// Package cli lays out the commands of the tool.
//
// The depth of a command reflects how often it runs and whom it addresses:
// project commands run in every repository and often, tending a suite runs in
// one repository and rarely. That is why `check` stays at the top level and
// whatever makes no sense in a project goes under `suite`. There are no
// synonyms: `convy suite pull` is not introduced next to `convy pull`.
package cli

import (
	"fmt"
	"io"
	"os"
)

// ExitCode is the exit status of the process.
type ExitCode int

const (
	// OK means the check passed and the work is done.
	OK ExitCode = 0
	// Failed means the check found errors.
	Failed ExitCode = 1
	// Usage means the command was typed wrong or run in the wrong context.
	Usage ExitCode = 2
)

// Env is the environment of a run. It is pulled out so that commands can be
// tested without a process.
type Env struct {
	Dir string
	In  io.Reader
	Out io.Writer
	Err io.Writer
	// Interactive says whether input comes from a terminal. A command that
	// asks questions refuses to start without one rather than blocking on an
	// answer nobody is there to give.
	Interactive bool
}

// Run parses the arguments and executes the command.
func Run(env Env, args []string) ExitCode {
	if len(args) == 0 {
		usage(env.Out)
		return Usage
	}

	switch args[0] {
	case "suite":
		return runSuite(env, args[1:])
	case "add", "pull", "list", "check":
		fmt.Fprintf(env.Err, "the %q command is not implemented yet\n", args[0])
		return Usage
	case "help", "-h", "--help":
		usage(env.Out)
		return OK
	default:
		fmt.Fprintf(env.Err, "unknown command %q\n\n", args[0])
		usage(env.Err)
		return Usage
	}
}

func runSuite(env Env, args []string) ExitCode {
	if len(args) == 0 {
		fmt.Fprintln(env.Err, "convy suite: a subcommand is required — init, add, rule, retire, list or check")
		return Usage
	}
	switch args[0] {
	case "check":
		return runSuiteCheck(env, args[1:])
	case "init":
		return runSuiteInit(env, args[1:])
	case "add":
		return runSuiteAdd(env, args[1:])
	case "rule":
		return runSuiteRule(env, args[1:])
	case "retire":
		return runSuiteRetire(env, args[1:])
	case "list":
		return runSuiteList(env, args[1:])
	default:
		fmt.Fprintf(env.Err, "unknown subcommand %q for convy suite\n", args[0])
		return Usage
	}
}

// usage prints the help grouped under headings: a flat list hides the levels.
func usage(w io.Writer) {
	fmt.Fprint(w, `convy — tending development conventions.

In a project:
  convy add <topic>   subscribe and assemble          (not implemented)
  convy pull          reassemble what is subscribed   (not implemented)
  convy list          what is wired up and available  (not implemented)
  convy check         check the form of what is here  (not implemented)

In a suite:
  convy suite init    start a suite: a directory and a manifest
  convy suite add     add a convention: a file, a topic and a prefix
  convy suite rule    add a rule: the next number, the blocks in order
  convy suite retire  retire a rule, a convention or a topic — never reusing it
  convy suite list    what the suite holds, and what a component would take
  convy suite check   suite integrity: prefixes, topics, axes, links, form

The commands that change something run in two modes. Bare, they ask for every
field with a hint attached — that mode is for a person. With flags, they take
everything at once and ask nothing — that mode is for agents and scripts.

`)
}

// Main is the entry point of the process.
func Main() int {
	dir, err := os.Getwd()
	if err != nil {
		fmt.Fprintln(os.Stderr, "cannot determine the current directory:", err)
		return int(Usage)
	}
	env := Env{
		Dir:         dir,
		In:          os.Stdin,
		Out:         os.Stdout,
		Err:         os.Stderr,
		Interactive: terminal(os.Stdin),
	}
	return int(Run(env, os.Args[1:]))
}

// terminal reports whether a file is a character device, which is as close as
// the standard library gets to asking whether a person is on the other end.
func terminal(f *os.File) bool {
	info, err := f.Stat()
	if err != nil {
		return false
	}
	return info.Mode()&os.ModeCharDevice != 0
}