// FilterExpression and ProjectionExpression support
// FilterExpression:    post-retrieval filter applied to Scan/Query results
// ProjectionExpression: return only specified attributes from items
package dynamodb

import "core:encoding/json"
import "core:strconv"
import "core:strings"

// ============================================================================
// ProjectionExpression
//
// A comma-separated list of attribute names (with optional #name substitution)
// that specifies which attributes to return.
// ============================================================================

parse_projection_expression :: proc(
	request_body: []byte,
	attribute_names: Maybe(map[string]string),
) -> (paths: []string, ok: bool) {
	data, parse_err := json.parse(request_body, allocator = context.temp_allocator)
	if parse_err != nil {
		return nil, false
	}
	defer json.destroy_value(data)

	root, root_ok := data.(json.Object)
	if !root_ok {
		return nil, false
	}

	pe_val, found := root["ProjectionExpression"]
	if !found {
		return nil, false // absent is not an error, caller should check
	}

	pe_str, str_ok := pe_val.(json.String)
	if !str_ok {
		return nil, false
	}

	// Split by comma and resolve names
	parts := strings.split(string(pe_str), ",")
	result := make([dynamic]string)

	for part in parts {
		trimmed := strings.trim_space(part)
		if len(trimmed) == 0 {
			continue
		}

		resolved, res_ok := resolve_attribute_name(trimmed, attribute_names)
		if !res_ok {
			delete(result)
			return nil, false
		}
		append(&result, resolved)
	}

	return result[:], true
}

// Apply projection to a single item — returns a new item with only the specified attributes
apply_projection :: proc(item: Item, projection: []string) -> Item {
	if len(projection) == 0 {
		// No projection — return a deep copy of the full item
		return item_deep_copy(item)
	}

	projected := make(Item)
	for path in projection {
		if val, found := item[path]; found {
			projected[strings.clone(path)] = attr_value_deep_copy(val)
		}
	}
	return projected
}

// Deep copy an entire item
item_deep_copy :: proc(item: Item) -> Item {
	result := make(Item)
	for key, val in item {
		result[strings.clone(key)] = attr_value_deep_copy(val)
	}
	return result
}

// ============================================================================
// FilterExpression
//
// A condition expression applied post-retrieval. Supports:
//   - Comparisons:  path = :val,  path <> :val,  path < :val, etc.
//   - BETWEEN:      path BETWEEN :lo AND :hi
//   - IN:           path IN (:v1, :v2, :v3)
//   - begins_with:  begins_with(path, :prefix)
//   - contains:     contains(path, :substr)
//   - attribute_exists(path)
//   - attribute_not_exists(path)
//   - AND / OR / NOT combinators
//
// This is a recursive-descent parser for condition expressions.
// ============================================================================

// Parsed filter node (expression tree)
Filter_Node_Type :: enum {
	Comparison,        // path op value
	Between,           // path BETWEEN lo AND hi
	In,                // path IN (v1, v2, ...)
	Begins_With,       // begins_with(path, value)
	Contains,          // contains(path, value)
	Attribute_Exists,  // attribute_exists(path)
	Attribute_Not_Exists, // attribute_not_exists(path)
	And,               // left AND right
	Or,                // left OR right
	Not,               // NOT child
}

Comparison_Op :: enum {
	EQ,  // =
	NE,  // <>
	LT,  // <
	LE,  // <=
	GT,  // >
	GE,  // >=
}

Filter_Node :: struct {
	type:     Filter_Node_Type,
	// For Comparison
	path:     string,
	comp_op:  Comparison_Op,
	value:    Attribute_Value,
	// For Between
	value2:   Maybe(Attribute_Value),
	// For In
	in_values: []Attribute_Value,
	// For And/Or
	left:     ^Filter_Node,
	right:    ^Filter_Node,
	// For Not
	child:    ^Filter_Node,
}

filter_node_destroy :: proc(node: ^Filter_Node) {
	if node == nil {
		return
	}

	attr_value_destroy(&node.value)
	if v2, ok := node.value2.?; ok {
		v2_copy := v2
		attr_value_destroy(&v2_copy)
	}
	for &iv in node.in_values {
		attr_value_destroy(&iv)
	}
	if node.in_values != nil {
		delete(node.in_values)
	}

	if node.left != nil {
		filter_node_destroy(node.left)
		free(node.left)
	}
	if node.right != nil {
		filter_node_destroy(node.right)
		free(node.right)
	}
	if node.child != nil {
		filter_node_destroy(node.child)
		free(node.child)
	}
}

