// mgsh (git shell) — Go port of the original Perl mgsh (mwx'2026).
//
// A small interactive shell / command-line wrapper around a self-hosted bare
// git server, reachable over ssh. It manages a flat set of projects living
// under a base directory (default $HOME/src, or /db/src on Linux).
//
// Configuration lives in ~/.mgshrc and/or MGSH_* environment variables; see
// config.go and the README.
package main

import (
	"fmt"
	"io"
	"os"
	"os/user"
	"path/filepath"
	"strings"

	"github.com/chzyer/readline"
)

// VERSION is a var (not const) so the build script can inject the current build
// number via -ldflags "-X main.VERSION=...". The default is used for a plain
// `go build`.
var VERSION = "4.0.0"

const INFO = "mwx'2026"

// Global runtime state.
var (
	baseCfg  Config // global configuration: ~/.mgshrc + MGSH_*
	cfg      Config // effective configuration: baseCfg + the project's .mgshrc
	cfgPRJ   string // project whose .mgshrc is currently applied
	cfgFresh bool   // whether cfg has been resolved at least once
	BASE     string // project base directory (baseCfg.Base)
	URL      string // ssh:// clone/push URL
	PRJ      string // current project (may be empty)
	DIR      string // current working directory (BASE or BASE/PRJ)
	HOST     string // short hostname
	USER     string // current user name
	BPLSTATE string // "/OFF" if build.pl symlink points at a *.off file
	BRANCH   string // current git branch of the active project (if any)
	DIRTY    bool   // whether the active project has uncommitted changes
	useColor bool   // whether to render ANSI colors
)

func main() {
	// Answered before setup(), which exits when nothing is configured yet: an
	// update has to work on a machine that has never run mgsh, and `--version`
	// is what the freshly downloaded binary is probed with, right there.
	if updateFlags() {
		return
	}

	setup()
	useColor = readline.IsTerminal(int(os.Stdout.Fd()))

	fmt.Println(banner())

	// preset project from the first argument (interactive launch: `mgsh myproj`)
	if len(os.Args) > 1 && validProject(os.Args[1]) && isDir(BASE+"/"+os.Args[1]) {
		PRJ = os.Args[1]
	}

	// command-line mode: `mgsh <command> [args...]`
	clCmd, cmdline, isHelp := parseArgs()
	if isHelp {
		help()
		return
	}
	if clCmd != 0 {
		PRJ = projectFromCwd()
		if clCmd == 2 {
			cmdline = strings.TrimSpace(cmdline + " " + PRJ)
		}
		updateDirState()
		runCommand(cmdline)
		updateNote() // after the output: a footer, not a headline
		return
	}

	updateNote() // before the prompt: a session starts here, not when it ends
	runInteractive()
}

// updateFlags answers the self-update options and reports whether it did. They
// are deliberately spelled with dashes and kept out of parseArgs: `mgsh update`
// is the command for everyday use, and these are what works when there is no
// configuration to read yet.
func updateFlags() bool {
	if len(os.Args) < 2 {
		return false
	}
	switch os.Args[1] {
	case "--version":
		fmt.Printf("mgsh %s\n", VERSION)
	case "--update":
		if err := selfUpdate.install(os.Stdout); err != nil {
			fmt.Fprintf(os.Stderr, "mgsh: %v\n", err)
			os.Exit(1)
		}
	case "--check-update":
		if err := selfUpdate.check(os.Stdout); err != nil {
			fmt.Fprintf(os.Stderr, "mgsh: %v\n", err)
			os.Exit(1)
		}
	case updateRefreshFlag: // the background run, not in the help
		selfUpdate.refresh()
	default:
		return false
	}
	return true
}

// updateNote prints the once-a-day hint, when there is one. It costs nothing:
// the line comes from the note in the cache directory, and the asking behind it
// happens in the background, at most once a day.
func updateNote() {
	if hint := selfUpdate.daily(); hint != "" {
		fmt.Fprintln(os.Stderr, col(cDark, hint))
	}
}

