// Package versions is the builder's state `versions` (novox/hq design 51 *The versions*, ADR 0606): one key per name,
// tag and version, written only by the builder under compare-and-set, read by others only through the builder's tool
// builder_versions or its events (ADR 0596 §2). It holds what each version is (its fingerprint, commit, source revision
// and digest) and where it stands: numbered, published, refused with its reason, or removed with its time, reason and the
// event that removed it.
//
// The state is declared in the builder's old `state` section (ADR 0619: the builder is one of the foundation's nine
// parts), history one; its cap is 64 MiB, the most the template state allows (ADR 0595 §3), and past 80 % of it the
// builder writes a finding, cleared below it (Fill).
package versions

import (
	"encoding/json"
	"errors"
	"fmt"
	"sort"
	"strconv"
	"strings"
	"time"
)

// State is the builder state's name; Bucket the bucket the bus keeps it in.
const (
	State  = "versions"
	Bucket = "mesh-delivery-builder_versions"
	// Cap is the bucket's cap in bytes (64 MiB); FullPercent the share of it past which the builder writes its finding.
	Cap         = 64 << 20
	FullPercent = 80
	// DefaultSeries is the series of a name whose manifest declares none (design 32).
	DefaultSeries = "0.1"
)

// The states a version is in.
const (
	Numbered  = "numbered"
	Published = "published"
	Refused   = "refused"
	Removed   = "removed"
	// Kept is a tagged version its seat kept whole on remove: another tag names its digest, so the store cannot remove the
	// tag alone (review round 2; the registry seats' `kept`). Its Reason is the seat's (shared-digest), KeptWith the
	// other tags; it is asked no more.
	Kept = "kept"
)

// The kinds the builder numbers: a package per source revision, the rest per fingerprint (design 51).
const (
	KindPackage = "package"
	KindImage   = "image"
	KindBundle  = "bundle"
	KindArchive = "archive"
)

// Entry is one key of the state: a version of a name, tagged or not.
type Entry struct {
	Name    string `json:"name"`
	Kind    string `json:"kind"`
	Series  string `json:"series"`
	Version string `json:"version"`
	// Tag is the cleaned tag of a tagged version (`feat-x`); empty for a trunk version.
	Tag         string `json:"tag,omitempty"`
	Module      string `json:"module"`
	Fingerprint string `json:"fingerprint"`
	Commit      string `json:"commit,omitempty"`
	// Revision is the source revision a package's version is numbered for (one version per revision, design 51).
	Revision string `json:"revision,omitempty"`
	// Digest is the digest the build recorded (an image's manifest, a blob's, Go's h1: hash).
	Digest string `json:"digest,omitempty"`
	// Seat is the registry seat it is published to.
	Seat  string    `json:"seat,omitempty"`
	State string    `json:"state"`
	At    time.Time `json:"at"`
	// Reason is why it was refused or removed: the holder's reason, a branch's end, retention, the sweep.
	Reason string `json:"reason,omitempty"`
	// Repository is a tagged version's repository: its branch's end removes it (Untagged).
	Repository string `json:"repository,omitempty"`
	// KeptWith are the other tags naming its digest, when its seat kept it (Kept).
	KeptWith []string `json:"kept_with,omitempty"`
	// RemovedBy is the id of the event that removed it.
	RemovedBy string `json:"removed_by,omitempty"`
	// RefusedDigest is the digest the holder refused: one other than Digest means the seat was offered other bytes under
	// this number, which builder_publish_again refuses to publish again (design 51 *Tools of the builder*).
	RefusedDigest string `json:"refused_digest,omitempty"`
	// Merge is the forge bridge's sequence of the merge that numbered it, for merge order.
	Merge uint64 `json:"merge,omitempty"`
}

// Valid says what is wrong with an entry, or nil.
func (e Entry) Valid() error {
	switch {
	case strings.TrimSpace(e.Name) == "":
		return errors.New("a version names no name")
	case e.Version == "":
		return fmt.Errorf("%s: a version with no version", e.Name)
	}
	switch e.State {
	case Numbered, Published, Refused, Removed, Kept:
	default:
		return fmt.Errorf("%s@%s: unknown state %q", e.Name, e.Version, e.State)
	}
	switch e.Kind {
	case KindPackage, KindImage, KindBundle, KindArchive:
	default:
		return fmt.Errorf("%s@%s: unknown kind %q", e.Name, e.Version, e.Kind)
	}
	if _, _, err := SplitSeries(e.Series); err != nil {
		return fmt.Errorf("%s@%s: %w", e.Name, e.Version, err)
	}
	return nil
}

// Encode and Decode are the value's bytes.
func Encode(e Entry) ([]byte, error) {
	if err := e.Valid(); err != nil {
		return nil, err
	}
	return json.Marshal(e)
}

func Decode(raw []byte) (Entry, error) {
	var e Entry
	if err := json.Unmarshal(raw, &e); err != nil {
		return Entry{}, err
	}
	return e, e.Valid()
}

