// DynamoDB Expression Parser
// Parses KeyConditionExpression with ExpressionAttributeNames and ExpressionAttributeValues
// Supports: pk = :pk, pk = :pk AND sk > :sk, begins_with(sk, :prefix), BETWEEN, etc.
package dynamodb

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

// ============================================================================
// Sort Key Condition Operators
// ============================================================================

Sort_Key_Operator :: enum {
	EQ,          // =
	LT,          // <
	LE,          // <=
	GT,          // >
	GE,          // >=
	BETWEEN,     // BETWEEN x AND y
	BEGINS_WITH, // begins_with(sk, prefix)
}

// ============================================================================
// Parsed Structures
// ============================================================================

Sort_Key_Condition :: struct {
	sk_name:  string,
	operator: Sort_Key_Operator,
	value:    Attribute_Value,
	value2:   Maybe(Attribute_Value),
}

sort_key_condition_destroy :: proc(skc: ^Sort_Key_Condition) {
	delete(skc.sk_name)  // Free the cloned string
	attr_value_destroy(&skc.value)
	if v2, ok := skc.value2.?; ok {
		v2_copy := v2
		attr_value_destroy(&v2_copy)
	}
}

Key_Condition :: struct {
	pk_name:      string,
	pk_value:     Attribute_Value,
	sk_condition: Maybe(Sort_Key_Condition),
}

key_condition_destroy :: proc(kc: ^Key_Condition) {
	delete(kc.pk_name)  // Free the cloned string
	attr_value_destroy(&kc.pk_value)
	if skc, ok := kc.sk_condition.?; ok {
		skc_copy := skc
		sort_key_condition_destroy(&skc_copy)
	}
}

// Get the raw partition key value bytes for building storage keys
key_condition_get_pk_bytes :: proc(kc: ^Key_Condition) -> ([]byte, bool) {
	#partial switch v in kc.pk_value {
	case String:
		return transmute([]byte)string(v), true
	case DDB_Number:
		// Use canonical encoding for numbers in keys!
		return encode_ddb_number_for_sort(v), true
	case Binary:
		return transmute([]byte)string(v), true
	}
	return nil, false
}

// ============================================================================
// Tokenizer
// ============================================================================

Tokenizer :: struct {
	input: string,
	pos:   int,
}

tokenizer_init :: proc(input: string) -> Tokenizer {
	return Tokenizer{input = input, pos = 0}
}

tokenizer_next :: proc(t: ^Tokenizer) -> Maybe(string) {
	// Skip whitespace
	for t.pos < len(t.input) && is_whitespace(t.input[t.pos]) {
		t.pos += 1
	}

	if t.pos >= len(t.input) {
		return nil
	}

	start := t.pos
	c := t.input[t.pos]

	// Single-character tokens
	if c == '(' || c == ')' || c == ',' {
		t.pos += 1
		return t.input[start:t.pos]
	}

	// Two-character operators
	if t.pos + 1 < len(t.input) {
		two := t.input[t.pos:t.pos + 2]
		if two == "<=" || two == ">=" || two == "<>" {
			t.pos += 2
			return two
		}
	}

	// Single-character operators
	if c == '=' || c == '<' || c == '>' {
		t.pos += 1
		return t.input[start:t.pos]
	}

	// Identifier or keyword (includes :placeholder and #name)
	for t.pos < len(t.input) && is_ident_char(t.input[t.pos]) {
		t.pos += 1
	}

	if t.pos > start {
		return t.input[start:t.pos]
	}

	// Unknown character, skip it
	t.pos += 1
	return tokenizer_next(t)
}

@(private = "file")
is_whitespace :: proc(c: byte) -> bool {
	return c == ' ' || c == '\t' || c == '\n' || c == '\r'
}

@(private = "file")
is_ident_char :: proc(c: byte) -> bool {
	return (c >= 'a' && c <= 'z') ||
	       (c >= 'A' && c <= 'Z') ||
	       (c >= '0' && c <= '9') ||
	       c == '_' || c == ':' || c == '#' || c == '-' || c == '.'
}

// ---------------------------------------------------------------------------
// Helper: convert Maybe(string) tokens into (string, bool) so or_return works.
// ---------------------------------------------------------------------------

// Package-visible: used by update.odin and filter.odin
next_token :: proc(t: ^Tokenizer) -> (tok: string, ok: bool) {
	if v, has := tokenizer_next(t).?; has {
		tok = v
		ok = true
		return
	}
	return
}

