package tests

import (
	"bytes"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"math/big"
	"os"
	"strings"

	"github.com/ethereum/go-ethereum/rlp"
)

// RLPTest is the JSON structure of a single RLP test.
type RLPTest struct {
	// If the value of In is "INVALID" or "VALID", the test
	// checks whether Out can be decoded into a value of
	// type interface{}.
	//
	// For other JSON values, In is treated as a driver for
	// calls to rlp.Stream. The test also verifies that encoding
	// In produces the bytes in Out.
	In interface{}

	// Out is a hex-encoded RLP value.
	Out string
}

// RunRLPTest runs the tests in the given file, skipping tests by name.
func RunRLPTest(file string, skip []string) error {
	f, err := os.Open(file)
	if err != nil {
		return err
	}
	defer f.Close()
	return RunRLPTestWithReader(f, skip)
}

// RunRLPTest runs the tests encoded in r, skipping tests by name.
func RunRLPTestWithReader(r io.Reader, skip []string) error {
	var tests map[string]*RLPTest
	if err := readJson(r, &tests); err != nil {
		return err
	}
	for _, s := range skip {
		delete(tests, s)
	}
	for name, test := range tests {
		if err := test.Run(); err != nil {
			return fmt.Errorf("test %q failed: %v", name, err)
		}
	}
	return nil
}

// Run executes the test.
func (t *RLPTest) Run() error {
	outb, err := hex.DecodeString(t.Out)
	if err != nil {
		return fmt.Errorf("invalid hex in Out")
	}

	// Handle simple decoding tests with no actual In value.
	if t.In == "VALID" || t.In == "INVALID" {
		return checkDecodeInterface(outb, t.In == "VALID")
	}

	// Check whether encoding the value produces the same bytes.
	in := translateJSON(t.In)
	b, err := rlp.EncodeToBytes(in)
	if err != nil {
		return fmt.Errorf("encode failed: %v", err)
	}
	if !bytes.Equal(b, outb) {
		return fmt.Errorf("encode produced %x, want %x", b, outb)
	}
	// Test stream decoding.
	s := rlp.NewStream(bytes.NewReader(outb), 0)
	return checkDecodeFromJSON(s, in)
}

func checkDecodeInterface(b []byte, isValid bool) error {
	err := rlp.DecodeBytes(b, new(interface{}))
	switch {
	case isValid && err != nil:
		return fmt.Errorf("decoding failed: %v", err)
	case !isValid && err == nil:
		return fmt.Errorf("decoding of invalid value succeeded")
	}
	return nil
}

// translateJSON makes test json values encodable with RLP.
func translateJSON(v interface{}) interface{} {
	switch v := v.(type) {
	case float64:
		return uint64(v)
	case string:
		if len(v) > 0 && v[0] == '#' { // # starts a faux big int.
			big, ok := new(big.Int).SetString(v[1:], 10)
			if !ok {
				panic(fmt.Errorf("bad test: bad big int: %q", v))
			}
			return big
		}
		return []byte(v)
	case []interface{}:
		new := make([]interface{}, len(v))
		for i := range v {
			new[i] = translateJSON(v[i])
		}
		return new
	default:
		panic(fmt.Errorf("can't handle %T", v))
	}
}

// checkDecodeFromJSON decodes from s guided by exp. exp drives the
// Stream by invoking decoding operations (Uint, Big, List, ...) based
// on the type of each value. The value decoded from the RLP stream
// must match the JSON value.
func checkDecodeFromJSON(s *rlp.Stream, exp interface{}) error {
	switch exp := exp.(type) {
	case uint64:
		i, err := s.Uint()
		if err != nil {
			return addStack("Uint", exp, err)
		}
		if i != exp {
			return addStack("Uint", exp, fmt.Errorf("result mismatch: got %d", i))
		}
	case *big.Int:
		big := new(big.Int)
		if err := s.Decode(&big); err != nil {
			return addStack("Big", exp, err)
		}
		if big.Cmp(exp) != 0 {
			return addStack("Big", exp, fmt.Errorf("result mismatch: got %d", big))
		}
	case []byte:
		b, err := s.Bytes()
		if err != nil {
			return addStack("Bytes", exp, err)
		}
		if !bytes.Equal(b, exp) {
			return addStack("Bytes", exp, fmt.Errorf("result mismatch: got %x", b))
		}
	case []interface{}:
		if _, err := s.List(); err != nil {
			return addStack("List", exp, err)
		}
		for i, v := range exp {
			if err := checkDecodeFromJSON(s, v); err != nil {
				return addStack(fmt.Sprintf("[%d]", i), exp, err)
			}
		}
		if err := s.ListEnd(); err != nil {
			return addStack("ListEnd", exp, err)
		}
	default:
		panic(fmt.Errorf("unhandled type: %T", exp))
	}
	return nil
}

func addStack(op string, val interface{}, err error) error {
	lines := strings.Split(err.Error(), "\n")
	lines = append(lines, fmt.Sprintf("\t%s: %v", op, val))
	return errors.New(strings.Join(lines, "\n"))
}