package file

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"maps"
	"os"
	"os/signal"
	"path"
	"path/filepath"
	"strings"
	"syscall"
	"text/template"

	"github.com/Masterminds/sprig/v3"
	"github.com/fsnotify/fsnotify"
	"github.com/rs/zerolog/log"
	"github.com/traefik/paerser/file"
	"github.com/traefik/traefik/v3/pkg/config/dynamic"
	"github.com/traefik/traefik/v3/pkg/observability/logs"
	"github.com/traefik/traefik/v3/pkg/provider"
	"github.com/traefik/traefik/v3/pkg/safe"
	"github.com/traefik/traefik/v3/pkg/tls"
	"github.com/traefik/traefik/v3/pkg/types"
)

// ProviderName is the file provider name.
const ProviderName = "file"

var _ provider.Provider = (*Provider)(nil)

// Provider holds configurations of the provider.
type Provider struct {
	Directory                 string `description:"Load dynamic configuration from one or more .yml or .toml files in a directory." json:"directory,omitempty" toml:"directory,omitempty" yaml:"directory,omitempty" export:"true"`
	Watch                     bool   `description:"Watch provider." json:"watch,omitempty" toml:"watch,omitempty" yaml:"watch,omitempty" export:"true"`
	Filename                  string `description:"Load dynamic configuration from a file." json:"filename,omitempty" toml:"filename,omitempty" yaml:"filename,omitempty" export:"true"`
	DebugLogGeneratedTemplate bool   `description:"Enable debug logging of generated configuration template." json:"debugLogGeneratedTemplate,omitempty" toml:"debugLogGeneratedTemplate,omitempty" yaml:"debugLogGeneratedTemplate,omitempty" export:"true"`
}

// SetDefaults sets the default values.
func (p *Provider) SetDefaults() {
	p.Watch = true
	p.Filename = ""
}

// Init the provider.
func (p *Provider) Init() error {
	return nil
}

// Provide allows the file provider to provide configurations to traefik
// using the given configuration channel.
func (p *Provider) Provide(configurationChan chan<- dynamic.Message, pool *safe.Pool) error {
	logger := log.With().Str(logs.ProviderName, ProviderName).Logger()

	if p.Watch {
		var watchItems []string

		switch {
		case len(p.Directory) > 0:
			watchItems = append(watchItems, p.Directory)

			fileList, err := os.ReadDir(p.Directory)
			if err != nil {
				return fmt.Errorf("unable to read directory %s: %w", p.Directory, err)
			}

			for _, entry := range fileList {
				if entry.IsDir() {
					// ignore sub-dir
					continue
				}
				if !isFileSupported(entry.Name()) {
					// ignore unsupported file extension
					continue
				}
				watchItems = append(watchItems, path.Join(p.Directory, entry.Name()))
			}
		case len(p.Filename) > 0:
			if !isFileSupported(p.Filename) {
				return fmt.Errorf("unsupported file extension for file %s", p.Filename)
			}
			watchItems = append(watchItems, filepath.Dir(p.Filename), p.Filename)
		default:
			return errors.New("error using file configuration provider, neither filename nor directory is defined")
		}

		if err := p.addWatcher(pool, watchItems, configurationChan, p.applyConfiguration); err != nil {
			return err
		}
	}

	pool.GoCtx(func(ctx context.Context) {
		signals := make(chan os.Signal, 1)
		signal.Notify(signals, syscall.SIGHUP)

		for {
			select {
			case <-ctx.Done():
				return
			// signals only receives SIGHUP events.
			case <-signals:
				if err := p.applyConfiguration(configurationChan); err != nil {
					logger.Error().Err(err).Msg("Error while building configuration")
				}
			}
		}
	})

	if err := p.applyConfiguration(configurationChan); err != nil {
		if p.Watch {
			logger.Err(err).Msg("Error while building configuration (for the first time)")
			return nil
		}

