// Copyright 2022 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package bp2build

import (
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"

	"android/soong/android"
	"android/soong/shared"
)

// A tree structure that describes what to do at each directory in the created
// symlink tree. Currently it is used to enumerate which files/directories
// should be excluded from symlinking. Each instance of "node" represents a file
// or a directory. If excluded is true, then that file/directory should be
// excluded from symlinking. Otherwise, the node is not excluded, but one of its
// descendants is (otherwise the node in question would not exist)
type node struct {
	name     string
	excluded bool // If false, this is just an intermediate node
	children map[string]*node
}

// Ensures that the node for the given path exists in the tree and returns it.
func ensureNodeExists(root *node, path string) *node {
	if path == "" {
		return root
	}

	if path[len(path)-1] == '/' {
		path = path[:len(path)-1] // filepath.Split() leaves a trailing slash
	}

	dir, base := filepath.Split(path)

	// First compute the parent node...
	dn := ensureNodeExists(root, dir)

	// then create the requested node as its direct child, if needed.
	if child, ok := dn.children[base]; ok {
		return child
	} else {
		dn.children[base] = &node{base, false, make(map[string]*node)}
		return dn.children[base]
	}
}

// Turns a list of paths to be excluded into a tree made of "node" objects where
// the specified paths are marked as excluded.
func treeFromExcludePathList(paths []string) *node {
	result := &node{"", false, make(map[string]*node)}

	for _, p := range paths {
		ensureNodeExists(result, p).excluded = true
	}

	return result
}

func mergeBuildFiles(output string, srcBuildFile string, generatedBuildFile string, verbose bool) error {

	srcBuildFileContent, err := os.ReadFile(srcBuildFile)
	if err != nil {
		return err
	}

	generatedBuildFileContent, err := os.ReadFile(generatedBuildFile)
	if err != nil {
		return err
	}

	// There can't be a package() call in both the source and generated BUILD files.
	// bp2build will generate a package() call for licensing information, but if
	// there's no licensing information, it will still generate a package() call
	// that just sets default_visibility=public. If the handcrafted build file
	// also has a package() call, we'll allow it to override the bp2build
	// generated one if it doesn't have any licensing information. If the bp2build
	// one has licensing information and the handcrafted one exists, we'll leave
	// them both in for bazel to throw an error.
	packageRegex := regexp.MustCompile(`(?m)^package\s*\(`)
	packageDefaultVisibilityRegex := regexp.MustCompile(`(?m)^package\s*\(\s*default_visibility\s*=\s*\[\s*"//visibility:public",?\s*]\s*\)`)
	if packageRegex.Find(srcBuildFileContent) != nil {
		if verbose && packageDefaultVisibilityRegex.Find(generatedBuildFileContent) != nil {
			fmt.Fprintf(os.Stderr, "Both '%s' and '%s' have a package() target, removing the first one\n",
				generatedBuildFile, srcBuildFile)
		}
		generatedBuildFileContent = packageDefaultVisibilityRegex.ReplaceAll(generatedBuildFileContent, []byte{})
	}

	outFile, err := os.Create(output)
	if err != nil {
		return err
	}

	_, err = outFile.Write(generatedBuildFileContent)
	if err != nil {
		return err
	}

	if generatedBuildFileContent[len(generatedBuildFileContent)-1] != '\n' {
		_, err = outFile.WriteString("\n")
		if err != nil {
			return err
		}
	}

	_, err = outFile.Write(srcBuildFileContent)
	return err
}

// Calls readdir() and returns it as a map from the basename of the files in dir
// to os.FileInfo.
func readdirToMap(dir string) map[string]os.FileInfo {
	entryList, err := ioutil.ReadDir(dir)
	result := make(map[string]os.FileInfo)

	if err != nil {
		if os.IsNotExist(err) {
			// It's okay if a directory doesn't exist; it just means that one of the
			// trees to be merged contains parts the other doesn't
			return result
		} else {
			fmt.Fprintf(os.Stderr, "Cannot readdir '%s': %s\n", dir, err)
			os.Exit(1)
		}
	}

	for _, fi := range entryList {
		result[fi.Name()] = fi
	}

	return result
}

// Creates a symbolic link at dst pointing to src
func symlinkIntoForest(topdir, dst, src string) {
	err := os.Symlink(shared.JoinPath(topdir, src), shared.JoinPath(topdir, dst))
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cannot create symlink at '%s' pointing to '%s': %s", dst, src, err)
		os.Exit(1)
	}
}

func isDir(path string, fi os.FileInfo) bool {
	if (fi.Mode() & os.ModeSymlink) != os.ModeSymlink {
		return fi.IsDir()
	}

	fi2, statErr := os.Stat(path)
	if statErr == nil {
		return fi2.IsDir()
	}

	// Check if this is a dangling symlink. If so, treat it like a file, not a dir.
	_, lstatErr := os.Lstat(path)
	if lstatErr != nil {
		fmt.Fprintf(os.Stderr, "Cannot stat or lstat '%s': %s\n%s\n", path, statErr, lstatErr)
		os.Exit(1)
	}

	return false
}

// Recursively plants a symlink forest at forestDir. The symlink tree will
// contain every file in buildFilesDir and srcDir excluding the files in
// exclude. Collects every directory encountered during the traversal of srcDir
// into acc.
func plantSymlinkForestRecursive(cfg android.Config, topdir string, forestDir string, buildFilesDir string, srcDir string, exclude *node, acc *[]string, okay *bool) {
	if exclude != nil && exclude.excluded {
		// This directory is not needed, bail out
		return
	}

