/*
Copyright © The ESO Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package template

import (
	"bytes"
	"fmt"
	"maps"
	"strings"
	tpl "text/template"

	"github.com/spf13/pflag"
	corev1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/util/yaml"
	"sigs.k8s.io/controller-runtime/pkg/client"

	esapi "github.com/external-secrets/external-secrets/apis/externalsecrets/v1"
	"github.com/external-secrets/external-secrets/runtime/feature"
	"github.com/external-secrets/external-secrets/runtime/template/v2/sprig"
)

var tplFuncs = tpl.FuncMap{
	"pkcs12key":      pkcs12key,
	"pkcs12keyPass":  pkcs12keyPass,
	"pkcs12cert":     pkcs12cert,
	"pkcs12certPass": pkcs12certPass,

	"pemToPkcs12":               pemToPkcs12,
	"pemToPkcs12Pass":           pemToPkcs12Pass,
	"fullPemToPkcs12":           fullPemToPkcs12,
	"fullPemToPkcs12Pass":       fullPemToPkcs12Pass,
	"pemTruststoreToPKCS12":     pemTruststoreToPKCS12,
	"pemTruststoreToPKCS12Pass": pemTruststoreToPKCS12Pass,

	"filterPEM":       filterPEM,
	"filterCertChain": filterCertChain,
	"certSANs":        certSANs,

	"jwkPublicKeyPem":  jwkPublicKeyPem,
	"jwkPrivateKeyPem": jwkPrivateKeyPem,

	"toYaml":   toYAML,
	"fromYaml": fromYAML,

	"rsaDecrypt": rsaDecrypt,
}

var leftDelim, rightDelim string

var (
	errConvertingToUnstructured = "failed to convert object to unstructured: %w"
	errConvertingToObject       = "failed to convert unstructured to object: %w"
)

// FuncMap returns the template function map so other templating calls can use the same extra functions.
func FuncMap() tpl.FuncMap {
	return tplFuncs
}

const (
	errParse                = "unable to parse template at key %s: %s"
	errExecute              = "unable to execute template at key %s: %s"
	errDecodePKCS12WithPass = "unable to decode pkcs12 with password: %s"
	errDecodeCertWithPass   = "unable to decode pkcs12 certificate with password: %s"
	errParsePrivKey         = "unable to parse private key type"

	pemTypeCertificate = "CERTIFICATE"
	pemTypeKey         = "PRIVATE KEY"
)

func init() {
	maps.Copy(tplFuncs, sprig.TxtFuncMap())
	fs := pflag.NewFlagSet("template", pflag.ExitOnError)
	fs.StringVar(&leftDelim, "template-left-delimiter", "{{", "templating left delimiter")
	fs.StringVar(&rightDelim, "template-right-delimiter", "}}", "templating right delimiter")
	feature.Register(feature.Feature{
		Flags: fs,
	})
}

func applyToTarget(k string, val []byte, target string, obj client.Object) error {
	target = strings.ToLower(target)
	switch target {
	case "annotations":
		annotations := obj.GetAnnotations()
		if annotations == nil {
			annotations = make(map[string]string)
		}
		annotations[k] = string(val)
		obj.SetAnnotations(annotations)
	case "labels":
		labels := obj.GetLabels()
		if labels == nil {
			labels = make(map[string]string)
		}
		labels[k] = string(val)
		obj.SetLabels(labels)
	case "data":
		if err := setField(obj, "data", k, val); err != nil {
			return fmt.Errorf("failed to set data field on object: %w", err)
		}
	case "spec":
		if err := setField(obj, "spec", k, val); err != nil {
			return fmt.Errorf("failed to set data field on object: %w", err)
		}
	default:
		parts := strings.Split(target, ".")
		if len(parts) == 0 {
			return fmt.Errorf("invalid path: %s", target)
		}

		unstructured, err := runtime.DefaultUnstructuredConverter.ToUnstructured(obj)
		if err != nil {
			return fmt.Errorf(errConvertingToUnstructured, err)
		}

