module transform

import v3.flat

// try_expand_if_guard detects an if-guard pattern where the condition is a
// decl_assign whose RHS is a call returning an optional (?T) or result (!T).
// When detected it expands:
//   if val := maybe_call() { body }
// into:
//   __or_tmp_N := maybe_call()
//   if !__or_tmp_N.is_error { val := __or_tmp_N.data; body... }
//
fn (mut t Transformer) try_expand_if_guard(_id flat.NodeId, node flat.Node) ?[]flat.NodeId {
    if node.kind != .if_expr || node.children_count < 2 {
        return none
    }
    cond_id := t.a.child(&node, 0)
    cond := t.a.nodes[int(cond_id)]
    if cond.kind != .decl_assign || cond.children_count < 2 {
        return none
    }
    lhs_id := t.a.child(&cond, 0)
    rhs_id := t.a.child(&cond, 1)
    lhs := t.a.nodes[int(lhs_id)]
    if lhs.kind != .ident || lhs.value.len == 0 {
        return none
    }
    lhs_ids := t.multi_assign_lhs_ids(cond)
    if lhs_ids.len == 1 {
        if info := t.map_index_info(rhs_id) {
            return t.expand_map_index_if_guard(node, lhs.value, info)
        }
        if info := t.array_index_info(rhs_id) {
            return t.expand_array_index_if_guard(node, lhs.value, info)
        }
    }
    mut rhs_type := t.optional_result_expr_type_name(rhs_id)
    if !t.is_optional_type_name(rhs_type) {
        return none
    }
    rhs_type = t.qualify_optional_type(rhs_type)
    value_type := t.optional_base_type(rhs_type)
    tmp_name := t.new_temp('if_guard')
    rhs_expr := t.transform_expr(rhs_id)
    mut prelude := []flat.NodeId{}
    t.drain_pending(mut prelude)
    tmp_decl := t.make_decl_assign_typed(tmp_name, rhs_expr, rhs_type)
    ok_cond := t.make_selector(t.make_ident(tmp_name), 'ok', 'bool')
    mut value_decls := []flat.NodeId{}
    if lhs_ids.len > 1 {
        if rhs_types := t.multi_return_types_for_expr(rhs_id, lhs_ids.len) {
            for i, lhs_item_id in lhs_ids {
                lhs_item := t.a.nodes[int(lhs_item_id)]
                if lhs_item.kind != .ident || lhs_item.value == '_' {
                    continue
                }
                field_type := rhs_types[i].name()
                payload := t.make_selector(t.make_ident(tmp_name), 'value', value_type)
                field := t.make_selector(payload, 'arg${i}', field_type)
                value_decls << t.make_decl_assign_typed(lhs_item.value, field, field_type)
            }
        }
    }
    if value_decls.len == 0 {
        value_decls << t.make_decl_assign_typed(lhs.value, t.make_selector(t.make_ident(tmp_name),
            'value', value_type), value_type)
    }

    then_id := t.a.child(&node, 1)
    then_node := t.a.nodes[int(then_id)]
    if lhs_ids.len > 1 {
        if rhs_types := t.multi_return_types_for_expr(rhs_id, lhs_ids.len) {
            for i, lhs_item_id in lhs_ids {
                lhs_item := t.a.nodes[int(lhs_item_id)]
                if lhs_item.kind == .ident && lhs_item.value.len > 0 && lhs_item.value != '_' {
                    t.set_var_type(lhs_item.value, rhs_types[i].name())
                }
            }
        }
    } else {
        t.set_var_type(lhs.value, value_type)
    }
    mut then_children := []flat.NodeId{}
    for value_decl in value_decls {
        then_children << value_decl
    }
    if then_node.kind == .block {
        then_children << t.transform_stmts(t.a.children_of(&then_node))
    } else {
        then_children << t.transform_stmt(then_id)
    }
    then_block := t.make_block(then_children)

    mut else_block := flat.empty_node
    if node.children_count >= 3 {
        else_id := t.a.child(&node, 2)
        else_node := t.a.nodes[int(else_id)]
        else_block = t.transform_if_guard_else_block(else_id, else_node, tmp_name)
    }
    mut expanded := []flat.NodeId{cap: prelude.len + 2}
    for stmt in prelude {
        expanded << stmt
    }
    expanded << tmp_decl
    expanded << t.make_if(ok_cond, then_block, else_block)
    return expanded
}

// optional_result_expr_type_name supports optional result expr type name handling for Transformer.
fn (t &Transformer) optional_result_expr_type_name(id flat.NodeId) string {
    if int(id) < 0 {
        return ''
    }
    if !isnil(t.tc) {
        node := t.a.nodes[int(id)]
        if node.kind == .call {
            if name := t.tc.resolved_call_name(id) {
                if ret := t.tc.fn_ret_types[name] {
                    ret_name := ret.name()
                    if t.is_optional_type_name(ret_name) {
                        return ret_name
                    }
                }
            }
            ret_name := t.get_call_return_type(id, node)
            if t.is_optional_type_name(ret_name) {
                return ret_name
            }
        }
        if typ := t.tc.expr_type(id) {
            typ_name := typ.name()
            if t.is_optional_type_name(typ_name) {
                return typ_name
            }
        }
    }
    return t.node_type(id)
}

// transform_if_guard_else_block transforms transform if guard else block data for transform.
fn (mut t Transformer) transform_if_guard_else_block(else_id flat.NodeId, else_node flat.Node, err_source string) flat.NodeId {
    saved_var_types := t.var_types.clone()
    t.set_var_type('err', 'IError')
    mut children := []flat.NodeId{}
    err_value := if err_source.len > 0 {
        t.make_selector(t.make_ident(err_source), 'err', 'IError')
    } else {
        t.make_struct_init('IError')
    }
    children << t.make_decl_assign_typed('err', err_value, 'IError')
    if else_node.kind == .block {
        children << t.transform_stmts(t.a.children_of(&else_node))
    } else if else_node.kind == .if_expr {
        children << t.transform_else_if_expr(else_id, else_node)
    } else {
        children << t.transform_stmt(else_id)
    }
    t.var_types = saved_var_types
    return t.make_block(children)
}

