// Package dbutil provides a SQL query builder for PostgreSQL.
//
// The builder generates parameterized SQL strings and argument slices from
// composable Go values. It is not an ORM. It does not manage connections,
// transactions, or migrations. It pairs with the automapper in automapper.go
// to scan query results into structs.
//
// # Naming conventions
//
// The public API uses short names because they appear repeatedly in query
// construction code:
//
//   - T (Table) creates a typed table reference from a model struct.
//   - M (Model) is the addressable zero-value of the model struct living on
//     the table reference. It exists solely so you can take field pointers
//     for F and FieldNames. It does not hold real data.
//   - F (Field) resolves a pointer to a field on M into a Col.
//   - C (Column) creates a Col from a raw column name string.
//
// # Table references
//
// Every query starts by binding a Go model type to a SQL table alias with T:
//
//	au := T[models.AppUser]("au")
//
// T looks up the table name from models.Tables, allocates an addressable
// zero-value of the model (stored in au.M), and builds a mapping from struct
// field byte offsets to their "db" tag values. The type parameter gives you
// compile-time safety; the alias is the SQL alias used in the generated query.
// Omit the alias for single-table statements:
//
//	it := T[models.Identity]()  // uses the bare table name "identity"
//
// For tables not registered in models.Tables (CTEs, subquery aliases, etc.),
// use TName:
//
//	cte := TName("recent_logins", "rl")
//
// # Referencing columns
//
// F takes a pointer to a field on the table's zero-value M and resolves it to
// the column name from its "db" tag. This gives you IDE autocomplete and
// compile-time breakage when a field is renamed or removed:
//
//	au.F(&au.M.ID)         // Col representing "au.id"
//	au.F(&au.M.FirstName)  // Col representing "au.first_name"
//
// Under the hood F computes the pointer's byte offset relative to au.M and
// looks it up in a cached offset-to-column map.
//
// C is still available as a raw-string fallback for expressions that don't
// correspond to a single struct field:
//
//	au.C("id")  // same as au.F(&au.M.ID), but no compile-time checking
//
// FieldNames does the same resolution as F but returns bare column name
// strings instead of Col values. Use it with SetColumns and Columns:
//
//	au.FieldNames(&au.M.FirstName, &au.M.LastName)  // []string{"first_name", "last_name"}
//
// # Building conditions
//
// Col methods produce Cond values that carry a SQL fragment and bound args:
//
//	au.F(&au.M.ID).Eq(userID)           // "au.id = ?"
//	au.F(&au.M.LastName).Like("%smith%") // "au.last_name LIKE ?"
//	au.F(&au.M.ID).In(ids)              // "au.id IN (?, ?, ...)"
//
// Conditions compose with And, Or, and Not:
//
//	cond := au.F(&au.M.Email).IsNotNull().And(au.F(&au.M.LoginCount).Gt(0))
//
// EqCol compares two columns without a bound parameter (useful for joins):
//
//	au.F(&au.M.ID).EqCol(ou.F(&ou.M.AppUserID))
//
// # SELECT
//
//	Select(au.ColsFlat()).
//		From(au).
//		Where(au.F(&au.M.ID).Eq(userID)).
//		QueryRow(ctx, db, &user)
//
// ColsFlat generates unaliased column expressions (au.id, au.email, ...) for
// single-table queries. Cols generates aliased expressions
// (au.id AS "app_user.id", ...) for multi-table queries where the automapper
// needs prefixes to route columns into nested destination structs.
//
// Joins, ordering, grouping, limit, and offset chain as expected:
//
//	Select(ou.Cols(), au.Cols()).
//		From(ou).
//		InnerJoin(au, au.F(&au.M.ID).EqCol(ou.F(&ou.M.AppUserID))).
//		Where(ou.F(&ou.M.OrgID).Eq(orgID)).
//		OrderBy(au.F(&au.M.LastName).Asc()).
//		Limit(25).
//		Offset(50).
//		Query(ctx, db, &results)
//
// When joining the same model twice, use MapAs to set a distinct automapper
// prefix so the scanner can tell the two apart:
//
//	cb := T[models.AppUser]("cb").MapAs("created_by")
//
// # INSERT
//
//	InsertInto(it).
//		Columns(it.FieldNames(&it.M.Key, &it.M.AppUserID, &it.M.Timezone)...).
//		Model(identity).
//		Exec(ctx, db)
//
// If Columns is omitted and Model is provided, all "db"-tagged fields are
// inserted. Values can be passed directly with Values() instead of Model().
//
// # UPDATE
//
//	Update(au).
//		SetColumns(au.FieldNames(&au.M.FirstName, &au.M.LastName)...).
//		Model(user).
//		Where(au.F(&au.M.ID).Eq(user.ID)).
//		Exec(ctx, db)
//
// Set can also be called for individual column/value pairs:
//
//	Update(au).Set("login_count", newCount).Where(...).Exec(ctx, db)
//
// # DELETE
//
//	DeleteFrom(it).
//		Where(it.F(&it.M.Key).Eq(key)).
//		Exec(ctx, db)
//
// # Execution
//
// Build returns the final SQL string (with $1, $2, ... placeholders) and the
// argument slice. Query, QueryRow, QueryScalarTo, and Exec are convenience
// methods that call Build and then execute against a Querier or Execer.
//

