// Package content loads the Markdown source of truth in content/ into documents
// that both renderers (Mode A static pages, Mode B corpus) read.
//
// The schema is frozen; see docs/content-schema.md. This package does not
// re-implement the validator (tools/validate_content.py is the gate). It does
// enforce the invariants the renderer needs, and it fails loudly rather than
// rendering a broken page.
package content

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

	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/stage"
	"gopkg.in/yaml.v3"
)

// Confidence values. These are displayed on the page and are never promoted.
const (
	ConfidenceDelivered  = "delivered"
	ConfidenceRunning    = "running"
	ConfidenceInProgress = "in-progress"
	ConfidenceAbandoned  = "abandoned"
	ConfidenceHistoric   = "historic"
)

// Area is one of the six top-level navigation areas. Structure lives in code
// (it comes from reference/content-map.md, not from the content tree); the
// documents that fill it live in content/.
type Area struct {
	Key    string
	Title  string
	Role   string
	Blurb  string
}

// Areas is the fixed navigation order from reference/content-map.md.
var Areas = []Area{
	{Key: "ai", Title: "AI & Agentic Systems", Role: "AI / LLM Engineer",
		Blurb: "Harnesses, subagents and skills, memory, model routing and cost, retrieval, voice, guardrails, agent observability."},
	{Key: "platform", Title: "Platform & Infrastructure", Role: "Platform / DevOps Engineer",
		Blurb: "Declarative hosts, packaging, a fifty-container Docker estate, networking, storage and restore-tested backups, observability."},
	{Key: "edge", Title: "Edge & Devices", Role: "Edge / IoT Engineer",
		Blurb: "Twenty-node fleet on constrained devices, custom radio, solar power, deep sleep, sensors and actuation — and the failures."},
	{Key: "products", Title: "Products", Role: "",
		Blurb: "Three active businesses, built and run rather than advised on."},
	{Key: "history", Title: "History", Role: "",
		Blurb: "2000–2014: agencies, clients, engagements, and the code that survives from them."},
	{Key: "about", Title: "About", Role: "",
		Blurb: "The narrative, the non-IT work that came first, education, and how to get in touch."},
}

// Positioning is the site's single line of introduction.
const (
	Positioning = "Twenty-five years shipping software. Now building agent systems, the platforms under them, and the hardware at the edge."
	SupportLine = "…and it all runs unattended."
	Location    = "Melbourne"
)

// AreaByKey returns the area with the given key.
func AreaByKey(key string) (Area, bool) {
	for _, a := range Areas {
		if a.Key == key {
			return a, true
		}
	}
	return Area{}, false
}

// Metric is one approved chip on a page, e.g. {label: "edge nodes", value: 20}.
type Metric struct {
	Label string `yaml:"label"`
	Value any    `yaml:"value"`
}

// String renders the chip value with its label: "20 edge nodes".
func (m Metric) String() string {
	return fmt.Sprintf("%v %s", m.Value, m.Label)
}

// Artefact is a drill-down link. Every URL must resolve to a file in this
// repository; nothing external is allowed.
type Artefact struct {
	Type  string `yaml:"type"` // repo | image | video | doc
	Label string `yaml:"label"`
	URL   string `yaml:"url"`
}

// Document is one Markdown file plus its front-matter.
type Document struct {
	ID           string     `yaml:"id"`
	Area         string     `yaml:"area"`
	Level        int        `yaml:"level"`
	Title        string     `yaml:"title"`
	Claim        string     `yaml:"claim"`
	Confidence   string     `yaml:"confidence"`
	Period       string     `yaml:"period"`
	Tech         []string   `yaml:"tech"`
	Metrics      []Metric   `yaml:"metrics"`
	Artefacts    []Artefact `yaml:"artefacts"`
	Public       bool       `yaml:"public"`
	LastVerified string     `yaml:"last_verified"`
	Tags         []string   `yaml:"tags"`