// transform_else_if_expr transforms transform else if expr data for transform.
fn (mut t Transformer) transform_else_if_expr(else_id flat.NodeId, else_node flat.Node) flat.NodeId {
    if expanded := t.try_expand_if_guard(else_id, else_node) {
        return t.make_block(expanded)
    }
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    new_if := t.transform_if_branches_with_smartcast(else_id, else_node)
    mut local_pending := t.pending_stmts.clone()
    t.pending_stmts = outer_pending
    if local_pending.len == 0 {
        return new_if
    }
    local_pending << new_if
    return t.make_block(local_pending)
}

// expand_map_index_if_guard builds expand map index if guard data for transform.
fn (mut t Transformer) expand_map_index_if_guard(node flat.Node, lhs_name string, info MapIndexInfo) ?[]flat.NodeId {
    map_expr := t.stable_expr_for_reuse(info.base_id)
    key_name := t.new_temp('map_key')
    ptr_name := t.new_temp('map_ptr')
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    key_expr := t.transform_expr(info.key_id)
    mut prelude := []flat.NodeId{}
    t.drain_pending(mut prelude)
    prelude << t.make_decl_assign_typed(key_name, key_expr, info.key_type)
    prelude << t.make_decl_assign_typed(ptr_name, t.make_map_get_check_expr(map_expr,
        info.base_type, key_name), 'voidptr')

    ptr_ident := t.make_ident(ptr_name)
    found_cond := t.make_infix(.ne, ptr_ident, t.a.add(.nil_literal))
    ptr_value := t.make_prefix(.mul, t.make_cast('&${info.value_type}', t.make_ident(ptr_name),
        '&${info.value_type}'))
    value_decl := t.make_decl_assign_typed(lhs_name, ptr_value, info.value_type)

    then_id := t.a.child(&node, 1)
    then_node := t.a.nodes[int(then_id)]
    t.set_var_type(lhs_name, info.value_type)
    mut then_children := []flat.NodeId{}
    then_children << value_decl
    if then_node.kind == .block {
        then_children << t.transform_stmts(t.a.children_of(&then_node))
    } else {
        then_children << t.transform_stmt(then_id)
    }
    then_block := t.make_block(then_children)

    mut else_block := flat.empty_node
    if node.children_count >= 3 {
        else_id := t.a.child(&node, 2)
        else_node := t.a.nodes[int(else_id)]
        else_block = if else_node.kind == .block {
            t.make_block(t.transform_stmts(t.a.children_of(&else_node)))
        } else if else_node.kind == .if_expr {
            t.transform_else_if_expr(else_id, else_node)
        } else {
            t.make_block(t.transform_stmt(else_id))
        }
    }
    t.pending_stmts = outer_pending
    mut expanded := []flat.NodeId{cap: prelude.len + 1}
    for stmt in prelude {
        expanded << stmt
    }
    expanded << t.make_if(found_cond, then_block, else_block)
    return expanded
}

// expand_array_index_if_guard builds expand array index if guard data for transform.
fn (mut t Transformer) expand_array_index_if_guard(node flat.Node, lhs_name string, info ArrayIndexInfo) ?[]flat.NodeId {
    array_expr := t.stable_expr_for_reuse(info.base_id)
    index_name := t.new_temp('arr_idx')
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    index_expr := t.transform_expr(info.index_id)
    mut prelude := []flat.NodeId{}
    t.drain_pending(mut prelude)
    prelude << t.make_decl_assign_typed(index_name, index_expr, 'int')

    idx_ident := t.make_ident(index_name)
    lower_ok := t.make_infix(.ge, idx_ident, t.make_int_literal(0))
    upper_ok := t.make_infix(.lt, t.make_ident(index_name), t.make_selector(array_expr, 'len',
        'int'))
    found_cond := t.make_infix(.logical_and, lower_ok, upper_ok)

    then_id := t.a.child(&node, 1)
    then_node := t.a.nodes[int(then_id)]
    saved_var_types := t.var_types.clone()
    mut then_children := []flat.NodeId{}
    mut guard_value_type := info.value_type
    mut value_expr := t.make_index(array_expr, t.make_ident(index_name), info.value_type)
    if t.is_optional_type_name(info.value_type) {
        guard_value_type = t.optional_base_type(t.qualify_optional_type(info.value_type))
        opt_name := t.new_temp('arr_opt')
        value_expr = t.make_selector(t.make_ident(opt_name), 'value', guard_value_type)
        then_children << t.make_decl_assign_typed(opt_name, t.make_index(array_expr,
            t.make_ident(index_name), info.value_type), info.value_type)
    }
    then_children << t.make_decl_assign_typed(lhs_name, value_expr, guard_value_type)
    t.set_var_type(lhs_name, guard_value_type)
    if then_node.kind == .block {
        then_children << t.transform_stmts(t.a.children_of(&then_node))
    } else {
        then_children << t.transform_stmt(then_id)
    }
    t.var_types = saved_var_types
    then_block := t.make_block(then_children)

    mut else_block := flat.empty_node
    if node.children_count >= 3 {
        else_id := t.a.child(&node, 2)
        else_node := t.a.nodes[int(else_id)]
        else_block = if else_node.kind == .block {
            t.make_block(t.transform_stmts(t.a.children_of(&else_node)))
        } else if else_node.kind == .if_expr {
            t.transform_else_if_expr(else_id, else_node)
        } else {
            t.make_block(t.transform_stmt(else_id))
        }
    }
    mut selected_block := then_block
    if t.is_optional_type_name(info.value_type) && then_children.len > 0 {
        opt_decl := then_children[0]
        opt_name := t.a.nodes[int(t.a.child(&t.a.nodes[int(opt_decl)], 0))].value
        ok_cond := t.make_selector(t.make_ident(opt_name), 'ok', 'bool')
        mut inner_children := []flat.NodeId{}
        for i in 1 .. then_children.len {
            inner_children << then_children[i]
        }
        inner_if := t.make_if(ok_cond, t.make_block(inner_children), else_block)
        selected_block = t.make_block([opt_decl, inner_if])
    }
    t.pending_stmts = outer_pending
    mut expanded := []flat.NodeId{cap: prelude.len + 1}
    for stmt in prelude {
        expanded << stmt
    }
    expanded << t.make_if(found_cond, selected_block, else_block)
    return expanded
}

