canaad-core 0.1.0

//! JSON parsing with duplicate key detection.
//!
//! The standard `serde_json` library silently drops duplicate keys,
//! keeping only the last value. This module implements custom parsing
//! that detects and rejects duplicate keys per the AAD specification.

use crate::error::{AadError, JsonType};
use crate::types::{
    ExtensionValue, Extensions, FieldKey, Purpose, Resource, SafeInt, Tenant, RESERVED_KEYS,
};
use serde_json::{Map, Value};
use std::collections::HashSet;

/// Maximum serialized AAD size in bytes (16 KiB).
pub const MAX_AAD_SIZE: usize = 16 * 1024;

/// Current supported schema version.
pub const CURRENT_VERSION: u64 = 1;

/// Parsed AAD fields before full validation.
#[derive(Debug)]
pub struct ParsedAad {
    /// Schema version
    pub version: SafeInt,
    /// Tenant identifier
    pub tenant: Tenant,
    /// Resource path
    pub resource: Resource,
    /// Usage purpose
    pub purpose: Purpose,
    /// Optional timestamp
    pub timestamp: Option<SafeInt>,
    /// Extension fields
    pub extensions: Extensions,
}

/// Parses JSON with duplicate key detection.
///
/// This function manually scans the JSON to detect duplicate keys before
/// parsing with `serde_json`, since `serde_json` silently drops duplicates.
///
/// # Errors
///
/// Returns `DuplicateKey` if a duplicate key is found.
/// Returns `InvalidJson` if the JSON syntax is invalid.
pub fn parse_json_with_duplicate_check(json: &str) -> Result<Value, AadError> {
    check_for_duplicate_keys(json)?;
    serde_json::from_str(json).map_err(|e| AadError::InvalidJson { message: e.to_string() })
}

/// Checks for duplicate keys in a JSON string.
fn check_for_duplicate_keys(json: &str) -> Result<(), AadError> {
    let chars: Vec<char> = json.chars().collect();
    let mut i = 0;
    let mut key_stack: Vec<HashSet<String>> = Vec::new();

    while i < chars.len() {
        match chars[i] {
            '{' => {
                key_stack.push(HashSet::new());
                i += 1;
            }
            '}' => {
                key_stack.pop();
                i += 1;
            }
            '[' | ']' | ',' | ':' => {
                i += 1;
            }
            '"' => {
                let (s, end_pos) = parse_json_string(&chars, i)?;
                let mut j = end_pos;
                while j < chars.len() && chars[j].is_whitespace() {
                    j += 1;
                }
                if j < chars.len() && chars[j] == ':' {
                    if let Some(keys) = key_stack.last_mut() {
                        if !keys.insert(s.clone()) {
                            return Err(AadError::DuplicateKey { key: s });
                        }
                    }
                }
                i = end_pos;
            }
            c if c.is_whitespace() => {
                i += 1;
            }
            _ => {
                while i < chars.len()
                    && !matches!(chars[i], '{' | '}' | '[' | ']' | ',' | ':' | '"')
                    && !chars[i].is_whitespace()
                {
                    i += 1;
                }
            }
        }
    }
    Ok(())
}

/// Parses a JSON string starting at position `start` (which must be a '"').
fn parse_json_string(chars: &[char], start: usize) -> Result<(String, usize), AadError> {
    if chars.get(start) != Some(&'"') {
        return Err(AadError::InvalidJson { message: "expected string".to_string() });
    }

    let mut result = String::new();
    let mut i = start + 1;

    while i < chars.len() {
        match chars[i] {
            '"' => return Ok((result, i + 1)),
            '\\' => {
                i = parse_escape_sequence(chars, i, &mut result)?;
            }
            c => {
                result.push(c);
                i += 1;
            }
        }
    }

