// Copyright 2024 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package pgcatalog

import (
	"io"

	"github.com/dolthub/go-mysql-server/sql"

	"github.com/dolthub/doltgresql/server/tables"
	pgtypes "github.com/dolthub/doltgresql/server/types"
)

// PgSequencesName is a constant to the pg_sequences name.
const PgSequencesName = "pg_sequences"

// InitPgSequences handles registration of the pg_sequences handler.
func InitPgSequences() {
	tables.AddHandler(PgCatalogName, PgSequencesName, PgSequencesHandler{})
}

// PgSequencesHandler is the handler for the pg_sequences table.
type PgSequencesHandler struct{}

var _ tables.Handler = PgSequencesHandler{}

// Name implements the interface tables.Handler.
func (p PgSequencesHandler) Name() string {
	return PgSequencesName
}

// RowIter implements the interface tables.Handler.
func (p PgSequencesHandler) RowIter(ctx *sql.Context, _ sql.Partition) (sql.RowIter, error) {
	cache, err := getPgCatalogCache(ctx)
	if err != nil {
		return nil, err
	}

	if cache.sequences == nil {
		err = cachePgSequences(ctx, cache)
		if err != nil {
			return nil, err
		}
	}

	return &pgSequencesRowIter{
		sequences: cache.sequences,
		idx:       0,
	}, nil
}

// PkSchema implements the interface tables.Handler.
func (p PgSequencesHandler) PkSchema() sql.PrimaryKeySchema {
	return sql.PrimaryKeySchema{
		Schema:     pgSequencesSchema,
		PkOrdinals: nil,
	}
}

// pgSequencesSchema is the schema for pg_sequences.
var pgSequencesSchema = sql.Schema{
	{Name: "schemaname", Type: pgtypes.Name, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "sequencename", Type: pgtypes.Name, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "sequenceowner", Type: pgtypes.Name, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "data_type", Type: pgtypes.Text, Default: nil, Nullable: true, Source: PgSequencesName}, // TODO: regtype type
	{Name: "start_value", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "min_value", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "max_value", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "increment_by", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "cycle", Type: pgtypes.Bool, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "cache_size", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
	{Name: "last_value", Type: pgtypes.Int64, Default: nil, Nullable: true, Source: PgSequencesName},
}

// pgSequencesRowIter is the sql.RowIter for the pg_sequences table.
type pgSequencesRowIter struct {
	sequences []*pgSequence
	idx       int
}

var _ sql.RowIter = (*pgSequencesRowIter)(nil)

// Next implements the interface sql.RowIter.
func (iter *pgSequencesRowIter) Next(_ *sql.Context) (sql.Row, error) {
	if iter.idx >= len(iter.sequences) {
		return nil, io.EOF
	}
	sequence := iter.sequences[iter.idx].sequence
	schemaName := iter.sequences[iter.idx].schema
	iter.idx++

	var lastValue interface{}
	if sequence.HasBeenCalled {
		if sequence.IsAtEnd {
			lastValue = sequence.Current
		} else {
			lastValue = sequence.Current - sequence.Increment
		}
	}

	return sql.Row{
		schemaName,                     // schemaname
		sequence.Id.SequenceName(),     // sequencename
		nil,                            // sequenceowner
		sequence.DataTypeID.TypeName(), // data_type
		sequence.Start,                 // start_value
		sequence.Minimum,               // min_value
		sequence.Maximum,               // max_value
		sequence.Increment,             // increment_by
		sequence.Cycle,                 // cycle
		sequence.Cache,                 // cache_size
		lastValue,                      // last_value
	}, nil
}

// Close implements the interface sql.RowIter.
func (iter *pgSequencesRowIter) Close(_ *sql.Context) error {
	return nil
}