package cli

import (
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	"git.vakhrushev.me/av/convy/internal/doc"
	"git.vakhrushev.me/av/convy/internal/lang"
	"git.vakhrushev.me/av/convy/internal/suite"
)

// Retirement is the one operation in the model whose mistakes cannot be undone.
// A text rewritten badly gets rewritten again; a prefix handed out twice is a
// reference from a foreign repository that now points at a different statement,
// and that is discovered by its content rather than by any check.
//
// So the command does the bookkeeping the discipline otherwise leans on
// attention for: it writes the date, it words the stub out of the suite's own
// vocabulary, it moves the name into the retired half instead of deleting it,
// and it refuses whatever would leave a reference pointing at nothing.

var ruleIDRe = regexp.MustCompile(`^([A-Z]{4})-(\d+)$`)

func runSuiteRetire(env Env, args []string) ExitCode {
	fs := flag.NewFlagSet("convy suite retire", flag.ContinueOnError)
	fs.SetOutput(env.Err)
	root := fs.String("root", "", "root of the suite; by default it is looked up upwards")
	rule := fs.String("rule", "", "identifier of a rule to retire, PREFIX-N")
	prefix := fs.String("prefix", "", "prefix of a convention to retire together with its file")
	topic := fs.String("topic", "", "name of a topic to retire")
	reason := fs.String("reason", "", "why it is being retired")
	date := fs.String("date", "", "date of retirement; today by default")
	if err := fs.Parse(args); err != nil {
		return Usage
	}

	dir, code := suiteRoot(env, *root)
	if code != OK {
		return code
	}
	s, err := suite.Load(dir)
	if err != nil {
		fmt.Fprintln(env.Err, err)
		return Usage
	}

	when := *date
	if when == "" {
		when = time.Now().Format("2006-01-02")
	}

	given := map[string]string{"rule": *rule, "prefix": *prefix, "topic": *topic, "reason": *reason}
	talk := newDialogue(env)
	if len(args) == 0 {
		if !env.Interactive {
			fmt.Fprintln(env.Err, "convy suite retire without arguments asks questions, and there is no terminal to ask on; pass one of --rule, --prefix, --topic together with --reason")
			return Usage
		}
		if err := askRetire(env, talk, s, given); err != nil {
			return Usage
		}
	} else if err := resolve(retireFields(s), given); err != nil {
		fmt.Fprintln(env.Err, err)
		return Usage
	}

	targets := 0
	for _, key := range []string{"rule", "prefix", "topic"} {
		if given[key] != "" {
			targets++
		}
	}
	if targets != 1 {
		fmt.Fprintln(env.Err, "name exactly one of --rule, --prefix, --topic: the three retire different things and undo differently")
		return Usage
	}

	// The dialogue is built once and carried through: a second one over the
	// same input would find it drained, because the first reads ahead.
	var d *dialogue
	if env.Interactive {
		d = talk
	}
	switch {
	case given["rule"] != "":
		return retireRule(env, d, s, given, when)
	case given["prefix"] != "":
		return retirePrefix(env, d, s, given, when)
	default:
		return retireTopic(env, d, s, given, when)
	}
}

func retireFields(s *suite.Suite) []Field {
	return []Field{{
		Flag:     "rule",
		Ask:      "Rule",
		Optional: true,
		Check: func(v string) error {
			if !ruleIDRe.MatchString(v) {
				return fmt.Errorf("a rule is named by its identifier, PREFIX-N")
			}
			return nil
		},
	}, {
		Flag:     "prefix",
		Ask:      "Prefix",
		Optional: true,
		Check: func(v string) error {
			if _, ok := s.Manifest.PathOf(v); !ok {
				return fmt.Errorf("the suite declares no live prefix %s", v)
			}
			return nil
		},
	}, {
		Flag:     "topic",
		Ask:      "Topic",
		Optional: true,
		Check: func(v string) error {
			if !s.Manifest.TopicLive(v) {
				return fmt.Errorf("the suite declares no live topic %q", v)
			}
			return nil
		},
	}, {
		Flag: "reason",
		Ask:  "Reason",
		Hint: "Why it is going. The reason outlives the thing itself — it is what a reader finds in place of what they were looking for.",
	}}
}