// try_expand_if_expr_value detects an if-expression used as a value and
// lowers it to a mutable temporary so that the C backend sees a simple
// variable instead of a gcc statement-expression.
//
//   x := if cond { a } else { b }
// becomes:
//   mut __if_tmp_N := zero_value
//   if cond { __if_tmp_N = a } else { __if_tmp_N = b }
//   x := __if_tmp_N
fn (mut t Transformer) try_expand_if_expr_value(id flat.NodeId, node flat.Node) ?flat.NodeId {
    if node.kind != .if_expr {
        return none
    }
    // An if-expression used as a value must have both then and else branches.
    if node.children_count < 3 {
        return none
    }
    mut result_type := t.if_expr_result_type(id, node)
    if result_type.len == 0 || result_type == 'void' {
        return none
    }
    return t.try_expand_if_expr_value_for_type(id, node, result_type)
}

// try_expand_if_expr_value_for_type
// supports helper handling in transform.
fn (mut t Transformer) try_expand_if_expr_value_for_type(id flat.NodeId, node flat.Node, result_type string) ?flat.NodeId {
    if node.kind != .if_expr || node.children_count < 3 || result_type.len == 0
        || result_type == 'void' {
        return none
    }
    mut actual_result_type := result_type
    branch_type := t.if_expr_branch_result_type(node)
    if t.if_expr_branch_overrides_sum_target(branch_type, result_type) {
        actual_result_type = branch_type
    }
    tmp_name := t.new_temp('if_val')
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()

    mut prelude := []flat.NodeId{}
    prelude << t.make_decl_assign_typed(tmp_name, t.zero_value_for_type(actual_result_type),
        actual_result_type)
    for stmt in t.build_if_value_chain(id, tmp_name, actual_result_type) {
        prelude << stmt
    }

    t.pending_stmts = outer_pending
    for stmt in prelude {
        t.pending_stmts << stmt
    }
    tmp := t.make_ident(tmp_name)
    t.a.nodes[int(tmp)].typ = actual_result_type
    return tmp
}

// if_expr_branch_overrides_sum_target supports if_expr_branch_overrides_sum_target handling.
fn (t &Transformer) if_expr_branch_overrides_sum_target(branch_type string, target_type string) bool {
    if branch_type.len == 0 || target_type.len == 0 {
        return false
    }
    if branch_type.starts_with('[]') {
        branch_elem := branch_type[2..]
        target_short := if target_type.contains('.') {
            target_type.all_after_last('.')
        } else {
            target_type
        }
        branch_short := if branch_elem.contains('.') {
            branch_elem.all_after_last('.')
        } else {
            branch_elem
        }
        if target_short == branch_short {
            return true
        }
    }
    resolved_target := t.resolve_sum_name(target_type)
    if resolved_target.len == 0 || resolved_target !in t.sum_types {
        return false
    }
    clean_branch := t.trim_pointer_type(branch_type)
    branch_sum := t.resolve_sum_name(clean_branch)
    variant_sum := t.resolve_sum_name(t.find_sum_type_for_variant(clean_branch))
    return branch_sum != resolved_target && variant_sum != resolved_target
}

// if_expr_result_type supports if expr result type handling for Transformer.
fn (t &Transformer) if_expr_result_type(id flat.NodeId, node flat.Node) string {
    mut node_typ := ''
    if node.typ.len > 0 {
        typ := t.normalize_type_alias(node.typ)
        if typ !in ['array', 'map'] {
            node_typ = typ
        }
    }
    mut checked_typ := ''
    if !isnil(t.tc) {
        if typ := t.tc.expr_type(id) {
            name := typ.name()
            if name.len > 0 {
                checked_typ = t.normalize_type_alias(name)
            }
        }
    }
    branch_typ := t.if_expr_branch_result_type(node)
    if branch_typ.starts_with('[]') && t.is_fixed_array_type(checked_typ)
        && fixed_array_elem_type(checked_typ) == branch_typ[2..] {
        return branch_typ
    }
    if branch_typ.starts_with('[]') && t.is_fixed_array_type(node_typ)
        && fixed_array_elem_type(node_typ) == branch_typ[2..] {
        return branch_typ
    }
    if branch_typ.starts_with('[]') && !checked_typ.starts_with('[]') && !node_typ.starts_with('[]') {
        return branch_typ
    }
    if t.if_expr_branch_type_overrides(branch_typ, checked_typ) {
        return branch_typ
    }
    if t.if_expr_branch_type_overrides(branch_typ, node_typ) {
        return branch_typ
    }
    if checked_typ.len > 0 && checked_typ !in ['array', 'map'] {
        return checked_typ
    }
    if node_typ.len > 0 {
        return node_typ
    }
    if branch_typ.len > 0 {
        return branch_typ
    }
    return ''
}

// if_expr_branch_type_overrides supports if expr branch type overrides handling for Transformer.
fn (t &Transformer) if_expr_branch_type_overrides(branch_typ string, stale_typ string) bool {
    if branch_typ.len == 0 || stale_typ.len == 0 || branch_typ == stale_typ {
        return false
    }
    if stale_typ in ['array', 'map', 'unknown'] {
        return true
    }
    if stale_typ in t.enum_types && branch_typ == 'int' {
        return false
    }
    if stale_typ.starts_with('&') && branch_typ.starts_with('&') {
        stale_inner := stale_typ[1..]
        branch_inner := branch_typ[1..]
        if stale_inner in ['int', 'void', 'unknown'] && branch_inner !in ['int', 'void', 'unknown'] {
            return true
        }
    }
    if stale_typ.starts_with('[]') || t.is_fixed_array_type(stale_typ) {
        return !branch_typ.starts_with('[]') && !t.is_fixed_array_type(branch_typ)
    }
    if stale_typ.starts_with('map[') {
        return !branch_typ.starts_with('map[')
    }
    return false
}

