// Copyright 2024 Jeremy Wall <jeremy@marzhillstudios.com>
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.

//! A set of zero copy utility classes for managing cursor like access through slices.
use std::fmt::Debug;
use std::iter::Iterator;
use std::ops::Index;

#[cfg(test)]
mod test;

/// A trait for types that can have an offset as a count of processed items.
pub trait Offsetable {
    fn get_offset(&self) -> usize;
}

impl Offsetable for usize {
    fn get_offset(&self) -> usize {
        return *self;
    }
}

/// A trait for types that can seek to an index.
pub trait Seekable {
    fn seek(&mut self, u: usize) -> usize;
}

/// Trait for Inputs that can report current lines and columns in a text input.
pub trait Positioned: Offsetable {
    fn line(&self) -> usize;
    fn column(&self) -> usize;
}

/// SpanRange encompasses the valid Ops::Range types for use with the Span trait.
pub enum SpanRange {
    Range(std::ops::Range<usize>),
    RangeTo(std::ops::RangeTo<usize>),
    RangeFrom(std::ops::RangeFrom<usize>),
    RangeFull(std::ops::RangeFull),
}

impl From<std::ops::Range<usize>> for SpanRange {
    fn from(value: std::ops::Range<usize>) -> Self {
        SpanRange::Range(value)
    }
}

impl From<std::ops::RangeTo<usize>> for SpanRange {
    fn from(value: std::ops::RangeTo<usize>) -> Self {
        SpanRange::RangeTo(value)
    }
}

impl From<std::ops::RangeFrom<usize>> for SpanRange {
    fn from(value: std::ops::RangeFrom<usize>) -> Self {
        SpanRange::RangeFrom(value)
    }
}

impl From<std::ops::RangeFull> for SpanRange {
    fn from(value: std::ops::RangeFull) -> Self {
        SpanRange::RangeFull(value)
    }
}

/// An input that can provide a span of a range of the input.
pub trait Span<O> {
    fn span<R: Into<SpanRange>>(&self, idx: R) -> O;
}

/// The interface for types that can peek ahead to the next item.
pub trait Peekable<O> {
    fn peek_next(&self) -> Option<O>;
}

/// A Cloneable Iterator that can report an offset as a count of processed Items.
pub trait Cursor: Iterator + Clone + Offsetable {
    fn curr(&self) -> Self::Item;
}

/// Implements `InputIter` for any slice of T.
#[derive(Debug)]
pub struct SliceCursor<'a, T: Debug + 'a> {
    source: &'a [T],
    offset: usize,
}

impl<'a, T: Debug + 'a> SliceCursor<'a, T> {
    /// new constructs a SliceIter from a Slice of T.
    pub fn new(source: &'a [T]) -> Self {
        SliceCursor {
            source,
            offset: 0,
        }
    }
}

impl<'a, T: Debug + 'a> Iterator for SliceCursor<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        match self.source.get(self.offset) {
            Some(item) => {
                self.offset += 1;
                Some(item)
            }
            None => None,
        }
    }
}

impl<'a, T: Debug + 'a> Offsetable for SliceCursor<'a, T> {
    fn get_offset(&self) -> usize {
        self.offset
    }
}

impl<'a, It> Positioned for SliceCursor<'a, It>
where
    It: Positioned + Debug,
{
    fn line(&self) -> usize {
        match self.peek_next() {
            Some(i) => i.line(),
            None => 0,
        }
    }

    fn column(&self) -> usize {
        match self.peek_next() {
            Some(i) => i.column(),
            None => 0,
        }
    }
}

impl<'a, T: Debug + 'a> Clone for SliceCursor<'a, T> {
    fn clone(&self) -> Self {
        SliceCursor {
            source: self.source,
            offset: self.offset,
        }
    }
}

impl<'a, T: Debug + 'a> Cursor for SliceCursor<'a, T> {
    fn curr(&self) -> Self::Item {
        if self.offset >= self.source.len() {
            self.source.get(self.source.len() - 1).unwrap()
        } else {
            if self.offset == 0 {
                self.source.get(self.offset).unwrap()
            } else {
                self.source.get(self.offset - 1).unwrap()
            }
        }
    }
}