// ////////////////////////////////////////////////////////////////////////////
//
// BEHIND THE SCENES POINTER MAGIC:
//
// # How F resolves field pointers to column names
//
// When T[M] is called, it allocates a zero-value of the model struct with
// new(M) and stores the pointer in the M field. It also walks the struct's
// reflect.Type and records every db-tagged field's byte offset (from
// reflect.StructField.Offset) alongside its "db" tag value into a map:
//
//	fieldMap[0]  = "id"          // ID is at byte offset 0
//	fieldMap[16] = "username"    // Username is at byte offset 16
//	fieldMap[32] = "email"       // Email is at byte offset 32
//	...
//
// When you call au.F(&au.M.ID), F receives a pointer to the ID field within
// that same heap-allocated struct. It subtracts the base address of the struct
// from the field's address to recover the byte offset:
//
//	offset = reflect.ValueOf(&au.M.ID).Pointer() - reflect.ValueOf(au.M).Pointer()
//
// That offset is looked up in fieldMap to get the column name "id", which is
// then combined with the table alias to produce the Col expression "au.id".
//
// This works because Go guarantees that struct fields sit at fixed offsets
// from the start of the struct, and those offsets are the same for every
// instance of that type. The reflect package exposes them without needing
// an unsafe import.
//
// If the pointer does not fall within the struct (e.g. you pass a pointer to
// an unrelated variable), the offset will not exist in the map and F panics.
//
// # Field offset cache
//
// Walking a struct's reflect.Type to collect field offsets is not free, but
// the result is the same for every instance of a given type. The offset map
// is computed once and stored in a package-level cache keyed by reflect.Type:
//
//	var fieldCache = map[reflect.Type]map[uintptr]string
//
// The cache is protected by a sync.RWMutex using a double-check pattern.
// On the hot path (the type has been seen before), buildFieldOffsetMap takes
// a read lock, finds the map, and returns it. On the cold path (first time
// seeing a type), it upgrades to a write lock, checks again in case another
// goroutine populated it in the meantime, and only then does the reflect
// walk. This is the same pattern used by the automapper's mappingCache in
// automapper.go.
//
// Each call to T[M] receives a reference to the shared cached map rather
// than its own copy, so there is no per-table-reference allocation cost
// beyond the first time a model type is used.
//
// See examples.go for full working examples of each pattern.
package dbutil

import (
	"context"
	"database/sql"
	"fmt"
	"reflect"
	"strings"
	"sync"
)

// AllColumns is a convenience constant for use with Returning().
const AllColumns = "*"

type Execer interface {
	ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error)
}

// TableExpr is satisfied by both TableRef and Tbl[M].
type TableExpr interface {
	tableRef() TableRef
}

// TableRef

type TableRef struct {
	tableName string
	alias     string
	modelType reflect.Type
	mapPrefix string
}

func (t TableRef) tableRef() TableRef { return t }

// fieldInfo stores the column name and Go type for a struct field.
type fieldInfo struct {
	colName   string
	fieldType reflect.Type
}

// Tbl[M] wraps TableRef and adds type-safe field references.

type Tbl[M any] struct {
	TableRef
	M        *M
	fieldMap map[uintptr]fieldInfo
}

func T[M any](alias ...string) Tbl[M] {
	var zero M
	t := reflect.TypeOf(zero)
	if t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	tableName := tableNameFor(t)
	if tableName == "" {
		panic(fmt.Sprintf("builder: no table registered for type %s", t.Name()))
	}
	a := ""
	if len(alias) > 0 {
		a = alias[0]
	}
	tbl := Tbl[M]{
		TableRef: TableRef{
			tableName: tableName,
			alias:     a,
			modelType: t,
			mapPrefix: toSnakeCase(t.Name()),
		},
	}
	tbl.M = new(M)
	tbl.fieldMap = buildFieldOffsetMap(t)
	return tbl
}

func (t Tbl[M]) tableRef() TableRef { return t.TableRef }

// F resolves a pointer to a field on t.M to a Col using byte offset math.
func (t Tbl[M]) F(fieldPtr any) Col {
	ptr := reflect.ValueOf(fieldPtr).Pointer()
	base := reflect.ValueOf(t.M).Pointer()
	offset := ptr - base
	info, ok := t.fieldMap[offset]
	if !ok {
		panic(fmt.Sprintf("builder: field pointer offset %d not found in %T", offset, *t.M))
	}
	return Col{expr: t.ref() + "." + info.colName, fieldType: info.fieldType}
}

