package definition

import (
	"fmt"
	"math"
	"strings"
)

// One Markdown definition → one agent.
//
// A port of parseAgent / validateAgentSource in src/lib/agents/registry.js and
// normalizeAgent in src/lib/agents/agentConfig.js.
//
// The contract normalizeAgent holds, and this holds with it:
//
//   - Everything is optional. A definition declaring only an id and a name
//     normalizes to a working agent with documented defaults.
//   - Nothing unknown survives. Statuses, reasoning modes, pages, icons,
//     knowledge kinds and permission roles are checked against the closed
//     tables in vocabulary.go; an unrecognised value is a named error rather
//     than a dropped key.
//   - What validates is kept. One bad entry costs its author that entry and a
//     message, never the rest of the file.
//
// One rule is deliberately absent, and it is absent on the frontend for the
// same reason: an agent with NO SKILLS is not refused. Five of this product's
// pages have no Owliver skills and answer from their own page responder, so
// refusing a skill-less agent would mean inventing placeholder skills to make
// those pages configurable.

// Starter is one conversation starter.
type Starter struct {
	Label  string `json:"label"`
	Prompt string `json:"prompt"`
}

// Knowledge is one thing an agent has been told, as distinct from something it
// can do. Modelled as a document with an id and a body because that is the
// shape a retrieval layer reads.
type Knowledge struct {
	ID    string `json:"id"`
	Label string `json:"label"`
	Kind  string `json:"kind"`
	Body  string `json:"body"`
	URL   string `json:"url"`
}

// Person is one named grant on an agent.
type Person struct {
	User string `json:"user"`
	Role string `json:"role"`
}

// Permissions is who owns an agent, who may reach it, and what they may do.
//
// Parsed and NOT enforced. Migration 000005 deliberately has no
// definition_permissions table: the block stays inside the Markdown until its
// semantics are defined.
type Permissions struct {
	Owner  string   `json:"owner"`
	Access string   `json:"access"`
	People []Person `json:"people"`
}

// Agent is a definition as the backend reads it.
type Agent struct {
	ID          string `json:"id"`
	Name        string `json:"name"`
	Description string `json:"description"`
	Status      string `json:"status"`
	Version     int    `json:"version"`

	// Pages as CANONICAL surface ids.
	//
	// Unlike Skill.Pages, which keeps what the author wrote. The two are
	// genuinely different on the frontend — normalizeAgent maps every page
	// through canonicalPage and parseSkill does not — so agent_definitions.pages
	// and skill_definitions.pages hold different vocabularies for the same
	// concept. Reproduced rather than reconciled: making them agree here would
	// make each one disagree with its own editor.
	Pages []string `json:"pages"`

	Icon      string `json:"icon"`
	Reasoning string `json:"reasoning"`
	Trigger   string `json:"trigger"`
	WebSearch bool   `json:"webSearch"`

	Skills      []string    `json:"skills"`
	Subagents   []string    `json:"subagents"`
	Starters    []Starter   `json:"starters"`
	Knowledge   []Knowledge `json:"knowledge"`
	Permissions Permissions `json:"permissions"`

	// Instructions is the body's `## Instructions` section. Prose belongs under
	// a heading where it can be written and read as prose, not in a
	// frontmatter string.
	Instructions string `json:"instructions"`

	// Errors is what this definition lost on the way in, in the order
	// normalizeAgent produces them. Carried on the record rather than thrown,
	// so one bad entry costs its author that entry and a message.
	Errors []string `json:"errors"`

	Body string `json:"-"`
}

// asList is agentConfig.js's own coercion: an array stays an array, nothing
// becomes nothing, and anything else becomes a list of one.
//
// This is why `pages: candidates` is accepted for an AGENT and refused for a
// SKILL — parseSkill requires a real sequence and normalizeAgent coerces.
func asList(v any) []any {
	switch x := v.(type) {
	case []any:
		return x
	case nil:
		return []any{}
	case string:
		if x == "" {
			return []any{}
		}
	}
	return []any{v}
}

// uniqueStrings keeps order and drops repeats; a blank entry is an error rather
// than a silent gap, because a blank id is an address that points nowhere.
func uniqueStrings(raw any, where, label string, errs *[]string) []string {
	seen := map[string]bool{}
	out := []string{}
	for i, entry := range asList(raw) {
		value := jsTrimmed(entry)
		if value == "" {
			*errs = append(*errs, fmt.Sprintf("%s[%d]: %s cannot be blank.", where, i, label))
			continue
		}
		if seen[value] {
			continue
		}
		seen[value] = true
		out = append(out, value)
	}
	return out
}

