// Package seeder loads the frontend's demo dataset into PostgreSQL.
//
// Source of truth is the frontend, not this package. `seed/fixtures/seed.json`
// is produced by executing src/api/seed.js through Vite and serialising what it
// exports, so ids, dates, numbers and enum values arrive exactly as the demo
// has them — no transcription step, and nothing to drift. Shift records are the
// one exception: they are generated (see shifts.go) because their dates are
// anchored to now.
//
// Idempotency strategy: EXPLICIT UPSERT inside a single transaction.
//
// Every record's primary key is derived deterministically from its source id
// (uuid v5 over a fixed namespace), so re-running the seeder targets exactly the
// same rows and `ON CONFLICT (id) DO UPDATE` restores each one to its seeded
// values. Records created through the API survive a re-seed. A column the
// fixture does not carry is left as it is.
//
// Shift records are the one collection that is also PRUNED — see
// pruneShiftRecords. Upsert alone cannot converge a rolling window, and shift
// records are the only collection that is a rolling window.
package seeder

import (
	"context"
	"crypto/sha1"
	"encoding/json"
	"fmt"
	"os"
	"sort"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/krow/krow-backend/go-api/internal/domain"
	"github.com/krow/krow-backend/go-api/internal/orgctx"
)

// namespace is a fixed UUID used to derive record ids from source ids. Changing
// it re-keys the entire dataset, so it is a constant, not configuration.
var namespace = [16]byte{
	0x6b, 0x72, 0x6f, 0x77, 0x2d, 0x73, 0x65, 0x65,
	0x64, 0x2d, 0x76, 0x31, 0x00, 0x00, 0x00, 0x01,
}

// DeterministicUUID derives a stable v5 UUID from a source id.
func DeterministicUUID(name string) string {
	h := sha1.New()
	h.Write(namespace[:])
	h.Write([]byte(name))
	var b [16]byte
	copy(b[:], h.Sum(nil))
	b[6] = (b[6] & 0x0f) | 0x50 // version 5
	b[8] = (b[8] & 0x3f) | 0x80 // RFC 4122 variant
	return fmt.Sprintf("%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:16])
}

// Fixture is the serialised frontend dataset.
type Fixture struct {
	DemoUser map[string]any              `json:"demoUser"`
	Entities map[string][]map[string]any `json:"entities"`
}

// Result counts what was written, by entity.
type Result struct {
	OrgID  string
	Counts map[string]int
	// Pruned is how many stale shift records this run removed. Reported rather
	// than silent: a delete during a seed should never be something you have to
	// read the source to discover.
	Pruned int
}

// entityOrder is insertion order, chosen so every foreign key is satisfied by
// the time it is referenced.
var entityOrder = []string{
	"RoleCategory", "Certification", "Badge", "Course", "LearningPath",
	"JobPosting", "WorkerProfile", "JobApplication", "AIInterview", "Staff",
	"Assignment", "ShiftRecord", "Evidence", "UserActivity",
}

// entityTable maps a frontend entity name to its table.
var entityTable = map[string]string{
	"RoleCategory": "role_categories", "Certification": "certifications",
	"Badge": "badges", "Course": "courses", "LearningPath": "learning_paths",
	"JobPosting": "job_postings", "WorkerProfile": "worker_profiles",
	"JobApplication": "job_applications", "AIInterview": "ai_interviews",
	"Staff": "staff", "Assignment": "assignments", "ShiftRecord": "shift_records",
	"Evidence": "evidence", "UserActivity": "user_activity",
}

// referenceFields are columns holding a source id that must be rewritten to the
// derived UUID. Every one of these is a real reference in the frontend data.
var referenceFields = map[string]bool{
	"job_posting_id": true, "application_id": true, "course_id": true,
	"staff_id": true, "assignment_id": true, "worker_profile_id": true,
	"interview_id": true, "position_id": true, "candidate_id": true,
	"user_id": true, "created_by": true,
}

// droppedFields are keys the fixture carries that no column exists for and no
// frontend code reads. Dropping them is deliberate and recorded here rather
// than being silent.
//
//	_order — a positional index used only while seed.js builds its course list
//	         (src/api/seed.js:1326). Nothing reads it.
var droppedFields = map[string]bool{"_order": true}

// Seeder loads a fixture into a database.
type Seeder struct {
	pool    *pgxpool.Pool
	fixture *Fixture
	now     time.Time
}

// Load reads a fixture from disk.
func Load(path string) (*Fixture, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read fixture %s: %w", path, err)
	}
	var f Fixture
	if err := json.Unmarshal(raw, &f); err != nil {
		return nil, fmt.Errorf("parse fixture %s: %w", path, err)
	}
	return &f, nil
}

