package nfs

import (
	"bytes"
	"context"
	"embed"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"text/template"
	"time"

	"github.com/darroyo/nasctl/internal/db"
	"github.com/darroyo/nasctl/internal/system"
)

const ModuleName = "nfs"

//go:embed exports.tmpl
var exportsTemplate embed.FS

type Config struct {
	ExportsPath string
	Reload      bool
}

type Module struct {
	cfg Config
}

type templateExport struct {
	Path       string
	ClientSpec string
}

type templateData struct {
	Exports []templateExport
}

func New(cfg Config) *Module {
	if cfg.ExportsPath == "" {
		cfg.ExportsPath = "/etc/exports"
	}
	return &Module{cfg: cfg}
}

func (m *Module) Name() string {
	return ModuleName
}

func (m *Module) IsDirty(ctx context.Context, database *db.DB) (bool, error) {
	return database.IsDirty(ModuleName)
}

func (m *Module) Apply(ctx context.Context, database *db.DB) error {
	if err := m.maybeBackup(database); err != nil {
		return err
	}

	exports, err := database.ListNFSExports()
	if err != nil {
		return err
	}

	content, err := m.renderConfig(exports)
	if err != nil {
		return err
	}

	if err := writeAtomic(m.cfg.ExportsPath, content); err != nil {
		return err
	}

	if m.cfg.Reload {
		stdout, stderr, err := system.Run(ctx, "exportfs", "-ra")
		if err != nil {
			return fmt.Errorf("exportfs -ra: %w (stdout=%q stderr=%q)", err, stdout, stderr)
		}
	}

	message := fmt.Sprintf("applied %d nfs export(s) to %s", len(exports), m.cfg.ExportsPath)
	if err := database.AppendApplyLog(ModuleName, message, true); err != nil {
		return err
	}
	return database.ClearDirty(ModuleName)
}

// clientSpec builds the "client(opts) client(opts)" segment of an exports line.
// If no clients are configured, it defaults to "*(opts)".
func clientSpec(clients []string, options string) string {
	opts := strings.TrimSpace(options)
	if opts == "" {
		opts = "ro"
	}
	if len(clients) == 0 {
		return fmt.Sprintf("*(%s)", opts)
	}
	specs := make([]string, 0, len(clients))
	for _, client := range clients {
		client = strings.TrimSpace(client)
		if client == "" {
			continue
		}
		specs = append(specs, fmt.Sprintf("%s(%s)", client, opts))
	}
	if len(specs) == 0 {
		return fmt.Sprintf("*(%s)", opts)
	}
	return strings.Join(specs, " ")
}

func (m *Module) renderConfig(exports []db.NFSExport) ([]byte, error) {
	tmplContent, err := exportsTemplate.ReadFile("exports.tmpl")
	if err != nil {
		return nil, fmt.Errorf("read exports template: %w", err)
	}

	tmpl, err := template.New("exports").Parse(string(tmplContent))
	if err != nil {
		return nil, fmt.Errorf("parse exports template: %w", err)
	}

	data := templateData{Exports: make([]templateExport, 0, len(exports))}
	for _, export := range exports {
		data.Exports = append(data.Exports, templateExport{
			Path:       export.Path,
			ClientSpec: clientSpec(export.Clients, export.Options),
		})
	}

	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, data); err != nil {
		return nil, fmt.Errorf("execute exports template: %w", err)
	}
	return buf.Bytes(), nil
}

func (m *Module) maybeBackup(database *db.DB) error {
	done, ok, err := database.GetSetting("backup.nfs.done")
	if err != nil {
		return err
	}
	if ok && done == "true" {
		return nil
	}
	if _, err := os.Stat(m.cfg.ExportsPath); os.IsNotExist(err) {
		return nil
	} else if err != nil {
		return nil
	}
	src, err := os.ReadFile(m.cfg.ExportsPath)
	if err != nil {
		return nil
	}
	backupPath := m.cfg.ExportsPath + ".nasctl.bak." + time.Now().Format("20060102T150405")
	if err := os.WriteFile(backupPath, src, 0o644); err != nil {
		return fmt.Errorf("backup exports: %w", err)
	}
	_ = database.SetSetting("backup.nfs.done", "true")
	return nil
}

func writeAtomic(path string, content []byte) error {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("create config dir: %w", err)
	}

	tmp, err := os.CreateTemp(dir, ".exports.*")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	tmpPath := tmp.Name()

	cleanup := func() {
		_ = tmp.Close()
		_ = os.Remove(tmpPath)
	}

	if _, err := tmp.Write(content); err != nil {
		cleanup()
		return fmt.Errorf("write temp config: %w", err)
	}
	if err := tmp.Chmod(0o644); err != nil {
		cleanup()
		return fmt.Errorf("chmod temp config: %w", err)
	}
	if err := tmp.Close(); err != nil {
		cleanup()
		return fmt.Errorf("close temp config: %w", err)
	}
	if err := os.Rename(tmpPath, path); err != nil {
		cleanup()
		return fmt.Errorf("rename temp config: %w", err)
	}
	return nil
}