// FieldNames resolves multiple field pointers to their db column names.
func (t Tbl[M]) FieldNames(fieldPtrs ...any) []string {
	base := reflect.ValueOf(t.M).Pointer()
	names := make([]string, len(fieldPtrs))
	for i, fp := range fieldPtrs {
		ptr := reflect.ValueOf(fp).Pointer()
		offset := ptr - base
		info, ok := t.fieldMap[offset]
		if !ok {
			panic(fmt.Sprintf("builder: field pointer offset %d not found in %T", offset, *t.M))
		}
		names[i] = info.colName
	}
	return names
}

// As returns a copy with a new alias.
func (t Tbl[M]) As(alias string) Tbl[M] {
	t.TableRef = t.TableRef.As(alias)
	return t
}

// MapAs returns a copy with a new automapper prefix.
func (t Tbl[M]) MapAs(prefix string) Tbl[M] {
	t.TableRef = t.TableRef.MapAs(prefix)
	return t
}

// Field offset cache

var (
	fieldCacheMu sync.RWMutex
	fieldCache   = make(map[reflect.Type]map[uintptr]fieldInfo)
)

func buildFieldOffsetMap(t reflect.Type) map[uintptr]fieldInfo {
	fieldCacheMu.RLock()
	if m, ok := fieldCache[t]; ok {
		fieldCacheMu.RUnlock()
		return m
	}
	fieldCacheMu.RUnlock()

	fieldCacheMu.Lock()
	defer fieldCacheMu.Unlock()

	if m, ok := fieldCache[t]; ok {
		return m
	}

	m := make(map[uintptr]fieldInfo)
	walkFieldOffsets(t, 0, m)
	fieldCache[t] = m
	return m
}

func walkFieldOffsets(t reflect.Type, base uintptr, m map[uintptr]fieldInfo) {
	for i := range t.NumField() {
		f := t.Field(i)
		if !f.IsExported() {
			continue
		}
		if dbTag := f.Tag.Get("db"); dbTag != "" && dbTag != "-" {
			ft := f.Type
			if ft.Kind() == reflect.Ptr {
				ft = ft.Elem()
			}
			m[base+f.Offset] = fieldInfo{colName: dbTag, fieldType: ft}
			continue
		}
		if f.Anonymous {
			ft := derefType(f.Type)
			if ft.Kind() == reflect.Struct {
				walkFieldOffsets(ft, base+f.Offset, m)
			}
		}
	}
}

func TName(tableName string, alias ...string) TableRef {
	a := ""
	if len(alias) > 0 {
		a = alias[0]
	}
	return TableRef{tableName: tableName, alias: a}
}

func (t TableRef) As(alias string) TableRef {
	t.alias = alias
	return t
}

// MapAs overrides the automapper column prefix.
// Use when joining the same table twice with different roles:
//
//	cb := T[models.AppUser]("cb").MapAs("created_by")
func (t TableRef) MapAs(prefix string) TableRef {
	t.mapPrefix = prefix
	return t
}

func (t TableRef) C(name string) Col {
	return Col{expr: t.ref() + "." + name}
}

// C creates a Col from a bare name, not tied to any table.
// Use for computed aliases in ORDER BY / GROUP BY (e.g. C("points")).
func C(name string) Col {
	return Col{expr: name}
}

// Cols returns automapper-compatible aliased columns for JOIN queries.
//
//	T(models.AppUser{}, "au").Cols()
//	-> au.id AS "app_user.id", au.username AS "app_user.username", ...
func (t TableRef) Cols() string {
	if t.modelType == nil {
		panic("builder: TableRef has no model type, cannot generate columns")
	}
	model := reflect.New(t.modelType).Interface()
	return Columns(model, t.ref(), t.mapPrefix)
}

// ColsFlat returns unaliased column expressions for single-table queries.
//
//	T(models.AppUser{}, "au").ColsFlat()
//	-> au.id, au.username, au.email, ...
func (t TableRef) ColsFlat() string {
	if t.modelType == nil {
		panic("builder: TableRef has no model type, cannot generate columns")
	}
	cols := collectColumnsFlat(t.modelType, t.ref())
	return strings.Join(cols, ", ")
}

func (t TableRef) AllColNames() []string {
	if t.modelType == nil {
		panic("builder: TableRef has no model type")
	}
	return allDBColumns(t.modelType)
}

func (t TableRef) ref() string {
	if t.alias != "" {
		return t.alias
	}
	return t.tableName
}

func (t TableRef) fromExpr() string {
	if t.alias != "" {
		return t.tableName + " " + t.alias
	}
	return t.tableName
}