		return err
	}

	return nil
}

// CreateConfiguration creates a provider configuration from content using templating.
func (p *Provider) CreateConfiguration(ctx context.Context, filename string, funcMap template.FuncMap, templateObjects any) (*dynamic.Configuration, error) {
	tmplContent, err := readFile(filename)
	if err != nil {
		return nil, fmt.Errorf("error reading configuration file: %s - %w", filename, err)
	}

	defaultFuncMap := sprig.TxtFuncMap()
	defaultFuncMap["normalize"] = provider.Normalize
	defaultFuncMap["split"] = strings.Split
	maps.Copy(defaultFuncMap, funcMap)

	tmpl := template.New(p.Filename).Funcs(defaultFuncMap)

	_, err = tmpl.Parse(tmplContent)
	if err != nil {
		return nil, err
	}

	var buffer bytes.Buffer
	err = tmpl.Execute(&buffer, templateObjects)
	if err != nil {
		return nil, err
	}

	renderedTemplate := buffer.String()
	if p.DebugLogGeneratedTemplate {
		logger := log.Ctx(ctx)
		logger.Debug().Msgf("Template content: %s", tmplContent)
		logger.Debug().Msgf("Rendering results: %s", renderedTemplate)
	}

	return p.decodeConfiguration(filename, renderedTemplate)
}

// DecodeConfiguration Decodes a *types.Configuration from a content.
func (p *Provider) DecodeConfiguration(filename string) (*dynamic.Configuration, error) {
	content, err := readFile(filename)
	if err != nil {
		return nil, fmt.Errorf("error reading configuration file: %s - %w", filename, err)
	}

	return p.decodeConfiguration(filename, content)
}

func (p *Provider) addWatcher(pool *safe.Pool, items []string, configurationChan chan<- dynamic.Message, callback func(chan<- dynamic.Message) error) error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return fmt.Errorf("error creating file watcher: %w", err)
	}

	for _, item := range items {
		log.Debug().Msgf("add watcher on: %s", item)
		err = watcher.Add(item)
		if err != nil {
			return fmt.Errorf("error adding file watcher for %s: %w", item, err)
		}
	}

	// Process events
	pool.GoCtx(func(ctx context.Context) {
		logger := log.With().Str(logs.ProviderName, ProviderName).Logger()
		defer watcher.Close()
		for {
			select {
			case <-ctx.Done():
				return
			case evt := <-watcher.Events:
				if p.Directory == "" {
					_, evtFileName := filepath.Split(evt.Name)
					_, confFileName := filepath.Split(p.Filename)
					if evtFileName == confFileName {
						err := callback(configurationChan)
						if err != nil {
							logger.Error().Err(err).Msg("Error occurred during watcher callback")
						}
					}
				} else {
					err := callback(configurationChan)
					if err != nil {
						logger.Error().Err(err).Msg("Error occurred during watcher callback")
					}
				}
			case err := <-watcher.Errors:
				logger.Error().Err(err).Msg("Watcher event error")
			}
		}
	})
	return nil
}

// applyConfiguration builds the configuration and sends it to the given configurationChan.
func (p *Provider) applyConfiguration(configurationChan chan<- dynamic.Message) error {
	configuration, err := p.buildConfiguration()
	if err != nil {
		return err
	}

	sendConfigToChannel(configurationChan, configuration)
	return nil
}

// buildConfiguration loads configuration either from file or a directory
// specified by 'Filename'/'Directory' and returns a 'Configuration' object.
func (p *Provider) buildConfiguration() (*dynamic.Configuration, error) {
	ctx := log.With().Str(logs.ProviderName, ProviderName).Logger().WithContext(context.Background())

	if len(p.Directory) > 0 {
		configurations, err := p.collectFileConfigs(ctx, p.Directory, "")
		if err != nil {
			return nil, fmt.Errorf("collecting file configs: %w", err)
		}

