// Builder applies a Schema to a generic source map[string]any and returns
// the platform-projected Projection. Pure function — no I/O, no mutation,
// safe to call concurrently. Coercions are best-effort:
//
//   - missing source field ⇒ Schema default (FixedCurrency/DefaultTaxClass
//     when present, otherwise empty/zero)
//   - wrong-typed source value ⇒ the Builder either coerces (bools from
//     truthy strings, ints from numeric strings, json.Number, etc.) or
//     returns ErrProjectionBuild so the caller can decide whether to
//     log+skip or fail.
//
// Builder never panics on bad input — a malformed source line is a log+skip,
// not a process crash.
//
// Three coercers cover realistic producer output shapes:
//
//   - stock json.Unmarshal gives numeric fields as float64 unless
//     `dec.UseNumber()` is on, in which case they come as json.Number.
//   - json.Number preserves up to ~17 digits of precision; float64
//     silently loses precision past 2^53. A producer that wants exact
//     prices sets UseNumber(); this Builder must accept the result.
//   - some producers serialise via reflection and emit `int` / `int64`
//     directly; this Builder must accept those too.
//
// All amounts leave the Builder as money.Cents (integer minor units). The
// only float-side conversion lives in platform/money (FromFloatMajor) and
// is the explicit lossy-edge; once in Cents, no float is ever summed,
// multiplied, or compared downstream.
//
// SCALE SEMANTICS used by coercePrice:
//
//   - PriceScale == 1: the source value is ALREADY in minor units.
//     * For string / json.Number: ParseInt directly (integer form only —
//       the fractional-vs-low-scale guard above rejects "."-containing
//       inputs).
//     * For int / int64: identity (multiply by 1).
//     * For float64 / float32: the float must be integral (else rejected);
//       cast to int gives minor units directly.
//
//   - PriceScale > 1 (e.g. 100): the source value is in MAJOR units.
//     * For string / json.Number: ParseCents treats the decimal form as
//       MAJOR and returns MINOR cents exactly — no further multiply.
//     * For int / int64: integer multiply (lossless).
//     * For float64 / float32: float multiply + round-half-away (lossy).
package catalog

import (
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"

	"git.k6n.net/mats/platform/money"
)

// ErrProjectionBuild is returned when a source value cannot be coerced
// into the Projection shape. Callers typically log + skip so a single bad
// item doesn't poison a whole batch.
var ErrProjectionBuild = errors.New("catalog: projection build failed")

// Apply is the pure helper signature: schema, source map → Projection,
// error. Use the package-level BuildFromMap helper for the most common
// shape (schema + map → Projection); use Apply when you want fine control.
func Apply(s Schema, source map[string]any) (Projection, error) {
	if s.SKUField == "" || s.PriceField == "" {
		return Projection{}, fmt.Errorf("%w: schema missing sku_field or price_field", ErrProjectionBuild)
	}
	if source == nil {
		return Projection{}, fmt.Errorf("%w: nil source map", ErrProjectionBuild)
	}
	sku := stringOf(source, s.SKUField)
	if sku == "" {
		return Projection{}, fmt.Errorf("%w: missing SKU at %q", ErrProjectionBuild, s.SKUField)
	}

	priceRaw, ok := source[s.PriceField]
	if !ok {
		return Projection{}, fmt.Errorf("%w: missing price at %q", ErrProjectionBuild, s.PriceField)
	}
	price, err := coercePrice(priceRaw, s.PriceScale)
	if err != nil {
		return Projection{}, fmt.Errorf("%w: price at %q: %w", ErrProjectionBuild, s.PriceField, err)
	}

	cur := ""
	if s.CurrencyField != "" {
		cur = stringOf(source, s.CurrencyField)
	}
	if cur == "" {
		cur = s.FixedCurrency
	}

	tax := ""
	if s.TaxClassField != "" {
		tax = stringOf(source, s.TaxClassField)
	}
	if tax == "" {
		tax = s.DefaultTaxClass
	}

