package commandkit

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

	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 {
	current := newExecution(a, ctx, streams)
	if a == nil {
		err := errors.New("cannot execute commands on a nil app")
		return current.finalize(Failure(err.Error()).WithCause(err), nil)
	}
	if ctx == nil {
		err := errors.New("invocation context must not be nil")
		return current.finalize(Failure(err.Error()).WithCause(err), nil)
	}
	routedSnapshot := current.snapshot
	current.route = resolveEnteredRoute(args, routedSnapshot)
	parsed := current.parse(current.route.args)
	current.reporter.applySelection(parsed.Reporting)
	var outcome Outcome
	path := parsed.Path
	if parsed.Failure != nil {
		outcome = Usage(parsed.Failure.Message)
	} else if current.route.kind == routeDiscovery {
		if parsed.HelpRequested {
			outcome = current.renderHelp(parsed.Path)
			path = clonePath(current.route.enteredPath)
		} else {
			entered := current.route.enteredPath.String()
			outcome = Usage(fmt.Sprintf("incomplete command path %q; use %q --help", entered, entered))
			path = clonePath(current.route.enteredPath)
		}
	} else {
		payload, ok := routedSnapshot.runners[parsed.Key]
		if !ok || payload == nil {
			outcome = current.renderHelp(parsed.Path)
		} else if parsed.HelpRequested || !payload.hasRun() {
			if _, err := payload.prepare(parsed.FlagValues, parsed.FlagSpellings, parsed.Operands, false); err != nil {
				outcome = classifyInputError(err)
			} else {
				outcome = current.renderHelp(parsed.Path)
			}
		} else {
			run, err := payload.prepare(parsed.FlagValues, parsed.FlagSpellings, parsed.Operands, true)
			if err != nil {
				outcome = classifyInputError(err)
			} else {
				outcome = run(current)
			}
		}
	}
	return current.finalize(outcome, path)
}

type execution struct {
	app      *App
	ctx      context.Context
	streams  Streams
	reporter *Reporter
	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,
		reporter:      current.reporter,
		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 {
	streams = normalizeStreams(streams)
	current := &execution{
		app:      app,
		ctx:      ctx,
		streams:  streams,
		reporter: newReporter(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 reduceReportingOccurrences(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 {
		err := errors.New("cannot render help on a nil app")
		return Failure(err.Error()).WithCause(err)
	}
	session := current.presentationSession()
	view := current.app.helpView(current.route, current.snapshot)
	return current.app.renderHelpViewOutcomeWithSession(view, current.reporter, session)
}

func (current *execution) renderHelpTargets(targets []string) Outcome {
	if current.app == nil {
		err := errors.New("cannot render help on a nil app")
		return Failure(err.Error()).WithCause(err)
	}
	snapshot := current.app.routeSnapshot()
	if snapshot == nil {
		err := errors.New("cannot render help without command metadata")
		return Failure(err.Error()).WithCause(err)
	}
	route := resolveEnteredRoute(targets, snapshot)
	// Explicit help targets are paths, not command invocations with operands.
	// Discovery routes have no canonical path and retain only trailing options.
	if route.kind == routeUnknown || len(route.args) != len(route.canonicalPath) {
		session := internalcobra.Prepare(snapshot.metadata, current.options)
		view := commandmeta.HelpView{EnteredPath: targets, CanonicalPath: targets}
		return current.app.renderHelpViewOutcomeWithSession(view, current.reporter, 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.reporter, 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) routeUsageLine() string {
	line := current.usageLine(clonePath(current.route.canonicalPath))
	canonical := strings.TrimSpace(current.app.identity.Name + " " + current.route.canonicalPath.String())
	entered := strings.TrimSpace(current.app.identity.Name + " " + current.route.enteredPath.String())
	line = strings.Replace(line, "Usage: "+canonical, "Usage: "+entered, 1)
	return line + "\nAlias for: " + canonical
}

func (current *execution) finalize(outcome Outcome, path []string) Outcome {
	if outcome.Kind == OutcomeUsage {
		details := append([]Detail(nil), outcome.Explanation.Details...)
		details = append(details, func(w io.Writer) error {
			line := current.usageText(path)
			if !strings.HasSuffix(line, "\n") {
				line += "\n"
			}
			_, err := io.WriteString(w, line)
			return err
		})
		outcome.Explanation.Details = details
	}
	return current.reporter.finalize(outcome, nil)
}

func (current *execution) usageText(path []string) string {
	switch {
	case current.route.kind == routeDiscovery && current.app != nil:
		return fmt.Sprintf("Usage: %s %s [command]", current.app.identity.Name, current.route.enteredPath.String())
	case current.route.kind == routeCanonical && !current.route.enteredPath.Equal(current.route.canonicalPath):
		return current.routeUsageLine()
	default:
		return current.usageLine(path)
	}
}

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)
}