		return provider.Merge(ctx, configurations, provider.ResourceStrategySkipDuplicates), nil
	}

	if len(p.Filename) > 0 {
		return p.loadFileConfig(ctx, p.Filename, true)
	}

	return nil, errors.New("error using file configuration provider, neither filename nor directory is defined")
}

func (p *Provider) loadFileConfig(ctx context.Context, filename string, parseTemplate bool) (*dynamic.Configuration, error) {
	var err error
	var configuration *dynamic.Configuration
	if parseTemplate {
		configuration, err = p.CreateConfiguration(ctx, filename, template.FuncMap{}, false)
	} else {
		configuration, err = p.DecodeConfiguration(filename)
	}
	if err != nil {
		return nil, err
	}

	if configuration.TLS != nil {
		configuration.TLS.Certificates = flattenCertificates(ctx, configuration.TLS)

		// TLS Options
		if configuration.TLS.Options != nil {
			for name, options := range configuration.TLS.Options {
				var caCerts []types.FileOrContent

				for _, caFile := range options.ClientAuth.CAFiles {
					content, err := caFile.Read()
					if err != nil {
						log.Ctx(ctx).Error().Err(err).Send()
						continue
					}

					caCerts = append(caCerts, types.FileOrContent(content))
				}
				options.ClientAuth.CAFiles = caCerts

				configuration.TLS.Options[name] = options
			}
		}

		// TLS stores
		if len(configuration.TLS.Stores) > 0 {
			for name, store := range configuration.TLS.Stores {
				if store.DefaultCertificate == nil {
					continue
				}

				content, err := store.DefaultCertificate.CertFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				store.DefaultCertificate.CertFile = types.FileOrContent(content)

				content, err = store.DefaultCertificate.KeyFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				store.DefaultCertificate.KeyFile = types.FileOrContent(content)

				configuration.TLS.Stores[name] = store
			}
		}
	}

	// HTTP ServersTransport
	if configuration.HTTP != nil && len(configuration.HTTP.ServersTransports) > 0 {
		for name, st := range configuration.HTTP.ServersTransports {
			var certificates []tls.Certificate
			for _, cert := range st.Certificates {
				content, err := cert.CertFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				cert.CertFile = types.FileOrContent(content)

				content, err = cert.KeyFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				cert.KeyFile = types.FileOrContent(content)

				certificates = append(certificates, cert)
			}

			configuration.HTTP.ServersTransports[name].Certificates = certificates

			var rootCAs []types.FileOrContent
			for _, rootCA := range st.RootCAs {
				content, err := rootCA.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}

				rootCAs = append(rootCAs, types.FileOrContent(content))
			}

			st.RootCAs = rootCAs
		}
	}

	// TCP ServersTransport
	if configuration.TCP != nil && len(configuration.TCP.ServersTransports) > 0 {
		for name, st := range configuration.TCP.ServersTransports {
			var certificates []tls.Certificate
			if st.TLS == nil {
				continue
			}
			for _, cert := range st.TLS.Certificates {
				content, err := cert.CertFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				cert.CertFile = types.FileOrContent(content)

				content, err = cert.KeyFile.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}
				cert.KeyFile = types.FileOrContent(content)

				certificates = append(certificates, cert)
			}

			configuration.TCP.ServersTransports[name].TLS.Certificates = certificates

			var rootCAs []types.FileOrContent
			for _, rootCA := range st.TLS.RootCAs {
				content, err := rootCA.Read()
				if err != nil {
					log.Ctx(ctx).Error().Err(err).Send()
					continue
				}

				rootCAs = append(rootCAs, types.FileOrContent(content))
			}

			st.TLS.RootCAs = rootCAs
		}
	}

	return configuration, nil
}

// collectFileConfigs recursively collects configurations from files in the given directory.
func (p *Provider) collectFileConfigs(ctx context.Context, directory, prefix string) ([]provider.NamedConfiguration, error) {
	var configurations []provider.NamedConfiguration