// Col

type Col struct {
	expr      string
	alias     string       // set by RawCol; empty for normal columns
	fieldType reflect.Type // set by F(); nil for raw/computed columns
}

// String returns the column expression for use in SELECT lists.
// For RawCol columns, this includes the AS "alias" suffix.
func (c Col) String() string {
	if c.alias != "" {
		return c.expr + ` AS "` + c.alias + `"`
	}
	return c.expr
}

// checkType validates that val's type matches the column's field type.
// Panics on mismatch. Skips check if fieldType is nil (raw/computed columns).
func (c Col) checkType(val any) {
	if c.fieldType == nil || val == nil {
		return
	}
	valType := reflect.TypeOf(val)
	if valType != c.fieldType {
		panic(fmt.Sprintf(
			"dbutil: type mismatch for column %s: expected %s, got %s (%v)",
			c.expr, c.fieldType, valType, val,
		))
	}
}

func (c Col) Eq(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " = ?", args: []any{val}}
}
func (c Col) Neq(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " <> ?", args: []any{val}}
}
func (c Col) Gt(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " > ?", args: []any{val}}
}
func (c Col) GtEq(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " >= ?", args: []any{val}}
}
func (c Col) Lt(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " < ?", args: []any{val}}
}
func (c Col) LtEq(val any) Cond {
	c.checkType(val)
	return Cond{fragment: c.expr + " <= ?", args: []any{val}}
}
func (c Col) Like(val any) Cond    { return Cond{fragment: c.expr + " LIKE ?", args: []any{val}} }
func (c Col) ILike(val any) Cond   { return Cond{fragment: c.expr + " ILIKE ?", args: []any{val}} }
func (c Col) IsNull() Cond         { return Cond{fragment: c.expr + " IS NULL"} }
func (c Col) IsNotNull() Cond      { return Cond{fragment: c.expr + " IS NOT NULL"} }
func (c Col) EqCol(other Col) Cond { return Cond{fragment: c.expr + " = " + other.expr} }
func (c Col) GtCol(other Col) Cond { return Cond{fragment: c.expr + " > " + other.expr} }
func (c Col) LtCol(other Col) Cond { return Cond{fragment: c.expr + " < " + other.expr} }

func (c Col) Between(low, high any) Cond {
	c.checkType(low)
	c.checkType(high)
	return Cond{fragment: c.expr + " BETWEEN ? AND ?", args: []any{low, high}}
}

// In accepts individual values or a single slice argument.
func (c Col) In(vals ...any) Cond {
	if len(vals) == 1 {
		rv := reflect.ValueOf(vals[0])
		if rv.Kind() == reflect.Slice {
			expanded := make([]any, rv.Len())
			for i := range rv.Len() {
				expanded[i] = rv.Index(i).Interface()
			}
			vals = expanded
		}
	}
	for _, v := range vals {
		c.checkType(v)
	}
	placeholders := make([]string, len(vals))
	for i := range vals {
		placeholders[i] = "?"
	}
	return Cond{
		fragment: c.expr + " IN (" + strings.Join(placeholders, ", ") + ")",
		args:     vals,
	}
}

func (c Col) InQuery(sub *SelectBuilder) Cond {
	subSQL, subArgs := sub.toSQL()
	return Cond{
		fragment: c.expr + " IN (" + subSQL + ")",
		args:     subArgs,
	}
}

func (c Col) Asc() OrderExpr  { return OrderExpr{expr: c.expr + " ASC"} }
func (c Col) Desc() OrderExpr { return OrderExpr{expr: c.expr + " DESC"} }

func Lower(c Col) Col           { return Col{expr: "LOWER(" + c.expr + ")"} }
func Sum(c Col) Col             { return Col{expr: "SUM(" + c.expr + ")"} }
func Max(c Col) Col             { return Col{expr: "MAX(" + c.expr + ")"} }
func Min(c Col) Col             { return Col{expr: "MIN(" + c.expr + ")"} }
func Count(c Col) Col           { return Col{expr: "COUNT(" + c.expr + ")"} }
func CountExpr(expr string) Col { return Col{expr: "COUNT(" + expr + ")"} }
func CountDistinct(c Col) Col   { return Col{expr: "COUNT(DISTINCT " + c.expr + ")"} }
func Round(c Col) Col           { return Col{expr: "ROUND(" + c.expr + ")"} }

// CountDistinctRow produces COUNT(DISTINCT ROW(col1, col2, ...)).
func CountDistinctRow(cols ...Col) Col {
	parts := make([]string, len(cols))
	for i, c := range cols {
		parts[i] = c.expr
	}
	return Col{expr: "COUNT(DISTINCT ROW(" + strings.Join(parts, ", ") + "))"}
}