// New builds a seeder. `now` anchors the generated shift records.
func New(pool *pgxpool.Pool, fixture *Fixture, now time.Time) *Seeder {
	return &Seeder{pool: pool, fixture: fixture, now: now}
}

// Run seeds everything in one transaction: either the whole dataset lands or
// none of it does.
func (s *Seeder) Run(ctx context.Context) (*Result, error) {
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return nil, err
	}
	defer func() { _ = tx.Rollback(ctx) }()

	orgID, err := s.upsertOrganization(ctx, tx)
	if err != nil {
		return nil, err
	}
	result := &Result{OrgID: orgID, Counts: map[string]int{}}

	n, err := s.upsertUser(ctx, tx, orgID)
	if err != nil {
		return nil, err
	}
	result.Counts["User"] = n

	for _, entity := range entityOrder {
		records := s.fixture.Entities[entity]
		if entity == "ShiftRecord" {
			records = BuildShifts(s.now)
		}
		count, err := s.upsertEntity(ctx, tx, orgID, entity, records)
		if err != nil {
			return nil, fmt.Errorf("seed %s: %w", entity, err)
		}
		result.Counts[entity] = count

		if entity == "ShiftRecord" {
			pruned, err := s.pruneShiftRecords(ctx, tx, orgID, records)
			if err != nil {
				return nil, fmt.Errorf("prune ShiftRecord: %w", err)
			}
			result.Pruned = pruned
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, err
	}
	return result, nil
}

// upsertOrganization creates the development organization the whole dataset
// belongs to. See internal/orgctx — this is not a tenant, it is a placeholder
// with a stable id so re-seeding is idempotent.
func (s *Seeder) upsertOrganization(ctx context.Context, tx pgx.Tx) (string, error) {
	id := DeterministicUUID("org:" + orgctx.DevOrgSlug)
	_, err := tx.Exec(ctx,
		`INSERT INTO organizations (id, name, slug) VALUES ($1::uuid, $2, $3::citext)
		 ON CONFLICT (id) DO UPDATE SET name = EXCLUDED.name, updated_date = now()`,
		id, orgctx.DevOrgName, orgctx.DevOrgSlug)
	return id, err
}

// upsertUser writes the demo user and splits its preferences into their own
// table, as api-contract.md §9 describes.
func (s *Seeder) upsertUser(ctx context.Context, tx pgx.Tx, orgID string) (int, error) {
	u := s.fixture.DemoUser
	if u == nil {
		return 0, nil
	}
	legacy, _ := u["id"].(string)
	id := DeterministicUUID("User:" + legacy)
	created := stringOr(u["created_date"], iso(s.now))

	_, err := tx.Exec(ctx,
		`INSERT INTO users (id, legacy_id, org_id, email, full_name, role, account_type, created_date, updated_date)
		 VALUES ($1::uuid, $2::text, $3::uuid, $4::citext, $5::text, $6::text, $7::text, $8::timestamptz, $8::timestamptz)
		 ON CONFLICT (id) DO UPDATE SET
		   email = EXCLUDED.email, full_name = EXCLUDED.full_name,
		   role = EXCLUDED.role, account_type = EXCLUDED.account_type,
		   created_date = EXCLUDED.created_date, updated_date = now()`,
		id, legacy, orgID,
		stringOr(u["email"], ""), stringOr(u["full_name"], ""),
		stringOr(u["role"], "admin"), stringOr(u["account_type"], "employer"), created)
	if err != nil {
		return 0, err
	}

	prefs, _ := u["preferences"].(map[string]any)
	if prefs == nil {
		prefs = map[string]any{}
	}
	extra := map[string]any{}
	for k, v := range prefs {
		switch k {
		case "owliverDefault", "compactDensity", "emailDigest":
		default:
			extra[k] = v
		}
	}
	extraJSON, err := json.Marshal(extra)
	if err != nil {
		return 0, err
	}
	_, err = tx.Exec(ctx,
		`INSERT INTO user_preferences (user_id, owliver_default, compact_density, email_digest, extra)
		 VALUES ($1::uuid, $2::boolean, $3::boolean, $4::boolean, $5::jsonb)
		 ON CONFLICT (user_id) DO UPDATE SET
		   owliver_default = EXCLUDED.owliver_default,
		   compact_density = EXCLUDED.compact_density,
		   email_digest    = EXCLUDED.email_digest,
		   extra           = EXCLUDED.extra,
		   updated_date    = now()`,
		id, boolOr(prefs["owliverDefault"], true), boolOr(prefs["compactDensity"], false),
		boolOr(prefs["emailDigest"], true), extraJSON)
	if err != nil {
		return 0, err
	}
	return 1, nil
}

