// Package complete provides shell completion generation for kportal.
// It supports bash, zsh, and fish shells with context-aware completions
// for flags, subcommands, config values, and Kubernetes resources.
package complete

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// Shell represents a supported shell type
type Shell string

const (
	ShellBash Shell = "bash"
	ShellZsh  Shell = "zsh"
	ShellFish Shell = "fish"
)

// Installer handles shell completion installation
type Installer struct {
	shell     Shell
	prefixDir string
}

// NewInstaller creates a new completion installer for the specified shell
func NewInstaller(shell Shell) *Installer {
	return &Installer{
		shell:     shell,
		prefixDir: getDefaultPrefixDir(shell),
	}
}

// getDefaultPrefixDir returns the default completion directory for a shell
func getDefaultPrefixDir(shell Shell) string {
	home, err := os.UserHomeDir()
	if err != nil {
		home = os.Getenv("HOME")
	}
	if home == "" {
		home = "/tmp"
	}

	switch shell {
	case ShellBash:
		// Check common bash completion directories
		dirs := []string{
			"/etc/bash_completion.d",
			filepath.Join(home, ".local", "share", "bash-completion", "completions"),
			filepath.Join(home, ".bash_completion.d"),
		}
		for _, dir := range dirs {
			if pathExists(dir) {
				return dir
			}
		}
		// Fallback to user dir (best-effort create; Install reports write errors)
		userDir := filepath.Join(home, ".local", "share", "bash-completion", "completions")
		ensureDir(userDir)
		return userDir

	case ShellZsh:
		dirs := []string{
			filepath.Join(home, ".zsh", "completions"),
			filepath.Join(home, ".oh-my-zsh", "completions"),
		}
		for _, dir := range dirs {
			if pathExists(dir) {
				return dir
			}
		}
		// Fallback to standard zsh site-functions
		usrShare := "/usr/local/share/zsh/site-functions"
		if pathExists(usrShare) {
			return usrShare
		}
		userDir := filepath.Join(home, ".zsh", "completions")
		ensureDir(userDir)
		return userDir

	case ShellFish:
		dir := filepath.Join(home, ".config", "fish", "completions")
		ensureDir(dir)
		return dir
	}

	return ""
}

// Install installs the completion script for the shell
func (i *Installer) Install() error {
	script, err := Generate(i.shell)
	if err != nil {
		return fmt.Errorf("failed to generate completion script: %w", err)
	}

	filename := i.getCompletionFilename()
	filepath := filepath.Join(i.prefixDir, filename)

	// Check if already installed
	if pathExists(filepath) {
		return fmt.Errorf("completion file already exists: %s (remove it first to reinstall)", filepath)
	}

	// #nosec G306 -- completion scripts are non-secret and must be world-readable by the shell
	if err := os.WriteFile(filepath, []byte(script), 0o644); err != nil {
		return fmt.Errorf("failed to write completion file: %w", err)
	}

	return nil
}

// Uninstall removes the completion script
func (i *Installer) Uninstall() error {
	filename := i.getCompletionFilename()
	filepath := filepath.Join(i.prefixDir, filename)

	if err := os.Remove(filepath); err != nil {
		return fmt.Errorf("failed to remove completion file: %w", err)
	}

	return nil
}

// getCompletionFilename returns the filename for the completion script
func (i *Installer) getCompletionFilename() string {
	switch i.shell {
	case ShellBash:
		return "_kportal"
	case ShellZsh:
		return "_kportal"
	case ShellFish:
		return "kportal.fish"
	}
	return "_kportal"
}

// Print prints the completion script to stdout
func Print(shell Shell) error {
	script, err := Generate(shell)
	if err != nil {
		return err
	}
	fmt.Print(script)
	return nil
}

// Generate generates the completion script for the specified shell
func Generate(shell Shell) (string, error) {
	switch shell {
	case ShellBash:
		return generateBash()
	case ShellZsh:
		return generateZsh()
	case ShellFish:
		return generateFish()
	default:
		return "", fmt.Errorf("unsupported shell: %s", shell)
	}
}

// generateBash generates bash completion script
func generateBash() (string, error) {
	var sb strings.Builder

	bashScript := `# kportal shell completion - bash
# Generated by kportal

# Don't interfere with other completions
if [[ -n "${BASH_COMPLETION_VERSINFO:-}" ]]; then
    return
fi

_kportal()
{
    local cur prev words cword split=false
    _init_completion -s || return

