package capsule_test

import (
	"bytes"
	"context"
	"encoding/hex"
	"errors"
	"io"
	"os"
	"path/filepath"
	"testing"

	datekeys "g.activething.com/go/DateKeys"
	"g.activething.com/go/DateKeys/capsule"
	"g.activething.com/go/DateKeys/internal/testkit"
)

func seedFixtures(f *testing.F, part func(testkit.Parts) []byte) {
	for _, name := range fixtureNames {
		b, err := os.ReadFile(filepath.Join(fixtureDir, name+".dkc"))
		if err != nil {
			f.Fatal(err)
		}
		p, err := testkit.Split(b)
		if err != nil {
			f.Fatal(err)
		}
		f.Add(part(p))
	}
}

// whole keeps the first 512 bytes of the payload: the pre-unlock checks read
// only its age header, and small inputs keep the fuzzer fast.
func whole(p testkit.Parts) []byte {
	payload := p.Payload
	if len(payload) > 512 {
		payload = payload[:512]
	}
	return testkit.Join(p.Prelude, p.Header, p.Sealed, payload)
}

func FuzzParsePrelude(f *testing.F) {
	seedFixtures(f, func(p testkit.Parts) []byte { return p.Prelude })
	f.Fuzz(func(t *testing.T, b []byte) {
		p, err := capsule.ParsePrelude(b)
		if err != nil {
			if datekeys.Code(err) == "" {
				t.Fatalf("error without a normative code: %v", err)
			}
			return
		}
		got := p.Bytes()
		if !bytes.Equal(got[:], b[:capsule.PreludeSize]) {
			t.Fatal("accepted a prelude that does not re-encode to its input")
		}
	})
}

func FuzzDecodeHeader(f *testing.F) {
	seedFixtures(f, func(p testkit.Parts) []byte { return p.Header })
	f.Fuzz(func(t *testing.T, b []byte) {
		h, err := capsule.DecodeHeader(b)
		if err != nil {
			if datekeys.Code(err) == "" {
				t.Fatalf("error without a normative code: %v", err)
			}
			return
		}
		re, err := capsule.EncodeHeader(h)
		if err != nil || !bytes.Equal(re, b) {
			t.Fatal("accepted a PUBLIC_HEADER that does not re-encode to its input")
		}
	})
}

func FuzzDecodeControl(f *testing.F) {
	for _, name := range fixtureNames {
		fx := loadFixture(f, name)
		b, _ := hexDecode(fx.ControlCBOR)
		f.Add(b)
	}
	f.Fuzz(func(t *testing.T, b []byte) {
		c, err := capsule.DecodeControl(b)
		if err != nil {
			if datekeys.Code(err) == "" {
				t.Fatalf("error without a normative code: %v", err)
			}
			return
		}
		re, err := capsule.EncodeControl(c)
		if err != nil || !bytes.Equal(re, b) {
			t.Fatal("accepted a CONTROL_CBOR that does not re-encode to its input")
		}
	})
}

// FuzzInspect feeds whole capsules to the pre-unlock validation, and to Open
// with a source that never has the release: a capsule that Inspect rejects
// must not cause a request, and nothing may pass the release step. The
// cryptographic steps after it are exercised by the mutation corpus; keeping
// them out of this target keeps it fast.
func FuzzInspect(f *testing.F) {
	seedFixtures(f, whole)
	reg := testkit.Registry()
	far := testkit.Fixed(testkit.Genesis().AddDate(5, 0, 0))
	f.Fuzz(func(t *testing.T, b []byte) {
		_, err := capsule.Inspect(bytes.NewReader(b), capsule.InspectOptions{Registry: reg})
		if err != nil && datekeys.Code(err) == "" {
			t.Fatalf("error without a normative code: %v", err)
		}
		src := testkit.NewSource()
		o := capsule.OpenOptions{Registry: reg, Source: src, Now: far}
		_, openErr := capsule.Open(context.Background(), io.Discard, bytes.NewReader(b), o)
		switch {
		case openErr == nil:
			t.Fatal("opened without a release")
		case datekeys.Code(openErr) == "":
			t.Fatalf("error without a normative code: %v", openErr)
		case err != nil && src.Calls != 0:
			t.Fatal("a capsule rejected by Inspect caused a release request")
		case err == nil && !errors.Is(openErr, datekeys.ErrReleaseUnavailable) && !errors.Is(openErr, datekeys.ErrAccessRequired):
			t.Fatalf("a capsule accepted by Inspect failed before the release step: %v", openErr)
		}
	})
}

func hexDecode(s string) ([]byte, error) { return hex.DecodeString(s) }