package hashcash_test

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"math/big"
	"testing"
	"time"

	"git.eeqj.de/sneak/neoirc/internal/hashcash"
)

const testBits = 2

// mintStampWithDate creates a valid hashcash stamp using
// the given date string.
func mintStampWithDate(
	tb testing.TB,
	bits int,
	resource string,
	date string,
) string {
	tb.Helper()

	prefix := fmt.Sprintf(
		"1:%d:%s:%s::", bits, date, resource,
	)

	for {
		counterVal, err := rand.Int(
			rand.Reader, big.NewInt(1<<48),
		)
		if err != nil {
			tb.Fatalf("random counter: %v", err)
		}

		stamp := prefix + hex.EncodeToString(
			counterVal.Bytes(),
		)
		hash := sha256.Sum256([]byte(stamp))

		if hasLeadingZeroBits(hash[:], bits) {
			return stamp
		}
	}
}

// hasLeadingZeroBits checks if hash has at least numBits
// leading zero bits. Duplicated here for test minting.
func hasLeadingZeroBits(
	hash []byte,
	numBits int,
) bool {
	fullBytes := numBits / 8
	remainBits := numBits % 8

	for idx := range fullBytes {
		if hash[idx] != 0 {
			return false
		}
	}

	if remainBits > 0 && fullBytes < len(hash) {
		mask := byte(0xFF << (8 - remainBits))

		if hash[fullBytes]&mask != 0 {
			return false
		}
	}

	return true
}

func todayDate() string {
	return time.Now().UTC().Format("060102")
}

func TestMintAndValidate(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	stamp := mintStampWithDate(
		t, testBits, "test-resource", todayDate(),
	)

	err := validator.Validate(stamp, testBits)
	if err != nil {
		t.Fatalf("valid stamp rejected: %v", err)
	}
}

func TestReplayDetection(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	stamp := mintStampWithDate(
		t, testBits, "test-resource", todayDate(),
	)

	err := validator.Validate(stamp, testBits)
	if err != nil {
		t.Fatalf("first use failed: %v", err)
	}

	err = validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("replay not detected")
	}
}

func TestResourceMismatch(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("correct-resource")
	stamp := mintStampWithDate(
		t, testBits, "wrong-resource", todayDate(),
	)

	err := validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("expected resource mismatch error")
	}
}

func TestInvalidStampFormat(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")

	err := validator.Validate(
		"not:a:valid:stamp", testBits,
	)
	if err == nil {
		t.Fatal("expected error for bad format")
	}
}

func TestBadVersion(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	stamp := fmt.Sprintf(
		"2:%d:%s:%s::abc123",
		testBits, todayDate(), "test-resource",
	)

	err := validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("expected bad version error")
	}
}

func TestInsufficientDifficulty(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	// Claimed bits=1, but we require testBits=2.
	stamp := fmt.Sprintf(
		"1:1:%s:%s::counter",
		todayDate(), "test-resource",
	)

	err := validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("expected insufficient bits error")
	}
}

func TestExpiredStamp(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	oldDate := time.Now().Add(-72 * time.Hour).
		UTC().Format("060102")
	stamp := mintStampWithDate(
		t, testBits, "test-resource", oldDate,
	)

	err := validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("expected expired stamp error")
	}
}

func TestZeroBitsSkipsValidation(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")

	err := validator.Validate("garbage", 0)
	if err != nil {
		t.Fatalf("zero bits should skip: %v", err)
	}
}

func TestLongDateFormat(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	longDate := time.Now().UTC().Format("060102150405")
	stamp := mintStampWithDate(
		t, testBits, "test-resource", longDate,
	)

	err := validator.Validate(stamp, testBits)
	if err != nil {
		t.Fatalf("long date stamp rejected: %v", err)
	}
}

func TestBadDateFormat(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")
	stamp := fmt.Sprintf(
		"1:%d:BADDATE:%s::counter",
		testBits, "test-resource",
	)

	err := validator.Validate(stamp, testBits)
	if err == nil {
		t.Fatal("expected bad date error")
	}
}

func TestMultipleUniqueStamps(t *testing.T) {
	t.Parallel()

	validator := hashcash.NewValidator("test-resource")

	for range 5 {
		stamp := mintStampWithDate(
			t, testBits, "test-resource", todayDate(),
		)

		err := validator.Validate(stamp, testBits)
		if err != nil {
			t.Fatalf("unique stamp rejected: %v", err)
		}
	}
}

func TestHigherBitsStillValid(t *testing.T) {
	t.Parallel()

	// Mint with bits=4 but validate requiring only 2.
	validator := hashcash.NewValidator("test-resource")
	stamp := mintStampWithDate(
		t, 4, "test-resource", todayDate(),
	)

	err := validator.Validate(stamp, testBits)
	if err != nil {
		t.Fatalf(
			"higher-difficulty stamp rejected: %v",
			err,
		)
	}
}