// if_expr_branch_result_type supports if expr branch result type handling for Transformer.
fn (t &Transformer) if_expr_branch_result_type(node flat.Node) string {
    mut result := ''
    if node.children_count >= 2 {
        then_smartcasts :=
            t.smartcast_contexts_from_is_exprs(t.extract_all_is_exprs(t.a.child(&node, 0)))
        then_type := t.stmt_value_type_with_smartcasts(t.a.child(&node, 1), then_smartcasts)
        if then_type.len > 0 {
            result = t.merge_if_expr_types(result, t.normalize_type_alias(then_type))
        }
    }
    if node.children_count >= 3 {
        else_id := t.a.child(&node, 2)
        else_node := t.a.nodes[int(else_id)]
        else_type := if else_node.kind == .if_expr {
            t.if_expr_result_type(else_id, else_node)
        } else {
            t.stmt_value_type(else_id)
        }
        if else_type.len > 0 {
            result = t.merge_if_expr_types(result, t.normalize_type_alias(else_type))
        }
    }
    return result
}

// smartcast_contexts_from_is_exprs converts smartcast contexts from is exprs data for transform.
fn (t &Transformer) smartcast_contexts_from_is_exprs(infos []IsExprInfo) []SmartcastContext {
    mut result := []SmartcastContext{cap: infos.len}
    for info in infos {
        result << SmartcastContext{
            expr_name:     info.expr_name
            variant_name:  info.variant_name
            sum_type_name: info.sum_type_name
        }
    }
    return result
}

// stmt_value_type_with_smartcasts
// supports helper handling in transform.
fn (t &Transformer) stmt_value_type_with_smartcasts(id flat.NodeId, contexts []SmartcastContext) string {
    if int(id) < 0 {
        return ''
    }
    node := t.a.nodes[int(id)]
    match node.kind {
        .expr_stmt {
            if node.children_count > 0 {
                return t.node_type_with_smartcasts(t.a.child(&node, node.children_count - 1),
                    contexts)
            }
            return ''
        }
        .block {
            for i := node.children_count - 1; i >= 0; i-- {
                typ := t.stmt_value_type_with_smartcasts(t.a.child(&node, i), contexts)
                if typ.len > 0 {
                    return typ
                }
            }
            return ''
        }
        else {
            return t.node_type_with_smartcasts(id, contexts)
        }
    }
}

// node_type_with_smartcasts supports node type with smartcasts handling for Transformer.
fn (t &Transformer) node_type_with_smartcasts(id flat.NodeId, contexts []SmartcastContext) string {
    if int(id) < 0 {
        return ''
    }
    node := t.a.nodes[int(id)]
    match node.kind {
        .ident {
            if sc := t.find_smartcast_in_context(node.value, contexts) {
                return t.smartcast_target_type(sc)
            }
            return t.node_type(id)
        }
        .selector {
            if node.children_count == 0 {
                return t.node_type(id)
            }
            full_key := t.expr_key(id)
            if full_key.len > 0 {
                if sc := t.find_smartcast_in_context(full_key, contexts) {
                    return t.smartcast_target_type(sc)
                }
            }
            base_id := t.a.child(&node, 0)
            base_key := t.expr_key(base_id)
            if base_key.len > 0 {
                if sc := t.find_smartcast_in_context(base_key, contexts) {
                    variant_type := t.qualify_variant(sc.variant_name, sc.sum_type_name)
                    if ftyp := t.lookup_struct_field_type(variant_type, node.value) {
                        return ftyp
                    }
                    if ftyp := t.lookup_struct_field_type(sc.variant_name, node.value) {
                        return ftyp
                    }
                }
            }
            base_type := t.node_type_with_smartcasts(base_id, contexts)
            clean_base := if base_type.starts_with('&') { base_type[1..] } else { base_type }
            if ftyp := t.lookup_struct_field_type(clean_base, node.value) {
                return ftyp
            }
            return t.node_type(id)
        }
        .prefix {
            if node.children_count == 0 {
                return t.node_type(id)
            }
            child_type := t.node_type_with_smartcasts(t.a.child(&node, 0), contexts)
            if node.op == .amp && child_type.len > 0 {
                return '&${child_type}'
            }
            if node.op == .mul && child_type.starts_with('&') {
                return child_type[1..]
            }
            if node.op == .not {
                return 'bool'
            }
            return t.node_type(id)
        }
        .paren {
            if node.children_count > 0 {
                return t.node_type_with_smartcasts(t.a.child(&node, 0), contexts)
            }
            return t.node_type(id)
        }
        .array_literal {
            if node.typ.len > 0 {
                typ := t.normalize_type_alias(node.typ)
                if typ != 'array' {
                    return typ
                }
            }
            if node.children_count > 0 {
                elem_type := t.node_type_with_smartcasts(t.a.child(&node, 0), contexts)
                if elem_type.len > 0 {
                    return '[]${elem_type}'
                }
            }
            return t.node_type(id)
        }
        .index {
            base_type := if node.children_count > 0 {
                t.node_type_with_smartcasts(t.a.child(&node, 0), contexts)
            } else {
                ''
            }
            if node.value == 'range' && base_type.starts_with('[]') {
                return base_type
            }
            if base_type.starts_with('[]') {
                return base_type[2..]
            }
            return t.node_type(id)
        }
        .if_expr {
            return t.if_expr_result_type(id, node)
        }
        .match_stmt {
            return t.match_expr_type(node)
        }
        else {
            return t.node_type(id)
        }
    }
}

// find_smartcast_in_context resolves find smartcast in context information for transform.
fn (t &Transformer) find_smartcast_in_context(expr_name string, contexts []SmartcastContext) ?SmartcastContext {
    mut i := contexts.len - 1
    for i >= 0 {
        if contexts[i].expr_name == expr_name {
            return contexts[i]
        }
        i--
    }
    return t.find_smartcast(expr_name)
}

// merge_if_expr_types supports merge if expr types handling for Transformer.
fn (t &Transformer) merge_if_expr_types(current string, next string) string {
    if current.len == 0 {
        return next
    }
    if next.len == 0 || current == next {
        return current
    }
    if current == 'array' && next.starts_with('[]') {
        return next
    }
    if next == 'array' && current.starts_with('[]') {
        return current
    }
    if current.starts_with('[]') && t.is_fixed_array_type(next)
        && current[2..] == fixed_array_elem_type(next) {
        return current
    }
    if next.starts_with('[]') && t.is_fixed_array_type(current)
        && next[2..] == fixed_array_elem_type(current) {
        return next
    }
    if current.starts_with('[]') && !next.starts_with('[]') && current[2..] == next {
        return current
    }
    if next.starts_with('[]') && !current.starts_with('[]') && next[2..] == current {
        return next
    }
    return current
}