    # Complete the value expected after the previous flag
    case "$prev" in
        -c|--config)
            _filedir yaml
            return
            ;;
        --log-format)
            COMPREPLY=( $(compgen -W "text json" -- "$cur") )
            return
            ;;
        --convert)
            _filedir json
            return
            ;;
        --convert-output)
            _filedir yaml
            return
            ;;
        --context)
            # Complete from kubectl contexts
            if command -v kubectl &> /dev/null; then
                COMPREPLY=( $(compgen -W "$(kubectl config get-contexts -o name 2>/dev/null)" -- "$cur") )
            fi
            return
            ;;
        --shell)
            COMPREPLY=( $(compgen -W "bash zsh fish" -- "$cur") )
            return
            ;;
    esac

    # Handle option splitting (e.g., -c=value)
    [[ "$cur" == -*=* ]] && split=true
    [[ "$split" == true ]] && prev="${cur%%=*}"

    # Subcommand-specific completion
    case "${words[1]}" in
        generate)
            if [[ "$cur" == -* ]]; then
                COMPREPLY=( $(compgen -W "--context --config --dry-run" -- "$cur") )
            elif command -v kubectl &> /dev/null; then
                COMPREPLY=( $(compgen -W "$(kubectl config get-contexts -o name 2>/dev/null)" -- "$cur") )
            fi
            return
            ;;
        completion)
            COMPREPLY=( $(compgen -W "--install --uninstall --shell" -- "$cur") )
            return
            ;;
    esac

    # Top-level options
    if [[ "$cur" == -* ]]; then
        COMPREPLY=( $(compgen -W "-c -v --check --headless --log-format --version --update --convert --convert-output" -- "$cur") )
        return
    fi

    # Top-level subcommands
    COMPREPLY=( $(compgen -W "generate completion" -- "$cur") )
}

# Register completion
complete -F _kportal kportal

# Also complete for common aliases
complete -F _kportal kp
`

	sb.WriteString(bashScript)
	return sb.String(), nil
}

// generateZsh generates zsh completion script
func generateZsh() (string, error) {
	var sb strings.Builder

	// Per-flag zsh _arguments descriptors. Completion scripts are static text, so
	// these are literals (single source of truth — keep in sync with the CLI flags).
	flagDescs := []string{
		`'-c[Path to configuration file]:config file:_files -g "*.yaml"'`,
		`'-v[Enable verbose logging]'`,
		`'--version[Show version and exit]'`,
		`'--update[Check for updates]'`,
		`'--check[Validate configuration]'`,
		`'--headless[Run without UI]'`,
		`'--log-format[Log format: text or json]:format:(text json)'`,
		`'--convert[Convert kftray config]:input file:_files -g "*.json"'`,
		`'--convert-output[Output file]:output file:_files -g "*.yaml"'`,
	}

	sb.WriteString(`#compdef kportal

# kportal shell completion - zsh
# Generated by kportal

_kportal()
{
    local -a commands flags generate_flags completion_flags

    commands=(
        'generate:Interactively generate forwards from cluster'
        'completion:Generate shell completion scripts'
    )

    flags=(
`)

	for _, desc := range flagDescs {
		fmt.Fprintf(&sb, "        %s\n", desc)
	}

	sb.WriteString(`    )

    generate_flags=(
        '--context[Kubernetes context]:context:->ctx'
        '--config[Config file]:file:_files -g "*.yaml"'
        '--dry-run[Print without saving]'
    )

    completion_flags=(
        '--install[Install completions for the shell]'
        '--uninstall[Remove installed completions]'
        '--shell[Shell type]:shell:(bash zsh fish)'
    )

    _arguments -s $flags '1: :->command' '*:: :->args'

    case $state in
        command)
            _describe 'command' commands
            ;;
        args)
            case ${words[1]} in
                generate)
                    _arguments -s $generate_flags
                    if [[ "$words[CURRENT]" == --context ]]; then
                        if command -v kubectl &> /dev/null; then
                            local -a contexts
                            contexts=(${(f)"$(kubectl config get-contexts -o name 2>/dev/null)"})
                            _describe 'context' contexts
                        fi
                    fi
                    ;;
                completion)
                    _arguments -s $completion_flags
                    ;;
            esac
            ;;
    esac
}

