package publish

import (
	"context"
	"errors"

	"go.maximumdirect.net/releasekit/internal/git"
)

// Evidence is the identity captured when one publication was attempted.
type Evidence struct {
	RepositoryDir   string `json:"repository_dir,omitempty"`
	ModuleDir       string `json:"module_dir,omitempty"`
	ModulePath      string `json:"module_path,omitempty"`
	Version         string `json:"version,omitempty"`
	Tag             string `json:"tag,omitempty"`
	CandidateCommit string `json:"candidate_commit,omitempty"`
	TagObject       string `json:"tag_object,omitempty"`
	Endpoint        string `json:"endpoint,omitempty"`
	Remote          string `json:"remote,omitempty"`
	RecordedAt      string `json:"recorded_at,omitempty"`
}

// Observation combines the original evidence with authoritative remote state.
type Observation struct {
	Evidence          Evidence
	State             State
	ObservedTagObject string
	ObservedCommit    string
}

// RecoveryError describes why a later publication observation is unresolved.
type RecoveryError struct {
	Kind          string
	RecordPath    string
	MissingFields []string
	cause         error
}

func (e *RecoveryError) Error() string {
	if e == nil {
		return ""
	}
	message := "publication recovery " + e.Kind
	if e.cause != nil {
		return message + ": " + git.DisplayError(e.cause).Error()
	}
	return message
}
func (e *RecoveryError) Unwrap() error {
	if e == nil {
		return nil
	}
	return e.cause
}

func classify(evidence Evidence, remoteTag git.RemoteRef) (Observation, error) {
	result := Observation{Evidence: evidence, State: Unknown, ObservedTagObject: remoteTag.Object, ObservedCommit: remoteTag.Peeled}
	missing := []string{}
	if evidence.Endpoint == "" {
		missing = append(missing, "endpoint")
	}
	if evidence.Tag == "" {
		missing = append(missing, "tag")
	}
	if len(missing) > 0 {
		return result, &RecoveryError{Kind: "missing_evidence", MissingFields: missing}
	}
	if remoteTag.State == git.RefAbsent {
		result.State = NotPublished
		return result, nil
	}
	if evidence.TagObject == "" {
		return result, &RecoveryError{Kind: "missing_evidence", MissingFields: []string{"tag_object"}}
	}
	if remoteTag.State != git.RefPresent {
		return result, &RecoveryError{Kind: "inconsistent_observation", cause: git.ErrRemoteStateUnreadable}
	}
	if !git.EqualObjectID(remoteTag.Object, evidence.TagObject) {
		result.State = Conflict
		return result, nil
	}
	if remoteTag.Peeled != "" {
		if evidence.CandidateCommit == "" {
			return result, &RecoveryError{Kind: "missing_evidence", MissingFields: []string{"candidate_commit"}}
		}
		if !git.EqualObjectID(remoteTag.Peeled, evidence.CandidateCommit) {
			result.State = Conflict
			return result, nil
		}
	}
	result.State = Published
	return result, nil
}

func observe(ctx context.Context, evidence Evidence) (Observation, error) {
	if err := ctx.Err(); err != nil {
		return Observation{Evidence: evidence, State: Unknown}, &RecoveryError{Kind: "canceled", cause: err}
	}
	if evidence.Endpoint == "" || evidence.Tag == "" {
		return classify(evidence, git.RemoteRef{})
	}
	if evidence.TagObject != "" && !git.ValidObjectID(evidence.TagObject) {
		return Observation{Evidence: evidence, State: Unknown}, &RecoveryError{Kind: "invalid_evidence"}
	}
	if evidence.CandidateCommit != "" && !git.ValidObjectID(evidence.CandidateCommit) {
		return Observation{Evidence: evidence, State: Unknown}, &RecoveryError{Kind: "invalid_evidence"}
	}
	valid, err := git.ValidateTagRef(ctx, evidence.RepositoryDir, evidence.Tag)
	if err != nil {
		return Observation{Evidence: evidence, State: Unknown}, observationFailure(ctx, err)
	}
	if !valid {
		return Observation{Evidence: evidence, State: Unknown}, &RecoveryError{Kind: "invalid_evidence"}
	}
	endpoint, err := git.ObserveEndpoint(ctx, evidence.RepositoryDir, evidence.Endpoint, evidence.Remote)
	if err != nil {
		return Observation{Evidence: evidence, State: Unknown}, observationFailure(ctx, err)
	}
	ref, err := endpoint.QueryTag(ctx, evidence.RepositoryDir, evidence.Tag)
	if err != nil {
		return Observation{Evidence: evidence, State: Unknown}, observationFailure(ctx, err)
	}
	result, err := classify(evidence, ref)
	if err != nil && ctx.Err() != nil {
		return result, &RecoveryError{Kind: "canceled", cause: ctx.Err()}
	}
	return result, err
}

func observationFailure(ctx context.Context, err error) *RecoveryError {
	kind := "remote_observation"
	switch {
	case errors.Is(err, git.ErrEndpointChanged):
		kind = "endpoint_changed"
	case errors.Is(err, git.ErrTransportConfiguration):
		kind = "transport_configuration"
	}
	return recoveryFailure(ctx, kind, err)
}

// Reconcile observes the recorded endpoint and classifies its exact tag.
func Reconcile(ctx context.Context, evidence Evidence) (Observation, error) {
	return observe(ctx, evidence)
}

// recoveryFailure classifies failed operations while preserving caller cancellation.
func recoveryFailure(ctx context.Context, kind string, err error) *RecoveryError {
	if contextErr := ctx.Err(); contextErr != nil {
		return &RecoveryError{Kind: "canceled", cause: contextErr}
	}
	return &RecoveryError{Kind: kind, cause: err}
}