// Package lldapexport implements the LLDAP → canonical export tool (spec §7 — migration contract).
// It reads all users and groups from the LLDAP directory via a UserRepository, validates each
// entry against the canonical LDAP schema, and writes a canonical-export.yaml snapshot.
package lldapexport

import (
	"context"
	"fmt"
	"os"
	"sort"
	"time"

	"gopkg.in/yaml.v3"

	"keycape/internal/domain"
	"keycape/internal/server/telemetry"
	"keycape/internal/validator"
)

// Group enumeration modes recorded on an ExportResult. They are the export's
// own statement about how much of the directory it could see.
const (
	// EnumerationDirectory means every group was read from the directory,
	// so groups nobody belongs to are present in the snapshot.
	EnumerationDirectory = "directory"

	// EnumerationMembershipDerived means groups were discovered by walking
	// each user's memberships. Empty and unreferenced groups are absent by
	// construction; such a snapshot is not a complete directory export.
	EnumerationMembershipDerived = "membership-derived"
)

// ExportResult is the structured output of a single export run.
type ExportResult struct {
	Users       []domain.User       `yaml:"users"`
	Groups      []domain.Group      `yaml:"groups"`
	Memberships []domain.Membership `yaml:"memberships"`
	ExportedAt  time.Time           `yaml:"exportedAt"`

	// GroupEnumeration is EnumerationDirectory or EnumerationMembershipDerived.
	// It is written unconditionally: a consumer must not have to infer from an
	// absent field whether the snapshot covers the whole directory.
	GroupEnumeration string `yaml:"groupEnumeration"`

	ProfileVersion        string   `yaml:"profileVersion"`
	IncompatibilityReport []string `yaml:"incompatibilityReport,omitempty"`
}

// Complete reports whether the run enumerated the whole directory and read
// every entry it attempted. Only a complete run may be described as a full
// directory snapshot.
func (r *ExportResult) Complete() bool {
	return r.GroupEnumeration == EnumerationDirectory && len(r.IncompatibilityReport) == 0
}

// Exporter reads from a UserRepository, validates, and writes canonical-export.yaml.
type Exporter struct {
	repo    domain.UserRepository
	mode    validator.Mode
	emitter telemetry.Emitter
}

// New creates a new Exporter.
func New(repo domain.UserRepository, mode validator.Mode, emitter telemetry.Emitter) *Exporter {
	return &Exporter{
		repo:    repo,
		mode:    mode,
		emitter: emitter,
	}
}

// Export reads all users and groups, validates them, builds ExportResult,
// emits telemetry, and writes the YAML file to outputFile.
// Validation failures are captured in IncompatibilityReport — they are not fatal.
func (e *Exporter) Export(ctx context.Context, outputFile string) (*ExportResult, error) {
	// 1. List all users from the repository.
	users, err := e.repo.ListUsers(ctx)
	if err != nil {
		return nil, fmt.Errorf("lldapexport: list users: %w", err)
	}

	// 2. Enumerate groups. A directory-wide enumeration is the only way to
	//    see groups nobody belongs to, so prefer it and fall back to walking
	//    user memberships only when the repository cannot provide one.
	groups, memberships, enumeration, readErrs, err := e.enumerateGroups(ctx, users)
	if err != nil {
		return nil, err
	}

	// 3. Validate each user against the canonical LDAP schema.
	incompatibilities := readErrs
	validatedUsers := make([]domain.User, 0, len(users))
	for _, u := range users {
		snap := validator.Snapshot{Users: []domain.User{u}}
		report := validator.Validate(snap, e.mode)
		if !report.Passed {
			for _, r := range report.Structural {
				if !r.Passed {
					incompatibilities = append(incompatibilities,
						fmt.Sprintf("user %q structural/%s: %s", u.Username, r.Rule, r.Message))
				}
			}
			for _, r := range report.Semantic {
				if !r.Passed {
					incompatibilities = append(incompatibilities,
						fmt.Sprintf("user %q semantic/%s: %s", u.Username, r.Rule, r.Message))
				}
			}
		}
		validatedUsers = append(validatedUsers, u)
	}

