// Package cmd is the kettle command tree.
//
// Commands are values, not init() side effects on a framework: each one carries
// the metadata a human needs (what it does, what it takes, worked examples) in
// the same struct that carries the code. That is deliberate — the skills kettle
// writes into a project are generated from this list, so a command whose flags
// changed cannot ship with documentation that says otherwise.
//
// The tree is flat. `kettle new`, not `kettle issue new`: an agent pays for
// every token of every invocation, and the grouping that matters for reading is
// carried in Group and only shows up in the docs.
package cmd

import (
	"flag"
	"fmt"
	"os"
	"sort"
	"strings"
)

// Groups, in the order they are presented. They name the layer a command
// belongs to, which is the one thing a reader has to keep straight: the domain
// works offline and the tracker does not exist to it.
const (
	GroupProject = "project"
	GroupIssue   = "issue"
	GroupSync    = "sync"
	GroupAPI     = "api"
)

var groupOrder = []string{GroupProject, GroupIssue, GroupSync, GroupAPI}

var groupBlurb = map[string]string{
	GroupProject: "the project itself",
	GroupIssue:   "issues as units of work — offline, no tracker involved",
	GroupSync:    "moving issues between the store and the tracker",
	GroupAPI:     "everything else Gitea has, reached directly — not issues",
}

// Example is one worked invocation. Both halves are shown in help and in the
// generated skill docs.
type Example struct {
	Cmd  string
	What string
}

// Command is one verb.
type Command struct {
	// Name is what the user types.
	Name string
	// Group is the layer it belongs to; documentation only.
	Group string
	// Args is the positional-argument spec, e.g. "<id> [<id>…]".
	Args string
	// Short is one line, shown in the command list.
	Short string
	// Long is the full explanation, shown by `kettle help <name>`.
	Long string
	// Examples are worked invocations.
	Examples []Example
	// Setup registers this command's flags on fs and returns the function that
	// runs it, closing over them. Splitting it this way lets the doc generator
	// walk the flags without running anything.
	Setup func(fs *flag.FlagSet) func(args []string) error
}

var registry []*Command

func register(c *Command) { registry = append(registry, c) }

// Commands lists every command, sorted by group and then by name.
func Commands() []*Command {
	out := append([]*Command{}, registry...)
	sort.SliceStable(out, func(i, j int) bool {
		gi, gj := groupIndex(out[i].Group), groupIndex(out[j].Group)
		if gi != gj {
			return gi < gj
		}
		return out[i].Name < out[j].Name
	})
	return out
}

// Lookup finds a command by name.
func Lookup(name string) *Command {
	for _, c := range registry {
		if c.Name == name {
			return c
		}
	}
	return nil
}

// Flags returns this command's flags without running it — what the doc
// generator walks.
func (c *Command) Flags() []*flag.Flag {
	fs := flag.NewFlagSet(c.Name, flag.ContinueOnError)
	fs.SetOutput(discard{})
	c.Setup(fs)
	var out []*flag.Flag
	fs.VisitAll(func(f *flag.Flag) { out = append(out, f) })
	return out
}

// Usage is the one-line synopsis.
func (c *Command) Usage() string {
	s := "kettle " + c.Name
	if c.Args != "" {
		s += " " + c.Args
	}
	return s
}

// SilentError carries an exit status for a command that has already said
// everything it has to say. `check` uses it: findings went to stdout and a
// second copy on stderr would be noise.
type SilentError struct{ Code int }

func (e SilentError) Error() string { return "" }

// Fail is the error every command returns for an ordinary failure. Main
// prefixes it with the command name.
func Fail(format string, a ...any) error { return fmt.Errorf(format, a...) }

