package cli

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

// Action tells main what the user asked for.
type Action int

const (
	Run Action = iota
	ShowHelp
	ShowVersion
)

// Result is everything Parse extracts from the command line.
type Result struct {
	Action  Action
	HelpTag string // when Action == ShowHelp; "" means all
	Options *Options
	URIs    []string
}

// Parse resolves args into options and URIs, applying the layered override
// order: built-in defaults, then the config file, then proxy
// environment variables, then the command line (last wins).
func Parse(args []string) (*Result, error) {
	cmdVals, uris, action, helpTag, err := parseArgs(args)
	if err != nil {
		return nil, err
	}
	if action != Run {
		return &Result{Action: action, HelpTag: helpTag}, nil
	}

	opts := newOptions()
	applyDefaults(opts)

	if noConf, _ := boolWord(cmdVals["no-conf"]); !noConf {
		explicit := cmdVals["conf-path"]
		path, fromUser := confPath(explicit)
		if err := applyConfig(opts, path, fromUser); err != nil {
			return nil, err
		}
	}
	applyEnv(opts)

	for name, val := range cmdVals {
		if err := set(opts, name, val); err != nil {
			return nil, err
		}
	}
	return &Result{Action: Run, Options: opts, URIs: uris}, nil
}

// parseArgs walks the argument list once. It recognises --long, --long=val,
// -x, -xval, -x val and short bool bundles like -cq. Like getopt_long, it
// permutes: a non-flag token becomes a URI but scanning continues so flags may
// follow URIs. A bare "--" is a hard terminator forcing the rest to URIs.
// --help/-h and --version/-v short-circuit. Values are returned raw; layering
// happens in Parse.
func parseArgs(args []string) (vals map[string]string, uris []string, action Action, helpTag string, err error) {
	vals = map[string]string{}
	for i := 0; i < len(args); i++ {
		a := args[i]
		switch {
		case a == "--": // end of options: the rest are URIs
			uris = append(uris, args[i+1:]...)
			return
		case a == "-" || !strings.HasPrefix(a, "-"): // URI (or stdin); keep scanning
			uris = append(uris, a)
			continue
		case strings.HasPrefix(a, "--"):
			name, val, hasVal := strings.Cut(a[2:], "=")
			if name == "help" {
				return vals, uris, ShowHelp, val, nil
			}
			if name == "version" {
				return vals, uris, ShowVersion, "", nil
			}
			o := byLong[name]
			if o == nil {
				return nil, nil, Run, "", fmt.Errorf("unknown option --%s", name)
			}
			if !hasVal {
				if o.Kind == Bool {
					val = "true"
				} else {
					if i+1 >= len(args) {
						return nil, nil, Run, "", fmt.Errorf("option --%s needs a value", name)
					}
					i++
					val = args[i]
				}
			}
			accumulate(vals, o, val)
		default: // short flags: -x, -xval, -x val, bundles -cq
			j := 1
			for j < len(a) {
				c := a[j]
				if c == 'h' {
					return vals, uris, ShowHelp, "", nil
				}
				if c == 'v' {
					return vals, uris, ShowVersion, "", nil
				}
				o := byShort[c]
				if o == nil {
					return nil, nil, Run, "", fmt.Errorf("unknown option -%c", c)
				}
				if o.Kind == Bool {
					accumulate(vals, o, "true")
					j++
					continue
				}
				// value-taking short: rest of token, else next arg.
				val := a[j+1:]
				if val == "" {
					if i+1 >= len(args) {
						return nil, nil, Run, "", fmt.Errorf("option -%c needs a value", c)
					}
					i++
					val = args[i]
				}
				accumulate(vals, o, val)
				break // consumed the rest of the token as the value
			}
		}
	}
	return
}

// accumulate stores a value, joining repeatable List options with newlines.
func accumulate(vals map[string]string, o *Opt, val string) {
	if o.Kind == List {
		vals[o.Long] = appendList(vals[o.Long], val)
		return
	}
	vals[o.Long] = val
}

// appendList is the single home of the List newline-join rule, shared by the
// raw-parse layer (accumulate) and the resolved layer (set). An empty prev (the
// option not yet seen) yields val unchanged, so the first value carries no
// leading newline.
func appendList(prev, val string) string {
	if prev == "" {
		return val
	}
	return prev + "\n" + val
}

func applyDefaults(o *Options) {
	for i := range options {
		opt := &options[i]
		if opt.Default != "" {
			o.vals[opt.Long] = opt.Default
		}
	}
}

