package publish

import (
	"context"
	"fmt"

	"gitea.maximumdirect.net/eric/distributor/internal/bundle"
	"gitea.maximumdirect.net/eric/distributor/internal/config"
	"gitea.maximumdirect.net/eric/distributor/internal/state"
	"gitea.maximumdirect.net/eric/distributor/internal/storage"
	"gitea.maximumdirect.net/eric/distributor/internal/transform"
)

type Action string

const (
	ActionPublishNew           Action = "publish_new"
	ActionReplaceOlder         Action = "replace_older"
	ActionSkipSame             Action = "skip_same"
	ActionSkipDestinationNewer Action = "skip_destination_newer"
	ActionFailConflict         Action = "fail_conflict"
	ActionFailUnmanaged        Action = "fail_unmanaged"
	ActionForceReplace         Action = "force_replace"
)

type Request struct {
	PipelineID            string
	DestinationID         string
	SourceBundle          bundle.Bundle
	SourceBackend         storage.Backend
	DestinationBackend    storage.Backend
	DestinationBundlePath string
	PathMapping           string
	Publish               config.PublishPolicy
	Transform             config.Transform
	Links                 *config.Links
	State                 config.StatePolicy
	Reconciliation        config.ReconciliationPolicy
	Transformers          TransformerResolver
	Transfer              config.TransferPolicy
	DistributorVersion    string
	Force                 bool
}

type TransformerResolver interface {
	Get(name string) (transform.Transformer, bool)
}

type Plan struct {
	PipelineID            string
	DestinationID         string
	BundleID              string
	BundlePath            string
	DestinationBundlePath string
	PathMapping           string
	Action                Action
	Reason                string
	Force                 bool
	PrimaryURL            string
	StateMode             string
	OwnerScope            state.OwnerScope
	Reconciliation        config.ReconciliationPolicy
	Outputs               []Output
	ExistingState         *state.DistributorState
	ExistingSharedRoot    *state.SharedRootState
	OtherOwnerOutputs     []state.SharedRootOutputFile
	RetainedOwnerOutputs  []state.SharedRootOutputFile
	OwnerOutputsToDelete  []state.SharedRootOutputFile
	OwnerOutputsToWrite   []Output
}

type Output struct {
	SourcePath      string
	DestinationPath string
	Kind            string
	Transform       string
	URL             string
	Data            []byte
	SHA256          string
	Size            int64
}

func Build(ctx context.Context, req Request) (Plan, error) {
	if err := validateRequest(req); err != nil {
		return Plan{}, err
	}
	outputs, err := PlanOutputs(ctx, req)
	if err != nil {
		return Plan{}, err
	}
	outputs, primaryURL, err := PlanLinks(req, outputs)
	if err != nil {
		return Plan{}, err
	}
	status, err := inspectDestination(ctx, req.DestinationBackend, req.DestinationBundlePath)
	if err != nil {
		return Plan{}, err
	}
	comparison := compareDestination(req, status)
	action, reason := actionForComparison(comparison, req.Transfer, req.Force)
	reconciliation := normalizeReconciliation(req.Reconciliation)
	stateMode := normalizeState(req.State).Mode
	plan := Plan{
		PipelineID:            req.PipelineID,
		DestinationID:         req.DestinationID,
		BundleID:              req.SourceBundle.Manifest.ID,
		BundlePath:            req.SourceBundle.RootRelativePath,
		DestinationBundlePath: req.DestinationBundlePath,
		PathMapping:           req.PathMapping,
		Action:                action,
		Reason:                reason,
		Force:                 action == ActionForceReplace,
		PrimaryURL:            primaryURL,
		StateMode:             stateMode,
		OwnerScope:            state.CurrentOwnerScope(req.PipelineID, req.DestinationID),
		Reconciliation:        reconciliation,
		Outputs:               outputs,
		ExistingState:         status.State,
		ExistingSharedRoot:    status.SharedRoot,
	}
	if stateMode == config.StateModeSharedRoot {
		sharedDetails, err := planSharedRootOwner(ctx, req, status, action, reconciliation, outputs)
		plan.OtherOwnerOutputs = sharedDetails.OtherOwnerOutputs
		plan.RetainedOwnerOutputs = sharedDetails.RetainedOwnerOutputs
		plan.OwnerOutputsToDelete = sharedDetails.OwnerOutputsToDelete
		plan.OwnerOutputsToWrite = sharedDetails.OwnerOutputsToWrite
		if err != nil {
			plan.Action = sharedDetails.Action
			plan.Reason = sharedDetails.Reason
			return plan, err
		}
	}
	if action == ActionFailConflict || action == ActionFailUnmanaged {
		return plan, fmt.Errorf("%s: %s", action, reason)
	}
	return plan, nil
}

