package delivery

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

// **Asks: a build or a check step is a message a build node pulls when it has a free slot** (novox/hq ADR 0525, as
// ADR 0536 §4 changes it; issue 1887). The builder puts a trunk fingerprint's build on the delivery stream of the
// artifact's language and a candidate's on the check stream; the checker puts a check of one level on the check stream,
// and a re-judge after a trunk move on the recheck stream. Each build module claims the node seat of its language
// (`node-build-go`, `node-build-node`, `node-build-image`), whose accepted kinds the broker derives as the work queue
// `SEAT_NODE_BUILD_<LANGUAGE>` with one shared pull worker per kind; a holder pulls delivery first, then check, then
// recheck, at most its node's build capacity at once (ADR 0525 §4, §5).
//
// **An ask is one whole job on one node** (ADR 0525 §3): a build ask is the fetch, the build (or copy) of each artifact
// and the push; a check ask is the fetch, the digest and the tests of one level. Its end is written on the build module's
// step key `<node>.<ask id>` (StepsBucket), which the asker watches with AskStepWatch (ADR 0525 §6).

// The kinds of ask: the seat's accepted kinds, in the order a holder pulls them.
const (
	AskDelivery = "delivery"
	AskCheck    = "check"
	AskRecheck  = "recheck"
)

// AskKinds are the accepted kinds of a build seat, in the order a holder pulls them (ADR 0536 §4).
var AskKinds = []string{AskDelivery, AskCheck, AskRecheck}

// The languages of the build seats: each is one build module's (mesh-build-<language>) and one seat's
// (node-build-<language>).
const (
	AskGo    = "go"
	AskNode  = "node"
	AskImage = "image"
)

// AskLanguages are the build seats' languages.
var AskLanguages = []string{AskGo, AskNode, AskImage}

// StepAskVersion is the version of an Ask value; a reader refuses another (ErrUnknownVersion).
const StepAskVersion = 1

func checkAskKind(kind string) error {
	for _, k := range AskKinds {
		if kind == k {
			return nil
		}
	}
	return fmt.Errorf("delivery: the ask kind %q is not delivery, check or recheck", kind)
}

func checkAskLanguage(language string) error {
	for _, l := range AskLanguages {
		if language == l {
			return nil
		}
	}
	return fmt.Errorf("delivery: the ask language %q is not go, node or image", language)
}

// BuildSeat is the node seat a build module of language claims: node-build-<language>.
func BuildSeat(language string) (string, error) {
	if err := checkAskLanguage(language); err != nil {
		return "", err
	}
	return "node-build-" + language, nil
}

// BuildModuleOf is the build module that holds language's seat: mesh-build-<language>.
func BuildModuleOf(language string) (string, error) {
	if err := checkAskLanguage(language); err != nil {
		return "", err
	}
	return "mesh-build-" + language, nil
}

// AskSubject is the subject an ask of kind for language is published on: the seat's accept subject,
// `mesh.seat.node-build-<language>.accept.<kind>` (mesh-controller internal/broker SeatStreams).
func AskSubject(language, kind string) (string, error) {
	seat, err := BuildSeat(language)
	if err != nil {
		return "", err
	}
	if err := checkAskKind(kind); err != nil {
		return "", err
	}
	return "mesh.seat." + seat + ".accept." + kind, nil
}

// ParseAskSubject is the inverse of AskSubject; it refuses a subject of another seat or kind.
func ParseAskSubject(subject string) (language, kind string, err error) {
	rest, ok := strings.CutPrefix(subject, "mesh.seat.node-build-")
	if !ok {
		return "", "", fmt.Errorf("delivery: %q is not a build seat's accept subject", subject)
	}
	language, kind, ok = strings.Cut(rest, ".accept.")
	if !ok {
		return "", "", fmt.Errorf("delivery: %q is not a build seat's accept subject", subject)
	}
	if want, err := AskSubject(language, kind); err != nil || want != subject {
		return "", "", fmt.Errorf("delivery: %q is not a build seat's accept subject: %v", subject, err)
	}
	return language, kind, nil
}

