package crypto

import (
	"fmt"
	"strings"

	"github.com/mitchellh/mapstructure"
	"github.com/zitadel/passwap"
	"github.com/zitadel/passwap/argon2"
	"github.com/zitadel/passwap/bcrypt"
	"github.com/zitadel/passwap/md5"
	"github.com/zitadel/passwap/pbkdf2"
	"github.com/zitadel/passwap/scrypt"
	"github.com/zitadel/passwap/verifier"

	"github.com/zitadel/zitadel/internal/zerrors"
)

type Hasher struct {
	*passwap.Swapper
	Prefixes []string
}

func (h *Hasher) EncodingSupported(encodedHash string) bool {
	for _, prefix := range h.Prefixes {
		if strings.HasPrefix(encodedHash, prefix) {
			return true
		}
	}
	return false
}

type HashName string

const (
	HashNameArgon2   HashName = "argon2"   // used for the common argon2 verifier
	HashNameArgon2i  HashName = "argon2i"  // hash only
	HashNameArgon2id HashName = "argon2id" // hash only
	HashNameBcrypt   HashName = "bcrypt"   // hash and verify
	HashNameMd5      HashName = "md5"      // verify only, as hashing with md5 is insecure and deprecated
	HashNameScrypt   HashName = "scrypt"   // hash and verify
	HashNamePBKDF2   HashName = "pbkdf2"   // hash and verify
)

type HashMode string

// HashMode defines a underlying [hash.Hash] implementation
// for algorithms like pbkdf2
const (
	HashModeSHA1   HashMode = "sha1"
	HashModeSHA224 HashMode = "sha224"
	HashModeSHA256 HashMode = "sha256"
	HashModeSHA384 HashMode = "sha384"
	HashModeSHA512 HashMode = "sha512"
)

type HashConfig struct {
	Verifiers []HashName
	Hasher    HasherConfig
}

func (c *HashConfig) NewHasher() (*Hasher, error) {
	verifiers, vPrefixes, err := c.buildVerifiers()
	if err != nil {
		return nil, zerrors.ThrowInvalidArgument(err, "CRYPT-sahW9", "password hash config invalid")
	}
	hasher, hPrefixes, err := c.Hasher.buildHasher()
	if err != nil {
		return nil, zerrors.ThrowInvalidArgument(err, "CRYPT-Que4r", "password hash config invalid")
	}
	return &Hasher{
		Swapper:  passwap.NewSwapper(hasher, verifiers...),
		Prefixes: append(hPrefixes, vPrefixes...),
	}, nil
}

type prefixVerifier struct {
	prefixes []string
	verifier verifier.Verifier
}

// map HashNames to Verifier instances.
var knowVerifiers = map[HashName]prefixVerifier{
	HashNameArgon2: {
		// only argon2i and argon2id are suppored.
		// The Prefix constant also covers argon2d.
		prefixes: []string{argon2.Prefix},
		verifier: argon2.Verifier,
	},
	HashNameBcrypt: {
		prefixes: []string{bcrypt.Prefix},
		verifier: bcrypt.Verifier,
	},
	HashNameMd5: {
		prefixes: []string{md5.Prefix},
		verifier: md5.Verifier,
	},
	HashNameScrypt: {
		prefixes: []string{scrypt.Prefix, scrypt.Prefix_Linux},
		verifier: scrypt.Verifier,
	},
	HashNamePBKDF2: {
		prefixes: []string{pbkdf2.Prefix},
		verifier: pbkdf2.Verifier,
	},
}

func (c *HashConfig) buildVerifiers() (verifiers []verifier.Verifier, prefixes []string, err error) {
	verifiers = make([]verifier.Verifier, len(c.Verifiers))
	prefixes = make([]string, 0, len(c.Verifiers)+1)
	for i, name := range c.Verifiers {
		v, ok := knowVerifiers[name]
		if !ok {
			return nil, nil, fmt.Errorf("invalid verifier %q", name)
		}
		verifiers[i] = v.verifier
		prefixes = append(prefixes, v.prefixes...)
	}
	return verifiers, prefixes, nil
}

type HasherConfig struct {
	Algorithm HashName
	Params    map[string]any `mapstructure:",remain"`
}

func (c *HasherConfig) buildHasher() (hasher passwap.Hasher, prefixes []string, err error) {
	switch c.Algorithm {
	case HashNameArgon2i:
		return c.argon2i()
	case HashNameArgon2id:
		return c.argon2id()
	case HashNameBcrypt:
		return c.bcrypt()
	case HashNameScrypt:
		return c.scrypt()
	case HashNamePBKDF2:
		return c.pbkdf2()
	case "":
		return nil, nil, fmt.Errorf("missing hasher algorithm")
	case HashNameArgon2, HashNameMd5:
		fallthrough
	default:
		return nil, nil, fmt.Errorf("invalid algorithm %q", c.Algorithm)
	}
}

