//! This module implements **[Flexstr]**, which uses an internal enum
//! to hold either a fixed string of up to a maximum length, or an owned [String].

#![allow(unused_variables)]
#![allow(non_snake_case)]
#![allow(non_camel_case_types)]
#![allow(unused_parens)]
#![allow(unused_assignments)]
#![allow(unused_mut)]
#![allow(unused_imports)]
#![allow(dead_code)]
extern crate alloc;
use crate::tstr;
use crate::zstr;

#[cfg(feature = "std")]
use crate::fstr;

use crate::shared_structs::Strunion;
use crate::shared_structs::Strunion::*;
use crate::{str12, str128, str16, str192, str24, str256, str32, str4, str48, str64, str8, str96};
use alloc::string::String;
use alloc::vec::Vec;
use core::cmp::{min, Ordering};
use core::ops::Add;

/// **This type is only available with the `flex-str` option.**
/// A `Flexstr<N>` is represented internally as a `tstr<N>` if the length of
/// the string is less than N bytes, and by an owned String otherwise.
/// The structure satisfies the following axiom:
/// >   *For N <= 256, a `Flexstr<N>` is represented internally by an
///     owned String if and only if the length of the string is greater than
///     or equal to N*.
///
/// For example, a `Flexstr<16>` will hold a string of up to 15 bytes
/// in an u8-array of size 16. The first byte of the array holds the length of
/// the string.  If subsequent operations such as [Flexstr::push_str]
/// extends the string past 15 bytes, the representation will switch to an owned
/// String.  Conversely, an operation such as [Flexstr::truncate]
/// may switch the representation back to a fixed string.
/// The default N is 32.  **The largest N for which the axiom holds
/// is 256.**  For all N>256, the internal representation is always an owned
/// string.
///
/// Example:
/// ```ignore
///  let mut s:Flexstr<8> = Flexstr::from("abcdef");
///  assert!(s.is_fixed());
///  s.push_str("ghijk");
///  assert!(s.is_owned());
///  s.truncate(7);
///  assert!(s.is_fixed());
/// ```
///
/// The intended use of this datatype is for
/// situations when the lengths of strings are *usually* less than N, with
/// only occasional exceptions that require a different representation.
/// However, unlike the other string types in this crate, a Flexstr cannot be
/// copied and is thus subject to **move semantics**.  The serde serialization
/// option is also supported (`features serde`).
///
/// In addition, this type impls the `Add` trait for string concatenation:
///
/// ```ignore
///  let a = flexstr8::from("abcd");
///  let b = &a + "efg";
///  assert_eq!(&b,"abcdefg");
/// ```
///
#[derive(Clone, Eq)]
pub struct Flexstr<const N: usize = 32> {
    inner: Strunion<N>,
}
impl<const N: usize> Flexstr<N> {
    /// Creates a new `Flexstr<N>` with given &str.
    pub fn make(s: &str) -> Self {
        if s.len() < N && N <= 256 {
            Flexstr {
                inner: fixed(tstr::<N>::from(s)),
            }
        } else {
            Flexstr {
                inner: owned(String::from(s)),
            }
        }
    } //make

    /// Creates a `Flexstr<N>` by consuming a given string.  However, if the
    /// string has length less than N, then a fixed representation will be used.
    pub fn from_string(s: String) -> Self {
        if s.len() < N && N <= 256 {
            Flexstr {
                inner: fixed(tstr::<N>::from(&s[..])),
            }
        } else {
            Flexstr { inner: owned(s) }
        }
    }

    /// creates a `Flexstr<N>` from a given `tstr<N>`
    pub fn from_tstr(s: tstr<N>) -> Self {
        Flexstr { inner: fixed(s) }
    }

    #[cfg(feature = "serde")]
    /// this function is only added for uniformity in serde implementation
    pub fn try_make(s: &str) -> Result<Flexstr<N>, &str> {
        Ok(Flexstr::make(s))
    }

