package app

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"time"

	"github.com/owen/vibedns/internal/auditlog"
	"github.com/owen/vibedns/internal/config"
	"github.com/owen/vibedns/internal/database"
	"github.com/owen/vibedns/internal/models"
	"github.com/owen/vibedns/internal/version"
)

// ConfigExportVersion is the schema version of the export format. It is
// checked on import so a future format change fails loudly rather than being
// half-applied.
const ConfigExportVersion = 1

// ConfigExport is a portable snapshot of the configuration.
//
// It deliberately excludes the administrator password hash and every API token
// hash: an export is meant to be copied between machines and checked into a
// configuration repository, so it must not carry credentials.
type ConfigExport struct {
	FormatVersion int       `json:"format_version"`
	ExportedAt    time.Time `json:"exported_at"`
	AppVersion    string    `json:"app_version"`

	Settings map[string]string `json:"settings"`
	Zones    []ExportedZone    `json:"zones"`
	Networks []ExportedNetwork `json:"networks"`
	Policies []ExportedPolicy  `json:"policies"`
	Lists    []ExportedList    `json:"lists"`
}

// ExportedZone is a zone with its records.
type ExportedZone struct {
	models.Zone
	Records []models.Record `json:"records"`
}

// ExportedNetwork is a network with the names of its policies.
type ExportedNetwork struct {
	models.Network
	PolicyNames []string `json:"policy_names"`
}

// ExportedPolicy is a policy with the names of its lists.
type ExportedPolicy struct {
	models.Policy
	ListNames []string `json:"list_names"`
}

// ExportedList is a domain list with its domains.
type ExportedList struct {
	models.DomainList
	Domains []ExportedDomain `json:"domains"`
}

// ExportedDomain is one entry in a domain list.
type ExportedDomain struct {
	Domain          string `json:"domain"`
	MatchSubdomains bool   `json:"match_subdomains"`
	Comment         string `json:"comment,omitempty"`
}

// ExportConfig builds a configuration export.
//
// includeDomains controls whether imported blocklists are included. A single
// blocklist can hold hundreds of thousands of domains that are reproducible
// from their source URL, so the default export omits them.
func (a *App) ExportConfig(ctx context.Context, includeDomains bool) (*ConfigExport, error) {
	stored, err := a.DB.Settings(ctx)
	if err != nil {
		return nil, Internal(err, "The settings could not be exported.")
	}
	// The CSRF signing key is a secret and is regenerated per installation.
	delete(stored, keyCSRFSecret)

	out := &ConfigExport{
		FormatVersion: ConfigExportVersion,
		ExportedAt:    time.Now().UTC(),
		AppVersion:    version.Version,
		Settings:      stored,
	}

	zones, err := a.DB.Zones(ctx, database.ZoneFilter{})
	if err != nil {
		return nil, Internal(err, "The zones could not be exported.")
	}
	for _, z := range zones {
		recs, err := a.DB.ZoneRecordsRaw(ctx, z.ID)
		if err != nil {
			return nil, Internal(err, "The zone records could not be exported.")
		}
		out.Zones = append(out.Zones, ExportedZone{Zone: z, Records: recs})
	}

	nets, err := a.DB.Networks(ctx, "", true)
	if err != nil {
		return nil, Internal(err, "The networks could not be exported.")
	}
	for _, n := range nets {
		e := ExportedNetwork{Network: n}
		for _, p := range n.Policies {
			e.PolicyNames = append(e.PolicyNames, p.Name)
		}
		e.Network.Policies = nil // names carry the relationship instead of IDs
		out.Networks = append(out.Networks, e)
	}

	policies, err := a.DB.Policies(ctx)
	if err != nil {
		return nil, Internal(err, "The policies could not be exported.")
	}
	for _, p := range policies {
		e := ExportedPolicy{Policy: p}
		e.ListNames = append(append([]string{}, p.BlacklistName...), p.AllowlistName...)
		e.Policy.BlacklistIDs, e.Policy.AllowlistIDs = nil, nil
		out.Policies = append(out.Policies, e)
	}

	lists, err := a.DB.DomainLists(ctx, "", "")
	if err != nil {
		return nil, Internal(err, "The lists could not be exported.")
	}
	for _, l := range lists {
		e := ExportedList{DomainList: l}
		if includeDomains {
			err := a.DB.ExportDomains(ctx, l.ID, func(domain string, sub bool) {
				e.Domains = append(e.Domains, ExportedDomain{Domain: domain, MatchSubdomains: sub})
			})
			if err != nil {
				return nil, Internal(err, "The list domains could not be exported.")
			}
		}
		out.Lists = append(out.Lists, e)
	}
	return out, nil
}

// WriteConfigExport writes an export as indented JSON.
func (a *App) WriteConfigExport(ctx context.Context, w io.Writer, includeDomains bool) error {
	export, err := a.ExportConfig(ctx, includeDomains)
	if err != nil {
		return err
	}
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	if err := enc.Encode(export); err != nil {
		return Internal(err, "The export could not be written.")
	}
	return nil
}

// ImportReport summarises what a configuration import created.
type ImportReport struct {
	Zones     int      `json:"zones"`
	Records   int      `json:"records"`
	Networks  int      `json:"networks"`
	Policies  int      `json:"policies"`
	Lists     int      `json:"lists"`
	Domains   int      `json:"domains"`
	Settings  int      `json:"settings"`
	Skipped   int      `json:"skipped"`
	Conflicts []string `json:"conflicts,omitempty"`
}

