package tokenengine

import (
	"encoding/json"
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"

	"github.com/urpi/go-bananas/internal/domain"
)

// FlatToken is one resolved token: its dotted path, its resolved type and the
// exact CSS-ready value.
type FlatToken struct {
	// Path is the dotted token path, e.g. "color.semantic.background".
	Path string
	// Kind is the resolved token type.
	Kind Kind
	// Value is the raw author-supplied value.
	Value any
	// CSS is the value as it appears in a custom property declaration.
	CSS string
	// Description is the token's $description, if any.
	Description string
	// Derived marks tokens computed by the engine rather than authored.
	Derived bool
}

// Doc is a parsed, resolved token document for one appearance.
type Doc struct {
	// Theme is the theme the document was derived from.
	Theme *domain.Theme
	// Appearance is the colour scheme that was resolved.
	Appearance domain.Appearance
	// Tokens are the leaves in deterministic path order.
	Tokens []FlatToken
	// byPath indexes Tokens for O(1) lookup.
	byPath map[string]FlatToken
	// palettes lists palette names discovered in the document.
	palettes []string
}

// Lookup returns a token by dotted path.
func (d *Doc) Lookup(path string) (FlatToken, bool) {
	t, ok := d.byPath[path]
	return t, ok
}

// Palettes returns the palette names present in the document.
func (d *Doc) Palettes() []string { return d.palettes }

// PalettesOf returns the shade steps defined for one palette, sorted so that
// scale output is deterministic.
func (d *Doc) PalettesOf(palette string) []string {
	var steps []string
	prefix := "color." + palette + "."
	for _, t := range d.Tokens {
		if strings.HasPrefix(t.Path, prefix) {
			steps = append(steps, strings.TrimPrefix(t.Path, prefix))
		}
	}
	sort.Slice(steps, func(i, j int) bool { return shadeLess(steps[i], steps[j]) })
	return steps
}

// Variables renders the document as CSS custom property name to value.
func (d *Doc) Variables() map[string]string {
	out := make(map[string]string, len(d.Tokens))
	for _, t := range d.Tokens {
		out[VariableName(t.Path)] = t.CSS
	}
	return out
}

// VariableOrder returns the CSS variable names in deterministic order, which is
// the order the generated stylesheet uses.
func (d *Doc) VariableOrder() []string {
	out := make([]string, 0, len(d.Tokens))
	for _, t := range d.Tokens {
		out = append(out, VariableName(t.Path))
	}
	return out
}

// shadeLess orders numeric shades numerically and anything else lexically, so
// 50, 100, 200 ... 950 and custom names both come out sensibly.
func shadeLess(a, b string) bool {
	an, aerr := strconv.Atoi(a)
	bn, berr := strconv.Atoi(b)
	if aerr == nil && berr == nil {
		return an < bn
	}
	if aerr == nil {
		return true
	}
	if berr == nil {
		return false
	}
	return a < b
}

// Resolve merges the base token document with the overrides for the requested
// appearance and returns a flat, ordered token list.
//
// Overrides are a partial document of the same shape as the base, deep-merged
// one level at a time. A leaf in the override replaces the corresponding leaf
// in the base; a nested object in the override merges with its counterpart.
func Resolve(theme *domain.Theme, appearance domain.Appearance) *Doc {
	base := theme.Tokens.Clone()
	if base == nil {
		base = domain.TokenDoc{}
	}
	merged := applyOverrides(base, overridesFor(base, appearance))

	doc := &Doc{
		Theme:      theme,
		Appearance: appearance,
		byPath:     make(map[string]FlatToken),
		palettes:   paletteNames(merged),
	}
	collect(merged, "", nil, doc)
	sort.Slice(doc.Tokens, func(i, j int) bool { return doc.Tokens[i].Path < doc.Tokens[j].Path })
	for _, t := range doc.Tokens {
		doc.byPath[t.Path] = t
	}
	return doc
}

// overridesFor extracts the override sub-document for one appearance.
func overridesFor(doc domain.TokenDoc, appearance domain.Appearance) map[string]any {
	appearances, ok := asMap(doc[AppearancesKey])
	if !ok {
		return nil
	}
	override, _ := asMap(appearances[string(appearance)])
	return override
}

// applyOverrides deep-merges override into base, returning a new document.
func applyOverrides(base domain.TokenDoc, override map[string]any) domain.TokenDoc {
	out := make(domain.TokenDoc, len(base))
	for k, v := range base {
		out[k] = v
	}
	for k, v := range override {
		if overrideMap, ok := asMap(v); ok {
			if baseMap, ok := asMap(out[k]); ok {
				out[k] = map[string]any(applyOverrides(domain.TokenDoc(baseMap), overrideMap))
				continue
			}
		}
		out[k] = v
	}
	return out
}

