// Package recipe loads and runs named, deterministic, hand-editable tasks.
//
// A recipe is one plain-text file in recipes/, written so that Sam can change
// it by hand without a build step. It names the app, the parameters it needs,
// the screens it must never tap on, and the ordered steps that do the work.
// Steps talk about text ("tap the element whose text is Search"), never about
// coordinates, so a recipe never taps blindly (FR-4, FR-5, FR-8).
//
// # File format
//
// A recipe file is a list of lines. Blank lines and lines starting with "#"
// are ignored.
//
// Directives are "key: value" lines placed before the steps:
//
//	task: spotify_play            unique name, must match the file name
//	description: ...              one line, for humans
//	app: com.spotify.music        the package the recipe drives
//	param: query                  a parameter the caller must supply (repeatable)
//	row_id: com.spotify:id/row_root   container id for list rows (optional)
//	row_menu: More options        label of a row's own action button (optional)
//	step_timeout: 20s             default per-step timeout (FR-11)
//	total_timeout: 120s           whole-recipe timeout (FR-11)
//
// A guard names a screen Artemis must never act on. Guards are checked when a
// step cannot find its target, so the failure names the real problem:
//
//	guard "Log in" => Spotify is signed out; sign in on the phone and retry
//
// Steps are "- " lines, run in order:
//
//   - launch                  start the recipe's app
//   - foreground 30s          wait until the recipe's app is in front
//   - wait   "Search" 30s     wait for an element whose text matches
//   - wait   id:search_box 30s  wait for an element by resource id. The short
//     name after the "/" is enough. Use this when a
//     label rotates (the Maps search box does); it is
//     still a named match, never a coordinate (FR-4).
//   - wait   exact "Pause" 60s retry 3
//     if it never appears, re-run the step above and
//     wait again (a busy phone can drop a tap)
//   - playing "{query}" 30s retry 3
//     wait until the app's media session is PLAYING and its
//     title matches the text; with no text, wait for PLAYING
//     alone (a radio plays a different track every few minutes)
//   - wait_gone "Recents" 30s wait until no element matches the text
//   - expect_change 10s       the screen is read before the step above, so this
//     fails with "the app stopped consuming input" when
//     that step's input left the screen unchanged (a wedged app)
//   - tap    "Search"         tap the element whose text matches (FR-4)
//   - tap    exact "Pause"    tap an element whose text matches exactly
//   - tap_if "Clear search query"  tap it when it is on screen, else skip
//   - tap_row "{query}" 30s   tap the list row that best matches the text
//   - menu_row "{query}" 30s  open the More options menu of that row
//   - scroll down             scroll the current list ("down" or "up")
//   - type   "{query}"        type into the focused field
//   - key    enter            send a named key event
//   - back / home             press a system key
//   - sleep  1s               wait a fixed time
//
// A step may name its own failure reason with "else":
//
//   - wait "Go to song radio" 20s else "this track offers no Song radio"
//
// {name} placeholders are replaced with the value of parameter "name". The
// trailing "30s" on wait/tap/tap_row steps is that step's timeout.
//
// tap_row and menu_row also record the row they chose as "row", so a later step
// can refer to it with {row} — for example to check that the context menu that
// opened belongs to the row that was pressed:
//
//   - menu_row "{query}" 40s
//   - wait "{row}" 20s else "the context menu opened on the wrong row"
package recipe

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"
)

// Recipe is one parsed task.
type Recipe struct {
	Task         string
	Description  string
	App          string
	Params       []string
	RowID        string
	RowMenu      string
	StepTimeout  time.Duration
	TotalTimeout time.Duration
	Guards       []Guard
	Steps        []Step
	Source       string
}

// Guard is a screen Artemis must never act on, with the reason to report.
type Guard struct {
	Text   string
	Reason string
}

// Step is one ordered action.
type Step struct {
	Verb    string
	Args    []string
	Exact   bool
	Timeout time.Duration
	// Retry, on a wait step, re-runs the preceding step and waits again, up to
	// this many extra times. A busy phone can drop a tap.
	Retry int
	// Reason, when set with "else", is the step's named failure (FR-8). A wait
	// for a label a screen may simply not offer reads better as "this track
	// offers no Song radio" than as "text did not appear".
	Reason string
	Line   int
}

