package consul

import (
	"context"
	"time"

	metrics "github.com/armon/go-metrics"
	log "github.com/hashicorp/go-hclog"

	"github.com/hashicorp/consul/api"
	"github.com/hashicorp/nomad/client/allocrunner/taskrunner/interfaces"
	"github.com/hashicorp/nomad/nomad/structs"
)

// heartbeater is the subset of consul agent functionality needed by script
// checks to heartbeat
type heartbeater interface {
	UpdateTTL(id, output, status string) error
}

// contextExec allows canceling a ScriptExecutor with a context.
type contextExec struct {
	// pctx is the parent context. A subcontext will be created with Exec's
	// timeout.
	pctx context.Context

	// exec to be wrapped in a context
	exec interfaces.ScriptExecutor
}

func newContextExec(ctx context.Context, exec interfaces.ScriptExecutor) *contextExec {
	return &contextExec{
		pctx: ctx,
		exec: exec,
	}
}

type execResult struct {
	buf  []byte
	code int
	err  error
}

// Exec a command until the timeout expires, the context is canceled, or the
// underlying Exec returns.
func (c *contextExec) Exec(timeout time.Duration, cmd string, args []string) ([]byte, int, error) {
	resCh := make(chan execResult, 1)

	// Don't trust the underlying implementation to obey timeout
	ctx, cancel := context.WithTimeout(c.pctx, timeout)
	defer cancel()

	go func() {
		output, code, err := c.exec.Exec(timeout, cmd, args)
		select {
		case resCh <- execResult{output, code, err}:
		case <-ctx.Done():
		}
	}()

	select {
	case res := <-resCh:
		return res.buf, res.code, res.err
	case <-ctx.Done():
		return nil, 0, ctx.Err()
	}
}

// scriptHandle is returned by scriptCheck.run by cancelling a scriptCheck and
// waiting for it to shutdown.
type scriptHandle struct {
	// cancel the script
	cancel func()
	exitCh chan struct{}
}

// wait returns a chan that's closed when the script exits
func (s *scriptHandle) wait() <-chan struct{} {
	return s.exitCh
}

// scriptCheck runs script checks via a ScriptExecutor and updates the
// appropriate check's TTL when the script succeeds.
type scriptCheck struct {
	allocID  string
	taskName string

	id    string
	check *structs.ServiceCheck
	exec  interfaces.ScriptExecutor
	agent heartbeater

	// lastCheckOk is true if the last check was ok; otherwise false
	lastCheckOk bool

	logger     log.Logger
	shutdownCh <-chan struct{}
}

// newScriptCheck creates a new scriptCheck. run() should be called once the
// initial check is registered with Consul.
func newScriptCheck(allocID, taskName, checkID string, check *structs.ServiceCheck,
	exec interfaces.ScriptExecutor, agent heartbeater, logger log.Logger,
	shutdownCh <-chan struct{}) *scriptCheck {

	logger = logger.ResetNamed("consul.checks").With("task", taskName, "alloc_id", allocID, "check", check.Name)
	return &scriptCheck{
		allocID:     allocID,
		taskName:    taskName,
		id:          checkID,
		check:       check,
		exec:        exec,
		agent:       agent,
		lastCheckOk: true, // start logging on first failure
		logger:      logger,
		shutdownCh:  shutdownCh,
	}
}

// run this script check and return its cancel func. If the shutdownCh is
// closed the check will be run once more before exiting.
func (s *scriptCheck) run() *scriptHandle {
	ctx, cancel := context.WithCancel(context.Background())
	exitCh := make(chan struct{})

	// Wrap the original ScriptExecutor in one that obeys context
	// cancelation.
	ctxExec := newContextExec(ctx, s.exec)

	go func() {
		defer close(exitCh)
		timer := time.NewTimer(0)
		defer timer.Stop()
		for {
			// Block until check is removed, Nomad is shutting
			// down, or the check interval is up
			select {
			case <-ctx.Done():
				// check has been removed
				return
			case <-s.shutdownCh:
				// unblock but don't exit until after we heartbeat once more
			case <-timer.C:
				timer.Reset(s.check.Interval)
			}
			metrics.IncrCounter([]string{"client", "consul", "script_runs"}, 1)

			// Execute check script with timeout
			output, code, err := ctxExec.Exec(s.check.Timeout, s.check.Command, s.check.Args)
			switch err {
			case context.Canceled:
				// check removed during execution; exit
				return
			case context.DeadlineExceeded:
				metrics.IncrCounter([]string{"client", "consul", "script_timeouts"}, 1)
				// If no error was returned, set one to make sure the task goes critical
				if err == nil {
					err = context.DeadlineExceeded
				}

				// Log deadline exceeded every time as it's a
				// distinct issue from checks returning
				// failures
				s.logger.Warn("check timed out", "timeout", s.check.Timeout)
			}

			state := api.HealthCritical
			switch code {
			case 0:
				state = api.HealthPassing
			case 1:
				state = api.HealthWarning
			}

			var outputMsg string
			if err != nil {
				state = api.HealthCritical
				outputMsg = err.Error()
			} else {
				outputMsg = string(output)
			}

			// Actually heartbeat the check
			err = s.agent.UpdateTTL(s.id, outputMsg, state)
			select {
			case <-ctx.Done():
				// check has been removed; don't report errors
				return
			default:
			}

			if err != nil {
				if s.lastCheckOk {
					s.lastCheckOk = false
					s.logger.Warn("updating check failed", "error", err)
				} else {
					s.logger.Debug("updating check still failing", "error", err)
				}

			} else if !s.lastCheckOk {
				// Succeeded for the first time or after failing; log
				s.lastCheckOk = true
				s.logger.Info("updating check succeeded")
			}

			select {
			case <-s.shutdownCh:
				// We've been told to exit and just heartbeated so exit
				return
			default:
			}
		}
	}()
	return &scriptHandle{cancel: cancel, exitCh: exitCh}
}