	// 4. Order every collection on a stable key so an unchanged directory
	//    exports byte-identically across runs.
	sort.Slice(validatedUsers, func(i, j int) bool { return validatedUsers[i].ID < validatedUsers[j].ID })
	sort.Slice(groups, func(i, j int) bool { return groups[i].ID < groups[j].ID })
	sort.Slice(memberships, func(i, j int) bool {
		if memberships[i].GroupID != memberships[j].GroupID {
			return memberships[i].GroupID < memberships[j].GroupID
		}
		return memberships[i].UserID < memberships[j].UserID
	})

	// 5. Build ExportResult.
	result := &ExportResult{
		Users:                 validatedUsers,
		Groups:                groups,
		Memberships:           memberships,
		ExportedAt:            time.Now().UTC(),
		GroupEnumeration:      enumeration,
		ProfileVersion:        "0.1",
		IncompatibilityReport: incompatibilities,
	}

	// 6. Emit migration_event telemetry. A snapshot that skipped an entry or
	//    could not enumerate the directory is reported as partial — calling it
	//    a success is what let an incomplete export pass unnoticed.
	outcome := "partial"
	if result.Complete() {
		outcome = "success"
	}
	e.emitter.Emit(ctx, telemetry.Event{
		Timestamp: time.Now().UTC(),
		EventType: telemetry.EventMigration,
		Endpoint:  "lldap-export",
		Result:    outcome,
	})

	// 7. Write YAML to output file.
	data, err := yaml.Marshal(result)
	if err != nil {
		return nil, fmt.Errorf("lldapexport: marshal YAML: %w", err)
	}
	// 0600: the snapshot is a directory dump -- every username, display name,
	// email and group membership in the estate. Not credential material, but not
	// world-readable either (KEY-WP-0026).
	if err := os.WriteFile(outputFile, data, 0o600); err != nil {
		return nil, fmt.Errorf("lldapexport: write file %q: %w", outputFile, err)
	}

	return result, nil
}

// enumerateGroups returns the directory's groups and memberships, the
// enumeration mode that produced them, and any read failures to record in the
// incompatibility report.
//
// A failed directory enumeration is fatal: the caller asked for the whole
// directory and cannot be handed a silently smaller one. A failed per-user
// lookup in the fallback path is reported rather than fatal, because the
// fallback is already known to be incomplete and the report is where that is
// stated.
func (e *Exporter) enumerateGroups(ctx context.Context, users []domain.User) (
	groups []domain.Group, memberships []domain.Membership, enumeration string, readErrs []string, err error,
) {
	if lister, ok := e.repo.(domain.GroupLister); ok {
		groups, err = lister.ListGroups(ctx)
		if err != nil {
			return nil, nil, "", nil, fmt.Errorf("lldapexport: list groups: %w", err)
		}
		for _, g := range groups {
			for _, memberID := range g.Members {
				memberships = append(memberships, domain.Membership{UserID: memberID, GroupID: g.ID})
			}
		}
		return groups, memberships, EnumerationDirectory, nil, nil
	}

	readErrs = append(readErrs, "export incomplete: the directory adapter cannot enumerate groups, "+
		"so groups with no members are absent from this snapshot")

	groupMap := make(map[string]domain.Group)
	for _, u := range users {
		userGroups, lookupErr := e.repo.LookupGroups(ctx, u.ID)
		if lookupErr != nil {
			readErrs = append(readErrs,
				fmt.Sprintf("user %q group lookup failed, memberships omitted: %v", u.Username, lookupErr))
			continue
		}
		for _, g := range userGroups {
			if _, seen := groupMap[g.ID]; !seen {
				groupMap[g.ID] = g
			}
			// Derive the membership from the pair actually observed. The
			// group's own Members list is not populated on this path.
			memberships = append(memberships, domain.Membership{UserID: u.ID, GroupID: g.ID})
		}
	}
	groups = make([]domain.Group, 0, len(groupMap))
	for _, g := range groupMap {
		groups = append(groups, g)
	}
	return groups, memberships, EnumerationMembershipDerived, readErrs, nil
}