// Defaults used when a recipe does not set its own timeouts or labels.
const (
	DefaultStepTimeout  = 20 * time.Second
	DefaultTotalTimeout = 120 * time.Second
	// DefaultRowMenu is the label of a row's own action button. Spotify's list
	// row action carries the content description "More options for song ...".
	DefaultRowMenu = "More options"
)

// validKeys are the directive names a recipe file may use.
var validKeys = map[string]bool{
	"task":          true,
	"description":   true,
	"app":           true,
	"param":         true,
	"row_id":        true,
	"row_menu":      true,
	"step_timeout":  true,
	"total_timeout": true,
}

// verbs lists the step verbs and how many arguments each takes.
var verbs = map[string]struct {
	min, max   int
	durArg     bool // the single argument is a duration
	allowExact bool
}{
	"launch":        {0, 1, false, false},
	"foreground":    {0, 1, false, false},
	"wait":          {1, 2, false, true},
	"playing":       {0, 2, false, false},
	"wait_gone":     {1, 2, false, true},
	"expect_change": {1, 1, true, false},
	"tap":           {1, 2, false, true},
	"tap_if":        {1, 1, false, true},
	"tap_row":       {1, 2, false, true},
	"menu_row":      {1, 2, false, false},
	"scroll":        {1, 1, false, false},
	"type":          {1, 1, false, false},
	"key":           {1, 1, false, false},
	"back":          {0, 0, false, false},
	"home":          {0, 0, false, false},
	"sleep":         {1, 1, true, false},
}

// keyNames are the key event names a recipe may use.
var keyNames = map[string]bool{
	"enter":  true,
	"back":   true,
	"home":   true,
	"power":  true,
	"wakeup": true,
	"escape": true,
}

// Load reads and parses one recipe file.
func Load(path string) (*Recipe, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	rec, err := Parse(string(raw))
	if err != nil {
		return nil, fmt.Errorf("%s: %w", path, err)
	}
	rec.Source = path
	if rec.Task == "" {
		rec.Task = strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
	}
	return rec, nil
}

// List loads every recipe in dir, sorted by task name.
func List(dir string) ([]*Recipe, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("read recipes directory %s: %w", dir, err)
	}
	var out []*Recipe
	for _, e := range entries {
		if e.IsDir() || strings.HasPrefix(e.Name(), ".") {
			continue
		}
		rec, err := Load(filepath.Join(dir, e.Name()))
		if err != nil {
			return nil, err
		}
		out = append(out, rec)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Task < out[j].Task })
	return out, nil
}

// Find loads the recipe for one task name from dir.
func Find(dir, task string) (*Recipe, error) {
	recipes, err := List(dir)
	if err != nil {
		return nil, err
	}
	for _, r := range recipes {
		if r.Task == task {
			return r, nil
		}
	}
	names := make([]string, 0, len(recipes))
	for _, r := range recipes {
		names = append(names, r.Task)
	}
	if len(names) == 0 {
		return nil, fmt.Errorf("no recipes in %s", dir)
	}
	return nil, fmt.Errorf("no recipe named %q in %s (have: %s)", task, dir, strings.Join(names, ", "))
}

// Parse turns the body of a recipe file into a Recipe.
func Parse(src string) (*Recipe, error) {
	rec := &Recipe{
		StepTimeout:  DefaultStepTimeout,
		TotalTimeout: DefaultTotalTimeout,
		RowMenu:      DefaultRowMenu,
	}

	for i, raw := range strings.Split(src, "\n") {
		lineNo := i + 1
		line := strings.TrimSpace(raw)
		switch {
		case line == "", strings.HasPrefix(line, "#"):
			continue
		case line == "steps:":
			continue
		case strings.HasPrefix(line, "-"):
			step, err := parseStep(strings.TrimSpace(strings.TrimPrefix(line, "-")), lineNo)
			if err != nil {
				return nil, err
			}
			rec.Steps = append(rec.Steps, *step)
		case strings.HasPrefix(line, "guard "):
			guard, err := parseGuard(line, lineNo)
			if err != nil {
				return nil, err
			}
			rec.Guards = append(rec.Guards, *guard)
		default:
			if err := rec.parseDirective(line, lineNo); err != nil {
				return nil, err
			}
		}
	}