// build_if_value_chain builds if value chain data for transform.
fn (mut t Transformer) build_if_value_chain(if_id flat.NodeId, target_name string, target_type string) []flat.NodeId {
    if_node := t.a.nodes[int(if_id)]
    if if_node.kind != .if_expr || if_node.children_count < 2 {
        return []flat.NodeId{}
    }
    if guard_chain := t.build_if_value_guard_chain(if_node, target_name, target_type) {
        return guard_chain
    }
    cond_id := t.a.child(&if_node, 0)
    then_id := t.a.child(&if_node, 1)
    has_else := if_node.children_count >= 3

    all_is := t.extract_all_is_exprs(cond_id)
    new_cond := t.transform_and_chain_smartcasts(cond_id)
    mut result := []flat.NodeId{}
    t.drain_pending(mut result)

    for info in all_is {
        t.push_smartcast(info.expr_name, info.variant_name, info.sum_type_name)
    }
    then_block := t.if_value_branch_block(then_id, target_name, target_type)
    for _ in all_is {
        t.pop_smartcast()
    }

    mut else_block := flat.empty_node
    if has_else {
        else_id := t.a.child(&if_node, 2)
        else_node := t.a.nodes[int(else_id)]
        if else_node.kind == .if_expr {
            else_block = t.make_block(t.build_if_value_chain(else_id, target_name, target_type))
        } else {
            else_block = t.if_value_branch_block(else_id, target_name, target_type)
        }
    }
    result << t.make_if(new_cond, then_block, else_block)
    return result
}

// build_if_value_guard_chain builds if value guard chain data for transform.
fn (mut t Transformer) build_if_value_guard_chain(if_node flat.Node, target_name string, target_type string) ?[]flat.NodeId {
    if if_node.children_count < 3 {
        return none
    }
    cond_id := t.a.child(&if_node, 0)
    cond := t.a.nodes[int(cond_id)]
    if cond.kind != .decl_assign || cond.children_count < 2 {
        return none
    }
    lhs_id := t.a.child(&cond, 0)
    rhs_id := t.a.child(&cond, 1)
    lhs := t.a.nodes[int(lhs_id)]
    if lhs.kind != .ident || lhs.value.len == 0 {
        return none
    }
    if info := t.map_index_info(rhs_id) {
        return t.build_map_index_if_value_guard_chain(if_node, lhs.value, info, target_name,
            target_type)
    }
    if info := t.array_index_info(rhs_id) {
        return t.build_array_index_if_value_guard_chain(if_node, lhs.value, info, target_name,
            target_type)
    }
    mut rhs_type := t.optional_result_expr_type_name(rhs_id)
    if !t.is_optional_type_name(rhs_type) {
        return none
    }
    rhs_type = t.qualify_optional_type(rhs_type)
    value_type := t.optional_base_type(rhs_type)
    tmp_name := t.new_temp('if_guard')
    rhs_expr := t.transform_expr(rhs_id)
    mut result := []flat.NodeId{}
    t.drain_pending(mut result)
    result << t.make_decl_assign_typed(tmp_name, rhs_expr, rhs_type)
    ok_cond := t.make_selector(t.make_ident(tmp_name), 'ok', 'bool')
    value_decl := t.make_decl_assign_typed(lhs.value, t.make_selector(t.make_ident(tmp_name),
        'value', value_type), value_type)

    saved_var_types := t.var_types.clone()
    t.set_var_type(lhs.value, value_type)
    then_id := t.a.child(&if_node, 1)
    then_block0 := t.if_value_branch_block(then_id, target_name, target_type)
    mut then_children := []flat.NodeId{cap: int(t.a.nodes[int(then_block0)].children_count) + 1}
    then_children << value_decl
    then_children << t.a.children_of(&t.a.nodes[int(then_block0)])
    then_block := t.make_block(then_children)
    t.var_types = saved_var_types

    else_id := t.a.child(&if_node, 2)
    else_node := t.a.nodes[int(else_id)]
    else_block := if else_node.kind == .if_expr {
        t.make_block(t.build_if_value_chain(else_id, target_name, target_type))
    } else {
        t.if_value_branch_block(else_id, target_name, target_type)
    }
    result << t.make_if(ok_cond, then_block, else_block)
    return result
}

// build_map_index_if_value_guard_chain supports build_map_index_if_value_guard_chain handling.
fn (mut t Transformer) build_map_index_if_value_guard_chain(if_node flat.Node, lhs_name string, info MapIndexInfo, target_name string, target_type string) []flat.NodeId {
    map_expr := t.stable_expr_for_reuse(info.base_id)
    key_name := t.new_temp('map_key')
    ptr_name := t.new_temp('map_ptr')
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    key_expr := t.transform_expr(info.key_id)
    mut result := []flat.NodeId{}
    t.drain_pending(mut result)
    result << t.make_decl_assign_typed(key_name, key_expr, info.key_type)
    result << t.make_decl_assign_typed(ptr_name, t.make_map_get_check_expr(map_expr,
        info.base_type, key_name), 'voidptr')
    ptr_ident := t.make_ident(ptr_name)
    found_cond := t.make_infix(.ne, ptr_ident, t.a.add(.nil_literal))

    saved_var_types := t.var_types.clone()
    mut then_children := []flat.NodeId{}
    if lhs_name != '_' {
        ptr_value := t.make_prefix(.mul, t.make_cast('&${info.value_type}', t.make_ident(ptr_name),
            '&${info.value_type}'))
        then_children << t.make_decl_assign_typed(lhs_name, ptr_value, info.value_type)
        t.set_var_type(lhs_name, info.value_type)
    }
    then_id := t.a.child(&if_node, 1)
    then_block0 := t.if_value_branch_block(then_id, target_name, target_type)
    then_children << t.a.children_of(&t.a.nodes[int(then_block0)])
    then_block := t.make_block(then_children)
    t.var_types = saved_var_types

    else_id := t.a.child(&if_node, 2)
    else_node := t.a.nodes[int(else_id)]
    else_block := if else_node.kind == .if_expr {
        t.make_block(t.build_if_value_chain(else_id, target_name, target_type))
    } else {
        t.if_value_branch_block(else_id, target_name, target_type)
    }
    t.pending_stmts = outer_pending
    result << t.make_if(found_cond, then_block, else_block)
    return result
}