// ImportConfig applies a configuration export.
//
// Objects that already exist are skipped rather than overwritten, and reported
// in Conflicts, so an import can never silently destroy configuration that is
// already in production.
func (a *App) ImportConfig(ctx context.Context, actor auditlog.Actor, r io.Reader, applySettings bool) (*ImportReport, error) {
	var in ConfigExport
	dec := json.NewDecoder(r)
	dec.DisallowUnknownFields()
	if err := dec.Decode(&in); err != nil {
		return nil, Invalid("The import file could not be read as a VibeDNS configuration export: %v", err)
	}
	if in.FormatVersion != ConfigExportVersion {
		return nil, Invalid("This export uses format version %d, but this server understands version %d.",
			in.FormatVersion, ConfigExportVersion)
	}

	rep := &ImportReport{}

	// Lists first: policies reference them by name.
	listIDs := map[string]int64{}
	for _, l := range in.Lists {
		existing, err := a.DB.DomainLists(ctx, l.Kind, l.Name)
		if err != nil {
			return nil, Internal(err, "Existing lists could not be checked.")
		}
		var id int64
		found := false
		for _, e := range existing {
			if e.Name == l.Name && e.Kind == l.Kind {
				id, found = e.ID, true
				break
			}
		}
		if !found {
			created, err := a.DB.CreateDomainList(ctx, l.DomainList)
			if err != nil {
				rep.Skipped++
				rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("list %q could not be created", l.Name))
				continue
			}
			id = created.ID
			rep.Lists++
		} else {
			rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("list %q already exists and was left unchanged", l.Name))
		}
		listIDs[l.Kind+"/"+l.Name] = id

		if len(l.Domains) > 0 {
			rows := make([]database.ImportDomain, 0, len(l.Domains))
			for _, d := range l.Domains {
				rows = append(rows, database.ImportDomain{
					Domain: d.Domain, MatchSubdomains: d.MatchSubdomains, Comment: d.Comment,
				})
			}
			imported, _, err := a.DB.ImportDomains(ctx, id, rows)
			if err != nil {
				return nil, Internal(err, "The list domains could not be imported.")
			}
			rep.Domains += imported
		}
	}

	// Policies next: networks reference them by name.
	policyIDs := map[string]int64{}
	existingPolicies, err := a.DB.Policies(ctx)
	if err != nil {
		return nil, Internal(err, "Existing policies could not be checked.")
	}
	for _, p := range existingPolicies {
		policyIDs[p.Name] = p.ID
	}
	for _, p := range in.Policies {
		if _, exists := policyIDs[p.Name]; exists {
			rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("policy %q already exists and was left unchanged", p.Name))
			continue
		}
		var ids []int64
		for _, name := range p.ListNames {
			if id, ok := listIDs[models.KindBlacklist+"/"+name]; ok {
				ids = append(ids, id)
			} else if id, ok := listIDs[models.KindAllowlist+"/"+name]; ok {
				ids = append(ids, id)
			}
		}
		created, err := a.DB.CreatePolicy(ctx, p.Policy, ids)
		if err != nil {
			rep.Skipped++
			continue
		}
		policyIDs[p.Name] = created.ID
		rep.Policies++
	}

	// Networks.
	existingNets, err := a.DB.Networks(ctx, "", false)
	if err != nil {
		return nil, Internal(err, "Existing networks could not be checked.")
	}
	netNames := map[string]bool{}
	for _, n := range existingNets {
		netNames[n.Name] = true
	}
	for _, n := range in.Networks {
		if netNames[n.Name] {
			rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("network %q already exists and was left unchanged", n.Name))
			continue
		}
		var ids []int64
		for _, name := range n.PolicyNames {
			if id, ok := policyIDs[name]; ok {
				ids = append(ids, id)
			}
		}
		if _, err := a.DB.CreateNetwork(ctx, n.Network, ids); err != nil {
			rep.Skipped++
			continue
		}
		rep.Networks++
	}

	// Zones and their records.
	for _, z := range in.Zones {
		if _, err := a.DB.ZoneByName(ctx, z.Name); err == nil {
			rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("zone %s already exists and was left unchanged", z.Name))
			continue
		}
		zone := z.Zone
		zone.ID = 0
		created, err := a.DB.CreateZone(ctx, zone)
		if err != nil {
			rep.Skipped++
			rep.Conflicts = append(rep.Conflicts, fmt.Sprintf("zone %s could not be created", z.Name))
			continue
		}
		rep.Zones++
		if len(z.Records) > 0 {
			if err := a.DB.AppendZoneRecords(ctx, created.ID, z.Records); err != nil {
				return nil, Internal(err, "The zone records could not be imported.")
			}
			rep.Records += len(z.Records)
		}
	}

	if applySettings && len(in.Settings) > 0 {
		settings := config.LoadSettings(in.Settings)
		if err := settings.Validate(); err != nil {
			rep.Conflicts = append(rep.Conflicts,
				fmt.Sprintf("settings were not applied because they are invalid: %v", err))
		} else {
			delete(in.Settings, keyCSRFSecret)
			if err := a.DB.SetSettings(ctx, in.Settings); err != nil {
				return nil, Internal(err, "The settings could not be imported.")
			}
			rep.Settings = len(in.Settings)
		}
	}

	a.Audit.Record(ctx, actor, "config.import", auditlog.ObjectConfig, "", "configuration import",
		auditlog.Changes(
			"zones", fmt.Sprint(rep.Zones), "records", fmt.Sprint(rep.Records),
			"networks", fmt.Sprint(rep.Networks), "policies", fmt.Sprint(rep.Policies),
			"lists", fmt.Sprint(rep.Lists), "domains", fmt.Sprint(rep.Domains)))
	a.Runtime.RequestReload()
	return rep, nil
}