// Package vault issues independently owned MongoDB leases through Vault AppRole.
package vault

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"net/http"
	"net/url"
	"os"
	"regexp"
	"strings"
	"time"

	"git.sendico.io/tech/sxchnge/shared/database/source"
	merrors "git.sendico.io/tech/sxchnge/shared/errors"
)

type Config struct {
	Address      string `mapstructure:"address"`
	DatabaseRole string `mapstructure:"role"`
	RoleIDFile   string `mapstructure:"role_id_file"`
	SecretIDFile string `mapstructure:"secret_id_file"`
}
type Issuer struct {
	config Config
	uri    *url.URL
	http   *http.Client
}

func New(config Config, uri string) (*Issuer, error) {
	endpoint, err := url.Parse(config.Address)
	if err != nil || endpoint.Host == "" || (endpoint.Scheme != "http" && endpoint.Scheme != "https") || endpoint.User != nil || endpoint.RawQuery != "" || endpoint.Fragment != "" {
		return nil, merrors.InvalidArgument("invalid Vault address")
	}
	if !regexp.MustCompile(`^[a-zA-Z0-9_-]+$`).MatchString(config.DatabaseRole) || config.RoleIDFile == "" || config.SecretIDFile == "" {
		return nil, merrors.InvalidArgument("Vault database role and AppRole files are required")
	}
	database, err := url.Parse(uri)
	if err != nil || database.Scheme != "mongodb" || database.Host == "" || database.User != nil {
		return nil, merrors.InvalidArgument("Vault requires a MongoDB URI without embedded credentials")
	}
	return &Issuer{config: config, uri: database, http: &http.Client{Timeout: 10 * time.Second, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}}, nil
}

type response struct {
	Auth struct {
		Token string `json:"client_token"`
		TTL   int    `json:"lease_duration"`
	} `json:"auth"`
	TTL     int    `json:"lease_duration"`
	LeaseID string `json:"lease_id"`
	Data    struct {
		Username string `json:"username"`
		Password string `json:"password"`
	} `json:"data"`
}

func (i *Issuer) request(ctx context.Context, path, token string, body any) (response, error) {
	var out response
	var input io.Reader
	method := http.MethodGet
	if body != nil {
		raw, err := json.Marshal(body)
		if err != nil {
			return out, merrors.InternalWrap(err, "encode Vault request")
		}
		input = bytes.NewReader(raw)
		method = http.MethodPost
	}
	req, err := http.NewRequestWithContext(ctx, method, strings.TrimRight(i.config.Address, "/")+"/v1/"+path, input)
	if err != nil {
		return out, merrors.OpaqueWrap(merrors.ErrInvalidArg, err, "create Vault request")
	}
	req.Header.Set("Content-Type", "application/json")
	if token != "" {
		req.Header.Set("X-Vault-Token", token)
	}
	res, err := i.http.Do(req)
	if err != nil {
		return out, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "Vault request failed")
	}
	defer res.Body.Close()
	if res.StatusCode < 200 || res.StatusCode >= 300 {
		return out, merrors.ServiceUnavailable("Vault request was rejected")
	}
	if res.StatusCode == http.StatusNoContent {
		return out, nil
	}
	if err = json.NewDecoder(io.LimitReader(res.Body, 1<<20)).Decode(&out); err != nil {
		return out, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "invalid Vault response")
	}
	return out, nil
}

func (i *Issuer) Issue(ctx context.Context) (source.Lease, error) {
	var lease source.Lease
	role, err := os.ReadFile(i.config.RoleIDFile)
	if err != nil {
		return lease, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "read Vault AppRole identity")
	}
	secret, err := os.ReadFile(i.config.SecretIDFile)
	if err != nil {
		return lease, merrors.OpaqueWrap(merrors.ErrServiceUnavailable, err, "read Vault AppRole credential")
	}
	started := time.Now()
	login, err := i.request(ctx, "auth/approle/login", "", map[string]string{"role_id": strings.TrimSpace(string(role)), "secret_id": strings.TrimSpace(string(secret))})
	if err != nil {
		return lease, err
	}
	if login.Auth.Token == "" {
		return lease, merrors.FailedPrecondition("Vault returned no application identity")
	}
	// One token owns one database lease. Revoking it never touches Agent's token
	// or the replacement generation, and requires only the default self policy.
	revoke := func(ctx context.Context) error {
		_, err := i.request(ctx, "auth/token/revoke-self", login.Auth.Token, map[string]any{})
		return err
	}
	if login.Auth.TTL <= 0 {
		cleanup, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		_ = revoke(cleanup)
		return lease, merrors.FailedPrecondition("Vault returned no bounded identity lifetime")
	}
	credential, err := i.request(ctx, "database/creds/"+i.config.DatabaseRole, login.Auth.Token, nil)
	if err != nil || credential.Data.Username == "" || credential.Data.Password == "" || credential.TTL <= 0 || credential.LeaseID == "" {
		cleanup, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		_ = revoke(cleanup)
		if err != nil {
			return lease, err
		}
		return lease, merrors.FailedPrecondition("Vault returned incomplete database credentials")
	}
	uri := *i.uri
	uri.User = url.UserPassword(credential.Data.Username, credential.Data.Password)
	return source.Lease{URI: uri.String(), ExpiresAt: started.Add(time.Duration(min(login.Auth.TTL, credential.TTL)) * time.Second), Revoke: revoke}, nil
}