// build_array_index_if_value_guard_chain supports build_array_index_if_value_guard_chain handling.
fn (mut t Transformer) build_array_index_if_value_guard_chain(if_node flat.Node, lhs_name string, info ArrayIndexInfo, target_name string, target_type string) []flat.NodeId {
    array_expr := t.stable_expr_for_reuse(info.base_id)
    index_name := t.new_temp('arr_idx')
    outer_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    index_expr := t.transform_expr(info.index_id)
    mut result := []flat.NodeId{}
    t.drain_pending(mut result)
    result << t.make_decl_assign_typed(index_name, index_expr, 'int')
    idx_ident := t.make_ident(index_name)
    lower_ok := t.make_infix(.ge, idx_ident, t.make_int_literal(0))
    upper_ok := t.make_infix(.lt, t.make_ident(index_name), t.make_selector(array_expr, 'len',
        'int'))
    found_cond := t.make_infix(.logical_and, lower_ok, upper_ok)

    saved_var_types := t.var_types.clone()
    mut then_children := []flat.NodeId{}
    mut opt_decl := flat.empty_node
    mut opt_name := ''
    if lhs_name != '_' {
        mut value_type := info.value_type
        mut value := t.make_index(array_expr, t.make_ident(index_name), info.value_type)
        if t.is_optional_type_name(info.value_type) {
            value_type = t.optional_base_type(t.qualify_optional_type(info.value_type))
            opt_name = t.new_temp('arr_opt')
            opt_decl = t.make_decl_assign_typed(opt_name, t.make_index(array_expr,
                t.make_ident(index_name), info.value_type), info.value_type)
            value = t.make_selector(t.make_ident(opt_name), 'value', value_type)
        }
        then_children << t.make_decl_assign_typed(lhs_name, value, value_type)
        t.set_var_type(lhs_name, value_type)
    } else if t.is_optional_type_name(info.value_type) {
        opt_name = t.new_temp('arr_opt')
        opt_decl = t.make_decl_assign_typed(opt_name, t.make_index(array_expr,
            t.make_ident(index_name), info.value_type), info.value_type)
    }
    then_id := t.a.child(&if_node, 1)
    then_block0 := t.if_value_branch_block(then_id, target_name, target_type)
    then_children << t.a.children_of(&t.a.nodes[int(then_block0)])
    then_block := t.make_block(then_children)
    t.var_types = saved_var_types

    else_id := t.a.child(&if_node, 2)
    else_node := t.a.nodes[int(else_id)]
    else_block := if else_node.kind == .if_expr {
        t.make_block(t.build_if_value_chain(else_id, target_name, target_type))
    } else {
        t.if_value_branch_block(else_id, target_name, target_type)
    }
    t.pending_stmts = outer_pending
    mut selected_block := then_block
    if t.is_optional_type_name(info.value_type) && opt_name.len > 0 {
        ok_cond := t.make_selector(t.make_ident(opt_name), 'ok', 'bool')
        inner_if := t.make_if(ok_cond, then_block, else_block)
        selected_block = t.make_block([opt_decl, inner_if])
    }
    result << t.make_if(found_cond, selected_block, else_block)
    return result
}

// if_value_branch_block supports if value branch block handling for Transformer.
fn (mut t Transformer) if_value_branch_block(branch_id flat.NodeId, target_name string, target_type string) flat.NodeId {
    if int(branch_id) < 0 {
        return t.make_block([]flat.NodeId{})
    }
    branch := t.a.nodes[int(branch_id)]
    if branch.kind == .if_expr {
        return t.make_block(t.build_if_value_chain(branch_id, target_name, target_type))
    }
    if branch.kind != .block {
        mut result := []flat.NodeId{}
        value := t.transform_if_branch_value(branch_id, target_type)
        t.drain_pending(mut result)
        result << t.make_assign(t.make_ident(target_name), value)
        return t.make_block(result)
    }
    if branch.children_count == 0 {
        return t.make_block([]flat.NodeId{})
    }

    mut stmt_ids := []flat.NodeId{cap: int(branch.children_count)}
    for i in 0 .. branch.children_count {
        stmt_ids << t.a.child(&branch, i)
    }
    mut result := []flat.NodeId{}
    if stmt_ids.len > 1 {
        for stmt in t.transform_stmts(stmt_ids[..stmt_ids.len - 1]) {
            result << stmt
        }
    }

    tail_id := stmt_ids[stmt_ids.len - 1]
    tail := t.a.nodes[int(tail_id)]
    if tail.kind == .return_stmt {
        tail_stmts := t.transform_stmt(tail_id)
        t.drain_pending(mut result)
        for stmt in tail_stmts {
            result << stmt
        }
        return t.make_block(result)
    }
    if tail.kind == .expr_stmt && tail.children_count > 0 {
        inner_id := t.a.child(&tail, 0)
        inner := t.a.nodes[int(inner_id)]
        if inner.kind == .call && t.is_noreturn_call(inner) {
            tail_stmts := t.transform_stmt(tail_id)
            t.drain_pending(mut result)
            for stmt in tail_stmts {
                result << stmt
            }
            return t.make_block(result)
        }
        if t.node_type(inner_id) == 'void' {
            tail_stmts := t.transform_stmt(tail_id)
            t.drain_pending(mut result)
            for stmt in tail_stmts {
                result << stmt
            }
            return t.make_block(result)
        }
        value := t.transform_if_branch_value(inner_id, target_type)
        t.drain_pending(mut result)
        result << t.make_assign(t.make_ident(target_name), value)
        return t.make_block(result)
    }
    if tail.kind == .block && t.stmt_value_type(tail_id).len > 0 {
        value := t.transform_if_branch_value(tail_id, target_type)
        t.drain_pending(mut result)
        result << t.make_assign(t.make_ident(target_name), value)
        return t.make_block(result)
    }
    if tail.kind == .match_stmt {
        value := t.transform_if_branch_value(tail_id, target_type)
        t.drain_pending(mut result)
        result << t.make_assign(t.make_ident(target_name), value)
        return t.make_block(result)
    }
    if tail.kind == .if_expr {
        value := t.transform_if_branch_value(tail_id, target_type)
        t.drain_pending(mut result)
        result << t.make_assign(t.make_ident(target_name), value)
        return t.make_block(result)
    }
    if t.is_stmt_kind(tail.kind) {
        tail_stmts := t.transform_stmt(tail_id)
        t.drain_pending(mut result)
        for stmt in tail_stmts {
            result << stmt
        }
        return t.make_block(result)
    }
    value := t.transform_if_branch_value(tail_id, target_type)
    t.drain_pending(mut result)
    result << t.make_assign(t.make_ident(target_name), value)
    return t.make_block(result)
}

