package build

import (
	"context"
	"errors"
	"fmt"
	"slices"
	"sort"
	"strings"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/delivery"
	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
)

// ErrConflict is what a Store answers when a Create finds the key or an Update finds another revision than the one given.
var ErrConflict = errors.New("the key exists or changed")

// Store is the builder's bucket (builds): create and compare-and-set, each answering the key's new revision. Only the
// builder's credential writes it (ADR 0429 clause 5).
type Store interface {
	Get(ctx context.Context, key string) (value []byte, revision uint64, found bool, err error)
	Create(ctx context.Context, key string, value []byte) (uint64, error)
	Update(ctx context.Context, key string, value []byte, revision uint64) (uint64, error)
	// Keys are every key of the bucket.
	Keys(ctx context.Context) ([]string, error)
}

// Claimer claims fingerprints for the builder instance By (ADR 0429 clause 5: a builder claims a fingerprint by creating
// its key and moves it by compare-and-set).
type Claimer struct {
	Store Store
	By    string
}

// Claim is a build the builder holds: its key, the revision the next write must be made at and the value last written.
type Claim struct {
	Key   string
	Rev   uint64
	Build delivery.BuilderBuild
	// Gone are the references of a done key the artifact store no longer holds, for which it was claimed again
	// (ClaimOptions.Stored; issue 1937): said in the log and the key's step.
	Gone []string
	// Unasked is why the store could not be asked about a done key taken as it stands to publish: said in the log.
	Unasked error
}

// ClaimOptions say what the builder knows about the moment of a claim.
type ClaimOptions struct {
	// TakeOver takes a key found building whoever holds it: the builder has just started and looks at the key for the first
	// time, and a build left building by a builder that is gone, on this node or another, is nobody's (ADR 0478 clause 6).
	TakeOver bool
	// ImageBuilder says whether a node runs a healthy image build module now: a key failed for NoImageBuilderPrefix is taken
	// again only then. Nil means none does.
	ImageBuilder func() bool
	// Trunk is whether the trunk's record names this fingerprint. A done key whose image or package has no reference was
	// built as a candidate's, which never pushes or publishes (ADR 0487 clause 12, ADR 0498 clauses 5 and 6); on the trunk it
	// is taken again to publish them, an image only when an image builder runs (ImageBuilder).
	Trunk bool
	// Published says whether a package version `<name>@<version>` is published: one of the builder's done keys names it as
	// a package's reference. A key queued waiting for a version (BuilderBuild.Waits) is taken only once it is (ADR 0500
	// clause 6). Nil means none is.
	Published func(ref string) bool
	// Stored answers which of the references given the artifact store no longer holds (the controller's verb held,
	// mesh-sdk delivery.HeldVerb; novox/hq issue 1937). A done key of the trunk's fingerprint is asked before it is left
	// done: the store's nightly collector deletes a blob nothing holds, and a key the controller never took in holds
	// nothing, so a key whose blob is gone is claimed building as a new revision and built again. Nil asks nothing.
	Stored func(ctx context.Context, references []string) (gone []string, err error)
}

// StoredReferences are the references of a done build's bundles and archives that name a blob in the artifact store
// (`artifact-store://<module>/<artifact>/blobs/<digest>`): what the store's collector can delete. An image or an upstream
// copy is a manifest, which the collector keeps, and a package lives in the package registry.
func StoredReferences(b delivery.BuilderBuild) []string {
	var out []string
	for _, a := range b.Artifacts {
		if strings.HasPrefix(a.Reference, "artifact-store://") && strings.Contains(a.Reference, "/blobs/") &&
			!slices.Contains(out, a.Reference) {
			out = append(out, a.Reference)
		}
	}
	return out
}

// GoneStep is the step a key claimed again for gone blobs says (issue 1937).
func GoneStep(gone []string) string {
	return "claimed again: the artifact store no longer holds " + strings.Join(gone, ", ")
}

