//! Input validation for GraphQL mutations and queries.
//!
//! This module provides the validation pipeline that processes GraphQL input
//! variables and validates them against defined validation rules before
//! execution.

use serde_json::Value;

use crate::{
    error::{FraiseQLError, Result, ValidationFieldError},
    schema::CompiledSchema,
    validation::ValidationRule,
};

/// Validation error aggregator - collects multiple validation errors.
#[derive(Debug, Clone, Default)]
pub struct ValidationErrorCollection {
    /// All collected validation errors.
    pub errors: Vec<ValidationFieldError>,
}

impl ValidationErrorCollection {
    /// Create a new empty error collection.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Add an error to the collection.
    pub fn add_error(&mut self, error: ValidationFieldError) {
        self.errors.push(error);
    }

    /// Check if there are any errors.
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        self.errors.is_empty()
    }

    /// Get the number of errors.
    #[must_use]
    pub const fn len(&self) -> usize {
        self.errors.len()
    }

    /// Convert to a FraiseQL error.
    #[must_use]
    pub fn to_error(&self) -> FraiseQLError {
        if self.errors.is_empty() {
            FraiseQLError::validation("No validation errors")
        } else if self.errors.len() == 1 {
            let err = &self.errors[0];
            FraiseQLError::Validation {
                message: err.to_string(),
                path:    Some(err.field.clone()),
            }
        } else {
            let messages: Vec<String> = self.errors.iter().map(|e| e.to_string()).collect();
            FraiseQLError::Validation {
                message: format!("Multiple validation errors: {}", messages.join("; ")),
                path:    None,
            }
        }
    }
}

/// Validate a scalar value against a custom scalar type definition.
///
/// This function validates a JSON value against a custom scalar type registered
/// in the schema, checking both validation rules and ELO expressions.
///
/// # Arguments
///
/// * `value` - The JSON value to validate
/// * `scalar_type_name` - Name of the custom scalar type (e.g., "`LibraryCode`")
/// * `schema` - The compiled schema containing custom scalar definitions
///
/// # Errors
///
/// Returns a validation error if the value doesn't match the custom scalar definition.
pub fn validate_custom_scalar_from_schema(
    value: &Value,
    scalar_type_name: &str,
    schema: &CompiledSchema,
) -> Result<()> {
    // Check if this is a custom scalar type
    if schema.custom_scalars.exists(scalar_type_name) {
        schema.custom_scalars.validate(scalar_type_name, value)
    } else {
        // Not a custom scalar, pass through (built-in type)
        Ok(())
    }
}

/// Validate JSON input against validation rules.
///
/// This function recursively validates a JSON value against a set of
/// validation rules, collecting all errors that occur.
///
/// # Errors
///
/// Returns [`FraiseQLError::Validation`] if any rule is violated (e.g., string
/// too short, value out of range, or a required field is null).
pub fn validate_input(value: &Value, field_path: &str, rules: &[ValidationRule]) -> Result<()> {
    let mut errors = ValidationErrorCollection::new();

    match value {
        Value::String(s) => {
            for rule in rules {
                if let Err(FraiseQLError::Validation { message, .. }) =
                    validate_string_field(s, field_path, rule)
                {
                    if let Some(field_err) = extract_field_error(&message) {
                        errors.add_error(field_err);
                    }
                }
            }
        },
        Value::Null => {
            for rule in rules {
                if rule.is_required() {
                    errors.add_error(ValidationFieldError::new(
                        field_path,
                        "required",
                        "Field is required",
                    ));
                }
            }
        },
        _ => {
            // Other types (number, bool, array, object) have different validation logic
        },
    }

    if errors.is_empty() {
        Ok(())
    } else {
        Err(errors.to_error())
    }
}

/// Validate a string field against a validation rule.
pub(crate) fn validate_string_field(
    value: &str,
    field_path: &str,
    rule: &ValidationRule,
) -> Result<()> {
    match rule {
        ValidationRule::Required => {
            if value.is_empty() {
                return Err(FraiseQLError::Validation {
                    message: format!(
                        "Field validation failed: {}",
                        ValidationFieldError::new(field_path, "required", "Field is required")
                    ),
                    path:    Some(field_path.to_string()),
                });
            }
            Ok(())
        },
        ValidationRule::Pattern { pattern, message } => {
            if pattern.is_match(value) {
                Ok(())
            } else {
                let msg = message.clone().unwrap_or_else(|| "Pattern mismatch".to_string());
                Err(FraiseQLError::Validation {
                    message: format!(
                        "Field validation failed: {}",
                        ValidationFieldError::new(field_path, "pattern", msg)
                    ),
                    path:    Some(field_path.to_string()),
                })
            }
        },
        ValidationRule::Length { min, max } => {
            let len = value.len();
            let valid = if let Some(m) = min { len >= *m } else { true }
                && if let Some(m) = max { len <= *m } else { true };

            if valid {
                Ok(())
            } else {
                let msg = match (min, max) {
                    (Some(m), Some(x)) => format!("Length must be between {} and {}", m, x),
                    (Some(m), None) => format!("Length must be at least {}", m),
                    (None, Some(x)) => format!("Length must be at most {}", x),
                    (None, None) => "Length validation failed".to_string(),
                };
                Err(FraiseQLError::Validation {
                    message: format!(
                        "Field validation failed: {}",
                        ValidationFieldError::new(field_path, "length", msg)
                    ),
                    path:    Some(field_path.to_string()),
                })
            }
        },
        ValidationRule::Enum { values } => {
            if values.contains(&value.to_string()) {
                Ok(())
            } else {
                Err(FraiseQLError::Validation {
                    message: format!(
                        "Field validation failed: {}",
                        ValidationFieldError::new(
                            field_path,
                            "enum",
                            format!("Must be one of: {}", values.join(", "))
                        )
                    ),
                    path:    Some(field_path.to_string()),
                })
            }
        },
        _ => Ok(()), // Other rule types handled elsewhere
    }
}

/// Extract field error information from an error message.
fn extract_field_error(message: &str) -> Option<ValidationFieldError> {
    // Format: "Field validation failed: field (rule): message"
    if message.contains("Field validation failed:") {
        if let Some(field_start) = message.find("Field validation failed: ") {
            let rest = &message[field_start + "Field validation failed: ".len()..];
            if let Some(paren_start) = rest.find('(') {
                if let Some(paren_end) = rest.find(')') {
                    let field = rest[..paren_start].trim().to_string();
                    let rule_type = rest[paren_start + 1..paren_end].to_string();
                    let msg_start = rest.find(": ").unwrap_or(0) + 2;
                    let message_text = rest[msg_start..].to_string();
                    return Some(ValidationFieldError::new(field, rule_type, message_text));
                }
            }
        }
    }
    None
}