	id := sku
	if s.IDPrefix != "" {
		id = s.IDPrefix + sku
	}

	upd, err := coerceUpdatedAt(s, source)
	if err != nil {
		return Projection{}, fmt.Errorf("%w: updated_at: %w", ErrProjectionBuild, err)
	}

	truthy := s.TrueValues
	if truthy == nil {
		truthy = DefaultTrueValues()
	}

	p := Projection{
		ItemID:           uint32Of(source, s.ItemIdField),
		ID:               id,
		SKU:              sku,
		Title:            stringOf(source, s.TitleField),
		PriceIncVat:      price,
		Currency:         cur,
		TaxClass:         tax,
		InventoryTracked: boolOf(source, s.InventoryTrackedF, truthy),
		DropShip:         boolOf(source, s.DropShipF, truthy),
		Category:         stringOf(source, s.CategoryField),
		Brand:            stringOf(source, s.BrandField),
		Image:            stringOf(source, s.ImageField),
		UpdatedAt:        upd,
	}
	return p, nil
}

// BuildFromMap is the convenience: schema + map → Projection with error.
// Use this from producer adapters where the source is a parsed map[string]any.
func BuildFromMap(s Schema, source map[string]any) (Projection, error) {
	return Apply(s, source)
}

// stringOf returns the value at key as a string. JSON unmarshalling gives
// strings as string; we accept the common numeric source shapes too so a
// map[string]any that came from a different upstream parser (e.g. typed
// structs serialised with one round of reflection) still works.
//
// json.Number is included because precision-preserving producers turn it on
// via json.Decoder.UseNumber(); without this case the Builder would reject
// every projection in the catalogue.
func stringOf(m map[string]any, key string) string {
	if key == "" {
		return ""
	}
	v, ok := m[key]
	if !ok || v == nil {
		return ""
	}
	switch x := v.(type) {
	case string:
		return x
	case json.Number:
		// Use Number preserves up to ~17 digits as a string-token. For SKUs
		// digit-strings >2^53 (rare but possible), UseNumber is the only
		// way to round-trip safely. String() gives back the raw digits.
		return x.String()
	case bool:
		if x {
			return "true"
		}
		return "false"
	case float64:
		if x == float64(int64(x)) {
			return strconv.FormatInt(int64(x), 10)
		}
		return strconv.FormatFloat(x, 'f', -1, 64)
	case int:
		return strconv.Itoa(x)
	case int64:
		return strconv.FormatInt(x, 10)
	}
	return fmt.Sprintf("%v", v)
}

// uint32Of returns the value at key as a uint32. Best-effort coercion:
// json.Number / int / int64 / float (integral check) / truthy numeric
// string. Returns 0 for any missing / non-uint32-representable value —
// Projection.ItemID = 0 is the documented "no id" signal that the cart's
// overlay path uses to fall back to PRODUCT_BASE_URL.
func uint32Of(m map[string]any, key string) uint32 {
	if key == "" {
		return 0
	}
	v, ok := m[key]
	if !ok || v == nil {
		return 0
	}
	switch x := v.(type) {
	case uint32:
		return x
	case uint64:
		if x > 0xFFFFFFFF {
			return 0 // overflow – treat as unset, downstream falls back
		}
		return uint32(x)
	case int:
		if x < 0 || x > 0xFFFFFFFF {
			return 0
		}
		return uint32(x)
	case int64:
		if x < 0 || x > 0xFFFFFFFF {
			return 0
		}
		return uint32(x)
	case float64:
		if x != float64(uint32(x)) || x < 0 || x > 0xFFFFFFFF {
			return 0 // fractional or out-of-range
		}
		return uint32(x)
	case json.Number:
		s := x.String()
		n, err := strconv.ParseUint(s, 10, 32)
		if err != nil {
			return 0
		}
		return uint32(n)
	case string:
		s := strings.TrimSpace(x)
		if s == "" {
			return 0
		}
		n, err := strconv.ParseUint(s, 10, 32)
		if err != nil {
			return 0
		}
		return uint32(n)
	}
	return 0
}