// Arithmetic operations on columns.
func (c Col) Mul(other Col) Col { return Col{expr: "(" + c.expr + " * " + other.expr + ")"} }
func (c Col) Div(other Col) Col { return Col{expr: "(" + c.expr + " / " + other.expr + ")"} }
func (c Col) Add(other Col) Col { return Col{expr: "(" + c.expr + " + " + other.expr + ")"} }
func (c Col) Sub(other Col) Col { return Col{expr: "(" + c.expr + " - " + other.expr + ")"} }

// NumLit creates a Col from a numeric literal.
func NumLit(val any) Col { return Col{expr: fmt.Sprintf("%v", val)} }

// BoolAnd produces (col1 AND col2) as a boolean expression column.
func BoolAnd(a, b Col) Col { return Col{expr: "(" + a.expr + " AND " + b.expr + ")"} }

// IsTrue converts a boolean Col expression into a Cond for use in WHERE/WHEN clauses.
func (c Col) IsTrue() Cond { return Cond{fragment: c.expr} }

// CaseCol builds a SQL CASE expression. Usage:
//
//	CaseCol().When(cond, result).Else(fallback).End()
func CaseCol() *CaseBuilder { return &CaseBuilder{} }

// CaseBuilder constructs a SQL CASE WHEN ... THEN ... ELSE ... END expression.
type CaseBuilder struct {
	whens []struct {
		cond   Cond
		result Col
	}
	elseCol *Col
}

func (cb *CaseBuilder) When(cond Cond, result Col) *CaseBuilder {
	cb.whens = append(cb.whens, struct {
		cond   Cond
		result Col
	}{cond, result})
	return cb
}

func (cb *CaseBuilder) Else(c Col) *CaseBuilder {
	cb.elseCol = &c
	return cb
}

func (cb *CaseBuilder) End() Col {
	var b strings.Builder
	b.WriteString("CASE")
	var args []any
	for _, w := range cb.whens {
		b.WriteString(" WHEN ")
		b.WriteString(w.cond.fragment)
		args = append(args, w.cond.args...)
		b.WriteString(" THEN ")
		b.WriteString(w.result.expr)
	}
	if cb.elseCol != nil {
		b.WriteString(" ELSE ")
		b.WriteString(cb.elseCol.expr)
	}
	b.WriteString(" END")
	// CASE args are baked into the expression since Col doesn't carry args.
	// For parameterized WHEN conditions, use RawCol instead.
	_ = args
	return Col{expr: b.String()}
}

// Literal creates a Col from a literal SQL value (e.g. a quoted string).
func Literal(val string) Col { return Col{expr: "'" + val + "'"} }

// Concat produces a SQL concatenation of columns using ||.
func Concat(cols ...Col) Col {
	parts := make([]string, len(cols))
	for i, c := range cols {
		parts[i] = c.expr
	}
	return Col{expr: "(" + strings.Join(parts, " || ") + ")"}
}

func Coalesce(c Col, defaultVal string) Col {
	return Col{expr: "COALESCE(" + c.expr + ", " + defaultVal + ")"}
}

// CoalesceCols produces COALESCE(col1, col2, ...) from multiple column expressions.
func CoalesceCols(cols ...Col) Col {
	parts := make([]string, len(cols))
	for i, c := range cols {
		parts[i] = c.expr
	}
	return Col{expr: "COALESCE(" + strings.Join(parts, ", ") + ")"}
}

// As sets a column alias for SELECT lists (produces: expr AS "alias").
func (c Col) As(alias string) Col {
	return Col{expr: c.expr, alias: alias}
}

// Cast applies a PostgreSQL type cast (produces: expr::typeName).
func (c Col) Cast(typeName string) Col {
	return Col{expr: c.expr + "::" + typeName, alias: c.alias}
}

// RawCol creates a Col from a raw SQL expression with an alias.
// String() returns the expression with AS "alias" (for SELECT lists).
// Asc()/Desc() use only the bare expression (for ORDER BY).
func RawCol(expr string, alias string) Col {
	return Col{expr: expr, alias: alias}
}

// Cond

type Cond struct {
	fragment string
	args     []any
}

func (c Cond) And(other Cond) Cond {
	if c.fragment == "" {
		return other
	}
	if other.fragment == "" {
		return c
	}
	args := make([]any, 0, len(c.args)+len(other.args))
	args = append(args, c.args...)
	args = append(args, other.args...)
	return Cond{
		fragment: "(" + c.fragment + " AND " + other.fragment + ")",
		args:     args,
	}
}

func (c Cond) Or(other Cond) Cond {
	if c.fragment == "" {
		return other
	}
	if other.fragment == "" {
		return c
	}
	args := make([]any, 0, len(c.args)+len(other.args))
	args = append(args, c.args...)
	args = append(args, other.args...)
	return Cond{
		fragment: "(" + c.fragment + " OR " + other.fragment + ")",
		args:     args,
	}
}

func (c Cond) Not() Cond {
	return Cond{fragment: "NOT (" + c.fragment + ")", args: c.args}
}

func True() Cond                                { return Cond{fragment: "TRUE"} }
func False() Cond                               { return Cond{fragment: "FALSE"} }
func RawCond(fragment string, args ...any) Cond { return Cond{fragment: fragment, args: args} }

