Initial commit

Makefile

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+VERSION := $(shell git describe --abbrev=0 --tags --always)
+LDFLAGS := -X main.Version=$(VERSION)
+
+# ==================================================================================== #
+# HELPERS
+# ==================================================================================== #
+
+## help: print this help message
+.PHONY: help
+help:
+	@echo "Usage:"
+	@sed -n "s/^##//p" ${MAKEFILE_LIST} | column -t -s ":" |  sed -e "s/^/ /"
+
+.PHONY: confirm
+confirm:
+	@echo "Are you sure? (y/n) \c"
+	@read answer; \
+	if [ "$$answer" != "y" ]; then \
+		echo "Aborting."; \
+		exit 1; \
+	fi
+
+# ==================================================================================== #
+# QUALITY CONTROL
+# ==================================================================================== #
+
+## audit: run quality control checks
+.PHONY: audit
+audit: test
+	go mod tidy -diff
+	go mod verify
+	test -z "$(shell gofmt -l .)" 
+	go vet ./...
+	go run honnef.co/go/tools/cmd/staticcheck@latest -checks=all,-ST1000,-U1000 ./...
+	go run golang.org/x/vuln/cmd/govulncheck@latest ./...
+
+## test: run all tests
+.PHONY: test
+test:
+	go test -v -race -buildvcs ./...
+
+# ==================================================================================== #
+# DEVELOPMENT
+# ==================================================================================== #
+
+## tidy: tidy and format all .go files
+.PHONY: tidy
+tidy:
+	go mod tidy
+	go fmt ./...
+
+## build/edgo: build the cmd/edgo application
+.PHONY: build/edgo
+build/edgo:
+	@go build -v -ldflags "$(LDFLAGS)" -o=./tmp/edgo ./cmd/edgo
+
+## run/edgo: run the cmd/edgo application
+.PHONY: run/edgo
+run/edgo: build/edgo
+	@./tmp/edgo
+
+# vim: set tabstop=4 shiftwidth=4 noexpandtab

README.md

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+# edgo
+
+A minimal implementation of the classic Unix line editor `ed` written in Go.
+
+## Usage
+
+### Basic Operation
+
+```bash
+# Start with empty buffer
+edgo
+
+# Edit a file
+edgo filename.txt
+
+# Start with custom prompt
+edgo -p "* "
+```
+
+### Command Line Flags
+
+- `-p string`: Set custom prompt (default "\*")
+- `-v`: Display version information and exit
+
+### Example Session
+
+```
+$ edgo
+*a
+hello world
+line two
+.
+*w file.txt
+2
+*q
+```
+
+Please make sure to update tests as appropriate.
+
+## TODO
+
+- [ ] print buffer size on load
+- [ ] don't show prompt when appending/inserting
+- [ ] support basic error messages
+- [ ] enable showing error messages with H similar to P
+- [ ] Line ranges (e.g., `1,5p`)
+- [ ] Search commands (`/pattern/`)
+- [ ] Substitute command (`s/old/new/`)
+- [ ] Copy/move lines
+- [ ] Undo functionality

cmd/edgo/command.go

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+package main
+
+import "strings"
+
+type Command struct {
+	name string
+}
+
+func parseCommand(input string) Command {
+	return Command{name: strings.TrimLeft(input, " ")}
+}

cmd/edgo/commands.go

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+package main
+
+import "fmt"
+
+func (ed *Editor) cmdQuit() error {
+	ed.running = false
+	return nil
+}
+
+func (ed *Editor) cmdTogglePrompt() error {
+	ed.isPromptShown = !ed.isPromptShown
+	return nil
+}
+
+func (ed *Editor) cmdToggleShowFullError() error {
+	ed.isFullErrorShown = !ed.isFullErrorShown
+
+	if ed.isFullErrorShown {
+		ed.cmdShowLastError()
+	}
+
+	return nil
+}
+
+func (ed *Editor) cmdShowLastError() error {
+	if ed.lastError != nil {
+		fmt.Fprintln(ed.writer, ed.lastError)
+	}
+	return nil
+}

cmd/edgo/editor.go

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+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+)
+
+type Editor struct {
+	lastError        error
+	reader           io.Reader
+	writer           io.Writer
+	prompt           string
+	mode             EditorMode
+	isPromptShown    bool
+	isFullErrorShown bool
+	running          bool
+}
+
+func NewEditor(reader io.Reader, writer io.Writer, prompt string, isPromptShown bool) *Editor {
+	return &Editor{
+		reader:        reader,
+		writer:        writer,
+		prompt:        prompt,
+		isPromptShown: isPromptShown,
+		mode:          ModeCommand,
+	}
+}
+
+func (ed *Editor) printPrompt() {
+	if ed.isPromptShown {
+		fmt.Fprint(ed.writer, ed.prompt)
+	}
+}
+
+func (ed *Editor) printError() {
+	fmt.Fprintln(ed.writer, "?")
+	if ed.isFullErrorShown {
+		fmt.Fprintln(ed.writer, ed.lastError)
+	}
+}
+
+func (ed *Editor) executeCommand(cmd Command) {
+	var err error
+
+	switch cmd.name {
+	case "P":
+		err = ed.cmdTogglePrompt()
+	case "h":
+		err = ed.cmdShowLastError()
+	case "H":
+		err = ed.cmdToggleShowFullError()
+	case "q":
+		err = ed.cmdQuit()
+	case "Q":
+		err = ed.cmdQuit()
+	default:
+		err = ErrUnknownCommand
+		ed.printError()
+	}
+
+	if err != nil {
+		ed.lastError = err
+	}
+}
+
+func (ed *Editor) Run() error {
+	scanner := bufio.NewScanner(ed.reader)
+	ed.running = true
+
+	for ed.running {
+		ed.printPrompt()
+
+		if !scanner.Scan() {
+			if err := scanner.Err(); err != nil {
+				return fmt.Errorf("input error: %w", err)
+			}
+			break
+		}
+
+		cmd := parseCommand(scanner.Text())
+		ed.executeCommand(cmd)
+	}
+
+	return nil
+}

cmd/edgo/errors.go

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+package main
+
+import "errors"
+
+var ErrUnknownCommand = errors.New("unknown command")

cmd/edgo/main.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+var Version = "v0.0.0"
+
+func main() {
+	var (
+		promptFlag     = flag.String("p", "", "Specify a command prompt. This may be toggled on and off with the P command.")
+		displayVersion = flag.Bool("v", false, "Display version and exit")
+	)
+
+	flag.Parse()
+
+	if *displayVersion {
+		fmt.Printf("%s version %s\n", os.Args[0], Version)
+		os.Exit(0)
+	}
+
+	isPromptShown := *promptFlag != ""
+	prompt := *promptFlag
+	if prompt == "" {
+		prompt = "*"
+	}
+
+	editor := NewEditor(os.Stdin, os.Stdout, prompt, isPromptShown)
+	if err := editor.Run(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
+}

cmd/edgo/mode.go

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+package main
+
+type EditorMode int
+
+const (
+	ModeCommand EditorMode = iota
+)

go.mod

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+module github.com/eckertalex/edgo
+
+go 1.23.2

test.txt

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+A spark begins its climb in line one,
+By line two, the night’s song has begun.
+A hush drifts down like snow by three,
+Then line four hums a midnight key.
+Five's a whisper, soft and slow,
+Six draws shadows long and low.
+Seven spins the stars on cue,
+Eight wraps the world in twilight's blue.