    Err(AadError::InvalidJson { message: "unterminated string".to_string() })
}

/// Parses an escape sequence starting at backslash position.
fn parse_escape_sequence(
    chars: &[char],
    backslash_pos: usize,
    result: &mut String,
) -> Result<usize, AadError> {
    let i = backslash_pos;
    if i + 1 >= chars.len() {
        return Err(AadError::InvalidJson { message: "unterminated escape sequence".to_string() });
    }

    let mut pos = i + 1;
    match chars[pos] {
        '"' => result.push('"'),
        '\\' => result.push('\\'),
        '/' => result.push('/'),
        'b' => result.push('\x08'),
        'f' => result.push('\x0c'),
        'n' => result.push('\n'),
        'r' => result.push('\r'),
        't' => result.push('\t'),
        'u' => {
            pos = parse_unicode_escape(chars, pos, result)?;
            return Ok(pos);
        }
        c => {
            return Err(AadError::InvalidJson {
                message: format!("invalid escape sequence: \\{c}"),
            });
        }
    }
    Ok(pos + 1)
}

/// Parses a unicode escape sequence (\uXXXX).
fn parse_unicode_escape(
    chars: &[char],
    u_pos: usize,
    result: &mut String,
) -> Result<usize, AadError> {
    if u_pos + 4 >= chars.len() {
        return Err(AadError::InvalidJson { message: "invalid unicode escape".to_string() });
    }

    let hex: String = chars[u_pos + 1..u_pos + 5].iter().collect();
    let code_point = u16::from_str_radix(&hex, 16).map_err(|_| AadError::InvalidJson {
        message: format!("invalid unicode escape: \\u{hex}"),
    })?;

    // Handle surrogate pairs
    if (0xD800..=0xDBFF).contains(&code_point) {
        if let Some(cp) = try_parse_surrogate_pair(chars, u_pos, code_point) {
            if let Some(c) = char::from_u32(cp) {
                result.push(c);
                return Ok(u_pos + 11);
            }
        }
    }

    // Regular BMP character
    if let Some(c) = char::from_u32(u32::from(code_point)) {
        result.push(c);
    } else {
        use std::fmt::Write;
        let _ = write!(result, "\\u{hex}");
    }
    Ok(u_pos + 5)
}

/// Tries to parse a surrogate pair, returning the combined code point if successful.
fn try_parse_surrogate_pair(chars: &[char], u_pos: usize, high: u16) -> Option<u32> {
    if u_pos + 10 >= chars.len() {
        return None;
    }
    if chars[u_pos + 5] != '\\' || chars[u_pos + 6] != 'u' {
        return None;
    }

    let hex2: String = chars[u_pos + 7..u_pos + 11].iter().collect();
    let low = u16::from_str_radix(&hex2, 16).ok()?;

    if !(0xDC00..=0xDFFF).contains(&low) {
        return None;
    }

    let high = u32::from(high);
    let low = u32::from(low);
    Some(0x10000 + ((high - 0xD800) << 10) + (low - 0xDC00))
}

/// Parses and validates an AAD JSON object.
///
/// This function:
/// 1. Checks for duplicate keys
/// 2. Parses the JSON
/// 3. Validates all fields according to the AAD spec
///
/// # Errors
///
/// Returns an error if the JSON is invalid, contains duplicate keys,
/// or violates any AAD specification constraints.
pub fn parse_aad(json: &str) -> Result<ParsedAad, AadError> {
    if json.len() > MAX_AAD_SIZE {
        return Err(AadError::SerializedTooLarge {
            max_bytes: MAX_AAD_SIZE,
            actual_bytes: json.len(),
        });
    }

    let value = parse_json_with_duplicate_check(json)?;
    let obj = value.as_object().ok_or_else(|| AadError::InvalidJson {
        message: "AAD must be a JSON object".to_string(),
    })?;

    let version = extract_version(obj)?;
    validate_field_names(obj)?;

    let tenant = extract_string_field(obj, "tenant").and_then(Tenant::new)?;
    let resource = extract_string_field(obj, "resource").and_then(Resource::new)?;
    let purpose = extract_string_field(obj, "purpose").and_then(Purpose::new)?;
    let timestamp = extract_optional_timestamp(obj)?;
    let extensions = extract_extensions(obj)?;