// runInteractive drives the colored, history- and completion-enabled REPL.
func runInteractive() {
	home, _ := os.UserHomeDir()

	rl, err := readline.NewEx(&readline.Config{
		Prompt:            promptString(),
		HistoryFile:       filepath.Join(home, ".mgsh_history"),
		AutoComplete:      completer(),
		InterruptPrompt:   "^C",
		EOFPrompt:         "quit",
		HistorySearchFold: true,
	})
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	defer rl.Close()

	for {
		updateDirState()
		rl.SetPrompt(promptString())
		line, err := rl.Readline()
		if err == readline.ErrInterrupt { // Ctrl-C: clear a typed line, else quit
			if len(line) == 0 {
				break
			}
			continue
		} else if err == io.EOF { // Ctrl-D
			break
		} else if err != nil { // detached/broken terminal: don't spin
			fmt.Fprintln(os.Stderr, err)
			break
		}
		if !runCommand(strings.TrimSpace(line)) {
			break
		}
	}
}

// projectFromCwd derives the active project from the working directory: the
// first path element below BASE, so running `mgsh push` from deep inside a
// project still addresses the project itself and not the subdirectory.
// Returns "" when the working directory is outside BASE.
func projectFromCwd() string {
	pwd, err := os.Getwd()
	if err != nil || !strings.HasPrefix(pwd, BASE+"/") {
		return ""
	}
	rel := pwd[len(BASE)+1:]
	if i := strings.IndexByte(rel, '/'); i >= 0 {
		rel = rel[:i]
	}
	if !validProject(rel) {
		return ""
	}
	return rel
}

// parseArgs mirrors the original command-line dispatch table. It returns the
// "CLCMD" class (0 = interactive, 1 = plain, 2 = append project name), the raw
// command line, and whether `help` was requested.
func parseArgs() (int, string, bool) {
	if len(os.Args) < 2 {
		return 0, "", false
	}
	a0 := os.Args[1]
	if a0 == "help" {
		return 0, "", true
	}
	cls := map[string]int{
		"clone": 2, "init": 2, "log": 2,
		"push": 1, "pushremote": 1, "deleteremote": 1, "list": 1, "tag": 1, "archive": 1, "show": 1,
		"pull": 1, "fetch": 1, "status": 1, "diff": 1, "overview": 1,
		"config": 1, "count": 1, "login": 1, "cloneall": 1, "release": 1,
		"update": 1,
	}
	if c, ok := cls[a0]; ok {
		return c, strings.Join(os.Args[1:], " "), false
	}
	return 0, "", false
}

func setup() {
	// the *global* configuration has to stand on its own: mgsh must be usable
	// outside any project, where no project .mgshrc can fill in the blanks.
	baseCfg = loadConfig()
	if miss := baseCfg.missingRequired(); len(miss) > 0 {
		fmt.Fprintf(os.Stderr, "mgsh: not configured — missing required settings: %s\n", strings.Join(miss, ", "))
		fmt.Fprintf(os.Stderr, "edit %s or set the corresponding MGSH_* environment variables, then run mgsh again.\n", configFile())
		os.Exit(1)
	}
	BASE = baseCfg.Base
	if !isDir(BASE) {
		fmt.Fprintf(os.Stderr, "%s not found\n", BASE)
		os.Exit(1)
	}

	applyProjectConfig() // no project yet: cfg = baseCfg, URL from it
	HOST = shortHostname()
	if u, err := user.Current(); err == nil {
		USER = u.Username
	}

