package agents

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"path/filepath"
	"strings"
	"time"

	"g.fc.run/misc/byre/internal/api"
	"g.fc.run/misc/byre/internal/git"
	"g.fc.run/misc/byre/internal/mcp"
	"g.fc.run/misc/byre/internal/store"
	"g.fc.run/misc/byre/internal/todo"
)

func (m *Manager) CreateTask(ctx context.Context, project api.Project, title, createdBy, base, actor string) (api.Task, error) {
	return m.createTask(ctx, project, api.Task{Title: title, CreatedBy: createdBy}, base, actor)
}

func (m *Manager) StartTodo(ctx context.Context, project api.Project, creator api.User, title, model, actor string) (api.Task, error) {
	if creator.GitName == "" || creator.GitEmail == "" {
		return api.Task{}, ErrNoGitIdentity
	}

	src, found, err := git.ReadFile(project.RepoPath, project.DefaultBranch, todo.File)
	if err != nil {
		return api.Task{}, err
	}
	if !found {
		return api.Task{}, fmt.Errorf("%w: %s has no %s", store.ErrNotFound, project.DefaultBranch, todo.File)
	}
	item, found := todo.Find(todo.Parse(src), title)
	if !found {
		return api.Task{}, fmt.Errorf("%w: %s on %s has no item %q", store.ErrNotFound, todo.File, project.DefaultBranch, title)
	}

	tasks, err := m.store.ListTasks(ctx, project.Id)
	if err != nil {
		return api.Task{}, err
	}
	for _, t := range tasks {
		if t.Status == api.TaskStatusActive && t.TodoItem != nil && *t.TodoItem == title {
			return api.Task{}, fmt.Errorf("%w: task %s is already working on %q", ErrConflict, t.Id, title)
		}
	}

	task, err := m.createTask(ctx, project, api.Task{Title: item.Title, CreatedBy: creator.Login, TodoItem: &item.Title}, project.DefaultBranch, actor)
	if err != nil {
		return api.Task{}, err
	}

	_, err = m.create(ctx, task, creator, todoPrompt(item), model, actor, nil)
	if err != nil {
		return api.Task{}, fmt.Errorf("task %s created, but its agent did not start: %w", task.Id, err)
	}
	return task, nil
}

func todoPrompt(item api.TodoItem) string {
	return fmt.Sprintf("Work on this item from %[1]s at the repo root:\n\n%[2]s\n\nWhen the work is done, remove this item from %[1]s in this worktree, so the removal lands in the same merge as the work.",
		todo.File, todo.Markdown(item))
}

func (m *Manager) createTask(ctx context.Context, project api.Project, t api.Task, base, actor string) (api.Task, error) {
	t.Id = store.NewID()
	t.ProjectId = project.Id
	if t.MergeTitle == "" {
		t.MergeTitle = t.Title
	}
	t.Branch = "byre/" + t.Id
	t.WorktreePath = filepath.Join(m.worktreeRoot, project.Id, t.Id)
	t.Status = api.TaskStatusActive
	t.CreatedAt = time.Now().UTC()

	var err error
	t.BaseRef, err = git.AddWorktree(project.RepoPath, t.WorktreePath, t.Branch, base)
	if err != nil {
		return api.Task{}, err
	}

	err = m.store.CreateTask(ctx, t, actor)
	if err != nil {
		return api.Task{}, err
	}
	return t, nil
}

type createTaskArgs struct {
	Title  string `json:"title"`
	Prompt string `json:"prompt"`
	Base   string `json:"base"`
	Model  string `json:"model"`
}

func (m *Manager) createTaskTool(l *live) mcp.Tool {
	return mcp.Tool{
		Name: "create_task",
		Description: "Create a new byre task in this project, with its own branch and worktree, and start an agent on it with prompt as its first message. " +
			"Use it to run independent pieces of work in parallel. The new agent sees nothing of your context, so the prompt must be a complete brief. " +
			"base picks the starting commit: default_branch starts from the project's default branch; this_task starts from this task's HEAD, " +
			"which includes your committed work but not uncommitted edits (byre commits at the end of each turn). " +
			"Returns at once with the new task's id; the new agent runs on its own.",
		InputSchema: json.RawMessage(`{
			"type": "object",
			"properties": {
				"title": {"type": "string", "description": "Short task title, shown in the task list."},
				"prompt": {"type": "string", "description": "The new agent's first message: a complete, self-contained brief."},
				"base": {"type": "string", "enum": ["default_branch", "this_task"]},
				"model": {"type": "string", "description": "Model for the new agent. Defaults to this session's model."}
			},
			"required": ["title", "prompt", "base"]
		}`),
		Handler: func(ctx context.Context, raw json.RawMessage) (string, error) {
			return m.createTaskFromAgent(ctx, l, raw)
		},
	}
}

func (m *Manager) createTaskFromAgent(ctx context.Context, l *live, raw json.RawMessage) (string, error) {
	args := createTaskArgs{}
	err := json.Unmarshal(raw, &args)
	if err != nil {
		return "", fmt.Errorf("malformed create_task call: %w", err)
	}

	if strings.TrimSpace(args.Title) == "" || strings.TrimSpace(args.Prompt) == "" {
		return "", errors.New("title and prompt are required")
	}

	sess, err := m.store.GetSession(ctx, l.id)
	if err != nil {
		return "", err
	}
	project, err := m.store.GetProject(ctx, l.projectID)
	if err != nil {
		return "", err
	}
	creator, err := m.store.GetUser(ctx, sess.CreatedBy)
	if err != nil {
		return "", err
	}

	base := ""
	switch args.Base {
	case "default_branch":
		base = project.DefaultBranch
	case "this_task":
		base, err = git.Head(l.dir)
		if err != nil {
			return "", err
		}
	default:
		return "", fmt.Errorf("base must be default_branch or this_task, not %q", args.Base)
	}

	model := args.Model
	if model == "" {
		model = sess.Model
	}

	task, err := m.CreateTask(ctx, project, args.Title, creator.Login, base, creator.Login)
	if err != nil {
		return "", err
	}

	_, err = m.create(ctx, task, creator, args.Prompt, model, agentActor, nil)
	if err != nil {
		return "", fmt.Errorf("task %s created, but its agent did not start: %w", task.Id, err)
	}

	return fmt.Sprintf("Task %s %q created from %s and its agent started.", task.Id, task.Title, task.BaseRef), nil
}