func validateRequest(req Request) error {
	if req.PipelineID == "" {
		return fmt.Errorf("pipeline id is required")
	}
	if req.DestinationID == "" {
		return fmt.Errorf("destination id is required")
	}
	if req.SourceBackend == nil {
		return fmt.Errorf("source backend is required")
	}
	if req.DestinationBackend == nil {
		return fmt.Errorf("destination backend is required")
	}
	if err := config.ValidatePublishTransformPolicy(req.Publish, req.Transform); err != nil {
		return fmt.Errorf("publish/transform policy: %w", err)
	}
	switch normalizeReconciliation(req.Reconciliation).Mode {
	case config.ReconciliationModeReplace, config.ReconciliationModeMerge:
	default:
		return fmt.Errorf("reconciliation.mode must be %s or %s", config.ReconciliationModeReplace, config.ReconciliationModeMerge)
	}
	switch normalizeState(req.State).Mode {
	case config.StateModeSingleOwner, config.StateModeSharedRoot:
	default:
		return fmt.Errorf("state.mode must be %s or %s", config.StateModeSingleOwner, config.StateModeSharedRoot)
	}
	return nil
}

func normalizeReconciliation(policy config.ReconciliationPolicy) config.ReconciliationPolicy {
	if policy.Mode == "" {
		policy.Mode = config.ReconciliationModeReplace
	}
	return policy
}

func normalizeState(policy config.StatePolicy) config.StatePolicy {
	if policy.Mode == "" {
		policy.Mode = config.StateModeSingleOwner
	}
	return policy
}

func compareDestination(req Request, status state.DestinationStatus) state.Comparison {
	if normalizeState(req.State).Mode == config.StateModeSharedRoot {
		scope := state.CurrentOwnerScope(req.PipelineID, req.DestinationID)
		comparison := state.CompareSharedRootOwner(req.SourceBundle.Manifest, scope, status)
		if req.PathMapping != config.PathMappingFixed || comparison.Outcome != state.OutcomeDifferentSourceConflict {
			return comparison
		}
		destinationManifest, ok := sharedRootComparisonManifest(status, scope)
		if !ok {
			return comparison
		}
		if destinationManifest.Created.Before(req.SourceBundle.Manifest.Created) {
			return state.Comparison{Outcome: state.OutcomeDestinationOlder, Reason: "fixed destination source is older than selected source"}
		}
		if destinationManifest.Created.After(req.SourceBundle.Manifest.Created) {
			return state.Comparison{Outcome: state.OutcomeDestinationNewer, Reason: "fixed destination source is newer than selected source"}
		}
		return comparison
	}
	comparison := state.Compare(req.SourceBundle.Manifest, req.PipelineID, req.DestinationID, status)
	if req.PathMapping != config.PathMappingFixed || comparison.Outcome != state.OutcomeDifferentSourceConflict || status.State == nil {
		return comparison
	}
	destinationManifest := status.State.Source.Manifest
	if destinationManifest.Created.Before(req.SourceBundle.Manifest.Created) {
		return state.Comparison{Outcome: state.OutcomeDestinationOlder, Reason: "fixed destination source is older than selected source"}
	}
	if destinationManifest.Created.After(req.SourceBundle.Manifest.Created) {
		return state.Comparison{Outcome: state.OutcomeDestinationNewer, Reason: "fixed destination source is newer than selected source"}
	}
	return comparison
}