// pruneShiftRecords deletes this organization's shift rows that this run did
// not generate.
//
// WHY THIS EXISTS, and why it is the only place the seeder deletes anything:
//
// A shift's stable id is `shift_<worker>_<NN>`, where NN counts the shift's
// position from the OLDEST end of the rolling 56-day window
// (attendanceSeed.js:190 and shifts.go:167 — the port is faithful, the scheme
// is the problem). That number is a position, not an identity, so it means a
// different date every day the window slides. Measured against a database
// seeded one day earlier: all 114 surviving ids had moved to a different date,
// and one — `shift_marcus_41` — was orphaned, because Marcus works Mon–Fri and
// a Saturday window holds 40 of his shifts rather than 41.
//
// Upsert can rewrite the rows it still generates. It has no way to remove the
// one it no longer generates, so the collection ratchets up to the historical
// maximum and never returns to the size the generator actually produces.
//
// Deleting is safe here in a way it would not be for any other collection:
// ShiftRecord is `Ops: OpList` (api-contract.md §2 — there is no
// POST /shift-records, and U1 in §11 is exactly the question of where these
// records come from), so every row is seeder-owned and no API call can create
// one. shift_records is also a leaf table: no foreign key points at it, so
// nothing cascades. Between them, this delete cannot reach data the seeder did
// not write.
//
// Note what this does NOT do: it invents no records and changes no generated
// value. After it, the collection is exactly what BuildShifts produced for
// s.now — which is what a regenerated rolling window means.
func (s *Seeder) pruneShiftRecords(ctx context.Context, tx pgx.Tx, orgID string,
	records []map[string]any) (int, error) {

	// A generation that produced nothing is a bug in BuildShifts, not an
	// instruction to empty the table: `id <> ALL('{}')` is true for every row.
	// Refuse rather than wipe.
	if len(records) == 0 {
		return 0, nil
	}

	keep := make([]string, 0, len(records))
	for _, rec := range records {
		legacy, _ := rec["id"].(string)
		if legacy == "" {
			return 0, fmt.Errorf("generated shift record has no id")
		}
		keep = append(keep, DeterministicUUID("ShiftRecord:"+legacy))
	}

	tag, err := tx.Exec(ctx,
		`DELETE FROM shift_records WHERE org_id = $1::uuid AND id <> ALL($2::uuid[])`,
		orgID, keep)
	if err != nil {
		return 0, err
	}
	return int(tag.RowsAffected()), nil
}

// upsertEntity writes one collection.
func (s *Seeder) upsertEntity(ctx context.Context, tx pgx.Tx, orgID, entity string, records []map[string]any) (int, error) {
	table := entityTable[entity]
	res, ok := domain.ResourceByTable[table]
	if !ok {
		return 0, fmt.Errorf("no resource descriptor for table %s", table)
	}
	for _, rec := range records {
		if err := s.upsertRecord(ctx, tx, orgID, entity, res, rec); err != nil {
			id, _ := rec["id"].(string)
			return 0, fmt.Errorf("record %s: %w", id, err)
		}
	}
	return len(records), nil
}

func (s *Seeder) upsertRecord(ctx context.Context, tx pgx.Tx, orgID, entity string,
	res *domain.Resource, rec map[string]any) error {

	legacy, _ := rec["id"].(string)
	if legacy == "" {
		return fmt.Errorf("record has no id")
	}

	// user_activity's primary key is a GENERATED ALWAYS AS IDENTITY bigint, not
	// a uuid, so no explicit id can be supplied for it. Its stable identity is
	// legacy_id, which is what the upsert conflicts on instead.
	idCol, _ := res.Column("id")
	generatedID := idCol.Kind != domain.KindUUID
	conflictTarget := "id"

	values := map[string]any{
		"legacy_id": legacy,
		"org_id":    orgID,
	}
	if generatedID {
		conflictTarget = "legacy_id"
	} else {
		values["id"] = DeterministicUUID(entity + ":" + legacy)
	}

	created := stringOr(rec["created_date"], iso(s.now))
	values["created_date"] = created
	if _, hasUpdated := res.Column("updated_date"); hasUpdated {
		// The fixture carries updated_date only on job applications, where the
		// gap from created_date is what buildHires reads as time-to-hire.
		// Everywhere else the column is NOT NULL and the record has never been
		// modified, so it takes the creation instant.
		values["updated_date"] = stringOr(rec["updated_date"], created)
	}

	for key, value := range rec {
		switch key {
		case "id", "created_date", "updated_date":
			continue
		}
		if droppedFields[key] {
			continue
		}
		col, ok := res.Column(key)
		if !ok {
			return fmt.Errorf("field %q has no column on %s", key, res.Table)
		}
		if referenceFields[key] && col.Kind == domain.KindUUID {
			str, isStr := value.(string)
			if !isStr || str == "" {
				values[key] = nil
				continue
			}
			values[key] = DeterministicUUID(referencedEntity(key) + ":" + str)
			continue
		}
		values[key] = value
	}