    /// length of the string in bytes. This is a constant-time operation.
    #[inline]
    pub fn len(&self) -> usize {
        match &self.inner {
            fixed(s) => s.len(),
            owned(s) => s.len(),
        } //match
    } //len

    /// creates an empty string, equivalent to [Flexstr::default]
    #[inline]
    pub fn new() -> Self {
        Self::default()
    }

    /// length in number of characters as opposed to bytes: this is
    /// not necessarily a constant time operation.
    pub fn charlen(&self) -> usize {
        match &self.inner {
            fixed(s) => s.charlen(),
            owned(s) => {
                s.chars().count()
                //let v: Vec<_> = s.chars().collect();
                //v.len()
            }
        } //match
    } //charlen

    /// converts fstr to &str, possibly using using [core::str::from_utf8_unchecked].  Since
    /// Flexstr can only be built from valid utf8 sources, this function
    /// is safe.
    pub fn to_str(&self) -> &str {
        match &self.inner {
            fixed(s) => s.to_str(),
            owned(s) => &s[..],
        } //match
    } //to_str

    /// same functionality as [Flexstr::to_str], but only uses
    ///[core::str::from_utf8] and may technically panic.
    pub fn as_str(&self) -> &str //{self.to_str()}
    {
        match &self.inner {
            fixed(s) => s.as_str(),
            owned(s) => &s[..],
        } //match
    }

    /// retrieves a copy of the underlying fixed string, if it is a fixed string.
    /// Note that since the `tstr` type is not exported, this function should
    /// be used in conjunction with one of the public aliases [str4]-[str256].
    /// For example,
    /// ```ignore
    ///   let s = Flexstr::<8>::from("abcd");
    ///   let t:str8 = s.get_str().unwrap();
    /// ```
    pub fn get_str(&self) -> Option<tstr<N>> {
        if let fixed(s) = &self.inner {
            Some(*s)
        } else {
            None
        }
    } //get_str

    /// if the underlying representation of the string is an owned string,
    /// return the owned string, leaving an empty string in its place.
    pub fn take_string(&mut self) -> Option<String> {
        if let owned(s) = &mut self.inner {
            let mut temp = fixed(tstr::new());
            core::mem::swap(&mut self.inner, &mut temp);
            if let owned(t) = temp {
                Some(t)
            } else {
                None
            }
        } else {
            None
        }
    } //take_owned

    /// this function consumes the Flexstr and returns an owned string
    pub fn to_string(self) -> String {
        match self.inner {
            fixed(s) => s.to_string(),
            owned(s) => s,
        } //match
    } //to_string

    /// returns the nth char of the string, if it exists
    pub fn nth(&self, n: usize) -> Option<char> {
        self.to_str().chars().nth(n)
    }

    /// returns the nth byte of the string as a char.  This function
    /// is designed to be quicker than [Flexstr::nth] and does not check
    /// for bounds.
    pub fn nth_bytechar(&self, n: usize) -> char {
        match &self.inner {
            fixed(s) => s.nth_ascii(n),
            owned(s) => s.as_bytes()[n] as char,
        }
    } //nth_bytechar

    /// alias for [Self::nth_bytechar] (for backwards compatibility)
    pub fn nth_ascii(&self, n: usize) -> char {
        self.nth_bytechar(n)
    }

    /// returns a u8-slice that represents the underlying string. The first
    /// byte of the slice is **not** the length of the string regarless of
    /// the internal representation.
    pub fn as_bytes(&self) -> &[u8] {
        match &self.inner {
            fixed(f) => f.as_bytes(),
            owned(s) => s.as_bytes(),
        } //match
    }

