package commandkit

import (
	"context"
	"errors"
	"fmt"
	"io"

	internalcobra "gitea.maximumdirect.net/eric/CommandKit/internal/cobra"
	commandmeta "gitea.maximumdirect.net/eric/CommandKit/internal/commandmeta"
)

// Execute parses and dispatches one invocation. args excludes the executable
// name. Supplied values are converted before command input construction; help
// does not construct caller inputs or run acquisition callbacks. CommandKit
// writes diagnostics to streams.Err and leaves process exit to the caller. A
// nil context returns an operational failure, and nil streams are replaced with
// io.Discard.
func (a *App) Execute(ctx context.Context, args []string, streams Streams) Outcome {
	if ctx == nil {
		return a.present(Failure(errors.New("invocation context must not be nil")), nil, streams)
	}
	streams = normalizeStreams(streams)
	current := newExecution(a, ctx, streams)
	routedSnapshot := current.snapshot
	current.route = resolveEnteredRoute(args, routedSnapshot)
	parsed := current.parse(current.route.args)
	if parsed.Failure != nil {
		return current.present(Usage(errors.New(parsed.Failure.Message)), parsed.Path)
	}
	if current.route.kind == routeDiscovery {
		if parsed.HelpRequested {
			return current.present(current.renderHelp(parsed.Path), clonePath(current.route.enteredPath))
		}
		entered := current.route.enteredPath.String()
		return current.present(Usage(fmt.Errorf("incomplete command path %q; use %q --help", entered, entered)), clonePath(current.route.enteredPath))
	}
	payload, ok := routedSnapshot.runners[parsed.Key]
	if !ok || payload == nil {
		return current.present(current.renderHelp(parsed.Path), parsed.Path)
	}
	if parsed.HelpRequested || !payload.hasRun() {
		if _, err := payload.prepare(parsed.FlagValues, parsed.Operands, false); err != nil {
			return current.present(Usage(err), parsed.Path)
		}
		return current.present(current.renderHelp(parsed.Path), parsed.Path)
	}
	run, err := payload.prepare(parsed.FlagValues, parsed.Operands, true)
	if err != nil {
		return current.present(Usage(err), parsed.Path)
	}
	return current.present(run(current), parsed.Path)
}

type execution struct {
	app      *App
	ctx      context.Context
	streams  Streams
	options  commandmeta.ParseOptions
	snapshot *routingSnapshot
	session  *internalcobra.Session
	route    routeResult
}

type commandExecution struct {
	invocation            Invocation
	renderHelpTargetsFunc func([]string) Outcome
}

func (current *execution) commandContext() commandExecution {
	return commandExecution{
		invocation:            current.invocation(),
		renderHelpTargetsFunc: current.renderHelpTargets,
	}
}

func (current *execution) invocation() Invocation {
	return Invocation{
		Context:       current.ctx,
		Streams:       current.streams,
		enteredPath:   current.route.enteredPath.String(),
		canonicalPath: current.route.canonicalPath.String(),
	}
}

func (current commandExecution) renderHelpTargets(targets []string) Outcome {
	return current.renderHelpTargetsFunc(targets)
}

func newExecution(app *App, ctx context.Context, streams Streams) *execution {
	current := &execution{
		app:     app,
		ctx:     ctx,
		streams: streams,
		options: commandmeta.ParseOptions{Context: ctx, Out: streams.Out, Err: streams.Err},
	}
	if app != nil {
		current.snapshot = app.routeSnapshot()
	}
	return current
}

func (current *execution) parse(args []string) commandmeta.Result {
	if current.app == nil {
		return commandmeta.Result{Failure: &commandmeta.Failure{Message: "cannot parse commands on a nil app"}}
	}
	if current.session == nil {
		current.prepareSession()
	}
	return current.session.Parse(args)
}

func (current *execution) prepareSession() {
	if current.app == nil {
		return
	}
	if current.snapshot == nil {
		current.snapshot = current.app.routeSnapshot()
	}
	options := current.options
	if current.snapshot != nil {
		switch current.route.kind {
		case routeCanonical:
			options.FlagAliases = current.snapshot.flagAliases[current.route.canonicalPath.Key()].neutralRecords()
		case routeDiscovery:
			options.FlagAliases = current.snapshot.discoveryFlags[current.route.discoveryPath.Key()].neutralRecords()
		}
		current.session = internalcobra.Prepare(current.snapshot.metadata, options)
	}
}

func (current *execution) presentationSession() *internalcobra.Session {
	if current.app == nil {
		return nil
	}
	snapshot := current.app.routeSnapshot()
	if current.session == nil || current.snapshot != snapshot {
		current.snapshot = snapshot
		current.session = nil
		current.prepareSession()
	}
	return current.session
}

func (current *execution) renderHelp(path []string) Outcome {
	if current.app == nil {
		return Failure(errors.New("cannot render help on a nil app"))
	}
	session := current.presentationSession()
	view := current.app.helpView(current.route, current.snapshot)
	return current.app.renderHelpViewOutcomeWithSession(view, current.streams, session)
}

