package publish

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"github.com/tegwick/fluid-core/internal/contract"
	"github.com/tegwick/fluid-core/internal/evidence"
	"github.com/tegwick/fluid-core/internal/intent"
	"github.com/tegwick/fluid-core/internal/policy"
	"github.com/tegwick/fluid-core/internal/signing"
)

// Check runs one deterministic verification stage.
//
// Blueprint section 15 lists contract, regression, security, backend contract,
// performance, complexity and static policy checks. Implementations plug in
// here; the pipeline only cares that each returns a verdict and its evidence.
type Check interface {
	// Stage names which pipeline step this check belongs to.
	Stage() Stage
	// Run reports whether the candidate passes, with evidence either way.
	Run(context.Context, Candidate) StageResult
}

// CheckFunc adapts a function to Check.
type CheckFunc struct {
	StageName Stage
	Fn        func(context.Context, Candidate) StageResult
}

// Stage implements Check.
func (c CheckFunc) Stage() Stage { return c.StageName }

// Run implements Check.
func (c CheckFunc) Run(ctx context.Context, cand Candidate) StageResult {
	return c.Fn(ctx, cand)
}

// Pipeline implements the Blueprint section 35 publication pipeline.
//
// It is the only path from Candidate to Verified. Nothing else in the codebase
// constructs a Verified value, which is what makes "AI-generated artifacts are
// untrusted until verified" (invariant 9) a property of the code rather than a
// rule people are asked to remember.
type Pipeline struct {
	checks  []Check
	gate    *policy.Gate
	signer  *signing.Signer
	store   evidence.Store
	intents *intent.Store
	now     func() time.Time
}

// Options configures a pipeline.
type Options struct {
	// Checks run in pipeline order. A stage with no check is recorded as passed
	// with an explicit note, so a gap in verification is visible in the report
	// rather than invisible by omission.
	Checks []Check
	// Gate is the deterministic policy gate. Required.
	Gate *policy.Gate
	// Signer produces the signature that makes a descriptor routable. Required.
	Signer *signing.Signer
	// Store records the audit trail. Required.
	Store evidence.Store
	// Intents resolves the governing intent for a candidate. Required.
	Intents *intent.Store
}

// New returns a pipeline.
func New(o Options) (*Pipeline, error) {
	switch {
	case o.Gate == nil:
		return nil, fmt.Errorf("pipeline requires a policy gate")
	case o.Signer == nil:
		return nil, fmt.Errorf("pipeline requires a signer")
	case o.Store == nil:
		return nil, fmt.Errorf("pipeline requires an evidence store")
	case o.Intents == nil:
		return nil, fmt.Errorf("pipeline requires an intent store")
	}
	return &Pipeline{
		checks:  o.Checks,
		gate:    o.Gate,
		signer:  o.Signer,
		store:   o.Store,
		intents: o.Intents,
		now:     time.Now,
	}, nil
}

// PromotionRequest carries what the gate needs beyond the descriptor itself.
type PromotionRequest struct {
	AdaptationClasses     []contract.AdaptationClass
	ComplexityDelta       float64
	RequestedTrafficShare float64
	Approved              bool
	ApprovedBy            *contract.Actor
}

// Run takes a candidate through every stage.
//
// On failure it returns the report alongside the error: a rejected candidate is
// normal (invariant 14), and the reasons are evidence worth keeping rather than
// an exception to discard.
func (p *Pipeline) Run(ctx context.Context, cand Candidate, req PromotionRequest) (Verified, Report, error) {
	report := Report{Revision: cand.ID()}

	byStage := map[Stage][]Check{}
	for _, c := range p.checks {
		byStage[c.Stage()] = append(byStage[c.Stage()], c)
	}

	governing, intentErr := p.intents.GoverningIntent(ctx, cand.ID())
	if intentErr != nil {
		// Fall back to the active intent: a candidate is normally bound to its
		// intent at publish time, which has not happened yet.
		governing, intentErr = p.intents.Active(ctx)
	}

	for _, stage := range Stages {
		switch stage {
		case StageSign:
			// Signing is not a check; it is what the checks earn.
			continue
		case StagePublish:
			continue
		case StagePolicyCheck:
			result := p.runPolicyGate(cand, req, governing, intentErr)
			report.Stages = append(report.Stages, result)
			p.record(ctx, cand, result)
			if !result.Passed {
				return Verified{}, report, &ErrRejected{Revision: cand.ID(), Failure: result}
			}
			continue
		}

		checks := byStage[stage]
		if len(checks) == 0 {
			// An unchecked stage is recorded as such. Silence here would let a
			// pipeline with no security check look identical to one that passed.
			result := StageResult{
				Stage:  stage,
				Passed: true,
				Detail: "no check configured for this stage",
			}
			report.Stages = append(report.Stages, result)
			p.record(ctx, cand, result)
			continue
		}