    /// changes a character at character position i to c.  This function
    /// requires that c is in the same character class (ascii or unicode)
    /// as the char being replaced.  It never shuffles the bytes underneath.
    /// The function returns true if the change was successful.
    pub fn set(&mut self, i: usize, c: char) -> bool {
        match &mut self.inner {
            fixed(s) => s.set(i, c),
            owned(s) => unsafe {
                let ref mut cbuf = [0u8; 4];
                c.encode_utf8(cbuf);
                let clen = c.len_utf8();
                if let Some((bi, rc)) = s.char_indices().nth(i) {
                    if clen == rc.len_utf8() {
                        s.as_bytes_mut()[bi..bi + clen].copy_from_slice(&cbuf[..clen]);
                        //self.chrs[bi + 1..bi + clen + 1].copy_from_slice(&cbuf[..clen]);
                        //for k in 0..clen {self.chrs[bi+k+1] = cbuf[k];}
                        return true;
                    }
                }
                return false;
            },
        } //match
    } //set

    /// returns whether the internal representation is a fixed string (tstr)
    pub fn is_fixed(&self) -> bool {
        match &self.inner {
            fixed(_) => true,
            owned(_) => false,
        }
    } //is_fixed

    /// returns whether the internal representation is an owned String
    pub fn is_owned(&self) -> bool {
        !self.is_fixed()
    }

    /// applies the destructive closure only if the internal representation
    /// is a fixed string
    pub fn if_fixed<F>(&mut self, f: F)
    where
        F: FnOnce(&mut tstr<N>),
    {
        if let fixed(s) = &mut self.inner {
            f(s);
        }
    }

    /// applies the destructive closure only if the internal representation
    /// is a fixed string
    pub fn if_owned<F>(&mut self, f: F)
    where
        F: FnOnce(&mut str),
    {
        if let owned(s) = &mut self.inner {
            f(s);
        }
    }

    /// applies closure f if the internal representation is a fixed string,
    /// or closure g if the internal representation is an owned string.
    pub fn map_or<F, G, U>(&self, f: F, g: G) -> U
    where
        F: FnOnce(&tstr<N>) -> U,
        G: FnOnce(&str) -> U,
    {
        match &self.inner {
            fixed(s) => f(s),
            owned(s) => g(&s[..]),
        } //match
    } //map

    /// version of [Flexstr::map_or] accepting FnMut closures
    pub fn map_or_mut<F, G, U>(&mut self, f: &mut F, g: &mut G) -> U
    where
        F: FnMut(&mut tstr<N>) -> U,
        G: FnMut(&mut str) -> U,
    {
        match &mut self.inner {
            fixed(s) => f(s),
            owned(s) => g(&mut s[..]),
        } //match
    } //map

    /// This function will append the Flexstr with the given slice,
    /// switching to the owned-String representation if necessary.  The function
    /// returns true if the resulting string uses a `tstr<N>` type, and
    /// false if the representation is an owned string.
    pub fn push_str(&mut self, s: &str) -> bool {
        match &mut self.inner {
            fixed(fs) if fs.len() + s.len() < N => {
                fs.push(s);
                true
            }
            fixed(fs) => {
                let fss = fs.to_string() + s;
                self.inner = owned(fss);
                false
            }
            owned(ns) => {
                ns.push_str(s);
                false
            }
        } //match
    } //push_str

    /// appends string with a single character, switching to the String
    /// representation if necessary.  Returns true if resulting string
    /// remains fixed.
    pub fn push(&mut self, c: char) -> bool {
        let clen = c.len_utf8();
        match &mut self.inner {
            owned(s) => {
                s.push(c);
                false
            }
            fixed(s) if s.len() + clen >= N => {
                let mut fss = s.to_string();
                fss.push(c);
                self.inner = owned(fss);
                false
            }
            fixed(s) => {
                let mut buf = [0u8; 4];
                let bstr = c.encode_utf8(&mut buf);
                s.push(bstr);
                true
            }
        } //match
    } //push

    /// alias for push
    #[inline]
    pub fn push_char(&mut self, c: char) -> bool {
        self.push(c)
    }

