package pipeline

import (
	"fmt"
	"reflect"
	"strings"

	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
)

// PreparedPipeline owns the constructed, run-local implementation set for one
// resolved pipeline. Its implementation values are private so execution cannot
// replace or reconfigure them after preparation.
type PreparedPipeline struct {
	Input  ModuleBinding
	Chunk  ModuleBinding
	Steps  []PreparedPipelineStep
	Output ModuleBinding

	resolved               ResolvedPipeline
	dependencies           ModuleDependencies
	input                  contracts.InputAdapter
	chunker                contracts.Chunker
	chunkValidators        preparedValidatorChain
	output                 contracts.OutputEncoder
	artifactCodecs         *ArtifactCodecRegistry
	evidencePlan           *preparedEvidencePlan
	checkpointFingerprints []CheckpointFingerprint
}

type PreparedPipelineStep struct {
	ID            string
	ArtifactLanes []PreparedArtifactLane
	lanes         []preparedLaneExecutor
}

type PreparedArtifactLane struct {
	Resolved ResolvedArtifactLane
}

type preparedLaneExecutor struct {
	resolved            ResolvedArtifactLane
	typed               *preparedTypedLane
	extractValidators   preparedValidatorChain
	mergeValidators     preparedValidatorChain
	normalizeValidators preparedValidatorChain
}

type preparedTypedLane struct {
	extractor  any
	merger     any
	normalizer any
	extract    typedExtractOperation
	merge      typedMergeOperation
	normalize  typedNormalizeOperation
	codec      artifactCodecEntry
}

type preparedEvidencePlan struct {
	policy EvidenceContextPolicy
	lanes  []preparedEvidenceLane
}

type preparedEvidenceLane struct {
	laneID  string
	kind    contracts.ArtifactKind
	project func(any) ([]source.SourceRef, error)
}

type preparedValidatorChain struct {
	resolved   ResolvedValidatorChain
	validators []preparedValidator
}

type preparedValidator struct {
	resolved      ResolvedValidator
	typed         any
	typedValidate typedValidateOperation
	chunk         contracts.ChunkValidator
	serialized    contracts.SerializedValidator
}

// Prepare validates all configured options and constructs every selected
// module and validator before any operation method can run.
func Prepare(resolved ResolvedPipeline, registries Registries, deps ModuleDependencies) (*PreparedPipeline, error) {
	if err := validateResolvedPipeline(resolved); err != nil {
		return nil, err
	}
	if err := validateRegistrySet(resolved, registries); err != nil {
		return nil, err
	}
	stable := cloneResolvedPipeline(resolved)
	prepared := &PreparedPipeline{
		Input:          cloneModuleBinding(stable.Input),
		Chunk:          cloneModuleBinding(stable.Chunk),
		Output:         cloneModuleBinding(stable.Output),
		resolved:       stable,
		dependencies:   deps,
		artifactCodecs: registries.ArtifactCodecs,
	}
	request := func(binding ModuleBinding, references contracts.ReferenceSet) BuildRequest {
		return BuildRequest{Dependencies: deps, Options: binding.Options, References: references}
	}

	input, err := registries.Inputs.BuildWithRequest(stable.Input.Module, request(stable.Input, contracts.ReferenceSet{}))
	if err != nil {
		return nil, constructionError(stable.ID, "", StageInput, stable.Input.Module, "", err)
	}
	prepared.input = input

	chunker, err := registries.Chunkers.BuildWithRequest(stable.Chunk.Module, request(stable.Chunk, stable.ChunkReferences.ReferenceSet))
	if err != nil {
		return nil, constructionError(stable.ID, "", StageChunk, stable.Chunk.Module, "", err)
	}
	prepared.chunker = chunker
	prepared.chunkValidators, err = prepareValidatorChain(stable, registries, deps, StageChunk, "", stable.Chunk.Module, stable.ChunkReferences.ReferenceSet)
	if err != nil {
		return nil, err
	}

	prepared.Steps = make([]PreparedPipelineStep, len(stable.Steps))
	for stepIndex, step := range stable.Steps {
		preparedStep := PreparedPipelineStep{
			ID:            step.ID,
			ArtifactLanes: make([]PreparedArtifactLane, 0, len(step.ArtifactLanes)),
			lanes:         make([]preparedLaneExecutor, 0, len(step.ArtifactLanes)),
		}
		for _, lane := range step.ArtifactLanes {
			executor, err := prepareLane(stable, lane, registries, deps)
			if err != nil {
				return nil, err
			}
			preparedStep.ArtifactLanes = append(preparedStep.ArtifactLanes, PreparedArtifactLane{Resolved: cloneResolvedArtifactLane(lane)})
			preparedStep.lanes = append(preparedStep.lanes, executor)
		}
		prepared.Steps[stepIndex] = preparedStep
	}

