//! 标准库：string（split, trim, substring, replace, contains, upper, lower, starts_with, ends_with）

use crate::error::RuntimeError;
use crate::interpreter::{Runtime, Value};
use std::cell::RefCell;
use std::rc::Rc;

fn require_string(val: &Value, arg_name: &str) -> Result<String, RuntimeError> {
    match val {
        Value::String(s) => Ok(s.clone()),
        _ => Err(RuntimeError::RuntimeError {
            message: format!("{} must be a string", arg_name),
            token: None,
        }),
    }
}

// ============================================================================
// split(str, delim) → array of substrings
// ============================================================================

pub fn split(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.len() < 2 {
        return Err(RuntimeError::RuntimeError {
            message: "split() expects 2 arguments (string, delimiter)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let delim = require_string(&args[1], "Second argument (delimiter)")?;

    let parts: Vec<Value> = if delim.is_empty() {
        // Split by empty string → characters
        s.chars().map(|c| Value::String(c.to_string())).collect()
    } else {
        s.split(&delim).map(|p| Value::String(p.to_string())).collect()
    };

    Ok(Value::Array(Rc::new(RefCell::new(parts))))
}

// ============================================================================
// trim(str) → string with leading/trailing whitespace removed
// ============================================================================

pub fn trim(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.is_empty() {
        return Err(RuntimeError::RuntimeError {
            message: "trim() expects 1 argument (string)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "Argument")?;
    Ok(Value::String(s.trim().to_string()))
}

// ============================================================================
// substring(str, start, len?) → substring
// ============================================================================

pub fn substring(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.is_empty() {
        return Err(RuntimeError::RuntimeError {
            message: "substring() expects at least 2 arguments (string, start, len?)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let start = as_usize(&args[1], "Second argument (start)")?;
    let chars: Vec<char> = s.chars().collect();
    let start = start.min(chars.len());
    let end = if args.len() >= 3 {
        (start + as_usize(&args[2], "Third argument (length)")?).min(chars.len())
    } else {
        chars.len()
    };
    Ok(Value::String(chars[start..end].iter().collect()))
}

// ============================================================================
// replace(str, old, new) → string with all occurrences replaced
// ============================================================================

pub fn replace(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.len() < 3 {
        return Err(RuntimeError::RuntimeError {
            message: "replace() expects 3 arguments (string, old, new)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let old = require_string(&args[1], "Second argument (old)")?;
    let new = require_string(&args[2], "Third argument (new)")?;

    if old.is_empty() {
        return Err(RuntimeError::RuntimeError {
            message: "replace(): 'old' must not be empty".into(),
            token: None,
        });
    }

    Ok(Value::String(s.replace(&old, &new)))
}

// ============================================================================
// contains(str, needle) → bool
// ============================================================================

pub fn contains(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.len() < 2 {
        return Err(RuntimeError::RuntimeError {
            message: "contains() expects 2 arguments (string, needle)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let needle = require_string(&args[1], "Second argument (needle)")?;
    Ok(Value::Bool(s.contains(&needle)))
}

// ============================================================================
// upper(str) → uppercase (ASCII)
// ============================================================================

pub fn upper(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.is_empty() {
        return Err(RuntimeError::RuntimeError {
            message: "upper() expects 1 argument (string)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "Argument")?;
    Ok(Value::String(s.to_ascii_uppercase()))
}

// ============================================================================
// lower(str) → lowercase (ASCII)
// ============================================================================

pub fn lower(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.is_empty() {
        return Err(RuntimeError::RuntimeError {
            message: "lower() expects 1 argument (string)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "Argument")?;
    Ok(Value::String(s.to_ascii_lowercase()))
}

// ============================================================================
// starts_with(str, prefix) → bool
// ============================================================================

pub fn starts_with(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.len() < 2 {
        return Err(RuntimeError::RuntimeError {
            message: "starts_with() expects 2 arguments (string, prefix)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let prefix = require_string(&args[1], "Second argument (prefix)")?;
    Ok(Value::Bool(s.starts_with(&prefix)))
}

// ============================================================================
// ends_with(str, suffix) → bool
// ============================================================================

pub fn ends_with(_interp: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    if args.len() < 2 {
        return Err(RuntimeError::RuntimeError {
            message: "ends_with() expects 2 arguments (string, suffix)".into(),
            token: None,
        });
    }
    let s = require_string(&args[0], "First argument")?;
    let suffix = require_string(&args[1], "Second argument (suffix)")?;
    Ok(Value::Bool(s.ends_with(&suffix)))
}

// ============================================================================
// Helper
// ============================================================================

fn as_usize(val: &Value, arg_name: &str) -> Result<usize, RuntimeError> {
    match val {
        Value::Number(n) => {
            if *n < 0.0 || n.fract() != 0.0 {
                return Err(RuntimeError::RuntimeError {
                    message: format!("{} must be a non-negative integer, got {}", arg_name, n),
                    token: None,
                });
            }
            Ok(*n as usize)
        }
        _ => Err(RuntimeError::RuntimeError {
            message: format!("{} must be a number", arg_name),
            token: None,
        }),
    }
}