package engine

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"jarl/internal/auth"
	"jarl/internal/importer"
	"jarl/internal/model"
	"jarl/internal/validate"
)

// ImportResult is returned by Import.
type ImportResult struct {
	Report    *importer.Report `json:"report"`
	Changeset *model.Changeset `json:"changeset"`
	Result    *Result          `json:"result,omitempty"`
	Applied   bool             `json:"applied"`
}

// Import loads an existing BIND configuration into Jarl. The import becomes
// a changeset; if the configuration is valid it is applied right away
// (writing Jarl's files), otherwise it stays open so problems can be fixed
// before applying.
func (e *Engine) Import(ctx context.Context, mainPath string, p *auth.Principal, dryRun bool) (*ImportResult, error) {
	cur, err := e.store.LoadState(ctx)
	if err != nil {
		return nil, err
	}
	if len(cur.Zones)+len(cur.Views)+len(cur.ACLs)+len(cur.Keys)+len(cur.Options) > 0 {
		return nil, errf(KindConflict, "Jarl already has a configuration; import only works into an empty Jarl")
	}
	st, rep, err := importer.Import(ctx, mainPath, importer.Options{Tools: e.tools, Alloc: e.store.AllocateIDs, User: p.Name()})
	if err != nil {
		return nil, errf(KindBadRequest, "reading %s: %v", mainPath, err)
	}
	// Keep Jarl's own settings (defaults for new zones), but take the
	// name servers and contact from the imported zones if unset.
	st.Settings = cur.Settings
	if len(st.Settings.Nameservers) == 0 || st.Settings.RName == "" {
		for _, z := range st.SortedZones() {
			if z.Type != model.ZonePrimary {
				continue
			}
			if len(st.Settings.Nameservers) == 0 {
				for _, r := range st.ZoneRecords(z.ID) {
					if r.Name == z.Name && r.Type == "NS" {
						st.Settings.Nameservers = append(st.Settings.Nameservers, r.Data)
					}
				}
			}
			if st.Settings.RName == "" {
				st.Settings.RName = z.SOA.RName
			}
			break
		}
	}
	ops := DiffOps(cur, st)
	now := e.Now()
	for i := range ops {
		ops[i].AddedAt = now
	}
	out := &ImportResult{Report: rep}
	cs := &model.Changeset{Description: "import from " + mainPath, UserID: p.User.ID, Username: p.Name(), Via: "import", Status: model.ChangesetOpen, Ops: ops}
	if dryRun {
		out.Changeset = cs
		return out, nil
	}
	if err := e.store.CreateChangeset(ctx, cs); err != nil {
		return nil, err
	}
	out.Changeset = cs
	e.audit(ctx, p, "import", "changeset", cs.ID, mainPath, cs.ID, "success", fmt.Sprintf("%d zones, %d records", len(st.Zones), len(st.Records)), nil)
	res, err := e.Apply(ctx, cs.ID, p, ApplyOptions{NoReload: true})
	out.Result = res
	if err != nil {
		// Leave the changeset open for fixing.
		if _, ok := AsError(err); ok {
			return out, nil
		}
		return out, err
	}
	out.Applied = true
	return out, nil
}

// AdoptResult describes an adoption.
type AdoptResult struct {
	MainConfig string         `json:"main_config"`
	Backup     string         `json:"backup"`
	Serials    []SerialChange `json:"serials"`
	Already    bool           `json:"already_adopted"`
}

// mainConfigText is what Jarl writes to named's main configuration file.
func mainConfigText(jarlConf, backup string) string {
	return fmt.Sprintf(`// %s
//
// This server's DNS configuration is managed by Jarl. Jarl generates the
// file included below; make changes through the Jarl web UI, API or CLI.
// The configuration from before Jarl took over was saved as:
//   %s

