// Package taskassignment defines the durable handoff between the scheduler and workers.
package taskassignment

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"slices"

	"gitea.dev/actionslib/pkg/model"
	runnerv1 "gitea.dev/actionslib/runner/v1"
	"google.golang.org/protobuf/proto"

	"git.ddupan.top/panxiao81/gitea-dynamic-runner/internal/taskidentity"
)

const wireVersion = 1

type Backend string

const (
	BackendPod Backend = "pod"
	BackendVM  Backend = "vm"
)

// Assignment is the only document persisted in the handoff queue.
type Assignment struct {
	ID       string
	Backend  Backend
	Task     *runnerv1.Task
	Identity taskidentity.Identity
}

type envelope struct {
	Version  int                   `json:"version"`
	ID       string                `json:"id"`
	Backend  Backend               `json:"backend"`
	Task     []byte                `json:"task"`
	Identity taskidentity.Identity `json:"identity"`
}

// New derives all trusted assignment fields from the task fetched from Gitea.
func New(task *runnerv1.Task, trustDomain string) (Assignment, error) {
	if task == nil || task.GetId() <= 0 {
		return Assignment{}, errors.New("positive Gitea task ID is required")
	}
	identity, err := taskidentity.FromTask(task, trustDomain)
	if err != nil {
		return Assignment{}, err
	}
	backend, err := backendFromTask(task)
	if err != nil {
		return Assignment{}, err
	}
	return Assignment{
		ID:       fmt.Sprintf("gitea-task-%d", task.GetId()),
		Backend:  backend,
		Task:     task,
		Identity: identity,
	}, nil
}

func backendFromTask(task *runnerv1.Task) (Backend, error) {
	workflow, err := model.ReadWorkflow(bytes.NewReader(task.GetWorkflowPayload()))
	if err != nil {
		return "", fmt.Errorf("parse task workflow for backend: %w", err)
	}
	jobIDs := workflow.GetJobIDs()
	if len(jobIDs) != 1 || workflow.GetJob(jobIDs[0]) == nil {
		return "", fmt.Errorf("task workflow must contain exactly one non-empty job")
	}
	labels := workflow.GetJob(jobIDs[0]).RunsOnLabels()
	if !slices.Contains(labels, "self-hosted") {
		return "", fmt.Errorf("task runs-on labels must include self-hosted: %v", labels)
	}
	hasPod := slices.Contains(labels, string(BackendPod))
	hasVM := slices.Contains(labels, string(BackendVM))
	if hasPod == hasVM {
		return "", fmt.Errorf("task runs-on labels must select exactly one of pod or vm: %v", labels)
	}
	if hasPod {
		return BackendPod, nil
	}
	return BackendVM, nil
}

// Marshal encodes a versioned assignment. Protobuf preserves the exact Gitea task.
func Marshal(assignment Assignment) ([]byte, error) {
	if assignment.Task == nil {
		return nil, errors.New("assignment task is required")
	}
	task, err := proto.Marshal(assignment.Task)
	if err != nil {
		return nil, fmt.Errorf("marshal Gitea task: %w", err)
	}
	return json.Marshal(envelope{
		Version: wireVersion,
		ID:      assignment.ID, Backend: assignment.Backend,
		Task: task, Identity: assignment.Identity,
	})
}

// Unmarshal re-derives trusted fields instead of trusting duplicated queue metadata.
func Unmarshal(data []byte, trustDomain string) (Assignment, error) {
	var wire envelope
	if err := json.Unmarshal(data, &wire); err != nil {
		return Assignment{}, fmt.Errorf("decode assignment: %w", err)
	}
	if wire.Version != wireVersion {
		return Assignment{}, fmt.Errorf("unsupported assignment version %d", wire.Version)
	}
	task := new(runnerv1.Task)
	if err := proto.Unmarshal(wire.Task, task); err != nil {
		return Assignment{}, fmt.Errorf("unmarshal Gitea task: %w", err)
	}
	canonical, err := New(task, trustDomain)
	if err != nil {
		return Assignment{}, err
	}
	if wire.ID != canonical.ID || wire.Backend != canonical.Backend || wire.Identity != canonical.Identity {
		return Assignment{}, errors.New("assignment metadata does not match its Gitea task")
	}
	return canonical, nil
}