package catalog

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
)

const productCursorVersion = 1

// productCursor is an opaque keyset bookmark for product list pages.
// Encoded as URL-safe base64 JSON in the `cursor` query param.
type productCursor struct {
	V     int    `json:"v"`
	ID    string `json:"id"`
	SB    string `json:"sb"`
	SO    string `json:"so"`
	K     string `json:"k"`
	Blank bool   `json:"b,omitempty"`
}

// HasProductCursor reports whether the filter requests keyset pagination.
func HasProductCursor(f ListFilter) bool {
	return strings.TrimSpace(f.Cursor) != "" || strings.TrimSpace(f.AfterID) != ""
}

// EncodeProductCursor builds an opaque cursor from a product list row.
func EncodeProductCursor(f ListFilter, item map[string]any) (string, error) {
	f = NormalizeListFilter(f)
	id := stringifyID(item["id"])
	if id == "" {
		return "", fmt.Errorf("missing id")
	}
	cur := productCursor{
		V:  productCursorVersion,
		ID: id,
		SB: f.SortBy,
		SO: f.SortOrder,
	}
	switch f.SortBy {
	case "name":
		name := productSortName(item)
		cur.Blank = name == ""
		cur.K = strings.ToLower(name)
	case "createdAt":
		ts, ok := asTime(item["created_at"])
		if !ok {
			return "", fmt.Errorf("missing created_at")
		}
		cur.K = ts.UTC().Format(time.RFC3339Nano)
	default: // updatedAt
		ts, ok := asTime(item["updated_at"])
		if !ok {
			return "", fmt.Errorf("missing updated_at")
		}
		cur.K = ts.UTC().Format(time.RFC3339Nano)
	}
	raw, err := json.Marshal(cur)
	if err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(raw), nil
}

// DecodeProductCursor parses an opaque product list cursor.
func DecodeProductCursor(raw string) (productCursor, error) {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return productCursor{}, fmt.Errorf("empty cursor")
	}
	b, err := base64.RawURLEncoding.DecodeString(raw)
	if err != nil {
		return productCursor{}, fmt.Errorf("invalid cursor encoding")
	}
	var cur productCursor
	if err := json.Unmarshal(b, &cur); err != nil {
		return productCursor{}, fmt.Errorf("invalid cursor payload")
	}
	if cur.V != productCursorVersion {
		return productCursor{}, fmt.Errorf("unsupported cursor version")
	}
	if _, err := uuid.Parse(cur.ID); err != nil {
		return productCursor{}, fmt.Errorf("invalid cursor id")
	}
	switch cur.SB {
	case "name", "updatedAt", "createdAt":
	default:
		return productCursor{}, fmt.Errorf("invalid cursor sort")
	}
	if cur.SO != "asc" && cur.SO != "desc" {
		return productCursor{}, fmt.Errorf("invalid cursor order")
	}
	return cur, nil
}

// NextProductCursor returns next_cursor / next_after_id when the page is full.
// When the page length equals limit there may still be no further rows (rare);
// clients should treat an empty follow-up page as the end.
func NextProductCursor(f ListFilter, items []map[string]any, limit int) (nextCursor, nextAfterID string) {
	f = NormalizeListFilter(f)
	if limit <= 0 || len(items) < limit {
		return "", ""
	}
	last := items[len(items)-1]
	nextAfterID = stringifyID(last["id"])
	enc, err := EncodeProductCursor(f, last)
	if err != nil {
		return "", nextAfterID
	}
	return enc, nextAfterID
}

func (c productCursor) matchesFilter(f ListFilter) bool {
	f = NormalizeListFilter(f)
	return c.SB == f.SortBy && c.SO == f.SortOrder
}