    Ok(ParsedAad { version, tenant, resource, purpose, timestamp, extensions })
}

/// Extracts and validates the version field.
fn extract_version(obj: &Map<String, Value>) -> Result<SafeInt, AadError> {
    match obj.get("v") {
        None => Err(AadError::MissingRequiredField { field: "v" }),
        Some(v) => {
            let n = v.as_u64().ok_or_else(|| AadError::WrongFieldType {
                field: "v",
                expected: "integer",
                actual: JsonType::from(v),
            })?;
            if n != CURRENT_VERSION {
                return Err(AadError::UnsupportedVersion { version: n });
            }
            SafeInt::new(n)
        }
    }
}

/// Validates all field names in the object.
fn validate_field_names(obj: &Map<String, Value>) -> Result<(), AadError> {
    for key in obj.keys() {
        if RESERVED_KEYS.contains(&key.as_str()) {
            continue;
        }
        let field_key = FieldKey::new(key.clone()).map_err(|_| AadError::InvalidFieldKey {
            key: key.clone(),
            reason: "field keys must match pattern [a-z_]+".to_string(),
        })?;
        if !key.starts_with("x_") {
            return Err(AadError::UnknownField { field: key.clone(), version: CURRENT_VERSION });
        }
        field_key.validate_as_extension()?;
    }
    Ok(())
}

/// Extracts a required string field.
fn extract_string_field(obj: &Map<String, Value>, field: &'static str) -> Result<String, AadError> {
    obj.get(field).map_or_else(
        || Err(AadError::MissingRequiredField { field }),
        |v| {
            v.as_str().map(String::from).ok_or_else(|| AadError::WrongFieldType {
                field,
                expected: "string",
                actual: JsonType::from(v),
            })
        },
    )
}

/// Extracts the optional timestamp field.
fn extract_optional_timestamp(obj: &Map<String, Value>) -> Result<Option<SafeInt>, AadError> {
    match obj.get("ts") {
        None => Ok(None),
        Some(v) => {
            let n = v.as_u64().ok_or_else(|| {
                v.as_i64().map_or_else(
                    || AadError::WrongFieldType {
                        field: "ts",
                        expected: "integer",
                        actual: JsonType::from(v),
                    },
                    |i| AadError::NegativeInteger { value: i },
                )
            })?;
            Ok(Some(SafeInt::new(n)?))
        }
    }
}

/// Extracts all extension fields.
fn extract_extensions(obj: &Map<String, Value>) -> Result<Extensions, AadError> {
    let mut extensions = Extensions::new();
    for (key, value) in obj {
        if key.starts_with("x_") {
            let field_key = FieldKey::new(key)?;
            field_key.validate_as_extension()?;
            let ext_value = parse_extension_value(value)?;
            extensions.insert(field_key, ext_value);
        }
    }
    Ok(extensions)
}

/// Parses an extension value (string or integer).
fn parse_extension_value(value: &Value) -> Result<ExtensionValue, AadError> {
    match value {
        Value::String(s) => ExtensionValue::string(s),
        Value::Number(n) => n.as_u64().map_or_else(
            || {
                n.as_i64().map_or_else(
                    || {
                        Err(AadError::WrongFieldType {
                            field: "extension",
                            expected: "string or integer",
                            actual: JsonType::Number,
                        })
                    },
                    |i| Err(AadError::NegativeInteger { value: i }),
                )
            },
            ExtensionValue::integer,
        ),
        _ => Err(AadError::WrongFieldType {
            field: "extension",
            expected: "string or integer",
            actual: JsonType::from(value),
        }),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_valid_minimal() {
        let json = r#"{"v":1,"tenant":"org_abc","resource":"secrets/db","purpose":"encryption"}"#;
        let result = parse_aad(json);
        assert!(result.is_ok());

        let aad = result.unwrap();
        assert_eq!(aad.version.value(), 1);
        assert_eq!(aad.tenant.as_str(), "org_abc");
        assert_eq!(aad.resource.as_str(), "secrets/db");
        assert_eq!(aad.purpose.as_str(), "encryption");
        assert!(aad.timestamp.is_none());
        assert!(aad.extensions.is_empty());
    }

