package engine

import (
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"strings"
)

type resolvedFilesystemContext struct {
	native    *nativeNamespace
	hostToken *namespaceToken
	rootPath  string
	basePath  string
	mainPath  string
}

func resolveFilesystemContext(source Source, context *FilesystemContext, main parsedSource, hostToken *namespaceToken) (resolvedFilesystemContext, *Diagnostic) {
	if nativeContext(source, context) {
		return resolveNativeFilesystemContext(source, context)
	}
	return resolveHostFilesystemContext(source, context, main, hostToken)
}

func resolveNativeFilesystemContext(source Source, context *FilesystemContext) (resolvedFilesystemContext, *Diagnostic) {
	var namespace *nativeNamespace
	resolved := resolvedFilesystemContext{rootPath: ".", basePath: "."}
	if source.kind == sourceFilesystem {
		namespace = source.namespace
		resolved.mainPath = source.path
		resolved.basePath = path.Dir(source.path)
		if context != nil && context.Root != "" {
			resolved.rootPath = context.Root
		}
	} else if context != nil && context.FS != nil {
		namespace = context.FS.namespace
		resolved.rootPath, resolved.basePath = context.Root, context.BaseDir
	}
	if namespace == nil || nilFilesystem(namespace.filesystem) || !fs.ValidPath(resolved.rootPath) || !fs.ValidPath(resolved.basePath) {
		value := optionDiagnostic(CodeOptionsInvalid, "filesystem context is invalid")
		return resolvedFilesystemContext{}, &value
	}
	resolved.native = namespace
	if !containsNativePath(resolved.rootPath, resolved.basePath) || resolved.mainPath != "" && !containsNativePath(resolved.rootPath, resolved.mainPath) {
		value := importDiagnostic(CodeImportOutsideRoot, "selected source and import base must stay inside the configuration root", nil)
		return resolvedFilesystemContext{}, &value
	}
	return resolved, nil
}

func resolveHostFilesystemContext(source Source, context *FilesystemContext, main parsedSource, hostToken *namespaceToken) (resolvedFilesystemContext, *Diagnostic) {
	if main.source == nil || main.document == nil {
		value := importDiagnostic(CodeImportInvalid, "imports require a selected configuration source", nil)
		return resolvedFilesystemContext{}, &value
	}
	resolved := resolvedFilesystemContext{hostToken: hostToken}
	if source.kind == sourceFile {
		if context != nil && context.BaseDir != "" {
			value := optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")
			return resolvedFilesystemContext{}, &value
		}
		canonical := main.source.Path
		if canonical == "" {
			var err error
			canonical, err = canonicalExistingPath(source.path)
			if err != nil {
				value := importDiagnostic(CodeImportInvalid, "selected source path could not be canonicalized", nil)
				return resolvedFilesystemContext{}, &value
			}
		}
		resolved.mainPath = canonical
		resolved.basePath = filepath.Dir(canonical)
		resolved.rootPath = resolved.basePath
		if context != nil && context.Root != "" {
			rootPath, err := canonicalExistingPath(context.Root)
			if err != nil {
				value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
				return resolvedFilesystemContext{}, &value
			}
			resolved.rootPath = rootPath
		}
	} else {
		if context == nil || context.BaseDir == "" || context.Root == "" {
			value := optionDiagnostic(CodeOptionsInvalid, "byte and reader imports require absolute base and root directories")
			return resolvedFilesystemContext{}, &value
		}
		if !filepath.IsAbs(context.BaseDir) || !filepath.IsAbs(context.Root) {
			value := optionDiagnostic(CodeOptionsInvalid, "byte and reader import base and root directories must be absolute")
			return resolvedFilesystemContext{}, &value
		}
		var err error
		resolved.basePath, err = canonicalExistingPath(context.BaseDir)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "import base directory could not be canonicalized", nil)
			return resolvedFilesystemContext{}, &value
		}
		resolved.rootPath, err = canonicalExistingPath(context.Root)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
			return resolvedFilesystemContext{}, &value
		}
	}
	if !containedPath(resolved.rootPath, resolved.basePath) || resolved.mainPath != "" && !containedPath(resolved.rootPath, resolved.mainPath) {
		value := importDiagnostic(CodeImportOutsideRoot, "selected source and import base must stay inside the configuration root", nil)
		return resolvedFilesystemContext{}, &value
	}
	return resolved, nil
}

func containsNativePath(root, name string) bool {
	if !fs.ValidPath(name) || !fs.ValidPath(root) {
		return false
	}
	return root == "." || name == root || strings.HasPrefix(name, root+"/")
}

func validateResolvedFilesystemDirectories(resolved resolvedFilesystemContext) *Diagnostic {
	for _, directory := range []string{resolved.rootPath, resolved.basePath} {
		var info fs.FileInfo
		var err error
		if resolved.native != nil {
			info, err = fs.Stat(resolved.native.filesystem, directory)
		} else {
			info, err = os.Stat(directory)
		}
		if err != nil || !info.IsDir() {
			value := importDiagnostic(CodeImportInvalid, "configuration root and import base must be directories", nil)
			return &value
		}
	}
	return nil
}

func openResolvedFilesystemAccess(resolved resolvedFilesystemContext) (*filesystemAccess, error) {
	if resolved.native != nil {
		access := newNativeAccess(resolved.native.filesystem, resolved.rootPath, resolved.native.token)
		access.label = resolved.native.label
		return access, nil
	}
	access, err := openHostAccess(resolved.rootPath)
	if err != nil {
		return nil, err
	}
	if resolved.hostToken != nil {
		access.token = resolved.hostToken
	}
	return access, nil
}