package seeds

import (
	"encoding/json"
	"fmt"
)

// RowSeed is what a registry row carries of its record's seed (column
// seed_source): enough for the activator to place the snapshot on first
// wake (spec §3.4) without reading the record.
type RowSeed struct {
	ID     string `json:"id"`
	Kind   string `json:"kind"`
	SHA256 string `json:"sha256,omitempty"`
	Bytes  int64  `json:"bytes,omitempty"`
	State  string `json:"state"`
}

// Encode is the column's value: compact JSON in field order.
func (r RowSeed) Encode() string {
	b, _ := json.Marshal(r) // strings and an int64 cannot fail to marshal
	return string(b)
}

// ParseRowSeed reads a seed_source column. "" is no seed: (nil, nil).
func ParseRowSeed(s string) (*RowSeed, error) {
	if s == "" {
		return nil, nil
	}
	var r RowSeed
	if err := json.Unmarshal([]byte(s), &r); err != nil {
		return nil, fmt.Errorf("seeds: seed_source column: %w", err)
	}
	if !ValidID(r.ID) {
		return nil, fmt.Errorf("seeds: seed_source column: id %q is not a seed id", r.ID)
	}
	return &r, nil
}

// Placeable reports whether the restore fallback applies (spec §3.4: a row
// whose record seed is ready, swapped or placed).
func (r RowSeed) Placeable() bool {
	switch r.State {
	case StateReady, StateSwapped, StatePlaced:
		return true
	}
	return false
}