// askRetire walks the dialogue: what kind of thing, which one, and why.
func askRetire(env Env, d *dialogue, s *suite.Suite, given map[string]string) error {
	fields := retireFields(s)

	kind, err := d.ask(Field{
		Ask:     "What is being retired",
		Hint:    "A rule keeps its number and turns into a stub; a convention takes its file with it; a topic goes once no layer of it is left.",
		Options: []string{"rule", "convention", "topic"},
		Default: "rule",
	})
	if err != nil {
		fmt.Fprintln(env.Err, "\ninterrupted, nothing was written")
		return err
	}

	flagOf := map[string]string{"rule": "rule", "convention": "prefix", "topic": "topic"}[kind]
	for _, f := range fields {
		if f.Flag != flagOf && f.Flag != "reason" {
			continue
		}
		f.Optional = false
		answer, err := d.ask(f)
		if err != nil {
			fmt.Fprintln(env.Err, "\ninterrupted, nothing was written")
			return err
		}
		given[f.Flag] = answer
	}
	return nil
}

// retireRule replaces the norm and the rationale with a stub, keeping the
// heading and the number. The number stays taken forever, so a reference from a
// foreign repository lands on the explanation instead of on nothing.
func retireRule(env Env, d *dialogue, s *suite.Suite, given map[string]string, when string) ExitCode {
	m := ruleIDRe.FindStringSubmatch(given["rule"])
	num, _ := strconv.Atoi(m[2])
	target, ok := s.ByPrefix[m[1]]
	if !ok {
		fmt.Fprintf(env.Err, "the suite declares no live prefix %s\n", m[1])
		return Usage
	}

	var found *doc.Rule
	for i := range target.Rules {
		if target.Rules[i].Num == num {
			found = &target.Rules[i]
		}
	}
	if found == nil {
		fmt.Fprintf(env.Err, "%s holds no rule numbered %d\n", target.Path, num)
		return Usage
	}
	if _, already := found.Block(lang.Retired); already {
		fmt.Fprintf(env.Err, "%s is retired already\n", found.ID())
		return Usage
	}

	if d != nil {
		ok, err := d.confirm(fmt.Sprintf(
			"%s in %s loses its norm and its rationale, keeping the number. Go on?", found.ID(), target.Path))
		if err != nil || !ok {
			fmt.Fprintln(env.Out, "nothing was written")
			return Usage
		}
	}

	name := filepath.Join(s.Root, filepath.FromSlash(target.Path))
	body, err := os.ReadFile(name)
	if err != nil {
		fmt.Fprintln(env.Err, err)
		return Failed
	}
	lines := strings.Split(string(body), "\n")

	stub := fmt.Sprintf("**%s %s.** %s", s.Vocab.MarkWord(lang.Retired), when, given["reason"])
	replacement := append([]string{""}, wrap(stub, 78)...)
	replacement = append(replacement, "")

	out := make([]string, 0, len(lines))
	out = append(out, lines[:found.Line]...)
	out = append(out, replacement...)
	if found.End < len(lines) {
		out = append(out, lines[found.End:]...)
	}
	if err := os.WriteFile(name, []byte(strings.Join(out, "\n")), 0o644); err != nil {
		fmt.Fprintln(env.Err, err)
		return Failed
	}

	fmt.Fprintf(env.Out, "\n%s is retired in %s\n", found.ID(), target.Path)
	fmt.Fprintf(env.Out, "the number stays taken, and a reference to it now lands on the reason\n")
	return OK
}

// retirePrefix retires a convention together with its file. The rules of that
// file cease to exist, so the command refuses while anything still points at
// them: a stub can stand in for a rule, but nothing stands in for a file.
func retirePrefix(env Env, d *dialogue, s *suite.Suite, given map[string]string, when string) ExitCode {
	prefix := given["prefix"]
	target, ok := s.ByPrefix[prefix]
	if !ok {
		fmt.Fprintf(env.Err, "the suite declares no live prefix %s\n", prefix)
		return Usage
	}

	if pointing := referencesTo(s, prefix, target); len(pointing) > 0 {
		fmt.Fprintf(env.Err, "%s is still pointed at, so retiring it would leave references resolving to nothing:\n", prefix)
		for _, where := range pointing {
			fmt.Fprintf(env.Err, "  %s\n", where)
		}
		fmt.Fprintln(env.Err, "move or retire those rules first")
		return Usage
	}