// Main runs argv (without the program name) and returns the exit status.
func Main(argv []string) int {
	if len(argv) == 0 {
		printUsage(os.Stdout)
		return 0
	}

	name := argv[0]
	switch name {
	case "help", "-h", "--help":
		if len(argv) > 1 {
			c := Lookup(argv[1])
			if c == nil {
				fmt.Fprintf(os.Stderr, "kettle: no command %q\n", argv[1])
				return 2
			}
			printCommand(os.Stdout, c)
			return 0
		}
		printUsage(os.Stdout)
		return 0
	}

	c := Lookup(name)
	if c == nil {
		fmt.Fprintf(os.Stderr, "kettle: no command %q — try `kettle help`\n", name)
		return 2
	}

	fs := flag.NewFlagSet(name, flag.ContinueOnError)
	fs.Usage = func() { printCommand(os.Stderr, c) }
	run := c.Setup(fs)
	if err := fs.Parse(permute(fs, argv[1:])); err != nil {
		if err == flag.ErrHelp {
			return 0
		}
		return 2
	}

	switch err := run(fs.Args()).(type) {
	case nil:
		return 0
	case SilentError:
		return err.Code
	default:
		fmt.Fprintf(os.Stderr, "kettle %s: %v\n", name, err)
		return 1
	}
}

func printUsage(w *os.File) {
	fmt.Fprint(w, "kettle — issues as local markdown, and the tracker they sync with\n\n")
	fmt.Fprint(w, "usage: kettle <command> [flags] [args]\n")

	current := ""
	for _, c := range Commands() {
		if c.Group != current {
			current = c.Group
			fmt.Fprintf(w, "\n%s — %s\n", current, groupBlurb[current])
		}
		fmt.Fprintf(w, "  %-11s %s\n", c.Name, c.Short)
	}
	fmt.Fprint(w, "\n`kettle help <command>` for one command in full.\n")
}

func printCommand(w *os.File, c *Command) {
	fmt.Fprintf(w, "%s\n\n%s\n", c.Usage(), c.Short)
	if c.Long != "" {
		fmt.Fprintf(w, "\n%s\n", strings.TrimSpace(c.Long))
	}
	if flags := c.Flags(); len(flags) > 0 {
		fmt.Fprint(w, "\nflags:\n")
		for _, f := range flags {
			name := "--" + f.Name
			if f.DefValue != "" && f.DefValue != "false" {
				name += "=" + f.DefValue
			}
			fmt.Fprintf(w, "  %-22s %s\n", name, f.Usage)
		}
	}
	if len(c.Examples) > 0 {
		fmt.Fprint(w, "\nexamples:\n")
		for _, e := range c.Examples {
			fmt.Fprintf(w, "  %s\n      %s\n", e.Cmd, e.What)
		}
	}
}

// permute moves flags ahead of positional arguments.
//
// The standard flag package stops parsing at the first non-flag argument, so
// `kettle ac <id> --check 3` would hand --check to the command as a positional
// and tick nothing. Every other CLI an operator uses interleaves the two, and
// a tool that silently ignores a flag because of where it was typed is worse
// than one that rejects it.
//
// A flag that takes a value swallows the next argument, which is why this needs
// the FlagSet: only the set knows whether --check wants one. `--` ends the
// permutation, and everything after it is positional whatever it looks like.
func permute(fs *flag.FlagSet, args []string) []string {
	var flags, positional []string
	for i := 0; i < len(args); i++ {
		a := args[i]
		if a == "--" {
			positional = append(positional, args[i+1:]...)
			break
		}
		if len(a) < 2 || a[0] != '-' {
			positional = append(positional, a)
			continue
		}
		flags = append(flags, a)
		if strings.Contains(a, "=") {
			continue
		}
		f := fs.Lookup(strings.TrimLeft(a, "-"))
		// An unknown flag consumes nothing; Parse will reject it by name in a
		// moment, which is a better message than one about its value.
		if f == nil || isBoolFlag(f.Value) {
			continue
		}
		if i+1 < len(args) {
			i++
			flags = append(flags, args[i])
		}
	}
	return append(flags, positional...)
}

func isBoolFlag(v flag.Value) bool {
	b, ok := v.(interface{ IsBoolFlag() bool })
	return ok && b.IsBoolFlag()
}

func groupIndex(g string) int {
	for i, name := range groupOrder {
		if name == g {
			return i
		}
	}
	return len(groupOrder)
}

type discard struct{}

func (discard) Write(p []byte) (int, error) { return len(p), nil }