package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"strings"
	"time"

	"github.com/novox/mesh-controller/internal/catalogue"
	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// following acts on what the catalogue announces.
//
// **It holds the stores, not a copy of the decision.** What to do about an upgrade is read when
// one arrives, so changing it takes effect on the next upgrade rather than on the next restart of
// the control plane.
type following struct{ open *stores }

// Upgraded sends the machines running a module the version the catalogue now considers current —
// or records that they are behind, which is the default and needs no record.
//
// **Recording is not a second code path.** A machine that is not running what the mesh would send
// it is already something the mesh notices and reports; that is what `status` and `push --behind`
// are built on. So "record it" is the absence of an action, and the only thing this has to decide
// is whether to act.
func (f following) Upgraded(ctx context.Context, u link.Upgraded) error {
	inv := f.open.inventory

	// The store read first, and an outage there said as one, so the announcement is held and asked
	// again (novox/hq issue 083). Only here: a push that fails further down is not asked again.
	decision, err := inv.UpgradeOf(ctx, u.Module)
	if err != nil {
		return notNow(err)
	}
	on, err := inv.Running(ctx, u.Module)
	if err != nil {
		return notNow(err)
	}
	if len(on) == 0 {
		fmt.Printf("%s moved to %s; no machine runs it\n", u.Module, shortCommit(u.Commit))
		return nil
	}
	if !decision.RollOut {
		// Named rather than counted, and said even though nothing happens: an upgrade that was
		// deliberately not rolled out and an upgrade that was never noticed look identical in a
		// log that only speaks when it acts.
		fmt.Printf("%s moved to %s; %s %s behind it, and this mesh records upgrades rather than "+
			"rolling them out — `push --behind` when you want them\n",
			u.Module, shortCommit(u.Commit), readableList(on), isAre(len(on)))
		return nil
	}

	if decision.Together {
		fmt.Printf("%s moved to %s; sending %s together\n",
			u.Module, shortCommit(u.Commit), readableList(on))
		return sendTo(ctx, f.open, on)
	}
	// One at a time, and stopping at the first that fails.
	//
	// **Stopping is the point.** The machines are done one after another precisely so that a
	// version that breaks the first one does not reach the rest; carrying on past a failure would
	// make this the same as sending them together, only slower.
	fmt.Printf("%s moved to %s; sending %s one at a time\n",
		u.Module, shortCommit(u.Commit), readableList(on))
	for _, node := range on {
		if err := sendTo(ctx, f.open, []string{node}); err != nil {
			return fmt.Errorf("%s did not take %s, so the machines after it were left alone: %w",
				node, u.Module, err)
		}
	}
	return nil
}

// readableList names machines the way a sentence does, because this is read by a person deciding
// whether an upgrade went where they expected.
func readableList(names []string) string {
	switch len(names) {
	case 0:
		return "nothing"
	case 1:
		return names[0]
	case 2:
		return names[0] + " and " + names[1]
	}
	return strings.Join(names[:len(names)-1], ", ") + " and " + names[len(names)-1]
}

func shortCommit(commit string) string {
	if len(commit) > 8 {
		return commit[:8]
	}
	return commit
}

func isAre(n int) string {
	if n == 1 {
		return "is"
	}
	return "are"
}

// upgradeCommand says what should happen when a module's current version moves.
func upgradeCommand(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("upgrade", flag.ContinueOnError)
	together := set.Bool("together", false,
		"send every machine running it at once, instead of one after another")
	positionals, err := parseAround(set, args)
	if err != nil {
		return err
	}
	if len(positionals) == 0 {
		return errors.New("upgrade <module> [roll-out|record] [--together]")
	}
	module := positionals[0]

	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory

	if len(positionals) == 1 {
		decision, err := inv.UpgradeOf(ctx, module)
		if err != nil {
			return err
		}
		fmt.Println(sayUpgrade(module, decision))
		return nil
	}

	var decision inventory.Upgrade
	switch positionals[1] {
	case "roll-out":
		decision = inventory.Upgrade{RollOut: true, Together: *together}
	case "record":
		if *together {
			// Refused rather than ignored: --together only means anything for a roll-out, and
			// accepting it here would store a preference that never applies and looks like it does.
			return errors.New("`--together` says how to roll out, so it cannot be given with " +
				"`record`, which is the choice not to")
		}
		decision = inventory.Upgrade{}
	default:
		return fmt.Errorf("upgrade <module> roll-out|record — not %q", positionals[1])
	}
	if err := inv.SetUpgradeOf(ctx, module, decision); err != nil {
		return err
	}
	fmt.Println(sayUpgrade(module, decision))
	return nil
}

func sayUpgrade(module string, u inventory.Upgrade) string {
	if !u.RollOut {
		return fmt.Sprintf("when %s moves, the mesh records it and the machines running it are "+
			"reported as behind", module)
	}
	if u.Together {
		return fmt.Sprintf("when %s moves, every machine running it is sent the new version "+
			"together", module)
	}
	return fmt.Sprintf("when %s moves, the machines running it are sent the new version one at "+
		"a time, stopping at the first that fails", module)
}