// AskStream is the work-queue stream of language's seat, as the broker names a seat's stream: SEAT_NODE_BUILD_<LANGUAGE>.
func AskStream(language string) (string, error) {
	seat, err := BuildSeat(language)
	if err != nil {
		return "", err
	}
	return "SEAT_" + strings.ToUpper(strings.ReplaceAll(seat, "-", "_")), nil
}

// AskWorker is the shared pull consumer of one kind on language's stream, filtered on that kind's subject:
// SEAT_NODE_BUILD_<LANGUAGE>_<KIND>_worker. Every holder of the seat pulls from it, so the work is shared without a
// holder knowing the others (ADR 0190), and the kinds' workers are apart so a holder can pull them in their order.
func AskWorker(language, kind string) (string, error) {
	stream, err := AskStream(language)
	if err != nil {
		return "", err
	}
	if err := checkAskKind(kind); err != nil {
		return "", err
	}
	return stream + "_" + strings.ToUpper(kind) + "_worker", nil
}

// An ask id is a step id of the form buildstep.NewID gives: the time in milliseconds in base 36 (8 or 9 digits) and six
// random hex digits. Its form keeps it apart from a module's or a node's name in a key.
var askIDOK = regexp.MustCompile(`^[0-9a-z]{8,9}[0-9a-f]{6}$`)

func checkAskID(id string) error {
	if !askIDOK.MatchString(id) {
		return fmt.Errorf("delivery: %q is not an ask id (base-36 milliseconds and six hex digits)", id)
	}
	return nil
}

// StepAsk is the message on a build seat's stream: who asked what, of which kind and language, and the one whole job.
// Exactly one of Build and Check is set: a delivery ask is a build; a check ask a build (a candidate's fingerprint) or a
// check; a recheck ask a check; an image ask is always a build.
type StepAsk struct {
	V        int    `json:"v"`
	ID       string `json:"id"`
	Kind     string `json:"kind"`
	Language string `json:"language"`
	// Asker is the module that put the ask (mesh-delivery-builder or mesh-delivery-checker); the stream's grant is what
	// makes it true, this field only names it to a reader.
	Asker string    `json:"asker"`
	At    time.Time `json:"at"`
	Build *BuildJob `json:"build,omitempty"`
	Check *CheckJob `json:"check,omitempty"`
}

// BuildJob is a build ask's job: fetch the commit (unless every artifact is a copy), then build or copy each artifact,
// pushing it when Publish says so, and answer each artifact's digest and reference (BuildAnswer).
type BuildJob struct {
	// Module is the module's name; Path its directory in the repository (the build tool's `module`, "." for its root).
	Module string `json:"module"`
	Path   string `json:"path,omitempty"`
	// FP is the fingerprint the build is of (the builder's key), named for a reader of the ask.
	FP string `json:"fp,omitempty"`
	// Fetch is the fetch tool's arguments, as the build module's fetch tool takes them (buildstep.FetchRequest's Args);
	// absent when every artifact is a copy.
	Fetch map[string]any `json:"fetch,omitempty"`
	// Artifacts are built in this order.
	Artifacts []AskArtifact `json:"artifacts"`
	// Publish says the build pushes an image or publishes a package: a trunk build only (ADR 0487 clause 12).
	Publish bool `json:"publish,omitempty"`
	// Toolchain is the toolchain the fingerprint was computed with; a build module running another refuses the ask.
	Toolchain *ToolchainUsed `json:"toolchain,omitempty"`
}

// AskArtifact is one artifact of a build ask: built from the fetched tree, or copied from From, an upstream pin (ADR
// 0498 clause 4).
type AskArtifact struct {
	Artifact string `json:"artifact"`
	From     string `json:"from,omitempty"`
}

