// Package cobra adapts CommandKit's neutral command declarations to Cobra and
// pflag. Backend types and failures remain inside this package.
package cobra

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"strconv"
	"strings"

	commandmeta "gitea.maximumdirect.net/eric/CommandKit/internal/commandmeta"
	"gitea.maximumdirect.net/eric/CommandKit/internal/commandpath"

	spfcobra "github.com/spf13/cobra"
	"github.com/spf13/pflag"
)

// Session owns one mutable backend tree for a single command invocation.
type Session struct {
	metadata     *commandmeta.Command
	root         *spfcobra.Command
	declarations map[*spfcobra.Command]*commandmeta.Command
}

// Prepare constructs a fresh backend tree for one invocation.
func Prepare(root *commandmeta.Command, options commandmeta.ParseOptions) *Session {
	session := &Session{}
	if root == nil {
		return session
	}
	session.metadata = root
	options = normalizeOptions(options)
	session.root, session.declarations = buildTree(root, options)
	return session
}

// Metadata returns the neutral tree used to prepare this session.
func (session *Session) Metadata() *commandmeta.Command {
	if session == nil {
		return nil
	}
	return session.metadata
}

// Parse routes leading command words and parses flags on this session's tree.
func (session *Session) Parse(argv []string) commandmeta.Result {
	result := commandmeta.Result{}
	if session == nil || session.root == nil {
		return failure(result, "command tree is nil")
	}
	leading, tail := splitRoutingPrefix(argv)
	selected, unconsumed, err := session.root.Find(leading)
	if err != nil {
		return failure(result, err.Error())
	}
	if selected == nil {
		return failure(result, "no command was selected")
	}
	selectedNode := session.declarations[selected]
	if selectedNode == nil {
		return failure(result, "selected command is not part of the declared tree")
	}
	result.Key = selectedNode.Key
	var pathOK bool
	selectedPath, pathOK := pathFor(selected, session.declarations)
	if !pathOK {
		return failure(result, "selected command is not part of the declared tree")
	}
	result.Path = []string(selectedPath)
	consumed := len(leading) - len(unconsumed)
	if consumed != len(selectedPath) || !commandpath.FromTokens(leading[:consumed]).Equal(selectedPath) {
		return failure(result, "command path must match a registered command exactly")
	}

	remaining := append(commandpath.CloneTokens(unconsumed), tail...)
	if err := selected.ParseFlags(remaining); err != nil {
		return failure(result, err.Error())
	}
	operands := selected.Flags().Args()

	result.Operands = append([]string(nil), operands...)
	result.FlagValues = make([][]string, len(selectedNode.Flags))
	for index, flag := range selectedNode.Flags {
		if value := selected.Flags().Lookup(flag.Name); value != nil {
			result.FlagValues[index] = value.Value.(*rawValue).valuesCopy()
		}
	}
	if helpFlag := selected.Flags().Lookup("help"); helpFlag != nil {
		helpRequested, err := helpFlag.Value.(*rawValue).lastBool()
		if err != nil {
			return failure(result, err.Error())
		}
		result.HelpRequested = helpRequested
	}
	if !selectedNode.Runnable && len(result.Operands) > 0 {
		return failure(result, "unknown command or unexpected group operands: "+strings.Join(result.Operands, " "))
	}
	return result
}

// RenderHelp renders registered metadata for an exact path on this session.
func (session *Session) RenderHelp(path []string) (string, *commandmeta.Failure) {
	if session == nil || session.root == nil {
		return "", &commandmeta.Failure{Message: "command tree is nil"}
	}
	selected, remaining, err := session.root.Find(path)
	if err != nil {
		return "", &commandmeta.Failure{Message: fmt.Sprintf("unknown help path %q", commandpath.FromTokens(path).String()), Usage: true}
	}
	declaration := session.declarations[selected]
	selectedPath, pathOK := pathFor(selected, session.declarations)
	if declaration == nil || !pathOK || len(remaining) != 0 || !commandpath.FromTokens(path).Equal(selectedPath) {
		return "", &commandmeta.Failure{Message: fmt.Sprintf("unknown help path %q", commandpath.FromTokens(path).String()), Usage: true}
	}
	buffer := new(bytes.Buffer)
	previousOut, previousErr := selected.OutOrStdout(), selected.ErrOrStderr()
	selected.SetOut(buffer)
	selected.SetErr(buffer)
	defer func() {
		selected.SetOut(previousOut)
		selected.SetErr(previousErr)
	}()
	if err := selected.Usage(); err != nil {
		return "", &commandmeta.Failure{Message: err.Error()}
	}
	return buffer.String(), nil
}