// inheritedKind carries the type down the tree so that a group may declare
// "$type" once and have every leaf inherit it, as DTCG specifies.
func collect(node map[string]any, prefix string, inherited *Kind, doc *Doc) {
	if node == nil {
		return
	}
	if isLeaf(node) {
		collectLeaf(node, prefix, inherited, doc)
		return
	}
	if raw, ok := node[TypeKey].(string); ok {
		k := Kind(raw)
		inherited = &k
	}
	keys := make([]string, 0, len(node))
	for k := range node {
		if strings.HasPrefix(k, "$") {
			continue
		}
		keys = append(keys, k)
	}
	sort.Strings(keys)
	for _, k := range keys {
		child, ok := asMap(node[k])
		if !ok {
			continue
		}
		path := k
		if prefix != "" {
			path = prefix + "." + k
		}
		collect(child, path, inherited, doc)
	}
}

// collectLeaf records a single token leaf.
func collectLeaf(node map[string]any, path string, inherited *Kind, doc *Doc) {
	kind := Kind("")
	if inherited != nil {
		kind = *inherited
	}
	if raw, ok := node[TypeKey].(string); ok {
		kind = Kind(raw)
	}
	value := node[ValueKey]

	if kind == "" {
		kind = inferKind(value)
	}
	if kind == "" {
		return
	}

	t := FlatToken{
		Path:  path,
		Kind:  kind,
		Value: value,
		CSS:   renderValue(kind, value),
	}
	if d, ok := node[DescKey].(string); ok {
		t.Description = d
	}
	doc.Tokens = append(doc.Tokens, t)
	doc.byPath[path] = t
}

// inferKind guesses a leaf's type when neither the leaf nor an ancestor
// declared one. Guessing keeps hand-written documents usable; validation still
// reports the inferred type so authors can make it explicit.
func inferKind(v any) Kind {
	switch t := v.(type) {
	case string:
		if _, err := ParseColor(t); err == nil && strings.HasPrefix(strings.TrimSpace(t), "#") {
			return KindColor
		}
		if strings.ContainsAny(t, "()") {
			return KindShadow
		}
		return KindFontFamily
	case float64, int, json.Number:
		return KindNumber
	case []any:
		return KindCubicBezier
	default:
		return ""
	}
}

// renderValue converts a token value into its CSS form, appending the
// canonical unit for unit-bearing kinds when the author omitted it.
func renderValue(kind Kind, value any) string {
	switch kind {
	case KindDimension, KindFontSize, KindLetterSpacing, KindDuration:
		if n, ok := toFloat(value); ok {
			return FormatNumber(n) + kind.UnitSuffix()
		}
	case KindNumber, KindFontWeight, KindLineHeight:
		if n, ok := toFloat(value); ok {
			return FormatNumber(n)
		}
	}
	return stringify(value)
}

// stringify renders any supported value as a CSS literal.
func stringify(value any) string {
	switch t := value.(type) {
	case nil:
		return ""
	case string:
		return t
	case bool:
		return strconv.FormatBool(t)
	case float64:
		return FormatNumber(t)
	case int:
		return FormatNumber(float64(t))
	case json.Number:
		return t.String()
	case []any:
		parts := make([]string, len(t))
		for i, p := range t {
			parts[i] = stringify(p)
		}
		return strings.Join(parts, ", ")
	default:
		// Complex values are stored as pre-formatted CSS strings by the editor,
		// so this is the only safe rendering.
		return fmt.Sprint(t)
	}
}

func toFloat(v any) (float64, bool) {
	switch t := v.(type) {
	case float64:
		return t, true
	case int:
		return float64(t), true
	case int64:
		return float64(t), true
	case json.Number:
		f, err := t.Float64()
		return f, err == nil
	case string:
		f, err := strconv.ParseFloat(strings.TrimSpace(t), 64)
		return f, err == nil
	default:
		return 0, false
	}
}

// validateNumeric accepts a JSON number or a numeric string.
func validateNumeric(v any) error {
	switch t := v.(type) {
	case float64:
		if math.IsNaN(t) || math.IsInf(t, 0) {
			return fmt.Errorf("value must be finite")
		}
		return nil
	case int, int64:
		return nil
	case json.Number:
		f, err := t.Float64()
		if err != nil {
			return fmt.Errorf("value %q is not numeric", t.String())
		}
		if math.IsNaN(f) || math.IsInf(f, 0) {
			return fmt.Errorf("value must be finite")
		}
		return nil
	case string:
		if _, err := strconv.ParseFloat(strings.TrimSpace(t), 64); err != nil {
			return fmt.Errorf("value %q is not numeric", t)
		}
		return nil
	default:
		return fmt.Errorf("expected a number, got %T", v)
	}
}