// Key is the state's key of a name's version: two tokens, the name and the version each escaped (EscapeToken), so a
// name's versions are the keys under NameFilter and no name's keys fall under another's.
func Key(name, version string) string { return EscapeToken(name) + "." + EscapeToken(version) }

// NameFilter is the key filter of every version of name.
func NameFilter(name string) string { return EscapeToken(name) + ".*" }

// EscapeToken makes s one token of a bus key: letters, digits, '-', '_' and '/' stay; '=' and every other byte become
// '=' and two hex digits ('.' is "=2E", '@' "=40"). Two different strings never escape alike.
func EscapeToken(s string) string {
	var b strings.Builder
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z', c >= '0' && c <= '9', c == '-', c == '_', c == '/':
			b.WriteByte(c)
		default:
			fmt.Fprintf(&b, "=%02X", c)
		}
	}
	return b.String()
}

// SplitSeries reads a series `<major>.<minor>`.
func SplitSeries(series string) (major, minor int, err error) {
	a, b, ok := strings.Cut(series, ".")
	if !ok {
		return 0, 0, fmt.Errorf("series %q is not <major>.<minor>", series)
	}
	if major, err = strconv.Atoi(a); err != nil || major < 0 {
		return 0, 0, fmt.Errorf("series %q is not <major>.<minor>", series)
	}
	if minor, err = strconv.Atoi(b); err != nil || minor < 0 {
		return 0, 0, fmt.Errorf("series %q is not <major>.<minor>", series)
	}
	return major, minor, nil
}

// Patch is the count of a trunk version of series (`0.1.14` → 14), read leniently: a leading 'v' and a path prefix
// (`go/v0.1.13`) are dropped; ok is false for a version of another series or a tagged one.
func Patch(series, version string) (int, bool) {
	if i := strings.LastIndex(version, "/"); i >= 0 {
		version = version[i+1:]
	}
	version = strings.TrimPrefix(version, "v")
	if strings.ContainsAny(version, "-+") {
		return 0, false
	}
	rest, ok := strings.CutPrefix(version, series+".")
	if !ok {
		return 0, false
	}
	n, err := strconv.Atoi(rest)
	if err != nil || n < 0 {
		return 0, false
	}
	return n, true
}

// Floor is what the three sources answered for a name (design 51 *The floor*, ADR 0606 §3): the seat's versions, the
// package's git tags (the forge bridge's bridge_tags) and the pseudo-versions consumers require (the indexer's
// indexer_requirements). A source not answered is listed in Silent.
type Floor struct {
	Seat         []string `json:"seat,omitempty"`
	Tags         []string `json:"tags,omitempty"`
	Requirements []string `json:"requirements,omitempty"`
	// Silent names the sources that did not answer: "seat", "bridge_tags", "indexer_requirements".
	Silent []string `json:"silent,omitempty"`
}

// The floor's sources, as Floor.Silent names them.
const (
	SourceSeat         = "seat"
	SourceTags         = "bridge_tags"
	SourceRequirements = "indexer_requirements"
)

// Known is whether every source answered.
func (f Floor) Known() bool { return len(f.Silent) == 0 }

// Highest is the highest count of series the floor's three sources name, -1 when none names one. A pseudo-version
// (`v0.1.14-0.2026…-abc`) counts as the version below it was cut from, so its base (`0.1.13`) counts: Go orders it
// before `0.1.14`.
func (f Floor) Highest(series string) int {
	high := -1
	for _, list := range [][]string{f.Seat, f.Tags, f.Requirements} {
		for _, v := range list {
			n, ok := Patch(series, v)
			if !ok {
				n, ok = pseudoBase(series, v)
			}
			if ok && n > high {
				high = n
			}
		}
	}
	return high
}

// pseudoBase is the count a Go pseudo-version stands on: `v0.1.14-0.<time>-<hash>` is cut after `v0.1.13`.
func pseudoBase(series, version string) (int, bool) {
	version = strings.TrimPrefix(version, "v")
	base, rest, ok := strings.Cut(version, "-")
	if !ok || !strings.HasPrefix(rest, "0.") || strings.Count(rest, "-") != 1 {
		return 0, false
	}
	n, ok := Patch(series, base)
	if !ok || n == 0 {
		return 0, false
	}
	return n - 1, true
}

// Next is the next trunk version of name in series: one above the highest of the trunk versions entries hold and the
// floor (design 51: a name with none starts at `<series>.0`).
func Next(entries []Entry, series string, floor Floor) string {
	high := floor.Highest(series)
	for _, e := range entries {
		if e.Tag != "" || e.Series != series {
			continue
		}
		if n, ok := Patch(series, e.Version); ok && n > high {
			high = n
		}
	}
	return fmt.Sprintf("%s.%d", series, high+1)
}

// Decision is what the builder does with a trunk build at its claim.
type Decision struct {
	// Version is the version the build is published under; empty when it is built unnumbered (Unnumbered) or waits (Wait).
	Version string
	// Keep is true when the version is one entries already hold for this fingerprint or source revision.
	Keep bool
	// Publish is false only for a package's revision held published: it publishes nothing (design 51).
	Publish bool
	// Unnumbered: an image, bundle or archive whose floor is not known is built and published by its digest, numbered
	// once the floor answers (ADR 0617 §1).
	Unnumbered bool
	// Wait: a package whose floor is not known waits for it (a package is published only under its version).
	Wait bool
	// Why is said in the build log.
	Why string
}