	output, err := registries.Outputs.BuildWithRequest(stable.Output.Module, request(stable.Output, contracts.ReferenceSet{}))
	if err != nil {
		return nil, constructionError(stable.ID, "", StageOutput, stable.Output.Module, "", err)
	}
	prepared.output = output
	prepared.evidencePlan, err = prepareEvidencePlan(stable, registries, output)
	if err != nil {
		return nil, err
	}
	prepared.checkpointFingerprints, err = collectPreparedCheckpointFingerprints(prepared)
	if err != nil {
		return nil, err
	}
	return prepared, nil
}

func prepareEvidencePlan(resolved ResolvedPipeline, registries Registries, output contracts.OutputEncoder) (*preparedEvidencePlan, error) {
	provider, ok := output.(EvidenceContextPolicyProvider)
	if !ok {
		return nil, nil
	}
	policy := cloneEvidenceContextPolicy(provider.EvidenceContextPolicy())
	if !policy.Enabled {
		return nil, nil
	}
	if policy.WindowUnits < 0 {
		return nil, constructionError(resolved.ID, "", StageOutput, resolved.Output.Module, "", fmt.Errorf("evidence window units must not be negative"))
	}
	lanes, err := normalizeEvidenceLaneIDs(policy.LaneIDs)
	if err != nil {
		return nil, constructionError(resolved.ID, "", StageOutput, resolved.Output.Module, "", err)
	}
	policy.LaneIDs = lanes
	active := make(map[string]ResolvedArtifactLane)
	for _, lane := range resolved.AllArtifactLanes() {
		active[lane.ID] = lane
	}
	plan := &preparedEvidencePlan{policy: cloneEvidenceContextPolicy(policy)}
	for _, laneID := range policy.LaneIDs {
		lane, ok := active[laneID]
		if !ok {
			continue
		}
		if registries.ArtifactEvidence == nil {
			return nil, constructionError(resolved.ID, laneID, StageOutput, resolved.Output.Module, "", fmt.Errorf("artifact evidence registry must not be nil for active evidence lane"))
		}
		evidence, _, evidenceErr := registries.ArtifactEvidence.entry(lane.ArtifactKind)
		if evidenceErr != nil {
			return nil, constructionError(resolved.ID, laneID, StageOutput, resolved.Output.Module, "", evidenceErr)
		}
		codecType, ok := registries.ArtifactCodecs.valueType(lane.ArtifactKind)
		if !ok {
			return nil, constructionError(resolved.ID, laneID, StageOutput, resolved.Output.Module, "", fmt.Errorf("artifact codec %q has no Go type", lane.ArtifactKind))
		}
		if evidence.valueType != codecType {
			return nil, constructionError(resolved.ID, laneID, StageOutput, resolved.Output.Module, "", fmt.Errorf("artifact evidence kind %q requires Go type %s, but active artifact codec uses %s", lane.ArtifactKind, typeName(evidence.valueType), typeName(codecType)))
		}
		plan.lanes = append(plan.lanes, preparedEvidenceLane{laneID: laneID, kind: lane.ArtifactKind, project: evidence.project})
	}
	return plan, nil
}

func prepareLane(pipeline ResolvedPipeline, lane ResolvedArtifactLane, registries Registries, deps ModuleDependencies) (preparedLaneExecutor, error) {
	executor := preparedLaneExecutor{resolved: cloneResolvedArtifactLane(lane)}
	request := func(binding ModuleBinding, references contracts.ReferenceSet) BuildRequest {
		return BuildRequest{Dependencies: deps, Options: binding.Options, References: references}
	}
	extractEntry, ok := registries.Extractors.typedEntry(lane.Extract.Module)
	if !ok {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageExtract, lane.Extract.Module, "", fmt.Errorf("typed construction entry is not registered"))
	}
	module, err := buildErasedModule(extractEntry.builder, request(lane.Extract, lane.ExtractReferences.ReferenceSet), lane.Extract.Module, "extractor")
	if err != nil {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageExtract, lane.Extract.Module, "", err)
	}
	codec, _, codecErr := registries.ArtifactCodecs.entry(lane.ArtifactKind)
	if codecErr != nil {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageExtract, lane.Extract.Module, "", codecErr)
	}
	executor.typed = &preparedTypedLane{extractor: module, extract: extractEntry.extract, codec: codec}

	executor.extractValidators, err = prepareValidatorChain(pipeline, registries, deps, StageExtract, lane.ID, lane.Extract.Module, lane.ExtractReferences.ReferenceSet)
	if err != nil {
		return preparedLaneExecutor{}, err
	}