	// Deterministic column order keeps the generated SQL stable.
	names := make([]string, 0, len(values))
	for k := range values {
		names = append(names, k)
	}
	sort.Strings(names)

	cols := make([]string, 0, len(names))
	placeholders := make([]string, 0, len(names))
	updates := make([]string, 0, len(names))
	args := make([]any, 0, len(names))

	for _, name := range names {
		col, ok := res.Column(name)
		if !ok {
			return fmt.Errorf("no column %q on %s", name, res.Table)
		}
		bound, err := bindSeedValue(*col, values[name])
		if err != nil {
			return err
		}
		args = append(args, bound)
		cols = append(cols, name)
		placeholders = append(placeholders, fmt.Sprintf("$%d::%s", len(args), col.PGType))
		if name != conflictTarget {
			updates = append(updates, fmt.Sprintf("%s = EXCLUDED.%s", name, name))
		}
	}

	q := fmt.Sprintf(
		"INSERT INTO %s (%s) VALUES (%s) ON CONFLICT (%s) DO UPDATE SET %s",
		res.Table, strings.Join(cols, ", "), strings.Join(placeholders, ", "),
		conflictTarget, strings.Join(updates, ", "))

	_, err := tx.Exec(ctx, q, args...)
	return err
}

// referencedEntity says which entity a reference column points at, so the
// derived UUID is built from the same namespace the target was written with.
func referencedEntity(field string) string {
	switch field {
	case "job_posting_id", "position_id":
		return "JobPosting"
	case "application_id":
		return "JobApplication"
	case "course_id":
		return "Course"
	case "staff_id":
		return "Staff"
	case "assignment_id":
		return "Assignment"
	case "worker_profile_id", "candidate_id":
		return "WorkerProfile"
	case "interview_id":
		return "AIInterview"
	case "user_id", "created_by":
		return "User"
	}
	return ""
}

// bindSeedValue converts a fixture value into something pgx can send. It is
// deliberately separate from the repository's binder: the seeder writes
// server-owned columns (id, legacy_id, org_id, created_date) that the API never
// accepts from a client.
func bindSeedValue(col domain.Column, v any) (any, error) {
	if v == nil {
		return nil, nil
	}
	switch col.Kind {
	case domain.KindTextArray:
		switch t := v.(type) {
		case []any:
			out := make([]string, 0, len(t))
			for _, e := range t {
				s, ok := e.(string)
				if !ok {
					return nil, fmt.Errorf("%s: expected an array of strings", col.Name)
				}
				out = append(out, s)
			}
			return out, nil
		case []string:
			return t, nil
		}
		return nil, fmt.Errorf("%s: expected an array", col.Name)

	case domain.KindJSON:
		raw, err := json.Marshal(v)
		if err != nil {
			return nil, fmt.Errorf("%s: %w", col.Name, err)
		}
		return raw, nil

	case domain.KindInt:
		switch t := v.(type) {
		case float64:
			return int64(t), nil
		case int:
			return int64(t), nil
		case int64:
			return t, nil
		}
		return nil, fmt.Errorf("%s: expected a number, got %T", col.Name, v)

	case domain.KindFloat:
		switch t := v.(type) {
		case float64:
			return t, nil
		case int:
			return float64(t), nil
		}
		return nil, fmt.Errorf("%s: expected a number, got %T", col.Name, v)

	case domain.KindBool:
		if b, ok := v.(bool); ok {
			return b, nil
		}
		return nil, fmt.Errorf("%s: expected a boolean, got %T", col.Name, v)

	default:
		if s, ok := v.(string); ok {
			return s, nil
		}
		return nil, fmt.Errorf("%s: expected a string, got %T", col.Name, v)
	}
}

func stringOr(v any, fallback string) string {
	if s, ok := v.(string); ok && s != "" {
		return s
	}
	return fallback
}

func boolOr(v any, fallback bool) bool {
	if b, ok := v.(bool); ok {
		return b
	}
	return fallback
}