	if len(rec.Steps) == 0 {
		return nil, fmt.Errorf("recipe has no steps")
	}
	return rec, nil
}

func (rec *Recipe) parseDirective(line string, lineNo int) error {
	key, value, ok := strings.Cut(line, ":")
	if !ok {
		return fmt.Errorf("line %d: expected \"key: value\", a \"guard ...\" line or a \"- step\" line, got %q", lineNo, line)
	}
	key = strings.ToLower(strings.TrimSpace(key))
	value = strings.TrimSpace(value)
	if !validKeys[key] {
		return fmt.Errorf("line %d: unknown setting %q", lineNo, key)
	}

	switch key {
	case "task":
		rec.Task = value
	case "description":
		rec.Description = value
	case "app":
		rec.App = value
	case "param":
		if value == "" {
			return fmt.Errorf("line %d: param needs a name", lineNo)
		}
		rec.Params = append(rec.Params, value)
	case "row_id":
		rec.RowID = value
	case "row_menu":
		if value == "" {
			return fmt.Errorf("line %d: row_menu needs a label", lineNo)
		}
		rec.RowMenu = value
	case "step_timeout":
		d, err := parseDuration(value)
		if err != nil {
			return fmt.Errorf("line %d: step_timeout: %w", lineNo, err)
		}
		rec.StepTimeout = d
	case "total_timeout":
		d, err := parseDuration(value)
		if err != nil {
			return fmt.Errorf("line %d: total_timeout: %w", lineNo, err)
		}
		rec.TotalTimeout = d
	}
	return nil
}

func parseGuard(line string, lineNo int) (*Guard, error) {
	body := strings.TrimSpace(strings.TrimPrefix(line, "guard"))
	text, reason, ok := strings.Cut(body, "=>")
	if !ok {
		return nil, fmt.Errorf("line %d: a guard line needs \"guard \\\"text\\\" => reason\"", lineNo)
	}
	tokens, err := tokenize(text, lineNo)
	if err != nil {
		return nil, err
	}
	if len(tokens) != 1 {
		return nil, fmt.Errorf("line %d: a guard needs exactly one quoted text, got %d", lineNo, len(tokens))
	}
	reason = strings.TrimSpace(reason)
	if reason == "" {
		return nil, fmt.Errorf("line %d: a guard needs a reason after =>", lineNo)
	}
	return &Guard{Text: tokens[0], Reason: reason}, nil
}

func parseStep(body string, lineNo int) (*Step, error) {
	tokens, err := tokenize(body, lineNo)
	if err != nil {
		return nil, err
	}
	if len(tokens) == 0 {
		return nil, fmt.Errorf("line %d: empty step", lineNo)
	}

	verb := strings.ToLower(tokens[0])
	spec, ok := verbs[verb]
	if !ok {
		return nil, fmt.Errorf("line %d: unknown step verb %q", lineNo, tokens[0])
	}
	step := &Step{Verb: verb, Line: lineNo}
	args := tokens[1:]

	if spec.allowExact && len(args) > 0 && strings.EqualFold(args[0], "exact") {
		step.Exact = true
		args = args[1:]
	}

	// "retry N" is pulled out first, so the timeout can still be the last word.
	for i := 0; i < len(args); i++ {
		if !strings.EqualFold(args[i], "retry") {
			continue
		}
		if i+1 >= len(args) {
			return nil, fmt.Errorf("line %d: retry needs a number, as in retry 3", lineNo)
		}
		n, err := strconv.Atoi(args[i+1])
		if err != nil || n < 1 {
			return nil, fmt.Errorf("line %d: retry needs a positive number, got %q", lineNo, args[i+1])
		}
		if verb != "wait" && verb != "playing" && verb != "expect_change" {
			return nil, fmt.Errorf("line %d: retry is only allowed on a wait, playing or expect_change step", lineNo)
		}
		step.Retry = n
		args = append(args[:i], args[i+2:]...)
		break
	}

