// Copyright 2020-2022 the Pinniped contributors. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

// Package discovery provides a handler for the OIDC discovery endpoint.
package discovery

import (
	"bytes"
	"encoding/json"
	"net/http"

	"go.pinniped.dev/generated/latest/apis/supervisor/idpdiscovery/v1alpha1"
	oidcapi "go.pinniped.dev/generated/latest/apis/supervisor/oidc"
	"go.pinniped.dev/internal/oidc"
)

// Metadata holds all fields (that we care about) from the OpenID Provider Metadata section in the
// OpenID Connect Discovery specification:
// https://openid.net/specs/openid-connect-discovery-1_0.html#rfc.section.3.
type Metadata struct {
	// vvv Required vvv

	Issuer string `json:"issuer"`

	AuthorizationEndpoint string `json:"authorization_endpoint"`
	TokenEndpoint         string `json:"token_endpoint"`
	JWKSURI               string `json:"jwks_uri"`

	ResponseTypesSupported           []string `json:"response_types_supported"`
	ResponseModesSupported           []string `json:"response_modes_supported"`
	SubjectTypesSupported            []string `json:"subject_types_supported"`
	IDTokenSigningAlgValuesSupported []string `json:"id_token_signing_alg_values_supported"`

	// ^^^ Required ^^^

	// vvv Optional vvv

	TokenEndpointAuthMethodsSupported []string `json:"token_endpoint_auth_methods_supported"`
	ScopesSupported                   []string `json:"scopes_supported"`
	ClaimsSupported                   []string `json:"claims_supported"`

	// https://datatracker.ietf.org/doc/html/rfc8414#section-2 says, “If omitted, the authorization server does not support PKCE.”
	CodeChallengeMethodsSupported []string `json:"code_challenge_methods_supported"`

	// ^^^ Optional ^^^

	// vvv Custom vvv

	v1alpha1.OIDCDiscoveryResponse

	// ^^^ Custom ^^^
}

// NewHandler returns an http.Handler that serves an OIDC discovery endpoint.
func NewHandler(issuerURL string) http.Handler {
	oidcConfig := Metadata{
		Issuer:                issuerURL,
		AuthorizationEndpoint: issuerURL + oidc.AuthorizationEndpointPath,
		TokenEndpoint:         issuerURL + oidc.TokenEndpointPath,
		JWKSURI:               issuerURL + oidc.JWKSEndpointPath,
		OIDCDiscoveryResponse: v1alpha1.OIDCDiscoveryResponse{
			SupervisorDiscovery: v1alpha1.OIDCDiscoveryResponseIDPEndpoint{
				PinnipedIDPsEndpoint: issuerURL + oidc.PinnipedIDPsPathV1Alpha1,
			},
		},
		ResponseTypesSupported:            []string{"code"},
		ResponseModesSupported:            []string{"query", "form_post"},
		SubjectTypesSupported:             []string{"public"},
		IDTokenSigningAlgValuesSupported:  []string{"ES256"},
		TokenEndpointAuthMethodsSupported: []string{"client_secret_basic"},
		CodeChallengeMethodsSupported:     []string{"S256"},
		ScopesSupported:                   []string{oidcapi.ScopeOpenID, oidcapi.ScopeOfflineAccess, oidcapi.ScopeRequestAudience, oidcapi.ScopeUsername, oidcapi.ScopeGroups},
		ClaimsSupported:                   []string{oidcapi.IDTokenClaimUsername, oidcapi.IDTokenClaimGroups, oidcapi.IDTokenClaimAdditionalClaims},
	}

	var b bytes.Buffer
	encodeErr := json.NewEncoder(&b).Encode(&oidcConfig)
	encodedMetadata := b.Bytes()

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			http.Error(w, `Method not allowed (try GET)`, http.StatusMethodNotAllowed)
			return
		}

		if encodeErr != nil {
			http.Error(w, encodeErr.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		if _, err := w.Write(encodedMetadata); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	})
}