use std::{borrow::Cow, iter::{self, repeat_n}, mem};
use itertools::Itertools;
use ratatui::{style::{Color, Style, Stylize}, text::Span};

use crate::{BYTES_PER_CHUNK, BYTES_PER_LINE, CHUNKS_PER_LINE, buffer::{Buffer, Mode, PartialAction}, utilities::{CustomGreys, empty_span, HasCardinality}, cursor::InCursor};

impl Buffer {
	pub fn render_chunks(
		&self,
		address: usize,
		bytes: &[u8; BYTES_PER_LINE]
	) -> impl Iterator<Item=Span<'static>> {
		let (chunks, remainder) = bytes.as_chunks::<BYTES_PER_CHUNK>();
		
		assert!(remainder.is_empty(), "BYTES_PER_LINE should be a multiple of BYTES_PER_CHUNK");
		
		#[allow(unstable_name_collisions)]
		chunks
			.iter()
			.copied()
			.zip((address..).step_by(BYTES_PER_CHUNK))
			.flat_map(|(chunk, address)| {
				self.render_chunk(address, &chunk).collect::<Vec<_>>()
			})
	}
	
	pub fn render_partial_chunks(
		&self,
		address: usize,
		bytes: &[u8]
	) -> impl Iterator<Item=Span<'static>> {
		let (chunks, remainder) = bytes.as_chunks::<BYTES_PER_CHUNK>();
		
		let remainder_address = address + chunks.len() * BYTES_PER_CHUNK;
		#[allow(clippy::if_not_else)]
		let remainder_chunks: Option<Vec<_>> = if !remainder.is_empty() {
			Some(self.render_partial_chunk(remainder_address, remainder).collect())
		} else {
			None
		};
		
		let chunks_rendered = chunks.len() + remainder_chunks.iter().len();
		let chunks_not_rendered = CHUNKS_PER_LINE - chunks_rendered;
		let spaces_per_chunk = BYTES_PER_CHUNK - 1 + 2;
		let bytes_not_rendered = BYTES_PER_LINE - bytes.len();
		
		let padding_width = 2 * bytes_not_rendered +
			spaces_per_chunk * chunks_not_rendered;
		
		#[allow(unstable_name_collisions)]
		chunks
			.iter()
			.copied()
			.zip((address..).step_by(BYTES_PER_CHUNK))
			.map(|(chunk, address)| self.render_chunk(address, &chunk).collect())
			.chain(remainder_chunks)
			.flatten()
			.chain(repeat_n(" ".into(), padding_width))
	}
	
	fn render_chunk(
		&self,
		address: usize,
		bytes: &[u8; BYTES_PER_CHUNK]
	) -> impl Iterator<Item=Span<'static>> {
		iter::once(self.render_large_space_before(address))
			.chain(
				bytes
					.iter()
					.copied()
					.zip(address..)
					.map(|(byte, address)| self.render_byte_at(address, byte))
					.interleave(
						(address..)
							.take(BYTES_PER_CHUNK)
							.skip(1)
							.map(|address| self.render_space_before(address))
					)
			)
	}
	
	fn render_partial_chunk(
		&self,
		address: usize,
		bytes: &[u8]
	) -> impl Iterator<Item=Span<'static>> {
		iter::once(self.render_large_space_before(address))
			.chain(
				bytes
					.iter()
					.copied()
					.zip(address..)
					.map(|(byte, address)| self.render_byte_at(address, byte))
					.interleave(
						(address..)
							.take(BYTES_PER_CHUNK)
							.skip(1)
							.map(|address| self.render_space_before(address))
					)
			)
	}
	
	fn render_byte_at(
		&self,
		address: usize,
		byte: u8
	) -> Span<'static> {
		// TODO: checking this with lots of selections is slow
		if self.partial_action == Some(PartialAction::Replace) &&
		   iter::once(&self.primary_cursor)
			.chain(&self.cursors)
			.any(|cursor| cursor.contains(address).is_some())
		{
			let replaced_byte = self.partial_replace.unwrap_or(0) << 4;
			
			self.render_byte_without_replace_preview(address, replaced_byte)
				.black()
		} else {
			self.render_byte_without_replace_preview(address, byte)
		}
	}
	
	fn render_byte_without_replace_preview(
		&self,
		address: usize,
		byte: u8
	) -> Span<'static> {
		const SPAN_FOR_BYTE: [Span; u8::CARDINALITY] = create_byte_lookup_table();
		
		let span = SPAN_FOR_BYTE[byte as usize].clone();
		
