package commandkit

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

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

// Execute parses and dispatches one invocation. args excludes the executable
// name. 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)
	parsed := a.parse(args, internalcobra.ParseOptions{
		Context: ctx,
		Out:     streams.Out,
		Err:     streams.Err,
	})
	if parsed.Failure != nil {
		return a.present(Usage(errors.New(parsed.Failure.Message)), parsed.Path, streams)
	}
	command, ok := a.commandAt(parsed.Path)
	if !ok || command.payload == nil {
		return a.present(a.renderHelpOutcome(parsed.Path, streams), parsed.Path, streams)
	}
	if parsed.HelpRequested || !command.payload.hasRun() {
		if _, err := command.payload.prepare(parsed.FlagValues, parsed.Operands, false); err != nil {
			return a.present(Usage(err), parsed.Path, streams)
		}
		return a.present(a.renderHelpOutcome(parsed.Path, streams), parsed.Path, streams)
	}
	buildInput, err := command.payload.prepare(parsed.FlagValues, parsed.Operands, true)
	if err != nil {
		return a.present(Usage(err), parsed.Path, streams)
	}
	input := buildInput()
	if err := command.payload.checkInput(input); err != nil {
		return a.present(Usage(err), parsed.Path, streams)
	}
	outcome := command.payload.run(Invocation{Context: ctx, Streams: streams}, input)
	return a.present(outcome, parsed.Path, streams)
}

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) commandAt(path []string) (Command, bool) {
	if a == nil {
		return Command{}, false
	}
	if len(path) == 0 {
		return Command{}, true
	}
	command, ok := a.commands[path[0]]
	if !ok || (command.reserved && command.command.payload == nil) {
		return Command{}, false
	}
	current := command.command
	for _, name := range path[1:] {
		found := false
		for _, child := range current.children {
			if child.name == name {
				current = child
				found = true
				break
			}
		}
		if !found {
			return Command{}, false
		}
	}
	return current, true
}

func (a *App) present(outcome Outcome, path []string, streams Streams) 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(configkit.SeverityError, outcome.Cause.Error()))
	}
	if outcome.Kind == OutcomeUsage {
		diagnostics = append(diagnostics, MessageDiagnostic(configkit.SeverityError, a.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 {
	name := "command"
	if a != nil && a.identity.Name != "" {
		name = a.identity.Name
	}
	if a != nil {
		if usage, failure := internalcobra.UsageLine(a.bridgeTree(), path); failure == nil {
			return "Usage: " + usage
		}
	}
	return fmt.Sprintf("Usage: %s [command]", name)
}

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