// transform_if_branch_value transforms transform if branch value data for transform.
fn (mut t Transformer) transform_if_branch_value(id flat.NodeId, target_type string) flat.NodeId {
    if t.is_sum_type_name(target_type) {
        return t.wrap_sum_value(id, target_type)
    }
    if converted := t.fixed_array_value_to_dynamic(id, target_type) {
        return converted
    }
    return t.transform_expr_for_type(id, target_type)
}

// transform_is_condition transforms an `x is Type` condition node into the
// common sum-type tag comparison used by all C emission paths.
fn (mut t Transformer) transform_is_condition(cond_id flat.NodeId) flat.NodeId {
    if int(cond_id) < 0 {
        return cond_id
    }
    cond := t.a.nodes[int(cond_id)]
    if cond.kind != .is_expr {
        return cond_id
    }
    // is_expr: child[0] is the expression being checked, value is the type name.
    if cond.children_count < 1 {
        return cond_id
    }
    variant_name := cond.value
    if variant_name.len == 0 {
        return cond_id
    }
    return t.transform_is_expr(cond_id, cond)
}

// transform_and_chain_smartcasts handles conditions like
// `x is T && x.field > 0` where the second operand should see x
// narrowed to T through a smartcast.
//
// It walks a left-associative chain of .logical_and nodes. When a
// term is an is_expr it pushes a smartcast so subsequent terms
// (and the then-branch) see the narrowed type.
//
// Currently passes through unchanged but is structured to detect
// the pattern for future expansion.
fn (mut t Transformer) transform_and_chain_smartcasts(cond_id flat.NodeId) flat.NodeId {
    if int(cond_id) < 0 {
        return cond_id
    }
    cond := t.a.nodes[int(cond_id)]
    if cond.kind == .decl_assign {
        return t.transform_if_guard_condition(cond)
    }
    if cond.kind != .infix || cond.op !in [.logical_and, .logical_or] {
        // Not an && chain -- preserve bare smartcast checks and fully transform
        // ordinary conditions.
        if cond.kind == .is_expr {
            return t.transform_is_condition(cond_id)
        }
        return t.transform_expr(cond_id)
    }
    if cond.children_count < 2 {
        return cond_id
    }
    lhs_id := t.a.child(&cond, 0)
    rhs_id := t.a.child(&cond, 1)
    lhs := t.a.nodes[int(lhs_id)]
    new_lhs := t.transform_and_chain_smartcasts(lhs_id)
    lhs_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    lhs_smartcasts := if cond.op == .logical_and {
        t.extract_all_is_exprs(lhs_id)
    } else {
        []IsExprInfo{}
    }
    for info in lhs_smartcasts {
        t.push_smartcast(info.expr_name, info.variant_name, info.sum_type_name)
    }
    mut new_rhs := t.transform_and_chain_smartcasts(rhs_id)
    rhs_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()
    for _ in lhs_smartcasts {
        t.pop_smartcast()
    }
    // The left operand always evaluates, so its pending statements may run before
    // the `&&`/`||`. The right operand is conditional, so any statements its
    // lowering produced (e.g. an `in [...]` / `or {}` temporary) must run only when
    // the right operand is actually reached — wrap them in a `({ ...; value; })`
    // statement-expression to preserve short-circuit evaluation.
    for stmt in lhs_pending {
        t.pending_stmts << stmt
    }
    if rhs_pending.len > 0 {
        mut block_stmts := rhs_pending.clone()
        block_stmts << t.make_expr_stmt(new_rhs)
        new_rhs = t.make_block(block_stmts)
        t.a.nodes[int(new_rhs)].typ = 'bool'
    }
    if lhs.kind == .is_expr && new_lhs == lhs_id && new_rhs == rhs_id {
        return cond_id
    }
    return t.make_infix(cond.op, new_lhs, new_rhs)
}

// transform_if_guard_condition transforms transform if guard condition data for transform.
fn (mut t Transformer) transform_if_guard_condition(node flat.Node) flat.NodeId {
    if node.kind != .decl_assign || node.children_count < 2 {
        return flat.empty_node
    }
    mut new_children := []flat.NodeId{cap: int(node.children_count)}
    for i in 0 .. node.children_count {
        child_id := t.a.child(&node, i)
        if i == 1 {
            new_children << t.transform_expr(child_id)
        } else {
            new_children << t.transform_lvalue(child_id)
        }
    }
    start := t.a.children.len
    for child in new_children {
        t.a.children << child
    }
    return t.a.add_node(flat.Node{
        kind:           .decl_assign
        op:             node.op
        children_start: start
        children_count: flat.child_count(new_children.len)
        pos:            node.pos
        value:          node.value
        typ:            node.typ
    })
}

// transform_if_branches_with_smartcast is the main if-expr handler that
// integrates smartcasting. When the condition contains an is_expr, it
// pushes a smartcast for the then-branch, transforms the body under
// that context, pops the smartcast, then transforms the else-block.
fn (mut t Transformer) transform_if_branches_with_smartcast(id flat.NodeId, node flat.Node) flat.NodeId {
    if node.kind != .if_expr || node.children_count < 2 {
        return id
    }
    cond_id := t.a.child(&node, 0)
    then_id := t.a.child(&node, 1)
    has_else := node.children_count >= 3
    else_id := if has_else { t.a.child(&node, 2) } else { flat.empty_node }

    all_is := t.extract_all_is_exprs(cond_id)
    new_cond_id := t.transform_and_chain_smartcasts(cond_id)
    cond_pending := t.pending_stmts.clone()
    t.pending_stmts.clear()

