package cli

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

	"git.vakhrushev.me/av/convy/internal/manifest"
	"git.vakhrushev.me/av/convy/internal/suite"
)

var (
	nameRe  = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*$`)
	kebabRe = regexp.MustCompile(`^[a-z0-9]+(-[a-z0-9]+)*$`)
)

func runSuiteAdd(env Env, args []string) ExitCode {
	fs := flag.NewFlagSet("convy suite add", flag.ContinueOnError)
	fs.SetOutput(env.Err)
	root := fs.String("root", "", "root of the suite; by default it is looked up upwards")
	topic := fs.String("topic", "", "name of the topic the convention belongs to")
	about := fs.String("about", "", "one line about the topic, for a new topic only")
	prefix := fs.String("prefix", "", "prefix of the rules, four uppercase Latin letters")
	title := fs.String("title", "", "title of the document")
	intro := fs.String("intro", "", "introductory prose, one or two sentences")
	langAxis := fs.String("lang", "", "language axis of the layer; empty means the base layer")
	stackAxis := fs.String("stack", "", "stack axis of the layer; empty means the base layer")
	file := fs.String("path", "", "path of the file from the root of the suite")
	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
	}

	given := map[string]string{
		"topic": *topic, "about": *about, "prefix": *prefix,
		"title": *title, "intro": *intro,
		"lang": *langAxis, "stack": *stackAxis, "path": *file,
	}

	if len(args) == 0 {
		if !env.Interactive {
			fmt.Fprintln(env.Err, "convy suite add without arguments asks questions, and there is no terminal to ask on; pass --topic, --prefix and --title")
			return Usage
		}
		if err := askAdd(env, s, given); err != nil {
			return Usage
		}
	} else {
		if err := resolve(addFields(s), given); err != nil {
			fmt.Fprintln(env.Err, err)
			return Usage
		}
		if given["path"] == "" {
			given["path"] = defaultPath(given)
		}
		if err := checkTopicAbout(s, given); err != nil {
			fmt.Fprintln(env.Err, err)
			return Usage
		}
	}

	return writeConvention(env, s, given)
}

// addFields describes what a convention needs to be added. The checks live here
// rather than at the point of writing so that both modes apply the same ones.
func addFields(s *suite.Suite) []Field {
	return []Field{{
		Flag: "topic",
		Ask:  "Topic",
		Hint: "The focus the rules are about: time, config, db-schema. A topic is the unit of subscription — a consumer takes it whole. The name never changes and is never reused.",
		Check: func(v string) error {
			if !nameRe.MatchString(v) {
				return fmt.Errorf("a topic name travels into the file system of a consumer, so it is written in Latin letters and digits")
			}
			if s.Manifest.TopicRetired(v) {
				return fmt.Errorf("the topic %q is retired and cannot be handed out again", v)
			}
			return nil
		},
	}, {
		Flag: "prefix",
		Ask:  "Prefix of the rules",
		Hint: "Four uppercase Latin letters, unique across the suite, one per file. Pick a word that reads, not a formula: the prefix exists to be searched for. Rules will be numbered PREFIX-1, PREFIX-2.",
		Check: func(v string) error {
			if err := manifest.ValidPrefix(v); err != nil {
				return err
			}
			if _, taken := s.Manifest.PathOf(v); taken {
				return fmt.Errorf("the prefix %s is already taken in the suite", v)
			}
			if s.Manifest.PrefixRetired(v) {
				return fmt.Errorf("the prefix %s is retired and is never reissued", v)
			}
			return nil
		},
	}, {
		Flag: "title",
		Ask:  "Title of the document",
		Hint: "The level-one heading, in the language of the suite.",
	}, {
		Flag:     "lang",
		Ask:      "Language axis",
		Hint:     "The programming language this layer is about, if it is about one: go, python. Leave empty for the base layer, the one that reaches every copy.",
		Optional: true,
		Check:    axisCheck,
	}, {
		Flag:     "stack",
		Ask:      "Stack axis",
		Hint:     "The tool or framework this layer is about, if it is about one: htmx, ansible. Leave empty together with the language axis to get the base layer.",
		Optional: true,
		Check:    axisCheck,
	}, {
		Flag:     "intro",
		Ask:      "Introductory prose",
		Hint:     "One or two sentences on what the convention covers. Key words in capitals do not belong here: prose is never a norm.",
		Optional: true,
	}}
}

func axisCheck(v string) error {
	if !nameRe.MatchString(v) {
		return fmt.Errorf("an axis value becomes a directory name, so it is written in Latin letters and digits")
	}
	return nil
}