		// Navigate to the parent of the target field
		current := unstructured
		for i := range len(parts) - 1 {
			part := parts[i]
			if current[part] == nil {
				current[part] = make(map[string]any)
			}
			next, ok := current[part].(map[string]any)
			if !ok {
				return fmt.Errorf("path %s is not a map at segment %s", target, part)
			}
			current = next
		}

		// Set the value at the final key
		// Convert []byte to string to avoid base64 encoding when serializing
		lastPart := parts[len(parts)-1]
		current[lastPart] = tryParseYAML(string(val))

		// Convert back to the original object type
		if err := runtime.DefaultUnstructuredConverter.FromUnstructured(unstructured, obj); err != nil {
			return fmt.Errorf(errConvertingToObject, err)
		}
	}

	// all fields have been nilled out if they weren't set.
	if obj.GetLabels() == nil {
		obj.SetLabels(make(map[string]string))
	}
	if obj.GetAnnotations() == nil {
		obj.SetAnnotations(make(map[string]string))
	}

	return nil
}

func valueScopeApply(tplMap, data map[string][]byte, target string, secret client.Object) error {
	for k, v := range tplMap {
		val, err := execute(k, string(v), data)
		if err != nil {
			return fmt.Errorf(errExecute, k, err)
		}
		if err := applyToTarget(k, val, target, secret); err != nil {
			return fmt.Errorf("failed to apply to target: %w", err)
		}
	}
	return nil
}

func mapScopeApply(tpl string, data map[string][]byte, target string, secret client.Object) error {
	val, err := execute(tpl, tpl, data)
	if err != nil {
		return fmt.Errorf(errExecute, tpl, err)
	}

	target = strings.ToLower(target)
	switch target {
	case "annotations", "labels", "data":
		// normal route
		src := make(map[string]string)
		err = yaml.Unmarshal(val, &src)
		if err != nil {
			return fmt.Errorf("could not unmarshal template to 'map[string][]byte': %w", err)
		}
		for k, val := range src {
			if err := applyToTarget(k, []byte(val), target, secret); err != nil {
				return fmt.Errorf("failed to apply to target: %w", err)
			}
		}

		// we are done
		return nil
	}

	// for more complex path, we need to navigate to the last element of the path
	// creating objects in that path if they don't exist and then apply the parsed
	// structure at that location to the entire object.
	var parsed any
	if err := yaml.Unmarshal(val, &parsed); err != nil {
		return fmt.Errorf("could not unmarshal template YAML: %w", err)
	}

	return applyParsedToPath(parsed, target, secret)
}

// Execute renders the secret data as template. If an error occurs processing is stopped immediately.
func Execute(tpl, data map[string][]byte, scope esapi.TemplateScope, target string, secret client.Object) error {
	if tpl == nil {
		return nil
	}
	switch scope {
	case esapi.TemplateScopeKeysAndValues:
		for _, v := range tpl {
			err := mapScopeApply(string(v), data, target, secret)
			if err != nil {
				return err
			}
		}
	case esapi.TemplateScopeValues:
		err := valueScopeApply(tpl, data, target, secret)
		if err != nil {
			return err
		}
	default:
		return fmt.Errorf("unknown scope '%v': expected 'Values' or 'KeysAndValues'", scope)
	}
	return nil
}

func execute(k, val string, data map[string][]byte) ([]byte, error) {
	strValData := make(map[string]string, len(data))
	for k := range data {
		strValData[k] = string(data[k])
	}

	t, err := tpl.New(k).
		Option("missingkey=error").
		Funcs(tplFuncs).
		Delims(leftDelim, rightDelim).
		Parse(val)
	if err != nil {
		return nil, fmt.Errorf(errParse, k, err)
	}
	buf := bytes.NewBuffer(nil)
	err = t.Execute(buf, strValData)
	if err != nil {
		return nil, fmt.Errorf(errExecute, k, err)
	}
	return buf.Bytes(), nil
}