// cssLengthUnits are the units accepted for a bare dimension value.
var cssLengthUnits = []string{"px", "rem", "em", "%", "vh", "vw", "vmin", "vmax", "ch", "ex", "cm", "mm", "in", "pt", "pc", "svh", "lvh", "dvh", "ms", "s", "fr"}

// validateCSSLength accepts a number, a numeric string with a unit, or one of
// the CSS global keywords.
func validateCSSLength(v any) error {
	if err := validateNumeric(v); err != nil {
		if s, ok := v.(string); ok {
			trimmed := strings.ToLower(strings.TrimSpace(s))
			switch trimmed {
			case "auto", "min-content", "max-content", "fit-content", "inherit", "initial", "unset", "normal":
				return nil
			}
			for _, unit := range cssLengthUnits {
				if strings.HasSuffix(trimmed, unit) {
					if _, err := strconv.ParseFloat(strings.TrimSuffix(trimmed, unit), 64); err == nil {
						return nil
					}
				}
			}
			if strings.HasPrefix(trimmed, "clamp(") || strings.HasPrefix(trimmed, "calc(") ||
				strings.HasPrefix(trimmed, "min(") || strings.HasPrefix(trimmed, "max(") {
				// Function-based values are opaque to the validator; the browser
				// is the authority and will discard anything malformed.
				return nil
			}
			return fmt.Errorf("value %q is not a valid length", s)
		}
		return err
	}
	return nil
}

// Validate checks a token document and returns every finding.
func Validate(doc domain.TokenDoc) ValidationResult {
	result := ValidationResult{Valid: true, Issues: []Issue{}}

	issues := make([]violation, 0, 32)
	known := make(map[string]GroupSpec, len(Groups))
	for _, g := range Groups {
		known[g.Name] = g
	}

	for key, raw := range doc {
		if _, reserved := ReservedKeys[key]; reserved {
			continue
		}
		node, ok := asMap(raw)
		if !ok {
			issues = append(issues, violation{
				Path: key, Severity: SeverityError,
				Message: fmt.Sprintf("group %q must be an object", key),
				Hint:    "top-level keys are token groups, or one of " + strings.Join(sortedReservedKeys(), ", "),
			})
			continue
		}
		spec, ok := known[key]
		if !ok {
			issues = append(issues, violation{
				Path: key, Severity: SeverityError,
				Message: fmt.Sprintf("unknown token group %q", key),
				Hint:    "known groups: " + strings.Join(GroupNames(), ", "),
			})
			continue
		}
		validateGroup(spec, node, key, &issues)
	}

	if appearances, ok := asMap(doc[AppearancesKey]); ok {
		for name, raw := range appearances {
			if name != string(domain.AppearanceLight) && name != string(domain.AppearanceDark) {
				issues = append(issues, violation{
					Path: AppearancesKey + "." + name, Severity: SeverityError,
					Message: fmt.Sprintf("unknown appearance %q", name),
					Hint:    "use \"light\" or \"dark\"",
				})
				continue
			}
			node, ok := asMap(raw)
			if !ok {
				issues = append(issues, violation{
					Path: AppearancesKey + "." + name, Severity: SeverityError,
					Message: "appearance overrides must be an object",
				})
				continue
			}
			for group, groupRaw := range node {
				spec, ok := known[group]
				if !ok {
					issues = append(issues, violation{
						Path: AppearancesKey + "." + name + "." + group, Severity: SeverityError,
						Message: fmt.Sprintf("unknown token group %q", group),
					})
					continue
				}
				groupNode, ok := asMap(groupRaw)
				if !ok {
					continue
				}
				// Overrides are partial by design: only value validity is
				// checked, never completeness.
				validateLeaves(spec, groupNode, spec.Kind, group, AppearancesKey+"."+name+"."+group, &issues)
			}
		}
	} else if _, present := doc[AppearancesKey]; present {
		issues = append(issues, violation{
			Path: AppearancesKey, Severity: SeverityError,
			Message: AppearancesKey + " must be an object keyed by appearance",
			Hint:    `example: {"dark": {"color": {"semantic": {"background": {"$value": "#0b0f19"}}}}}`,
		})
	}