// Decide numbers a trunk build of kind for name in series at fingerprint and source revision, from what entries hold of
// the name and what the floor answered (design 51 *The versions*, ADR 0606, ADR 0617 §1):
//   - a package is numbered per source revision: a revision held published keeps its version and publishes nothing; a
//     revision numbered or refused but never stored is published again under the same version;
//   - an image, bundle or archive is numbered per fingerprint: a fingerprint already numbered keeps its number;
//   - otherwise the next version, when the floor is known; else an image, bundle or archive is built unnumbered and a
//     package waits.
func Decide(entries []Entry, kind, series, fingerprint, revision string, floor Floor) Decision {
	for _, e := range latestFirst(entries) {
		if e.Tag != "" || e.State == Removed {
			continue
		}
		switch {
		case kind == KindPackage && revision != "" && e.Revision == revision:
			if e.State == Published {
				return Decision{Version: e.Version, Keep: true, Why: fmt.Sprintf("version %s kept: source revision %s is published under it, and a package's content is its source", e.Version, revision)}
			}
			return Decision{Version: e.Version, Keep: true, Publish: true, Why: fmt.Sprintf("version %s kept: source revision %s was numbered %s but never stored, so it is published under it", e.Version, revision, e.State)}
		case kind != KindPackage && e.Fingerprint == fingerprint:
			return Decision{Version: e.Version, Keep: true, Publish: e.State != Published, Why: fmt.Sprintf("version %s kept: fingerprint %s is numbered under it", e.Version, fingerprint)}
		}
	}
	if !floor.Known() {
		silent := strings.Join(floor.Silent, ", ")
		if kind == KindPackage {
			return Decision{Wait: true, Why: "the package waits for its floor: " + silent + " did not answer"}
		}
		return Decision{Unnumbered: true, Publish: true, Why: "built unnumbered and published by its digest: the floor is not known (" + silent + " did not answer); numbered once it answers"}
	}
	v := Next(entries, series, floor)
	return Decision{Version: v, Publish: true, Why: "numbered " + v}
}

// CleanTag makes a branch or tag name a semver prerelease identifier: lower case, every run of characters other than
// letters and digits one '-', none at either end; "tag" when nothing is left.
func CleanTag(tag string) string {
	var b strings.Builder
	dash := false
	for _, r := range strings.ToLower(tag) {
		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') {
			b.WriteRune(r)
			dash = false
			continue
		}
		if !dash && b.Len() > 0 {
			b.WriteByte('-')
			dash = true
		}
	}
	out := strings.TrimSuffix(b.String(), "-")
	if out == "" {
		return "tag"
	}
	return out
}

// Tagged is the next tagged version of name for tag: below the next trunk version, never the latest
// (`0.1.15-feat-x.2`, design 51 *Tagged versions*); a package new in a group is numbered from its floor
// (`0.1.0-feat-x.1`).
func Tagged(entries []Entry, series, tag string, floor Floor) string {
	base := Next(entries, series, floor)
	tag = CleanTag(tag)
	n := 0
	prefix := base + "-" + tag + "."
	for _, e := range entries {
		if rest, ok := strings.CutPrefix(e.Version, prefix); ok {
			if k, err := strconv.Atoi(rest); err == nil && k > n {
				n = k
			}
		}
	}
	return fmt.Sprintf("%s%d", prefix, n+1)
}

// Fill is whether a bucket holding bytes of cap is past its finding's mark.
func Fill(bytes, capacity uint64) (share float64, full bool) {
	if capacity == 0 {
		return 0, false
	}
	share = float64(bytes) / float64(capacity)
	return share, bytes*100 >= capacity*FullPercent
}

// InOrder sorts a name's entries by version, trunk versions by count and tagged ones after the trunk version they stand
// below: the order builder_versions answers.
func InOrder(entries []Entry) []Entry {
	out := append([]Entry(nil), entries...)
	sort.SliceStable(out, func(i, j int) bool {
		ki, kj := orderKey(out[i]), orderKey(out[j])
		if ki.n != kj.n {
			return ki.n < kj.n
		}
		if ki.tagged != kj.tagged {
			return ki.tagged // a tagged version stands below the trunk version of its count
		}
		return out[i].Version < out[j].Version
	})
	return out
}

type order struct {
	n      int
	tagged bool
}

func orderKey(e Entry) order {
	v := e.Version
	tagged := false
	if i := strings.IndexByte(v, '-'); i >= 0 {
		v, tagged = v[:i], true
	}
	n, ok := Patch(e.Series, v)
	if !ok {
		n = -1
	}
	return order{n: n, tagged: tagged}
}

func latestFirst(entries []Entry) []Entry {
	out := InOrder(entries)
	for i, j := 0, len(out)-1; i < j; i, j = i+1, j-1 {
		out[i], out[j] = out[j], out[i]
	}
	return out
}