    // Transform then-block children under the smartcast context.
    saved_var_types := t.var_types.clone()
    for info in all_is {
        t.push_smartcast(info.expr_name, info.variant_name, info.sum_type_name)
    }
    then_node := t.a.nodes[int(then_id)]
    mut new_then_id := then_id
    if then_node.kind == .block {
        child_ids := t.a.children_of(&then_node)
        new_children := t.transform_stmts(child_ids)
        block_start := t.a.children.len
        for c in new_children {
            t.a.children << c
        }
        new_then_id = t.a.add_node(flat.Node{
            kind:           .block
            children_start: block_start
            children_count: flat.child_count(new_children.len)
        })
    }

    for _ in all_is {
        t.pop_smartcast()
    }
    t.var_types = saved_var_types

    // Transform else-block (no smartcast -- the is_expr was false here).
    mut new_else_id := flat.empty_node
    if has_else {
        else_node := t.a.nodes[int(else_id)]
        if else_node.kind == .if_expr {
            // else-if chain: recurse.
            new_else_id = t.transform_else_if_expr(else_id, else_node)
        } else if else_node.kind == .block {
            child_ids := t.a.children_of(&else_node)
            new_children := t.transform_stmts(child_ids)
            block_start := t.a.children.len
            for c in new_children {
                t.a.children << c
            }
            new_else_id = t.a.add_node(flat.Node{
                kind:           .block
                children_start: block_start
                children_count: flat.child_count(new_children.len)
            })
        } else {
            new_else_id = else_id
        }
    }

    // Rebuild the if_expr with (possibly) new children.
    if_start := t.a.children.len
    t.a.children << new_cond_id
    t.a.children << new_then_id
    mut child_count := 2
    if has_else {
        t.a.children << new_else_id
        child_count = 3
    }
    new_if := t.a.add_node(flat.Node{
        kind:           .if_expr
        children_start: if_start
        children_count: flat.child_count(child_count)
        typ:            node.typ
        pos:            node.pos
    })
    for pending in cond_pending {
        t.pending_stmts << pending
    }
    return new_if
}

// --- helpers ---

// IsExprInfo stores is expr info metadata used by transform.
struct IsExprInfo {
    expr_name     string
    variant_name  string
    sum_type_name string
}

// extract_all_is_exprs supports extract all is exprs handling for Transformer.
fn (t &Transformer) extract_all_is_exprs(cond_id flat.NodeId) []IsExprInfo {
    mut result := []IsExprInfo{}
    t.collect_is_exprs(cond_id, mut result)
    return result
}

// collect_is_exprs updates collect is exprs state for transform.
fn (t &Transformer) collect_is_exprs(cond_id flat.NodeId, mut result []IsExprInfo) {
    if int(cond_id) < 0 {
        return
    }
    cond := t.a.nodes[int(cond_id)]
    if cond.kind == .is_expr && cond.children_count >= 1 {
        expr_id := t.a.child(&cond, 0)
        ek := t.expr_key(expr_id)
        if ek.len > 0 && cond.value.len > 0 {
            expr_type := t.original_expr_type(expr_id)
            stn := t.sum_type_for_is_expr(expr_type, cond.value)
            if stn.len > 0 {
                result << IsExprInfo{
                    expr_name:     ek
                    variant_name:  cond.value
                    sum_type_name: stn
                }
            } else {
                if t.is_interface_type_name(expr_type) {
                    result << IsExprInfo{
                        expr_name:     ek
                        variant_name:  cond.value
                        sum_type_name: expr_type
                    }
                }
            }
        }
    }
    if cond.kind == .infix && cond.op == .logical_and && cond.children_count >= 2 {
        t.collect_is_exprs(t.a.child(&cond, 0), mut result)
        t.collect_is_exprs(t.a.child(&cond, 1), mut result)
    }
}

// extract_is_expr supports extract is expr handling for Transformer.
fn (t &Transformer) extract_is_expr(cond_id flat.NodeId) IsExprInfo {
    if int(cond_id) < 0 {
        return IsExprInfo{}
    }
    cond := t.a.nodes[int(cond_id)]
    if cond.kind == .is_expr && cond.children_count >= 1 {
        expr_id := t.a.child(&cond, 0)
        ek := t.expr_key(expr_id)
        if ek.len > 0 && cond.value.len > 0 {
            expr_type := t.original_expr_type(expr_id)
            return IsExprInfo{
                expr_name:     ek
                variant_name:  cond.value
                sum_type_name: t.sum_type_for_is_expr(expr_type, cond.value)
            }
        }
    }
    if cond.kind == .infix && cond.op == .logical_and && cond.children_count >= 2 {
        // Check left side first (is_expr is typically on the left of &&).
        lhs_id := t.a.child(&cond, 0)
        info := t.extract_is_expr(lhs_id)
        if info.expr_name.len > 0 {
            return info
        }
        // Check right side as fallback.
        rhs_id := t.a.child(&cond, 1)
        return t.extract_is_expr(rhs_id)
    }
    return IsExprInfo{}
}

// sum_type_for_is_expr supports sum type for is expr handling for Transformer.
fn (t &Transformer) sum_type_for_is_expr(expr_type string, variant string) string {
    clean_expr_type := t.trim_pointer_type(expr_type)
    resolved_expr_sum := t.resolve_sum_name(clean_expr_type)
    if resolved_expr_sum in t.sum_types {
        if _ := t.sum_variant_name(resolved_expr_sum, variant) {
            return clean_expr_type
        }
    }
    return t.find_sum_type_for_variant(variant)
}

// find_sum_type_for_variant returns the sum type name that contains
// the given variant, or '' if none is found.
fn (t &Transformer) find_sum_type_for_variant(variant string) string {
    mut best := ''
    for sum_name, variants in t.sum_types {
        for v in variants {
            if t.variant_names_match(v, variant) {
                if sum_name.contains('.') {
                    return sum_name
                }
                if best.len == 0 {
                    best = sum_name
                }
            }
        }
    }
    return best
}