package windows

import (
	"bytes"
	"crypto/sha256"
	"errors"
	"fmt"
	"strings"
	"unicode/utf8"

	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
)

// The Windows supervisor never resolves a shell through PATH.  ShellPaths is
// the already-defaulted configuration snapshot supplied by the daemon; the
// native launch adapter re-stats the selected path immediately before use.
type ShellPaths struct {
	CMD        string
	PowerShell string
}

var (
	ErrUnsupportedShell        = errors.New("shell is unsupported on Windows")
	ErrInvalidShellPath        = errors.New("Windows shell path must be an absolute executable path")
	ErrInvalidWrapperSource    = errors.New("invalid generated wrapper source")
	ErrWrapperTooLarge         = errors.New("generated wrapper exceeds the configured limit")
	ErrWrapperDigestMismatch   = errors.New("script body does not match its descriptor digest")
	ErrWrapperLengthMismatch   = errors.New("script body does not match its descriptor length")
	ErrInvalidWrapperPath      = errors.New("generated wrapper path is invalid")
	ErrInvalidWorkingDirectory = errors.New("Windows working directory is invalid")
)

// WrapperEncoding documents how the private generated file is encoded. CMD
// receives the source bytes unchanged; PowerShell gets a UTF-8 BOM so the
// inbox Windows PowerShell implementation does not interpret non-ASCII text
// using the legacy system code page.
type WrapperEncoding uint8

const (
	WrapperEncodingUTF8 WrapperEncoding = iota + 1
	WrapperEncodingUTF8BOM
)

// ShellPlan is the immutable invocation contract for one supported Windows
// shell. Arguments intentionally exclude the application name: the native
// adapter passes ApplicationName separately to CreateProcessAsUser while
// CommandLine contains the complete argv-compatible command line.
type ShellPlan struct {
	Type             rvboxv1.ShellType
	ApplicationName  string
	Arguments        []string
	WrapperExtension string
	Encoding         WrapperEncoding
}

// Wrapper is the private generated script body. Filename is never derived
// from caller input; the native materializer appends Extension to an
// unpredictable per-command basename.
type Wrapper struct {
	Extension string
	Encoding  WrapperEncoding
	Bytes     []byte
	SHA256    [sha256.Size]byte
}

// LaunchPlan contains only deterministic launch inputs. Handles, ACLs, Job
// Objects, token selection and release barriers belong to the platform-native
// supervisor and are deliberately absent here.
type LaunchPlan struct {
	ApplicationName  string
	Arguments        []string
	CommandLine      string
	WrapperPath      string
	WorkingDirectory string
	Environment      []uint16
}

// ResolveShell chooses exactly the configured executable for shellType. It
// does not consult PATH, COMSPEC, file associations, environment overrides,
// or a wrapper's extension.
func ResolveShell(shellType rvboxv1.ShellType, paths ShellPaths) (ShellPlan, error) {
	plan, err := shellTemplate(shellType)
	if err != nil {
		return ShellPlan{}, err
	}
	if shellType == rvboxv1.ShellType_SHELL_CMD {
		plan.ApplicationName = paths.CMD
	} else {
		plan.ApplicationName = paths.PowerShell
	}
	if err := ValidateWindowsExecutablePath(plan.ApplicationName); err != nil {
		return ShellPlan{}, fmt.Errorf("%w: %v", ErrInvalidShellPath, err)
	}
	return plan, nil
}

// BuildWrapper validates and copies command/script bytes. For script sources,
// descriptor length and SHA-256 are checked before any materialization. The
// returned bytes are safe to hand to a private generated-file writer.
func BuildWrapper(spec *rvboxv1.ExecutionSpec, scriptBody []byte, maxBytes uint64) (Wrapper, error) {
	if spec == nil {
		return Wrapper{}, ErrInvalidWrapperSource
	}
	plan, err := shellTemplate(spec.GetShellType())
	if err != nil {
		return Wrapper{}, err
	}
	var source []byte
	switch value := spec.Source.(type) {
	case *rvboxv1.ExecutionSpec_CommandText:
		if !utf8.ValidString(value.CommandText) {
			return Wrapper{}, fmt.Errorf("%w: command text is not UTF-8", ErrInvalidWrapperSource)
		}
		source = []byte(value.CommandText)
	case *rvboxv1.ExecutionSpec_Script:
		if value.Script == nil || len(value.Script.Sha256) != sha256.Size {
			return Wrapper{}, fmt.Errorf("%w: script descriptor is incomplete", ErrInvalidWrapperSource)
		}
		if uint64(len(scriptBody)) != value.Script.SizeBytes {
			return Wrapper{}, ErrWrapperLengthMismatch
		}
		digest := sha256.Sum256(scriptBody)
		if !bytes.Equal(digest[:], value.Script.Sha256) {
			return Wrapper{}, ErrWrapperDigestMismatch
		}
		source = append([]byte(nil), scriptBody...)
	default:
		return Wrapper{}, fmt.Errorf("%w: exactly one command or script source is required", ErrInvalidWrapperSource)
	}
	if uint64(len(source)) > maxBytes && maxBytes != 0 {
		return Wrapper{}, ErrWrapperTooLarge
	}
	if bytes.IndexByte(source, 0) >= 0 {
		return Wrapper{}, fmt.Errorf("%w: source contains NUL", ErrInvalidWrapperSource)
	}
	if plan.Encoding == WrapperEncodingUTF8BOM {
		source = append([]byte{0xef, 0xbb, 0xbf}, source...)
	}
	if uint64(len(source)) > maxBytes && maxBytes != 0 {
		return Wrapper{}, ErrWrapperTooLarge
	}
	return Wrapper{Extension: plan.WrapperExtension, Encoding: plan.Encoding, Bytes: source, SHA256: sha256.Sum256(source)}, nil
}