// Unpublished is whether a done build holds an image built without a push or a package built without a publish: it has
// no reference (a candidate's, ADR 0487 clause 12, ADR 0498 clauses 5 and 6).
func Unpublished(b delivery.BuilderBuild) bool { return len(UnpublishedModules(b)) > 0 }

// UnpublishedModules are the build modules that publish what a done build holds unpublished: the image build module for
// an image, the Node build module for a package; sorted, none when it holds nothing unpublished.
func UnpublishedModules(b delivery.BuilderBuild) []string {
	if b.State != delivery.BuildDone {
		return nil
	}
	var image, pkg bool
	for _, a := range b.Artifacts {
		image = image || (a.Kind == catalogue.ArtifactImage && a.Reference == "")
		pkg = pkg || (a.Kind == catalogue.ArtifactPackage && a.Reference == "")
	}
	var out []string
	if image {
		out = append(out, ImageBuildModule)
	}
	if pkg {
		out = append(out, buildrun.NodeBuildModule)
	}
	sort.Strings(out)
	return out
}

// publishable are the build modules of UnpublishedModules that can publish now: the image build module only while a node
// runs it (imageBuilder).
func publishable(b delivery.BuilderBuild, imageBuilder func() bool) []string {
	var out []string
	for _, bm := range UnpublishedModules(b) {
		if bm != ImageBuildModule || (imageBuilder != nil && imageBuilder()) {
			out = append(out, bm)
		}
	}
	return out
}

// Unreferenced is whether a done build holds a bundle, an archive or an upstream copy that names no reference: a key done
// before R4e, whose artifacts stayed on their build nodes (ADR 0498 clause 8). An artifact of no kind (a key written before
// kinds) is one too. Claim takes such a key again, once: its new revision names them.
func Unreferenced(b delivery.BuilderBuild) bool {
	if b.State != delivery.BuildDone {
		return false
	}
	for _, a := range b.Artifacts {
		if a.Reference == "" && (a.Kind == "" || stored(a.Kind)) {
			return true
		}
	}
	return false
}