// UsageLine returns Cobra's usage line for an exact path on this session.
func (session *Session) UsageLine(path []string) (string, *commandmeta.Failure) {
	if session == nil || session.root == nil {
		return "", &commandmeta.Failure{Message: "command tree is nil"}
	}
	selected, remaining, err := session.root.Find(path)
	declaration := session.declarations[selected]
	selectedPath, pathOK := pathFor(selected, session.declarations)
	if err != nil || declaration == nil || !pathOK || len(remaining) != 0 || !commandpath.FromTokens(path).Equal(selectedPath) {
		return "", &commandmeta.Failure{Message: "usage path is not registered"}
	}
	line := selected.UseLine()
	if selected.HasSubCommands() {
		line += " [command]"
	}
	return line, nil
}

// RenderHelp renders a fresh command tree for one help request.
func RenderHelp(root *commandmeta.Command, path []string) (string, *commandmeta.Failure) {
	return Prepare(root, commandmeta.ParseOptions{}).RenderHelp(path)
}

// UsageLine resolves a path on a fresh command tree.
func UsageLine(root *commandmeta.Command, path []string) (string, *commandmeta.Failure) {
	return Prepare(root, commandmeta.ParseOptions{}).UsageLine(path)
}

// Parse constructs a fresh command tree and parses one argv.
func Parse(root *commandmeta.Command, argv []string, options commandmeta.ParseOptions) commandmeta.Result {
	return Prepare(root, options).Parse(argv)
}

func normalizeOptions(options commandmeta.ParseOptions) commandmeta.ParseOptions {
	if options.Context == nil {
		options.Context = context.Background()
	}
	if options.In == nil {
		options.In = strings.NewReader("")
	}
	if options.Out == nil {
		options.Out = io.Discard
	}
	if options.Err == nil {
		options.Err = io.Discard
	}
	return options
}

func buildTree(root *commandmeta.Command, options commandmeta.ParseOptions) (*spfcobra.Command, map[*spfcobra.Command]*commandmeta.Command) {
	nodes := make(map[*spfcobra.Command]*commandmeta.Command)
	var build func(*commandmeta.Command) *spfcobra.Command
	build = func(declaration *commandmeta.Command) *spfcobra.Command {
		backend := &spfcobra.Command{
			Use:                commandUse(declaration),
			Short:              declaration.Summary,
			Long:               helpDescription(declaration),
			Args:               func(*spfcobra.Command, []string) error { return nil },
			SilenceErrors:      true,
			SilenceUsage:       true,
			DisableSuggestions: true,
		}
		if declaration.Runnable {
			backend.Run = func(*spfcobra.Command, []string) {}
		}
		backend.SetContext(options.Context)
		backend.SetIn(options.In)
		backend.SetOut(options.Out)
		backend.SetErr(options.Err)
		backend.SetHelpFunc(func(*spfcobra.Command, []string) {})
		backend.SetFlagErrorFunc(func(_ *spfcobra.Command, err error) error { return err })
		backend.SetUsageTemplate(usageTemplate)
		backend.Flags().SetInterspersed(true)
		backend.Flags().SortFlags = false
		backend.DisableAutoGenTag = true
		helpValue := &rawValue{boolean: true}
		backend.Flags().VarP(helpValue, "help", "h", "help for this command")
		helpFlag := backend.Flags().Lookup("help")
		helpFlag.NoOptDefVal = "true"
		helpFlag.Usage = "help for this command (default: false)"
		for _, declarationFlag := range declaration.Flags {
			value := &rawValue{boolean: declarationFlag.Boolean}
			backend.Flags().VarP(value, declarationFlag.Name, declarationFlag.Short, flagUsage(declarationFlag))
			backendFlag := backend.Flags().Lookup(declarationFlag.Name)
			backendFlag.DefValue = ""
			if declarationFlag.Boolean {
				backendFlag.NoOptDefVal = "true"
			}
		}
		// Cobra's automatic help flag is suppressed because CommandKit declares
		// and interprets the local help flag itself.
		backend.SetHelpCommand(nil)
		nodes[backend] = declaration
		for _, child := range declaration.Children {
			backend.AddCommand(build(child))
		}
		return backend
	}
	return build(root), nodes
}

const usageTemplate = `{{with (or .Long .Short)}}{{. | trimTrailingWhitespaces}}

{{end}}Usage:
  {{.UseLine}}{{if .HasSubCommands}}
  {{.CommandPath}} [command]{{end}}{{if .HasSubCommands}}

