package selfcompose

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"maps"
	"sort"
	"time"

	"git.novox.be/novox/mesh-sdk/go/delivery"

	"github.com/novox/mesh-host/internal/agent"
	"github.com/novox/mesh-host/internal/compose/frombus"
)

// **A check's candidate, composed in shadow on a call** (novox/hq ADR 0593 §7): the node seat's verb compose-candidate.
// Given the key of the indexer's candidate (delivery.CandidatesBucket, `<group>.<heads hash>`), the node composes itself
// twice from what its shadow holds (placement, records, the indexer's modules, its config values), with its own sealed
// values: once as it is, and once with the candidate's modules laid over the indexer's (each at the candidate's
// fingerprint, its manifest by digest and the indexer's verdict on it, ADR 0578 §3; a module the candidate removes left
// out). It answers per module placed here composed (its digest, and whether the candidate changes it), refused by the
// candidate, or held without it too, and the verdict of its own composition. It applies nothing and writes nothing: it
// composes on a copy of the shadow's inputs, so neither the shadow's answers nor the node's own composer move.

// errNotReady is a shadow that has not read every input yet.
var errNotReady = errors.New("this node's shadow has not read every input yet")

// ComposeCandidate is the node's answer to ask, within delivery.ComposeAnswerBound (or ctx's deadline, if sooner).
func (s *Shadow) ComposeCandidate(ctx context.Context, ask delivery.ComposeCandidateAsk) delivery.ComposeCandidateAnswer {
	began := time.Now()
	s.mu.Lock()
	c := s.c
	s.mu.Unlock()
	node := c.env.Node
	a := delivery.ComposeCandidateAnswer{Node: node, Candidate: ask.Candidate}
	refuse := func(why string) delivery.ComposeCandidateAnswer {
		a.Verdict, a.Refused, a.Modules, a.Own = delivery.ComposeCandidateRefused, why, nil, delivery.ModuleComposed{}
		a.Took = time.Since(began).Milliseconds()
		return a
	}
	// A node that cannot compose now (its shadow not ready, a read the bus did not answer, the bound passed) answers
	// unready: the checker takes it as no answer (ADR 0593 §9) by the verdict, the words only saying why.
	unready := func(why string) delivery.ComposeCandidateAnswer {
		a = refuse(why)
		a.Verdict = delivery.ComposeCandidateUnready
		return a
	}
	if _, _, err := delivery.ParseCompositionKey(ask.Candidate); err != nil {
		return refuse(err.Error())
	}
	ctx, cancel := context.WithTimeout(ctx, delivery.ComposeAnswerBound)
	defer cancel()
	if !s.ready.Load() {
		return unready(errNotReady.Error())
	}
	base := c.scratch()
	raw, err := base.get(ctx, delivery.CandidatesBucket, ask.Candidate)
	if err != nil {
		return unready(fmt.Sprintf("the indexer's candidate %s cannot be read: %v", ask.Candidate, err))
	}
	if raw == nil {
		return refuse("the indexer holds no candidate " + ask.Candidate)
	}
	cand, err := delivery.DecodeCandidate(raw)
	if err != nil {
		return refuse(fmt.Sprintf("the indexer's candidate %s cannot be read: %v", ask.Candidate, err))
	}
	laid := c.scratch()
	touched, err := laid.layCandidate(ctx, cand)
	if err != nil {
		return unready(err.Error())
	}