// Announceable is every build this mesh recorded, in the shape the builder announces one.
//
// **The catalogue asks for this when it starts, and the answer is the graph's foundation**
// (novox/hq 04-ISSUES/050). A durable queue keeps what arrived after it existed, so a running
// catalogue misses nothing — but the modules built before it first ran were announced to a queue
// that did not exist, and on a fresh mesh those are always the same three: the shared base, the
// store the catalogue runs on, and the catalogue itself.
//
// **Announced as fetchable, recorded as what it is** (novox/hq 04-ISSUES/102). A build is
// recorded by digest and path; the catalogue hears the builder's own announcements, which name
// the store's address, so a replay composes the address back in — the store's address as the
// network reaches it NOW, which is the whole point of not having recorded the old one. With no
// store on the network yet, the recorded form goes as it is.
func (f following) Announceable(ctx context.Context) ([]link.Announcement, error) {
	builds, err := f.open.inventory.Announceable(ctx)
	if err != nil {
		return nil, err
	}
	address, err := whereTheStoreIs(ctx, f.open.inventory, "")
	if err != nil {
		return nil, err
	}
	out := make([]link.Announcement, 0, len(builds))
	for _, b := range builds {
		a := link.Announcement{
			Module: b.Module, Commit: b.Commit, Repository: b.Repository,
			Path: b.Path, Ref: b.Ref, Against: b.Against,
		}
		if len(b.Manifest) > 0 {
			a.Manifest = b.Manifest
			if address != "" {
				a.Manifest = routedManifest(b.Manifest, b.Made, address)
			}
		}
		for _, made := range routedArtifacts(b.Made, address) {
			a.Made = append(a.Made, link.MadeArtifact{
				Name: made.Name, Kind: made.Kind, Reference: made.Reference,
			})
		}
		out = append(out, a)
	}
	return out, nil
}

// notNow marks a store that could not be read right now, so the announcement is held rather than
// lost; anything else is returned as it was.
func notNow(err error) error {
	if inventory.Unreachable(err) {
		return fmt.Errorf("%w: %w", link.ErrTryAgain, err)
	}
	return err
}

// SourceMoved is the forge announcing a merge: every module recorded as built from that
// repository and branch is marked as moved to the merge commit, and built — bases first, so a
// module that stands on another's artifact is built after it and not against the old one
// (novox/hq 04-ISSUES/131). Nothing is pushed here: what a finished build does to the machines
// running the module is the upgrade's decision, taken when the catalogue announces it.
func (f following) SourceMoved(ctx context.Context, m link.SourceMoved) error {
	inv := f.open.inventory
	entries, err := inv.Catalogued(ctx)
	if err != nil {
		return notNow(err)
	}
	read, err := inv.ReadRepositories(ctx)
	if err != nil {
		return notNow(err)
	}

