package delivery

import (
	"encoding/json"
	"fmt"
	"regexp"
	"strings"
)

// The controller's compositions (novox/hq ADR 0539 clauses 1 to 4). A **composition** is one module's resources
// composed for one node at one fingerprint, written by the controller, which keeps the inputs. It lives in a bucket of
// each node, `composed-<node>`, which only that node's node-engine reads (a composition can carry a sealed value), under
// `<node>.<module>.<fingerprint hex>`, and the node's own resources (adoption, firewall openings, accounts, the
// resolver, identities and groups) under `<node>.node`. Beside it, under the same key in `mesh-controller_composed`,
// which the assigner reads, the controller writes the composition's digest and its judgement of the move from the
// composition the node runs now (ComposedDigest). The controller writes both by compare-and-set while it holds the
// lease; the operator's credential is a second writer on the hand path alone (clause 10, mesh-hand-compose).
//
// A composition is derived state (clause 4): its key and its digest are deleted by the controller when its fingerprint
// is no longer among the module's five newest and no want names it, and each bucket keeps five revisions of a key.
const (
	// ComposedBucketPrefix starts the name of a node's bucket of compositions, ComposedBucketFor(node).
	ComposedBucketPrefix = "composed-"
	// ComposedHistory is the revisions a node's composition bucket keeps per key (ADR 0539 clause 4).
	ComposedHistory = 5
	// ControllerModule is the module of the controller, the writer of the compositions.
	ControllerModule = "mesh-controller"
	// ControllerComposedBucket is the controller's bucket of each composition's digest and judgement, `<owner
	// module>_<name>`, read by the assigner (ADR 0539 clauses 2 and 6).
	ControllerComposedBucket = ControllerModule + "_composed"
	// ControllerComposedHistory is the revisions that bucket keeps per key.
	ControllerComposedHistory = 5
	// ComposedKeep is how many of a module's newest fingerprints keep their compositions though no want names them
	// (ADR 0539 clause 4).
	ComposedKeep = 5
)

// nodeWord is the last part of a node's own key, in the have bucket and in a node's composition bucket alike.
const nodeWord = "node"

var bucketNode = regexp.MustCompile(`^[A-Za-z0-9_-]+$`)

// ComposedBucketFor is the name of a node's bucket of compositions, "composed-<node>", as declaration.FileBucketFor
// names a node's object bucket (ADR 0488 §4). The node name must be one a bucket and a subject token accept: letters,
// digits, '_' and '-'.
func ComposedBucketFor(node string) (string, error) {
	if node == "" {
		return "", fmt.Errorf("delivery: the node name is empty; a node's composition bucket is named for its node")
	}
	if !bucketNode.MatchString(node) {
		return "", fmt.Errorf("delivery: the node name %q is not one a bucket accepts: letters, digits, '_' and '-' only", node)
	}
	return ComposedBucketPrefix + node, nil
}

// ComposedKey is the key, in ComposedBucketFor(node) and in ControllerComposedBucket, of a module's composition for a
// node at a fingerprint: `<node>.<module>.<hex>`, the hex being the fingerprint's key part (FingerprintKeyPart). A
// module named `node` is refused, since `<node>.node` is the node's own key.
func ComposedKey(node, module, fingerprint string) (string, error) {
	have, err := HaveKey(node, module)
	if err != nil {
		return "", err
	}
	part, err := FingerprintKeyPart(fingerprint)
	if err != nil {
		return "", err
	}
	return have + "." + part, nil
}

// ComposedNodeKey is the key of a node's own composition: `<node>.node`.
func ComposedNodeKey(node string) (string, error) {
	return HaveNodeKey(node)
}

// ParseComposedKey is the inverse of ComposedKey and ComposedNodeKey: isNode is true for `<node>.node`, with module
// and fingerprint empty. It refuses any other shape, naming the key.
func ParseComposedKey(key string) (node, module, fingerprint string, isNode bool, err error) {
	refused := func(why error) (string, string, string, bool, error) {
		return "", "", "", false, fmt.Errorf("delivery: %q is not a composition key, <node>.<module>.<fingerprint hex> or <node>.node: %w", key, why)
	}
	parts := strings.Split(key, ".")
	switch len(parts) {
	case 2:
		if parts[1] != nodeWord {
			return refused(fmt.Errorf("a module's composition names its fingerprint"))
		}
		if err := checkName("node", parts[0]); err != nil {
			return refused(err)
		}
		return parts[0], "", "", true, nil
	case 3:
		node, module, isNode, err := ParseHaveKey(parts[0] + "." + parts[1])
		if err != nil {
			return refused(err)
		}
		if isNode {
			return refused(fmt.Errorf("the node's own key names no fingerprint"))
		}
		fp, err := ParseFingerprintKeyPart(parts[2])
		if err != nil {
			return refused(err)
		}
		return node, module, fp, false, nil
	}
	return refused(fmt.Errorf("it has %d parts", len(parts)))
}

// Judgement is the controller's judgement of a move from the composition a node runs, as its have names it, to a new
// one (ADR 0539 clauses 2 and 14, by ADR 0377 §3's tests).
type Judgement string

