package agentstatus

import (
	"context"
	"strings"

	"golang.org/x/sync/errgroup"
)

const codexCandidateValidationConcurrency = 3

type codexRuntimeCandidateValidationState string

const (
	codexRuntimeCandidateValidationReady       codexRuntimeCandidateValidationState = "ready"
	codexRuntimeCandidateValidationUnsupported codexRuntimeCandidateValidationState = "unsupported"
	codexRuntimeCandidateValidationFailed      codexRuntimeCandidateValidationState = "failed"
)

// codexRuntimeCandidateValidation keeps runtime facts separate from the
// selection decision. A successful app-server handshake establishes runtime
// capability; the version policy determines whether that candidate is eligible
// for use.
type codexRuntimeCandidateValidation struct {
	Candidate        codexRuntimeCandidate
	Version          string
	VersionSupported bool
	Probe            CodexProbeEvidence
	PackageLayout    CodexPackageLayoutEvidence
	State            codexRuntimeCandidateValidationState
	ReasonCode       string
}

func (s Service) validateCodexRuntimeCandidates(
	ctx context.Context,
	spec ProviderSpec,
	candidates []codexRuntimeCandidate,
) []codexRuntimeCandidateValidation {
	if len(candidates) == 0 {
		return nil
	}
	result := make([]codexRuntimeCandidateValidation, len(candidates))
	group, groupCtx := errgroup.WithContext(baseContext(ctx))
	jobs := make(chan int)
	workers := min(codexCandidateValidationConcurrency, len(candidates))
	for range workers {
		group.Go(func() error {
			for {
				select {
				case <-groupCtx.Done():
					return nil
				case index, ok := <-jobs:
					if !ok {
						return nil
					}
					result[index] = s.validateCodexRuntimeCandidate(groupCtx, spec, candidates[index])
				}
			}
		})
	}
dispatch:
	for index := range candidates {
		select {
		case <-groupCtx.Done():
			break dispatch
		case jobs <- index:
		}
	}
	close(jobs)
	_ = group.Wait()
	return result
}

func (s Service) validateCodexRuntimeCandidate(
	ctx context.Context,
	spec ProviderSpec,
	candidate codexRuntimeCandidate,
) codexRuntimeCandidateValidation {
	env := s.commandResolver().Env(s.adapterCommandEnv(ctx, spec))
	version := s.providerCLIVersion(ctx, spec, candidate.LauncherPath, env)
	probe := s.probeCodexRuntimeCandidate(ctx, candidate.LauncherPath, env)
	layout := s.scanCodexPackageLayout(candidate.LauncherPath)
	result := codexRuntimeCandidateValidation{
		Candidate:        candidate,
		Version:          version,
		VersionSupported: providerCLIVersionMeetsMinimum(spec, version),
		Probe:            probe,
		PackageLayout:    layout,
	}
	switch {
	case !probe.ProtocolReady:
		result.State = codexRuntimeCandidateValidationFailed
		result.ReasonCode = firstNonBlank(probe.Category, "acp_adapter_launch_failed")
	case !result.VersionSupported:
		result.State = codexRuntimeCandidateValidationUnsupported
		result.ReasonCode = "codex_version_unsupported"
	default:
		result.State = codexRuntimeCandidateValidationReady
	}
	return result
}

func (s Service) probeCodexRuntimeCandidate(ctx context.Context, launcherPath string, env []string) CodexProbeEvidence {
	launcherPath = strings.TrimSpace(launcherPath)
	if launcherPath == "" {
		return CodexProbeEvidence{Category: "acp_adapter_not_found"}
	}
	release, acquired := s.DetectionCommands.acquire(ctx)
	if !acquired {
		return CodexProbeEvidence{Category: "probe_canceled"}
	}
	defer release()
	return s.probeCodexAppServer(ctx, []string{launcherPath, "app-server"}, env)
}

type codexRuntimeImplicitSelection struct {
	CandidateIndex int
	Launchable     bool
	ReasonCode     string
	State          CodexRuntimeSelectionState
}

// decideCodexRuntimeImplicitSelection decides only when no user choice is
// persisted. Discovery order deliberately has no authority here: one healthy
// installation is safe to use implicitly, but two healthy installations require
// an explicit user choice so that PATH, Bun, npm, pnpm, or Homebrew precedence
// never becomes an accidental product policy.
func decideCodexRuntimeImplicitSelection(
	candidates []codexRuntimeCandidateValidation,
) codexRuntimeImplicitSelection {
	readyIndex := -1
	for index, candidate := range candidates {
		if candidate.State != codexRuntimeCandidateValidationReady {
			continue
		}
		if readyIndex >= 0 {
			return codexRuntimeImplicitSelection{
				CandidateIndex: -1,
				ReasonCode:     "codex_runtime_selection_required",
				State:          CodexRuntimeSelectionSelectionRequired,
			}
		}
		readyIndex = index
	}
	if readyIndex >= 0 {
		return codexRuntimeImplicitSelection{
			CandidateIndex: readyIndex,
			Launchable:     true,
			ReasonCode:     "codex_runtime_unique_ready_candidate",
			State:          CodexRuntimeSelectionImplicitUnique,
		}
	}
	if len(candidates) == 0 {
		return codexRuntimeImplicitSelection{
			CandidateIndex: -1,
			ReasonCode:     "cli_not_found",
			State:          CodexRuntimeSelectionUnavailable,
		}
	}
	return codexRuntimeImplicitSelection{
		CandidateIndex: 0,
		ReasonCode:     "no_ready_candidate",
		State:          CodexRuntimeSelectionUnavailable,
	}
}