package frombus

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

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

// Answer is a node's answer to its group's placement candidates (novox/hq ADR 0559 §4): s.Node composed in shadow with
// s.Placements laid over the trunk's placement (compose.CompositionsShadow, its own sealed values and boxes through r as
// for its own composition), compared with what it runs (delivery.CompareComposed). It applies nothing and writes
// nothing; head and revision are the candidate's, said back in the answer.
//
// The node's own composition is compared only where the node runs one. fps gives the build each module is composed at: what the node runs, and for a module the candidate places that the
// node does not run, the build the trunk holds; a placed module with none is added, with no build of it known. What the
// composition stands in for is judged: a value of a module the group adds (on this node or another: its credential, own
// secrets and boxes are made only once it is placed, ADR 0549 §5) is not yet issued, which is no refusal; any other
// stand-in is a value missing for a module the node runs, a refusal naming it ("node" when it is the node's own).
func Answer(ctx context.Context, r Reader, mesh Mesh, s Scope, fps map[string]string, running []delivery.Composed, head string, revision uint64) delivery.CandidateAnswer {
	a := delivery.CandidateAnswer{Head: head, Revision: revision}
	refuse := func(err error) delivery.CandidateAnswer {
		a.Refused = err.Error()
		a.Verdict = delivery.CandidateRefused
		return a
	}
	trunk, err := r.Placements(ctx)
	if err != nil {
		return refuse(fmt.Errorf("frombus: placement: %w", err))
	}
	if s.Running == nil {
		s.Running = running
	}
	// Every module it cannot compose is named, not the first only (issue 1126): a build it cannot read or take in, and
	// below, a module the composition refuses, each composed as a stub so the rest is composed and compared.
	failed := map[string]string{}
	in, err := input(ctx, r, mesh, s, func(module string, err error) { failed[module] = err.Error() })
	if err != nil {
		return refuse(err)
	}
	asConsumer, asProvider, err := compose.CredentialsNeeded(in, s.Node)
	if err != nil {
		return refuse(err)
	}
	// What the node runs, by module. A consumer's credential is asked only for a module it runs: the vault refuses the
	// whole ask for a consuming module not assigned to the node (mesh-vault's own), and a module the candidate adds is
	// assigned only after the merge (ADR 0549 §5), so its credential is left missing, a stand-in answered as not yet
	// issued under Added (review of L2b, round 1, finding 1).
	runs := map[string]bool{}
	for _, c := range running {
		if c.Module != "" {
			runs[c.Module] = true
		}
	}
	var consumed []compose.CredentialKey
	for _, k := range asConsumer {
		if runs[k.ConsumerModule] {
			consumed = append(consumed, k)
		}
	}
	asConsumer = consumed
	if len(asConsumer)+len(asProvider) > 0 {
		if in.Credentials, in.Issued, err = r.Credentials(ctx, s.Node, asConsumer, asProvider); err != nil {
			return refuse(fmt.Errorf("frombus: the credentials of %s: %w", s.Node, err))
		}
	}
	composed, skipped, stood, err := compose.CompositionsShadow(in, s.Node, fps)
	for err != nil {
		module := culprit(in, s.Node, fps, failed, err)
		if module == "" {
			// Not one module's: the node's own (a value served elsewhere, the mesh's network), said once as the node's.
			if len(failed) == 0 {
				return refuse(err)
			}
			failed[delivery.HaveNodeWord] = err.Error()
			composed, skipped, stood = nil, nil, nil
			break
		}
		failed[module] = err.Error()
		in = stubbed(in, s.Node, module)
		composed, skipped, stood, err = compose.CompositionsShadow(in, s.Node, fps)
	}
	// The node's own composition is judged only where the node runs one: one that runs none applies it only once a want
	// names it (the node agent's own composer hands it on that want alone), so a candidate does not add it.
	runsOwn := false
	for _, c := range running {
		runsOwn = runsOwn || c.Module == ""
	}
	if !runsOwn {
		for key, c := range composed {
			if c.Module == "" {
				delete(composed, key)
			}
		}
	}
	if _, whole := failed[delivery.HaveNodeWord]; whole {
		// Nothing composed to compare: every refusal is said, and nothing else.
		for _, m := range sortedKeys(failed) {
			a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
		}
		a.Verdict = delivery.VerdictOf(a)
		return a
	}
	// A module the composition folds inside the node's own is judged there: the agent also says it runs by module, from
	// the declaration it kept before the switch (agent.Everything), which is no removal (issue 1126, seed #531).
	if len(s.InOwn) > 0 {
		var judged []delivery.Composed
		for _, c := range running {
			if c.Module == "" || !slices.Contains(s.InOwn, c.Module) {
				judged = append(judged, c)
			}
		}
		running = judged
	}
	cmp := delivery.CompareComposedWith(composed, running, s.SameValue)
	// The answer rides in the node's have key: its shown bodies are bounded, the rest named only.
	budget := MaxShown
	for i := range cmp.Differs {
		kept := cmp.Differs[i].Bodies[:0]
		for _, b := range cmp.Differs[i].Bodies {
			if n := len(b.Composed) + len(b.Running); n <= budget {
				budget -= n
				kept = append(kept, b)
			} else {
				kept = append(kept, delivery.ResourceBodies{ID: b.ID, Why: b.Why})
				a.Note = "some differing resources are named without their bodies: the answer holds at most " +
					fmt.Sprint(MaxShown) + " bytes of them"
			}
		}
		cmp.Differs[i].Bodies = kept
	}
	// A refused module was composed as a stub: what it composed is no difference; its refusal is said.
	notFailed := func(m string) bool { _, ok := failed[m]; return !ok }
	a.Same = slices.DeleteFunc(cmp.Same, func(m string) bool { return !notFailed(m) })
	a.Removed = slices.DeleteFunc(cmp.Removed, func(m string) bool { return !notFailed(m) })
	a.Differs = slices.DeleteFunc(cmp.Differs, func(d delivery.ModuleDiffers) bool { return !notFailed(d.Module) })
	cmp.Added = slices.DeleteFunc(cmp.Added, func(d delivery.ModuleAdded) bool { return !notFailed(d.Module) })
	skipped = slices.DeleteFunc(skipped, func(m string) bool { return !notFailed(m) })

