package collections

import (
	"bytes"
	"context"
	"fmt"

	"cosmossdk.io/collections/codec"
)

// Item is a type declaration based on Map
// with a non-existent key.
type Item[V any] Map[noKey, V]

// NewItem instantiates a new Item instance, given the value encoder of the item V.
// Name and prefix must be unique within the schema and name must match the format specified by NameRegex, or
// else this method will panic.
func NewItem[V any](
	schema *SchemaBuilder,
	prefix Prefix,
	name string,
	valueCodec codec.ValueCodec[V],
) Item[V] {
	item := (Item[V])(NewMap[noKey](schema, prefix, name, noKey{}, valueCodec))
	return item
}

// Get gets the item, if it is not set it returns an ErrNotFound error.
// If value decoding fails then an ErrEncoding is returned.
func (i Item[V]) Get(ctx context.Context) (V, error) {
	return (Map[noKey, V])(i).Get(ctx, noKey{})
}

// Set sets the item in the store. If Value encoding fails then an ErrEncoding is returned.
func (i Item[V]) Set(ctx context.Context, value V) error {
	return (Map[noKey, V])(i).Set(ctx, noKey{}, value)
}

// Has reports whether the item exists in the store or not.
// Returns an error in case encoding fails.
func (i Item[V]) Has(ctx context.Context) (bool, error) {
	return (Map[noKey, V])(i).Has(ctx, noKey{})
}

// Remove removes the item in the store.
func (i Item[V]) Remove(ctx context.Context) error {
	return (Map[noKey, V])(i).Remove(ctx, noKey{})
}

// noKey defines a KeyCodec which decodes nothing.
type noKey struct{}

func (noKey) Stringify(_ noKey) string              { return "no_key" }
func (noKey) KeyType() string                       { return "no_key" }
func (noKey) Size(_ noKey) int                      { return 0 }
func (noKey) Encode(_ []byte, _ noKey) (int, error) { return 0, nil }
func (noKey) Decode(_ []byte) (int, noKey, error)   { return 0, noKey{}, nil }
func (noKey) EncodeJSON(_ noKey) ([]byte, error)    { return []byte(`"item"`), nil }
func (noKey) DecodeJSON(b []byte) (noKey, error) {
	if !bytes.Equal(b, []byte(`"item"`)) {
		return noKey{}, fmt.Errorf("%w: invalid item json key bytes", ErrEncoding)
	}
	return noKey{}, nil
}
func (k noKey) EncodeNonTerminal(_ []byte, _ noKey) (int, error) { panic("must not be called") }
func (k noKey) DecodeNonTerminal(_ []byte) (int, noKey, error)   { panic("must not be called") }
func (k noKey) SizeNonTerminal(_ noKey) int                      { panic("must not be called") }