package configkit

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

func validateFilesystemContext(source Source, context *FilesystemContext, main parsedSource) *Diagnostic {
	rootPath, _, _, diagnostic := importFilesystem(source, context, main)
	if diagnostic != nil {
		return diagnostic
	}
	root, err := os.OpenRoot(rootPath)
	if err != nil {
		value := globFilesystemDiagnostic(err, "configuration root could not be opened", Location{})
		value.Primary = nil
		return &value
	}
	if err := root.Close(); err != nil {
		value := importDiagnostic(CodeImportRead, "configuration root could not be closed", nil)
		return &value
	}
	return nil
}

func filesystemOptionDiagnostics(source Source, context *FilesystemContext) []Diagnostic {
	switch source.kind {
	case sourceNone:
		return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "NoSource cannot use filesystem context")}
	case sourceFile:
		if context.BaseDir != "" {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")}
		}
	case sourceBytes, sourceReader:
		if context.BaseDir == "" || context.Root == "" {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "byte and reader filesystem context requires base and root directories")}
		}
		if !filepath.IsAbs(context.BaseDir) || !filepath.IsAbs(context.Root) {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "byte and reader filesystem base and root directories must be absolute")}
		}
	}
	return nil
}

func importFilesystem(source Source, context *FilesystemContext, main parsedSource) (rootPath, basePath, mainPath string, diagnostic *Diagnostic) {
	if main.source == nil || main.document == nil {
		value := importDiagnostic(CodeImportInvalid, "imports require a selected configuration source", nil)
		return "", "", "", &value
	}

	if source.kind == sourceFile {
		if context != nil && context.BaseDir != "" {
			value := optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")
			return "", "", "", &value
		}
		canonical, err := canonicalExistingPath(source.path)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "selected source path could not be canonicalized", nil)
			return "", "", "", &value
		}
		mainPath = canonical
		basePath = filepath.Dir(canonical)
		rootPath = 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 "", "", "", &value
			}
		}
	} else {
		if context == nil || context.BaseDir == "" || context.Root == "" {
			value := optionDiagnostic(CodeOptionsInvalid, "byte and reader imports require absolute base and root directories")
			return "", "", "", &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 "", "", "", &value
		}
		var err error
		basePath, err = canonicalExistingPath(context.BaseDir)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "import base directory could not be canonicalized", nil)
			return "", "", "", &value
		}
		rootPath, err = canonicalExistingPath(context.Root)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
			return "", "", "", &value
		}
	}
	if !containedPath(rootPath, basePath) || (mainPath != "" && !containedPath(rootPath, mainPath)) {
		value := importDiagnostic(CodeImportOutsideRoot, "selected source and import base must stay inside the configuration root", nil)
		return "", "", "", &value
	}
	for _, candidate := range []string{rootPath, basePath} {
		info, err := os.Stat(candidate)
		if err != nil || !info.IsDir() {
			value := importDiagnostic(CodeImportInvalid, "configuration root and import base must be directories", nil)
			return "", "", "", &value
		}
	}
	return rootPath, basePath, mainPath, nil
}

func canonicalExistingPath(name string) (string, error) {
	absolute, err := filepath.Abs(name)
	if err != nil {
		return "", err
	}
	return filepath.EvalSymlinks(filepath.Clean(absolute))
}

func containedPath(root, target string) bool {
	relative, err := filepath.Rel(root, target)
	if err != nil || filepath.IsAbs(relative) {
		return false
	}
	return relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))
}