// ============================================================================
// Expression Parsing
// ============================================================================

parse_key_condition_expression :: proc(
	expression: string,
	attribute_names: Maybe(map[string]string),
	attribute_values: map[string]Attribute_Value,
) -> (kc: Key_Condition, ok: bool) {
	t := tokenizer_init(expression)

	pk_name_token := next_token(&t) or_return
	pk_name_unowned := resolve_attribute_name(pk_name_token, attribute_names) or_return
	pk_name := strings.clone(pk_name_unowned)  // Clone for safe storage

	eq_token := next_token(&t) or_return
	if eq_token != "=" {
		delete(pk_name) // free on error
		return
	}

	pk_value_token := next_token(&t) or_return
	pk_value, pk_ok := resolve_attribute_value(pk_value_token, attribute_values)
	if !pk_ok {
		delete(pk_name) // free on error
		return
	}

	sk_condition: Maybe(Sort_Key_Condition) = nil

	// Optional "AND ..."
	if and_token, has_and := tokenizer_next(&t).?; has_and {
		if !strings.equal_fold(and_token, "AND") {
			delete(pk_name) // free on error
			attr_value_destroy(&pk_value)
			return
		}

		skc, skc_ok := parse_sort_key_condition(&t, attribute_names, attribute_values)
		if !skc_ok {
			delete(pk_name) // free on error
			attr_value_destroy(&pk_value)
			return
		}
		sk_condition = skc
	}

	// Verify all tokens were consumed (no trailing garbage)
	if trailing := tokenizer_next(&t); trailing != nil {
		delete(pk_name)
		attr_value_destroy(&pk_value)
		if skc, has_skc := sk_condition.?; has_skc {
			skc_copy := skc
			sort_key_condition_destroy(&skc_copy)
		}
		return
	}

	kc = Key_Condition{
		pk_name      = pk_name,
		pk_value     = pk_value,
		sk_condition = sk_condition,
	}
	ok = true
	return
}

@(private = "file")
parse_sort_key_condition :: proc(
	t: ^Tokenizer,
	attribute_names: Maybe(map[string]string),
	attribute_values: map[string]Attribute_Value,
) -> (skc: Sort_Key_Condition, ok: bool) {
	first_token := next_token(t) or_return

	if strings.equal_fold(first_token, "begins_with") {
		skc, ok = parse_begins_with(t, attribute_names, attribute_values)
		return
	}

	sk_name_unowned := resolve_attribute_name(first_token, attribute_names) or_return
	sk_name := strings.clone(sk_name_unowned)  // Clone for safe storage

	op_token := next_token(t) or_return
	operator, op_ok := parse_operator(op_token)
	if !op_ok {
		delete(sk_name)  // free on error
		return
	}

	value_token := next_token(t) or_return
	value, val_ok := resolve_attribute_value(value_token, attribute_values)
	if !val_ok {
		delete(sk_name)  // free on error
		return
	}

	value2: Maybe(Attribute_Value) = nil
	if operator == .BETWEEN {
		// IMPORTANT: after allocating `value`, do NOT use `or_return` without cleanup.
		and_token, tok_ok := next_token(t)
		if !tok_ok || !strings.equal_fold(and_token, "AND") {
			delete(sk_name)  // free on error
			attr_value_destroy(&value)
			return
		}

		value2_token, tok2_ok := next_token(t)
		if !tok2_ok {
			delete(sk_name)  // free on error
			attr_value_destroy(&value)
			return
		}

		v2, v2_ok := resolve_attribute_value(value2_token, attribute_values)
		if !v2_ok {
			delete(sk_name)  // free on error
			attr_value_destroy(&value)
			return
		}
		value2 = v2
	}

	skc = Sort_Key_Condition{
		sk_name  = sk_name,
		operator = operator,
		value    = value,
		value2   = value2,
	}
	ok = true
	return
}

@(private = "file")
parse_begins_with :: proc(
	t: ^Tokenizer,
	attribute_names: Maybe(map[string]string),
	attribute_values: map[string]Attribute_Value,
) -> (skc: Sort_Key_Condition, ok: bool) {
	lparen := next_token(t) or_return
	if lparen != "(" {
		return
	}

	sk_name_token := next_token(t) or_return
	sk_name_unowned := resolve_attribute_name(sk_name_token, attribute_names) or_return
	sk_name := strings.clone(sk_name_unowned)  // Clone for safe storage

	comma := next_token(t) or_return
	if comma != "," {
		delete(sk_name)  // free on error
		return
	}

	value_token := next_token(t) or_return
	value, val_ok := resolve_attribute_value(value_token, attribute_values)
	if !val_ok {
		delete(sk_name)  // free on error
		return
	}

