package definition

import (
	"fmt"
	"strings"
)

// One Markdown definition → one skill.
//
// A port of parseSkill and validateSkillSource in src/lib/skills/registry.js,
// restricted to the definition contract — see the package documentation in
// definition.go for exactly where that boundary is and why the `ui:` and
// `owliver:` blocks are on the other side of it.

// Level is one rung of a workforce ladder, read from the body's own headings.
type Level struct {
	Level   string `json:"level"`
	Label   string `json:"label"`
	Summary string `json:"summary"`
}

// Skill is a definition as the backend reads it.
//
// The five fields migration 000005 projects into columns — ID, Name,
// Description, Status, Pages — are the compatibility contract; the rest is
// carried because it is free once the frontmatter is parsed and because the
// conformance suite compares it.
type Skill struct {
	ID          string `json:"id"`
	Name        string `json:"name"`
	Description string `json:"description"`
	Status      string `json:"status"`

	// Pages as the AUTHOR WROTE THEM, not canonicalised.
	//
	// This is not an oversight and must not be "fixed": parseSkill keeps the
	// declared strings, so a skill written against `Talent Pool` is registered
	// under `Talent Pool` and resolved through normalizeKey at every use.
	// Agents are the other way round — see Agent.Pages. Canonicalising here
	// would make the backend's projection disagree with the editor's.
	Pages []string `json:"pages"`

	Kind             string   `json:"kind"`
	Category         string   `json:"category"`
	Actions          []string `json:"actions"`
	Triggers         []string `json:"triggers"`
	DeclaredTriggers bool     `json:"declaredTriggers"`
	Prompt           *string  `json:"prompt"`
	SkillID          *string  `json:"skillId"`
	Levels           []Level  `json:"levels"`

	// Body is the Markdown after the frontmatter, trimmed. The definition
	// itself is NEVER rewritten — see Definition.Markdown.
	Body string `json:"-"`

	// Deferred names the frontmatter blocks whose semantics this package does
	// not check and the frontend does. Empty for every definition the backend
	// can fully validate on its own. See package documentation.
	Deferred []string `json:"deferred,omitempty"`
}

// AuthoredPath is the origin an authored definition has when the caller names
// none. It is a value rather than an absence for one reason: it is the
// frontend's own default parameter.
//
//	parseSkill(raw, { path = 'custom', custom = false } = {})
//	parseAgent(raw, { path = 'custom', custom = false } = {})
//
// validateSkillSource and validateAgentSource both call their parser with no
// path, so every definition the EDITOR checks derives its last-resort id from
// the literal string `custom`. That is the same call the backend is making — a
// definition submitted to the API is authored, not shipped — so the backend
// must derive the same id.
//
// The difference is reachable and it is not cosmetic. A definition with no
// `id:`, no `name:` and a valid `pages:` list gets the id `custom` on the
// frontend, passes the id-format check and is ACCEPTED. Deriving no id here
// would refuse it with "The frontmatter needs an `id`." — a definition that
// validates in the editor and fails on save, which is the exact failure mode
// this package exists to prevent. Fixture case: id-omitted-unnamed.
const AuthoredPath = "custom"

// Options carries what the caller knows that the definition does not.
type Options struct {
	// Path is the definition's origin, used only as the last fallback for an
	// id. Leave it empty for anything authored rather than shipped — which is
	// what the backend always has — and it becomes AuthoredPath, exactly as the
	// frontend's default parameter does.
	Path string
}

// path is the origin an id is derived from, with the frontend's default
// applied.
func (o Options) path() string {
	if o.Path == "" {
		return AuthoredPath
	}
	return o.Path
}

// ParseSkill reads a skill definition.
//
// Returns a *Error when the frontmatter cannot be read. A definition with no
// frontmatter at all is not an error here: it parses to a skill carrying the
// derived id and no pages, and ValidateSkill is what refuses it — the same
// division of labour the frontend has.
func ParseSkill(raw string, opts Options) (*Skill, error) {
	doc, err := ParseFrontmatter(raw)
	if err != nil {
		return nil, err
	}
	data := doc.Data

	declaredPages, _ := data["pages"].([]any)