	applyGlobalGitConfig()
	loadAliases()
}

// applyGlobalGitConfig writes the configured git identity to ~/.gitconfig, but
// only the values that actually differ — every mgsh invocation runs this, and a
// plain `mgsh status` has no business rewriting the user's global config. The
// current settings are read in one go rather than one process per key.
func applyGlobalGitConfig() {
	want := map[string]string{}
	if baseCfg.GitName != "" {
		want["user.name"] = baseCfg.GitName
	}
	if baseCfg.GitEmail != "" {
		want["user.email"] = baseCfg.GitEmail
	}
	if baseCfg.PushDefault != "" {
		want["push.default"] = baseCfg.PushDefault
	}
	if len(want) == 0 {
		return
	}

	have := map[string]string{}
	if out, err := gitCapture("", "config", "--global", "--list"); err == nil {
		for _, ln := range splitLines(out) {
			if i := strings.IndexByte(ln, '='); i > 0 {
				have[ln[:i]] = ln[i+1:]
			}
		}
	}
	for k, v := range want {
		if have[k] != v {
			git("", "config", "--global", k, v)
		}
	}
}

// applyProjectConfig re-resolves cfg whenever the active project changes: the
// project's own .mgshrc overrides the global settings, so a single project can
// live on a different server or mirror to a different place. Resolving once per
// project change rather than once per prompt keeps the REPL loop free of I/O.
func applyProjectConfig() {
	if cfgFresh && PRJ == cfgPRJ {
		return
	}
	cfgFresh, cfgPRJ = true, PRJ

	dir := ""
	if PRJ != "" && isDir(BASE+"/"+PRJ) {
		dir = BASE + "/" + PRJ
	}
	cfg = resolveConfig(baseCfg, dir)
	URL = fmt.Sprintf("ssh://%s@%s:%s%s", cfg.GitUser, cfg.GitHost, cfg.GitPort, cfg.GitPath)
}

// reloadConfig re-reads ~/.mgshrc and the project's .mgshrc, so an edit takes
// effect without restarting the shell. An edit that breaks the global config is
// rejected rather than applied — the running shell keeps working.
func reloadConfig() {
	fresh := loadConfig()
	if miss := fresh.missingRequired(); len(miss) > 0 {
		errorln("keeping the previous configuration — " + configFile() +
			" is missing: " + strings.Join(miss, ", "))
		return
	}
	if fresh.Base != BASE {
		errorln("'base' changed to " + fresh.Base + " — restart mgsh to use it")
		fresh.Base = BASE
	}
	baseCfg = fresh
	cfgFresh = false
	applyProjectConfig()
}

// updateDirState recomputes DIR, the build.pl OFF marker and the current
// branch / dirty flag for the active project. Run once per loop iteration, so
// it stays deliberately cheap.
func updateDirState() {
	BRANCH = ""
	DIRTY = false
	applyProjectConfig()

	if PRJ != "" && isDir(BASE+"/"+PRJ) {
		DIR = BASE + "/" + PRJ
		BPLSTATE = ""
		bp := DIR + "/build.pl"
		if fi, err := os.Lstat(bp); err == nil && fi.Mode()&os.ModeSymlink != 0 {
			if target, err := os.Readlink(bp); err == nil && strings.HasSuffix(target, ".off") {
				BPLSTATE = "/OFF"
			}
		}
		if isDir(DIR + "/.git") {
			if out, err := gitCapture(DIR, "rev-parse", "--abbrev-ref", "HEAD"); err == nil {
				BRANCH = strings.TrimSpace(out)
			}
			if out, err := gitCapture(DIR, "status", "--porcelain"); err == nil && strings.TrimSpace(out) != "" {
				DIRTY = true
			}
		}
	} else {
		DIR = BASE
		BPLSTATE = ""
	}
}

// originURL returns the active project's own origin URL, or "" when it is not a
// repository or has no origin. `--local` matters: a plain `git config` walks up
// into an enclosing repository and would report a foreign origin for a project
// that has no repository of its own.
func originURL() string {
	if !isDir(DIR + "/.git") {
		return ""
	}
	out, err := gitCapture(DIR, "config", "--local", "remote.origin.url")
	if err != nil {
		return ""
	}
	return strings.TrimSpace(out)
}