package adminassets

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"strings"

	webassets "ymhut-box/server/unified-management/web"
)

const (
	ModeEmbedded = "embedded"
	ModeDisk     = "disk"
)

type Diagnostics struct {
	Mode            string `json:"mode"`
	Source          string `json:"source"`
	BuildID         string `json:"buildId,omitempty"`
	CompiledBuildID string `json:"compiledBuildId,omitempty"`
	ManifestStatus  string `json:"manifestStatus"`
	ManifestEntries int    `json:"manifestEntries"`
	Ready           bool   `json:"ready"`
	ValidationError string `json:"validationError,omitempty"`
}

type Service struct {
	mode        string
	diskRoot    string
	embedRoot   string
	diagnostics Diagnostics
}

type manifestEntry struct {
	File           string   `json:"file"`
	CSS            []string `json:"css"`
	Assets         []string `json:"assets"`
	Imports        []string `json:"imports"`
	DynamicImports []string `json:"dynamicImports"`
}

type buildMetadata struct {
	BuildID string `json:"buildId"`
}

type fileReader func(string) ([]byte, error)

func New(mode, diskRoot, compiledBuildID string) *Service {
	mode = strings.ToLower(strings.TrimSpace(mode))
	if mode != ModeDisk && mode != ModeEmbedded {
		mode = DefaultMode()
	}
	service := &Service{
		mode:      mode,
		diskRoot:  diskRoot,
		embedRoot: "admin/dist",
	}
	service.diagnostics = service.validate(compiledBuildID)
	return service
}

func DefaultMode() string {
	if webassets.Embedded {
		return ModeEmbedded
	}
	return ModeDisk
}

func (s *Service) Mode() string {
	return s.mode
}

func (s *Service) Diagnostics() Diagnostics {
	return s.diagnostics
}

func (s *Service) ReadFile(name string) ([]byte, error) {
	name, err := cleanAssetPath(name)
	if err != nil {
		return nil, err
	}
	if !s.diagnostics.Ready {
		return nil, errors.New("admin asset source failed validation")
	}
	if s.mode == ModeEmbedded {
		return webassets.ReadFile(s.embedRoot + "/" + name)
	}
	return os.ReadFile(filepath.Join(s.diskRoot, filepath.FromSlash(name)))
}

func ValidateDisk(root, compiledBuildID string) Diagnostics {
	return validateSource(ModeDisk, root, compiledBuildID, func(name string) ([]byte, error) {
		return os.ReadFile(filepath.Join(root, filepath.FromSlash(name)))
	})
}

func ValidateEmbedded(compiledBuildID string) Diagnostics {
	const root = "admin/dist"
	return validateSource(ModeEmbedded, root, compiledBuildID, func(name string) ([]byte, error) {
		return webassets.ReadFile(root + "/" + name)
	})
}

func (s *Service) validate(compiledBuildID string) Diagnostics {
	if s.mode == ModeEmbedded {
		if !webassets.Embedded {
			return Diagnostics{
				Mode: s.mode, Source: s.embedRoot, CompiledBuildID: compiledBuildID,
				ManifestStatus: "unavailable", ValidationError: "binary was built without embed_web",
			}
		}
		return ValidateEmbedded(compiledBuildID)
	}
	return ValidateDisk(s.diskRoot, compiledBuildID)
}

func validateSource(mode, source, compiledBuildID string, read fileReader) Diagnostics {
	result := Diagnostics{
		Mode: mode, Source: source, CompiledBuildID: strings.TrimSpace(compiledBuildID),
		ManifestStatus: "invalid",
	}
	fail := func(err error) Diagnostics {
		result.ValidationError = err.Error()
		return result
	}
	if _, err := read("index.html"); err != nil {
		return fail(fmt.Errorf("read index.html: %w", err))
	}
	metadataBytes, err := read("admin-build.json")
	if err != nil {
		return fail(fmt.Errorf("read admin-build.json: %w", err))
	}
	var metadata buildMetadata
	if err := json.Unmarshal(metadataBytes, &metadata); err != nil {
		return fail(fmt.Errorf("parse admin-build.json: %w", err))
	}
	result.BuildID = strings.TrimSpace(metadata.BuildID)
	if result.BuildID == "" {
		return fail(errors.New("admin-build.json has an empty buildId"))
	}
	if result.CompiledBuildID != "" && result.CompiledBuildID != "dev" && result.BuildID != result.CompiledBuildID {
		return fail(fmt.Errorf("admin build ID %q does not match binary build ID %q", result.BuildID, result.CompiledBuildID))
	}
	manifestBytes, err := read("asset-manifest.json")
	if err != nil {
		return fail(fmt.Errorf("read asset-manifest.json: %w", err))
	}
	manifest := map[string]manifestEntry{}
	if err := json.Unmarshal(manifestBytes, &manifest); err != nil {
		return fail(fmt.Errorf("parse asset-manifest.json: %w", err))
	}
	if len(manifest) == 0 {
		return fail(errors.New("asset-manifest.json is empty"))
	}
	for key, entry := range manifest {
		if strings.TrimSpace(entry.File) == "" {
			return fail(fmt.Errorf("manifest entry %q has no output file", key))
		}
		for _, dependencyKey := range append(append([]string{}, entry.Imports...), entry.DynamicImports...) {
			if _, ok := manifest[dependencyKey]; !ok {
				return fail(fmt.Errorf("manifest entry %q references missing entry %q", key, dependencyKey))
			}
		}
		files := append([]string{entry.File}, entry.CSS...)
		files = append(files, entry.Assets...)
		for _, name := range files {
			name, cleanErr := cleanAssetPath(name)
			if cleanErr != nil {
				return fail(fmt.Errorf("manifest entry %q: %w", key, cleanErr))
			}
			data, readErr := read(name)
			if readErr != nil {
				return fail(fmt.Errorf("manifest entry %q is missing %s: %w", key, name, readErr))
			}
			if len(data) == 0 {
				return fail(fmt.Errorf("manifest entry %q references empty file %s", key, name))
			}
		}
	}
	result.ManifestEntries = len(manifest)
	result.ManifestStatus = "valid"
	result.Ready = true
	return result
}

func cleanAssetPath(name string) (string, error) {
	name = filepath.ToSlash(strings.TrimSpace(name))
	name = strings.TrimPrefix(name, "./")
	if name == "" || strings.HasPrefix(name, "/") || strings.Contains(name, "\\") {
		return "", fmt.Errorf("invalid admin asset path %q", name)
	}
	cleaned := filepath.ToSlash(filepath.Clean(name))
	if cleaned == "." || cleaned == ".." || strings.HasPrefix(cleaned, "../") {
		return "", fmt.Errorf("invalid admin asset path %q", name)
	}
	return cleaned, nil
}

func IsMissing(err error) bool {
	return errors.Is(err, fs.ErrNotExist)
}