// askAdd walks the dialogue, asking for the topic description only when the
// topic is new and for the path once the axis is known.
func askAdd(env Env, s *suite.Suite, given map[string]string) error {
	d := newDialogue(env)
	fields := addFields(s)

	for _, f := range fields {
		answer, err := d.ask(f)
		if err != nil {
			fmt.Fprintln(env.Err, "\ninterrupted, nothing was written")
			return err
		}
		given[f.Flag] = answer

		if f.Flag != "topic" {
			continue
		}
		if s.Manifest.TopicLive(answer) {
			fmt.Fprintf(env.Out, "  the topic is known, this will be another layer of it\n")
			continue
		}
		about, err := d.ask(Field{
			Flag: "about",
			Ask:  "One line about the topic",
			Hint: "It goes into the manifest and builds the table of conventions in a consumer's README.",
		})
		if err != nil {
			fmt.Fprintln(env.Err, "\ninterrupted, nothing was written")
			return err
		}
		given["about"] = about
	}

	answer, err := d.ask(Field{
		Flag:    "path",
		Ask:     "Path of the file",
		Hint:    "Where the file lies in the suite. The directory tree documents the tie between layers for a human; what a layer actually is comes from the front matter.",
		Default: defaultPath(given),
	})
	if err != nil {
		fmt.Fprintln(env.Err, "\ninterrupted, nothing was written")
		return err
	}
	given["path"] = answer
	return nil
}

// checkTopicAbout guards the one field whose need depends on another: a new
// topic has to be described, a known one is described already.
func checkTopicAbout(s *suite.Suite, given map[string]string) error {
	if s.Manifest.TopicLive(given["topic"]) {
		return nil
	}
	if given["about"] == "" {
		return fmt.Errorf("the topic %q is new to the suite, so --about is required: the line describes it in the manifest and in a consumer's README", given["topic"])
	}
	return nil
}

// defaultPath puts a file where the axis says it belongs. The path is
// documentation, not a declaration — but documentation that agrees with the
// declaration costs nothing to produce.
func defaultPath(given map[string]string) string {
	topic := given["topic"]
	switch {
	case given["lang"] != "":
		return path.Join("conventions/lang", given["lang"], topic+".md")
	case given["stack"] != "":
		return path.Join("conventions/stack", given["stack"], topic+".md")
	}
	return path.Join("conventions", topic+".md")
}

// writeConvention writes the file and splices the manifest. The file goes first
// and the manifest second, because a file the manifest does not declare is
// reported by the check, while a declared file that is missing is an error the
// author has to undo by hand.
func writeConvention(env Env, s *suite.Suite, given map[string]string) ExitCode {
	if given["lang"] != "" && given["stack"] != "" {
		// Both axes at once is a layer meaningful only when language and tool
		// coincide. The model allows it; the default path does not express
		// it, so the path has to be given explicitly.
		if given["path"] == "" {
			fmt.Fprintln(env.Err, "a layer on both axes needs --path: the tree cannot express two axes at once")
			return Usage
		}
	}
	rel := filepath.ToSlash(given["path"])
	name := filepath.Join(s.Root, filepath.FromSlash(rel))
	if _, err := os.Stat(name); err == nil {
		fmt.Fprintf(env.Err, "%s already exists\n", rel)
		return Usage
	}

	base := baseLayerOf(s, given["topic"])
	if base == "" && given["lang"] == "" && given["stack"] == "" {
		// The first layer of a topic and no axis: this is the base one.
	} else if base == "" {
		fmt.Fprintf(env.Out, "note: the topic has no base layer yet, so this one stands alone\n")
	} else if given["lang"] == "" && given["stack"] == "" {
		fmt.Fprintf(env.Err, "the topic %q already holds a base layer (%s): a second one would put two base texts in one assembled file\n", given["topic"], base)
		return Usage
	}

	body := conventionSkeleton(s, given, base, rel)
	if err := os.MkdirAll(filepath.Dir(name), 0o755); err != nil {
		fmt.Fprintln(env.Err, err)
		return Usage
	}
	if err := os.WriteFile(name, []byte(body), 0o644); err != nil {
		fmt.Fprintln(env.Err, err)
		return Usage
	}

