From ba46937c3cf0a6c2fc602f6d52532e21982a885c Mon Sep 17 00:00:00 2001
From: bth <git@bth.moi>
Date: Mon, 19 Jan 2026 11:20:37 -0800
Subject: [PATCH] sort : port over full code, fix flag value iteration skipping
 in parseArgs

---
 pipe/pipe.go | 29 ++++++++++++++++++
 sort/sort.go | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 110 insertions(+), 2 deletions(-)
 create mode 100644 pipe/pipe.go

diff --git a/pipe/pipe.go b/pipe/pipe.go
new file mode 100644
index 0000000..2629823
--- /dev/null
+++ b/pipe/pipe.go
@@ -0,0 +1,29 @@
+package pipe
+
+import (
+	"errors"
+	"io"
+	"log"
+	"os"
+	"strings"
+)
+
+const Newline string = "\n"
+
+func isStdinLoaded() bool {
+	stat, _ := os.Stdin.Stat()
+	return (stat.Mode() & os.ModeCharDevice) == 0
+}
+
+func GetStdin() ([]string, error) {
+	if !isStdinLoaded() {
+		return nil, errors.New("stdin not loaded")
+	}
+	data, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// TODO: there's got to be a better way:
+	s, _ := strings.CutSuffix(string(data), Newline)
+	return strings.Split(s, Newline), nil
+}
diff --git a/sort/sort.go b/sort/sort.go
index 08513f2..7d21ec7 100644
--- a/sort/sort.go
+++ b/sort/sort.go
@@ -1,14 +1,20 @@
 package sort
 
 import (
+	"fmt"
 	"log"
+	"os"
+	"slices"
+	"strings"
 
 	"github.com/brtholomy/um/go/flags"
+	"github.com/brtholomy/um/go/pipe"
 )
 
 type options struct {
 	Source flags.Flag[string]
 	Key    flags.Flag[string]
+	Write  flags.Flag[bool]
 	Help   flags.Flag[bool]
 }
 
@@ -16,20 +22,27 @@ func initOpts() options {
 	return options{
 		flags.Flag[string]{"--source", "-s", "", "path to source list. reads from stdin if omitted."},
 		flags.Flag[string]{"--key", "-k", "", "path to sort key"},
+		flags.Flag[bool]{"--write", "-w", false, "write sorted list back to --key file"},
 		flags.Flag[bool]{"--help", "-h", false, "show help"},
 	}
 }
 
 func parseArgs(args []string) options {
 	opts := initOpts()
-	for i, arg := range args {
+
+	for i := 0; i < len(args); i++ {
+		arg := args[i]
 		switch {
 		case arg == opts.Source.Long || arg == opts.Source.Short:
 			flags.ValidValueOrExit(args, i)
 			opts.Source.Val = args[i+1]
+			i++
 		case arg == opts.Key.Long || arg == opts.Key.Short:
 			flags.ValidValueOrExit(args, i)
 			opts.Key.Val = args[i+1]
+			i++
+		case arg == opts.Write.Long || arg == opts.Write.Short:
+			opts.Write.Val = true
 		case arg == opts.Help.Long || arg == opts.Help.Short:
 			flags.Help("sort", opts)
 		default:
@@ -37,10 +50,76 @@ func parseArgs(args []string) options {
 			flags.Help("sort", opts)
 		}
 	}
+	if !opts.Key.IsSet() {
+		log.Printf("um sort: %s is required", opts.Key.Long)
+		flags.Help("sort", opts)
+	}
 	return opts
 }
 
+// reads files from stdin if present, otherwise from the filename:
+func fileListSplitMaybeStdin(f string) []string {
+	filelist, err := pipe.GetStdin()
+	if err != nil {
+		filelist = fileListSplit(f)
+	}
+	return filelist
+}
+
+// opens the given filename and splits into lines:
+func fileListSplit(f string) []string {
+	dat, err := os.ReadFile(f)
+	if err != nil {
+		// if this fails all is lost. just exit.
+		log.Fatal(fmt.Errorf("um sort: error opening file: %s\n%w", f, err))
+	}
+	return strings.Split(string(dat), pipe.Newline)
+}
+
+// record the order of the given filelist.
+func kMap(kslice []string) map[string]int {
+	m := make(map[string]int, 0)
+	for i, l := range kslice {
+		m[l] = i
+	}
+	return m
+}
+
+// write out the provided source slice while respecting the order provided by kmap
+func sort(sslice []string, kmap map[string]int) string {
+	oslice := make([]string, max(len(sslice), len(kmap))+1)
+	for _, l := range sslice {
+		// lines not represented in the key get appended to the end:
+		if _, ok := kmap[l]; !ok {
+			// we don't care that this might leave empty strings between:
+			oslice = append(oslice, l)
+			continue
+		}
+		// NOTE: raison d'etre of this whole thang:
+		// if present in the key, respect the order:
+		oslice[kmap[l]] = l
+	}
+	// delete empties and add a final newline
+	oslice = slices.DeleteFunc(oslice, func(e string) bool { return e == "" })
+	return strings.Join(oslice, pipe.Newline) + pipe.Newline
+}
+
+func Write(file string, content string) {
+	if err := os.WriteFile(file, []byte(content), 0664); err != nil {
+		log.Fatal(err)
+	}
+}
+
 func Sort(args []string) {
 	opts := parseArgs(args)
-	log.Println(opts)
+
+	sslice := fileListSplitMaybeStdin(opts.Source.Val)
+	kslice := fileListSplit(opts.Key.Val)
+	kmap := kMap(kslice)
+	out := sort(sslice, kmap)
+	if opts.Write.Val {
+		Write(opts.Key.Val, out)
+	} else {
+		fmt.Print(out)
+	}
 }