package items

import (
	"context"
	"strings"
)

// Field length limits enforced on input.
const (
	maxTitleLen       = 200
	maxDescriptionLen = 2000
)

// Service holds the business rules for items. It depends only on the
// Repository interface; main wires the Bun implementation in.
type Service struct {
	repo Repository
}

// NewService returns a Service over the given repository.
func NewService(repo Repository) *Service {
	return &Service{repo: repo}
}

// CreateInput is the request body for creating an item.
type CreateInput struct {
	Title       string `json:"title"`
	Description string `json:"description"`
	Status      Status `json:"status"`
}

// UpdateInput patches only provided fields (nil = leave untouched), which
// is why every field is a pointer.
type UpdateInput struct {
	Title       *string `json:"title"`
	Description *string `json:"description"`
	Status      *Status `json:"status"`
}

// List validates the filter and delegates to the repository.
func (s *Service) List(ctx context.Context, f Filter) ([]Item, error) {
	f, err := normalizeFilter(f)
	if err != nil {
		return nil, err
	}
	return s.repo.List(ctx, f)
}

// Get returns one item.
func (s *Service) Get(ctx context.Context, id int64) (Item, error) {
	return s.repo.Get(ctx, id)
}

// Create validates input and stores a new item.
func (s *Service) Create(ctx context.Context, in CreateInput) (Item, error) {
	item := Item{
		Title:       strings.TrimSpace(in.Title),
		Description: strings.TrimSpace(in.Description),
	}
	if item.Title == "" {
		return Item{}, &ValidationError{Field: "title", Reason: "required"}
	}
	if len(item.Title) > maxTitleLen {
		return Item{}, &ValidationError{Field: "title", Reason: "must be at most 200 characters"}
	}
	if len(item.Description) > maxDescriptionLen {
		return Item{}, &ValidationError{Field: "description", Reason: "must be at most 2000 characters"}
	}

	switch in.Status {
	case "":
		item.Status = StatusActive
	case StatusActive, StatusArchived:
		item.Status = in.Status
	default:
		return Item{}, &ValidationError{Field: "status", Reason: "must be active or archived"}
	}

	if err := s.repo.Create(ctx, &item); err != nil {
		return Item{}, err
	}
	return item, nil
}

// Update applies a partial patch to an existing item.
func (s *Service) Update(ctx context.Context, id int64, in UpdateInput) (Item, error) {
	if in.Title == nil && in.Description == nil && in.Status == nil {
		return Item{}, &ValidationError{Field: "body", Reason: "at least one field must be set"}
	}

	item, err := s.repo.Get(ctx, id)
	if err != nil {
		return Item{}, err
	}

	if in.Title != nil {
		item.Title = strings.TrimSpace(*in.Title)
		if item.Title == "" {
			return Item{}, &ValidationError{Field: "title", Reason: "required"}
		}
		if len(item.Title) > maxTitleLen {
			return Item{}, &ValidationError{Field: "title", Reason: "must be at most 200 characters"}
		}
	}
	if in.Description != nil {
		item.Description = strings.TrimSpace(*in.Description)
		if len(item.Description) > maxDescriptionLen {
			return Item{}, &ValidationError{Field: "description", Reason: "must be at most 2000 characters"}
		}
	}
	if in.Status != nil {
		if !in.Status.Valid() {
			return Item{}, &ValidationError{Field: "status", Reason: "must be active or archived"}
		}
		item.Status = *in.Status
	}

	if err := s.repo.Update(ctx, &item); err != nil {
		return Item{}, err
	}
	return item, nil
}

// Delete removes an item.
func (s *Service) Delete(ctx context.Context, id int64) error {
	return s.repo.Delete(ctx, id)
}

// normalizeFilter applies paging defaults and validates the status filter.
func normalizeFilter(f Filter) (Filter, error) {
	switch f.Status {
	case "":
	case StatusActive, StatusArchived:
	default:
		return Filter{}, &ValidationError{Field: "status", Reason: "must be active or archived"}
	}
	if f.Limit <= 0 {
		f.Limit = DefaultLimit
	}
	if f.Limit > MaxLimit {
		f.Limit = MaxLimit
	}
	if f.Offset < 0 {
		f.Offset = 0
	}
	return f, nil
}