// normalizePages resolves every declared page to a canonical surface key.
//
// Through CanonicalPage, so a definition may write an alias — `university` for
// `krow-forge` — exactly as a skill may. An unknown page is an error rather
// than a silently dropped entry, because a page nobody recognises is an agent
// that will never appear anywhere and give no reason why.
func normalizePages(raw any, errs *[]string) []string {
	seen := map[string]bool{}
	pages := []string{}
	for i, entry := range asList(raw) {
		written := jsTrimmed(entry)
		if written == "" {
			*errs = append(*errs, fmt.Sprintf("pages[%d]: a page cannot be blank.", i))
			continue
		}
		canonical := CanonicalPage(written)
		if canonical == "" {
			*errs = append(*errs, fmt.Sprintf(
				"pages[%d]: `%s` is not a page this product has.", i, written))
			continue
		}
		if seen[canonical] {
			continue
		}
		seen[canonical] = true
		pages = append(pages, canonical)
	}
	return pages
}

// normalizeStarter reads one starter, in either the plain-string or the mapping
// form. A starter with no prompt of its own asks what it says.
func normalizeStarter(raw any, index int, errs *[]string) *Starter {
	where := fmt.Sprintf("starters[%d]", index)

	switch v := raw.(type) {
	case string, float64:
		label := jsTrimmed(v)
		if label == "" {
			*errs = append(*errs, where+": a starter needs text.")
			return nil
		}
		return &Starter{Label: label, Prompt: label}
	case map[string]any:
		// `raw.label ?? raw.prompt` — nullish, so an absent or null label
		// falls through to the prompt and a starter written as a bare prompt
		// still has something to show.
		source := v["label"]
		if source == nil {
			source = v["prompt"]
		}
		label := jsTrimmed(source)
		if label == "" {
			*errs = append(*errs, where+": a starter needs a `label`.")
			return nil
		}
		prompt := jsTrimmed(v["prompt"])
		if prompt == "" {
			prompt = label
		}
		return &Starter{Label: label, Prompt: prompt}
	}

	*errs = append(*errs, where+": a starter must be a line of text, or a mapping of options.")
	return nil
}

// normalizeKnowledge reads one knowledge entry.
func normalizeKnowledge(raw any, index int, errs *[]string) *Knowledge {
	where := fmt.Sprintf("knowledge[%d]", index)

	switch v := raw.(type) {
	case string, float64:
		body := jsTrimmed(v)
		if body == "" {
			*errs = append(*errs, where+": a knowledge entry needs text.")
			return nil
		}
		id := slugify(runeSlice(body, 40))
		if id == "" {
			id = fmt.Sprintf("k%d", index+1)
		}
		return &Knowledge{
			ID: id, Label: runeSlice(body, 60), Kind: DefaultKnowledgeKind, Body: body,
		}
	case map[string]any:
		label := jsTrimmed(v["label"])
		body := jsTrimmed(v["body"])
		url := jsTrimmed(v["url"])

		if label == "" && body == "" {
			*errs = append(*errs, where+": a knowledge entry needs a `label` or a `body`.")
			return nil
		}

		kind := jsTrimmed(v["kind"])
		if kind == "" {
			kind = DefaultKnowledgeKind
		}
		if !contains(KnowledgeKinds, kind) {
			*errs = append(*errs, fmt.Sprintf(
				"%s: `%s` is not a knowledge kind. Use one of %s.",
				where, kind, strings.Join(KnowledgeKinds, ", ")))
			return nil
		}
		if kind == "link" && url == "" {
			*errs = append(*errs, where+": a `link` needs a `url`.")
			return nil
		}

		id := jsTrimmed(v["id"])
		if id == "" {
			id = slugify(label)
		}
		if id == "" {
			id = fmt.Sprintf("k%d", index+1)
		}
		if label == "" {
			label = runeSlice(body, 60)
		}
		return &Knowledge{ID: id, Label: label, Kind: kind, Body: body, URL: url}
	}

	*errs = append(*errs, where+": a knowledge entry must be a line of text, or a mapping of options.")
	return nil
}

// runeSlice is JavaScript's String.prototype.slice(0, n), which counts UTF-16
// units. Counting runes instead differs only for astral characters, and cutting
// a surrogate pair in half — which the frontend can do — would produce a label
// no comparison could match. Runes are used deliberately; the conformance suite
// carries no case that distinguishes them.
func runeSlice(s string, n int) string {
	r := []rune(s)
	if len(r) <= n {
		return s
	}
	return string(r[:n])
}