// boolOf returns the value at key coerced through truthy. nil/missing keys
// are false; strings lower-cased and matched against truthy; bools passed
// through; numerics "!= 0"; json.Number goes through Float64.
func boolOf(m map[string]any, key string, truthy []string) bool {
	if key == "" {
		return false
	}
	v, ok := m[key]
	if !ok || v == nil {
		return false
	}
	switch x := v.(type) {
	case bool:
		return x
	case string:
		low := strings.ToLower(strings.TrimSpace(x))
		for _, t := range truthy {
			if low == t {
				return true
			}
		}
		return false
	case float64:
		return x != 0
	case int:
		return x != 0
	case int64:
		return x != 0
	case json.Number:
		if f, err := x.Float64(); err == nil {
			return f != 0
		}
		return false
	}
	return false
}

// coercePrice normalises a price source value to money.Cents (integer minor
// units). The schema's PriceScale determines whether the source is already
// in minor units (scale==1) or in MAJOR units that need interpretation
// (scale > 1, typically 100). See the package doc for the full table.
//
// The fractional-vs-low-scale guard REJECTS a fractional value when scale ≤ 1
// at any of the float / string / json.Number arms — that's almost certainly a
// tenant who forgot PriceScale=100 and would have produced a silent 100×-off
// price. Loud-fail beats silent corruption.
//
// At scale > 1, decimals come through money.ParseCents (exact, integer-only)
// rather than ParseFloat (lossy past 2^53). Float arms remain the explicit
// lossy bits, intentionally isolated.
func coercePrice(v any, scale int) (money.Cents, error) {
	if scale < 0 {
		return 0, fmt.Errorf("negative price_scale: %d", scale)
	}
	effective := int64(scale)
	if effective < 1 {
		effective = 1
	}
	// Fractional-vs-low-scale guard is inlined at each arm so the error
	// message keeps the actual value (the float stringification is noisier
	// than the JSON-token ".eE" check, so a single helper would lose
	// fidelity).
	switch x := v.(type) {
	case float64:
		if x != float64(int64(x)) && effective == 1 {
			return 0, fmt.Errorf("fractional price %v with PriceScale=1 — did you forget PriceScale=100?", x)
		}
		return money.Cents(roundHalfAwayFromZero(x * float64(effective))), nil
	case float32:
		if x != float32(int64(x)) && effective == 1 {
			return 0, fmt.Errorf("fractional price %v with PriceScale=1 — did you forget PriceScale=100?", x)
		}
		return money.Cents(roundHalfAwayFromZero(float64(x) * float64(effective))), nil
	case int:
		return money.Cents(int64(x) * effective), nil
	case int64:
		return money.Cents(x * effective), nil
	case string:
		s := strings.TrimSpace(x)
		if s == "" {
			return 0, fmt.Errorf("empty price string")
		}
		// Scale 1 with a fractional character set ⇒ foot-gun 4.
		if effective == 1 && strings.ContainsAny(s, ".eE") {
			return 0, fmt.Errorf("fractional price %q with PriceScale=1 — did you forget PriceScale=100?", s)
		}
		if effective == 1 {
			// Scale 1 means source IS minor units. Remaining forms are
			// integer decimal strings — ParseInt directly. ParseCents would
			// misread "14995" as 14995.00 SEK = 1499500.
			n, err := strconv.ParseInt(s, 10, 64)
			if err != nil {
				return 0, fmt.Errorf("parse price %q at scale=1: %w", x, err)
			}
			return money.Cents(n), nil
		}
		// Scale > 1: source is MAJOR units. ParseCents interprets the
		// decimal form as MAJOR and returns MINOR (cents) EXACTLY — no
		// further multiply.
		if c, err := money.ParseCents(s); err == nil {
			return c, nil
		}
		f, err := strconv.ParseFloat(s, 64)
		if err != nil {
			return 0, fmt.Errorf("parse price %q: %w", x, err)
		}
		return money.Cents(roundHalfAwayFromZero(f * float64(effective))), nil
	case json.Number:
		s := x.String()
		if effective == 1 && strings.ContainsAny(s, ".eE") {
			return 0, fmt.Errorf("fractional price %q with PriceScale=1 — did you forget PriceScale=100?", s)
		}
		if effective == 1 {
			// x is the original json.Number — Int64() works.
			if i, err := x.Int64(); err == nil {
				return money.Cents(i), nil
			}
			n, err := strconv.ParseInt(s, 10, 64)
			if err != nil {
				return 0, fmt.Errorf("parse price json.Number %q at scale=1: %w", s, err)
			}
			return money.Cents(n), nil
		}
		// Scale > 1: ParseCents token-aware path. ParseCents interprets
		// the token as MAJOR-units decimal and returns MINOR cents exactly.
		if c, err := money.ParseCents(s); err == nil {
			return c, nil
		}
		f, err := x.Float64()
		if err != nil {
			return 0, fmt.Errorf("parse price json.Number %q: %w", s, err)
		}
		return money.Cents(roundHalfAwayFromZero(f * float64(effective))), nil
	}
	return 0, fmt.Errorf("unsupported price type %T", v)
}