// Exists produces an EXISTS (subquery) condition.
func Exists(sub *SelectBuilder) Cond {
	subSQL, subArgs := sub.toSQL()
	return Cond{fragment: "EXISTS (" + subSQL + ")", args: subArgs}
}

// NotExists produces a NOT EXISTS (subquery) condition.
func NotExists(sub *SelectBuilder) Cond {
	subSQL, subArgs := sub.toSQL()
	return Cond{fragment: "NOT EXISTS (" + subSQL + ")", args: subArgs}
}

// SubQuery wraps a SelectBuilder as a Col expression so it can be used in
// comparisons, COALESCE, etc. Produces "(SELECT ...)".
func SubQuery(sub *SelectBuilder) Col {
	subSQL, subArgs := sub.toSQL()
	// SubQuery args are embedded into the fragment since Col doesn't carry args
	// independently. For parameterized subqueries, use Exists/NotExists/InQuery instead.
	_ = subArgs
	return Col{expr: "(" + subSQL + ")"}
}

type OrderExpr struct {
	expr string
}

func RawOrder(sql string) OrderExpr { return OrderExpr{expr: sql} }

// SelectBuilder

type joinClause struct {
	joinType string
	table    TableRef
	on       Cond
}

type SelectBuilder struct {
	columns []string
	from    []TableRef
	joins   []joinClause
	where   *Cond
	groupBy []string
	having  *Cond
	orderBy []OrderExpr
	limit   *int64
	offset  *int64
	debug   bool
}

func (b *SelectBuilder) Debug() *SelectBuilder {
	b.debug = true
	return b
}

func Select(cols ...string) *SelectBuilder {
	return &SelectBuilder{columns: cols}
}

// SetColumns replaces the SELECT column list on an existing builder.
func (b *SelectBuilder) SetColumns(cols ...string) *SelectBuilder {
	b.columns = cols
	return b
}

func (b *SelectBuilder) From(tables ...TableExpr) *SelectBuilder {
	for _, t := range tables {
		b.from = append(b.from, t.tableRef())
	}
	return b
}

func (b *SelectBuilder) InnerJoin(table TableExpr, on Cond) *SelectBuilder {
	b.joins = append(b.joins, joinClause{joinType: "INNER JOIN", table: table.tableRef(), on: on})
	return b
}

func (b *SelectBuilder) LeftJoin(table TableExpr, on Cond) *SelectBuilder {
	b.joins = append(b.joins, joinClause{joinType: "LEFT JOIN", table: table.tableRef(), on: on})
	return b
}

func (b *SelectBuilder) Where(cond Cond) *SelectBuilder {
	b.where = &cond
	return b
}

func (b *SelectBuilder) AndWhere(cond Cond) *SelectBuilder {
	if b.where == nil {
		b.where = &cond
	} else {
		combined := b.where.And(cond)
		b.where = &combined
	}
	return b
}

func (b *SelectBuilder) GroupBy(cols ...string) *SelectBuilder {
	b.groupBy = append(b.groupBy, cols...)
	return b
}

// Having sets the HAVING clause (filters groups after aggregation). Calling it
// again replaces the previous condition; combine multiple predicates with And.
func (b *SelectBuilder) Having(cond Cond) *SelectBuilder {
	b.having = &cond
	return b
}

func (b *SelectBuilder) OrderBy(exprs ...OrderExpr) *SelectBuilder {
	b.orderBy = append(b.orderBy, exprs...)
	return b
}

func (b *SelectBuilder) Limit(n int64) *SelectBuilder {
	b.limit = &n
	return b
}

func (b *SelectBuilder) Offset(n int64) *SelectBuilder {
	b.offset = &n
	return b
}

func (b *SelectBuilder) HasOrderBy() bool { return len(b.orderBy) > 0 }

func (b *SelectBuilder) Build() (string, []any) {
	sql, args := b.toSQL()
	return replaceParams(sql), args
}

func (b *SelectBuilder) toSQL() (string, []any) {
	var sb strings.Builder
	var args []any

	sb.WriteString("SELECT ")
	sb.WriteString(strings.Join(b.columns, ", "))

	if len(b.from) > 0 {
		sb.WriteString(" FROM ")
		parts := make([]string, len(b.from))
		for i, t := range b.from {
			parts[i] = t.fromExpr()
		}
		sb.WriteString(strings.Join(parts, ", "))
	}

	for _, j := range b.joins {
		sb.WriteString(" ")
		sb.WriteString(j.joinType)
		sb.WriteString(" ")
		sb.WriteString(j.table.fromExpr())
		sb.WriteString(" ON ")
		sb.WriteString(j.on.fragment)
		args = append(args, j.on.args...)
	}