func sharedRootComparisonManifest(status state.DestinationStatus, scope state.OwnerScope) (bundle.Manifest, bool) {
	if status.SharedRoot != nil {
		return status.SharedRoot.SourceManifest(scope)
	}
	if status.State != nil && status.State.PipelineID == scope.PipelineID && status.State.DestinationID == scope.DestinationID {
		return status.State.Source.Manifest, true
	}
	return bundle.Manifest{}, false
}

type sharedRootPlanDetails struct {
	Action               Action
	Reason               string
	OtherOwnerOutputs    []state.SharedRootOutputFile
	RetainedOwnerOutputs []state.SharedRootOutputFile
	OwnerOutputsToDelete []state.SharedRootOutputFile
	OwnerOutputsToWrite  []Output
}

func planSharedRootOwner(ctx context.Context, req Request, status state.DestinationStatus, action Action, reconciliation config.ReconciliationPolicy, outputs []Output) (sharedRootPlanDetails, error) {
	scope := state.CurrentOwnerScope(req.PipelineID, req.DestinationID)
	details := sharedRootPlanDetails{Action: action}
	if !isWriteAction(action) {
		details.OtherOwnerOutputs = otherOwnerOutputs(status, scope)
		return details, nil
	}

	plannedPaths := outputPaths(outputs)
	if conflict, ok := sharedRootPathOwnershipConflict(status, scope, plannedPaths); ok {
		reason := fmt.Sprintf("destination output path %s is owned by %s/%s", conflict.Path, conflict.Owner.PipelineID, conflict.Owner.DestinationID)
		details.Action = ActionFailConflict
		details.Reason = reason
		return details, fmt.Errorf("%s: %s", ActionFailConflict, reason)
	}
	if err := rejectSharedRootUnmanagedCollisions(ctx, req.DestinationBackend, req.DestinationBundlePath, status, scope, plannedPaths); err != nil {
		details.Action = ActionFailUnmanaged
		details.Reason = err.Error()
		return details, fmt.Errorf("%s: %s", ActionFailUnmanaged, err)
	}

	details.OtherOwnerOutputs = otherOwnerOutputs(status, scope)
	ownerOutputs := currentOwnerOutputs(status, scope)
	planned := make(map[string]struct{}, len(plannedPaths))
	for _, path := range plannedPaths {
		planned[path] = struct{}{}
	}
	for _, output := range ownerOutputs {
		if _, exists := planned[output.Path]; exists {
			continue
		}
		if action == ActionReplaceOlder && reconciliation.Mode == config.ReconciliationModeReplace {
			details.OwnerOutputsToDelete = append(details.OwnerOutputsToDelete, output)
			continue
		}
		if action == ActionReplaceOlder && reconciliation.Mode == config.ReconciliationModeMerge {
			details.RetainedOwnerOutputs = append(details.RetainedOwnerOutputs, output)
		}
	}
	details.OwnerOutputsToWrite = append([]Output(nil), outputs...)
	return details, nil
}

func isWriteAction(action Action) bool {
	switch action {
	case ActionPublishNew, ActionReplaceOlder, ActionForceReplace:
		return true
	default:
		return false
	}
}

func outputPaths(outputs []Output) []string {
	paths := make([]string, 0, len(outputs))
	for _, output := range outputs {
		paths = append(paths, output.DestinationPath)
	}
	return paths
}

func sharedRootPathOwnershipConflict(status state.DestinationStatus, scope state.OwnerScope, paths []string) (state.PathOwnershipConflict, bool) {
	if status.SharedRoot != nil {
		return status.SharedRoot.PathOwnershipConflict(scope, paths)
	}
	return state.PathOwnershipConflict{}, false
}

func rejectSharedRootUnmanagedCollisions(ctx context.Context, backend storage.Backend, bundlePath string, status state.DestinationStatus, scope state.OwnerScope, paths []string) error {
	for _, path := range paths {
		if pathManagedBySharedRootStatus(status, scope, path) {
			continue
		}
		destinationPath, err := storage.Join(bundlePath, path)
		if err != nil {
			return err
		}
		if _, err := backend.Stat(ctx, destinationPath); err == nil {
			return fmt.Errorf("destination output path %s exists but is not managed by destination state", storage.DisplayPath(path))
		} else if !storage.IsNotFound(err) {
			return err
		}
	}
	return nil
}