    /// remove and return last character in string, if it exists
    pub fn pop(&mut self) -> Option<char> {
        if self.len() == 0 {
            return None;
        }
        match &mut self.inner {
            fixed(s) => s.pop_char(),
            owned(s) if s.len() > N => s.pop(),
            owned(s) => {
                // change representation
                let lastchar = s.pop();
                self.inner = fixed(tstr::from(&s));
                lastchar
            }
        } //match
    } //pop

    /// alias for [Self::pop]
    pub fn pop_char(&mut self) -> Option<char> {
        self.pop()
    }

    /// this function truncates a string at the indicated byte position,
    /// returning true if the truncated string is fixed, and false if owned.
    /// The operation has no effect if n is larger than the length of the
    /// string.  The operation will **panic** if n is not on a character
    /// boundary, similar to [String::truncate].
    pub fn truncate(&mut self, n: usize) -> bool {
        match &mut self.inner {
            fixed(fs) if n < fs.len() => {
                fs.truncate_bytes(n);
                true
            }
            fixed(_) => true,
            owned(s) if n < N => {
                assert!(s.is_char_boundary(n));
                self.inner = fixed(tstr::<N>::from(&s[..n]));
                true
            }
            owned(s) => {
                if n < s.len() {
                    s.truncate(n);
                }
                false
            }
        } //match
    } //truncate

    /// resets string to empty
    pub fn clear(&mut self) {
        match &mut self.inner {
            fixed(s) => {
                s.clear();
            }
            owned(s) => {
                self.inner = fixed(tstr::default());
            }
        }
    } //clear

    /// returns string corresponding to slice indices as a copy or clone.
    pub fn substr(&self, start: usize, end: usize) -> Flexstr<N> {
        match &self.inner {
            fixed(s) => Flexstr {
                inner: fixed(s.substr(start, end)),
            },
            owned(s) => Self::from(&s[start..end]),
        }
    } //substr

    /// Splits the string into a `tstr<N>` portion and a String portion.
    /// The structure inherits the fixed part and the String returned will
    /// contain the extra bytes that does not fit.  Example:
    ///
    /// ```
    ///  # use fixedstr::*;
    ///   let mut fs:Flexstr<4> = Flexstr::from("abcdefg");
    ///   let extras = fs.split_off();
    ///   assert!( &fs=="abc" && &extras=="defg" && fs.is_fixed());
    /// ```
    pub fn split_off(&mut self) -> String {
        match &mut self.inner {
            fixed(s) => String::default(),
            owned(s) => {
                let answer = String::from(&s[N - 1..]);
                self.inner = fixed(tstr::<N>::from(&s[..N - 1]));
                answer
            }
        } //match
    } //split_off

    /// in-place modification of ascii string to lower-case
    pub fn make_ascii_lowercase(&mut self) {
        match &mut self.inner {
            fixed(s) => {
                s.make_ascii_lowercase();
            }
            owned(s) => {
                s.as_mut_str().make_ascii_lowercase();
            }
        } //match
    } //make_ascii_lowercase

    /// in-place modification of ascii string to upper-case
    pub fn make_ascii_uppercase(&mut self) {
        match &mut self.inner {
            fixed(s) => {
                s.make_ascii_uppercase();
            }
            owned(s) => {
                s.as_mut_str().make_ascii_uppercase();
            }
        } //match
    }

    /// Tests for ascii case-insensitive equality with another string.
    /// This function does not test if either string is ascii.
    pub fn case_insensitive_eq<TA>(&self, other: TA) -> bool
    where
        TA: AsRef<str>,
    {
        if self.len() != other.as_ref().len() {
            return false;
        }
        let obytes = other.as_ref().as_bytes();
        let sbytes = self.as_bytes();
        for i in 0..self.len() {
            let mut c = sbytes[i];
            if (c > 64 && c < 91) {
                c = c | 32;
            } // make lowercase
            let mut d = obytes[i];
            if (d > 64 && d < 91) {
                d = d | 32;
            } // make lowercase
            if c != d {
                return false;
            }
        } //for
        true
    } //case_insensitive_eq