	if !s.Manifest.TopicLive(given["topic"]) {
		s.Manifest.Topics.Add(given["topic"], given["about"])
	}
	s.Manifest.Prefixes.Add(given["prefix"], rel)
	if err := s.Manifest.Save(); err != nil {
		fmt.Fprintf(env.Err, "%s was written, but the manifest was not: %s\n", rel, err)
		return Failed
	}

	fmt.Fprintf(env.Out, "\ncreated %s\n", rel)
	fmt.Fprintf(env.Out, "updated %s: prefix %s", manifest.Name, given["prefix"])
	if given["about"] != "" {
		fmt.Fprintf(env.Out, ", topic %s", given["topic"])
	}
	fmt.Fprintf(env.Out, "\n\nwrite the first rule as ### %s-1, then run convy suite check\n", given["prefix"])
	if !kebabRe.MatchString(given["topic"]) {
		fmt.Fprintf(env.Out, "note: lower kebab-case is the recommended shape for a topic name\n")
	}
	return OK
}

// baseLayerOf returns the path of the base layer of a topic, if the suite holds
// one.
func baseLayerOf(s *suite.Suite, topic string) string {
	for _, d := range s.Layers(topic) {
		if !d.Front.Axis() {
			return d.Path
		}
	}
	return ""
}

// conventionSkeleton builds the file: front matter, title, prose and the
// language version line. The line is rendered out of the suite's vocabulary,
// which is the whole point of the vocabulary being a property of the language
// rather than of the code — what the tool writes, the tool also accepts.
func conventionSkeleton(s *suite.Suite, given map[string]string, base, rel string) string {
	var b strings.Builder
	b.WriteString("---\n")
	fmt.Fprintf(&b, "topic: %s\n", given["topic"])
	fmt.Fprintf(&b, "prefix: %s\n", given["prefix"])
	if given["lang"] != "" {
		fmt.Fprintf(&b, "lang: %s\n", given["lang"])
	}
	if given["stack"] != "" {
		fmt.Fprintf(&b, "stack: %s\n", given["stack"])
	}
	if base != "" {
		fmt.Fprintf(&b, "extends: %s\n", extendsRef(s, base, rel))
	}
	b.WriteString("---\n\n")

	fmt.Fprintf(&b, "# %s\n\n", given["title"])
	if given["intro"] != "" {
		fmt.Fprintf(&b, "%s\n\n", given["intro"])
	}
	b.WriteString(s.Vocab.VersionLine())
	b.WriteString("\n")
	return b.String()
}

// extendsRef writes the base layer the way the suite already writes it: from
// the directory the two files share, when that form names one file and no more.
//
// The short form is what a reader expects, but two layers of one topic usually
// carry the same file name, so a tail like "time.md" can fit both the base
// layer and the file being written. Where that happens the reference falls back
// to the path from the root of the suite, which fits exactly one file always.
func extendsRef(s *suite.Suite, base, rel string) string {
	short := base
	shared := path.Dir(rel)
	for shared != "." && shared != "/" {
		if rest, ok := strings.CutPrefix(base, path.Dir(shared)+"/"); ok {
			short = rest
			break
		}
		shared = path.Dir(shared)
	}
	if short == base || unambiguous(s, short, base, rel) {
		return short
	}
	return base
}

// unambiguous reports whether a tail names the base layer and nothing else,
// counting the file about to be written as one of the suite's own.
func unambiguous(s *suite.Suite, short, base, rel string) bool {
	paths := []string{rel}
	for _, d := range s.Docs {
		paths = append(paths, d.Path)
	}
	hits := 0
	for _, p := range paths {
		if p == short || strings.HasSuffix(p, "/"+short) {
			hits++
		}
	}
	return hits == 1 && (base == short || strings.HasSuffix(base, "/"+short))
}

// suiteRoot settles the directory a suite command works in.
func suiteRoot(env Env, given string) (string, ExitCode) {
	if given != "" {
		return given, OK
	}
	found, err := manifest.Find(env.Dir)
	if err != nil {
		fmt.Fprintf(env.Err, "not a conventions suite: no %s here or above\n", manifest.Name)
		fmt.Fprintln(env.Err, "convy suite init starts one")
		return "", Usage
	}
	return found, OK
}