package delivery

import (
	"bytes"
	"encoding/json"
	"fmt"
	"time"
)

// A composition that does not exist yet is asked of the node-engine (novox/hq ADR 0593 §7): the seat node-engine's verb
// compose-candidate, served by each node's engine alone, composes a check's candidate in shadow with the node's own
// sealed values and the indexer's manifest verdicts, applies and writes nothing, and answers within the asker's bound.
// The checker asks every placed node in parallel and makes the check's composition verdict from the answers; a node
// that does not answer within the bound is named "not composed on that node: no answer" and the check passes with that
// warning (§9). This is the contract only: the composing is the node-engine's own.

const (
	// EngineComposeCandidateVerb is the verb's name on the seat node-engine (catalogue.EngineSeat).
	EngineComposeCandidateVerb = "compose-candidate"
	// ComposeAnswerBound is the default of the checker's setting compose-answer-bound: how long it waits for a node's
	// answer (ADR 0593 §7, §9).
	ComposeAnswerBound = 60 * time.Second
	// ComposeNoAnswer is the words a check's verdict names a node with that did not answer within the bound (ADR 0593 §9).
	ComposeNoAnswer = "not composed on that node: no answer"

	// ComposeCandidateComposed and ComposeCandidateRefused are an answer's verdict: no module and not the node's own composition is
	// refused by the candidate, or at least one is (or the node could not compose with it at all, Refused).
	ComposeCandidateComposed = "composed"
	ComposeCandidateRefused  = "refused"
	// ComposeCandidateUnready is the verdict of a node that cannot compose yet (its shadow not ready, its agent
	// starting): no module is named, Refused says why in words, and the checker takes it as a node that did not answer
	// (ComposeNoAnswer, ADR 0593 §9), deciding by this verdict and never by the words.
	ComposeCandidateUnready = "unready"

	// The states of one module's composition with the candidate: composed (Digest set), refused by the candidate
	// (Words set), or held, refused without the candidate too (Words set), which counts toward no verdict.
	ModuleComposedState = "composed"
	ModuleRefusedState  = "refused"
	ModuleHeldState     = "held"
)

// ComposeCandidateAsk is the verb's input: Candidate is the key of the indexer's candidate (CompositionKey,
// `<escaped group>.<heads hash>`); the engine reads that candidate itself and lays its modules over its placement.
// Input asks the engine to answer too the composition input it composed the candidate from (its own node's scope, the
// catalogue left out as composer.Request.Input says): the checker puts it into the request a build module's composer
// runs over, for a group that changes the node-engine's composition code (ADR 0593 §7).
type ComposeCandidateAsk struct {
	Candidate string `json:"candidate"`
	Input     bool   `json:"input,omitempty"`
}

// ComposeCandidateAnswer is the verb's answer: the node, the candidate, the verdict, every module placed on the node
// sorted by name, the node's own composition (Own, Module "node"), why the node could not compose with the candidate at
// all (Refused: Modules is then empty and Verdict refused, or unready when it cannot compose yet), how long the engine took in milliseconds, and, when asked
// (ComposeCandidateAsk.Input), the composition input it composed from.
type ComposeCandidateAnswer struct {
	V         int              `json:"v"`
	Node      string           `json:"node"`
	Candidate string           `json:"candidate"`
	Verdict   string           `json:"verdict"`
	Modules   []ModuleComposed `json:"modules"`
	Own       ModuleComposed   `json:"own"`
	Refused   string           `json:"refused,omitempty"`
	Took      int64            `json:"took"`
	Input     json.RawMessage  `json:"input,omitempty"`
}

// ModuleComposed is one module's composition with the candidate: the fingerprint it was composed at (the candidate's
// FP2 for a module the candidate touches, else its newest done build as composed-<node> holds it), its state, the
// composition's digest when composed (ComposedDigestOf), whether the candidate changes it from the one composed without
// it (the checker's "what the change reaches on this node"), and why, for a refused or held one.
type ModuleComposed struct {
	Module  string `json:"module"`
	FP      string `json:"fp,omitempty"`
	State   string `json:"state"`
	Digest  string `json:"digest,omitempty"`
	Changed bool   `json:"changed,omitempty"`
	Words   string `json:"words,omitempty"`
}

func (a ComposeCandidateAsk) check() error {
	if _, _, err := ParseCompositionKey(a.Candidate); err != nil {
		return fmt.Errorf("delivery: a compose-candidate ask names no candidate: %w", err)
	}
	return nil
}