// appendRawKeyset adds a keyset predicate for raw_products (alias rp).
func appendRawKeyset(f ListFilter, cur productCursor, args []any, where []string) ([]any, []string, error) {
	id, err := uuid.Parse(cur.ID)
	if err != nil {
		return args, where, fmt.Errorf("invalid cursor id")
	}
	dirAfter := keysetOp(f.SortOrder)
	switch f.SortBy {
	case "name":
		nameExpr := `COALESCE(NULLIF(rp.mapped_data->>'name', ''), NULLIF(rp.mapped_data->>'title', ''), '')`
		blankExpr := fmt.Sprintf(`(CASE WHEN %s = '' THEN 1 ELSE 0 END)`, nameExpr)
		args = append(args, boolToInt(cur.Blank), cur.K, id)
		b, k, i := len(args)-2, len(args)-1, len(args)
		where = append(where, fmt.Sprintf(`(
			%s > $%d
			OR (%s = $%d AND LOWER(%s) %s $%d)
			OR (%s = $%d AND LOWER(%s) = $%d AND rp.id %s $%d)
		)`, blankExpr, b, blankExpr, b, nameExpr, dirAfter, k, blankExpr, b, nameExpr, k, dirAfter, i))
		return args, where, nil
	case "createdAt":
		ts, err := time.Parse(time.RFC3339Nano, cur.K)
		if err != nil {
			ts, err = time.Parse(time.RFC3339, cur.K)
		}
		if err != nil {
			return args, where, fmt.Errorf("invalid cursor timestamp")
		}
		args = append(args, ts, id)
		a, b := len(args)-1, len(args)
		where = append(where, fmt.Sprintf("(rp.created_at, rp.id) %s ($%d::timestamptz, $%d::uuid)", dirAfter, a, b))
		return args, where, nil
	default: // updatedAt
		ts, err := time.Parse(time.RFC3339Nano, cur.K)
		if err != nil {
			ts, err = time.Parse(time.RFC3339, cur.K)
		}
		if err != nil {
			return args, where, fmt.Errorf("invalid cursor timestamp")
		}
		args = append(args, ts, id)
		a, b := len(args)-1, len(args)
		where = append(where, fmt.Sprintf("(rp.updated_at, rp.id) %s ($%d::timestamptz, $%d::uuid)", dirAfter, a, b))
		return args, where, nil
	}
}

// appendProcessedKeyset adds a keyset predicate for processed_products (alias p).
func appendProcessedKeyset(f ListFilter, cur productCursor, args []any, where []string) ([]any, []string, error) {
	id, err := uuid.Parse(cur.ID)
	if err != nil {
		return args, where, fmt.Errorf("invalid cursor id")
	}
	dirAfter := keysetOp(f.SortOrder)
	switch f.SortBy {
	case "name":
		nameExpr := `COALESCE(NULLIF(p.processed_name, ''), NULLIF(p.name, ''), '')`
		blankExpr := fmt.Sprintf(`(CASE WHEN %s = '' THEN 1 ELSE 0 END)`, nameExpr)
		args = append(args, boolToInt(cur.Blank), cur.K, id)
		b, k, i := len(args)-2, len(args)-1, len(args)
		where = append(where, fmt.Sprintf(`(
			%s > $%d
			OR (%s = $%d AND LOWER(%s) %s $%d)
			OR (%s = $%d AND LOWER(%s) = $%d AND p.id %s $%d)
		)`, blankExpr, b, blankExpr, b, nameExpr, dirAfter, k, blankExpr, b, nameExpr, k, dirAfter, i))
		return args, where, nil
	case "createdAt":
		ts, err := time.Parse(time.RFC3339Nano, cur.K)
		if err != nil {
			ts, err = time.Parse(time.RFC3339, cur.K)
		}
		if err != nil {
			return args, where, fmt.Errorf("invalid cursor timestamp")
		}
		args = append(args, ts, id)
		a, b := len(args)-1, len(args)
		where = append(where, fmt.Sprintf("(p.created_at, p.id) %s ($%d::timestamptz, $%d::uuid)", dirAfter, a, b))
		return args, where, nil
	default: // updatedAt
		ts, err := time.Parse(time.RFC3339Nano, cur.K)
		if err != nil {
			ts, err = time.Parse(time.RFC3339, cur.K)
		}
		if err != nil {
			return args, where, fmt.Errorf("invalid cursor timestamp")
		}
		args = append(args, ts, id)
		a, b := len(args)-1, len(args)
		where = append(where, fmt.Sprintf("(p.updated_at, p.id) %s ($%d::timestamptz, $%d::uuid)", dirAfter, a, b))
		return args, where, nil
	}
}

func keysetOp(sortOrder string) string {
	if sortOrder == "asc" {
		return ">"
	}
	return "<"
}

func boolToInt(v bool) int {
	if v {
		return 1
	}
	return 0
}

func productSortName(item map[string]any) string {
	for _, key := range []string{"processed_name", "name"} {
		if s := strings.TrimSpace(stringifyID(item[key])); s != "" {
			return s
		}
	}
	return ""
}

func stringifyID(v any) string {
	switch t := v.(type) {
	case nil:
		return ""
	case string:
		return strings.TrimSpace(t)
	case uuid.UUID:
		return t.String()
	case [16]byte:
		return uuid.UUID(t).String()
	default:
		return strings.TrimSpace(fmt.Sprint(t))
	}
}

func asTime(v any) (time.Time, bool) {
	switch t := v.(type) {
	case time.Time:
		return t, true
	case *time.Time:
		if t == nil {
			return time.Time{}, false
		}
		return *t, true
	case string:
		if ts, err := time.Parse(time.RFC3339Nano, t); err == nil {
			return ts, true
		}
		if ts, err := time.Parse(time.RFC3339, t); err == nil {
			return ts, true
		}
	}
	return time.Time{}, false
}

