package ezdb

import (
	"fmt"
	"math/rand"
	"slices"
	"sort"
)

// CollectionTester is a convenience type to help build out collection testing with less boilerplate.
type CollectionTester[T any] struct {
	C Collection[T]

	Cmp  func(a, b T) error // Comparison function to assert equivalence between two documents.
	Data map[string]T       // Test data.
}

func (t *CollectionTester[T]) DeleteAll() error {
	if err := t.C.DeleteAll(); err != nil {
		return fmt.Errorf("failed to delete all documents: %v", err)
	}

	return nil
}

// DeleteOne tests that the collection safely deletes a single document.
// The document is not reinserted after deletion.
func (t *CollectionTester[T]) DeleteOne() error {
	// Select a random key.
	// This selects from the collection rather than test data to allow the function to be reused, so long as the collection has one document
	keys := t.C.GetAllKeys()
	if len(keys) == 0 {
		return fmt.Errorf("no documents")
	}
	n := rand.Intn(len(keys) - 1)
	key := keys[n]

	if err := t.C.Delete(key); err != nil {
		return fmt.Errorf("failed to delete document '%s': %v", key, err)
	}

	// Confirm document has been deleted
	has, err := t.C.Has(key)
	if err != nil {
		return fmt.Errorf("failed to test whether collection has deleted document '%s': %v", key, err)
	} else if has {
		return fmt.Errorf("expected collection not to have deleted document '%s'", key)
	}

	return nil
}

// Get tests that the collection retrieves all documents.
// The collection must be initialised.
func (t *CollectionTester[T]) Get() error {
	errs := Errors{}

	for key, data := range t.Data {
		actual, err := t.C.Get(key)
		if err != nil {
			errs = append(errs, fmt.Errorf("failed to get document '%s': %v", key, err))
		} else if err := t.Cmp(data, actual); err != nil {
			errs = append(errs, fmt.Errorf("comparison failed for document '%s': %v", key, err))
		}
	}

	return errs.Resolve()
}

func (t *CollectionTester[T]) GetAll() error {
	all, err := t.C.GetAll()
	if err != nil {
		return fmt.Errorf("failed to get all documents: %v", err)
	}

	errs := Errors{}
	for key, actual := range all {
		expected := t.Data[key]
		if err := t.Cmp(expected, actual); err != nil {
			errs = append(errs, fmt.Errorf("comparison failed for document '%s': %v", key, err))
		}
	}

	return errs.Resolve()
}

// Has tests that the collection has all documents.
// The collection must be initialised.
func (t *CollectionTester[T]) Has() error {
	errs := Errors{}

	for key := range t.Data {
		has, err := t.C.Has(key)
		if err != nil {
			return fmt.Errorf("failed to test whether collection has document '%s': %v", key, err)
		} else if !has {
			errs = append(errs, fmt.Errorf("expected collection to have document '%s'", key))
		}
	}

	return errs.Resolve()
}

// Init tests that the collection is correctly initialised.
// This opens the collection, deletes any existing data, and reinserts the test data.
func (t *CollectionTester[T]) Init() error {
	fs := []func() error{t.Open, t.DeleteAll, t.Put}
	for _, f := range fs {
		if err := f(); err != nil {
			return err
		}
	}

	return nil
}

// IterCount tests that the iterator counts documents correctly.
// The collection must be initialised.
func (t *CollectionTester[T]) IterCount() error {
	iter := t.C.Iter()
	actual := iter.Count()
	iter.Release()

	expected := len(t.Data)
	if expected != actual {
		return fmt.Errorf("incorrect document count (expected %d, got %d)", expected, actual)
	}

	return nil
}

// IterSortKeys tests that the iterator sorts correctly by key.
// The collection must be initialised.
func (t *CollectionTester[T]) IterSortKeys() error {
	ks := &keySort{
		a: []string{},
		f: func(a, b string) bool {
			return a < b
		},
	}
	for key := range t.Data {
		ks.a = append(ks.a, key)
	}

	sort.Stable(ks)
	sortedKeys := ks.Result()

	iter := t.C.Iter().SortKeys(ks.f)
	defer iter.Release()

	errs := Errors{}
	actual := 0
	for iter.Next() {
		key := iter.Key()
		if key != sortedKeys[actual] {
			expected := slices.Index(sortedKeys, key)
			errs = append(errs, fmt.Errorf("incorrect sort position of key '%s' (expected %d, got %d)", key, expected, actual))
		}
		actual++
	}

	return errs.Resolve()
}

// Open tests that the collection is opened.
func (t *CollectionTester[T]) Open() error {
	if err := t.C.Open(); err != nil {
		return fmt.Errorf("failed to open collection: %v", err)
	}
	return nil
}

// Put tests that the collection can store all documents.
func (t *CollectionTester[T]) Put() error {
	errs := Errors{}

	for key, data := range t.Data {
		if err := t.C.Put(key, data); err != nil {
			errs = append(errs, fmt.Errorf("failed to put document '%s': %v", key, err))
		}
	}

	return errs.Resolve()
}

func (t *CollectionTester[T]) Close() error {
	if err := t.C.Close(); err != nil {
		return fmt.Errorf("failed to close collection: %v", err)
	}

	return nil
}