package delegationtest

import (
	"os"
	"path/filepath"
	"slices"
	"time"

	"github.com/dave/jennifer/jen"
	"github.com/ipfs/go-cid"
	"github.com/libp2p/go-libp2p/core/crypto"

	"github.com/ucan-wg/go-ucan/did"
	"github.com/ucan-wg/go-ucan/did/didtest"
	"github.com/ucan-wg/go-ucan/pkg/command"
	"github.com/ucan-wg/go-ucan/pkg/policy"
	"github.com/ucan-wg/go-ucan/token/delegation"
)

const (
	tokenNamePrefix      = "Token"
	proorChainNamePrefix = "Proof"
)

var constantNonce = []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b}

type newDelegationParams struct {
	privKey crypto.PrivKey
	aud     did.DID
	sub     did.DID
	cmd     command.Command
	pol     policy.Policy
	opts    []delegation.Option
}

type token struct {
	name string
	id   cid.Cid
}

type proof struct {
	name string
	prf  []cid.Cid
}

type acc struct {
	name  string
	chain []cid.Cid
}

type variant struct {
	name    string
	variant func(*newDelegationParams)
}

func noopVariant() variant {
	return variant{
		name:    "",
		variant: func(_ *newDelegationParams) {},
	}
}

type generator struct {
	dlgs   []token
	chains []proof
}

func (g *generator) chainPersonas(personas []didtest.Persona, acc acc, vari variant) error {
	acc.name += personas[0].Name()

	proofName := acc.name
	if len(vari.name) > 0 {
		proofName += "_" + vari.name
	}
	g.createProofChain(proofName, acc.chain)

	if len(personas) < 2 {
		return nil
	}

	name := personas[0].Name() + personas[1].Name()

	params := newDelegationParams{
		privKey: personas[0].PrivKey(),
		aud:     personas[1].DID(),
		cmd:     NominalCommand,
		pol:     policy.Policy{},
		opts: []delegation.Option{
			delegation.WithSubject(didtest.PersonaAlice.DID()),
			delegation.WithNonce(constantNonce),
		},
	}

	// Create each nominal token and continue the chain
	id, err := g.createDelegation(params, name, vari)
	if err != nil {
		return err
	}
	acc.chain = append(acc.chain, id)
	err = g.chainPersonas(personas[1:], acc, vari)
	if err != nil {
		return err
	}

	// If the user is Carol, create variants for each invalid and/or optional
	// parameter and also continue the chain
	if personas[0] == didtest.PersonaCarol {
		variants := []variant{
			{name: "InvalidExpandedCommand", variant: func(p *newDelegationParams) {
				p.cmd = ExpandedCommand
			}},
			{name: "ValidAttenuatedCommand", variant: func(p *newDelegationParams) {
				p.cmd = AttenuatedCommand
			}},
			{name: "InvalidSubject", variant: func(p *newDelegationParams) {
				p.opts = append(p.opts, delegation.WithSubject(didtest.PersonaBob.DID()))
			}},
			{name: "InvalidExpired", variant: func(p *newDelegationParams) {
				// Note: this makes the generator not deterministic
				p.opts = append(p.opts, delegation.WithExpiration(time.Now().Add(time.Second)))
			}},
			{name: "InvalidInactive", variant: func(p *newDelegationParams) {
				nbf, err := time.Parse(time.RFC3339, "2070-01-01T00:00:00Z")
				if err != nil {
					panic(err)
				}
				p.opts = append(p.opts, delegation.WithNotBefore(nbf))
			}},
		}

		// Start a branch in the recursion for each of the variants
		for _, v := range variants {
			id, err := g.createDelegation(params, name, v)
			if err != nil {
				return err
			}

			// replace the previous Carol token id with the one from the variant
			acc.chain[len(acc.chain)-1] = id
			err = g.chainPersonas(personas[1:], acc, v)
			if err != nil {
				return err
			}
		}
	}
	return nil
}

func (g *generator) createDelegation(params newDelegationParams, name string, vari variant) (cid.Cid, error) {
	vari.variant(&params)

	tkn, err := delegation.New(params.privKey, params.aud, params.cmd, params.pol, params.opts...)
	if err != nil {
		return cid.Undef, err
	}

	data, id, err := tkn.ToSealed(params.privKey)
	if err != nil {
		return cid.Undef, err
	}

	dlgName := tokenNamePrefix + name
	if len(vari.name) > 0 {
		dlgName += "_" + vari.name
	}

	err = os.WriteFile(filepath.Join(tokenDir, dlgName+tokenExt), data, 0o644)
	if err != nil {
		return cid.Undef, err
	}

	g.dlgs = append(g.dlgs, token{
		name: dlgName,
		id:   id,
	})

	return id, nil
}

func (g *generator) createProofChain(name string, prf []cid.Cid) {
	if len(prf) < 1 {
		return
	}

	clone := make([]cid.Cid, len(prf))
	copy(clone, prf)

	g.chains = append(g.chains, proof{
		name: proorChainNamePrefix + name,
		prf:  clone,
	})
}

func (g *generator) writeGoFile() error {
	file := jen.NewFile("delegationtest")
	file.HeaderComment("Code generated by delegationtest - DO NOT EDIT.")

	refs := map[cid.Cid]string{}

	for _, d := range g.dlgs {
		refs[d.id] = d.name + "CID"

		file.Var().Defs(
			jen.Id(d.name+"CID").Op("=").Qual("github.com/ipfs/go-cid", "MustParse").Call(jen.Lit(d.id.String())),
			jen.Id(d.name).Op("=").Id("mustGetDelegation").Call(jen.Id(d.name+"CID")),
		)
		file.Line()
	}

	for _, c := range g.chains {
		g := jen.CustomFunc(jen.Options{
			Multi:     true,
			Separator: ",",
			Close:     "\n",
		}, func(g *jen.Group) {
			slices.Reverse(c.prf)
			for _, p := range c.prf {
				g.Id(refs[p])
			}
		})

		file.Var().Id(c.name).Op("=").Index().Qual("github.com/ipfs/go-cid", "Cid").Values(g)
		file.Line()
	}

	return file.Save("token_gen.go")
}