	*acc = append(*acc, srcDir)
	srcDirMap := readdirToMap(shared.JoinPath(topdir, srcDir))
	buildFilesMap := readdirToMap(shared.JoinPath(topdir, buildFilesDir))

	renamingBuildFile := false
	if _, ok := srcDirMap["BUILD"]; ok {
		if _, ok := srcDirMap["BUILD.bazel"]; !ok {
			if _, ok := buildFilesMap["BUILD.bazel"]; ok {
				renamingBuildFile = true
				srcDirMap["BUILD.bazel"] = srcDirMap["BUILD"]
				delete(srcDirMap, "BUILD")
			}
		}
	}

	allEntries := make(map[string]bool)
	for n := range srcDirMap {
		allEntries[n] = true
	}

	for n := range buildFilesMap {
		allEntries[n] = true
	}

	err := os.MkdirAll(shared.JoinPath(topdir, forestDir), 0777)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Cannot mkdir '%s': %s\n", forestDir, err)
		os.Exit(1)
	}

	for f := range allEntries {
		if f[0] == '.' {
			continue // Ignore dotfiles
		}

		// The full paths of children in the input trees and in the output tree
		forestChild := shared.JoinPath(forestDir, f)
		srcChild := shared.JoinPath(srcDir, f)
		if f == "BUILD.bazel" && renamingBuildFile {
			srcChild = shared.JoinPath(srcDir, "BUILD")
		}
		buildFilesChild := shared.JoinPath(buildFilesDir, f)

		// Descend in the exclusion tree, if there are any excludes left
		var excludeChild *node = nil
		if exclude != nil {
			if f == "BUILD.bazel" && renamingBuildFile {
				excludeChild = exclude.children["BUILD"]
			} else {
				excludeChild = exclude.children[f]
			}
		}

		srcChildEntry, sExists := srcDirMap[f]
		buildFilesChildEntry, bExists := buildFilesMap[f]

		if excludeChild != nil && excludeChild.excluded {
			if bExists {
				symlinkIntoForest(topdir, forestChild, buildFilesChild)
			}
			continue
		}

		sDir := false
		bDir := false
		if sExists {
			sDir = isDir(shared.JoinPath(topdir, srcChild), srcChildEntry)
		}

		if bExists {
			bDir = isDir(shared.JoinPath(topdir, buildFilesChild), buildFilesChildEntry)
		}

		if !sExists {
			if bDir && excludeChild != nil {
				// Not in the source tree, but we have to exclude something from under
				// this subtree, so descend
				plantSymlinkForestRecursive(cfg, topdir, forestChild, buildFilesChild, srcChild, excludeChild, acc, okay)
			} else {
				// Not in the source tree, symlink BUILD file
				symlinkIntoForest(topdir, forestChild, buildFilesChild)
			}
		} else if !bExists {
			if sDir && excludeChild != nil {
				// Not in the build file tree, but we have to exclude something from
				// under this subtree, so descend
				plantSymlinkForestRecursive(cfg, topdir, forestChild, buildFilesChild, srcChild, excludeChild, acc, okay)
			} else {
				// Not in the build file tree, symlink source tree, carry on
				symlinkIntoForest(topdir, forestChild, srcChild)
			}
		} else if sDir && bDir {
			// Both are directories. Descend.
			plantSymlinkForestRecursive(cfg, topdir, forestChild, buildFilesChild, srcChild, excludeChild, acc, okay)
		} else if !sDir && !bDir {
			// Neither is a directory. Merge them.
			srcBuildFile := shared.JoinPath(topdir, srcChild)
			generatedBuildFile := shared.JoinPath(topdir, buildFilesChild)
			// Add the src and generated build files as dependencies so that bp2build
			// is rerun when they change. Currently, this is only really necessary
			// for srcBuildFile, because if we regenerate the generated build files
			// we will always rerun the symlink forest generation as well. If that
			// is later split up into separate, fully dependency-tracing steps, then
			// we'll need srcBuildFile as well. Adding srcBuildFile here today
			// technically makes it a dependency of bp2build_workspace_marker, which
			// also implicitly outputs that file, but since bp2build_workspace_marker
			// will always have a newer timestamp than the generatedBuildFile it
			// shouldn't be a problem.
			*acc = append(*acc, srcBuildFile, generatedBuildFile)
			err = mergeBuildFiles(shared.JoinPath(topdir, forestChild), srcBuildFile, generatedBuildFile, cfg.IsEnvTrue("BP2BUILD_VERBOSE"))
			if err != nil {
				fmt.Fprintf(os.Stderr, "Error merging %s and %s: %s",
					srcBuildFile, generatedBuildFile, err)
				*okay = false
			}
		} else {
			// Both exist and one is a file. This is an error.
			fmt.Fprintf(os.Stderr,
				"Conflict in workspace symlink tree creation: both '%s' and '%s' exist and exactly one is a directory\n",
				srcChild, buildFilesChild)
			*okay = false
		}
	}
}

// Creates a symlink forest by merging the directory tree at "buildFiles" and
// "srcDir" while excluding paths listed in "exclude". Returns the set of paths
// under srcDir on which readdir() had to be called to produce the symlink
// forest.
func PlantSymlinkForest(cfg android.Config, topdir string, forest string, buildFiles string, srcDir string, exclude []string) []string {
	deps := make([]string, 0)
	os.RemoveAll(shared.JoinPath(topdir, forest))
	excludeTree := treeFromExcludePathList(exclude)
	okay := true
	plantSymlinkForestRecursive(cfg, topdir, forest, buildFiles, srcDir, excludeTree, &deps, &okay)
	if !okay {
		os.Exit(1)
	}
	return deps
}