package agent

import (
	"context"
	"crypto/ed25519"
	"errors"
	"fmt"

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

// The node-engine seat's read verb composition (issue 774): one module's composition beside what runs of it, so why a
// record module waits for a yes, or what its next apply would change, is read from the engine and not guessed from its
// have's words. It changes nothing.

// CompositionView is what the verb composition answers.
type CompositionView struct {
	Node   string `json:"node"`
	Module string `json:"module"`
	// Want is the module's want as the agent holds it; nil when it holds none.
	Want *WantView `json:"want,omitempty"`
	// Have is what the module's have key says now; nil when it says nothing.
	Have *HaveView `json:"have,omitempty"`
	// Composition is the revision read: the latest of the want's build, or the one whose digest was asked.
	Composition RevisionView `json:"composition"`
	// Revisions are the revisions of its key the bucket keeps, oldest first, each with its digest.
	Revisions []RevisionView `json:"revisions,omitempty"`
	// Runs is what runs of the module, and where that is known from; nil when nothing of it runs.
	Runs *RunsView `json:"runs,omitempty"`
	// Judged is the move from what runs to the composition read, as the agent judges it before an apply.
	Judged JudgedView `json:"judged"`
	// Diff is every resource that differs from what runs, when asked.
	Diff []delivery.ResourceChange `json:"diff,omitempty"`
}

// WantView is a want as the verb shows it.
type WantView struct {
	FP       string `json:"fp"`
	Composed string `json:"composed,omitempty"`
	Yes      string `json:"yes,omitempty"`
	Removed  bool   `json:"removed,omitempty"`
}

// HaveView is a have as the verb shows it.
type HaveView struct {
	FP        string `json:"fp,omitempty"`
	Composed  string `json:"composed,omitempty"`
	Phase     string `json:"phase"`
	Detail    string `json:"detail,omitempty"`
	Judgement string `json:"judgement,omitempty"`
	Waits     string `json:"waits,omitempty"`
}

// RevisionView is one revision of a composition key.
type RevisionView struct {
	Key       string `json:"key"`
	Revision  uint64 `json:"revision,omitempty"`
	Digest    string `json:"digest,omitempty"`
	Resources int    `json:"resources,omitempty"`
	Latest    bool   `json:"latest,omitempty"`
	// Refused is why the revision cannot be read or trusted.
	Refused string `json:"refused,omitempty"`
}

// RunsView is what runs of a module.
type RunsView struct {
	FP       string `json:"fp,omitempty"`
	Composed string `json:"composed,omitempty"`
	Phase    string `json:"phase,omitempty"`
	// From is applied (what this engine applied), have (what its have named at the start) or kept (the declaration the
	// node kept before the switch).
	From      string `json:"from"`
	Resources int    `json:"resources"`
}

// JudgedView is a move's judgement.
type JudgedView struct {
	Judgement string `json:"judgement"`
	Words     string `json:"words"`
	// WaitsForYes says the agent would wait for a person's yes before applying it: a module of policy record, a move that
	// recreates a container, moves data or cannot be judged, and no yes in its want for this digest.
	WaitsForYes bool `json:"waits_for_yes"`
}

