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
	Publish               config.PublishPolicy
	Transform             config.Transform
	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
	Action                Action
	Reason                string
	Force                 bool
	Outputs               []Output
	ExistingState         *state.DistributorState
}

type Output struct {
	SourcePath      string
	DestinationPath string
	Kind            string
	Transform       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
	}
	status, err := inspectDestination(ctx, req.DestinationBackend, req.DestinationBundlePath)
	if err != nil {
		return Plan{}, err
	}
	comparison := state.Compare(req.SourceBundle.Manifest, req.PipelineID, req.DestinationID, status)
	action, reason := actionForComparison(comparison, req.Transfer, req.Force)
	plan := Plan{
		PipelineID:            req.PipelineID,
		DestinationID:         req.DestinationID,
		BundleID:              req.SourceBundle.Manifest.ID,
		BundlePath:            req.SourceBundle.RootRelativePath,
		DestinationBundlePath: req.DestinationBundlePath,
		Action:                action,
		Reason:                reason,
		Force:                 action == ActionForceReplace,
		Outputs:               outputs,
		ExistingState:         status.State,
	}
	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)
	}
	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"
	}
}