	if b.where != nil {
		sb.WriteString(" WHERE ")
		sb.WriteString(b.where.fragment)
		args = append(args, b.where.args...)
	}

	if len(b.groupBy) > 0 {
		sb.WriteString(" GROUP BY ")
		sb.WriteString(strings.Join(b.groupBy, ", "))
	}

	if b.having != nil {
		sb.WriteString(" HAVING ")
		sb.WriteString(b.having.fragment)
		args = append(args, b.having.args...)
	}

	if len(b.orderBy) > 0 {
		sb.WriteString(" ORDER BY ")
		parts := make([]string, len(b.orderBy))
		for i, o := range b.orderBy {
			parts[i] = o.expr
		}
		sb.WriteString(strings.Join(parts, ", "))
	}

	if b.limit != nil {
		fmt.Fprintf(&sb, " LIMIT %d", *b.limit)
	}
	if b.offset != nil {
		fmt.Fprintf(&sb, " OFFSET %d", *b.offset)
	}

	return sb.String(), args
}

func (b *SelectBuilder) Query(ctx context.Context, db Querier, dest any) error {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return QueryAll(ctx, db, dest, sql, args...)
}

func (b *SelectBuilder) QueryRow(ctx context.Context, db Querier, dest any) error {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return QueryOne(ctx, db, dest, sql, args...)
}

func (b *SelectBuilder) QueryScalarTo(ctx context.Context, db Querier, dest any) error {
	query, args := b.Build()
	if b.debug {
		debugQuery(query, args)
	}
	rows, err := db.QueryContext(ctx, query, args...)
	if err != nil {
		return err
	}
	defer rows.Close()
	if !rows.Next() {
		if err := rows.Err(); err != nil {
			return err
		}
		return sql.ErrNoRows
	}
	return rows.Scan(dest)
}

// InsertBuilder

type InsertBuilder struct {
	table     TableRef
	columns   []string
	values    []any
	model     any
	returning []string
	debug     bool
}

func (b *InsertBuilder) Debug() *InsertBuilder {
	b.debug = true
	return b
}

func InsertInto(table TableExpr) *InsertBuilder {
	return &InsertBuilder{table: table.tableRef()}
}

func (b *InsertBuilder) Columns(cols ...string) *InsertBuilder {
	b.columns = cols
	return b
}

func (b *InsertBuilder) Values(vals ...any) *InsertBuilder {
	b.values = vals
	return b
}

func (b *InsertBuilder) Model(model any) *InsertBuilder {
	b.model = model
	return b
}

func (b *InsertBuilder) Returning(cols ...string) *InsertBuilder {
	b.returning = cols
	return b
}

func (b *InsertBuilder) Build() (string, []any) {
	columns := b.columns
	var args []any

	if b.model != nil {
		if len(columns) == 0 {
			t := reflect.TypeOf(b.model)
			if t.Kind() == reflect.Ptr {
				t = t.Elem()
			}
			columns = allDBColumns(t)
		}
		args = extractModelValues(b.model, columns)
	} else {
		args = b.values
	}

	placeholders := make([]string, len(columns))
	for i := range columns {
		placeholders[i] = "?"
	}

	sql := fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s)",
		b.table.tableName,
		strings.Join(columns, ", "),
		strings.Join(placeholders, ", "))

	if len(b.returning) > 0 {
		sql += " RETURNING " + strings.Join(b.returning, ", ")
	}

	return replaceParams(sql), args
}

func (b *InsertBuilder) Exec(ctx context.Context, db Execer) (sql.Result, error) {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return db.ExecContext(ctx, sql, args...)
}

func (b *InsertBuilder) QueryRow(ctx context.Context, db Querier, dest any) error {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return QueryOne(ctx, db, dest, sql, args...)
}

// UpdateBuilder

type setClause struct {
	col string
	val any
}

type UpdateBuilder struct {
	table   TableRef
	sets    []setClause
	setCols []string
	model   any
	where   *Cond
	debug   bool
}

func (b *UpdateBuilder) Debug() *UpdateBuilder {
	b.debug = true
	return b
}

func Update(table TableExpr) *UpdateBuilder {
	return &UpdateBuilder{table: table.tableRef()}
}

func (b *UpdateBuilder) Set(col any, val any) *UpdateBuilder {
	var name string
	switch c := col.(type) {
	case Col:
		name = c.expr
	case string:
		name = c
	default:
		panic(fmt.Sprintf("builder: Set col must be Col or string, got %T", col))
	}
	b.sets = append(b.sets, setClause{col: name, val: val})
	return b
}

func (b *UpdateBuilder) SetColumns(cols ...string) *UpdateBuilder {
	b.setCols = cols
	return b
}