	// after allocating `value`, avoid `or_return` so we can clean up
	rparen, tok_ok := next_token(t)
	if !tok_ok || rparen != ")" {
		delete(sk_name)  // free on error
		attr_value_destroy(&value)
		return
	}

	skc = Sort_Key_Condition{
		sk_name  = sk_name,
		operator = .BEGINS_WITH,
		value    = value,
		value2   = nil,
	}
	ok = true
	return
}

@(private = "file")
parse_operator :: proc(token: string) -> (Sort_Key_Operator, bool) {
	if token == "=" do return .EQ, true
	if token == "<" do return .LT, true
	if token == "<=" do return .LE, true
	if token == ">" do return .GT, true
	if token == ">=" do return .GE, true
	if strings.equal_fold(token, "BETWEEN") do return .BETWEEN, true
	return .EQ, false
}

// Package-visible: used by update.odin and filter.odin
resolve_attribute_name :: proc(token: string, names: Maybe(map[string]string)) -> (string, bool) {
	if len(token) > 0 && token[0] == '#' {
		if n, has_names := names.?; has_names {
			if resolved, found := n[token]; found {
				return resolved, true
			}
		}
		return "", false
	}
	return token, true
}

// Package-visible: used by update.odin and filter.odin
resolve_attribute_value :: proc(
	token: string,
	values: map[string]Attribute_Value,
) -> (Attribute_Value, bool) {
	if len(token) > 0 && token[0] == ':' {
		if original, found := values[token]; found {
			return attr_value_deep_copy(original), true
		}
		return nil, false
	}
	return nil, false
}

// ============================================================================
// Request Parsing Helpers
// ============================================================================

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

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

	names_val, found := root["ExpressionAttributeNames"]
	if !found {
		return nil
	}

	names_obj, names_ok := names_val.(json.Object)
	if !names_ok {
		return nil
	}

	result := make(map[string]string)

	for key, val in names_obj {
		str, str_ok := val.(json.String)
		if !str_ok {
			continue
		}
		result[strings.clone(key)] = strings.clone(string(str))
	}

	return result
}

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

	root, ok := data.(json.Object)
	if !ok {
		return make(map[string]Attribute_Value), false
	}

	values_val, found := root["ExpressionAttributeValues"]
	if !found {
		return make(map[string]Attribute_Value), true
	}

	values_obj, values_ok := values_val.(json.Object)
	if !values_ok {
		return make(map[string]Attribute_Value), false
	}

	result := make(map[string]Attribute_Value)

	for key, val in values_obj {
		attr, attr_ok := parse_attribute_value(val)
		if !attr_ok {
			continue
		}
		result[strings.clone(key)] = attr
	}

	return result, true
}

// ============================================================================
// FIX: Use JSON object lookup instead of fragile string scanning.
// This handles whitespace, field ordering, and escape sequences correctly.
// ============================================================================
parse_key_condition_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
	}

	kce_val, found := root["KeyConditionExpression"]
	if !found {
		return
	}

	kce_str, str_ok := kce_val.(json.String)
	if !str_ok {
		return
	}

	expr = string(kce_str)
	ok = true
	return
}

// Convenience: parse a complete Query key condition from request body
parse_query_key_condition :: proc(request_body: []byte) -> (kc: Key_Condition, ok: bool) {
	expression := parse_key_condition_expression_string(request_body) or_return

	attr_names := parse_expression_attribute_names(request_body)
	defer {
		if names, has_names := attr_names.?; has_names {
			for k, v in names {
				delete(k)
				delete(v)
			}
			names_copy := names
			delete(names_copy)
		}
	}

	attr_values, vals_ok := parse_expression_attribute_values(request_body)
	if !vals_ok {
		return
	}
	defer {
		for k, v in attr_values {
			delete(k)
			v_copy := v
			attr_value_destroy(&v_copy)
		}
		delete(attr_values)
	}

	kc, ok = parse_key_condition_expression(expression, attr_names, attr_values)
	return
}