package agent

import (
	"context"
	"errors"
	"fmt"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/declaration"
	"git.novox.be/novox/mesh-sdk/go/delivery"
	"github.com/novox/mesh-host/internal/judge"
)

// 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"`
	// Attempt is what the agent holds of the module's last apply that did not end running: failed, failed for a moment
	// of the bus, or held for a failed backup, with the want's revision that hold took as answered; nil when none
	// (issue 1585: why a module stays held was not readable from the engine).
	Attempt *AttemptView `json:"attempt,omitempty"`
	// Started says the agent has looked at the module once since it started (its baseline): what runs was taken from its
	// have, or it was applied.
	Started bool `json:"started"`
	// 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 []judge.ResourceChange `json:"diff,omitempty"`
	// Own is, of the node's own composition (module node), its own fields beside what runs names (issue 774: ace's
	// own composition dropped the provisioner client's account, and nothing read could show it).
	Own *OwnView `json:"own,omitempty"`
}

// OwnView is the node's own fields of a composition (delivery.NodeOwn) beside what runs of them, and what the node's
// composer held in its last pass.
type OwnView struct {
	// Provisioner is the account the provisioner's client runs as, as the revision read names it; RunsProvisioner as
	// what runs names it. Empty: the declaration names none, and every filled write is refused.
	Provisioner     string `json:"provisioner_account"`
	RunsProvisioner string `json:"runs_provisioner_account,omitempty"`
	// Adoption is the revision's adoption: the node adopted, and which of its modules are taken; nil for a converged node.
	Adoption *declaration.Adoption `json:"adoption,omitempty"`
	// Identities, Groups and Libraries count what the revision names of each.
	Identities int `json:"identities,omitempty"`
	Groups     int `json:"groups,omitempty"`
	Libraries  int `json:"libraries,omitempty"`
	// Held is each module the node's composer held in its last pass, with why.
	Held map[string]string `json:"held,omitempty"`
}

// WantView is a want as the verb shows it: as the agent holds it, at the revision of its key it last read.
type WantView struct {
	FP       string `json:"fp"`
	Composed string `json:"composed,omitempty"`
	Yes      string `json:"yes,omitempty"`
	Removed  bool   `json:"removed,omitempty"`
	// Self says the node composes the module itself (ADR 0547 §2).
	Self bool `json:"self,omitempty"`
	// Backup is the operator's answer to a failed backup the want carries, again or skip (ADR 0539 §16); empty when none.
	Backup string `json:"backup,omitempty"`
	Words  string `json:"words,omitempty"`
	// Revision is the revision of the want's key the agent read last.
	Revision uint64 `json:"revision"`
}

// AttemptView is the agent's record of a module's last apply that did not end running.
type AttemptView struct {
	FP       string `json:"fp"`
	Composed string `json:"composed,omitempty"`
	// WantRevision and CompositionRevision are the revisions of the want's and the composition's keys it was tried at.
	WantRevision        uint64 `json:"want_revision"`
	CompositionRevision uint64 `json:"composition_revision"`
	// Held says it is held for a failed backup; AnsweredRevision is the want's revision the hold took, so an answer
	// (again or skip) in a later revision releases it.
	Held             bool   `json:"held,omitempty"`
	AnsweredRevision uint64 `json:"answered_revision,omitempty"`
	// Transient says it failed because the bus did not answer for a moment, and is tried again by the clock.
	Transient bool `json:"transient,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,
			Self: w.Want.Self, Backup: w.Want.Backup, Words: w.Want.Words, Revision: w.Rev}
	} else if have != nil {
		fp = have.FP
	}
	if att, ok := a.attempt[module]; ok {
		view.Attempt = &AttemptView{FP: att.FP, Composed: att.Composed, WantRevision: att.WantRev, CompositionRevision: att.CompRev,
			Held: att.Held, AnsweredRevision: att.AnsweredRev, Transient: att.Transient}
	}
	view.Started = a.checked[module]
	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
	}
	if module == NodeModule {
		o := read.C.Own
		view.Own = &OwnView{Provisioner: o.Provisioner, Adoption: o.Adoption, Identities: len(o.Identities), Groups: len(o.Groups),
			Libraries: len(o.Libraries)}
		if running != nil {
			view.Own.RunsProvisioner = running.Own.Provisioner
		}
		if a.env.Held != nil {
			view.Own.Held = a.env.Held()
		}
	}
	j := judge.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 = judge.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 state keeps, oldest first, each with its digest (unsigned, ADR
// 0593 §6), 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 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
		}
		dig, err := delivery.ComposedDigestOf(c) // unsigned: a record, never verified (ADR 0593 §6)
		out = append(out, compNow{Raw: u.Value, C: c, Dig: dig, Rev: u.Revision, Err: err})
	}
	return out, nil
}