package commandkit

import (
	"fmt"
	"io"
	"strings"
	"unicode"

	internalcobra "go.maximumdirect.net/commandkit/internal/cobra"
	commandmeta "go.maximumdirect.net/commandkit/internal/commandmeta"
)

// Completion declares opt-in shell script generation for the executable
// basename used to invoke the application. Install it at the application root.
// Generated shell identifiers support letters, digits, underscores, dots,
// hyphens, and colons; a leading hyphen is not supported.
func Completion(executable string) Command {
	children := make([]Command, 0, 3)
	for _, shell := range []string{"bash", "zsh", "fish"} {
		shell := shell
		children = append(children, NewCommand(CommandSpec[struct{}]{
			Name: shell, Summary: "Generate " + shell + " completion script.",
			Run: func(invocation Invocation, _ struct{}) Outcome {
				_ = invocation.Reporter().RenderOutput(func(writer io.Writer) error {
					return internalcobra.CompletionScript(writer, executable, shell)
				})
				return Success()
			},
		}))
	}
	command := RootGroup("completion", "Generate shell completion scripts.", children...)
	command.record.completion = true
	if !validCompletionExecutable(executable) {
		return WithError(command, fmt.Errorf("unsupported completion executable basename %q", executable))
	}
	return command
}

// Cobra emits the basename into shell identifiers and unquoted command words.
func validCompletionExecutable(name string) bool {
	if name == "" || name == "." || name == ".." || strings.HasPrefix(name, "-") {
		return false
	}
	for _, ch := range name {
		if !(unicode.IsLetter(ch) || unicode.IsDigit(ch) || ch == '_' || ch == '-' || ch == ':' || ch == '.') {
			return false
		}
	}
	return true
}

// CompletionChoice is a literal suggested value and its optional description.
type CompletionChoice struct {
	// Value is inserted as data; it is not interpreted as shell source.
	Value string
	// Description is optional context displayed by shells that support it.
	Description string
}

// CompletionHint selects suggestions for a flag or positional value. Its zero
// value requests no value suggestions; hints do not constrain accepted input.
type CompletionHint struct {
	kind    completionHintKind
	choices *completionChoicesData
}

// Keep the public metadata structs comparable without exposing mutable choices.
type completionChoicesData struct {
	values []CompletionChoice
}

type completionHintKind uint8

const (
	completionNone completionHintKind = iota
	completionChoices
	completionFiles
	completionDirectories
)

// CompleteChoices suggests literal values matching the current value prefix.
// The supplied slice is copied. An empty list produces no suggestions. Empty
// values and values containing a newline, tab, or NUL cannot be presented as
// suggestions, but remain valid input if the command's converter accepts them.
func CompleteChoices(choices ...CompletionChoice) CompletionHint {
	hint := CompletionHint{kind: completionChoices}
	if len(choices) != 0 {
		hint.choices = &completionChoicesData{values: append([]CompletionChoice(nil), choices...)}
	}
	return hint
}

// CompleteFiles requests shell filename completion.
func CompleteFiles() CompletionHint { return CompletionHint{kind: completionFiles} }

// CompleteDirectories requests shell directory completion.
func CompleteDirectories() CompletionHint { return CompletionHint{kind: completionDirectories} }

// NoCompletion requests no value suggestions.
func NoCompletion() CompletionHint { return CompletionHint{} }

func bridgeCompletion(hint CompletionHint) commandmeta.CompletionHint {
	result := commandmeta.CompletionHint{}
	switch hint.kind {
	case completionChoices:
		result.Kind = commandmeta.CompletionChoices
		if hint.choices == nil {
			break
		}
		for _, choice := range hint.choices.values {
			result.Choices = append(result.Choices, commandmeta.CompletionChoice{Value: choice.Value, Description: choice.Description})
		}
	case completionFiles:
		result.Kind = commandmeta.CompletionFiles
	case completionDirectories:
		result.Kind = commandmeta.CompletionDirectories
	}
	return result
}