		if let Some(place_in_cursor) = self.primary_cursor.contains(address) {
			let head_color = match self.mode {
				Mode::Select => Color::Yellow,
				Mode::Normal => Color::Gray
			};
			
			match place_in_cursor {
				InCursor::Head => span.bg(head_color),
				InCursor::Rest => span.bg(Color::selection_tail_grey()),
			}
		} else {
			match self.cursors
				.iter()
				.find_map(|cursor| cursor.contains(address))
			{
				Some(InCursor::Head) => span.bg(Color::secondary_selection_head_grey()),
				Some(InCursor::Rest) => span.bg(Color::selection_tail_grey()),
				None => span,
			}
		}
	}
	
	fn render_large_space_before(&self, address: usize) -> Span<'static> {
		let span: Span = if self.marks.contains(&address) {
			" →".into()
		} else {
			"  ".into()
		};
		
		if !address.is_multiple_of(BYTES_PER_LINE) &&
			iter::once(&self.primary_cursor)
				.chain(&self.cursors)
				.any(|cursor| cursor.contains_space_before(address))
		{
			span.bg(Color::selection_tail_grey())
		} else {
			span
		}
	}
	
	fn render_space_before(&self, address: usize) -> Span<'static> {
		let span: Span = if self.marks.contains(&address) {
			"→".into()
		} else {
			" ".into()
		};
		
		if iter::once(&self.primary_cursor)
			.chain(&self.cursors)
			.any(|cursor| cursor.contains_space_before(address))
		{
			span.bg(Color::selection_tail_grey())
		} else {
			span
		}
	}
}

const fn create_byte_lookup_table() -> [Span<'static>; u8::CARDINALITY] {
	let mut result = [const { empty_span() }; u8::CARDINALITY];
	
	let mut index = 0;
	while index < u8::CARDINALITY {
		#[allow(clippy::cast_possible_truncation)]
		let byte = index as u8;
		
		result[index].style = style_for_byte(byte);
		mem::forget(mem::replace(&mut result[index].content, content_for_byte(byte)));
		index += 1;
	}
	
	result
}

const fn style_for_byte(byte: u8) -> Style {
	Style::new().fg(fg_for_byte(byte))
}

const fn fg_for_byte(byte: u8) -> Color {
	match byte {
		0x00       => Color::Rgb(0x80, 0x80, 0x80), // grey
		0x01..0x10 => Color::Rgb(0xFF, 0x71, 0xA9), // red
		0x10..0x20 => Color::Rgb(0xFF, 0x7A, 0x78), // salmon
		0x20..0x30 => Color::Rgb(0xFF, 0x81, 0x23), // red-orange
		0x30..0x40 => Color::Rgb(0xF7, 0x93, 0x00), // yellow-orange
		0x40..0x50 => Color::Rgb(0xE6, 0x9F, 0x00), // yellow
		0x50..0x60 => Color::Rgb(0xC1, 0xB2, 0x00), // green-yellow
		0x60..0x70 => Color::Rgb(0x82, 0xC6, 0x00), // lime
		0x70..0x80 => Color::Rgb(0x00, 0xD5, 0x00), // green
		0x80..0x90 => Color::Rgb(0x00, 0xD4, 0x59), // clover
		0x90..0xA0 => Color::Rgb(0x00, 0xD0, 0x91), // teal
		0xA0..0xB0 => Color::Rgb(0x00, 0xCC, 0xBB), // cyan
		0xB0..0xC0 => Color::Rgb(0x00, 0xC7, 0xDE), // light blue
		0xC0..0xD0 => Color::Rgb(0x00, 0xBE, 0xFF), // blue
		0xD0..0xE0 => Color::Rgb(0x6C, 0xAF, 0xFF), // blurple
		0xE0..0xF0 => Color::Rgb(0xB2, 0x98, 0xFF), // purple
		0xF0..0xFF => Color::Rgb(0xFF, 0x4D, 0xFF), // pink
		0xFF       => Color::White
	}
}

const fn content_for_byte(byte: u8) -> Cow<'static, str> {
	Cow::Borrowed(hex_for_byte(byte))
}

const fn hex_for_byte(byte: u8) -> &'static str {
	const LOOK_UP_TABLE: [&str; u8::CARDINALITY] = ["00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d", "2e", "2f", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b", "5c", "5d", "5e", "5f", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8a", "8b", "8c", "8d", "8e", "8f", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f", "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af", "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf", "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf", "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df", "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef", "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff"];
	
	LOOK_UP_TABLE[byte as usize]
}