	// `id:` always wins. An explicit id is the address other definitions and
	// stored preferences refer to, and deriving over the top of one would
	// silently rename a skill. Slugging the name is what an author means by
	// leaving it out; the filename is right only for a file, which is why it
	// is last.
	id := jsTrim(jsString(data["id"]))
	if !jsTruthy(data["id"]) {
		id = slugify(data["name"])
		if id == "" {
			id = fileStem(opts.path())
		}
	}

	levels := sectionLevels(doc.Body)

	// Two things wear the same format. A definition that names a ladder is a
	// workforce skill; nothing else distinguishes them, so an author declares
	// one by writing one rather than by setting a flag.
	kind := jsTrim(jsString(data["kind"]))
	if !jsTruthy(data["kind"]) {
		kind = "assistant"
		if len(levels) > 0 {
			kind = "workforce"
		}
	}

	skill := &Skill{
		ID:     id,
		Kind:   kind,
		Levels: levels,
		Body:   doc.Body,
		Name:   "Untitled skill",
		Pages:  stringsOf(declaredPages),
	}

	if jsTruthy(data["name"]) {
		skill.Name = jsString(data["name"])
	}
	if jsTruthy(data["description"]) {
		skill.Description = jsString(data["description"])
	}
	if s, ok := data["category"].(string); ok {
		skill.Category = jsTrim(s)
	}

	// The whole of a skill's lifecycle, and deliberately a coercion rather
	// than a check: the frontend reads anything that is not `inactive` as
	// `active`, so `status: bogus` registers as active rather than being
	// refused. Reproduced, not corrected — see the divergence note in
	// docs/phase-4d-parser-contract.md.
	skill.Status = "active"
	if s, ok := data["status"].(string); ok && s == "inactive" {
		skill.Status = "inactive"
	}

	if actions, ok := data["actions"].([]any); ok {
		skill.Actions = stringsOf(actions)
	} else {
		skill.Actions = []string{}
	}

	// A skill with no declared triggers answers to its own name, so a
	// definition that omits the field is still reachable by asking for it.
	// Explicit triggers replace the fallback rather than adding to it.
	triggers, hasTriggers := data["triggers"].([]any)
	skill.DeclaredTriggers = hasTriggers && len(triggers) > 0
	skill.Triggers = []string{}
	if skill.DeclaredTriggers {
		for _, t := range triggers {
			skill.Triggers = append(skill.Triggers, strings.ToLower(jsString(t)))
		}
	} else if jsTruthy(data["name"]) {
		skill.Triggers = append(skill.Triggers, strings.ToLower(jsString(data["name"])))
	}

	if jsTruthy(data["prompt"]) {
		p := jsString(data["prompt"])
		skill.Prompt = &p
	}

	// The capability in the skill graph a workforce definition governs:
	// `skill:`, or the id with a `-training` suffix dropped and dashes swapped
	// for underscores.
	if kind == "workforce" {
		base := id
		if jsTruthy(data["skill"]) {
			base = jsString(data["skill"])
		} else {
			base = strings.TrimSuffix(base, "-training")
		}
		s := strings.ReplaceAll(base, "-", "_")
		skill.SkillID = &s
	}

	skill.Deferred = deferredBlocks(data)
	return skill, nil
}

// sectionLevels reads the ladder a workforce definition defines, in order, from
// the body's own headings. A rung with no prose is not a rung.
func sectionLevels(body string) []Level {
	out := []Level{}
	for _, heading := range levelHeadings {
		summary := SectionText(body, heading)
		if summary == "" {
			continue
		}
		out = append(out, Level{
			Level:   strings.ToLower(heading),
			Label:   heading,
			Summary: summary,
		})
	}
	return out
}