// ============================================================================
// Filter Expression Parser
// ============================================================================

parse_filter_expression :: proc(
	expression: string,
	attribute_names: Maybe(map[string]string),
	attribute_values: map[string]Attribute_Value,
) -> (node: ^Filter_Node, ok: bool) {
	t := tokenizer_init(expression)
	node, ok = parse_or_expr(&t, attribute_names, attribute_values)
	return
}

parse_or_expr :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	left, left_ok := parse_and_expr(t, names, values)
	if !left_ok {
		return nil, false
	}

	for {
		saved_pos := t.pos
		tok_maybe := tokenizer_next(t)
		tok, has := tok_maybe.?
		if !has {
			break
		}

		if strings.equal_fold(tok, "OR") {
			right, right_ok := parse_and_expr(t, names, values)
			if !right_ok {
				filter_node_destroy(left)
				free(left)
				return nil, false
			}

			parent := new(Filter_Node)
			parent.type = .Or
			parent.left = left
			parent.right = right
			left = parent
		} else {
			t.pos = saved_pos
			break
		}
	}

	return left, true
}

parse_and_expr :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	left, left_ok := parse_not_expr(t, names, values)
	if !left_ok {
		return nil, false
	}

	for {
		saved_pos := t.pos
		tok_maybe := tokenizer_next(t)
		tok, has := tok_maybe.?
		if !has {
			break
		}

		if strings.equal_fold(tok, "AND") {
			right, right_ok := parse_not_expr(t, names, values)
			if !right_ok {
				filter_node_destroy(left)
				free(left)
				return nil, false
			}

			parent := new(Filter_Node)
			parent.type = .And
			parent.left = left
			parent.right = right
			left = parent
		} else {
			t.pos = saved_pos
			break
		}
	}

	return left, true
}

parse_not_expr :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	saved_pos := t.pos
	tok_maybe := tokenizer_next(t)
	tok, has := tok_maybe.?
	if !has {
		return nil, false
	}

	if strings.equal_fold(tok, "NOT") {
		child, child_ok := parse_primary_expr(t, names, values)
		if !child_ok {
			return nil, false
		}
		node := new(Filter_Node)
		node.type = .Not
		node.child = child
		return node, true
	}

	t.pos = saved_pos
	return parse_primary_expr(t, names, values)
}

parse_primary_expr :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	first_tok, first_ok := next_token(t)
	if !first_ok {
		return nil, false
	}

	// Parenthesized expression
	if first_tok == "(" {
		inner, inner_ok := parse_or_expr(t, names, values)
		if !inner_ok {
			return nil, false
		}
		rparen, rp_ok := next_token(t)
		if !rp_ok || rparen != ")" {
			filter_node_destroy(inner)
			free(inner)
			return nil, false
		}
		return inner, true
	}

	// Function-style: begins_with, contains, attribute_exists, attribute_not_exists
	if strings.equal_fold(first_tok, "begins_with") {
		return parse_filter_begins_with(t, names, values)
	}
	if strings.equal_fold(first_tok, "contains") {
		return parse_filter_contains(t, names, values)
	}
	if strings.equal_fold(first_tok, "attribute_exists") {
		return parse_filter_attr_exists(t, names, true)
	}
	if strings.equal_fold(first_tok, "attribute_not_exists") {
		return parse_filter_attr_exists(t, names, false)
	}

	// Comparison, BETWEEN, or IN: path op value
	path, path_ok := resolve_attribute_name(first_tok, names)
	if !path_ok {
		return nil, false
	}

	op_tok, op_ok := next_token(t)
	if !op_ok {
		return nil, false
	}

	// BETWEEN
	if strings.equal_fold(op_tok, "BETWEEN") {
		return parse_filter_between(t, path, names, values)
	}

	// IN
	if strings.equal_fold(op_tok, "IN") {
		return parse_filter_in(t, path, names, values)
	}

	// Comparison operators
	comp_op: Comparison_Op
	if op_tok == "=" {
		comp_op = .EQ
	} else if op_tok == "<>" {
		comp_op = .NE
	} else if op_tok == "<" {
		comp_op = .LT
	} else if op_tok == "<=" {
		comp_op = .LE
	} else if op_tok == ">" {
		comp_op = .GT
	} else if op_tok == ">=" {
		comp_op = .GE
	} else {
		return nil, false
	}

	val_tok, vt_ok := next_token(t)
	if !vt_ok {
		return nil, false
	}
	val, val_ok := resolve_attribute_value(val_tok, values)
	if !val_ok {
		return nil, false
	}

	node := new(Filter_Node)
	node.type = .Comparison
	node.path = path
	node.comp_op = comp_op
	node.value = val
	return node, true
}

parse_filter_begins_with :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	lparen, lp_ok := next_token(t)
	if !lp_ok || lparen != "(" {
		return nil, false
	}