func pathManagedBySharedRootStatus(status state.DestinationStatus, scope state.OwnerScope, path string) bool {
	if status.SharedRoot != nil {
		_, exists := status.SharedRoot.OutputOwner(path)
		return exists
	}
	if status.State != nil && status.State.PipelineID == scope.PipelineID && status.State.DestinationID == scope.DestinationID {
		_, exists := state.FindOutputByPath(status.State.Outputs, path)
		return exists
	}
	return false
}

func otherOwnerOutputs(status state.DestinationStatus, scope state.OwnerScope) []state.SharedRootOutputFile {
	if status.SharedRoot == nil {
		return nil
	}
	outputs := make([]state.SharedRootOutputFile, 0, len(status.SharedRoot.Outputs))
	for _, output := range status.SharedRoot.Outputs {
		if output.Owner != scope {
			outputs = append(outputs, output)
		}
	}
	return outputs
}

func currentOwnerOutputs(status state.DestinationStatus, scope state.OwnerScope) []state.SharedRootOutputFile {
	if status.SharedRoot != nil {
		outputs := make([]state.SharedRootOutputFile, 0, len(status.SharedRoot.Outputs))
		for _, output := range status.SharedRoot.Outputs {
			if output.Owner == scope {
				outputs = append(outputs, output)
			}
		}
		return outputs
	}
	if status.State != nil && status.State.PipelineID == scope.PipelineID && status.State.DestinationID == scope.DestinationID {
		outputs := make([]state.SharedRootOutputFile, 0, len(status.State.Outputs))
		for _, output := range status.State.Outputs {
			outputs = append(outputs, state.SharedRootOutputFile{
				Path:          output.Path,
				Kind:          output.Kind,
				SourcePath:    output.SourcePath,
				Transform:     output.Transform,
				URL:           output.URL,
				SHA256:        output.SHA256,
				Size:          output.Size,
				Owner:         scope,
				SourceID:      status.State.Source.Manifest.ID,
				SourceDigest:  status.State.Source.Manifest.Digest,
				SourceCreated: status.State.Source.Manifest.Created,
				CreatedAt:     output.CreatedAt,
				UpdatedAt:     output.UpdatedAt,
			})
		}
		return outputs
	}
	return nil
}

func actionForComparison(comparison state.Comparison, transfer config.TransferPolicy, force bool) (Action, string) {
	switch comparison.Outcome {
	case state.OutcomeDestinationAbsent:
		return ActionPublishNew, comparison.Reason
	case state.OutcomeDestinationUnmanaged:
		if force {
			return ActionForceReplace, "forced replacement of unmanaged destination content"
		}
		return ActionFailUnmanaged, comparison.Reason
	case state.OutcomeInvalidState:
		return ActionFailConflict, comparison.Reason
	case state.OutcomeIdentityMismatch, state.OutcomeSameCreatedConflict, state.OutcomeDifferentSourceConflict:
		if transfer.OnConflict == config.TransferActionReplace {
			if force {
				return ActionForceReplace, "forced replacement of conflicting destination state: " + comparison.Reason
			}
			return ActionFailConflict, "destination conflict replacement requires --force"
		}
		return ActionFailConflict, comparison.Reason
	case state.OutcomeSameSource:
		if transfer.OnDestinationSame == config.TransferActionFail {
			return ActionFailConflict, "destination matches source and transfer policy requires failure"
		}
		return ActionSkipSame, comparison.Reason
	case state.OutcomeDestinationOlder:
		if transfer.OnDestinationOlder == config.TransferActionFail {
			return ActionFailConflict, "destination is older and transfer policy requires failure"
		}
		return ActionReplaceOlder, comparison.Reason
	case state.OutcomeDestinationNewer:
		if transfer.OnDestinationNewer == config.TransferActionReplace {
			if force {
				return ActionForceReplace, "forced replacement of newer destination state"
			}
			return ActionFailConflict, "destination is newer and replacement requires --force"
		}
		if transfer.OnDestinationNewer == config.TransferActionFail {
			return ActionFailConflict, "destination is newer and transfer policy requires failure"
		}
		return ActionSkipDestinationNewer, comparison.Reason
	default:
		return ActionFailConflict, "unsupported comparison outcome"
	}
}