	// What the group adds, by node and module: placed by a candidate and not by the trunk on that node.
	added := map[string]bool{}
	for node, p := range s.Placements {
		if p == nil {
			continue
		}
		was := map[string]bool{}
		for _, m := range trunk[node].Modules {
			was[m.Module] = true
		}
		for _, m := range p.Modules {
			if !was[m.Module] {
				added[node+"/"+m.Module] = true
			}
		}
	}
	unissued := map[string][]string{}
	refusals := map[string][]string{}
	for _, x := range stood {
		node, module := standsInFor(x, s.Node)
		switch {
		case node == s.Node && runs[module]:
			// A value missing for a module the node runs is a refusal, whatever the trunk places (the seed's trunk is
			// empty, and every module counts as the group's).
			refusals[module] = append(refusals[module], x)
		case module != "" && added[node+"/"+module]:
			if node == s.Node {
				unissued[module] = append(unissued[module], x)
			} // another node's addition: the module here that carries it differs, which the assigner judges
		case module == "" || node != s.Node:
			// The node's own, or a value this node holds for a module elsewhere (a grant it provides): said as the node's.
			refusals[delivery.HaveNodeWord] = append(refusals[delivery.HaveNodeWord], x)
		default:
			refusals[module] = append(refusals[module], x)
		}
	}
	addedHere := map[string]delivery.ModuleAdded{}
	for _, m := range cmp.Added {
		addedHere[m.Module] = m
	}
	for _, m := range skipped { // placed, and no build given to compose it at
		addedHere[m] = delivery.ModuleAdded{Module: m, Unissued: []string{"no build of " + m + " is known to compose it at"}}
	}
	for m, xs := range unissued {
		got := addedHere[m]
		got.Module = m
		got.Unissued = append(got.Unissued, xs...)
		addedHere[m] = got
	}
	for _, m := range sortedKeys(addedHere) {
		a.Added = append(a.Added, addedHere[m])
	}
	for _, m := range sortedKeys(refusals) {
		if _, isAdded := addedHere[m]; isAdded {
			continue // a module the candidate adds here: what it lacks is said under Added
		}
		if _, isFailed := failed[m]; isFailed {
			continue // said below, as why it could not be composed
		}
		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: "stands in for " + strings.Join(refusals[m], ", ")})
	}
	for _, m := range sortedKeys(failed) {
		a.Refusals = append(a.Refusals, delivery.ModuleRefused{Module: m, Why: failed[m]})
	}
	sort.Slice(a.Refusals, func(i, j int) bool { return a.Refusals[i].Module < a.Refusals[j].Module })
	a.Verdict = delivery.VerdictOf(a)
	return a
}