    #[test]
    fn test_parse_with_timestamp() {
        let json = r#"{"v":1,"tenant":"org","resource":"res","purpose":"test","ts":1706400000}"#;
        let result = parse_aad(json);
        assert!(result.is_ok());

        let aad = result.unwrap();
        assert_eq!(aad.timestamp.unwrap().value(), 1_706_400_000);
    }

    #[test]
    fn test_parse_with_extension() {
        let json = r#"{"v":1,"tenant":"org","resource":"res","purpose":"test","x_vault_cluster":"us-east-1"}"#;
        let result = parse_aad(json);
        assert!(result.is_ok());

        let aad = result.unwrap();
        assert_eq!(aad.extensions.len(), 1);
    }

    #[test]
    fn test_duplicate_key_detection() {
        let json = r#"{"v":1,"tenant":"org","tenant":"other","resource":"res","purpose":"test"}"#;
        let result = parse_aad(json);
        assert!(matches!(result, Err(AadError::DuplicateKey { key }) if key == "tenant"));
    }

    #[test]
    fn test_missing_required_field() {
        let json = r#"{"v":1,"tenant":"org","resource":"res"}"#;
        let result = parse_aad(json);
        assert!(matches!(result, Err(AadError::MissingRequiredField { field: "purpose" })));
    }

    #[test]
    fn test_unknown_field() {
        let json = r#"{"v":1,"tenant":"org","resource":"res","purpose":"test","unknown":"value"}"#;
        let result = parse_aad(json);
        assert!(
            matches!(result, Err(AadError::UnknownField { field, version: 1 }) if field == "unknown")
        );
    }

    #[test]
    fn test_invalid_extension_key() {
        let json = r#"{"v":1,"tenant":"org","resource":"res","purpose":"test","x_foo":"value"}"#;
        let result = parse_aad(json);
        assert!(matches!(result, Err(AadError::InvalidExtensionKeyFormat { .. })));
    }

    #[test]
    fn test_unsupported_version() {
        let json = r#"{"v":2,"tenant":"org","resource":"res","purpose":"test"}"#;
        let result = parse_aad(json);
        assert!(matches!(result, Err(AadError::UnsupportedVersion { version: 2 })));
    }

    #[test]
    fn test_wrong_field_type() {
        let json = r#"{"v":"1","tenant":"org","resource":"res","purpose":"test"}"#;
        let result = parse_aad(json);
        assert!(matches!(
            result,
            Err(AadError::WrongFieldType { field: "v", expected: "integer", .. })
        ));
    }

    #[test]
    fn test_integer_out_of_range() {
        let json =
            r#"{"v":1,"tenant":"org","resource":"res","purpose":"test","ts":9007199254740992}"#;
        let result = parse_aad(json);
        assert!(matches!(result, Err(AadError::IntegerOutOfRange { .. })));
    }

    #[test]
    fn test_size_limit() {
        let big_resource = "x".repeat(MAX_AAD_SIZE + 1);
        let json =
            format!(r#"{{"v":1,"tenant":"org","resource":"{}","purpose":"test"}}"#, big_resource);
        let result = parse_aad(&json);
        assert!(matches!(result, Err(AadError::SerializedTooLarge { .. })));
    }

    #[test]
    fn test_unicode_escapes() {
        let json = r#"{"v":1,"tenant":"test\u0041","resource":"res","purpose":"test"}"#;
        let result = parse_aad(json);
        assert!(result.is_ok());
    }

    #[test]
    fn test_nested_duplicate_not_relevant() {
        let json = r#"{"v":1}"#;
        let result = parse_json_with_duplicate_check(json);
        assert!(result.is_ok());
    }
}