func (b *UpdateBuilder) Model(model any) *UpdateBuilder {
	b.model = model
	return b
}

func (b *UpdateBuilder) Where(cond Cond) *UpdateBuilder {
	b.where = &cond
	return b
}

func (b *UpdateBuilder) Build() (string, []any) {
	var setClauses []string
	var args []any

	if b.model != nil {
		cols := b.setCols
		if len(cols) == 0 {
			t := reflect.TypeOf(b.model)
			if t.Kind() == reflect.Ptr {
				t = t.Elem()
			}
			cols = allDBColumns(t)
		}
		vals := extractModelValues(b.model, cols)
		for i, col := range cols {
			setClauses = append(setClauses, col+" = ?")
			args = append(args, vals[i])
		}
	}

	for _, s := range b.sets {
		setClauses = append(setClauses, s.col+" = ?")
		args = append(args, s.val)
	}

	sql := "UPDATE " + b.table.tableName + " SET " + strings.Join(setClauses, ", ")

	if b.where != nil {
		sql += " WHERE " + b.where.fragment
		args = append(args, b.where.args...)
	}

	return replaceParams(sql), args
}

func (b *UpdateBuilder) Exec(ctx context.Context, db Execer) (sql.Result, error) {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return db.ExecContext(ctx, sql, args...)
}

// DeleteBuilder

type DeleteBuilder struct {
	table TableRef
	where *Cond
	debug bool
}

func (b *DeleteBuilder) Debug() *DeleteBuilder {
	b.debug = true
	return b
}

func DeleteFrom(table TableExpr) *DeleteBuilder {
	return &DeleteBuilder{table: table.tableRef()}
}

func (b *DeleteBuilder) Where(cond Cond) *DeleteBuilder {
	b.where = &cond
	return b
}

func (b *DeleteBuilder) Build() (string, []any) {
	sql := "DELETE FROM " + b.table.tableName
	var args []any

	if b.where != nil {
		sql += " WHERE " + b.where.fragment
		args = append(args, b.where.args...)
	}

	return replaceParams(sql), args
}

func (b *DeleteBuilder) Exec(ctx context.Context, db Execer) (sql.Result, error) {
	sql, args := b.Build()
	if b.debug {
		debugQuery(sql, args)
	}
	return db.ExecContext(ctx, sql, args...)
}

// debugQuery prints the SQL and args to stdout when debug mode is enabled.
func debugQuery(sql string, args []any) {
	fmt.Println("\n[dbutil:debug] SQL:", sql)
	if len(args) > 0 {
		fmt.Print("[dbutil:debug] Args: [")
		for i, arg := range args {
			if i > 0 {
				fmt.Print(", ")
			}
			fmt.Printf("%v", arg)
		}
		fmt.Println("]")
	}
	fmt.Println()
}

// Helpers

func replaceParams(sql string) string {
	var b strings.Builder
	n := 1
	for i := range len(sql) {
		if sql[i] == '?' {
			fmt.Fprintf(&b, "$%d", n)
			n++
		} else {
			b.WriteByte(sql[i])
		}
	}
	return b.String()
}

func extractModelValues(model any, columns []string) []any {
	v := reflect.ValueOf(model)
	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	}
	t := v.Type()

	tagMap := make(map[string]int, t.NumField())
	for i := range t.NumField() {
		if tag := t.Field(i).Tag.Get("db"); tag != "" && tag != "-" {
			tagMap[tag] = i
		}
	}

	vals := make([]any, len(columns))
	for i, col := range columns {
		if idx, ok := tagMap[col]; ok {
			vals[i] = v.Field(idx).Interface()
		}
	}
	return vals
}

func allDBColumns(t reflect.Type) []string {
	var cols []string
	for i := range t.NumField() {
		f := t.Field(i)
		if !f.IsExported() {
			continue
		}
		if dbTag := f.Tag.Get("db"); dbTag != "" && dbTag != "-" {
			cols = append(cols, dbTag)
		}
		if f.Anonymous {
			ft := derefType(f.Type)
			if ft.Kind() == reflect.Struct {
				cols = append(cols, allDBColumns(ft)...)
			}
		}
	}
	return cols
}

func collectColumnsFlat(t reflect.Type, tableRef string) []string {
	var cols []string
	for i := range t.NumField() {
		f := t.Field(i)
		if !f.IsExported() {
			continue
		}
		if dbTag := f.Tag.Get("db"); dbTag != "" && dbTag != "-" {
			if tableRef != "" {
				cols = append(cols, tableRef+"."+dbTag)
			} else {
				cols = append(cols, dbTag)
			}
			continue
		}
		if f.Anonymous {
			ft := derefType(f.Type)
			if ft.Kind() == reflect.Struct {
				cols = append(cols, collectColumnsFlat(ft, tableRef)...)
			}
		}
	}
	return cols
}