// Package laniakea provides a system for managing background and one-time
// runner functions that operate on a Bot instance, with support for
// asynchronous execution, timeouts, and lifecycle control.
//
// Runners are used for periodic tasks (e.g., cleanup, stats updates) or
// one-time initialization logic. They are executed via Bot.ExecRunners().
//
// Important: Runners are not thread-safe for concurrent modification.
// Builder methods (Onetime, Async, Timeout) must be called sequentially
// and only before Execute().
package laniakea

import (
	"time"
)

// RunnerFn is the function type for a runner. It receives a pointer to
// the Bot and returns an error if execution fails.
type RunnerFn[T DbContext] func(*Bot[T]) error

// Runner represents a configurable background or one-time task to be
// executed by a Bot.
//
// Runners are configured using builder methods: Onetime(), Async(), Timeout().
// Once Execute() is called, the Runner should not be modified.
//
// Execution semantics:
//   - onetime=true, async=false: Run once synchronously (blocks).
//   - onetime=true, async=true:  Run once in a goroutine (non-blocking).
//   - onetime=false, async=true: Run repeatedly in a goroutine with timeout.
//   - onetime=false, async=false: Invalid configuration — ignored with warning.
type Runner[T DbContext] struct {
	name    string        // Human-readable name for logging
	onetime bool          // If true, runs once; if false, runs periodically
	async   bool          // If true, runs in a goroutine; else, runs synchronously
	timeout time.Duration // Duration to wait between periodic executions (ignored if onetime=true)
	fn      RunnerFn[T]   // The function to execute
}

// NewRunner creates a new Runner with the given name and function.
// By default, the Runner is configured as async=true (non-blocking).
//
// Builder methods (Onetime, Async, Timeout) can be chained to customize behavior.
// DO NOT call builder methods concurrently or after Execute().
func NewRunner[T DbContext](name string, fn RunnerFn[T]) *Runner[T] {
	return &Runner[T]{
		name:    name,
		fn:      fn,
		async:   true, // Default: run asynchronously
		timeout: 0,    // Default: no timeout (ignored if onetime=true)
	}
}

// Onetime sets whether the runner executes once or repeatedly.
// If true, the runner runs only once.
// If false, the runner runs in a loop with the configured timeout.
func (r *Runner[T]) Onetime(onetime bool) *Runner[T] {
	r.onetime = onetime
	return r
}

// Async sets whether the runner executes synchronously or asynchronously.
// If true, the runner runs in a goroutine (non-blocking).
// If false, the runner blocks the caller during execution.
//
// Note: If onetime=false and async=false, the runner will be skipped with a warning.
func (r *Runner[T]) Async(async bool) *Runner[T] {
	r.async = async
	return r
}

// Timeout sets the duration to wait between repeated executions for
// non-onetime runners.
//
// If onetime=true, this value is ignored.
// If onetime=false and async=true, this timeout determines the sleep interval
// between loop iterations.
//
// A zero value (time.Duration(0)) is allowed but may trigger a warning
// if used with a background (non-onetime) async runner.
func (r *Runner[T]) Timeout(timeout time.Duration) *Runner[T] {
	r.timeout = timeout
	return r
}

// ExecRunners executes all runners registered on the Bot.
//
// It logs warnings for misconfigured runners:
//   - Sync, non-onetime runners are skipped (invalid configuration).
//   - Background (non-onetime, async) runners without a timeout trigger a warning.
//
// Execution logic:
//   - onetime + async: Runs once in a goroutine.
//   - onetime + sync:  Runs once synchronously; warns if slower than 2 seconds.
//   - !onetime + async: Runs in an infinite loop with timeout between iterations.
//   - !onetime + sync: Skipped with warning.
//
// This method is typically called once during bot startup.
func (bot *Bot[T]) ExecRunners() {
	bot.logger.Infoln("Executing runners...")
	for _, runner := range bot.runners {
		// Validate configuration
		if !runner.onetime && !runner.async {
			bot.logger.Warnf("Runner %s not onetime, but sync — skipping\n", runner.name)
			continue
		}
		if !runner.onetime && runner.async && runner.timeout == 0 {
			bot.logger.Warnf("Background runner \"%s\" has no timeout — may cause tight loop\n", runner.name)
		}

		if runner.onetime && runner.async {
			// One-time async: fire and forget
			go func(r Runner[T]) {
				err := r.fn(bot)
				if err != nil {
					bot.logger.Warnf("Runner %s failed: %s\n", r.name, err)
				}
			}(runner)
		} else if runner.onetime && !runner.async {
			// One-time sync: block until done
			t := time.Now()
			err := runner.fn(bot)
			if err != nil {
				bot.logger.Warnf("Runner %s failed: %s\n", runner.name, err)
			}
			elapsed := time.Since(t)
			if elapsed > time.Second*2 {
				bot.logger.Warnf("Runner %s too slow. Elapsed time %v >= 2s\n", runner.name, elapsed)
			}
		} else if !runner.onetime && runner.async {
			// Background loop: periodic execution
			go func(r Runner[T]) {
				for {
					err := r.fn(bot)
					if err != nil {
						bot.logger.Warnf("Runner %s failed: %s\n", r.name, err)
					}
					time.Sleep(r.timeout)
				}
			}(runner)
		}
		// Note: !onetime && !async is already skipped above
	}
}