	// A theme with no dark overrides will render identically in both schemes,
	// which is almost always a mistake for a theme that declares a dark
	// appearance as its default.
	appearancesMap, _ := asMap(doc[AppearancesKey])
	if _, hasDark := asMap(appearancesMap[string(domain.AppearanceDark)]); !hasDark {
		issues = append(issues, violation{
			Path: AppearancesKey, Severity: SeverityWarning,
			Message: "no dark appearance overrides are defined",
			Hint:    `add {"$appearances": {"dark": {...}}} so the dark scheme is intentional rather than accidental`,
		})
	}

	resolved := countLeaves(doc)
	result.TokenCount = resolved
	result.Issues = toIssues(issues)
	for _, i := range result.Issues {
		if i.Severity == SeverityError {
			result.Valid = false
			break
		}
	}
	return result
}

// toIssues converts and deterministically orders internal violations.
func toIssues(in []violation) []Issue {
	out := make([]Issue, 0, len(in))
	for _, v := range in {
		out = append(out, Issue(v))
	}
	sort.SliceStable(out, func(i, j int) bool {
		if ri, rj := severityRank(out[i].Severity), severityRank(out[j].Severity); ri != rj {
			return ri < rj
		}
		return out[i].Path < out[j].Path
	})
	return out
}

// sortedReservedKeys returns the reserved document keys in sorted order.
func sortedReservedKeys() []string {
	out := make([]string, 0, len(ReservedKeys))
	for k := range ReservedKeys {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// validateGroup checks one group's required and recommended tokens.
func validateGroup(spec GroupSpec, node map[string]any, prefix string, issues *[]violation) {
	validateLeaves(spec, node, spec.Kind, prefix, prefix, issues)
	for _, path := range spec.Recommended {
		if _, err := LookupIn(node, path); err != nil {
			*issues = append(*issues, violation{
				Path: prefix + "." + path, Severity: SeverityWarning,
				Message: fmt.Sprintf("recommended token %q is missing", path),
				Hint:    spec.Description,
			})
		}
	}
}

// validateLeaves walks a group tree checking every leaf value's validity.
func validateLeaves(spec GroupSpec, node map[string]any, kindDefault Kind, prefix, path string, issues *[]violation) {
	if isLeaf(node) {
		kind := kindDefault
		if raw, ok := node[TypeKey].(string); ok {
			kind = Kind(raw)
		} else if inferred := inferKind(node[ValueKey]); inferred != "" && kind == kindDefault {
			kind = inferred
		}
		if !kind.Valid() {
			*issues = append(*issues, violation{
				Path: path, Severity: SeverityError,
				Message: fmt.Sprintf("unknown $type %q", kind),
				Hint:    "omit $type to inherit the group's type",
			})
			return
		}
		if err := validateKindValue(kind, node[ValueKey]); err != nil {
			*issues = append(*issues, violation{
				Path: path, Severity: SeverityError,
				Message: err.Error(),
				Hint:    fmt.Sprintf("expected a %s value", kind),
			})
		}
		return
	}

	inherited := kindDefault
	if raw, ok := node[TypeKey].(string); ok {
		inherited = Kind(raw)
	}
	for _, key := range sortedMapKeys(node) {
		if strings.HasPrefix(key, "$") {
			continue
		}
		child, ok := asMap(node[key])
		if !ok {
			*issues = append(*issues, violation{
				Path: path + "." + key, Severity: SeverityError,
				Message: fmt.Sprintf("token must be an object with a %q property, got %T", ValueKey, node[key]),
				Hint:    `example: {"$type": "color", "$value": "#6366f1"}`,
			})
			continue
		}
		validateLeaves(spec, child, inherited, prefix, path+"."+key, issues)
	}
}

// sortedMapKeys returns the keys of m in sorted order.
func sortedMapKeys(m map[string]any) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// LookupIn walks a token document by dotted path and returns the leaf.
func LookupIn(doc map[string]any, path string) (map[string]any, error) {
	var current any = doc
	for _, segment := range strings.Split(path, ".") {
		node, ok := asMap(current)
		if !ok {
			return nil, fmt.Errorf("path %q: %q is not a group", path, segment)
		}
		next, exists := node[segment]
		if !exists {
			return nil, fmt.Errorf("path %q: %q not found", path, segment)
		}
		current = next
	}
	leaf, ok := asMap(current)
	if !ok || !isLeaf(leaf) {
		return nil, fmt.Errorf("path %q is not a token leaf", path)
	}
	return leaf, nil
}

