// Package pi implements host-side lifecycle operations for the Pi bundled in core.
package pi

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"time"
)

const stateFileVersion = 1

// Phase describes the durable point reached by a Pi update.
type Phase string

const (
	PhasePreflight  Phase = "preflight"
	PhaseBuilding   Phase = "building"
	PhaseRecreated  Phase = "recreated"
	PhaseVerified   Phase = "verified"
	PhaseRolledBack Phase = "rolled_back"
	PhaseFailed     Phase = "failed"
	PhaseNoop       Phase = "noop"
)

// Image is the non-secret recovery identity of a core image and its mounted volume names.
type Image struct {
	ID               string   `json:"id"`
	Reference        string   `json:"reference"`
	Volumes          []string `json:"volumes"`
	ConfigurationSHA string   `json:"configuration_sha256,omitempty"`
}

// Target records the immutable input selected by the operator. Source is either build or a
// digest-pinned image reference; it intentionally never contains credentials.
type Target struct {
	Version string `json:"version"`
	Source  string `json:"source"`
}

// State is recovery metadata stored below the installation project. It never stores environment
// values, secret paths, credentials, or command output.
type State struct {
	Version   int       `json:"version"`
	Phase     Phase     `json:"phase"`
	UpdatedAt time.Time `json:"updated_at"`
	Target    Target    `json:"target,omitempty"`
	Previous  Image     `json:"previous"`
	Candidate Image     `json:"candidate,omitempty"`
	Error     string    `json:"error,omitempty"`
}

func readState(path string) (State, error) {
	contents, err := os.ReadFile(path)
	if err != nil {
		return State{}, err
	}
	var state State
	if err := json.Unmarshal(contents, &state); err != nil {
		return State{}, errors.New("update recovery state is invalid")
	}
	if state.Version != stateFileVersion || state.Previous.ID == "" || state.Previous.Reference == "" {
		return State{}, errors.New("update recovery state is incomplete")
	}
	return state, nil
}

func writeState(path string, state State) error {
	if state.Previous.ID == "" || state.Previous.Reference == "" {
		return errors.New("refusing to write incomplete update recovery state")
	}
	state.Version = stateFileVersion
	state.UpdatedAt = time.Now().UTC()
	contents, err := json.MarshalIndent(state, "", "  ")
	if err != nil {
		return fmt.Errorf("encode update recovery state: %w", err)
	}
	contents = append(contents, '\n')
	directory := filepath.Dir(path)
	if err := os.MkdirAll(directory, 0o700); err != nil {
		return errors.New("could not create update recovery directory")
	}
	temporary, err := os.CreateTemp(directory, ".update-state-*.tmp")
	if err != nil {
		return errors.New("could not write update recovery state")
	}
	temporaryName := temporary.Name()
	defer os.Remove(temporaryName)
	if err := temporary.Chmod(0o600); err != nil {
		temporary.Close()
		return errors.New("could not protect update recovery state")
	}
	if _, err := temporary.Write(contents); err != nil {
		temporary.Close()
		return errors.New("could not write update recovery state")
	}
	if err := temporary.Close(); err != nil {
		return errors.New("could not write update recovery state")
	}
	if err := os.Rename(temporaryName, path); err != nil {
		return errors.New("could not finalize update recovery state")
	}
	return nil
}