	mergeEntry, ok := registries.Mergers.typedEntry(lane.Merge.Module, lane.ArtifactKind)
	if !ok {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageMerge, lane.Merge.Module, "", fmt.Errorf("typed construction entry is not registered"))
	}
	module, err = buildErasedModule(mergeEntry.builder, request(lane.Merge, lane.MergeReferences.ReferenceSet), lane.Merge.Module, "merger")
	if err != nil {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageMerge, lane.Merge.Module, "", err)
	}
	executor.typed.merger = module
	executor.typed.merge = mergeEntry.merge
	executor.mergeValidators, err = prepareValidatorChain(pipeline, registries, deps, StageMerge, lane.ID, lane.Merge.Module, lane.MergeReferences.ReferenceSet)
	if err != nil {
		return preparedLaneExecutor{}, err
	}

	normalizeEntry, ok := registries.Normalizers.typedEntry(lane.Normalize.Module, lane.ArtifactKind)
	if !ok {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageNormalize, lane.Normalize.Module, "", fmt.Errorf("typed construction entry is not registered"))
	}
	module, err = buildErasedModule(normalizeEntry.builder, request(lane.Normalize, lane.NormalizeReferences.ReferenceSet), lane.Normalize.Module, "normalizer")
	if err != nil {
		return preparedLaneExecutor{}, constructionError(pipeline.ID, lane.ID, StageNormalize, lane.Normalize.Module, "", err)
	}
	executor.typed.normalizer = module
	executor.typed.normalize = normalizeEntry.normalize
	executor.normalizeValidators, err = prepareValidatorChain(pipeline, registries, deps, StageNormalize, lane.ID, lane.Normalize.Module, lane.NormalizeReferences.ReferenceSet)
	if err != nil {
		return preparedLaneExecutor{}, err
	}
	return executor, nil
}

func prepareValidatorChain(pipeline ResolvedPipeline, registries Registries, deps ModuleDependencies, stage ModuleStage, laneID, moduleKey string, references contracts.ReferenceSet) (preparedValidatorChain, error) {
	resolved := resolvedValidatorChain(stage, laneID, moduleKey, pipeline.ValidatorChains)
	prepared := preparedValidatorChain{resolved: resolved}
	for _, validator := range resolved.Validators {
		request := BuildRequest{Dependencies: deps, Options: validator.Binding.Options, References: references}
		built, err := buildPreparedValidator(registries.Validators, validator, request)
		if err != nil {
			return preparedValidatorChain{}, constructionError(pipeline.ID, laneID, stage, moduleKey, validator.Binding.Module, err)
		}
		prepared.validators = append(prepared.validators, built)
	}
	return prepared, nil
}

func buildPreparedValidator(registry *ValidatorRegistry, resolved ResolvedValidator, request BuildRequest) (preparedValidator, error) {
	prepared := preparedValidator{resolved: resolved}
	key := resolved.Binding.Module
	var implementation any
	var err error
	switch resolved.Target {
	case ValidatorTargetTyped:
		entry, ok := registry.typedEntry(key, resolved.ArtifactKind)
		if !ok {
			return preparedValidator{}, fmt.Errorf("typed construction entry is not registered")
		}
		implementation, err = entry.builder(request)
		prepared.typed = implementation
		prepared.typedValidate = entry.validate
	case ValidatorTargetChunk:
		entry, ok := registry.chunkEntry(key)
		if !ok {
			return preparedValidator{}, fmt.Errorf("chunk construction entry is not registered")
		}
		prepared.chunk, err = entry.builder(request)
		implementation = prepared.chunk
	case ValidatorTargetSerialized:
		entry, ok := registry.serializedEntry(key)
		if !ok {
			return preparedValidator{}, fmt.Errorf("serialized construction entry is not registered")
		}
		prepared.serialized, err = entry.builder(request)
		implementation = prepared.serialized
	default:
		return preparedValidator{}, fmt.Errorf("validator construction target %q is not supported", resolved.Target)
	}
	if err != nil {
		return preparedValidator{}, err
	}
	if isNilImplementation(implementation) {
		return preparedValidator{}, fmt.Errorf("validator %q builder returned nil", key)
	}
	identity, ok := implementation.(interface {
		Name() string
		ExecutionClass() contracts.ExecutionClass
	})
	if !ok {
		return preparedValidator{}, fmt.Errorf("validator %q builder returned incompatible implementation %T", key, implementation)
	}
	if identity.Name() != key {
		return preparedValidator{}, fmt.Errorf("validator %q returned name %q", key, identity.Name())
	}
	if identity.ExecutionClass() != resolved.ExecutionClass {
		return preparedValidator{}, fmt.Errorf("validator %q returned execution class %q, want %q", key, identity.ExecutionClass(), resolved.ExecutionClass)
	}
	return prepared, nil
}

