package indexpointers

import (
	"context"
	"fmt"

	"github.com/grafana/loki/v3/pkg/dataobj"
	"github.com/grafana/loki/v3/pkg/dataobj/internal/metadata/indexpointersmd"
)

var sectionType = dataobj.SectionType{
	Namespace: "github.com/grafana/loki",
	Kind:      "indexpointers",
}

// CheckSection returns true if section is a indexpointers section.
func CheckSection(section *dataobj.Section) bool { return section.Type == sectionType }

// Section represents an opened indexpointers section.
type Section struct {
	reader  dataobj.SectionReader
	columns []*Column
}

// Open opens a Section from an underlying [dataobj.Section]. Open returns an
// error if the section metadata could not be read or if the provided ctx is
// canceled.
func Open(ctx context.Context, section *dataobj.Section) (*Section, error) {
	if !CheckSection(section) {
		return nil, fmt.Errorf("section is not a indexpointers section")
	}

	sec := &Section{reader: section.Reader}
	if err := sec.init(ctx); err != nil {
		return nil, fmt.Errorf("intializing section: %w", err)
	}
	return sec, nil
}

func (s *Section) init(ctx context.Context) error {
	dec := newDecoder(s.reader)
	metadata, err := dec.Metadata(ctx)
	if err != nil {
		return fmt.Errorf("failed to decode metadata: %w", err)
	}

	for _, col := range metadata.GetColumns() {
		colType, ok := convertColumnType(col.Type)
		if !ok {
			// Skip over unrecognized columns.
			continue
		}

		s.columns = append(s.columns, &Column{
			Section: s,
			Name:    col.Info.Name,
			Type:    colType,

			desc: col,
		})
	}

	return nil
}

// Columns returns the set of Columns in the section. The slice of returned
// sections must not be mutated.
//
// Unrecognized columns (e.g., when running older code against newer indexpointers
// sections) are skipped.
func (s *Section) Columns() []*Column { return s.columns }

// ColumnType represents the kind of information stored in a [Column].
type ColumnType int

const (
	ColumnTypeInvalid      ColumnType = iota // ColumnTypeInvalid is an invalid column.
	ColumnTypePath                           // ColumnTypePath is a column containing the path to the index object.
	ColumnTypeMinTimestamp                   // ColumnTypeMinTimestamp is a column containing the minimum timestamp of the index object.
	ColumnTypeMaxTimestamp                   // ColumnTypeMaxTimestamp is a column containing the maximum timestamp of the index object.
)

var columnTypeNames = map[ColumnType]string{
	ColumnTypeInvalid:      "invalid",
	ColumnTypePath:         "path",
	ColumnTypeMinTimestamp: "min_timestamp",
	ColumnTypeMaxTimestamp: "max_timestamp",
}

// String returns the human-readable name of ct.
func (ct ColumnType) String() string {
	text, ok := columnTypeNames[ct]
	if !ok {
		return fmt.Sprintf("ColumnType(%d)", ct)
	}
	return text
}

// A Column represents one of the columns in the indexpointers section. Valid columns
// can only be retrieved by calling [Section.Columns].
//
// Data in columns can be read by using a [Reader].
type Column struct {
	Section *Section
	Name    string
	Type    ColumnType

	desc *indexpointersmd.ColumnDesc // Column description used for further decoding and reading.
}

func convertColumnType(protoType indexpointersmd.ColumnType) (ColumnType, bool) {
	switch protoType {
	case indexpointersmd.COLUMN_TYPE_UNSPECIFIED:
		return ColumnTypeInvalid, true
	case indexpointersmd.COLUMN_TYPE_PATH:
		return ColumnTypePath, true
	case indexpointersmd.COLUMN_TYPE_MIN_TIMESTAMP:
		return ColumnTypeMinTimestamp, true
	case indexpointersmd.COLUMN_TYPE_MAX_TIMESTAMP:
		return ColumnTypeMaxTimestamp, true
	}
	return ColumnTypeInvalid, false
}