
	points, coins, err := s.outstanding.OrganizationOutstanding(ctx, organizationID)
	if err != nil {
		return nil, err
	}
	if changes == nil {
		changes = []models.LoyaltySettingChange{}
	}
	return &models.OrganizationLoyaltySettingsView{
		OrganizationLoyaltySettings: after,
		Impact:                      models.NewLoyaltySettingsImpact(points, coins, before, after),
		Changes:                     changes,
		DryRun:                      dryRun,
	}, nil
}