package oidc

import (
	"context"
	"fmt"
	"net/http"
	"net/url"

	"forge.cadoles.com/cadoles/bouncer/internal/proxy/director"
	"forge.cadoles.com/cadoles/bouncer/internal/proxy/director/layer/authn"
	"forge.cadoles.com/cadoles/bouncer/internal/store"
	"github.com/coreos/go-oidc/v3/oidc"
	"github.com/gorilla/sessions"
	"github.com/pkg/errors"
)

type Authenticator struct{}

func (a *Authenticator) PreAuthentication(w http.ResponseWriter, r *http.Request, layer *store.Layer, sess *sessions.Session) error {
	ctx := r.Context()

	originalURL, err := director.OriginalURL(ctx)
	if err != nil {
		return errors.WithStack(err)
	}

	options, err := fromStoreOptions(layer.Options)
	if err != nil {
		return errors.WithStack(err)
	}

	redirectURL := a.getRedirectURL(layer.Name, originalURL, options)
	logoutURL := a.getLogoutURL(layer.Name, originalURL, options)

	client, err := a.getClient(options, redirectURL.String())
	if err != nil {
		return errors.WithStack(err)
	}

	switch r.URL.Path {
	case redirectURL.Path:
		if err := client.HandleCallback(w, r, sess); err != nil {
			return errors.WithStack(err)
		}

	case logoutURL.Path:
		if err := client.HandleLogout(w, r, sess, options.OIDC.PostLogoutRedirectURL); err != nil {
			return errors.WithStack(err)
		}
	}

	return nil
}

// Authenticate implements authn.Authenticator.
func (a *Authenticator) Authenticate(w http.ResponseWriter, r *http.Request, layer *store.Layer, sess *sessions.Session) (*authn.User, error) {
	ctx := r.Context()

	originalURL, err := director.OriginalURL(ctx)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	options, err := fromStoreOptions(layer.Options)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	redirectURL := a.getRedirectURL(layer.Name, originalURL, options)

	client, err := a.getClient(options, redirectURL.String())
	if err != nil {
		return nil, errors.WithStack(err)
	}

	idToken, err := client.Authenticate(w, r, sess)
	if err != nil {
		if errors.Is(err, ErrLoginRequired) {
			return nil, errors.WithStack(authn.ErrSkipRequest)
		}

		return nil, errors.WithStack(err)
	}

	user, err := a.toUser(idToken, layer.Name, originalURL, options, sess)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	return user, nil
}

type claims struct {
	Issuer     string         `json:"iss"`
	Subject    string         `json:"sub"`
	Audience   string         `json:"aud"`
	Expiration int64          `json:"exp"`
	IssuedAt   int64          `json:"iat"`
	AuthTime   int64          `json:"auth_time"`
	Nonce      string         `json:"nonce"`
	ACR        string         `json:"acr"`
	AMR        string         `json:"amr"`
	AZP        string         `json:"amp"`
	Others     map[string]any `json:"-"`
}

func (c claims) AsAttrs() map[string]any {
	attrs := make(map[string]any)

	for key, val := range c.Others {
		attrs["claim_"+key] = val
	}

	attrs["claim_issuer"] = c.Issuer
	delete(attrs, "claim_iss")

	attrs["claim_subject"] = c.Subject
	delete(attrs, "claim_sub")

	attrs["claim_audience"] = c.Audience
	delete(attrs, "claim_aud")

	attrs["claim_expiration"] = c.Expiration
	delete(attrs, "claim_exp")

	attrs["claim_issued_at"] = c.IssuedAt
	delete(attrs, "claim_iat")

	if c.AuthTime != 0 {
		attrs["claim_auth_time"] = c.AuthTime
	}

	if c.Nonce != "" {
		attrs["claim_nonce"] = c.Nonce
	}

	if c.ACR != "" {
		attrs["claim_arc"] = c.ACR
	}

	if c.AMR != "" {
		attrs["claim_amr"] = c.AMR
	}

	if c.AZP != "" {
		attrs["claim_azp"] = c.AZP
	}

	return attrs
}

func (a *Authenticator) toUser(idToken *oidc.IDToken, layerName store.LayerName, originalURL *url.URL, options *LayerOptions, sess *sessions.Session) (*authn.User, error) {
	var claims claims

	if err := idToken.Claims(&claims); err != nil {
		return nil, errors.WithStack(err)
	}

	if err := idToken.Claims(&claims.Others); err != nil {
		return nil, errors.WithStack(err)
	}

	attrs := claims.AsAttrs()

	logoutURL := a.getLogoutURL(layerName, originalURL, options)
	attrs["logout_url"] = logoutURL.String()

	if accessToken, exists := sess.Values[sessionKeyAccessToken]; exists && accessToken != nil {
		attrs["access_token"] = accessToken
	}

	if refreshToken, exists := sess.Values[sessionKeyRefreshToken]; exists && refreshToken != nil {
		attrs["refresh_token"] = refreshToken
	}

	if tokenExpiry, exists := sess.Values[sessionKeyTokenExpiry]; exists && tokenExpiry != nil {
		attrs["token_expiry"] = tokenExpiry
	}

	user := authn.NewUser(idToken.Subject, attrs)

	return user, nil
}

func (a *Authenticator) getRedirectURL(layerName store.LayerName, u *url.URL, options *LayerOptions) *url.URL {
	return &url.URL{
		Scheme: u.Scheme,
		Host:   u.Host,
		Path:   fmt.Sprintf(options.OIDC.LoginCallbackPath, layerName),
	}
}

func (a *Authenticator) getLogoutURL(layerName store.LayerName, u *url.URL, options *LayerOptions) *url.URL {
	return &url.URL{
		Scheme: u.Scheme,
		Host:   u.Host,
		Path:   fmt.Sprintf(options.OIDC.LogoutPath, layerName),
	}
}

func (a *Authenticator) getClient(options *LayerOptions, redirectURL string) (*Client, error) {
	ctx := context.Background()

	if options.OIDC.SkipIssuerVerification {
		ctx = oidc.InsecureIssuerURLContext(ctx, options.OIDC.IssuerURL)
	}

	provider, err := oidc.NewProvider(ctx, options.OIDC.IssuerURL)
	if err != nil {
		return nil, errors.Wrap(err, "could not create oidc provider")
	}

	client := NewClient(
		WithCredentials(options.OIDC.ClientID, options.OIDC.ClientSecret),
		WithProvider(provider),
		WithRedirectURL(redirectURL),
		WithScopes(options.OIDC.Scopes...),
		WithAuthParams(options.OIDC.AuthParams),
	)

	return client, nil
}

var (
	_ authn.PreAuthentication = &Authenticator{}
	_ authn.Authenticator     = &Authenticator{}
)