package proxmox

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"maps"
	"net/http"
	"regexp"
	"slices"
	"strings"

	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider"
)

// permanentf and transientf classify an error at the source, so classify
// keeps that class no matter what wraps it later.
func permanentf(format string, args ...any) error {
	return fmt.Errorf("%w: %s", provider.ErrPermanent, fmt.Sprintf(format, args...))
}

func transientf(format string, args ...any) error {
	return fmt.Errorf("%w: %s", provider.ErrTransient, fmt.Sprintf(format, args...))
}

// apiError is a non-2xx answer from the API. It carries the status and the
// message only, never headers or the request URL, so no credential can leak
// through it (spec entry 14).
type apiError struct {
	Status  int
	Message string
	// Errors is a 400's per-parameter map.
	Errors map[string]string
}

func (e *apiError) Error() string {
	msg := fmt.Sprintf("proxmox API %d: %s", e.Status, e.Message)
	if len(e.Errors) == 0 {
		return msg
	}
	fields := make([]string, 0, len(e.Errors))
	for _, k := range slices.Sorted(maps.Keys(e.Errors)) {
		fields = append(fields, k+": "+e.Errors[k])
	}
	return msg + " (" + strings.Join(fields, "; ") + ")"
}

// newAPIError builds an apiError from a response: the body's message with
// its trailing newline trimmed, or the status reason phrase when the body
// has none, as for a 401 (spec entry 13, fact F1).
func newAPIError(status int, reason string, body []byte) *apiError {
	var b struct {
		Message string            `json:"message"`
		Errors  map[string]string `json:"errors"`
	}
	_ = json.Unmarshal(body, &b)
	e := &apiError{Status: status, Message: strings.TrimSpace(b.Message)}
	if e.Message == "" {
		e.Message = strings.TrimSpace(reason)
	}
	if e.Message == "" {
		e.Message = http.StatusText(status)
	}
	if len(b.Errors) > 0 {
		e.Errors = make(map[string]string, len(b.Errors))
		for k, v := range b.Errors {
			e.Errors[k] = strings.TrimSpace(v)
		}
	}
	return e
}

// The 500 messages the provider acts on, each backed by a captured response
// under testdata/.
var (
	vmConfigMissing = regexp.MustCompile(`^Configuration file '[^']*' does not exist$`)
)

const (
	msgAlreadyExists      = "config file already exists"
	msgAgentNotRunning    = "QEMU guest agent is not running"
	msgAgentNotConfigured = "No QEMU guest agent configured"
	msgNoSuchStorage      = "No such storage."
)

// server500 returns the message of err when it is, or wraps, an apiError
// with status 500.
func server500(err error) (string, bool) {
	var ae *apiError
	if !errors.As(err, &ae) || ae.Status != http.StatusInternalServerError {
		return "", false
	}
	return ae.Message, true
}

// isNotExist reports the missing-VM answer: the VM's config file is gone.
func isNotExist(err error) bool {
	msg, ok := server500(err)
	return ok && vmConfigMissing.MatchString(msg)
}

// isNoSuchStorage reports a storage the cluster does not know: a 400 whose
// storage field error is exactly msgNoSuchStorage. Other storage field
// errors, such as a clone onto a storage without image support, are not.
func isNoSuchStorage(err error) bool {
	var ae *apiError
	return errors.As(err, &ae) && ae.Status == http.StatusBadRequest && ae.Errors["storage"] == msgNoSuchStorage
}

// isAlreadyExists reports a clone onto a VMID that is taken.
func isAlreadyExists(err error) bool {
	msg, ok := server500(err)
	return ok && strings.HasSuffix(msg, msgAlreadyExists)
}

// isAgentNotRunning reports a VM with the agent enabled whose agent does not
// answer yet.
func isAgentNotRunning(err error) bool {
	msg, ok := server500(err)
	return ok && msg == msgAgentNotRunning
}

// isAgentNotConfigured reports a VM whose config no longer enables the agent.
func isAgentNotConfigured(err error) bool {
	msg, ok := server500(err)
	return ok && msg == msgAgentNotConfigured
}

// classify maps any error reaching the provider's boundary to one of the
// four contract sentinels, per spec entry 13. op is the contract operation:
// a vanished VM inside Create is Transient, because the contract forbids
// NotFound from Create.
func classify(op string, err error) error {
	if err == nil {
		return provider.ErrTransient
	}
	for _, class := range []error{provider.ErrNotFound, provider.ErrQuotaExceeded, provider.ErrPermanent, provider.ErrTransient} {
		if errors.Is(err, class) {
			return class
		}
	}
	var ae *apiError
	if errors.As(err, &ae) {
		return classifyAPI(op, err, ae)
	}
	if isTLSVerification(err) {
		return provider.ErrPermanent
	}
	// Everything else retries: context cancellation and deadlines,
	// net.OpError, io.EOF, and anything unrecognised.
	return provider.ErrTransient
}

func classifyAPI(op string, err error, ae *apiError) error {
	switch {
	case ae.Status >= 400 && ae.Status < 500:
		// 401 and 403 are credentials or privileges, 400 a request Proxmox
		// will never accept: all fixed by an admin, not by retrying.
		return provider.ErrPermanent
	case isNotExist(err):
		if op == "create" {
			return provider.ErrTransient
		}
		return provider.ErrNotFound
	default:
		// Other 500s (a lock, a taken VMID escaping the allocator, agent
		// states escaping Get), pveproxy's 595 and 596, and any other status.
		return provider.ErrTransient
	}
}

// isTLSVerification reports a certificate the client refused: the URL does
// not match the certificate, or the CA is wrong. An admin fixes the URL or
// caFile; retrying cannot.
func isTLSVerification(err error) bool {
	var (
		verr     *tls.CertificateVerificationError
		unknown  x509.UnknownAuthorityError
		hostname x509.HostnameError
		invalid  x509.CertificateInvalidError
	)
	return errors.As(err, &verr) || errors.As(err, &unknown) || errors.As(err, &hostname) || errors.As(err, &invalid)
}