// resolveRawCursor decodes cursor or loads sort keys for after_id on raw_products.
// missing=true means after_id was not found for this company (caller should return an empty page).
func (s *Service) resolveRawCursor(ctx context.Context, companyID uuid.UUID, f ListFilter) (cur productCursor, use bool, missing bool, err error) {
	if c := strings.TrimSpace(f.Cursor); c != "" {
		cur, err = DecodeProductCursor(c)
		if err != nil {
			return productCursor{}, false, false, ClientMsg("invalid cursor")
		}
		if !cur.matchesFilter(f) {
			return productCursor{}, false, false, ClientMsg("cursor sort mismatch")
		}
		return cur, true, false, nil
	}
	after := strings.TrimSpace(f.AfterID)
	if after == "" {
		return productCursor{}, false, false, nil
	}
	id, parseErr := uuid.Parse(after)
	if parseErr != nil {
		return productCursor{}, false, false, ClientMsg("invalid after_id")
	}
	var name string
	var createdAt, updatedAt time.Time
	scanErr := s.Pool.QueryRow(ctx, `
		SELECT COALESCE(NULLIF(mapped_data->>'name', ''), NULLIF(mapped_data->>'title', ''), ''),
			created_at, updated_at
		FROM raw_products
		WHERE id = $1 AND company_id = $2`, id, companyID).Scan(&name, &createdAt, &updatedAt)
	if scanErr != nil {
		if errors.Is(scanErr, pgx.ErrNoRows) {
			return productCursor{}, true, true, nil
		}
		return productCursor{}, false, false, scanErr
	}
	cur = productCursorFromRow(f, id.String(), name, createdAt, updatedAt)
	return cur, true, false, nil
}

// resolveProcessedCursor decodes cursor or loads sort keys for after_id on processed_products.
func (s *Service) resolveProcessedCursor(ctx context.Context, companyID uuid.UUID, f ListFilter) (cur productCursor, use bool, missing bool, err error) {
	if c := strings.TrimSpace(f.Cursor); c != "" {
		cur, err = DecodeProductCursor(c)
		if err != nil {
			return productCursor{}, false, false, ClientMsg("invalid cursor")
		}
		if !cur.matchesFilter(f) {
			return productCursor{}, false, false, ClientMsg("cursor sort mismatch")
		}
		return cur, true, false, nil
	}
	after := strings.TrimSpace(f.AfterID)
	if after == "" {
		return productCursor{}, false, false, nil
	}
	id, parseErr := uuid.Parse(after)
	if parseErr != nil {
		return productCursor{}, false, false, ClientMsg("invalid after_id")
	}
	var name, processedName string
	var createdAt, updatedAt time.Time
	scanErr := s.Pool.QueryRow(ctx, `
		SELECT COALESCE(name, ''), COALESCE(processed_name, ''), created_at, updated_at
		FROM processed_products
		WHERE id = $1 AND company_id = $2`, id, companyID).Scan(&name, &processedName, &createdAt, &updatedAt)
	if scanErr != nil {
		if errors.Is(scanErr, pgx.ErrNoRows) {
			return productCursor{}, true, true, nil
		}
		return productCursor{}, false, false, scanErr
	}
	display := strings.TrimSpace(processedName)
	if display == "" {
		display = strings.TrimSpace(name)
	}
	cur = productCursorFromRow(f, id.String(), display, createdAt, updatedAt)
	return cur, true, false, nil
}

func productCursorFromRow(f ListFilter, id, name string, createdAt, updatedAt time.Time) productCursor {
	cur := productCursor{
		V:  productCursorVersion,
		ID: id,
		SB: f.SortBy,
		SO: f.SortOrder,
	}
	switch f.SortBy {
	case "name":
		cur.Blank = name == ""
		cur.K = strings.ToLower(name)
	case "createdAt":
		cur.K = createdAt.UTC().Format(time.RFC3339Nano)
	default:
		cur.K = updatedAt.UTC().Format(time.RFC3339Nano)
	}
	return cur
}