// Package authstorage implements tht's hidden, stdin/stdout-only bridge for protected browser
// session files. It deliberately has no operator-facing commands or installation configuration.
package authstorage

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"unicode"

	"github.com/aritmolab/thothii/tools/tht/internal/safeio"
)

const (
	protocolVersion        = 1
	maximumProtocolBytes   = 64 * 1024
	maximumSessionBytes    = 16 * 1024
	maximumOIDCStateBytes  = 8 * 1024
	maximumAuthConfigBytes = 1024 * 1024
	defaultMaximumEntries  = 256
	maximumEntries         = 512
)

var (
	digestFilename     = regexp.MustCompile(`^[a-f0-9]{64}\.json$`)
	claimFilename      = regexp.MustCompile(`^[a-f0-9]{64}\.claim$`)
	oidcSlotFilename   = regexp.MustCompile(`^slot-(?:[0-5][0-9]|6[0-3])\.json$`)
	authConfigFilename = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]{0,249}\.yaml$`)
	errInvalid         = errors.New("auth storage request invalid")
)

type request struct {
	Version        int    `json:"version"`
	Operation      string `json:"operation"`
	Root           string `json:"root"`
	Directory      string `json:"directory,omitempty"`
	Filename       string `json:"filename,omitempty"`
	ContentBase64  string `json:"contentBase64,omitempty"`
	MaximumEntries int    `json:"maximumEntries,omitempty"`
	AfterName      string `json:"afterName,omitempty"`
	Continuation   bool   `json:"continuation,omitempty"`
}

type response struct {
	Version       int                             `json:"version"`
	OK            bool                            `json:"ok"`
	Created       bool                            `json:"created,omitempty"`
	Replaced      bool                            `json:"replaced,omitempty"`
	Removed       bool                            `json:"removed,omitempty"`
	Found         bool                            `json:"found,omitempty"`
	Claimed       bool                            `json:"claimed,omitempty"`
	ContentBase64 string                          `json:"contentBase64,omitempty"`
	Entries       *[]safeio.PrivateDirectoryEntry `json:"entries,omitempty"`
	More          *bool                           `json:"more,omitempty"`
	Validated     bool                            `json:"validated,omitempty"`
	Prepared      bool                            `json:"prepared,omitempty"`
}

// Run accepts exactly one strict JSON request on stdin and emits exactly one JSON response on
// stdout. All diagnostic text is fixed and goes only to stderr.
func Run(ctx context.Context, args []string, stdin io.Reader, stdout, stderr io.Writer) int {
	if len(args) != 0 || ctx == nil || stdin == nil || stdout == nil || stderr == nil {
		return fail(stderr)
	}
	if err := ctx.Err(); err != nil {
		return fail(stderr)
	}
	payload, err := io.ReadAll(io.LimitReader(stdin, maximumProtocolBytes+1))
	if err != nil || len(payload) > maximumProtocolBytes {
		return fail(stderr)
	}
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	var input request
	if err := decoder.Decode(&input); err != nil {
		return fail(stderr)
	}
	var extra any
	if err := decoder.Decode(&extra); err != io.EOF {
		return fail(stderr)
	}
	if err := ctx.Err(); err != nil {
		return fail(stderr)
	}
	result, err := execute(input)
	if err != nil || ctx.Err() != nil {
		return fail(stderr)
	}
	encoder := json.NewEncoder(stdout)
	encoder.SetEscapeHTML(false)
	if err := encoder.Encode(result); err != nil {
		return fail(stderr)
	}
	return 0
}

func fail(stderr io.Writer) int {
	_, _ = io.WriteString(stderr, "tht: auth storage request failed\n")
	return 1
}

