//! External names.
//!
//! These are identifiers for declaring entities defined outside the current
//! function. The name of an external declaration doesn't have any meaning to
//! Cranelift, which compiles functions independently.

use crate::ir::LibCall;
use core::cmp;
use core::fmt::{self, Write};
use core::str::FromStr;

const TESTCASE_NAME_LENGTH: usize = 16;

/// The name of an external is either a reference to a user-defined symbol
/// table, or a short sequence of ascii bytes so that test cases do not have
/// to keep track of a symbol table.
///
/// External names are primarily used as keys by code using Cranelift to map
/// from a `cranelift_codegen::ir::FuncRef` or similar to additional associated
/// data.
///
/// External names can also serve as a primitive testing and debugging tool.
/// In particular, many `.clif` test files use function names to identify
/// functions.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ExternalName {
    /// A name in a user-defined symbol table. Cranelift does not interpret
    /// these numbers in any way.
    User {
        /// Arbitrary.
        namespace: u32,
        /// Arbitrary.
        index: u32,
    },
    /// A test case function name of up to a hardcoded amount of ascii
    /// characters. This is not intended to be used outside test cases.
    TestCase {
        /// How many of the bytes in `ascii` are valid?
        length: u8,
        /// Ascii bytes of the name.
        ascii: [u8; TESTCASE_NAME_LENGTH],
    },
    /// A well-known runtime library function.
    LibCall(LibCall),
}

impl ExternalName {
    /// Creates a new external name from a sequence of bytes. Caller is expected
    /// to guarantee bytes are only ascii alphanumeric or `_`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use cranelift_codegen::ir::ExternalName;
    /// // Create `ExternalName` from a string.
    /// let name = ExternalName::testcase("hello");
    /// assert_eq!(name.to_string(), "%hello");
    /// ```
    pub fn testcase<T: AsRef<[u8]>>(v: T) -> Self {
        let vec = v.as_ref();
        let len = cmp::min(vec.len(), TESTCASE_NAME_LENGTH);
        let mut bytes = [0u8; TESTCASE_NAME_LENGTH];
        bytes[0..len].copy_from_slice(&vec[0..len]);

        Self::TestCase {
            length: len as u8,
            ascii: bytes,
        }
    }

    /// Create a new external name from user-provided integer indices.
    ///
    /// # Examples
    /// ```rust
    /// # use cranelift_codegen::ir::ExternalName;
    /// // Create `ExternalName` from integer indices
    /// let name = ExternalName::user(123, 456);
    /// assert_eq!(name.to_string(), "u123:456");
    /// ```
    pub fn user(namespace: u32, index: u32) -> Self {
        Self::User { namespace, index }
    }
}

impl Default for ExternalName {
    fn default() -> Self {
        Self::user(0, 0)
    }
}

impl fmt::Display for ExternalName {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Self::User { namespace, index } => write!(f, "u{}:{}", namespace, index),
            Self::TestCase { length, ascii } => {
                f.write_char('%')?;
                for byte in ascii.iter().take(length as usize) {
                    f.write_char(*byte as char)?;
                }
                Ok(())
            }
            Self::LibCall(lc) => write!(f, "%{}", lc),
        }
    }
}

impl FromStr for ExternalName {
    type Err = ();

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        // Try to parse as a libcall name, otherwise it's a test case.
        match s.parse() {
            Ok(lc) => Ok(Self::LibCall(lc)),
            Err(_) => Ok(Self::testcase(s.as_bytes())),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::ExternalName;
    use crate::ir::LibCall;
    use alloc::string::ToString;
    use core::u32;

    #[test]
    fn display_testcase() {
        assert_eq!(ExternalName::testcase("").to_string(), "%");
        assert_eq!(ExternalName::testcase("x").to_string(), "%x");
        assert_eq!(ExternalName::testcase("x_1").to_string(), "%x_1");
        assert_eq!(
            ExternalName::testcase("longname12345678").to_string(),
            "%longname12345678"
        );
        // Constructor will silently drop bytes beyond the 16th
        assert_eq!(
            ExternalName::testcase("longname123456789").to_string(),
            "%longname12345678"
        );
    }

    #[test]
    fn display_user() {
        assert_eq!(ExternalName::user(0, 0).to_string(), "u0:0");
        assert_eq!(ExternalName::user(1, 1).to_string(), "u1:1");
        assert_eq!(
            ExternalName::user(u32::MAX, u32::MAX).to_string(),
            "u4294967295:4294967295"
        );
    }

    #[test]
    fn parsing() {
        assert_eq!(
            "FloorF32".parse(),
            Ok(ExternalName::LibCall(LibCall::FloorF32))
        );
        assert_eq!(
            ExternalName::LibCall(LibCall::FloorF32).to_string(),
            "%FloorF32"
        );
    }
}