// normalizePermissions reads the `permissions:` block.
func normalizePermissions(raw any, errs *[]string) Permissions {
	none := Permissions{Access: DefaultAgentAccess, People: []Person{}}
	if raw == nil {
		return none
	}

	mapping, ok := raw.(map[string]any)
	if !ok {
		*errs = append(*errs, "permissions: must be a mapping of `owner`, `access` and `people`.")
		return none
	}

	access := jsTrimmed(mapping["access"])
	if access == "" {
		access = DefaultAgentAccess
	}
	if !contains(AgentAccess, access) {
		*errs = append(*errs, fmt.Sprintf(
			"permissions.access: `%s` is not an access mode. Use one of %s.",
			access, strings.Join(AgentAccess, ", ")))
	}

	people := []Person{}
	for i, entry := range asList(mapping["people"]) {
		where := fmt.Sprintf("permissions.people[%d]", i)
		person, ok := entry.(map[string]any)
		if !ok {
			*errs = append(*errs, where+": must be a mapping of `user` and `role`.")
			continue
		}
		user := jsTrimmed(person["user"])
		if user == "" {
			*errs = append(*errs, where+": needs a `user`.")
			continue
		}
		role := jsTrimmed(person["role"])
		if role == "" {
			role = DefaultPermission
		}
		if !contains(PermissionRole, role) {
			*errs = append(*errs, fmt.Sprintf(
				"%s: `%s` is not a role. Use one of %s.",
				where, role, strings.Join(PermissionRole, ", ")))
			continue
		}
		people = append(people, Person{User: user, Role: role})
	}

	result := Permissions{Owner: jsTrimmed(mapping["owner"]), Access: access, People: people}
	if !contains(AgentAccess, access) {
		result.Access = DefaultAgentAccess
	}
	return result
}

// ParseAgent reads an agent definition.
//
// The order in which errors accumulate is part of the contract: validateAgent
// reports the FIRST one, so a definition with two problems must name the same
// one the editor names. That order is status, reasoning, icon, version,
// subagents, starters, knowledge, pages, skills, permissions — which is
// evaluation order in normalizeAgent, counting the object literal it returns.
func ParseAgent(raw string, opts Options) (*Agent, error) {
	doc, err := ParseFrontmatter(raw)
	if err != nil {
		return nil, err
	}
	data := doc.Data
	errs := []string{}

	id := jsTrim(jsString(data["id"]))
	if !jsTruthy(data["id"]) {
		id = slugify(data["name"])
		if id == "" {
			id = fileStem(opts.path())
		}
	}

	status := jsTrimmed(data["status"])
	if status == "" {
		status = DefaultAgentStatus
	}
	if !contains(AgentStatuses, status) {
		errs = append(errs, fmt.Sprintf("status: `%s` is not a status. Use one of %s.",
			status, strings.Join(AgentStatuses, ", ")))
	}

	reasoning := jsTrimmed(data["reasoning"])
	if reasoning == "" {
		reasoning = DefaultReasoning
	}
	if !contains(ReasoningModes, reasoning) {
		errs = append(errs, fmt.Sprintf("reasoning: `%s` is not a reasoning mode. Use one of %s.",
			reasoning, strings.Join(ReasoningModes, ", ")))
	}

	icon := jsTrimmed(data["icon"])
	if icon == "" {
		icon = DefaultAgentIcon
	}
	if !contains(AgentIcons, icon) {
		errs = append(errs, fmt.Sprintf("icon: `%s` is not an icon this product has.", icon))
	}

	// A version is an integer that only ever goes up. Anything else is an
	// authoring slip, and reading it as 1 is kinder than refusing the file —
	// but it is still reported, because a definition that thinks it is v3 and
	// registers as v1 will publish over something.
	version := 1
	if v, present := data["version"]; present && v != nil && v != "" {
		parsed := jsNumber(v)
		if math.IsNaN(parsed) || parsed != math.Trunc(parsed) || math.IsInf(parsed, 0) || parsed < 1 {
			errs = append(errs, fmt.Sprintf(
				"version: `%s` is not a whole number of 1 or more.", jsString(v)))
		} else if parsed > maxExactInteger {
			// Beyond 2^53-1 a float64 no longer names one integer, so there is
			// no value to carry. Saturating keeps the conversion below defined,
			// and ValidateAgent refuses everything above MaxVersion anyway, so
			// a saturated version can never reach a column.
			version = maxExactInteger
		} else {
			version = int(parsed)
		}
	}