	// Derived by Load.
	Path  string `yaml:"-"` // path relative to the content root, e.g. edge/edge-fleet.md
	URL   string `yaml:"-"` // canonical page URL, e.g. /edge/edge-fleet/
	HTML  string `yaml:"-"` // rendered body
	Plain string `yaml:"-"` // body reduced to text, for the search index

	bodyRaw string // Markdown body, rendered by the markdown renderer

	// Backlinks are the documents that reference this one as an artefact.
	Backlinks []*Document `yaml:"-"`
}

// ResolvedArtefact is an Artefact with its target resolved.
type ResolvedArtefact struct {
	Artefact
	Target *Document // non-nil when the artefact is an L3/L2 document
	File   string    // absolute path on disk
	Rel    string    // path relative to the content root, e.g. assets/x.svg
	Href   string    // site URL: a page URL for documents, /assets/... for files
	Kind   string    // Fragment kind: text | code | diagram | image | video | links
}

// Set is every loaded document, indexed.
type Set struct {
	Root  string
	Docs  []*Document
	byID  map[string]*Document
	byRel map[string]*Document
}

// ByID returns the document with the given id.
func (s *Set) ByID(id string) (*Document, bool) {
	d, ok := s.byID[id]
	return d, ok
}

// ByRel returns the document at the given content-relative path.
func (s *Set) ByRel(rel string) (*Document, bool) {
	d, ok := s.byRel[rel]
	return d, ok
}

// InArea returns the public documents for an area, ordered L1, L2, L3.
func (s *Set) InArea(key string) []*Document {
	var out []*Document
	for _, d := range s.Docs {
		if d.Area == key {
			out = append(out, d)
		}
	}
	sort.SliceStable(out, func(i, j int) bool {
		if out[i].Level != out[j].Level {
			return out[i].Level < out[j].Level
		}
		return out[i].Title < out[j].Title
	})
	return out
}

// AreaLanding returns the L1 document for an area.
func (s *Set) AreaLanding(key string) (*Document, bool) {
	for _, d := range s.InArea(key) {
		if d.Level == 1 {
			return d, true
		}
	}
	return nil, false
}

// Load reads every Markdown file under root. Documents with public: false are
// loaded (so links to them still resolve) but are not published.
func Load(root string) (*Set, error) {
	info, err := os.Stat(root)
	if err != nil {
		return nil, fmt.Errorf("content root %q: %w", root, err)
	}
	if !info.IsDir() {
		return nil, fmt.Errorf("content root %q is not a directory", root)
	}

	s := &Set{Root: root, byID: map[string]*Document{}, byRel: map[string]*Document{}}

	err = filepath.WalkDir(root, func(p string, e os.DirEntry, err error) error {
		if err != nil {
			return err
		}
		name := e.Name()
		if e.IsDir() {
			if p != root && (strings.HasPrefix(name, ".") || strings.HasPrefix(name, "_")) {
				return filepath.SkipDir
			}
			return nil
		}
		if !strings.HasSuffix(name, ".md") || strings.HasPrefix(name, ".") {
			return nil
		}
		rel, rerr := filepath.Rel(root, p)
		if rerr != nil {
			return rerr
		}
		rel = filepath.ToSlash(rel)

		raw, rerr := os.ReadFile(p)
		if rerr != nil {
			return rerr
		}
		doc, derr := parse(rel, p, raw)
		if derr != nil {
			return derr
		}
		if prev, dup := s.byID[doc.ID]; dup {
			return fmt.Errorf("%s: duplicate id %q (already used by %s)", rel, doc.ID, prev.Path)
		}
		doc.URL = PageURL(doc)
		s.Docs = append(s.Docs, doc)
		s.byID[doc.ID] = doc
		s.byRel[rel] = doc
		return nil
	})
	if err != nil {
		return nil, err
	}
	if len(s.Docs) == 0 {
		return nil, fmt.Errorf("content root %q contains no documents", root)
	}
	sort.SliceStable(s.Docs, func(i, j int) bool {
		if s.Docs[i].Area != s.Docs[j].Area {
			return areaOrder(s.Docs[i].Area) < areaOrder(s.Docs[j].Area)
		}
		if s.Docs[i].Level != s.Docs[j].Level {
			return s.Docs[i].Level < s.Docs[j].Level
		}
		return s.Docs[i].ID < s.Docs[j].ID
	})