func (current *execution) renderHelpTargets(targets []string) Outcome {
	if current.app == nil {
		return Failure(errors.New("cannot render help on a nil app"))
	}
	snapshot := current.app.routeSnapshot()
	if snapshot == nil {
		return Failure(errors.New("cannot render help without command metadata"))
	}
	route := resolveEnteredRoute(targets, snapshot)
	if route.kind == routeUnknown {
		session := internalcobra.Prepare(snapshot.metadata, current.options)
		return current.app.renderHelpOutcomeWithSession(targets, current.streams, session)
	}
	options := current.options
	switch route.kind {
	case routeCanonical:
		options.FlagAliases = snapshot.flagAliases[route.canonicalPath.Key()].neutralRecords()
	case routeDiscovery:
		options.FlagAliases = snapshot.discoveryFlags[route.discoveryPath.Key()].neutralRecords()
	}
	session := internalcobra.Prepare(snapshot.metadata, options)
	view := current.app.helpView(route, snapshot)
	return current.app.renderHelpViewOutcomeWithSession(view, current.streams, session)
}

func (current *execution) usageLine(path []string) string {
	if current.app == nil {
		return "Usage: command [command]"
	}
	session := current.presentationSession()
	if session != nil {
		if usage, failure := session.UsageLine(path); failure == nil {
			return "Usage: " + usage
		}
	}
	return current.app.usageFallback()
}

func (current *execution) present(outcome Outcome, path []string) Outcome {
	return current.app.presentWithUsageLine(outcome, path, current.streams, current.usageLine)
}

func normalizeStreams(streams Streams) Streams {
	if streams.Out == nil {
		streams.Out = io.Discard
	}
	if streams.Err == nil {
		streams.Err = io.Discard
	}
	return streams
}

func (a *App) present(outcome Outcome, path []string, streams Streams) Outcome {
	return a.presentWithUsageLine(outcome, path, streams, a.usageLine)
}

func (a *App) presentWithUsageLine(outcome Outcome, path []string, streams Streams, usageLine func([]string) string) Outcome {
	if outcome.Kind == "" && outcome.Status == 0 && outcome.Domain == "" &&
		outcome.Cause == nil && outcome.DeliveryError == nil &&
		!outcome.ReportIncomplete && len(outcome.Diagnostics) == 0 {
		outcome.Kind = OutcomeSuccess
	}
	if outcome.DiagnosticDelivery == "" {
		outcome.DiagnosticDelivery = DeliveryNone
	}
	streams = normalizeStreams(streams)
	if outcome.DiagnosticDelivery == DeliveryComplete {
		return outcome
	}
	diagnostics := append([]Diagnostic(nil), outcome.Diagnostics...)
	if outcome.Cause != nil && !hasErrorDiagnostic(diagnostics) {
		diagnostics = append(diagnostics, MessageDiagnostic(SeverityError, outcome.Cause.Error()))
	}
	if outcome.Kind == OutcomeUsage {
		diagnostics = append(diagnostics, MessageDiagnostic(SeverityError, usageLine(path)))
	}
	outcome.Diagnostics = diagnostics
	if len(diagnostics) == 0 {
		return outcome
	}
	delivered := false
	for _, diagnostic := range diagnostics {
		if diagnostic.Write == nil {
			continue
		}
		delivered = true
		writer := &checkedWriter{writer: streams.Err}
		writeErr := diagnostic.Write(writer)
		if writer.failure != nil {
			if writeErr == nil {
				writeErr = writer.failure
			} else if !errors.Is(writeErr, writer.failure) {
				writeErr = errors.Join(writeErr, writer.failure)
			}
		}
		if writeErr != nil {
			return deliveryFailure(outcome, writeErr)
		}
	}
	if delivered {
		outcome.DiagnosticDelivery = DeliveryComplete
	}
	return outcome
}

func (a *App) usageLine(path []string) string {
	if a != nil {
		if usage, failure := internalcobra.UsageLine(a.routeSnapshot().metadata, path); failure == nil {
			return "Usage: " + usage
		}
	}
	return a.usageFallback()
}

func (a *App) usageFallback() string {
	name := "command"
	if a != nil && a.identity.Name != "" {
		name = a.identity.Name
	}
	return fmt.Sprintf("Usage: %s [command]", name)
}

func hasErrorDiagnostic(diagnostics []Diagnostic) bool {
	for _, diagnostic := range diagnostics {
		if diagnostic.Write != nil && diagnostic.Severity == SeverityError {
			return true
		}
	}
	return false
}

func deliveryFailure(outcome Outcome, err error) Outcome {
	if outcome.DeliveryError == nil {
		outcome.DeliveryError = err
	} else {
		outcome.DeliveryError = errors.Join(outcome.DeliveryError, err)
	}
	outcome.DiagnosticDelivery = DeliveryIncomplete
	if outcome.Kind != OutcomeDomain {
		outcome.Kind = OutcomeOperational
		outcome.Status = 1
	}
	return outcome
}

type checkedWriter struct {
	writer  io.Writer
	failure error
}

func (w *checkedWriter) Write(data []byte) (int, error) {
	n, err := w.writer.Write(data)
	if err == nil && n < len(data) {
		err = io.ErrShortWrite
	}
	if err != nil && w.failure == nil {
		w.failure = err
	}
	return n, err
}