// setData sets the data field of the object.
func setField(obj client.Object, field, k string, val []byte) error {
	m, err := runtime.DefaultUnstructuredConverter.ToUnstructured(obj)
	if err != nil {
		return fmt.Errorf(errConvertingToUnstructured, err)
	}
	_, ok := m[field]
	if !ok {
		m[field] = map[string]any{}
	}
	specMap, ok := m[field].(map[string]any)
	if !ok {
		return fmt.Errorf("failed to convert data to map[string][]byte")
	}

	// Secrets require base64-encoded []byte values in the data field
	// Other resources (ConfigMaps, custom resources) need plain string values
	_, isSecret := obj.(*corev1.Secret)
	if isSecret {
		// For Secrets, keep as []byte (will be base64-encoded during serialization)
		specMap[k] = val
	} else {
		// For generic (ConfigMaps, custom resources), use plain strings
		specMap[k] = string(val)
	}
	m[field] = specMap

	// Convert back to the original object type
	if err := runtime.DefaultUnstructuredConverter.FromUnstructured(m, obj); err != nil {
		return fmt.Errorf(errConvertingToObject, err)
	}
	return nil
}

// tryParseYAML attempts to parse a string value as YAML, returns original value if parsing fails.
func tryParseYAML(value any) any {
	str, ok := value.(string)
	if !ok {
		return value
	}

	var parsed any
	if err := yaml.Unmarshal([]byte(str), &parsed); err == nil {
		return parsed
	}

	return value
}

// applyParsedToPath applies a parsed YAML structure to a specific path in the object.
func applyParsedToPath(parsed any, target string, obj client.Object) error {
	unstructured, err := runtime.DefaultUnstructuredConverter.ToUnstructured(obj)
	if err != nil {
		return fmt.Errorf(errConvertingToUnstructured, err)
	}

	parts := strings.Split(target, ".")
	if len(parts) == 0 {
		return fmt.Errorf("invalid path: %s", target)
	}

	// single value, aka "spec"
	if len(parts) == 1 {
		unstructured[parts[0]] = parsed
	} else {
		// navigate to the last element of the path and apply the entire struct at that location.
		// build up the entire map structure that we are eventually going to apply.
		current := unstructured
		// this STOPS at the last part! That is important. for _, part := range parts does _include_ the last part
		for i := 0; i < len(parts)-1; i++ {
			part := parts[i]
			if current[part] == nil {
				current[part] = make(map[string]any)
			}
			next, ok := current[part].(map[string]any)
			if !ok {
				return fmt.Errorf("path %s is not a map at segment %s", target, part)
			}
			current = next
		}

		// once we constructed the entire segment, we finally apply our parsed object
		// MERGE the parsed content into existing content instead of replacing it
		lastPart := parts[len(parts)-1]
		if existing, exists := current[lastPart]; exists {
			// if both existing and new values are maps, merge them
			existingMap, existingOk := existing.(map[string]any)
			parsedMap, parsedOk := parsed.(map[string]any)

			if existingOk && parsedOk {
				maps.Copy(existingMap, parsedMap)

				current[lastPart] = existingMap
			} else {
				// existing or parsed value is not a map, replace entirely.
				// this might break if people are trying to overwrite
				// fields that aren't supposed to do that. but that's
				// on the user to keep in mind. If they are trying to
				// update a number field with a complex value, that's
				// going to error on update anyway.
				current[lastPart] = parsed
			}
		} else {
			// field doesn't exist yet, create it
			current[lastPart] = parsed
		}
	}

	// convert back to original object
	if err := runtime.DefaultUnstructuredConverter.FromUnstructured(unstructured, obj); err != nil {
		return fmt.Errorf(errConvertingToObject, err)
	}

	return nil
}