    /// Decodes a UTF-16 encodeded slice. If a decoding error is encountered
    /// or capacity exceeded, an `Err(s)` is returned where s is the
    /// the encoded string up to the point of the error.
    pub fn from_utf16(v: &[u16]) -> Result<Self, Self> {
        let mut s = Self::new();
        for c in char::decode_utf16(v.iter().cloned()) {
            if let Ok(c1) = c {
                if !s.push_char(c1) {
                    return Err(s);
                }
            } else {
                return Err(s);
            }
        }
        Ok(s)
    } //from_utf16
} //impl<N>

impl<const N: usize> Default for Flexstr<N> {
    fn default() -> Self {
        Flexstr {
            inner: fixed(tstr::<N>::default()),
        }
    }
}

/*
impl<const N:usize> core::hash::Hash for Flexstr<N>
{
  fn hash<H:core::hash::Hasher>(&self, state:&mut H) {
    self.as_str().hash(state)
  }
}//hash
*/

impl<const N: usize> core::ops::Deref for Flexstr<N> {
    type Target = str;
    fn deref(&self) -> &Self::Target {
        self.to_str()
    }
}

impl<T: AsRef<str> + ?Sized, const N: usize> core::convert::From<&T> for Flexstr<N> {
    fn from(s: &T) -> Self {
        Self::make(s.as_ref())
    }
}

impl<T: AsMut<str> + ?Sized, const N: usize> core::convert::From<&mut T> for Flexstr<N> {
    fn from(s: &mut T) -> Self {
        Self::make(s.as_mut())
    }
}

impl<const N: usize> core::cmp::PartialOrd for Flexstr<N> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        //Some(self.chrs[0..self.len].cmp(other.chrs[0..other.len]))
        Some(self.cmp(other))
    }
}

impl<const N: usize> core::cmp::Ord for Flexstr<N> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.to_str().cmp(other.to_str())
    }
}

impl<const N: usize> core::convert::AsRef<str> for Flexstr<N> {
    fn as_ref(&self) -> &str {
        self.to_str()
    }
}
impl<const N: usize> core::convert::AsMut<str> for Flexstr<N> {
    fn as_mut(&mut self) -> &mut str {
        match &mut self.inner {
            fixed(f) => f.as_mut(),
            owned(s) => s.as_mut(),
        } //match
    }
}

impl<const N: usize> PartialEq<&str> for Flexstr<N> {
    fn eq(&self, other: &&str) -> bool {
        &self.to_str() == other // see below
    } //eq
}

impl<const N: usize> PartialEq<&str> for &Flexstr<N> {
    fn eq(&self, other: &&str) -> bool {
        &self.to_str() == other
    } //eq
}
impl<'t, const N: usize> PartialEq<Flexstr<N>> for &'t str {
    fn eq(&self, other: &Flexstr<N>) -> bool {
        &other.to_str() == self
    }
}
impl<'t, const N: usize> PartialEq<&Flexstr<N>> for &'t str {
    fn eq(&self, other: &&Flexstr<N>) -> bool {
        &other.to_str() == self
    }
}

impl<const N: usize> core::fmt::Debug for Flexstr<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.pad(&self.to_str())
    }
} // Debug impl

impl<const N: usize> core::fmt::Display for Flexstr<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        //write!(f, "{}", self.to_str())
        f.pad(self.to_str())
    }
}

impl<const N: usize> core::fmt::Write for Flexstr<N> {
    fn write_str(&mut self, s: &str) -> core::fmt::Result {
        self.push_str(s);
        Ok(())
    } //write_str
} //core::fmt::Write trait

impl<const N: usize> core::convert::From<String> for Flexstr<N> {
    /// *will consume owned string and convert it to a fixed
    /// representation if its length is less than N*
    fn from(s: String) -> Self {
        if s.len() >= N {
            Flexstr { inner: owned(s) }
        } else {
            Flexstr {
                inner: fixed(tstr::<N>::from(&s[..])),
            }
        }
    }
} //from String