_kportal "$@"
`)

	return sb.String(), nil
}

// generateFish generates fish completion script
func generateFish() (string, error) {
	var sb strings.Builder

	sb.WriteString(`# kportal shell completion - fish
# Generated by kportal

# Main completion
complete -c kportal -f

# Subcommands
complete -c kportal -n '__fish_use_subcommand' -a 'generate' -d 'Interactively generate forwards from cluster'
complete -c kportal -n '__fish_use_subcommand' -a 'completion' -d 'Generate shell completion scripts'

# Global flags (main command uses single-dash -c and -v; words accept --)
complete -c kportal -s c -r -f -a '( __fish_complete_suffix .yaml )' -d 'Path to configuration file'
complete -c kportal -s v -d 'Enable verbose logging'
complete -c kportal -l version -d 'Show version and exit'
complete -c kportal -l update -d 'Check for updates'
complete -c kportal -l check -d 'Validate configuration'
complete -c kportal -l headless -d 'Run without UI'
complete -c kportal -l log-format -d 'Log format' -a 'text json' -f
complete -c kportal -l convert -r -f -a '( __fish_complete_suffix .json )' -d 'Convert kftray config'
complete -c kportal -l convert-output -r -f -a '( __fish_complete_suffix .yaml )' -d 'Output file'

# generate subcommand flags
complete -c kportal -n '__fish_seen_subcommand_from generate' -l context -d 'Kubernetes context' -a '(kubectl config get-contexts -o name 2>/dev/null)' -f
complete -c kportal -n '__fish_seen_subcommand_from generate' -l config -r -f -a '( __fish_complete_suffix .yaml )' -d 'Config file'
complete -c kportal -n '__fish_seen_subcommand_from generate' -l dry-run -d 'Print without saving'

# completion subcommand flags
complete -c kportal -n '__fish_seen_subcommand_from completion' -l install -d 'Install completions for the shell'
complete -c kportal -n '__fish_seen_subcommand_from completion' -l uninstall -d 'Remove installed completions'
complete -c kportal -n '__fish_seen_subcommand_from completion' -l shell -d 'Shell type' -a 'bash zsh fish' -f

# Aliases
complete -c kp -f
`)

	return sb.String(), nil
}

// InstallCompletions installs completions for the specified shell
// Prints instructions for manual installation if auto-install fails
func InstallCompletions(shell Shell) error {
	installer := NewInstaller(shell)

	if err := installer.Install(); err != nil {
		// Check if it's just "already exists" error
		if strings.Contains(err.Error(), "already exists") {
			fmt.Printf("Completion already installed at: %s/%s\n",
				installer.prefixDir, installer.getCompletionFilename())
			fmt.Println("Remove it first to reinstall, or source it manually:")
			return nil
		}

		// Try to print the script instead
		fmt.Println("Could not auto-install completions. To install manually, run:")
		fmt.Printf("  # %s\n", getInstallInstructions(shell))
		return nil
	}

	fmt.Printf("✅ Completions installed to: %s/%s\n",
		installer.prefixDir, installer.getCompletionFilename())
	fmt.Printf("\nTo enable %s completions, restart your shell or run:\n", shell)
	fmt.Printf("  source ~/%s\n", getSourceInstruction(shell))

	return nil
}

func getInstallInstructions(shell Shell) string {
	return fmt.Sprintf("kportal completion %s > <your-completion-dir>/_kportal", shell)
}

func getSourceInstruction(shell Shell) string {
	switch shell {
	case ShellBash:
		return ".bashrc"
	case ShellZsh:
		return ".zshrc"
	case ShellFish:
		return ".config/fish/config.fish # completions load automatically"
	}
	return "shell config"
}

// AutoDetectShell detects the current shell
func AutoDetectShell() Shell {
	shell := os.Getenv("SHELL")
	if shell == "" {
		return ShellBash // Default
	}

	if strings.HasSuffix(shell, "/bash") {
		return ShellBash
	}
	if strings.HasSuffix(shell, "/zsh") {
		return ShellZsh
	}
	if strings.HasSuffix(shell, "/fish") {
		return ShellFish
	}

	return ShellBash
}

// pathExists reports whether path exists on disk.
// #nosec G703 -- callers pass fixed completion paths derived from the user's own
// HOME and constant subdirectory names, never external/untrusted input.
func pathExists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

// ensureDir best-effort creates a completion directory. Errors are intentionally
// ignored: Install() surfaces any later write failure with a clear message.
// #nosec G703 -- path is derived from the user's own HOME and constant
// subdirectory names; 0o750 is appropriate for user-owned completion dirs.
func ensureDir(path string) {
	_ = os.MkdirAll(path, 0o750)
}