func buildErasedModule(builder func(BuildRequest) (any, error), request BuildRequest, key, kind string) (any, error) {
	implementation, err := builder(request)
	if err != nil {
		return nil, err
	}
	if isNilImplementation(implementation) {
		return nil, fmt.Errorf("%s %q builder returned nil", kind, key)
	}
	identity, ok := implementation.(interface{ Key() string })
	if !ok {
		return nil, fmt.Errorf("%s %q builder returned incompatible implementation %T", kind, key, implementation)
	}
	if identity.Key() != key {
		return nil, fmt.Errorf("%s %q returned key %q", kind, key, identity.Key())
	}
	return implementation, nil
}

func isNilImplementation(value any) bool {
	if value == nil {
		return true
	}
	reflected := reflect.ValueOf(value)
	switch reflected.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
		return reflected.IsNil()
	default:
		return false
	}
}

func constructionError(pipelineID, laneID string, stage ModuleStage, moduleKey, validatorKey string, cause error) error {
	scope := fmt.Sprintf("pipeline %q %s module %q", pipelineID, stage, moduleKey)
	if laneID != "" {
		scope = fmt.Sprintf("pipeline %q lane %q %s module %q", pipelineID, laneID, stage, moduleKey)
	}
	if strings.TrimSpace(validatorKey) != "" {
		scope += fmt.Sprintf(" validator %q", validatorKey)
	}
	return fmt.Errorf("prepare %s: %w", scope, cause)
}

func (registries Registries) catalog() ModuleCatalog {
	return ModuleCatalog{
		Inputs: registries.Inputs, Chunkers: registries.Chunkers, ArtifactCodecs: registries.ArtifactCodecs, ArtifactEvidence: registries.ArtifactEvidence,
		Extractors: registries.Extractors, Mergers: registries.Mergers, Normalizers: registries.Normalizers,
		Validators: registries.Validators, ValidatorChains: registries.ValidatorChains, Outputs: registries.Outputs,
	}
}

func validateRegistrySet(resolved ResolvedPipeline, registries Registries) error {
	if registries.Inputs == nil {
		return fmt.Errorf("input registry must not be nil")
	}
	if registries.Chunkers == nil {
		return fmt.Errorf("chunker registry must not be nil")
	}
	if registries.ArtifactCodecs == nil {
		return fmt.Errorf("artifact codec registry must not be nil")
	}
	if registries.Extractors == nil {
		return fmt.Errorf("extractor registry must not be nil")
	}
	if registries.Mergers == nil {
		return fmt.Errorf("merger registry must not be nil")
	}
	if registries.Normalizers == nil {
		return fmt.Errorf("normalizer registry must not be nil")
	}
	if registries.Validators == nil {
		for _, chain := range resolved.ValidatorChains {
			if len(chain.Validators) > 0 {
				return fmt.Errorf("validator registry must not be nil")
			}
		}
	}
	if registries.Outputs == nil {
		return fmt.Errorf("output encoder registry must not be nil")
	}
	return nil
}

func cloneResolvedPipeline(in ResolvedPipeline) ResolvedPipeline {
	out := in
	out.Input = cloneModuleBinding(in.Input)
	out.Chunk = cloneModuleBinding(in.Chunk)
	out.Output = cloneModuleBinding(in.Output)
	out.ChunkReferences = CloneReferenceTarget(in.ChunkReferences)
	out.ValidatorChains = cloneResolvedValidatorChains(in.ValidatorChains)
	if len(in.Steps) > 0 {
		out.Steps = make([]ResolvedPipelineStep, len(in.Steps))
		for i, step := range in.Steps {
			out.Steps[i] = ResolvedPipelineStep{ID: step.ID}
			if len(step.ArtifactLanes) > 0 {
				out.Steps[i].ArtifactLanes = make([]ResolvedArtifactLane, len(step.ArtifactLanes))
				for j, lane := range step.ArtifactLanes {
					out.Steps[i].ArtifactLanes[j] = cloneResolvedArtifactLane(lane)
				}
			}
		}
	}
	return out
}

func cloneResolvedArtifactLane(in ResolvedArtifactLane) ResolvedArtifactLane {
	out := in
	out.Extract = cloneModuleBinding(in.Extract)
	out.Merge = cloneModuleBinding(in.Merge)
	out.Normalize = cloneModuleBinding(in.Normalize)
	out.Validators = cloneModuleBindings(in.Validators)
	out.ExtractReferences = CloneReferenceTarget(in.ExtractReferences)
	out.MergeReferences = CloneReferenceTarget(in.MergeReferences)
	out.NormalizeReferences = CloneReferenceTarget(in.NormalizeReferences)
	return out
}