impl<'a, T: Debug + 'a> Span<&'a [T]> for SliceCursor<'a, T> {
    fn span<R: Into<SpanRange>>(&self, idx: R) -> &'a [T] {
        match idx.into() {
            SpanRange::Range(r) => self.source.index(r),
            SpanRange::RangeTo(r) => self.source.index(r),
            SpanRange::RangeFrom(r) => self.source.index(r),
            SpanRange::RangeFull(r) => self.source.index(r),
        }
    }
}

impl<'a> From<&'a str> for SliceCursor<'a, u8> {
    fn from(source: &'a str) -> Self {
        SliceCursor::new(source.as_bytes())
    }
}

impl<'a, T: Debug> From<&'a [T]> for SliceCursor<'a, T> {
    fn from(source: &'a [T]) -> Self {
        SliceCursor::new(source)
    }
}

impl<'a, T: Debug> From<&'a Vec<T>> for SliceCursor<'a, T> {
    fn from(source: &'a Vec<T>) -> Self {
        SliceCursor::new(source.as_slice())
    }
}

impl<'a, O: Debug> Peekable<&'a O> for SliceCursor<'a, O> {
    fn peek_next(&self) -> Option<&'a O> {
        self.source.get(self.offset)
    }
}

/// Implements `InputIter` for any slice of T.
#[derive(Debug)]
pub struct StrCursor<'a> {
    source: &'a str,
    offset: usize,
    line: usize,
    column: usize,
}

impl<'a> StrCursor<'a> {
    /// new constructs a StrIter from a Slice of T.
    pub fn new(source: &'a str) -> Self {
        StrCursor {
            source,
            offset: 0,
            line: 1,
            column: 1,
        }
    }
}

impl<'a> Iterator for StrCursor<'a> {
    type Item = &'a u8;

    fn next(&mut self) -> Option<Self::Item> {
        match self.source.as_bytes().get(self.offset) {
            // TODO count lines and columns.
            Some(item) => {
                self.offset += 1;
                if *item == b'\n' {
                    self.line += 1;
                    self.column = 1;
                } else {
                    self.column += 1;
                }
                Some(item)
            }
            None => None,
        }
    }
}

impl<'a> Offsetable for StrCursor<'a> {
    fn get_offset(&self) -> usize {
        self.offset
    }
}

impl<'a> Positioned for StrCursor<'a> {
    fn line(&self) -> usize {
        self.line
    }

    fn column(&self) -> usize {
        self.column
    }
}

impl<'a> Clone for StrCursor<'a> {
    fn clone(&self) -> Self {
        StrCursor {
            source: self.source,
            offset: self.offset,
            line: self.line,
            column: self.column,
        }
    }
}

impl<'a> Cursor for StrCursor<'a> {
    fn curr(&self) -> Self::Item {
        if self.offset >= self.source.len() {
            self.source.as_bytes().get(self.source.len() - 1).unwrap()
        } else {
            if self.offset == 0 {
                self.source.as_bytes().get(self.offset).unwrap()
            } else {
                self.source.as_bytes().get(self.offset - 1).unwrap()
            }
        }
    }
}

impl<'a> From<&'a str> for StrCursor<'a> {
    fn from(source: &'a str) -> Self {
        Self::new(source)
    }
}

impl<'a> Span<&'a str> for StrCursor<'a> {
    fn span<R: Into<SpanRange>>(&self, idx: R) -> &'a str {
        match idx.into() {
            SpanRange::Range(r) => self.source.index(r),
            SpanRange::RangeTo(r) => self.source.index(r),
            SpanRange::RangeFrom(r) => self.source.index(r),
            SpanRange::RangeFull(r) => self.source.index(r),
        }
    }
}

impl<'a> Seekable for StrCursor<'a> {
    fn seek(&mut self, to: usize) -> usize {
        let self_len = self.source.len();
        let offset = if self_len > to { to } else { self_len };
        self.offset = offset;
        self.offset
    }
}

impl<'a> Peekable<&'a u8> for StrCursor<'a> {
    fn peek_next(&self) -> Option<&'a u8> {
        self.source.as_bytes().get(self.offset)
    }
}