// Claim takes the build of module at fingerprint, or answers nil when it is not this builder's to build now:
//   - no key: it is created building, by this builder; a create that finds the key made meanwhile gets nothing;
//   - a done key is not taken again (the same source is never built twice), except one whose bundle, archive or upstream
//     copy names no reference (Unreferenced, a key done before R4e: ADR 0498 clause 8), which is claimed building as a new
//     revision and built whole, and one whose image or package was built unpublished as a candidate's once the trunk
//     names it (ClaimOptions.Trunk): that is taken as it stands, with the done value, and its builder writes the new
//     revision when the publishing build ends (ADR 0498 clause 6). From R4e one node builds each fingerprint (ADR 0478
//     clause 4), so a key built on one node is never built again for a second;
//   - a done key of the trunk's fingerprint whose bundle or archive blob the artifact store no longer holds
//     (ClaimOptions.Stored, issue 1937) is claimed building as a new revision and built whole, its step saying which;
//   - a failed key is taken again as a new revision of the same key (ADR 0429 clause 18), except one failed for a kind no
//     builder builds, for an upstream pinned by no digest or a package version taken (delivery.FailedUntilChanged: ADR 0478
//     clause 2, ADR 0498 clauses 4 and 5) or for digests that differ (buildrun.DigestsDifferPrefix, clause 4),
//     which wait for another fingerprint, and one failed for want of an image builder (NoImageBuilderPrefix), which waits for
//     another fingerprint or a node that runs the image build module (ClaimOptions.ImageBuilder);
//   - a key queued waiting for a package version (Waits) is claimed building as a new revision once that version is
//     published (ClaimOptions.Published, ADR 0500 clause 6), and not before;
//   - a key left queued or building by this builder is taken as it stands (ADR 0478 clause 5: a stopped builder takes its
//     own again when it starts), and so is one left by another builder when ClaimOptions.TakeOver (clause 6).
func (c Claimer) Claim(ctx context.Context, module, fingerprint, manifest string, opt ClaimOptions) (*Claim, error) {
	key, err := delivery.BuilderBuildKey(module, fingerprint)
	if err != nil {
		return nil, err
	}
	building := delivery.BuilderBuild{State: delivery.BuildBuilding, By: c.By, Step: "claimed", Manifest: manifest}
	value, rev, found, err := c.Store.Get(ctx, key)
	if err != nil {
		return nil, fmt.Errorf("%s: %w", key, err)
	}
	if !found {
		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Create(ctx, key, data) })
	}
	cur, err := delivery.DecodeBuilderBuild(value)
	if err != nil {
		return nil, fmt.Errorf("%s holds what is not a build: %w", key, err)
	}
	switch {
	case cur.State == delivery.BuildDone:
		if Unreferenced(cur) {
			return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
		}
		if opt.Trunk && opt.Stored != nil {
			if refs := StoredReferences(cur); len(refs) > 0 {
				gone, err := opt.Stored(ctx, refs)
				if err != nil {
					err = fmt.Errorf("%s: whether the artifact store still holds %s cannot be asked, so the key is "+
						"left done (the controller's take-in refuses it if one is gone): %w", key, strings.Join(refs, ", "), err)
					if len(publishable(cur, opt.ImageBuilder)) > 0 {
						return &Claim{Key: key, Rev: rev, Build: cur, Unasked: err}, nil
					}
					return nil, err
				}
				if len(gone) > 0 {
					again := building
					again.Step = GoneStep(gone)
					cl, err := c.write(ctx, key, again, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
					if cl != nil {
						cl.Gone = gone
					}
					return cl, err
				}
			}
		}
		if opt.Trunk && len(publishable(cur, opt.ImageBuilder)) > 0 {
			return &Claim{Key: key, Rev: rev, Build: cur}, nil
		}
		return nil, nil
	case cur.State == delivery.BuildFailed && (delivery.FailedUntilChanged(cur.Error) || strings.HasPrefix(cur.Error, buildrun.DigestsDifferPrefix)):
		return nil, nil
	case cur.State == delivery.BuildFailed && strings.HasPrefix(cur.Error, NoImageBuilderPrefix) && (opt.ImageBuilder == nil || !opt.ImageBuilder()):
		return nil, nil
	case cur.State == delivery.BuildFailed:
		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
	case cur.State == delivery.BuildQueued && cur.Waits != "":
		if opt.Published == nil || !opt.Published(cur.Waits) {
			return nil, nil // the package it waits for is not published yet
		}
		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
	case cur.By == c.By || opt.TakeOver:
		return &Claim{Key: key, Rev: rev, Build: cur}, nil
	}
	return nil, nil
}

func (c Claimer) write(_ context.Context, key string, b delivery.BuilderBuild, put func([]byte) (uint64, error)) (*Claim, error) {
	data, err := delivery.EncodeBuilderBuild(b)
	if err != nil {
		return nil, err
	}
	rev, err := put(data)
	if errors.Is(err, ErrConflict) {
		return nil, nil // another builder made it first
	}
	if err != nil {
		return nil, fmt.Errorf("%s: %w", key, err)
	}
	b.V = delivery.Version
	return &Claim{Key: key, Rev: rev, Build: b}, nil
}

// Finish moves the claimed key to b by compare-and-set at the claim's revision, and writes nothing when b is the value
// the key holds. A key that changed meanwhile is ErrConflict: the claim is no longer this builder's.
func (c Claimer) Finish(ctx context.Context, cl *Claim, b delivery.BuilderBuild) error {
	b.V = delivery.Version
	if delivery.SameBuilderBuild(cl.Build, b) {
		return nil
	}
	data, err := delivery.EncodeBuilderBuild(b)
	if err != nil {
		return err
	}
	rev, err := c.Store.Update(ctx, cl.Key, data, cl.Rev)
	if err != nil {
		return fmt.Errorf("%s: %w", cl.Key, err)
	}
	cl.Rev, cl.Build = rev, b
	return nil
}