	// "else \"reason\"" names this step's own failure, so a screen that simply
	// lacks a label can fail with the reason a human needs (FR-8).
	for i := 0; i < len(args); i++ {
		if !strings.EqualFold(args[i], "else") {
			continue
		}
		if i+1 >= len(args) {
			return nil, fmt.Errorf("line %d: else needs a reason, as in else \"that track has no radio\"", lineNo)
		}
		step.Reason = args[i+1]
		args = append(args[:i], args[i+2:]...)
		break
	}

	// A trailing duration is the step timeout, except for sleep where the
	// duration is the step itself.
	if !spec.durArg && len(args) > spec.min {
		if d, derr := parseDuration(args[len(args)-1]); derr == nil {
			step.Timeout = d
			args = args[:len(args)-1]
		}
	}

	if len(args) < spec.min || len(args) > spec.max {
		return nil, fmt.Errorf("line %d: %s takes %s, got %d", lineNo, verb, argRange(spec.min, spec.max), len(args))
	}
	step.Args = args

	if spec.durArg {
		d, derr := parseDuration(args[0])
		if derr != nil {
			return nil, fmt.Errorf("line %d: sleep: %w", lineNo, derr)
		}
		step.Timeout = d
	}
	if verb == "key" && !keyNames[strings.ToLower(args[0])] {
		return nil, fmt.Errorf("line %d: unknown key %q", lineNo, args[0])
	}
	return step, nil
}

func argRange(min, max int) string {
	switch {
	case min == max:
		return fmt.Sprintf("exactly %d argument(s)", min)
	case min == 0:
		return fmt.Sprintf("up to %d argument(s)", max)
	default:
		return fmt.Sprintf("%d or %d arguments", min, max)
	}
}

func parseDuration(s string) (time.Duration, error) {
	d, err := time.ParseDuration(strings.TrimSpace(s))
	if err != nil {
		return 0, fmt.Errorf("%q is not a duration (use 20s, 1500ms, 2m)", s)
	}
	if d <= 0 {
		return 0, fmt.Errorf("duration %q must be positive", s)
	}
	return d, nil
}

// tokenize splits a recipe line into words, treating a double-quoted run as one
// word. Backslash escapes the next character inside quotes.
func tokenize(s string, lineNo int) ([]string, error) {
	var out []string
	for i := 0; i < len(s); {
		switch {
		case s[i] == ' ' || s[i] == '\t':
			i++
		case s[i] == '"':
			var b strings.Builder
			j := i + 1
			for j < len(s) && s[j] != '"' {
				if s[j] == '\\' && j+1 < len(s) {
					j++
				}
				b.WriteByte(s[j])
				j++
			}
			if j >= len(s) {
				return nil, fmt.Errorf("line %d: unterminated quoted string", lineNo)
			}
			out = append(out, b.String())
			i = j + 1
		default:
			j := i
			for j < len(s) && s[j] != ' ' && s[j] != '\t' {
				j++
			}
			out = append(out, s[i:j])
			i = j
		}
	}
	return out, nil
}

// Substitute replaces {name} placeholders with parameter values.
//
// Every declared parameter must be present, and every placeholder must be
// declared: an unset value would otherwise be typed into the phone as an empty
// string.
func Substitute(text string, params map[string]string) (string, error) {
	var out strings.Builder
	for i := 0; i < len(text); {
		if text[i] != '{' {
			out.WriteByte(text[i])
			i++
			continue
		}
		end := strings.IndexByte(text[i:], '}')
		if end < 0 {
			return "", fmt.Errorf("unclosed { in %q", text)
		}
		name := text[i+1 : i+end]
		value, ok := params[name]
		if !ok {
			return "", fmt.Errorf("no value for parameter %q in %q", name, text)
		}
		if strings.TrimSpace(value) == "" {
			return "", fmt.Errorf("parameter %q is empty", name)
		}
		out.WriteString(value)
		i += end + 1
	}
	return out.String(), nil
}

// MissingParams returns the declared parameters that the caller did not supply.
func (rec *Recipe) MissingParams(params map[string]string) []string {
	var missing []string
	for _, name := range rec.Params {
		if strings.TrimSpace(params[name]) == "" {
			missing = append(missing, name)
		}
	}
	return missing
}