	for _, d := range s.Docs {
		for _, a := range d.Artefacts {
			ra, rerr := s.Resolve(d, a)
			if rerr != nil {
				return nil, rerr
			}
			if ra.Target != nil && ra.Target.ID != d.ID {
				ra.Target.Backlinks = append(ra.Target.Backlinks, d)
			}
		}
	}
	return s, nil
}

func areaOrder(key string) int {
	for i, a := range Areas {
		if a.Key == key {
			return i
		}
	}
	return len(Areas)
}

func parse(rel, abs string, raw []byte) (*Document, error) {
	fm, body, err := splitFrontMatter(string(raw))
	if err != nil {
		return nil, fmt.Errorf("%s: %w", rel, err)
	}
	var d Document
	dec := yaml.NewDecoder(strings.NewReader(fm))
	dec.KnownFields(true) // unknown front-matter fields are a schema violation
	if err := dec.Decode(&d); err != nil {
		return nil, fmt.Errorf("%s: front-matter: %w", rel, err)
	}
	d.Path = rel
	d.bodyRaw = body

	if err := d.check(rel); err != nil {
		return nil, err
	}
	return &d, nil
}

// BodyMarkdown returns the raw Markdown body (everything after the front-matter).
func (d *Document) BodyMarkdown() string { return d.bodyRaw }

func (d *Document) check(rel string) error {
	switch {
	case d.ID == "":
		return fmt.Errorf("%s: id is required", rel)
	case d.Title == "":
		return fmt.Errorf("%s: title is required", rel)
	case d.Claim == "":
		return fmt.Errorf("%s: claim is required", rel)
	}
	if _, ok := AreaByKey(d.Area); !ok {
		return fmt.Errorf("%s: unknown area %q", rel, d.Area)
	}
	if d.Level < 1 || d.Level > 3 {
		return fmt.Errorf("%s: level must be 1, 2 or 3, got %d", rel, d.Level)
	}
	switch d.Confidence {
	case ConfidenceDelivered, ConfidenceRunning, ConfidenceInProgress, ConfidenceAbandoned, ConfidenceHistoric:
	default:
		return fmt.Errorf("%s: unknown confidence %q", rel, d.Confidence)
	}
	if d.LastVerified == "" {
		return fmt.Errorf("%s: last_verified is required", rel)
	}
	stem := strings.TrimSuffix(path.Base(rel), ".md")
	if stem != d.ID {
		return fmt.Errorf("%s: id %q must equal the file name %q", rel, d.ID, stem)
	}
	for _, a := range d.Artefacts {
		if a.URL == "" || a.Label == "" {
			return fmt.Errorf("%s: artefact %q needs both label and url", rel, a.Label)
		}
		if strings.Contains(a.URL, "://") {
			return fmt.Errorf("%s: artefact %q uses an external URL; create an in-repo stub instead", rel, a.URL)
		}
	}
	return nil
}

func splitFrontMatter(src string) (fm, body string, err error) {
	src = strings.ReplaceAll(src, "\r\n", "\n")
	if !strings.HasPrefix(src, "---\n") {
		return "", "", fmt.Errorf("missing front-matter block on line 1")
	}
	rest := src[len("---\n"):]
	for _, delim := range []string{"\n---\n", "\n...\n"} {
		if i := strings.Index(rest, delim); i >= 0 {
			return rest[:i], rest[i+len(delim):], nil
		}
	}
	return "", "", fmt.Errorf("unterminated front-matter block")
}