	path_tok, path_ok := next_token(t)
	if !path_ok {
		return nil, false
	}
	path, path_resolved := resolve_attribute_name(path_tok, names)
	if !path_resolved {
		return nil, false
	}

	comma, comma_ok := next_token(t)
	if !comma_ok || comma != "," {
		return nil, false
	}

	val_tok, vt_ok := next_token(t)
	if !vt_ok {
		return nil, false
	}
	val, val_ok := resolve_attribute_value(val_tok, values)
	if !val_ok {
		return nil, false
	}

	rparen, rp_ok := next_token(t)
	if !rp_ok || rparen != ")" {
		attr_value_destroy(&val)
		return nil, false
	}

	node := new(Filter_Node)
	node.type = .Begins_With
	node.path = path
	node.value = val
	return node, true
}

parse_filter_contains :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	lparen, lp_ok := next_token(t)
	if !lp_ok || lparen != "(" {
		return nil, false
	}

	path_tok, path_ok := next_token(t)
	if !path_ok {
		return nil, false
	}
	path, path_resolved := resolve_attribute_name(path_tok, names)
	if !path_resolved {
		return nil, false
	}

	comma, comma_ok := next_token(t)
	if !comma_ok || comma != "," {
		return nil, false
	}

	val_tok, vt_ok := next_token(t)
	if !vt_ok {
		return nil, false
	}
	val, val_ok := resolve_attribute_value(val_tok, values)
	if !val_ok {
		return nil, false
	}

	rparen, rp_ok := next_token(t)
	if !rp_ok || rparen != ")" {
		attr_value_destroy(&val)
		return nil, false
	}

	node := new(Filter_Node)
	node.type = .Contains
	node.path = path
	node.value = val
	return node, true
}

parse_filter_attr_exists :: proc(
	t: ^Tokenizer,
	names: Maybe(map[string]string),
	exists: bool,
) -> (^Filter_Node, bool) {
	lparen, lp_ok := next_token(t)
	if !lp_ok || lparen != "(" {
		return nil, false
	}

	path_tok, path_ok := next_token(t)
	if !path_ok {
		return nil, false
	}
	path, path_resolved := resolve_attribute_name(path_tok, names)
	if !path_resolved {
		return nil, false
	}

	rparen, rp_ok := next_token(t)
	if !rp_ok || rparen != ")" {
		return nil, false
	}

	node := new(Filter_Node)
	node.type = .Attribute_Exists if exists else .Attribute_Not_Exists
	node.path = path
	return node, true
}

parse_filter_between :: proc(
	t: ^Tokenizer,
	path: string,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	lo_tok, lo_ok := next_token(t)
	if !lo_ok {
		return nil, false
	}
	lo_val, lo_val_ok := resolve_attribute_value(lo_tok, values)
	if !lo_val_ok {
		return nil, false
	}

	and_tok, and_ok := next_token(t)
	if !and_ok || !strings.equal_fold(and_tok, "AND") {
		attr_value_destroy(&lo_val)
		return nil, false
	}

	hi_tok, hi_ok := next_token(t)
	if !hi_ok {
		attr_value_destroy(&lo_val)
		return nil, false
	}
	hi_val, hi_val_ok := resolve_attribute_value(hi_tok, values)
	if !hi_val_ok {
		attr_value_destroy(&lo_val)
		return nil, false
	}

	node := new(Filter_Node)
	node.type = .Between
	node.path = path
	node.value = lo_val
	node.value2 = hi_val
	return node, true
}

parse_filter_in :: proc(
	t: ^Tokenizer,
	path: string,
	names: Maybe(map[string]string),
	values: map[string]Attribute_Value,
) -> (^Filter_Node, bool) {
	lparen, lp_ok := next_token(t)
	if !lp_ok || lparen != "(" {
		return nil, false
	}

	in_vals := make([dynamic]Attribute_Value)

	for {
		val_tok, vt_ok := next_token(t)
		if !vt_ok {
			for &v in in_vals {
				attr_value_destroy(&v)
			}
			delete(in_vals)
			return nil, false
		}

		val, val_ok := resolve_attribute_value(val_tok, values)
		if !val_ok {
			for &v in in_vals {
				attr_value_destroy(&v)
			}
			delete(in_vals)
			return nil, false
		}
		append(&in_vals, val)

		sep_tok, sep_ok := next_token(t)
		if !sep_ok {
			for &v in in_vals {
				attr_value_destroy(&v)
			}
			delete(in_vals)
			return nil, false
		}
		if sep_tok == ")" {
			break
		}
		if sep_tok != "," {
			for &v in in_vals {
				attr_value_destroy(&v)
			}
			delete(in_vals)
			return nil, false
		}
	}

	node := new(Filter_Node)
	node.type = .In
	node.path = path
	node.in_values = in_vals[:]
	return node, true
}