// deferredBlocks names the frontmatter this package does not semantically
// check. See the package documentation for why they are deferred rather than
// validated or rejected.
func deferredBlocks(data map[string]any) []string {
	out := []string{}
	for _, key := range []string{"ui", "owliver"} {
		if _, present := data[key]; present {
			out = append(out, key)
		}
	}
	if len(out) == 0 {
		return nil
	}
	return out
}

// stringsOf renders a parsed sequence as the strings the frontend would read
// out of it. Non-string entries are stringified rather than dropped, because
// that is what every consumer of `pages` and `actions` does with them.
func stringsOf(list []any) []string {
	out := make([]string, 0, len(list))
	for _, v := range list {
		out = append(out, jsString(v))
	}
	return out
}

func fileStem(path string) string {
	if path == "" {
		return ""
	}
	if i := strings.LastIndexByte(path, '/'); i >= 0 {
		path = path[i+1:]
	}
	return strings.TrimSuffix(path, ".md")
}

// ValidateSkill decides whether a skill definition may be stored.
//
// Returns nil when it may. The order is the order an author would fix things
// in, and every message below is the frontend's message character for
// character — an author who sees one in the editor and a different one from
// the API is being told about two different problems.
//
// Two rules are the backend's own and are marked as such: the size bound and
// the deferred-block rule. Both are explained in
// docs/phase-4d-parser-contract.md.
func ValidateSkill(raw string) error {
	if jsTrim(raw) == "" {
		return &Rejection{Message: "Paste or upload a Markdown definition."}
	}

	// The backend's own rule, from migration 000005's markdown_size CHECK. The
	// editor does not enforce it, so a definition over the bound is one the
	// frontend accepts and the DATABASE refuses; refusing it here turns a
	// constraint violation into a message. See the contract document.
	if n := len([]rune(raw)); n > MaxMarkdownLength {
		return &Rejection{
			BackendOnly: true,
			Message: fmt.Sprintf(
				"That definition is %d characters. The limit is %d.", n, MaxMarkdownLength),
		}
	}

	skill, err := ParseSkill(raw, Options{})
	if err != nil {
		// The subset reports the line it failed on, which is far more useful
		// than "could not be parsed".
		return &Rejection{Message: jsTrim("That definition could not be parsed. " + err.Error())}
	}

	if skill.ID == "" {
		return &Rejection{Message: "The frontmatter needs an `id`."}
	}
	if !isDefinitionID(skill.ID) {
		return &Rejection{Message: "`id` must be lower-case letters, numbers and dashes."}
	}
	// Faithful to the frontend, where `name` has already fallen back to
	// `Untitled skill` and this check can therefore never fire. Kept so the
	// two validators have the same shape and the same order.
	if skill.Name == "" {
		return &Rejection{Message: "The frontmatter needs a `name`."}
	}
	// The backend's own rule, and it must be asked BEFORE the generic one
	// below. A `ui:` block declares the pages it draws on, and parseSkill falls
	// back to those pages when `pages:` is absent — a fallback this package
	// cannot compute, because it does not read the `ui:` vocabulary. Rather
	// than report an empty page list it never really established, say what is
	// actually missing. No shipped definition relies on the fallback: all
	// nineteen that carry a `ui:` or `owliver:` block also declare `pages:`.
	if len(skill.Pages) == 0 && len(skill.Deferred) > 0 {
		return &Rejection{
			BackendOnly: true,
			Message:     "A definition with a `ui:` block needs an explicit `pages:` list.",
		}
	}
	if len(skill.Pages) == 0 {
		return &Rejection{Message: "The frontmatter needs at least one `pages` entry."}
	}

	unknown := []string{}
	for _, p := range skill.Pages {
		if !SurfaceExists(p) {
			unknown = append(unknown, p)
		}
	}
	if len(unknown) > 0 {
		plural := ""
		if len(unknown) > 1 {
			plural = "s"
		}
		return &Rejection{Message: fmt.Sprintf(
			"Unsupported page%s: %s. Supported pages: %s.",
			plural, strings.Join(unknown, ", "), strings.Join(SupportedPages, ", "))}
	}

	return nil
}