		for _, c := range checks {
			result := c.Run(ctx, cand)
			result.Stage = stage
			report.Stages = append(report.Stages, result)
			p.record(ctx, cand, result)
			if !result.Passed {
				return Verified{}, report, &ErrRejected{Revision: cand.ID(), Failure: result}
			}
		}
	}

	sig, err := p.signer.Sign(contract.RevisionDescriptorDocument{Revision: cand.Descriptor()})
	if err != nil {
		result := StageResult{Stage: StageSign, Passed: false, Detail: err.Error()}
		report.Stages = append(report.Stages, result)
		p.record(ctx, cand, result)
		return Verified{}, report, &ErrRejected{Revision: cand.ID(), Failure: result}
	}

	signResult := StageResult{
		Stage:  StageSign,
		Passed: true,
		Detail: fmt.Sprintf("signed with key %s", sig.KeyID),
	}
	report.Stages = append(report.Stages, signResult)
	p.record(ctx, cand, signResult)

	return Verified{
		descriptor: signedDescriptor(cand.Descriptor(), sig),
		origin:     cand.Origin(),
		report:     report,
	}, report, nil
}

// runPolicyGate applies the deterministic gate.
func (p *Pipeline) runPolicyGate(cand Candidate, req PromotionRequest, governing intent.Version, intentErr error) StageResult {
	if intentErr != nil {
		// No governing intent means no constitutional basis for the change.
		// Blueprint invariant 5 requires every revision to be governed by a
		// specific intent version, so this is a refusal, not a warning.
		return StageResult{
			Stage:  StagePolicyCheck,
			Passed: false,
			Detail: fmt.Sprintf("no governing interface evolution intent: %v", intentErr),
		}
	}

	decision := p.gate.Evaluate(policy.Input{
		Descriptor:            cand.Descriptor(),
		GoverningMode:         governing.Mode,
		AdaptationClasses:     req.AdaptationClasses,
		ComplexityDelta:       req.ComplexityDelta,
		RequestedTrafficShare: req.RequestedTrafficShare,
		Approved:              req.Approved,
		ApprovedBy:            req.ApprovedBy,
	})

	if decision.Allowed {
		return StageResult{
			Stage:    StagePolicyCheck,
			Passed:   true,
			Detail:   fmt.Sprintf("passed under %s at %s", governing.Version, governing.Mode),
			Evidence: []string{"intent:" + governing.Version},
		}
	}
	return StageResult{
		Stage:    StagePolicyCheck,
		Passed:   false,
		Detail:   joinReasons(decision.Reasons),
		Evidence: decision.Reasons,
	}
}

// record appends a stage outcome to the audit trail.
//
// Every arrow in the pipeline should be independently observable (Blueprint
// section 46), so stages are recorded as they happen rather than summarized at
// the end — a pipeline that crashes mid-run still leaves evidence of how far it
// got.
func (p *Pipeline) record(ctx context.Context, cand Candidate, r StageResult) {
	verdict := "PASSED"
	if !r.Passed {
		verdict = "FAILED"
	}

	_ = p.store.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID: contract.EventID(fmt.Sprintf("EV-%s-%s-%d",
			cand.ID(), r.Stage, p.now().UnixNano())),
		OccurredAt: p.now().UTC(),
		EntityType: contract.FluidEventEntityTypeRevision,
		EntityID:   string(cand.ID()),
		EventType:  fmt.Sprintf("%s_%s", r.Stage, verdict),
		Actor:      cand.Origin(),
		Reason:     r.Detail,
	})
}

// Publish records a verified revision and binds it to its governing intent.
//
// It takes a Verified rather than a Candidate: the type signature is the
// enforcement. There is no overload that accepts an unverified descriptor.
func (p *Pipeline) Publish(ctx context.Context, v Verified) error {
	d := v.Descriptor()

	if d.Signature == nil {
		return ErrNotVerified
	}

	body, err := json.Marshal(d)
	if err != nil {
		return err
	}
	if err := p.store.PutRecord(ctx, contract.KindRevision, string(d.ID), body); err != nil {
		return err
	}

	if err := p.intents.Bind(ctx, d.ID, d.Intent.Version); err != nil {
		return fmt.Errorf("published %s but failed to bind its intent: %w", d.ID, err)
	}

	return p.store.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID:            contract.EventID(fmt.Sprintf("EV-%s-PUBLISH-%d", d.ID, p.now().UnixNano())),
		OccurredAt:    p.now().UTC(),
		EntityType:    contract.FluidEventEntityTypeRevision,
		EntityID:      string(d.ID),
		EventType:     "REVISION_PUBLISHED",
		Actor:         v.Origin(),
		Inputs:        []string{d.Intent.Version},
		Reason: fmt.Sprintf("published %s in state %s, governed by %s, signed by %s",
			d.ID, d.State, d.Intent.Version, d.Signature.KeyID),
	})
}

func joinReasons(reasons []string) string {
	if len(reasons) == 0 {
		return "rejected"
	}
	s := reasons[0]
	for _, r := range reasons[1:] {
		s += "; " + r
	}
	return s
}