// ============================================================================
// Filter Expression Evaluation
// ============================================================================

evaluate_filter :: proc(item: Item, node: ^Filter_Node) -> bool {
	if node == nil {
		return true
	}

	switch node.type {
	case .Comparison:
		attr, found := item[node.path]
		if !found {
			return false
		}
		return evaluate_comparison(attr, node.comp_op, node.value)

	case .Between:
		attr, found := item[node.path]
		if !found {
			return false
		}
		lo_cmp := compare_attribute_values(attr, node.value)
		if v2, ok := node.value2.?; ok {
			hi_cmp := compare_attribute_values(attr, v2)
			return lo_cmp >= 0 && hi_cmp <= 0
		}
		return false

	case .In:
		attr, found := item[node.path]
		if !found {
			return false
		}
		for in_val in node.in_values {
			if compare_attribute_values(attr, in_val) == 0 {
				return true
			}
		}
		return false

	case .Begins_With:
		attr, found := item[node.path]
		if !found {
			return false
		}
		attr_str, attr_ok := attr_value_to_string_for_compare(attr)
		val_str, val_ok := attr_value_to_string_for_compare(node.value)
		if !attr_ok || !val_ok {
			return false
		}
		return strings.has_prefix(attr_str, val_str)

	case .Contains:
		attr, found := item[node.path]
		if !found {
			return false
		}
		return evaluate_contains(attr, node.value)

	case .Attribute_Exists:
		_, found := item[node.path]
		return found

	case .Attribute_Not_Exists:
		_, found := item[node.path]
		return !found

	case .And:
		return evaluate_filter(item, node.left) && evaluate_filter(item, node.right)

	case .Or:
		return evaluate_filter(item, node.left) || evaluate_filter(item, node.right)

	case .Not:
		return !evaluate_filter(item, node.child)
	}

	return false
}

evaluate_comparison :: proc(attr: Attribute_Value, op: Comparison_Op, val: Attribute_Value) -> bool {
	cmp := compare_attribute_values(attr, val)

	switch op {
	case .EQ: return cmp == 0
	case .NE: return cmp != 0
	case .LT: return cmp < 0
	case .LE: return cmp <= 0
	case .GT: return cmp > 0
	case .GE: return cmp >= 0
	}
	return false
}

evaluate_contains :: proc(attr: Attribute_Value, val: Attribute_Value) -> bool {
	// For strings: substring check
	#partial switch a in attr {
	case String:
		if v, ok := val.(String); ok {
			return strings.contains(string(a), string(v))
		}

	case String_Set:
		if v, ok := val.(String); ok {
			for s in a {
				if s == string(v) {
					return true
				}
			}
		}

	case Number_Set:
		if v, ok := val.(Number); ok {
			for n in a {
				if n == string(v) {
					return true
				}
			}
		}

	case List:
		for item in a {
			if compare_attribute_values(item, val) == 0 {
				return true
			}
		}
	}

	return false
}

// Compare two AttributeValues. Returns <0, 0, or >0.
// For mixed types, returns -2 (not comparable).
compare_attribute_values :: proc(a: Attribute_Value, b: Attribute_Value) -> int {
	a_str, a_ok := attr_value_to_string_for_compare(a)
	b_str, b_ok := attr_value_to_string_for_compare(b)

	if !a_ok || !b_ok {
		// Try bool comparison
		a_bool, a_is_bool := a.(Bool)
		b_bool, b_is_bool := b.(Bool)
		if a_is_bool && b_is_bool {
			if bool(a_bool) == bool(b_bool) {
				return 0
			}
			return -2
		}
		return -2
	}

	// For Numbers, do numeric comparison
	_, a_is_num := a.(Number)
	_, b_is_num := b.(Number)
	if a_is_num && b_is_num {
		a_val, a_parse := strconv.parse_f64(a_str)
		b_val, b_parse := strconv.parse_f64(b_str)
		if a_parse && b_parse {
			if a_val < b_val {
				return -1
			}
			if a_val > b_val {
				return 1
			}
			return 0
		}
	}

	return strings.compare(a_str, b_str)
}

// ============================================================================
// Request parsing helpers for FilterExpression
// ============================================================================

parse_filter_expression_string :: proc(request_body: []byte) -> (expr: string, ok: bool) {
	data, parse_err := json.parse(request_body, allocator = context.temp_allocator)
	if parse_err != nil {
		return
	}
	defer json.destroy_value(data)

	root, root_ok := data.(json.Object)
	if !root_ok {
		return
	}

	fe_val, found := root["FilterExpression"]
	if !found {
		return
	}

	fe_str, str_ok := fe_val.(json.String)
	if !str_ok {
		return
	}

	expr = string(fe_str)
	ok = true
	return
}