	var running []delivery.Composed
	if c.env.Running != nil {
		running = c.env.Running()
	}
	baseComps, baseHeld, baseErr := base.composeShadow(ctx, running, nil, nil)
	laidComps, laidHeld, laidErr := laid.composeShadow(ctx, running, touched, func(scope frombus.Scope) {
		if !ask.Input {
			return
		}
		in, err := frombus.Input(ctx, reader{c: laid}, laid.env.Mesh, scope)
		if err != nil {
			return
		}
		// The request's input carries no catalogue (composer.Request.Input): the cases give the manifests.
		in.Catalogue = nil
		for i := range in.Nodes {
			in.Nodes[i].Kept = nil
		}
		if body, err := json.Marshal(in); err == nil {
			a.Input = body
		}
	})
	if ctx.Err() != nil {
		return unready(fmt.Sprintf("the bound of %s passed before the node composed the candidate", delivery.ComposeAnswerBound))
	}
	switch {
	case laidErr != nil && BusFailed(laidErr):
		return unready("a read on the bus did not answer: " + laidErr.Error())
	case laidErr != nil && baseErr != nil:
		// The node composes none of its own without the candidate either: the candidate changes nothing of that.
		a.Verdict, a.Modules = delivery.ComposeCandidateComposed, []delivery.ModuleComposed{}
		a.Own = delivery.ModuleComposed{Module: delivery.HaveNodeWord, State: delivery.ModuleHeldState, Words: laidErr.Error()}
		a.Took = time.Since(began).Milliseconds()
		return a
	case laidErr != nil:
		return refuse(laidErr.Error())
	}
	byModule := func(comps map[string]delivery.Composed) map[string]delivery.Composed {
		out := map[string]delivery.Composed{}
		for _, comp := range comps {
			out[comp.Module] = comp
		}
		return out
	}
	was, now := byModule(baseComps), byModule(laidComps)
	one := func(module string) (delivery.ModuleComposed, bool) {
		m := delivery.ModuleComposed{Module: module}
		if module == "" {
			m.Module = delivery.HaveNodeWord
		}
		if why, held := laidHeld[module]; held {
			m.State, m.Words = delivery.ModuleRefusedState, why
			if _, before := baseHeld[module]; before || baseErr != nil {
				m.State = delivery.ModuleHeldState
			}
			return m, true
		}
		comp, ok := now[module]
		if !ok {
			return m, false
		}
		dig, err := delivery.ComposedDigestOf(comp)
		if err != nil {
			m.State, m.Words = delivery.ModuleRefusedState, err.Error()
			return m, true
		}
		m.State, m.FP, m.Digest = delivery.ModuleComposedState, comp.FP, dig
		if before, ok := was[module]; !ok {
			m.Changed = true
		} else if d, err := delivery.ComposedDigestOf(before); err != nil || d != dig {
			m.Changed = true
		}
		return m, true
	}
	modules := map[string]bool{}
	for m := range now {
		modules[m] = m != ""
	}
	for m := range laidHeld {
		modules[m] = m != "" && m != agent.NodeModule
	}
	names := make([]string, 0, len(modules))
	for m, isModule := range modules {
		if isModule {
			names = append(names, m)
		}
	}
	sort.Strings(names)
	a.Modules = []delivery.ModuleComposed{}
	refused := false
	for _, m := range names {
		if mc, ok := one(m); ok {
			a.Modules = append(a.Modules, mc)
			refused = refused || mc.State == delivery.ModuleRefusedState
		}
	}
	if own, ok := one(""); ok {
		a.Own = own
	} else {
		a.Own = delivery.ModuleComposed{Module: delivery.HaveNodeWord, State: delivery.ModuleHeldState,
			Words: "the node composes no composition of its own"}
	}
	refused = refused || a.Own.State == delivery.ModuleRefusedState
	a.Verdict = delivery.ComposeCandidateComposed
	if refused {
		a.Verdict = delivery.ComposeCandidateRefused
	}
	a.Took = time.Since(began).Milliseconds()
	return a
}

// scratch is a composer over a copy of what c holds of its inputs, for composing in shadow without moving c.
func (c *Composer) scratch() *Composer {
	out := New(c.env)
	c.mu.Lock()
	defer c.mu.Unlock()
	out.placements = maps.Clone(c.placements)
	out.records = maps.Clone(c.records)
	out.inOwn = maps.Clone(c.inOwn)
	out.modules = maps.Clone(c.modules)
	out.values = maps.Clone(c.values)
	out.manifests = maps.Clone(c.manifests)
	out.archives = maps.Clone(c.archives)
	out.builds = maps.Clone(c.builds)
	out.sealedOwn = maps.Clone(c.sealedOwn)
	out.ownHanded = maps.Clone(c.ownHanded)
	out.certified = c.certified
	out.placementKeys = c.placementKeys
	return out
}