// MaxShown bounds the bytes of shown resource bodies in one answer (delivery.ModuleDiffers.Bodies).
const MaxShown = 256 << 10

var (
	grantStandIn = regexp.MustCompile(`^the grant of \S+ for (\S+) on (\S+)$`)
	needsStandIn = regexp.MustCompile(`^(\S+) on (\S+) needs `)
)

// standsInFor is the node and module a stand-in of compose's words is for: an own secret `module/name`, a port
// `port module:port`, a grant `the grant of <provision> for <module> on <node>`, a need `<module> on <node> needs ...`;
// the module empty when the words name none (the certificate, the authority).
func standsInFor(x, node string) (string, string) {
	if m := grantStandIn.FindStringSubmatch(x); m != nil {
		return m[2], m[1]
	}
	if m := needsStandIn.FindStringSubmatch(x); m != nil {
		return m[2], m[1]
	}
	if rest, ok := strings.CutPrefix(x, "port "); ok {
		if module, _, ok := strings.Cut(rest, ":"); ok {
			return node, module
		}
	}
	if module, _, ok := strings.Cut(x, "/"); ok && !strings.Contains(x, " ") {
		return node, module
	}
	return node, ""
}

// culprit is the module placed on node whose composition the error is of: the first, in placement order, whose stub
// (compose.Stub) makes the composition succeed or fail otherwise; empty when none does (the error is not one module's).
// Modules already refused are passed over.
func culprit(in compose.Input, node string, fps map[string]string, failed map[string]string, err error) string {
	var assigned []string
	for _, n := range in.Nodes {
		if n.Name == node {
			assigned = n.Assigned
		}
	}
	// The modules the error names first: the words of a module's refusal open with its name.
	order := make([]string, 0, len(assigned))
	for _, m := range assigned {
		if strings.Contains(err.Error(), m) {
			order = append(order, m)
		}
	}
	for _, m := range assigned {
		if !strings.Contains(err.Error(), m) {
			order = append(order, m)
		}
	}
	for _, m := range order {
		if _, done := failed[m]; done {
			continue
		}
		if _, _, _, again := compose.CompositionsShadow(stubbed(in, node, m), node, fps); again == nil || again.Error() != err.Error() {
			return m
		}
	}
	return ""
}

// stubbed is in with module composed as a stub on node alone (compose.Stub, as node's Kept).
func stubbed(in compose.Input, node, module string) compose.Input {
	out := in
	out.Nodes = append([]compose.Node(nil), in.Nodes...)
	for i := range out.Nodes {
		if out.Nodes[i].Name != node {
			continue
		}
		man, ok := out.Nodes[i].Kept[module]
		if !ok {
			if man, ok = in.Catalogue[module]; !ok {
				return in
			}
		}
		kept := make(map[string]catalogue.Manifest, len(out.Nodes[i].Kept)+1)
		for k, v := range out.Nodes[i].Kept {
			kept[k] = v
		}
		kept[module] = compose.Stub(man)
		out.Nodes[i].Kept = kept
	}
	return out
}