func execute(input request) (response, error) {
	if input.Version != protocolVersion || !validOperationShape(input) {
		return response{}, errInvalid
	}
	if input.Operation == "validate-root" {
		if err := validateStorageLayout(input.Root); err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Validated: true}, nil
	}
	if input.Operation == "ensure-layout" {
		if err := ensureStorageLayout(input.Root); err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Prepared: true}, nil
	}
	if input.Operation == "read-auth-config" {
		root, err := existingPrivateRoot(input.Root)
		if err != nil {
			return response{}, errInvalid
		}
		contents, err := safeio.ReadCanonicalPrivateRegular(filepath.Join(root, input.Filename), maximumAuthConfigBytes)
		if err != nil {
			return response{}, errInvalid
		}
		return contentResponse(true, contents), nil
	}
	if !validDirectory(input.Directory) {
		return response{}, errInvalid
	}
	directory, err := storageDirectory(input.Root, input.Directory)
	if err != nil {
		return response{}, errInvalid
	}
	switch input.Operation {
	case "create":
		contents, err := decodeContents(input)
		if err != nil {
			return response{}, errInvalid
		}
		created, err := createPrivate(directory, input.Filename, contents)
		if err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Created: created}, nil
	case "read":
		contents, found, err := readPrivate(directory, input.Filename, recordMaximum(input.Directory))
		if err != nil {
			return response{}, errInvalid
		}
		return contentResponse(found, contents), nil
	case "replace":
		contents, err := decodeContents(input)
		if err != nil {
			return response{}, errInvalid
		}
		if err := safeio.ReplaceCanonicalRegular(filepath.Join(directory, input.Filename), contents, 0o600); err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Replaced: true}, nil
	case "remove":
		removed, err := removePrivate(directory, input.Filename)
		if err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Removed: removed}, nil
	case "list":
		limit := input.MaximumEntries
		if limit == 0 {
			limit = defaultMaximumEntries
		}
		if input.Continuation {
			page, err := safeio.ListCanonicalPrivateDirectoryPage(
				directory,
				limit,
				input.AfterName,
				digestFilename.MatchString,
			)
			if err != nil {
				return response{}, errInvalid
			}
			more := page.More
			return response{Version: protocolVersion, OK: true, Entries: &page.Entries, More: &more}, nil
		}
		entries, err := safeio.ListCanonicalPrivateDirectory(directory, limit)
		if err != nil {
			return response{}, errInvalid
		}
		for _, entry := range entries {
			if !digestFilename.MatchString(entry.Name) && !(input.Directory == "oidc" && (claimFilename.MatchString(entry.Name) || oidcSlotFilename.MatchString(entry.Name))) {
				return response{}, errInvalid
			}
		}
		return response{Version: protocolVersion, OK: true, Entries: &entries}, nil
	case "claim-consume":
		return claimConsume(directory, input.Filename)
	case "read-claim":
		contents, found, err := safeio.ReadCanonicalPrivateClaim(
			filepath.Join(directory, input.Filename),
			filepath.Join(directory, asClaimFilename(input.Filename)),
			maximumOIDCStateBytes,
		)
		if err != nil {
			return response{}, errInvalid
		}
		return contentResponse(found, contents), nil
	case "remove-claim":
		removed, err := safeio.RemoveCanonicalPrivateClaim(
			filepath.Join(directory, input.Filename),
			filepath.Join(directory, asClaimFilename(input.Filename)),
		)
		if err != nil {
			return response{}, errInvalid
		}
		return response{Version: protocolVersion, OK: true, Removed: removed}, nil
	default:
		return response{}, errInvalid
	}
}

func validOperationShape(input request) bool {
	noContents := input.ContentBase64 == ""
	noMaximumEntries := input.MaximumEntries == 0
	noAfterName := input.AfterName == ""
	noContinuation := !input.Continuation
	switch input.Operation {
	case "validate-root", "ensure-layout":
		return input.Directory == "" && input.Filename == "" && noContents && noMaximumEntries && noAfterName && noContinuation
	case "read-auth-config":
		return input.Directory == "" && authConfigFilename.MatchString(input.Filename) && noContents && noMaximumEntries && noAfterName && noContinuation
	case "create", "replace":
		return noMaximumEntries && noAfterName && noContinuation && (digestFilename.MatchString(input.Filename) || (input.Operation == "create" && input.Directory == "oidc" && oidcSlotFilename.MatchString(input.Filename)))
	case "read":
		return noContents && noMaximumEntries && noAfterName && noContinuation && (digestFilename.MatchString(input.Filename) || (input.Directory == "oidc" && oidcSlotFilename.MatchString(input.Filename)))
	case "remove":
		return noContents && noMaximumEntries && noAfterName && noContinuation && (digestFilename.MatchString(input.Filename) || (input.Directory == "oidc" && (claimFilename.MatchString(input.Filename) || oidcSlotFilename.MatchString(input.Filename))))
	case "list":
		return input.Filename == "" && noContents && input.MaximumEntries >= 0 && input.MaximumEntries <= maximumEntries &&
			((noContinuation && noAfterName) || (input.Continuation && input.Directory == "sessions" && input.MaximumEntries >= 1 && (noAfterName || digestFilename.MatchString(input.AfterName))))
	case "claim-consume", "read-claim", "remove-claim":
		return input.Directory == "oidc" && noContents && noMaximumEntries && noAfterName && noContinuation && digestFilename.MatchString(input.Filename)
	default:
		return false
	}
}

func preflightRoot(root string) (bool, error) {
	if !filepath.IsAbs(root) || filepath.Clean(root) != root || strings.IndexFunc(root, unicode.IsControl) >= 0 {
		return false, errInvalid
	}
	return safeio.PreflightPrivateDirectory(root)
}

func existingPrivateRoot(root string) (string, error) {
	exists, err := preflightRoot(root)
	if err != nil || !exists || safeio.ValidatePrivateDirectory(root) != nil {
		return "", errInvalid
	}
	return root, nil
}