// layCandidate lays the candidate's modules over the indexer's: each at its fingerprint, with its manifest's digest and
// the indexer's verdict on it (read from its verdicts, none read taken as accepted); a module the candidate removes goes.
// It answers the modules laid.
func (c *Composer) layCandidate(ctx context.Context, cand delivery.Candidate) (map[string]bool, error) {
	touched := map[string]bool{}
	for _, pull := range cand.Pulls {
		for module, cm := range pull.Fps {
			if cm.None2 == delivery.CandidateNoneNoModule {
				c.mu.Lock()
				delete(c.modules, module)
				c.mu.Unlock()
				continue
			}
			if cm.FP2 == "" {
				continue // no fingerprint at the preview: composed as the trunk holds it
			}
			m := delivery.Module{FP2: cm.FP2, Manifest: cm.Manifest, Repository: pull.Repository, Commit: pull.Head.Head}
			if cm.Manifest != "" {
				key, err := delivery.VerdictsKey(cm.Manifest)
				if err != nil {
					return nil, err
				}
				raw, err := c.get(ctx, delivery.VerdictsBucket, key)
				if err != nil {
					return nil, fmt.Errorf("the indexer's verdict on %s's manifest cannot be read: %w", module, err)
				}
				if raw != nil {
					v, err := delivery.DecodeManifestVerdict(raw)
					if err != nil {
						return nil, fmt.Errorf("the indexer's verdict on %s's manifest cannot be read: %w", module, err)
					}
					m.Verdict, m.Problems, m.Warnings = v.State, v.Problems, v.Warnings
				}
			}
			c.mu.Lock()
			c.modules[module] = m
			c.mu.Unlock()
			touched[module] = true
		}
	}
	return touched, nil
}

// composeShadow composes this node from what c holds, as the shadow composes it (shadowBuilds): each module at the build
// it runs, one placed and not run at the indexer's, and one the candidate laid (laid) at the candidate's. input, when
// given, is handed the scope.
func (c *Composer) composeShadow(ctx context.Context, running []delivery.Composed, laid map[string]bool, input func(frombus.Scope)) (map[string]delivery.Composed, map[string]string, error) {
	node := c.env.Node
	c.mu.Lock()
	placement, placed := c.placements[node]
	modules := maps.Clone(c.modules)
	inOwn := c.inOwnOf(placement)
	c.mu.Unlock()
	if !placed {
		return nil, nil, errors.New("this node's key in the seat's placement state is gone: it composes nothing of its own")
	}
	fps := shadowBuilds(running, placement, modules, inOwn)
	// A module the laid candidate changes is composed at the candidate's build, though the node runs another.
	for module := range fps {
		if mod, ok := modules[module]; ok && laid[module] {
			fps[module] = mod.FP2
		}
	}
	kept := map[string]string{}
	for module, fp := range fps {
		if mod, ok := modules[module]; ok && mod.FP2 == fp {
			continue
		}
		kept[module] = fp
	}
	wants := map[string]delivery.Want{agent.NodeModule: {}}
	for module, fp := range fps {
		wants[module] = delivery.Want{FP: fp}
	}
	c.mu.Lock()
	c.wants = wants
	c.mu.Unlock()
	scope := frombus.Scope{Node: node, KeptAt: kept, InOwn: inOwn, Running: running, SameValue: c.sameValue}
	if input != nil {
		input(scope)
	}
	comps, _, held, err := frombus.Compose(ctx, reader{c: c}, c.env.Mesh, scope, fps)
	if err != nil {
		return nil, nil, err
	}
	for key, comp := range comps {
		comps[key] = c.keepRunning(comp, running)
	}
	return comps, held, nil
}