package main

import (
	"fmt"
	"os"
	"sync"
)

var filesystem FileSystem = NewRealFileSystem()

// FileSystem abstracts filesystem operations so we can swap implementations
type FileSystem interface {
	Remove(path string) error
	RemoveAll(path string) error
	MkdirAll(path string, perm os.FileMode) error
	Symlink(source, target string) error
	Link(source, target string) error
	SummaryLines() []string
	IsDryRun() bool
}

const (
	opRemove    = "remove"
	opRemoveAll = "remove_all"
	opMkdirAll  = "mkdir_all"
	opSymlink   = "symlink"
	opHardlink  = "hardlink"
)

type operationRecord struct {
	kind   string
	source string
	target string
	err    error
	dryRun bool
}

func (r operationRecord) summaryLine() (string, bool) {
	if r.kind != opSymlink && r.kind != opHardlink {
		return "", false
	}

	kindLabel := "Symlink"
	if r.kind == opHardlink {
		kindLabel = "Hardlink"
	}

	status := "OK"
	if r.err != nil {
		status = fmt.Sprintf("FAIL: %v", r.err)
	} else if r.dryRun {
		status = "DRY-RUN"
	}

	return fmt.Sprintf("%s %s -> %s (%s)", kindLabel, r.source, r.target, status), true
}

type baseFileSystem struct {
	mu         sync.Mutex
	operations []operationRecord
}

func (b *baseFileSystem) addOperation(kind, source, target string, err error, dryRun bool) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.operations = append(b.operations, operationRecord{
		kind:   kind,
		source: source,
		target: target,
		err:    err,
		dryRun: dryRun,
	})
}

func (b *baseFileSystem) snapshot() []operationRecord {
	b.mu.Lock()
	defer b.mu.Unlock()
	ops := make([]operationRecord, len(b.operations))
	copy(ops, b.operations)
	return ops
}

func summarizeOperations(records []operationRecord) []string {
	var lines []string
	for _, record := range records {
		if line, ok := record.summaryLine(); ok {
			lines = append(lines, line)
		}
	}
	return lines
}

type realFileSystem struct {
	baseFileSystem
}

// NewRealFileSystem returns a filesystem implementation that writes to disk
func NewRealFileSystem() FileSystem {
	return &realFileSystem{}
}

func (fs *realFileSystem) Remove(path string) error {
	err := os.Remove(path)
	fs.addOperation(opRemove, "", path, err, false)
	return err
}

func (fs *realFileSystem) RemoveAll(path string) error {
	err := os.RemoveAll(path)
	fs.addOperation(opRemoveAll, "", path, err, false)
	return err
}

func (fs *realFileSystem) MkdirAll(path string, perm os.FileMode) error {
	err := os.MkdirAll(path, perm)
	fs.addOperation(opMkdirAll, "", path, err, false)
	return err
}

func (fs *realFileSystem) Symlink(source, target string) error {
	err := os.Symlink(source, target)
	fs.addOperation(opSymlink, source, target, err, false)
	return err
}

func (fs *realFileSystem) Link(source, target string) error {
	err := os.Link(source, target)
	fs.addOperation(opHardlink, source, target, err, false)
	return err
}

func (fs *realFileSystem) SummaryLines() []string {
	return summarizeOperations(fs.snapshot())
}

func (fs *realFileSystem) IsDryRun() bool {
	return false
}

type dryRunFileSystem struct {
	baseFileSystem
}

// NewDryRunFileSystem returns a filesystem implementation that only records operations
func NewDryRunFileSystem() FileSystem {
	return &dryRunFileSystem{}
}

func (fs *dryRunFileSystem) Remove(path string) error {
	fs.addOperation(opRemove, "", path, nil, true)
	return nil
}

func (fs *dryRunFileSystem) RemoveAll(path string) error {
	fs.addOperation(opRemoveAll, "", path, nil, true)
	return nil
}

func (fs *dryRunFileSystem) MkdirAll(path string, perm os.FileMode) error {
	fs.addOperation(opMkdirAll, "", path, nil, true)
	return nil
}

func (fs *dryRunFileSystem) Symlink(source, target string) error {
	fs.addOperation(opSymlink, source, target, nil, true)
	return nil
}

func (fs *dryRunFileSystem) Link(source, target string) error {
	fs.addOperation(opHardlink, source, target, nil, true)
	return nil
}

func (fs *dryRunFileSystem) SummaryLines() []string {
	return summarizeOperations(fs.snapshot())
}

func (fs *dryRunFileSystem) IsDryRun() bool {
	return true
}