// CheckJob is a check ask's job: fetch the head merged onto its trunk, digest the level's packages, take the kept
// verdicts for the digests that have one, and test the rest at Level, the packages the change's own tests are in first
// (CheckAnswer).
type CheckJob struct {
	// Fetch is the fetch tool's arguments (repository, commit, ref, base, and the build module's own: beside, package).
	Fetch map[string]any `json:"fetch"`
	Level string         `json:"level"`
	// Kept says the build module takes the kept verdicts of the checker's kept bucket (CheckerKeptBucket, by KeptKey)
	// for the packages whose digest has one, and tests only the others. A try that runs some tests (Run) keeps nothing.
	Kept bool `json:"kept,omitempty"`
	// Runner is the test step's runner ("workspace": the candidate's own build module judges it, ADR 0535 §4), used
	// when the merge changes a path under RunnerWhen (every merge when RunnerWhen is empty).
	Runner     string `json:"runner,omitempty"`
	RunnerWhen string `json:"runner_when,omitempty"`
	// Run is a try's test pattern (go test -run): the level runs it alone, digesting nothing.
	Run string `json:"run,omitempty"`
}

func (a StepAsk) check() error {
	if err := checkAskID(a.ID); err != nil {
		return err
	}
	if err := checkAskKind(a.Kind); err != nil {
		return err
	}
	if err := checkAskLanguage(a.Language); err != nil {
		return err
	}
	if err := checkName("asker", a.Asker); err != nil {
		return err
	}
	if a.At.IsZero() {
		return fmt.Errorf("delivery: the ask %s names no time", a.ID)
	}
	switch {
	case (a.Build == nil) == (a.Check == nil):
		return fmt.Errorf("delivery: the ask %s holds a build or a check, exactly one", a.ID)
	case a.Build != nil && a.Kind == AskRecheck:
		return fmt.Errorf("delivery: the ask %s is a build on the recheck stream, which carries checks alone", a.ID)
	case a.Check != nil && a.Kind == AskDelivery:
		return fmt.Errorf("delivery: the ask %s is a check on the delivery stream, which carries trunk builds alone", a.ID)
	case a.Check != nil && a.Language == AskImage:
		return fmt.Errorf("delivery: the ask %s is a check of an image, which has no tests", a.ID)
	}
	if a.Build != nil {
		return a.Build.check(a.ID)
	}
	return a.Check.check(a.ID)
}

func (b BuildJob) check(id string) error {
	if err := checkName("module", b.Module); err != nil {
		return err
	}
	if len(b.Artifacts) == 0 {
		return fmt.Errorf("delivery: the build ask %s names no artifact", id)
	}
	fetch := false
	for _, a := range b.Artifacts {
		if err := checkName("artifact", a.Artifact); err != nil {
			return err
		}
		fetch = fetch || a.From == ""
	}
	if fetch {
		if b.Path == "" {
			return fmt.Errorf("delivery: the build ask %s names no directory (path) for the module %s", id, b.Module)
		}
		if err := checkFetchArgs(id, b.Fetch); err != nil {
			return err
		}
	}
	return nil
}

func (c CheckJob) check(id string) error {
	if err := checkLevel(c.Level); err != nil {
		return err
	}
	return checkFetchArgs(id, c.Fetch)
}

var askCommitOK = regexp.MustCompile(`^[0-9a-f]{40}$`)

// checkFetchArgs refuses fetch arguments with no repository or no full commit; the rest is the build module's fetch to
// judge, as a direct call's is.
func checkFetchArgs(id string, args map[string]any) error {
	repository, _ := args["repository"].(string)
	commit, _ := args["commit"].(string)
	if repository == "" || !strings.Contains(repository, "/") {
		return fmt.Errorf("delivery: the ask %s fetches no repository <owner>/<name>", id)
	}
	if !askCommitOK.MatchString(commit) {
		return fmt.Errorf("delivery: the ask %s fetches no full commit", id)
	}
	return nil
}

// EncodeStepAsk is a as JSON at StepAskVersion; it refuses what DecodeStepAsk refuses.
func EncodeStepAsk(a StepAsk) ([]byte, error) {
	a.V = StepAskVersion
	a.At = a.At.UTC()
	if err := a.check(); err != nil {
		return nil, err
	}
	return json.Marshal(a)
}