func shellTemplate(shellType rvboxv1.ShellType) (ShellPlan, error) {
	switch shellType {
	case rvboxv1.ShellType_SHELL_SH, rvboxv1.ShellType_SHELL_BASH:
		return ShellPlan{Type: shellType, WrapperExtension: ".sh", Encoding: WrapperEncodingUTF8}, nil
	case rvboxv1.ShellType_SHELL_CMD:
		return ShellPlan{Type: shellType, Arguments: []string{"/D", "/S", "/C"}, WrapperExtension: ".cmd", Encoding: WrapperEncodingUTF8}, nil
	case rvboxv1.ShellType_SHELL_POWERSHELL:
		return ShellPlan{Type: shellType, Arguments: []string{"-NoLogo", "-NoProfile", "-NonInteractive", "-File"}, WrapperExtension: ".ps1", Encoding: WrapperEncodingUTF8BOM}, nil
	default:
		return ShellPlan{}, fmt.Errorf("%w: %s", ErrUnsupportedShell, shellType)
	}
}

// BuildLaunchPlan appends the generated wrapper path to the fixed shell
// argument vector and quotes the complete vector with the reviewed Windows
// routine. Environment is expected to be BuildEnvironmentBlock output.
func (plan ShellPlan) BuildLaunchPlan(wrapperPath, workingDirectory string, environment []uint16) (LaunchPlan, error) {
	if err := ValidateWindowsExecutablePath(plan.ApplicationName); err != nil {
		return LaunchPlan{}, fmt.Errorf("%w: %v", ErrInvalidShellPath, err)
	}
	if !validAbsoluteWindowsPath(wrapperPath) || strings.ToLower(strings.TrimSpace(wrapperPath)) != strings.ToLower(wrapperPath) || !strings.EqualFold(extensionOfWindowsPath(wrapperPath), plan.WrapperExtension) {
		return LaunchPlan{}, ErrInvalidWrapperPath
	}
	if !validAbsoluteWindowsPath(workingDirectory) {
		return LaunchPlan{}, ErrInvalidWorkingDirectory
	}
	arguments := append([]string(nil), plan.Arguments...)
	arguments = append(arguments, wrapperPath)
	full := append([]string{plan.ApplicationName}, arguments...)
	commandLine, err := BuildCommandLine(full)
	if err != nil {
		return LaunchPlan{}, err
	}
	return LaunchPlan{ApplicationName: plan.ApplicationName, Arguments: arguments, CommandLine: commandLine, WrapperPath: wrapperPath, WorkingDirectory: workingDirectory, Environment: append([]uint16(nil), environment...)}, nil
}

// ValidateWindowsExecutablePath applies the lexical checks that are possible
// before a native re-stat. The Windows adapter must still verify that the
// path names the same regular executable immediately before launch.
func ValidateWindowsExecutablePath(path string) error {
	if !validAbsoluteWindowsPath(path) || strings.TrimSpace(path) != path {
		return ErrInvalidShellPath
	}
	extension := strings.ToLower(extensionOfWindowsPath(path))
	switch extension {
	case ".exe", ".com", ".cmd", ".bat":
		return nil
	default:
		return fmt.Errorf("unsupported executable extension %q", extension)
	}
}

// ValidAbsoluteWindowsPath reports whether value passes the lexical absolute
// path checks. It does not touch the filesystem; native callers must still
// re-stat the object and verify its ACL immediately before use.
func ValidAbsoluteWindowsPath(value string) bool {
	return validAbsoluteWindowsPath(value)
}

func validAbsoluteWindowsPath(value string) bool {
	if value == "" || strings.IndexByte(value, 0) >= 0 || !utf8.ValidString(value) || strings.ContainsAny(value, "\r\n\t") {
		return false
	}
	value = strings.ReplaceAll(value, "/", `\`)
	if strings.HasPrefix(value, `\\`) {
		parts := strings.Split(strings.TrimPrefix(value, `\\`), `\`)
		if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
			return false
		}
	} else if len(value) < 3 || !((value[0] >= 'A' && value[0] <= 'Z') || (value[0] >= 'a' && value[0] <= 'z')) || value[1] != ':' || value[2] != '\\' {
		return false
	}
	for _, part := range strings.Split(value, `\`) {
		if part == "" || part == "." || part == ".." {
			continue
		}
		if strings.HasSuffix(part, " ") || strings.HasSuffix(part, ".") {
			return false
		}
		for _, character := range part {
			if character < 0x20 || character == 0x7f {
				return false
			}
		}
	}
	return true
}

func extensionOfWindowsPath(path string) string {
	path = strings.ReplaceAll(path, "/", `\`)
	index := strings.LastIndexByte(path, '\\')
	if index >= 0 {
		path = path[index+1:]
	}
	dot := strings.LastIndexByte(path, '.')
	if dot < 0 {
		return ""
	}
	return path[dot:]
}