// PageURL is the canonical URL for a document. Depth maps onto the URL path so
// the drill-down is legible: /edge/ · /edge/edge-fleet/ · /edge/a/edge-zigbee/.
func PageURL(d *Document) string {
	switch d.Level {
	case 1:
		return "/" + d.Area + "/"
	case 2:
		return "/" + d.Area + "/" + d.ID + "/"
	default:
		return "/" + d.Area + "/a/" + d.ID + "/"
	}
}

// Resolve maps an artefact reference onto a file, a site URL and a stage
// fragment kind. Paths may be repository-relative ("content/edge/l3/x.md") or
// document-relative ("./l3/x.md", "l3/x.md").
func (s *Set) Resolve(from *Document, a Artefact) (ResolvedArtefact, error) {
	rel := a.URL
	var target string
	switch {
	case strings.HasPrefix(rel, "content/"):
		target = strings.TrimPrefix(rel, "content/")
	case strings.HasPrefix(rel, "/") || strings.HasPrefix(rel, "../"):
		return ResolvedArtefact{}, fmt.Errorf("%s: artefact %q must not be root-absolute or escape the repo", from.Path, rel)
	default:
		target = path.Join(path.Dir(from.Path), rel)
	}
	target = path.Clean(target)

	out := ResolvedArtefact{Artefact: a, Rel: target}
	abs := filepath.Join(s.Root, filepath.FromSlash(target))
	st, err := os.Stat(abs)
	if err != nil {
		return out, fmt.Errorf("%s: artefact %q does not resolve to a file (%s)", from.Path, a.URL, target)
	}
	if st.IsDir() {
		return out, fmt.Errorf("%s: artefact %q resolves to a directory", from.Path, a.URL)
	}
	out.File = abs
	if strings.HasSuffix(target, ".md") {
		doc, ok := s.byRel[target]
		if !ok {
			return out, fmt.Errorf("%s: artefact %q is not a loaded document", from.Path, a.URL)
		}
		out.Target = doc
		out.Href = doc.URL
		out.Kind = stage.KindText
		return out, nil
	}
	out.Href = "/assets/" + strings.TrimPrefix(target, "assets/")
	out.Kind = KindForFile(target)
	return out, nil
}

var codeExtensions = map[string]string{
	".go": "go", ".js": "javascript", ".mjs": "javascript", ".ts": "typescript",
	".nix": "nix", ".php": "php", ".as": "actionscript", ".hpp": "cpp", ".h": "cpp",
	".c": "c", ".cpp": "cpp", ".py": "python", ".sh": "bash", ".yaml": "yaml",
	".yml": "yaml", ".json": "json", ".css": "css", ".sql": "sql", ".templ": "templ",
}

// KindForFile maps a file extension onto a stage fragment kind.
func KindForFile(name string) string {
	ext := strings.ToLower(path.Ext(name))
	if lang, ok := codeExtensions[ext]; ok && lang != "" {
		return stage.KindCode
	}
	switch ext {
	case ".svg":
		return stage.KindDiagram
	case ".png", ".jpg", ".jpeg", ".webp", ".gif", ".avif":
		return stage.KindImage
	case ".mp4", ".webm", ".mov":
		return stage.KindVideo
	case ".md":
		return stage.KindText
	}
	return stage.KindLinks
}

// LanguageFor returns the chroma language for a file, if it is code.
func LanguageFor(name string) string {
	return codeExtensions[strings.ToLower(path.Ext(name))]
}

// Truncate shortens s to at most n runes, on a word boundary where possible.
func Truncate(s string, n int) string {
	s = strings.TrimSpace(s)
	if len([]rune(s)) <= n {
		return s
	}
	r := []rune(s)[:n]
	if i := strings.LastIndex(string(r), " "); i > n/2 {
		return strings.TrimSpace(string(r)[:i]) + "…"
	}
	return strings.TrimSpace(string(r)) + "…"
}

// MetricValue renders a metric value for display.
func MetricValue(v any) string {
	switch t := v.(type) {
	case nil:
		return ""
	case string:
		return t
	case int:
		return strconv.Itoa(t)
	case bool:
		return strconv.FormatBool(t)
	default:
		return fmt.Sprint(t)
	}
}