impl<const M: usize> Flexstr<M> {
    /// returns a copy/clone of the string with new fixed capacity N.
    /// Example:
    /// ```
    ///  # use fixedstr::Flexstr;
    ///  let mut a:Flexstr<4> = Flexstr::from("ab");
    ///  let mut b:Flexstr<8> = a.resize();
    ///  b.push_str("cdef");
    ///  assert!(b.is_fixed());
    ///  a.push_str("1234");
    ///  assert!(a.is_owned());
    /// ```
    pub fn resize<const N: usize>(&self) -> Flexstr<N> {
        Flexstr::from(self)
    }
}

/* redundant
impl<const N:usize> Add for &Flexstr<N> {
  type Output = Flexstr<N>;
  fn add(self, other:Self) -> Self::Output {
    match (&self.inner, &other.inner) {
       (owned(a),b) => {
         let mut a2 = a.clone();
         a2.push_str(&other);
         Flexstr{inner:owned(a2)}
       },
       (a,owned(b)) => {
         let mut a2 = self.clone().to_string();
         a2.push_str(&other);
         Flexstr{inner:owned(a2)}
       },
       (fixed(a), fixed(b)) if a.len() + b.len() >= N => {
         let mut a2 = a.to_string();
         a2.push_str(&b);
         Flexstr{inner:owned(a2)}
       },
       (fixed(a), fixed(b)) => {
         let mut a2 = *a; //copy
         a2.push(&b);
         Flexstr{inner:fixed(a2)}
       }
    }//match
  }
}//Add
*/

impl<const N: usize, TA: AsRef<str>> Add<TA> for &Flexstr<N> {
    type Output = Flexstr<N>;
    fn add(self, other: TA) -> Self::Output {
        match (&self.inner, other.as_ref()) {
            (owned(a), b) => {
                let mut a2 = a.clone();
                a2.push_str(other.as_ref());
                Flexstr { inner: owned(a2) }
            }
            (fixed(a), b) if a.len() + b.len() >= N => {
                let mut a2 = a.to_string();
                a2.push_str(b);
                Flexstr { inner: owned(a2) }
            }
            (fixed(a), b) => {
                let mut a2 = *a; //copy
                a2.push(b);
                Flexstr { inner: fixed(a2) }
            }
        } //match
    }
} //Add, Rhs = &str

impl<const N: usize> Add<&Flexstr<N>> for &str {
    type Output = Flexstr<N>;
    fn add(self, other: &Flexstr<N>) -> Flexstr<N> {
        let mut a2 = Flexstr::from(self);
        a2.push_str(other);
        a2
    }
} //Add &str on left

impl<const N: usize> Add<Flexstr<N>> for &str {
    type Output = Flexstr<N>;
    fn add(self, other: Flexstr<N>) -> Flexstr<N> {
        let mut a2 = Flexstr::from(self);
        a2.push_str(&other);
        a2
    }
} //Add &str on left

impl<const N: usize> core::hash::Hash for Flexstr<N> {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.as_ref().hash(state);
    }
} //hash

impl<const N: usize> core::cmp::PartialEq for Flexstr<N> {
    fn eq(&self, other: &Self) -> bool {
        self.as_ref() == other.as_ref()
    }
} //eq

impl<const N: usize> core::str::FromStr for Flexstr<N> {
    type Err = &'static str;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Ok(Flexstr::from(s))
    }
}

/// convenient type aliases for [Flexstr]
pub type flexstr8 = Flexstr<8>;
pub type flexstr16 = Flexstr<16>;
pub type flexstr32 = Flexstr<32>;
pub type flexstr64 = Flexstr<64>;
pub type flexstr128 = Flexstr<128>;
pub type flexstr256 = Flexstr<256>;
