package engine

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

func validateFilesystemContext(source Source, context *FilesystemContext, main parsedSource) *Diagnostic {
	if source.kind == sourceNone && context.FS == nil {
		return validateAbsentHostFilesystemContext(context)
	}
	if nativeContext(source, context) {
		resolved, diagnostic := resolveNativeFilesystemContext(source, context)
		if diagnostic != nil {
			return diagnostic
		}
		return validateResolvedFilesystemDirectories(resolved)
	}
	resolved, diagnostic := resolveHostFilesystemContext(source, context, main, nil)
	if diagnostic != nil {
		return diagnostic
	}
	if diagnostic := validateResolvedFilesystemDirectories(resolved); diagnostic != nil {
		return diagnostic
	}
	root, err := os.OpenRoot(resolved.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 validateAbsentHostFilesystemContext(context *FilesystemContext) *Diagnostic {
	rootPath, err := canonicalExistingPath(context.Root)
	if err != nil {
		value := importDiagnostic(CodeImportInvalid, "configuration root could not be canonicalized", nil)
		return &value
	}
	basePath := rootPath
	if context.BaseDir != "" {
		basePath, err = canonicalExistingPath(context.BaseDir)
		if err != nil {
			value := importDiagnostic(CodeImportInvalid, "import base directory could not be canonicalized", nil)
			return &value
		}
	}
	if !containedPath(rootPath, basePath) {
		value := importDiagnostic(CodeImportOutsideRoot, "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
		}
	}
	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 absentFilesystemOptionDiagnostics(context)
	case sourceSearch:
		if context.FS != nil {
			return absentFilesystemOptionDiagnostics(context)
		}
		// A selected host file can derive its root; absence requires an
		// explicit root. Check that compatibility only after selection.
		if context.BaseDir != "" && !filepath.IsAbs(context.BaseDir) {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "filesystem base directory must be an absolute host path")}
		}
	case sourceFile:
		if context.FS != nil {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "host file sources cannot use a native filesystem context")}
		}
		if context.BaseDir != "" {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")}
		}
	case sourceFilesystem:
		if context.FS == nil || context.FS.namespace == nil || source.namespace == nil || context.FS.namespace.token != source.namespace.token {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "filesystem file context must use the source namespace")}
		}
		if context.BaseDir != "" {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "file sources determine their own import base directory")}
		}
		if context.Root != "" && !fs.ValidPath(context.Root) {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "filesystem root must be a slash-relative valid path")}
		}
	case sourceBytes, sourceReader, sourceMapping:
		if context.BaseDir == "" || context.Root == "" {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "byte and reader filesystem context requires base and root directories")}
		}
		if context.FS != nil {
			if context.FS.namespace == nil || !fs.ValidPath(context.BaseDir) || !fs.ValidPath(context.Root) {
				return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "filesystem base and root must be slash-relative valid paths")}
			}
		} else 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 absentFilesystemOptionDiagnostics(context *FilesystemContext) []Diagnostic {
	if context.FS != nil {
		if context.FS.namespace == nil || nilFilesystem(context.FS.namespace.filesystem) || context.BaseDir == "" || context.Root == "" || !fs.ValidPath(context.BaseDir) || !fs.ValidPath(context.Root) {
			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "native filesystem context requires a namespace, base, and root directory")}
		}
	} else if context.Root == "" || !filepath.IsAbs(context.Root) || context.BaseDir != "" && !filepath.IsAbs(context.BaseDir) {
		return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "absent-input filesystem root and base directories must be absolute host paths")}
	}
	return nil
}

func nativeContext(source Source, context *FilesystemContext) bool {
	return source.kind == sourceFilesystem || context != nil && context.FS != 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))
}