// decodeParams uses a mapstructure decoder from the Params map to dst.
// The decoder fails when there are unused fields in dst.
// It uses weak input typing, to allow conversion of env strings to ints.
func (c *HasherConfig) decodeParams(dst any) error {
	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
		ErrorUnused:      false,
		ErrorUnset:       true,
		WeaklyTypedInput: true,
		Result:           dst,
	})
	if err != nil {
		return err
	}
	return decoder.Decode(c.Params)
}

// argon2Params decodes [HasherConfig.Params] into a [argon2.Params] used as defaults.
// p is passed a copy and therfore will not be modified.
func (c *HasherConfig) argon2Params(p argon2.Params) (argon2.Params, error) {
	var dst struct {
		Time    uint32 `mapstructure:"Time"`
		Memory  uint32 `mapstructure:"Memory"`
		Threads uint8  `mapstructure:"Threads"`
	}
	if err := c.decodeParams(&dst); err != nil {
		return argon2.Params{}, fmt.Errorf("decode argon2i params: %w", err)
	}
	p.Time = dst.Time
	p.Memory = dst.Memory
	p.Threads = dst.Threads
	return p, nil
}

func (c *HasherConfig) argon2i() (passwap.Hasher, []string, error) {
	p, err := c.argon2Params(argon2.RecommendedIParams)
	if err != nil {
		return nil, nil, err
	}
	return argon2.NewArgon2i(p), []string{argon2.Prefix}, nil
}

func (c *HasherConfig) argon2id() (passwap.Hasher, []string, error) {
	p, err := c.argon2Params(argon2.RecommendedIDParams)
	if err != nil {
		return nil, nil, err
	}
	return argon2.NewArgon2id(p), []string{argon2.Prefix}, nil
}

func (c *HasherConfig) bcryptCost() (int, error) {
	var dst = struct {
		Cost int `mapstructure:"Cost"`
	}{}
	if err := c.decodeParams(&dst); err != nil {
		return 0, fmt.Errorf("decode bcrypt params: %w", err)
	}
	return dst.Cost, nil
}

func (c *HasherConfig) bcrypt() (passwap.Hasher, []string, error) {
	cost, err := c.bcryptCost()
	if err != nil {
		return nil, nil, err
	}
	return bcrypt.New(cost), []string{bcrypt.Prefix}, nil
}

func (c *HasherConfig) scryptParams() (scrypt.Params, error) {
	var dst = struct {
		Cost int `mapstructure:"Cost"`
	}{}
	if err := c.decodeParams(&dst); err != nil {
		return scrypt.Params{}, fmt.Errorf("decode scrypt params: %w", err)
	}
	p := scrypt.RecommendedParams // copy
	p.N = 1 << dst.Cost
	return p, nil
}

func (c *HasherConfig) scrypt() (passwap.Hasher, []string, error) {
	p, err := c.scryptParams()
	if err != nil {
		return nil, nil, err
	}
	return scrypt.New(p), []string{scrypt.Prefix, scrypt.Prefix_Linux}, nil
}

func (c *HasherConfig) pbkdf2Params() (p pbkdf2.Params, _ HashMode, _ error) {
	var dst = struct {
		Rounds uint32   `mapstructure:"Rounds"`
		Hash   HashMode `mapstructure:"Hash"`
	}{}
	if err := c.decodeParams(&dst); err != nil {
		return p, "", fmt.Errorf("decode pbkdf2 params: %w", err)
	}
	switch dst.Hash {
	case HashModeSHA1:
		p = pbkdf2.RecommendedSHA1Params
	case HashModeSHA224:
		p = pbkdf2.RecommendedSHA224Params
	case HashModeSHA256:
		p = pbkdf2.RecommendedSHA256Params
	case HashModeSHA384:
		p = pbkdf2.RecommendedSHA384Params
	case HashModeSHA512:
		p = pbkdf2.RecommendedSHA512Params
	}
	p.Rounds = dst.Rounds
	return p, dst.Hash, nil
}

func (c *HasherConfig) pbkdf2() (passwap.Hasher, []string, error) {
	p, hash, err := c.pbkdf2Params()
	if err != nil {
		return nil, nil, err
	}
	prefix := []string{pbkdf2.Prefix}
	switch hash {
	case HashModeSHA1:
		return pbkdf2.NewSHA1(p), prefix, nil
	case HashModeSHA224:
		return pbkdf2.NewSHA224(p), prefix, nil
	case HashModeSHA256:
		return pbkdf2.NewSHA256(p), prefix, nil
	case HashModeSHA384:
		return pbkdf2.NewSHA384(p), prefix, nil
	case HashModeSHA512:
		return pbkdf2.NewSHA512(p), prefix, nil
	default:
		return nil, nil, fmt.Errorf("unsuppored pbkdf2 hash mode: %s", hash)
	}
}