package api

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"time"

	"github.com/kindredsystems/silo/internal/db"
	"github.com/kindredsystems/silo/internal/kc"
)

// packKCFile gathers DB state and repacks silo/ entries in a .kc file.
func (s *Server) packKCFile(ctx context.Context, data []byte, item *db.Item, rev *db.Revision, meta *db.ItemMetadata) ([]byte, error) {
	manifest := &kc.Manifest{
		UUID:         item.ID,
		KCVersion:    derefStr(meta.KCVersion, "1.0"),
		RevisionHash: derefStr(meta.RevisionHash, ""),
		SiloInstance: derefStr(meta.SiloInstance, ""),
	}

	metadata := &kc.Metadata{
		SchemaName:     derefStr(meta.SchemaName, ""),
		Tags:           meta.Tags,
		LifecycleState: meta.LifecycleState,
		Fields:         meta.Fields,
	}

	// Build history from last 20 revisions.
	revisions, err := s.items.GetRevisions(ctx, item.ID)
	if err != nil {
		return nil, fmt.Errorf("getting revisions: %w", err)
	}
	limit := 20
	if len(revisions) < limit {
		limit = len(revisions)
	}
	history := make([]kc.HistoryEntry, limit)
	for i, r := range revisions[:limit] {
		labels := r.Labels
		if labels == nil {
			labels = []string{}
		}
		history[i] = kc.HistoryEntry{
			RevisionNumber: r.RevisionNumber,
			CreatedAt:      r.CreatedAt.UTC().Format(time.RFC3339),
			CreatedBy:      r.CreatedBy,
			Comment:        r.Comment,
			Status:         r.Status,
			Labels:         labels,
		}
	}

	// Build dependencies from item_dependencies table.
	var deps []kc.Dependency
	dbDeps, err := s.deps.ListByItem(ctx, item.ID)
	if err != nil {
		s.logger.Warn().Err(err).Str("part_number", item.PartNumber).Msg("kc: failed to query dependencies for packing")
	} else {
		deps = make([]kc.Dependency, len(dbDeps))
		for i, d := range dbDeps {
			deps[i] = kc.Dependency{
				UUID:         d.ChildUUID,
				PartNumber:   derefStr(d.ChildPartNumber, ""),
				Revision:     derefInt(d.ChildRevision, 0),
				Quantity:     derefFloat(d.Quantity, 0),
				Label:        derefStr(d.Label, ""),
				Relationship: d.Relationship,
			}
		}
	}
	if deps == nil {
		deps = []kc.Dependency{}
	}

	input := &kc.PackInput{
		Manifest:     manifest,
		Metadata:     metadata,
		History:      history,
		Dependencies: deps,
	}

	return kc.Pack(data, input)
}

// computeETag generates a quoted ETag from the revision number and metadata freshness.
func computeETag(rev *db.Revision, meta *db.ItemMetadata) string {
	var ts int64
	if meta != nil {
		ts = meta.UpdatedAt.UnixNano()
	} else {
		ts = rev.CreatedAt.UnixNano()
	}
	raw := fmt.Sprintf("%d:%d", rev.RevisionNumber, ts)
	h := sha256.Sum256([]byte(raw))
	return `"` + hex.EncodeToString(h[:8]) + `"`
}

// canSkipRepack returns true if the stored blob already has up-to-date silo/ data.
func canSkipRepack(rev *db.Revision, meta *db.ItemMetadata) bool {
	if meta == nil {
		return true // no metadata row = plain .fcstd
	}
	if meta.RevisionHash != nil && rev.FileChecksum != nil &&
		*meta.RevisionHash == *rev.FileChecksum &&
		meta.UpdatedAt.Before(rev.CreatedAt) {
		return true
	}
	return false
}

// derefStr returns the value of a *string pointer, or fallback if nil.
func derefStr(p *string, fallback string) string {
	if p != nil {
		return *p
	}
	return fallback
}

// derefInt returns the value of a *int pointer, or fallback if nil.
func derefInt(p *int, fallback int) int {
	if p != nil {
		return *p
	}
	return fallback
}

// derefFloat returns the value of a *float64 pointer, or fallback if nil.
func derefFloat(p *float64, fallback float64) float64 {
	if p != nil {
		return *p
	}
	return fallback
}