func (m ModuleComposed) check(node string) error {
	if m.Module == "" {
		return fmt.Errorf("delivery: a module's composition on %s names no module", node)
	}
	switch m.State {
	case ModuleComposedState:
		if m.Digest == "" {
			return fmt.Errorf("delivery: %s is composed on %s and names no digest", m.Module, node)
		}
	case ModuleRefusedState, ModuleHeldState:
		if m.Words == "" {
			return fmt.Errorf("delivery: %s is %s on %s and says no why", m.Module, m.State, node)
		}
	default:
		return fmt.Errorf("delivery: %s on %s is %q, neither %s, %s nor %s", m.Module, node, m.State,
			ModuleComposedState, ModuleRefusedState, ModuleHeldState)
	}
	return nil
}

func (a ComposeCandidateAnswer) check() error {
	if err := checkName("node", a.Node); err != nil {
		return err
	}
	if _, _, err := ParseCompositionKey(a.Candidate); err != nil {
		return err
	}
	if a.Took < 0 {
		return fmt.Errorf("delivery: the answer of %s took %d ms", a.Node, a.Took)
	}
	if a.Verdict == ComposeCandidateUnready && a.Refused == "" {
		return fmt.Errorf("delivery: %s is not ready to compose and its answer says no why", a.Node)
	}
	if a.Refused != "" {
		if len(a.Modules) > 0 || a.Verdict != ComposeCandidateRefused && a.Verdict != ComposeCandidateUnready {
			return fmt.Errorf("delivery: %s could not compose the candidate (%s), and its answer names modules or is neither %s nor %s",
				a.Node, a.Refused, ComposeCandidateRefused, ComposeCandidateUnready)
		}
		return nil
	}
	refused := false
	for i, m := range append([]ModuleComposed{a.Own}, a.Modules...) {
		if err := m.check(a.Node); err != nil {
			return err
		}
		if i > 1 && a.Modules[i-2].Module >= m.Module {
			return fmt.Errorf("delivery: the modules of %s's answer are not sorted and each once (%s after %s)", a.Node, m.Module, a.Modules[i-2].Module)
		}
		refused = refused || m.State == ModuleRefusedState
	}
	switch {
	case a.Own.Module != nodeWord:
		return fmt.Errorf("delivery: the node's own composition in %s's answer is named %q, not %q", a.Node, a.Own.Module, nodeWord)
	case refused && a.Verdict != ComposeCandidateRefused:
		return fmt.Errorf("delivery: %s's answer refuses a module and its verdict is %q", a.Node, a.Verdict)
	case !refused && a.Verdict != ComposeCandidateComposed:
		return fmt.Errorf("delivery: %s's answer refuses no module and its verdict is %q", a.Node, a.Verdict)
	}
	return nil
}

// strictDecode reads data into v, refusing an unknown key.
func strictDecode(data []byte, v any, what string) error {
	d := json.NewDecoder(bytes.NewReader(data))
	d.DisallowUnknownFields()
	if err := d.Decode(v); err != nil {
		return fmt.Errorf("delivery: %s does not fit its shape: %w", what, err)
	}
	return nil
}

// EncodeComposeCandidateAsk is a as JSON; it refuses an ask naming no candidate key.
func EncodeComposeCandidateAsk(a ComposeCandidateAsk) ([]byte, error) {
	if err := a.check(); err != nil {
		return nil, err
	}
	return json.Marshal(a)
}

// DecodeComposeCandidateAsk reads an ask strictly; it refuses an unknown key and what EncodeComposeCandidateAsk refuses.
func DecodeComposeCandidateAsk(data []byte) (ComposeCandidateAsk, error) {
	var a ComposeCandidateAsk
	if err := strictDecode(data, &a, "a compose-candidate ask"); err != nil {
		return ComposeCandidateAsk{}, err
	}
	return a, a.check()
}

// EncodeComposeCandidateAnswer is a as JSON at Version; it refuses an unknown state, a composed module without a digest,
// a refused or held one without words, a refusal of the whole naming modules, and a verdict the modules do not give.
func EncodeComposeCandidateAnswer(a ComposeCandidateAnswer) ([]byte, error) {
	if err := a.check(); err != nil {
		return nil, err
	}
	a.V = Version
	return json.Marshal(a)
}

// DecodeComposeCandidateAnswer reads an answer strictly; it refuses an unknown version (ErrUnknownVersion), an unknown
// key and what EncodeComposeCandidateAnswer refuses.
func DecodeComposeCandidateAnswer(data []byte) (ComposeCandidateAnswer, error) {
	if err := checkVersion(data); err != nil {
		return ComposeCandidateAnswer{}, err
	}
	var a ComposeCandidateAnswer
	if err := strictDecode(data, &a, "a compose-candidate answer"); err != nil {
		return ComposeCandidateAnswer{}, err
	}
	return a, a.check()
}