	if d != nil {
		ok, err := d.confirm(fmt.Sprintf(
			"%s goes, and %s is deleted. The prefix is never reissued. Go on?", target.Path, target.Path))
		if err != nil || !ok {
			fmt.Fprintln(env.Out, "nothing was written")
			return Usage
		}
	}

	note := fmt.Sprintf("%s, was %s: %s", when, target.Path, given["reason"])
	s.Manifest.Prefixes.Retire(prefix, note)
	if err := s.Manifest.Save(); err != nil {
		fmt.Fprintln(env.Err, err)
		return Failed
	}
	if err := os.Remove(filepath.Join(s.Root, filepath.FromSlash(target.Path))); err != nil {
		fmt.Fprintf(env.Err, "the manifest was updated, but the file was not removed: %s\n", err)
		return Failed
	}

	fmt.Fprintf(env.Out, "\n%s is retired and %s is gone\n", prefix, target.Path)
	if left := s.Layers(target.Front.Topic); len(left) == 1 {
		fmt.Fprintf(env.Out, "the topic %q has no layer left; retire the topic too if it is done\n", target.Front.Topic)
	}
	return OK
}

// retireTopic sends a topic name to the retired half. A topic lives as long as
// one layer of it does, so the command refuses while any layer is left.
func retireTopic(env Env, d *dialogue, s *suite.Suite, given map[string]string, when string) ExitCode {
	topic := given["topic"]
	if layers := s.Layers(topic); len(layers) > 0 {
		fmt.Fprintf(env.Err, "the topic %q still holds layers, and a topic lives as long as one of them does:\n", topic)
		for _, d := range layers {
			fmt.Fprintf(env.Err, "  %s\n", d.Path)
		}
		fmt.Fprintln(env.Err, "retire those conventions first")
		return Usage
	}

	if d != nil {
		ok, err := d.confirm(fmt.Sprintf(
			"the name %q goes to the retired half and is never handed to another topic. Go on?", topic))
		if err != nil || !ok {
			fmt.Fprintln(env.Out, "nothing was written")
			return Usage
		}
	}

	s.Manifest.Topics.Retire(topic, when+": "+given["reason"])
	if err := s.Manifest.Save(); err != nil {
		fmt.Fprintln(env.Err, err)
		return Failed
	}

	fmt.Fprintf(env.Out, "\nthe topic %q is retired\n", topic)
	return OK
}

// referencesTo finds where the rules of a prefix are pointed at from outside
// the file that owns them.
func referencesTo(s *suite.Suite, prefix string, own *doc.Document) []string {
	var out []string
	for _, d := range s.Docs {
		if d == own {
			continue
		}
		for _, ref := range refsOf(d, prefix) {
			out = append(out, fmt.Sprintf("%s:%d  %s", d.Path, ref.line, ref.text))
		}
	}
	return out
}

type refAt struct {
	line int
	text string
}

var anyRefRe = regexp.MustCompile(`\b[A-Z]{4}-\d+(?:\.\d+)?`)

func refsOf(d *doc.Document, prefix string) []refAt {
	var out []refAt
	for n := d.Body; n <= d.Len(); n++ {
		if d.Fenced(n) {
			continue
		}
		for _, text := range anyRefRe.FindAllString(doc.StripInline(d.Line(n)), -1) {
			if strings.HasPrefix(text, prefix+"-") {
				out = append(out, refAt{line: n, text: text})
			}
		}
	}
	return out
}

// wrap breaks a paragraph at a width, the way the text around it is written by
// hand. A stub that runs off in one long line reads as machine-made and gets
// reflowed by the next person to touch the file.
func wrap(text string, width int) []string {
	words := strings.Fields(text)
	if len(words) == 0 {
		return []string{""}
	}
	lines := []string{words[0]}
	for _, w := range words[1:] {
		last := len(lines) - 1
		if len([]rune(lines[last]))+1+len([]rune(w)) <= width {
			lines[last] += " " + w
			continue
		}
		lines = append(lines, w)
	}
	return lines
}