// The judgements of a move.
const (
	// JudgedRecreates is a move that recreates a container.
	JudgedRecreates Judgement = "recreates"
	// JudgedMovesData is a move that gives the module's data another place.
	JudgedMovesData Judgement = "moves-data"
	// JudgedNeither is a move that does neither, and the judgement of a composition the node never ran.
	JudgedNeither Judgement = "neither"
	// JudgedCannot is a move that cannot be judged, because the composition the node runs is gone or cannot be read.
	JudgedCannot Judgement = "cannot-judge"
	// JudgedUnchanged is a composition equal to the module's slice of the declaration the node last applied, for a node
	// whose have names no composition yet (the first want at the switch, novox/hq ADR 0540 clause 9): applying it
	// changes nothing on the node, so it needs no person's yes.
	JudgedUnchanged Judgement = "unchanged"
)

var digestForm = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)

func checkDigest(digest, of string) error {
	if !digestForm.MatchString(digest) {
		return fmt.Errorf("delivery: %s %q is not sha256:<64 lowercase hex digits>", of, digest)
	}
	return nil
}

// ComposedDigest is the value, in ControllerComposedBucket, beside a composition: its Digest (ComposedDigestOf), and
// the Judgement of the move to it from the composition the node runs now, whose digest is Against (empty when the node
// runs no composition of the module). Words say why, and are required for a move that cannot be judged. Rewritten when
// the node's have changes.
//
// Policy is the module's upgrade policy as the controller holds it (ADR 0236, ADR 0539 clause 14), with PolicyFrom
// where it comes from and PolicyWhy why: the assigner holds a move of a module of policy record from it, the operator's
// own choice (`upgrade` with policy) included. Rewritten when the policy changes. Empty on a composition made by hand
// (mesh-hand-compose), whose want the operator writes.
type ComposedDigest struct {
	V         int       `json:"v"`
	Digest    string    `json:"digest"`
	Judgement Judgement `json:"judgement"`
	Against   string    `json:"against,omitempty"`
	Words     string    `json:"words,omitempty"`
	// UserListOnly says the composition differs from the one the node's have names only in the bus's user list (the
	// bus module's file `<module>.bus-users`), whatever the judgement says of its mount: the assigner writes such a
	// revision into the bus node's want at once, outside the record hold, at the fingerprint the node runs (ADR 0539
	// clause 7).
	UserListOnly bool   `json:"user-list-only,omitempty"`
	Policy       string `json:"policy,omitempty"`
	PolicyFrom   string `json:"policy-from,omitempty"`
	PolicyWhy    string `json:"policy-why,omitempty"`
}

// The upgrade policies and their sources a composition's value names: catalogue.PolicyRoll, PolicyTogether and
// PolicyRecord, and catalogue.FromPerson, FromModule, FromBus, FromData and FromDefault, the same words (the compose
// package's test holds them equal; this package does not import the catalogue).
var (
	composedPolicies    = []string{"roll", "together", "record"}
	composedPolicyFroms = []string{"person", "module", "the bus", "irreplaceable data", "default"}
)

func oneOf(v string, of []string) bool {
	for _, o := range of {
		if v == o {
			return true
		}
	}
	return false
}

func (c ComposedDigest) check() error {
	if err := checkDigest(c.Digest, "the composition's digest"); err != nil {
		return err
	}
	if c.Against != "" {
		if err := checkDigest(c.Against, "the digest a move is judged against"); err != nil {
			return err
		}
	}
	switch c.Judgement {
	case JudgedRecreates, JudgedMovesData:
		if c.Against == "" {
			return fmt.Errorf("delivery: a move judged %s names the composition it is judged against", c.Judgement)
		}
	case JudgedNeither, JudgedUnchanged:
	case JudgedCannot:
		if c.Words == "" {
			return fmt.Errorf("delivery: a move that cannot be judged says why")
		}
	default:
		return fmt.Errorf("delivery: the judgement %q is not %s, %s, %s, %s or %s", c.Judgement, JudgedRecreates,
			JudgedMovesData, JudgedNeither, JudgedCannot, JudgedUnchanged)
	}
	if c.Policy != "" || c.PolicyFrom != "" {
		if !oneOf(c.Policy, composedPolicies) {
			return fmt.Errorf("delivery: the upgrade policy %q is not one of %v", c.Policy, composedPolicies)
		}
		if !oneOf(c.PolicyFrom, composedPolicyFroms) {
			return fmt.Errorf("delivery: the upgrade policy's source %q is not one of %v", c.PolicyFrom, composedPolicyFroms)
		}
	}
	return nil
}

// PolicyRecord is the policy whose moves the assigner holds for a person's yes (ADR 0539 clause 14).
const PolicyRecord = "record"

// EncodeComposedDigest is c as JSON at Version; it refuses an unknown judgement, a digest not of the sha256 form, a
// move judged to recreate or move data against nothing, and a move that cannot be judged without its reason.
func EncodeComposedDigest(c ComposedDigest) ([]byte, error) {
	if err := c.check(); err != nil {
		return nil, err
	}
	c.V = Version
	return json.Marshal(c)
}

// DecodeComposedDigest reads the value beside a composition; it refuses an unknown version (ErrUnknownVersion) and
// what EncodeComposedDigest refuses.
func DecodeComposedDigest(data []byte) (ComposedDigest, error) {
	var c ComposedDigest
	if err := decode(data, &c); err != nil {
		return ComposedDigest{}, err
	}
	if err := c.check(); err != nil {
		return ComposedDigest{}, err
	}
	return c, nil
}

// SameComposedDigest says whether two values are the same, so the controller writes only when they differ.
func SameComposedDigest(a, b ComposedDigest) bool { return a == b }