include "%s";
`, "named.conf", backup, jarlConf)
}

// Adopt switches named over to Jarl's configuration: it bumps every
// primary zone's serial, makes named's main configuration file include
// Jarl's named.conf (saving the old file), reloads named and checks that
// every zone is served from Jarl's files. On failure the old main
// configuration is restored.
func (e *Engine) Adopt(ctx context.Context, p *auth.Principal) (*AdoptResult, error) {
	main := e.cfg.MainConfig
	jarlConf := e.cfg.Paths.MainConfig()
	if main == "" || filepath.Clean(main) == filepath.Clean(jarlConf) {
		return nil, errf(KindBadRequest, "bind.main_config is not set (or is Jarl's own named.conf); nothing to adopt")
	}
	res := &AdoptResult{MainConfig: main}
	if ok, _ := e.Adopted(); ok {
		res.Already = true
		return res, nil
	}
	st, err := e.store.LoadState(ctx)
	if err != nil {
		return nil, err
	}
	if len(st.Zones) == 0 {
		return nil, errf(KindConflict, "Jarl has no zones yet; import your configuration (jarld import) or create zones first")
	}
	if ps := e.validate(st); validate.HasErrors(ps) {
		return nil, &Error{Kind: KindValidation, Message: "the configuration has errors; fix them before adopting: " + describeErrors(ps), Problems: validate.Errors(ps)}
	}
	// Bump every primary zone's serial so named (and secondaries) load
	// the zones from Jarl's files.
	var reqs []Request
	for _, z := range st.SortedZones() {
		if z.Type == model.ZonePrimary {
			policy := z.SerialPolicy
			if policy == "" {
				policy = st.Settings.SerialPolicy
			}
			next := NextSerial(z.SOA.Serial, policy, e.Now())
			reqs = append(reqs, NewRequest(OpZoneUpdate, z.ID, ZoneInput{SOA: &SOAInput{Serial: &next}}))
			res.Serials = append(res.Serials, SerialChange{ZoneID: z.ID, Zone: z.Name, View: st.ViewName(z), Old: z.SOA.Serial, New: next})
		}
	}
	if len(reqs) > 0 {
		if _, err := e.Submit(ctx, reqs, p, "adopt", "bump serials for adoption", ApplyOptions{NoReload: true, Force: true}); err != nil {
			return nil, fmt.Errorf("preparing zones: %w", err)
		}
	}
	// Make sure the files on disk are exactly Jarl's.
	if _, err := e.Resync(ctx, p, ApplyOptions{NoReload: true, Force: true}); err != nil {
		return nil, fmt.Errorf("writing Jarl's files: %w", err)
	}

	e.mu.Lock()
	defer e.mu.Unlock()
	old, err := os.ReadFile(main)
	if err != nil {
		return nil, fmt.Errorf("reading %s: %w", main, err)
	}
	fi, err := os.Stat(main)
	if err != nil {
		return nil, err
	}
	backup := main + ".pre-jarl-" + e.Now().Format("20060102-150405")
	res.Backup = backup
	text := mainConfigText(jarlConf, backup)
	// Check the new main configuration before touching anything.
	dir, err := os.MkdirTemp(e.cfg.StagingDir, "adopt-")
	if err != nil {
		return nil, err
	}
	defer os.RemoveAll(dir)
	staged := filepath.Join(dir, "named.conf")
	if err := os.WriteFile(staged, []byte(text), 0o640); err != nil {
		return nil, err
	}
	check, err := e.tools.CheckConfig(ctx, staged, true)
	if err != nil {
		return nil, err
	}
	if !check.OK {
		return nil, &Error{Kind: KindValidation, Message: "named-checkconf rejected the configuration:\n" + check.Output}
	}
	if err := os.WriteFile(backup, old, fi.Mode().Perm()); err != nil {
		return nil, fmt.Errorf("saving %s: %w", backup, err)
	}
	restore := func() {
		if err := os.WriteFile(main, old, fi.Mode().Perm()); err != nil {
			e.log.Error("restoring main configuration failed", "path", main, "err", err)
		}
		if err := e.tools.Reconfig(ctx); err != nil {
			e.log.Error("rndc reconfig after restoring failed", "err", err)
		}
	}
	tmp := main + ".jarl-new"
	if err := os.WriteFile(tmp, []byte(text), fi.Mode().Perm()); err != nil {
		return nil, err
	}
	copyOwner(fi, tmp)
	if err := os.Rename(tmp, main); err != nil {
		os.Remove(tmp)
		return nil, err
	}
	if err := e.tools.Reconfig(ctx); err != nil {
		restore()
		return nil, &Error{Kind: KindBIND, Message: "named rejected Jarl's configuration (the old configuration was restored): " + err.Error()}
	}
	st, err = e.store.LoadState(ctx)
	if err != nil {
		restore()
		return nil, err
	}
	deadline := time.Now().Add(e.cfg.ReloadTimeout)
	for _, z := range st.SortedZones() {
		if z.Type != model.ZonePrimary {
			continue
		}
		view := e.namedView(st, z)
		_ = e.tools.ReloadZone(ctx, z.Name, view)
		want := z.SOA.Serial
		for {
			zs, err := e.tools.ZoneStatus(ctx, z.Name, view)
			if err == nil && zs.HasSerial && zs.Serial == want && strings.Contains(zs.Files, e.cfg.Paths.ZoneDir) {
				break
			}
			if time.Now().After(deadline) {
				restore()
				detail := ""
				if err != nil {
					detail = err.Error()
				} else {
					detail = fmt.Sprintf("named serves serial %d from %s", zs.Serial, zs.Files)
				}
				return nil, &Error{Kind: KindBIND, Message: fmt.Sprintf("zone %s was not loaded from Jarl's file with serial %d (%s); the old configuration was restored", zoneDesc(st, z), want, detail)}
			}
			time.Sleep(100 * time.Millisecond)
		}
	}
	e.audit(ctx, p, "system.adopt", "", 0, main, 0, "success", "named now loads "+jarlConf+"; previous configuration saved as "+backup, nil)
	return res, nil
}