// applyConfig reads "name=value" lines (with # comments) into o. A missing
// file is silently ignored for the default path, but is fatal when the user
// named it explicitly via --conf-path: an explicitly requested config file
// that cannot be read is an error.
func applyConfig(o *Options, path string, explicit bool) error {
	if path == "" {
		return nil
	}
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) && !explicit {
			return nil // a missing default config file is not an error
		}
		return err
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		name, val, _ := strings.Cut(line, "=")
		name = strings.TrimSpace(strings.TrimPrefix(name, "--"))
		opt := byLong[name]
		if opt == nil {
			return fmt.Errorf("%s: unknown option %q", path, name)
		}
		if err := set(o, name, strings.TrimSpace(val)); err != nil {
			return err
		}
	}
	return sc.Err()
}

// applyEnv folds the conventional proxy environment variables into all-proxy
// unless it was already set explicitly.
func applyEnv(o *Options) {
	if o.set["all-proxy"] {
		return
	}
	for _, key := range []string{"all_proxy", "https_proxy", "http_proxy"} {
		if v := os.Getenv(key); v != "" {
			o.vals["all-proxy"] = v
			return
		}
	}
}

// set validates a value against its option descriptor and stores it, marking
// the option as explicitly set.
func set(o *Options, name, val string) error {
	opt := byLong[name]
	if opt == nil {
		return fmt.Errorf("unknown option %q", name)
	}
	if err := validate(opt, val); err != nil {
		return err
	}
	if opt.Kind == List && o.set[name] {
		val = appendList(o.vals[name], val)
	}
	o.vals[name] = val
	o.set[name] = true
	return nil
}

func validate(o *Opt, val string) error {
	switch o.Kind {
	case Bool:
		// Booleans accept true/false plus the yes/no/1/0/on/off spellings, but
		// nothing else, so e.g. --enable-dht=flase is a parse error. The accepted
		// set is boolWords, the same vocabulary the readers honour.
		if _, ok := boolWord(val); !ok {
			return fmt.Errorf("--%s: %q is not a boolean (true/false)", o.Long, val)
		}
	case Int:
		n, err := strconv.ParseInt(strings.TrimSpace(val), 10, 64)
		if err != nil {
			return fmt.Errorf("--%s: %q is not an integer", o.Long, val)
		}
		if err := checkBounds(o, n); err != nil {
			return err
		}
	case Size:
		n, err := parseSize(val)
		if err != nil {
			return fmt.Errorf("--%s: %v", o.Long, err)
		}
		if err := checkBounds(o, n); err != nil {
			return err
		}
	case Float:
		// seed-time and seed-ratio are both rates/durations that must be
		// non-negative; a negative SeedTime would fire the seed timer immediately
		// and a negative SeedRatio is silently ignored. Reject negatives here.
		// Opt.Min/Max are int64, so we only enforce the floor, not full bounds.
		f, err := strconv.ParseFloat(strings.TrimSpace(val), 64)
		if err != nil {
			return fmt.Errorf("--%s: %q is not a number", o.Long, val)
		}
		if f < 0 {
			return fmt.Errorf("--%s: %v below minimum 0", o.Long, f)
		}
	case Enum:
		for _, e := range o.Enum {
			if val == e {
				return nil
			}
		}
		return fmt.Errorf("--%s: %q not one of %s", o.Long, val, strings.Join(o.Enum, "|"))
	}
	return nil
}

// checkBounds enforces an Int/Size option's numeric range. Min defaults to a
// floor of 0 (negative sizes and counts are rejected); a zero Max means "no
// upper bound". For Size options n and the bounds are byte counts.
func checkBounds(o *Opt, n int64) error {
	if n < o.Min {
		return fmt.Errorf("--%s: %d below minimum %d", o.Long, n, o.Min)
	}
	if o.Max > 0 && n > o.Max {
		return fmt.Errorf("--%s: %d above maximum %d", o.Long, n, o.Max)
	}
	return nil
}

// confPath picks the config file and reports whether the user named it. An
// explicit --conf-path wins (and is treated as user-requested, so a missing
// file is fatal). Otherwise it falls back to $XDG_CONFIG_HOME/got/got.conf,
// then ~/.config/got/got.conf.
func confPath(explicit string) (path string, fromUser bool) {
	if explicit != "" {
		return explicit, true
	}
	// XDG_CONFIG_HOME is only honoured when it is an absolute path.
	if x := os.Getenv("XDG_CONFIG_HOME"); filepath.IsAbs(x) {
		return filepath.Join(x, "got", "got.conf"), false
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", false
	}
	return filepath.Join(home, ".config", "got", "got.conf"), false
}