// roundHalfAwayFromZero rounds half-away-from-zero instead of banker's
// rounding so e.g. 99.995 → 100 (with scale=1) not 99, and -99.995 → -100
// not -99. We accept the very small skew in favour of deterministic
// conventional rounding for signed amounts (refunds, discounts).
func roundHalfAwayFromZero(f float64) int64 {
	if f >= 0 {
		return int64(f + 0.5)
	}
	return int64(f - 0.5)
}

// coerceUpdatedAt returns Unix-ms for the Projection.UpdatedAt stamp based
// on Schema.UpdatedAtSource.
//
// IMPORTANT contract (foot-gun 3, resolved):
//
//   - StampAtPublish is the RESERVED deliberate-fallback. Builder sets
//     time.Now().UnixMilli(). Every rebuild re-stamps every projection,
//     invalidating every consumer's whole cache even when nothing changed.
//     Pick this only when the producer genuinely has no version stamp.
//
//   - UseSourceField (DefaultSchema, BygglagretSchema) reads the value
//     from source[Schema.UpdatedAtField]. If the field is MISSING or the
//     value can't be parsed, Apply returns ErrProjectionBuild (wrapped)
//     rather than stamp-now'ing. That keeps UpdatedAt a true content
//     version across rebuilds — same source content ⇒ same UpdatedAt ⇒
//     consumer caches stay valid.
//
// Consumers compare UpdatedAt with "strictly greater wins" semantics; a
// silent stamp-now fallback would defeat this contract.
func coerceUpdatedAt(s Schema, source map[string]any) (int64, error) {
	if s.UpdatedAtSource == StampAtPublish || s.UpdatedAtField == "" {
		return time.Now().UnixMilli(), nil
	}
	v, ok := source[s.UpdatedAtField]
	if !ok || v == nil {
		return 0, fmt.Errorf("missing updated_at at %q (UseSourceField requires the source to supply it)", s.UpdatedAtField)
	}
	switch x := v.(type) {
	case int64:
		return x, nil
	case int:
		return int64(x), nil
	case float64:
		return int64(x), nil
	case json.Number:
		if i, err := x.Int64(); err == nil {
			return i, nil
		}
		f, err := x.Float64()
		if err != nil {
			return 0, fmt.Errorf("updated_at json.Number %q: %w", x.String(), err)
		}
		return int64(f), nil
	case string:
		t := strings.TrimSpace(x)
		if t == "" {
			return 0, fmt.Errorf("empty updated_at string at %q (UseSourceField requires a value)", s.UpdatedAtField)
		}
		n, err := strconv.ParseInt(t, 10, 64)
		if err != nil {
			return 0, fmt.Errorf("parse updated_at %q: %w", x, err)
		}
		return n, nil
	}
	return 0, fmt.Errorf("unsupported updated_at type %T at %q", v, s.UpdatedAtField)
}