	// Two kinds of module are affected by one merge, and they are affected differently.
	//
	// A module **built from** this repository and branch has moved: the mesh records the new commit
	// as what its source now has, and only what the merge actually changed is rebuilt. A module that
	// only **packages source from** it has not moved — its own source is somewhere else, at the
	// commit it already records — so it is rebuilt and its record left alone. Writing this commit as
	// its source would make it permanently behind a repository its manifest does not come from.
	var from, packaging []inventory.Entry
	already := 0
	for _, e := range entries {
		switch {
		case sourceIs(e.Source, m):
			if e.Source.BuiltFrom == m.Commit {
				already++
				continue
			}
			// **A merge older than the last look at the source is history, not a move.** The forge
			// announces what it finds merged, and an old merge surfacing late would otherwise move
			// the recorded head backwards and rebuild everything built from that repository, once
			// per old merge (2026-09-28).
			if isHistory(m.MergedAt, e.Source.Seen) {
				continue
			}
			from = append(from, e)
		case readsFrom(read[e.Manifest.Module], m):
			packaging = append(packaging, e)
		}
	}
	if len(from) == 0 && len(packaging) == 0 {
		// "Already built from it" and "nothing reads it" are different facts, and reading the first
		// as the second sends somebody looking for a broken trigger when the mesh is up to date.
		if already > 0 {
			fmt.Printf("%s/%s merged into %s (%.8s); %d module(s) the mesh holds are already built "+
				"from it\n", m.Owner, m.Repo, m.Base, m.Commit, already)
			return nil
		}
		fmt.Printf("%s/%s merged into %s (%.8s); nothing the mesh holds reads it\n",
			m.Owner, m.Repo, m.Base, m.Commit)
		return nil
	}
	// The same judgement for the packaging kind, against the newest look at that repository by
	// anything built from it: they keep no record of it themselves, and a replayed old merge should
	// not rebuild them either.
	if isHistory(m.MergedAt, lastLookAt(entries, m)) {
		packaging = nil
	}
	touched := whatTheMergeTouched(from, entries, m)
	for _, e := range touched {
		if err := inv.SourceMoved(ctx, e.Manifest.Module, m.Commit); err != nil {
			return notNow(err)
		}
	}
	moved := append(append([]inventory.Entry{}, touched...), packaging...)
	if len(moved) == 0 {
		fmt.Printf("%s/%s merged into %s (%.8s); it changed nothing any module the mesh holds is "+
			"built from\n", m.Owner, m.Repo, m.Base, m.Commit)
		return nil
	}
	against, err := inv.BuiltAgainst(ctx)
	if err != nil {
		return notNow(err)
	}
	ordered := orderByBases(moved, against)
	names := make([]string, 0, len(ordered))
	for _, e := range ordered {
		names = append(names, e.Manifest.Module)
	}
	fmt.Printf("%s/%s merged into %s (%.8s); building %s\n",
		m.Owner, m.Repo, m.Base, m.Commit, strings.Join(names, ", "))
	if len(packaging) > 0 {
		var also []string
		for _, e := range packaging {
			also = append(also, e.Manifest.Module)
		}
		fmt.Printf("  %s package source from it, so they are rebuilt and their own source record "+
			"is left where it is\n", strings.Join(also, ", "))
	}
	var failed []string
	for _, e := range ordered {
		source := buildSource{Repository: e.Source.Repository, Seat: e.Source.Seat}
		if err := buildOne(ctx, source, e.Source.Path, e.Source.Ref, 20*time.Minute); err != nil {
			fmt.Printf("  %s: %v\n", e.Manifest.Module, err)
			failed = append(failed, e.Manifest.Module)
			// A base that failed is a reason to stop: what stands on it would be built against
			// the old one, and report success (novox/hq 04-ISSUES/131).
			if standsOn(ordered, e.Manifest.Module, against) {
				fmt.Printf("  stopping: %s is a base of what was still to build\n", e.Manifest.Module)
				break
			}
		}
	}
	if len(failed) > 0 {
		fmt.Printf("%d of %d not built: %s\n", len(failed), len(ordered), strings.Join(failed, ", "))
	}
	return nil
}

// sourceIs is whether a recorded source is the repository and branch a merge announced. A source on
// the git seat is recorded as its path on the forge; one elsewhere as the URL it was cloned from.
// An empty recorded ref is the repository's default branch, which is what a merge into the base
// branch of the forge's default means.
func sourceIs(s inventory.Source, m link.SourceMoved) bool {
	if !sameRepository(s.Repository, m) {
		return false
	}
	return s.Ref == "" || s.Ref == m.Base
}

// sameRepository is whether a recorded repository is the one a merge names, in either spelling it
// may have been recorded in: a path on the git seat, or the URL it was cloned from.
func sameRepository(repository string, m link.SourceMoved) bool {
	want := strings.ToLower(m.Owner + "/" + m.Repo)
	repo := strings.ToLower(strings.TrimSuffix(repository, ".git"))
	return repo == want || strings.HasSuffix(repo, "/"+want) ||
		(m.CloneURL != "" && repo == strings.ToLower(strings.TrimSuffix(m.CloneURL, ".git")))
}

// readsFrom is whether a module's build read the repository a merge names: the second repository its
// recipe packages source from. Its ref must be the branch that moved, or unset — the same rule a
// module's own source follows.
func readsFrom(read []inventory.ReadRepository, m link.SourceMoved) bool {
	for _, r := range read {
		if sameRepository(r.Repository, m) && (r.Ref == "" || r.Ref == m.Base) {
			return true
		}
	}
	return false
}

// lastLookAt is the most recent look at this repository by anything built from it.
func lastLookAt(entries []inventory.Entry, m link.SourceMoved) time.Time {
	var newest time.Time
	for _, e := range entries {
		if sameRepository(e.Source.Repository, m) && e.Source.Seen.After(newest) {
			newest = e.Source.Seen
		}
	}
	return newest
}