Available Commands:{{range .Commands}}
  {{rpad .Name .NamePadding}} {{.Short}}{{end}}{{end}}{{if .HasAvailableLocalFlags}}

Flags:
{{.LocalFlags.FlagUsages | trimTrailingWhitespaces}}{{end}}
`

func commandUse(command *commandmeta.Command) string {
	var parts []string
	for _, argument := range command.Arguments {
		name := argument.Name
		if argument.Min == 1 && argument.Max == 1 {
			parts = append(parts, name)
		} else if argument.Max == -1 {
			if argument.Min > 0 {
				parts = append(parts, name+"...")
			} else {
				parts = append(parts, "["+name+"...]")
			}
		} else {
			parts = append(parts, fmt.Sprintf("%s{%d..%d}", name, argument.Min, argument.Max))
		}
	}
	if len(parts) == 0 {
		return command.Name
	}
	return command.Name + " " + strings.Join(parts, " ")
}

func helpDescription(command *commandmeta.Command) string {
	var sections []string
	if description := strings.TrimSpace(command.Description); description != "" {
		sections = append(sections, description)
	}
	if len(command.Arguments) > 0 {
		lines := []string{"Arguments:"}
		for _, argument := range command.Arguments {
			maximum := fmt.Sprint(argument.Max)
			if argument.Max == -1 {
				maximum = "unbounded"
			}
			line := fmt.Sprintf("  %s (min %d, max %s)", argument.Name, argument.Min, maximum)
			if argument.Usage != "" {
				line += " — " + argument.Usage
			}
			lines = append(lines, line)
		}
		sections = append(sections, strings.Join(lines, "\n"))
	}
	return strings.Join(sections, "\n\n")
}

func flagUsage(flag commandmeta.Flag) string {
	var details []string
	if flag.Required {
		details = append(details, "required")
	}
	if flag.Repeated {
		details = append(details, "repeatable")
	}
	details = append(details, "default: "+flag.Default)
	usage := flag.Usage
	if usage != "" {
		usage += " (" + strings.Join(details, "; ") + ")"
	} else {
		usage = strings.Join(details, "; ")
	}
	return usage
}

func splitRoutingPrefix(argv []string) ([]string, []string) {
	for index, argument := range argv {
		if argument == "--" || (strings.HasPrefix(argument, "-") && argument != "-") {
			return commandpath.CloneTokens(argv[:index]), commandpath.CloneTokens(argv[index:])
		}
	}
	return commandpath.CloneTokens(argv), nil
}

func pathFor(selected *spfcobra.Command, declarations map[*spfcobra.Command]*commandmeta.Command) (commandpath.Path, bool) {
	var reverse []string
	for current := selected; current != nil; current = current.Parent() {
		declaration := declarations[current]
		if declaration == nil {
			return nil, false
		}
		if current.Parent() != nil {
			reverse = append(reverse, declaration.Name)
		}
	}
	for left, right := 0, len(reverse)-1; left < right; left, right = left+1, right-1 {
		reverse[left], reverse[right] = reverse[right], reverse[left]
	}
	return commandpath.FromTokens(reverse), true
}

func failure(result commandmeta.Result, message string) commandmeta.Result {
	result.Failure = &commandmeta.Failure{Message: message}
	return result
}

type rawValue struct {
	values  []string
	boolean bool
}

func (v *rawValue) Set(value string) error {
	v.values = append(v.values, value)
	return nil
}

func (v *rawValue) String() string {
	if len(v.values) > 0 {
		return v.values[len(v.values)-1]
	}
	return ""
}

func (v *rawValue) Type() string {
	if v.boolean {
		return "bool"
	}
	return "string"
}

func (v *rawValue) IsBoolFlag() bool { return v.boolean }

func (v *rawValue) valuesCopy() []string { return append([]string(nil), v.values...) }

func (v *rawValue) lastBool() (bool, error) {
	var value bool
	for _, raw := range v.values {
		parsed, err := strconv.ParseBool(raw)
		if err != nil {
			return false, fmt.Errorf("invalid boolean value %q for --help", raw)
		}
		value = parsed
	}
	return value, nil
}

var _ pflag.Value = (*rawValue)(nil)