// DecodeStepAsk reads an ask; it refuses an unknown version (ErrUnknownVersion), an unknown kind or language, an id that
// is not an ask id, a build and a check together or neither, a job on a stream that does not carry it, and a fetch with
// no repository or no full commit.
func DecodeStepAsk(data []byte) (StepAsk, error) {
	var probe struct {
		V *int `json:"v"`
	}
	if err := json.Unmarshal(data, &probe); err != nil {
		return StepAsk{}, fmt.Errorf("delivery: an ask is not JSON: %w", err)
	}
	if probe.V == nil || *probe.V != StepAskVersion {
		return StepAsk{}, fmt.Errorf("%w: an ask of version %v, this reader reads %d", ErrUnknownVersion, probe.V, StepAskVersion)
	}
	var a StepAsk
	if err := json.Unmarshal(data, &a); err != nil {
		return StepAsk{}, fmt.Errorf("delivery: an ask does not fit its shape: %w", err)
	}
	if err := a.check(); err != nil {
		return StepAsk{}, err
	}
	return a, nil
}

// BuildAnswer is a build ask's step result: each artifact's digest and, for a pushed one, its reference.
type BuildAnswer struct {
	Artifacts []AskBuilt     `json:"artifacts"`
	Toolchain *ToolchainUsed `json:"toolchain,omitempty"`
}

// AskBuilt is one artifact a build ask built.
type AskBuilt struct {
	Artifact  string `json:"artifact"`
	Digest    string `json:"digest"`
	Reference string `json:"reference,omitempty"`
}

// CheckAnswer is a check ask's step result, each part the build module's own tool's answer whole: the fetch's, the
// digest's (absent when nothing was digested), the kept verdicts taken, and one test result per test step run, in the
// order run. The checker judges and keeps from it as it did from the tools' answers.
type CheckAnswer struct {
	Fetch  json.RawMessage   `json:"fetch"`
	Digest json.RawMessage   `json:"digest,omitempty"`
	Kept   []KeptTaken       `json:"kept,omitempty"`
	Tests  []json.RawMessage `json:"tests,omitempty"`
}

// KeptTaken is a package whose kept verdict the check took instead of testing it.
type KeptTaken struct {
	Package string `json:"package"`
	Digest  string `json:"digest"`
	Tests   int    `json:"tests"`
}

// AskStepKey is the key, in the build module's StepsBucket, of the step that runs an ask on node: `<node>.<ask id>`
// (ADR 0525 §6). The node is the one that pulled the ask, which the asker learns from the key.
func AskStepKey(node, askID string) (string, error) {
	if err := checkAskID(askID); err != nil {
		return "", err
	}
	return StepKey(node, askID)
}

// AskStepWatch is the pattern an asker watches its ask's step with, the node a wildcard: `*.<ask id>`.
func AskStepWatch(askID string) (string, error) {
	if err := checkAskID(askID); err != nil {
		return "", err
	}
	return "*." + askID, nil
}

// ParseAskStepKey reads the node and the ask id from a step key of an ask; it refuses a key that is not `<node>.<ask
// id>`, such as a have key `<node>.<module>` or a step key a direct tool call wrote under another id form.
func ParseAskStepKey(key string) (node, askID string, err error) {
	node, askID, err = ParseStepKey(key)
	if err != nil {
		return "", "", err
	}
	if err := checkAskID(askID); err != nil {
		return "", "", fmt.Errorf("delivery: %q is not an ask's step key: %w", key, err)
	}
	return node, askID, nil
}

// PauseKey is the key, in a build module's StepsBucket, that keeps whether the module on node takes asks:
// `paused.<node>` (issue 1887's design limit 2: every holder pulls from one shared worker, so a node's pause is its holder
// not fetching, kept here so a restart keeps it). A pause key is never an ask's step key: its second part is a node.
func PauseKey(node string) (string, error) {
	if err := checkName("node", node); err != nil {
		return "", err
	}
	return "paused." + node, nil
}

// Pause is the value of a pause key: whether the node's module takes no asks, who said so and when.
type Pause struct {
	V      int       `json:"v"`
	Paused bool      `json:"paused"`
	By     string    `json:"by,omitempty"`
	At     time.Time `json:"at"`
}

// EncodePause is p as JSON at Version.
func EncodePause(p Pause) ([]byte, error) {
	p.V = Version
	p.At = p.At.UTC()
	return json.Marshal(p)
}

// DecodePause reads a pause value; it refuses an unknown version (ErrUnknownVersion).
func DecodePause(data []byte) (Pause, error) {
	var p Pause
	if err := decode(data, &p); err != nil {
		return Pause{}, err
	}
	return p, nil
}