	fileList, err := os.ReadDir(directory)
	if err != nil {
		return nil, fmt.Errorf("reading directory %s: %w", directory, err)
	}

	for _, item := range fileList {
		logger := log.Ctx(ctx).With().Str("filename", item.Name()).Logger()

		itemPath := filepath.Join(directory, item.Name())
		filename := item.Name()
		if prefix != "" {
			filename = filepath.Join(prefix, item.Name())
		}

		if item.IsDir() {
			sub, err := p.collectFileConfigs(ctx, itemPath, filename)
			if err != nil {
				return nil, fmt.Errorf("loading content configuration from subdirectory %s: %w", item, err)
			}
			configurations = append(configurations, sub...)
			continue
		}

		if !isFileSupported(item.Name()) {
			logger.Debug().Msg("Skipping file, unsupported extension")
			continue
		}

		c, err := p.loadFileConfig(ctx, itemPath, true)
		if err != nil {
			return nil, fmt.Errorf("%s: %w", itemPath, err)
		}

		configurations = append(configurations, provider.NamedConfiguration{
			Name:          filename,
			Configuration: c,
		})
	}

	return configurations, nil
}

func (p *Provider) decodeConfiguration(filePath, content string) (*dynamic.Configuration, error) {
	configuration := &dynamic.Configuration{
		HTTP: &dynamic.HTTPConfiguration{
			Routers:           make(map[string]*dynamic.Router),
			Middlewares:       make(map[string]*dynamic.Middleware),
			Services:          make(map[string]*dynamic.Service),
			ServersTransports: make(map[string]*dynamic.ServersTransport),
		},
		TCP: &dynamic.TCPConfiguration{
			Routers:           make(map[string]*dynamic.TCPRouter),
			Services:          make(map[string]*dynamic.TCPService),
			Middlewares:       make(map[string]*dynamic.TCPMiddleware),
			ServersTransports: make(map[string]*dynamic.TCPServersTransport),
		},
		TLS: &dynamic.TLSConfiguration{
			Stores:  make(map[string]tls.Store),
			Options: make(map[string]tls.Options),
		},
		UDP: &dynamic.UDPConfiguration{
			Routers:  make(map[string]*dynamic.UDPRouter),
			Services: make(map[string]*dynamic.UDPService),
		},
	}

	err := file.DecodeContent(content, strings.ToLower(filepath.Ext(filePath)), configuration)
	if err != nil {
		return nil, err
	}

	return configuration, nil
}

func sendConfigToChannel(configurationChan chan<- dynamic.Message, configuration *dynamic.Configuration) {
	configurationChan <- dynamic.Message{
		ProviderName:  "file",
		Configuration: configuration,
	}
}

func flattenCertificates(ctx context.Context, tlsConfig *dynamic.TLSConfiguration) []*tls.CertAndStores {
	var certs []*tls.CertAndStores
	for _, cert := range tlsConfig.Certificates {
		content, err := cert.Certificate.CertFile.Read()
		if err != nil {
			log.Ctx(ctx).Error().Err(err).Send()
			continue
		}
		cert.Certificate.CertFile = types.FileOrContent(string(content))

		content, err = cert.Certificate.KeyFile.Read()
		if err != nil {
			log.Ctx(ctx).Error().Err(err).Send()
			continue
		}
		cert.Certificate.KeyFile = types.FileOrContent(string(content))

		certs = append(certs, cert)
	}

	return certs
}

func readFile(filename string) (string, error) {
	if len(filename) > 0 {
		buf, err := os.ReadFile(filename)
		if err != nil {
			return "", err
		}
		return string(buf), nil
	}
	return "", fmt.Errorf("invalid filename: %s", filename)
}

func isFileSupported(filename string) bool {
	switch strings.ToLower(filepath.Ext(filename)) {
	case ".toml", ".yaml", ".yml":
		return true
	default:
		return false
	}
}