// SetIn writes a token leaf at a dotted path, creating intermediate groups.
func SetIn(doc domain.TokenDoc, path string, value any, kind Kind, description string) error {
	segments := strings.Split(path, ".")
	if len(segments) == 0 || segments[0] == "" {
		return fmt.Errorf("%w: empty token path", domain.ErrInvalid)
	}
	// Reject paths that would collide with structural keys.
	for i, seg := range segments {
		if _, reserved := ReservedKeys[seg]; reserved && i == 0 {
			return fmt.Errorf("%w: %q is a reserved key", domain.ErrInvalid, seg)
		}
		if seg == "" {
			return fmt.Errorf("%w: token path %q has an empty segment", domain.ErrInvalid, path)
		}
	}
	if _, ok := LookupGroup(segments[0]); !ok {
		return fmt.Errorf("%w: unknown token group %q", domain.ErrInvalid, segments[0])
	}

	current := doc
	for _, seg := range segments[:len(segments)-1] {
		child, ok := asMap(current[seg])
		if !ok {
			child = map[string]any{}
			current[seg] = child
		}
		current = child
	}
	leaf := map[string]any{ValueKey: value, TypeKey: string(kind)}
	if description != "" {
		leaf[DescKey] = description
	}
	current[segments[len(segments)-1]] = leaf
	return nil
}

// DeleteIn removes a token leaf at a dotted path. It reports whether the token
// existed so callers can distinguish a no-op delete from a real one.
func DeleteIn(doc domain.TokenDoc, path string) (bool, error) {
	segments := strings.Split(path, ".")
	if len(segments) < 2 {
		return false, fmt.Errorf("%w: refusing to delete top-level group %q", domain.ErrInvalid, path)
	}
	current := any(doc)
	for _, seg := range segments[:len(segments)-1] {
		node, ok := asMap(current)
		if !ok {
			return false, nil
		}
		child, exists := node[seg]
		if !exists {
			return false, nil
		}
		current = child
	}
	node, ok := asMap(current)
	if !ok {
		return false, nil
	}
	last := segments[len(segments)-1]
	if _, exists := node[last]; !exists {
		return false, nil
	}
	delete(node, last)
	pruneEmpty(node)
	return true, nil
}

// pruneEmpty removes group objects left empty by a delete, so that the stored
// document does not accumulate `{}` noise that would fail validation.
func pruneEmpty(node map[string]any) {
	for key, raw := range node {
		child, ok := asMap(raw)
		if !ok || len(child) == 0 {
			if ok && len(child) == 0 {
				delete(node, key)
			}
			continue
		}
		pruneEmpty(child)
		if len(child) == 0 {
			delete(node, key)
		}
	}
}

// countLeaves counts leaf tokens, excluding appearance overrides.
func countLeaves(node map[string]any) int {
	total := 0
	for key, raw := range node {
		if key == AppearancesKey || strings.HasPrefix(key, "$") {
			continue
		}
		child, ok := asMap(raw)
		if !ok {
			continue
		}
		if isLeaf(child) {
			total++
			continue
		}
		total += countLeaves(child)
	}
	return total
}

// RenameToken moves a token leaf to a new dotted path, preserving its value and
// description. It refuses to clobber an existing token unless overwrite is set.
func RenameToken(doc domain.TokenDoc, from, to string, overwrite bool) error {
	leaf, err := LookupIn(doc, from)
	if err != nil {
		return fmt.Errorf("%w: %s", domain.ErrNotFound, err.Error())
	}
	if _, err := LookupIn(doc, to); err == nil && !overwrite {
		return fmt.Errorf("%w: token %q already exists", domain.ErrConflict, to)
	}
	if _, err := DeleteIn(doc, from); err != nil {
		return err
	}
	value := leaf[ValueKey]
	description, _ := leaf[DescKey].(string)
	kind, ok := leaf[TypeKey].(string)
	if !ok {
		kind = string(inferKind(value))
	}
	return SetIn(doc, to, value, Kind(kind), description)
}

// EnsureDefaults fills any missing recommended token with the supplied default.
// It is used when duplicating a theme so the copy is immediately usable, and is
// deliberately not used on the request path for existing themes.
func EnsureDefaults(doc domain.TokenDoc, defaults domain.TokenDoc) int {
	applied := 0
	for key, raw := range defaults {
		if _, exists := doc[key]; exists {
			continue
		}
		if err := deepMergeMissing(doc, key, raw); err == nil {
			applied++
		}
	}
	return applied
}

// deepMergeMissing merges src into dst only where dst has no value.
func deepMergeMissing(dst domain.TokenDoc, key string, src any) error {
	srcMap, srcOK := asMap(src)
	dstMap, dstOK := asMap(dst[key])
	if srcOK && dstOK && !isLeaf(srcMap) {
		for k, v := range srcMap {
			if err := deepMergeMissing(dstMap, k, v); err != nil {
				return err
			}
		}
		return nil
	}
	dst[key] = src
	return nil
}