// Cthulhu screen reader.
// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

package lifecycle

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
)

type State string

const (
	StateNew      State = "New"
	StateStarting State = "Starting"
	StateRunning  State = "Running"
	StateStopping State = "Stopping"
	StateStopped  State = "Stopped"
	StateFailed   State = "Failed"
)

type Service struct {
	Name  string
	Start func(context.Context) error
	Stop  func(context.Context) error
}

type Runner struct {
	state    State
	services []Service
	started  []int
	logger   *slog.Logger
}

func New(services ...Service) (*Runner, error) {
	return NewWithLogger(nil, services...)
}

func NewWithLogger(logger *slog.Logger, services ...Service) (*Runner, error) {
	names := make(map[string]struct{}, len(services))
	for index, service := range services {
		switch {
		case service.Name == "":
			return nil, fmt.Errorf("service %d has no name", index)
		case service.Start == nil:
			return nil, fmt.Errorf("service %q has no start function", service.Name)
		case service.Stop == nil:
			return nil, fmt.Errorf("service %q has no stop function", service.Name)
		}
		if _, exists := names[service.Name]; exists {
			return nil, fmt.Errorf("duplicate service name %q", service.Name)
		}
		names[service.Name] = struct{}{}
	}
	return &Runner{
		state:    StateNew,
		services: append([]Service(nil), services...),
		logger:   logger,
	}, nil
}

func (runner *Runner) State() State {
	return runner.state
}

func (runner *Runner) Start(ctx context.Context) error {
	if ctx == nil {
		return errors.New("lifecycle start requires a non-nil context")
	}
	switch runner.state {
	case StateNew:
	case StateRunning, StateStarting, StateStopping, StateStopped, StateFailed:
		return fmt.Errorf("cannot start from state %s", runner.state)
	}

	runner.state = StateStarting
	for index, service := range runner.services {
		if err := ctx.Err(); err != nil {
			return runner.failStartup(fmt.Errorf("start %q canceled: %w", service.Name, err))
		}
		if err := service.Start(ctx); err != nil {
			return runner.failStartup(fmt.Errorf("start %q: %w", service.Name, err))
		}
		runner.started = append(runner.started, index)
	}
	runner.state = StateRunning
	return nil
}

func (runner *Runner) Stop(ctx context.Context) error {
	if ctx == nil {
		return errors.New("lifecycle stop requires a non-nil context")
	}
	switch runner.state {
	case StateNew:
		runner.state = StateStopped
		return nil
	case StateRunning:
	case StateStopped:
		return nil
	case StateStarting, StateStopping, StateFailed:
		return fmt.Errorf("cannot stop from state %s", runner.state)
	}

	runner.state = StateStopping
	stopError := runner.stopStartedServices(ctx)
	runner.state = StateStopped
	return stopError
}

func (runner *Runner) failStartup(startError error) error {
	runner.state = StateFailed
	runner.state = StateStopping
	stopError := runner.stopStartedServices(context.Background())
	runner.state = StateStopped
	return errors.Join(startError, stopError)
}

func (runner *Runner) stopStartedServices(ctx context.Context) error {
	var stopErrors []error
	for index := len(runner.started) - 1; index >= 0; index-- {
		serviceIndex := runner.started[index]
		service := runner.services[serviceIndex]
		if runner.logger != nil {
			runner.logger.Debug("lifecycle service stopping", "service", service.Name)
		}
		if err := service.Stop(ctx); err != nil {
			stopErrors = append(stopErrors, fmt.Errorf("stop %q: %w", service.Name, err))
			if runner.logger != nil {
				runner.logger.Warn("lifecycle service stop failed", "service", service.Name, "error", err)
			}
		} else if runner.logger != nil {
			runner.logger.Debug("lifecycle service stopped", "service", service.Name)
		}
	}
	runner.started = nil
	return errors.Join(stopErrors...)
}