// Package libdns defines core interfaces that should be implemented by DNS
// provider clients. They are small and idiomatic Go interfaces with
// well-defined semantics.
//
// Records are described independently of any particular zone, a convention
// that grants Record structs portability across zones. As such, record names
// are partially qualified, i.e. relative to the zone. For example, an A
// record called "sub" in zone "example.com." represents a fully-qualified
// domain name (FQDN) of "sub.example.com.". Implementations should expect
// that input records conform to this standard, while also ensuring that
// output records do; adjustments to record names may need to be made before
// or after provider API calls, for example, to maintain consistency with
// all other libdns provider implementations. Helper functions are available
// in this package to convert between relative and absolute names.
//
// Although zone names are a required input, libdns does not coerce any
// particular representation of DNS zones; only records. Since zone name and
// records are separate inputs in libdns interfaces, it is up to the caller
// to pair a zone's name with its records in a way that works for them.
//
// All interface implementations must be safe for concurrent/parallel use.
// For example, if AppendRecords() is called at the same time and two API
// requests are made to the provider at the same time, the result of both
// requests must be visible after they both complete; if the provider does
// not synchronize the writing of the zone file and one request overwrites
// the other, then the client implementation must take care to synchronize
// on behalf of the incompetent provider. This synchronization need not be
// global; for example: the scope of synchronization might only need to be
// within the same zone, allowing multiple requests at once as long as all
// of them are for different zones. (Exact logic depends on the provider.)
package libdns

import (
	"context"
	"strings"
	"time"
)

// RecordGetter can get records from a DNS zone.
type RecordGetter interface {
	// GetRecords returns all the records in the DNS zone.
	//
	// Implementations must honor context cancellation and be safe for
	// concurrent use.
	GetRecords(ctx context.Context, zone string) ([]Record, error)
}

// RecordAppender can non-destructively add new records to a DNS zone.
type RecordAppender interface {
	// AppendRecords creates the requested records in the given zone
	// and returns the populated records that were created. It never
	// changes existing records.
	//
	// Implementations must honor context cancellation and be safe for
	// concurrent use.
	AppendRecords(ctx context.Context, zone string, recs []Record) ([]Record, error)
}

// RecordSetter can set new or update existing records in a DNS zone.
type RecordSetter interface {
	// SetRecords updates the zone so that the records described in the
	// input are reflected in the output. It may create or overwrite
	// records or -- depending on the record type -- delete records to
	// maintain parity with the input. No other records are affected.
	// It returns the records which were set.
	//
	// Records that have an ID associating it with a particular resource
	// on the provider will be directly replaced. If no ID is given, this
	// method may use what information is given to do lookups and will
	// ensure that only necessary changes are made to the zone.
	//
	// Implementations must honor context cancellation and be safe for
	// concurrent use.
	SetRecords(ctx context.Context, zone string, recs []Record) ([]Record, error)
}

// RecordDeleter can delete records from a DNS zone.
type RecordDeleter interface {
	// DeleteRecords deletes the given records from the zone if they exist.
	// It returns the records that were deleted.
	//
	// Records that have an ID to associate it with a particular resource on
	// the provider will be directly deleted. If no ID is given, this method
	// may use what information is given to do lookups and delete only
	// matching records.
	//
	// Implementations must honor context cancellation and be safe for
	// concurrent use.
	DeleteRecords(ctx context.Context, zone string, recs []Record) ([]Record, error)
}

// Record is a generalized representation of a DNS record.
type Record struct {
	// provider-specific metadata
	ID string

	// general record fields
	Type  string
	Name  string // partially-qualified (relative to zone)
	Value string
	TTL   time.Duration

	// type-dependent record fields
	Priority int // used by MX, SRV, and URI records
}

// RelativeName makes fqdn relative to zone. For example, for a FQDN of
// "sub.example.com" and a zone of "example.com", it outputs "sub".
//
// If fqdn cannot be expressed relative to zone, the input fqdn is returned.
func RelativeName(fqdn, zone string) string {
	return strings.TrimSuffix(strings.TrimSuffix(fqdn, zone), ".")
}

// AbsoluteName makes name into a fully-qualified domain name (FQDN) by
// prepending it to zone and tidying up the dots. For example, an input
// of name "sub" and zone "example.com." will return "sub.example.com.".
func AbsoluteName(name, zone string) string {
	if zone == "" {
		return strings.Trim(name, ".")
	}
	if name == "" || name == "@" {
		return zone
	}
	if !strings.HasSuffix(name, ".") {
		name += "."
	}
	return name + zone
}