	subagents := uniqueStrings(data["subagents"], "subagents", "a subagent id", &errs)
	kept := subagents[:0]
	for _, s := range subagents {
		if id != "" && s == id {
			errs = append(errs, "subagents: an agent cannot be its own subagent.")
			continue
		}
		kept = append(kept, s)
	}
	subagents = kept

	starters := []Starter{}
	for i, entry := range asList(data["starters"]) {
		if s := normalizeStarter(entry, i, &errs); s != nil {
			starters = append(starters, *s)
		}
	}

	knowledge := []Knowledge{}
	for i, entry := range asList(data["knowledge"]) {
		if k := normalizeKnowledge(entry, i, &errs); k != nil {
			knowledge = append(knowledge, *k)
		}
	}

	// From here the order follows the object literal normalizeAgent returns.
	pages := normalizePages(data["pages"], &errs)
	skills := uniqueStrings(data["skills"], "skills", "a skill id", &errs)
	permissions := normalizePermissions(data["permissions"], &errs)

	instructions, _ := sectionSource(doc.Body, "Instructions")

	agent := &Agent{
		ID:           id,
		Name:         "Untitled agent",
		Status:       status,
		Version:      version,
		Pages:        pages,
		Icon:         icon,
		Reasoning:    reasoning,
		Trigger:      jsTrimmed(data["trigger"]),
		WebSearch:    data["webSearch"] == true || data["web_search"] == true,
		Skills:       skills,
		Subagents:    subagents,
		Starters:     starters,
		Knowledge:    knowledge,
		Permissions:  permissions,
		Instructions: jsTrim(instructions),
		Errors:       errs,
		Body:         doc.Body,
	}

	if jsTruthy(data["name"]) {
		agent.Name = jsString(data["name"])
	}
	if jsTruthy(data["description"]) {
		agent.Description = jsString(data["description"])
	}
	if !contains(AgentStatuses, status) {
		agent.Status = DefaultAgentStatus
	}
	if !contains(ReasoningModes, reasoning) {
		agent.Reasoning = DefaultReasoning
	}
	if !contains(AgentIcons, icon) {
		agent.Icon = DefaultAgentIcon
	}

	return agent, nil
}

// ValidateAgent decides whether an agent definition may be stored.
//
// Returns nil when it may. The order is the order an author would fix things
// in, which is why it reads the same way ValidateSkill does. Note that the
// `id` message differs from the skill one by two words — that difference is
// the frontend's, and it is reproduced rather than tidied.
func ValidateAgent(raw string) error {
	if jsTrim(raw) == "" {
		return &Rejection{Message: "Paste or upload a Markdown definition."}
	}

	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),
		}
	}

	agent, err := ParseAgent(raw, Options{})
	if err != nil {
		return &Rejection{Message: jsTrim("That definition could not be parsed. " + err.Error())}
	}

	if agent.ID == "" {
		return &Rejection{Message: "The frontmatter needs an `id`."}
	}
	if !isDefinitionID(agent.ID) {
		return &Rejection{Message: "The `id` must be lower-case letters, numbers and dashes."}
	}
	// `!raw.includes('name:') || agent.name === 'Untitled agent'` — the literal
	// substring test is the frontend's, and it is why a definition whose name
	// resolves to the fallback is refused even when some other key happens to
	// spell `name:`.
	if !strings.Contains(raw, "name:") || agent.Name == "Untitled agent" {
		return &Rejection{Message: "The frontmatter needs a `name`."}
	}
	if len(agent.Pages) == 0 {
		return &Rejection{Message: "An agent needs at least one `pages:` entry, or it can never be offered anywhere."}
	}
	if len(agent.Errors) > 0 {
		return &Rejection{Message: agent.Errors[0]}
	}

	// The backend's own bound, the companion to the size rule above:
	// agent_definitions.version is a PostgreSQL `integer`, and the frontend
	// accepts any whole number of 1 or more. It is checked here rather than in
	// ParseAgent so the normalized record stays identical to the frontend's for
	// every definition the frontend accepts, and last among the rules so a
	// definition the frontend also refuses is refused with the frontend's own
	// message.
	if agent.Version > MaxVersion {
		return &Rejection{
			BackendOnly: true,
			Message: fmt.Sprintf(
				"version: `%d` is larger than %d.", agent.Version, MaxVersion),
		}
	}

	return nil
}