package repository

import (
	"context"
	"time"

	"evobgp/internal/store"
)

const revisionPruneBatchSize = 50

// sqlPrunableRevisionsWhere appends prunable revision predicates (tenant + cutoff params).
func sqlPrunableRevisionsWhere(tenantParam, cutoffParam string) string {
	return `tenant_id = ` + tenantParam + `
		  AND created_at < ` + cutoffParam + `
		  AND id <> (
			SELECT id FROM config_revision
			WHERE tenant_id = ` + tenantParam + `
			ORDER BY created_at DESC
			LIMIT 1
		  )
		  AND NOT EXISTS (
			SELECT 1 FROM bgp_speaker AS sp
			WHERE sp.tenant_id = ` + tenantParam + `
			  AND (sp.last_applied_revision_id = config_revision.id OR sp.published_revision_id = config_revision.id)
		  )`
}

func (p *Postgres) EstimateRevisionPrune(tenantID string, cutoff time.Time, retentionMinutes int) (store.RevisionPruneEstimate, error) {
	ctx := context.Background()
	out := store.RevisionPruneEstimate{
		RetentionMinutes: retentionMinutes,
		CutoffAt:         cutoff.UTC(),
	}
	where := sqlPrunableRevisionsWhere("$1", "$2")
	var revBytes, previewBytes, rmpBytes, snapRowBytes int64
	err := p.pool.QueryRow(ctx, `
		WITH prunable AS (
			SELECT id, prefix_snapshot_id, content_hash, meta_json
			FROM config_revision
			WHERE `+where+`
		),
		freed_snaps AS (
			SELECT DISTINCT pr.prefix_snapshot_id AS snap_id
			FROM prunable pr
			WHERE pr.prefix_snapshot_id IS NOT NULL
			EXCEPT
			SELECT DISTINCT cr.prefix_snapshot_id
			FROM config_revision cr
			WHERE cr.prefix_snapshot_id IS NOT NULL
			  AND cr.id NOT IN (SELECT id FROM prunable)
		)
		SELECT
			(SELECT COUNT(*)::int FROM prunable),
			COALESCE((SELECT SUM(octet_length(content_hash) + octet_length(meta_json::text))::bigint FROM prunable), 0),
			COALESCE((
				SELECT SUM(octet_length(value))::bigint
				FROM config_revision_preview p
				JOIN prunable pr ON pr.id = p.revision_id
				CROSS JOIN LATERAL jsonb_each_text(COALESCE(p.fragments, '{}'::jsonb))
			), 0),
			COALESCE((
				SELECT SUM(octet_length(rmp.prefix) + octet_length(COALESCE(rmp.source, '')))::bigint
				FROM revision_materialized_prefix rmp
				WHERE rmp.revision_id IN (SELECT id FROM prunable)
			), 0),
			(SELECT COUNT(*)::int FROM freed_snaps),
			COALESCE((SELECT COUNT(*)::int FROM prefix_snapshot_row psr WHERE psr.snapshot_id IN (SELECT snap_id FROM freed_snaps)), 0),
			COALESCE((
				SELECT SUM(octet_length(psr.prefix) + octet_length(COALESCE(psr.source, '')))::bigint
				FROM prefix_snapshot_row psr
				WHERE psr.snapshot_id IN (SELECT snap_id FROM freed_snaps)
			), 0)`,
		tenantID, cutoff.UTC()).Scan(
		&out.RevisionCount,
		&revBytes,
		&previewBytes,
		&rmpBytes,
		&out.OrphanSnapshotCount,
		&out.PrefixRowCount,
		&snapRowBytes,
	)
	if err != nil {
		return out, err
	}
	out.BytesEstimate = revBytes + previewBytes + rmpBytes + snapRowBytes
	return out, nil
}

func (p *Postgres) PruneRevisionsWithStats(tenantID string, cutoff time.Time) (store.RevisionPruneResult, error) {
	ctx := context.Background()
	est, err := p.EstimateRevisionPrune(tenantID, cutoff, 0)
	if err != nil {
		return store.RevisionPruneResult{}, err
	}
	out := store.RevisionPruneResult{BytesEstimate: est.BytesEstimate}

	where := sqlPrunableRevisionsWhere("$1", "$2")
	for {
		cmd, err := p.pool.Exec(ctx, `
			DELETE FROM config_revision AS cr
			WHERE cr.id IN (
				SELECT id FROM config_revision
				WHERE `+where+`
				ORDER BY created_at ASC
				LIMIT $3
			)`, tenantID, cutoff.UTC(), revisionPruneBatchSize)
		if err != nil {
			return out, err
		}
		n := int(cmd.RowsAffected())
		out.DeletedRevisions += n
		if n < revisionPruneBatchSize {
			break
		}
	}

	for {
		snaps, rows, err := p.pruneUnreferencedPrefixSnapshots(ctx, revisionPruneBatchSize)
		if err != nil {
			return out, err
		}
		out.DeletedPrefixSnapshots += snaps
		out.DeletedPrefixRows += rows
		if snaps < revisionPruneBatchSize {
			break
		}
	}
	return out, nil
}

func (p *Postgres) PruneRevisionsBefore(tenantID string, cutoff time.Time) (int, error) {
	res, err := p.PruneRevisionsWithStats(tenantID, cutoff)
	if err != nil {
		return 0, err
	}
	return res.DeletedRevisions, nil
}

func (p *Postgres) pruneUnreferencedPrefixSnapshots(ctx context.Context, batchSize int) (deletedSnapshots int, deletedRows int, err error) {
	if !prefixSnapshotTableExists(ctx, p.pool) {
		return 0, 0, nil
	}
	var snapCount, rowCount int
	err = p.pool.QueryRow(ctx, `
		WITH doomed AS (
			SELECT ps.id FROM prefix_snapshot ps
			WHERE NOT EXISTS (
				SELECT 1 FROM config_revision cr WHERE cr.prefix_snapshot_id = ps.id
			)
			LIMIT $1
		)
		SELECT
			(SELECT COUNT(*)::int FROM doomed),
			(SELECT COUNT(*)::int FROM prefix_snapshot_row psr WHERE psr.snapshot_id IN (SELECT id FROM doomed))`,
		batchSize).Scan(&snapCount, &rowCount)
	if err != nil {
		return 0, 0, err
	}
	if snapCount == 0 {
		return 0, 0, nil
	}
	_, err = p.pool.Exec(ctx, `
		DELETE FROM prefix_snapshot
		WHERE id IN (
			SELECT ps.id FROM prefix_snapshot ps
			WHERE NOT EXISTS (
				SELECT 1 FROM config_revision cr WHERE cr.prefix_snapshot_id = ps.id
			)
			LIMIT $1
		)`, batchSize)
	if err != nil {
		return 0, 0, err
	}
	return snapCount, rowCount, nil
}