// whatTheMergeTouched narrows the modules built from a repository to the ones the merge changed.
//
// **A change inside no module's own directory is a change to what they share.** The forge lists the
// files a merge changed; a module is affected when one of them is inside its own directory, when it
// is built from the repository's root — everything there is its source — or when some changed file
// belongs to no module's directory at all, which is how a shared file, a build recipe or a
// dependency at the root rebuilds everything built from that repository.
//
// A change inside *another* module's directory is that module's business and not this one's, even
// when the mesh does not hold that module: `known` is every module this repository is known to hold,
// whatever branch it was registered from. That is also the limit of this — a repository whose shared
// code sits inside a directory the mesh has never seen a module in reads as shared, and everything
// is rebuilt. Rebuilding too much is the safe direction: the fault this whole path exists for is a
// mesh that believes it is current and is not (novox/hq 04-ISSUES/131).
func whatTheMergeTouched(candidates, known []inventory.Entry, m link.SourceMoved) []inventory.Entry {
	// Nothing said about the files, or not all of them said: everything built from it is affected.
	if len(m.Paths) == 0 || m.PathsTruncated {
		return candidates
	}
	var dirs []string
	for _, e := range known {
		if e.Source.Path != "" && sameRepository(e.Source.Repository, m) {
			dirs = append(dirs, e.Source.Path)
		}
	}
	for _, p := range m.Paths {
		if !insideAny(p, dirs) {
			return candidates
		}
	}
	var out []inventory.Entry
	for _, e := range candidates {
		if e.Source.Path == "" || anyInside(m.Paths, e.Source.Path) {
			out = append(out, e)
		}
	}
	return out
}

// inside is whether a changed file is in a directory: that directory itself, or under it.
func inside(path, dir string) bool {
	dir = strings.Trim(dir, "/")
	path = strings.TrimPrefix(path, "/")
	return path == dir || strings.HasPrefix(path, dir+"/")
}

// insideAny is whether a changed file is in any of these directories.
func insideAny(path string, dirs []string) bool {
	for _, dir := range dirs {
		if inside(path, dir) {
			return true
		}
	}
	return false
}

// anyInside is whether any of these changed files is in a directory.
func anyInside(paths []string, dir string) bool {
	for _, p := range paths {
		if inside(p, dir) {
			return true
		}
	}
	return false
}

// orderByBases is the entries with every base before what stands on it: a module whose build stood
// on another's artifact comes after that module. Entries outside the set are not waited for — they
// are not being rebuilt. Stable for what has no order between it.
//
// `against` is what each module's newest build stood on (inventory.BuiltAgainst): the edges are
// derived from builds, not declared, because a recorded manifest no longer carries `build.on`.
func orderByBases(entries []inventory.Entry, against map[string][]string) []inventory.Entry {
	inSet := map[string]bool{}
	for _, e := range entries {
		inSet[e.Manifest.Module] = true
	}
	var out []inventory.Entry
	placed := map[string]bool{}
	var place func(e inventory.Entry, seen map[string]bool)
	place = func(e inventory.Entry, seen map[string]bool) {
		name := e.Manifest.Module
		if placed[name] || seen[name] {
			return
		}
		seen[name] = true
		for _, base := range entries {
			if base.Manifest.Module != name && inSet[base.Manifest.Module] && standsOnModule(e, base.Manifest.Module, against) {
				place(base, seen)
			}
		}
		placed[name] = true
		out = append(out, e)
	}
	for _, e := range entries {
		place(e, map[string]bool{})
	}
	return out
}

// standsOn is whether anything in the set is built on the named module's artifacts.
func standsOn(entries []inventory.Entry, module string, against map[string][]string) bool {
	for _, e := range entries {
		if standsOnModule(e, module, against) {
			return true
		}
	}
	return false
}

// standsOnModule is whether an entry's build stood on the named module: by what its newest build
// recorded it was handed (`artifact-store://<module>/<artifact>@…`, the module's own artifact), or
// — for a module registered from a manifest and not yet built — by the base its manifest names.
func standsOnModule(e inventory.Entry, module string, against map[string][]string) bool {
	if e.Manifest.Module == module {
		return false
	}
	if e.Manifest.Build != nil {
		for _, on := range e.Manifest.Build.On {
			if on.Module == module {
				return true
			}
		}
	}
	prefix := catalogue.ArtifactStoreScheme + module + "/"
	for _, ref := range against[e.Manifest.Module] {
		if strings.HasPrefix(ref, prefix) {
			return true
		}
	}
	return false
}

// isHistory is whether a merge made at mergedAt predates the last time the source was seen. A merge
// with no time on it is taken as news: refusing it would silence a forge that says less.
func isHistory(mergedAt string, seen time.Time) bool {
	if mergedAt == "" || seen.IsZero() {
		return false
	}
	at, err := time.Parse(time.RFC3339, mergedAt)
	if err != nil {
		return false
	}
	return at.Before(seen)
}