func validateStorageLayout(root string) error {
	exists, err := preflightRoot(root)
	if err != nil {
		return errInvalid
	}
	if !exists {
		return nil
	}
	existingChildren := make([]string, 0, 2)
	for _, directory := range []string{"sessions", "oidc"} {
		path := filepath.Join(root, directory)
		if filepath.Dir(path) != root {
			return errInvalid
		}
		childExists, err := safeio.PreflightPrivateDirectory(path)
		if err != nil {
			return errInvalid
		}
		if childExists {
			existingChildren = append(existingChildren, path)
		}
	}
	// Close permission/identity races between the individual side-effect-free preflights.
	if safeio.ValidatePrivateDirectory(root) != nil {
		return errInvalid
	}
	for _, directory := range []string{"sessions", "oidc"} {
		if _, err := safeio.PreflightPrivateDirectory(filepath.Join(root, directory)); err != nil {
			return errInvalid
		}
	}
	for _, path := range existingChildren {
		if safeio.ValidatePrivateDirectory(path) != nil {
			return errInvalid
		}
	}
	return nil
}

func ensureStorageLayout(root string) error {
	if _, err := preflightRoot(root); err != nil || safeio.EnsurePrivateDirectory(root) != nil {
		return errInvalid
	}
	for _, directory := range []string{"sessions", "oidc"} {
		path := filepath.Join(root, directory)
		if filepath.Dir(path) != root || safeio.EnsurePrivateDirectory(path) != nil {
			return errInvalid
		}
	}
	if safeio.ValidatePrivateDirectory(root) != nil ||
		safeio.ValidatePrivateDirectory(filepath.Join(root, "sessions")) != nil ||
		safeio.ValidatePrivateDirectory(filepath.Join(root, "oidc")) != nil {
		return errInvalid
	}
	return nil
}

func contentResponse(found bool, contents []byte) response {
	if !found {
		return response{Version: protocolVersion, OK: true}
	}
	return response{Version: protocolVersion, OK: true, Found: true, ContentBase64: base64.StdEncoding.EncodeToString(contents)}
}

func storageDirectory(root, directory string) (string, error) {
	if _, err := preflightRoot(root); err != nil || safeio.EnsurePrivateDirectory(root) != nil {
		return "", errInvalid
	}
	path := filepath.Join(root, directory)
	if filepath.Dir(path) != root || safeio.EnsurePrivateDirectory(path) != nil {
		return "", errInvalid
	}
	return path, nil
}

func validDirectory(value string) bool {
	return value == "sessions" || value == "oidc"
}

func recordMaximum(directory string) int64 {
	if directory == "oidc" {
		return maximumOIDCStateBytes
	}
	return maximumSessionBytes
}

func decodeContents(input request) ([]byte, error) {
	contents, err := base64.StdEncoding.DecodeString(input.ContentBase64)
	if err != nil || len(contents) == 0 || int64(len(contents)) > recordMaximum(input.Directory) {
		return nil, errInvalid
	}
	return contents, nil
}

func createPrivate(directory, filename string, contents []byte) (bool, error) {
	path := filepath.Join(directory, filename)
	if _, err := os.Lstat(path); err == nil {
		if safeio.ValidatePrivateRegular(path) != nil {
			return false, errInvalid
		}
		return false, nil
	} else if !errors.Is(err, os.ErrNotExist) {
		return false, errInvalid
	}
	if err := safeio.WriteCanonicalNewPrivateFile(path, contents, 0o600); err == nil {
		return true, nil
	}
	if safeio.ValidatePrivateRegular(path) == nil {
		return false, nil
	}
	return false, errInvalid
}

func readPrivate(directory, filename string, maximum int64) ([]byte, bool, error) {
	path := filepath.Join(directory, filename)
	if _, err := os.Lstat(path); errors.Is(err, os.ErrNotExist) {
		return nil, false, nil
	} else if err != nil {
		return nil, false, errInvalid
	}
	contents, err := safeio.ReadCanonicalPrivateRegular(path, maximum)
	if err != nil {
		return nil, false, errInvalid
	}
	return contents, true, nil
}

func removePrivate(directory, filename string) (bool, error) {
	path := filepath.Join(directory, filename)
	if _, err := os.Lstat(path); errors.Is(err, os.ErrNotExist) {
		return false, nil
	} else if err != nil {
		return false, errInvalid
	}
	if err := safeio.RemoveCanonicalPrivateRegular(path); err != nil {
		return false, errInvalid
	}
	return true, nil
}

func claimConsume(directory, filename string) (response, error) {
	source := filepath.Join(directory, filename)
	claim := filepath.Join(directory, asClaimFilename(filename))
	claimed, err := safeio.ClaimCanonicalPrivateRegular(source, claim)
	if err != nil {
		return response{}, errInvalid
	}
	if !claimed {
		return response{Version: protocolVersion, OK: true}, nil
	}
	contents, found, err := safeio.ReadCanonicalPrivateClaim(source, claim, maximumOIDCStateBytes)
	if err != nil || !found {
		return response{}, errInvalid
	}
	removed, err := safeio.RemoveCanonicalPrivateClaim(source, claim)
	if err != nil || !removed {
		return response{}, errInvalid
	}
	return contentResponse(true, contents), nil
}

func asClaimFilename(filename string) string {
	return strings.TrimSuffix(filename, ".json") + ".claim"
}