// Composition reads one module's composition beside what runs of it: the want's build (else the have's), its latest
// revision or the one whose digest is given, and the move's judgement; with diff, the resources that differ.
func (a *Agent) Composition(ctx context.Context, module, digest string, diff bool) (CompositionView, error) {
	if module == "" {
		return CompositionView{}, errors.New("name the module, or node for the node's own composition")
	}
	view := CompositionView{Node: a.env.Node, Module: module}
	var have *Have
	if a.env.Haves != nil {
		if h, ok := a.env.Haves.Read(ctx, module); ok {
			have = &h
			phase := h.Phase
			if phase == "" {
				phase = string(delivery.PhaseRunning)
			}
			view.Have = &HaveView{FP: h.FP, Composed: h.Composed, Phase: phase, Detail: h.Detail, Judgement: h.Judgement, Waits: h.Waits}
		}
	}
	a.mu.Lock()
	w := a.wants[module]
	fp := ""
	if w.Present {
		fp = w.Want.FP
		view.Want = &WantView{FP: w.Want.FP, Composed: w.Want.Composed, Yes: w.Want.Yes, Removed: w.Want.Removed}
	} else if have != nil {
		fp = have.FP
	}
	latest, haveLatest := a.compositionFor(module, fp)
	r, ran := a.running[module]
	from, known := a.runningComposition(module)
	source := "applied"
	if _, ok := a.applied[module]; !ok {
		if _, ok := a.had[module]; ok {
			source = "have"
		} else {
			source = "kept"
		}
	}
	a.mu.Unlock()
	if module != NodeModule && fp == "" {
		return view, fmt.Errorf("%s has no want and no have on %s, so no build of it is composed here", module, a.env.Node)
	}
	key, err := a.compositionKey(module, fp)
	if err != nil {
		return view, err
	}
	revs, err := a.revisionsOf(ctx, key)
	if err != nil {
		return view, fmt.Errorf("the revisions of %s cannot be read: %w", key, err)
	}
	var read *compNow
	for i := range revs {
		c := revs[i]
		rv := RevisionView{Key: key, Revision: c.Rev, Digest: c.Dig, Resources: len(c.C.Resources),
			Latest: haveLatest && c.Rev == latest.Rev}
		if c.Err != nil {
			rv.Refused = c.Err.Error()
		}
		view.Revisions = append(view.Revisions, rv)
		if digest != "" && c.Err == nil && c.Dig == digest {
			read = &revs[i]
		}
	}
	switch {
	case digest != "" && read == nil && haveLatest && latest.Err == nil && latest.Dig == digest:
		read = &latest
	case digest != "" && read == nil:
		return view, fmt.Errorf("no revision of %s the bucket keeps has the digest %s; revisions lists those it keeps", key, digest)
	case read == nil && !haveLatest:
		return view, fmt.Errorf("the bucket holds no composition of %s at %s", module, fp)
	case read == nil:
		read = &latest
	}
	view.Composition = RevisionView{Key: key, Revision: read.Rev, Digest: read.Dig, Resources: len(read.C.Resources),
		Latest: haveLatest && read.Rev == latest.Rev}
	if read.Err != nil {
		view.Composition.Refused = read.Err.Error()
		return view, nil
	}
	var running *delivery.Composed
	if known {
		running = &from
		rv := &RunsView{From: source, Resources: len(from.Resources), FP: from.FP}
		if ran {
			rv.FP, rv.Composed, rv.Phase = r.FP, r.Composed, string(r.Phase)
		}
		view.Runs = rv
	}
	j := delivery.JudgeMove(running, read.C)
	view.Judged = JudgedView{Judgement: string(j.Judgement), Words: j.Words}
	if a.env.SelfComposed && a.env.Policy != nil && module != NodeModule && (!w.Present || w.Want.Yes != read.Dig) {
		switch j.Judgement {
		case delivery.JudgedRecreates, delivery.JudgedMovesData, delivery.JudgedCannot:
			view.Judged.WaitsForYes = a.env.Policy(ctx, module) == catalogue.PolicyRecord
		}
	}
	if diff {
		view.Diff = delivery.ChangedResources(running, read.C)
	}
	return view, nil
}

// compositionKey is a module's composition key at a build, or the node's own.
func (a *Agent) compositionKey(module, fp string) (string, error) {
	if module == NodeModule {
		return delivery.ComposedNodeKey(a.env.Node)
	}
	return delivery.ComposedKey(a.env.Node, module, fp)
}

// revisionsOf is every revision of a composition key the bucket keeps, oldest first, each with its digest as this node
// trusts it (its own unsigned with SelfComposed, else signed by a trusted key), or why it is refused. Nil Revisions
// reads none.
func (a *Agent) revisionsOf(ctx context.Context, key string) ([]compNow, error) {
	if a.env.Revisions == nil {
		return nil, nil
	}
	revs, err := a.env.Revisions(ctx, key)
	if err != nil {
		return nil, err
	}
	var trusted []ed25519.PublicKey
	if a.env.Trusted != nil {
		trusted = a.env.Trusted()
	}
	var out []compNow
	for _, u := range revs {
		if u.Deleted || u.Key != key {
			continue
		}
		c, err := delivery.DecodeComposed(u.Value)
		if err != nil {
			out = append(out, compNow{Raw: u.Value, Rev: u.Revision, Err: err})
			continue
		}
		var dig string
		if a.env.SelfComposed {
			dig, err = delivery.ComposedDigestOf(c) // the node's own: unsigned (ADR 0547 §2)
		} else {
			dig, err = delivery.VerifyComposed(c, trusted)
		}
		out = append(out, compNow{Raw: u.Value, C: c, Dig: dig, Rev: u.Revision, Err: err})
	}
	return out, nil
}