use anyhow::{anyhow, bail, Context, Result};
use std::collections::HashMap;

use crate::{handle::SpriteHandle, Content, ContentBuildContext};

pub(crate) mod syntax {
	use crate::{Content, ContentBuildContext};
	use anyhow::{anyhow, bail, Context, Ok, Result};
	use serde::Deserialize;
	use std::{collections::HashMap, path::PathBuf};

	use super::AnimSectionHandle;

	// Raw serde syntax structs.
	// These are never seen by code outside this crate.

	/// Convenience variants of sprite definitions
	#[derive(Debug, Deserialize)]
	#[serde(untagged)]
	pub enum Sprite {
		Static(StaticSprite),
		OneSection(SpriteSection),
		Complete(CompleteSprite),
	}

	/// Two ways to specify animation length
	#[derive(Debug, Deserialize)]
	pub enum TimingVariant {
		/// The duration of this whole section
		#[serde(rename = "duration")]
		Duration(f32),

		/// The fps of this section
		#[serde(rename = "fps")]
		Fps(f32),
	}

	#[derive(Debug, Deserialize)]
	pub struct Timing {
		#[serde(flatten)]
		pub variant: TimingVariant,
	}

	/// An unanimated sprite
	#[derive(Debug, Deserialize)]
	pub struct StaticSprite {
		pub file: PathBuf,
	}

	/// The proper, full sprite definition
	#[derive(Debug, Deserialize)]
	pub struct CompleteSprite {
		pub section: HashMap<String, SpriteSection>,
		pub start_at: SectionEdge,
	}

	/// A single animation section
	#[derive(Debug, Deserialize)]
	pub struct SpriteSection {
		pub frames: Vec<PathBuf>,
		pub timing: Timing,
		pub top: Option<SectionEdge>,
		pub bot: Option<SectionEdge>,
	}

	impl SpriteSection {
		pub fn add_to(
			&self,
			_build_context: &mut ContentBuildContext,
			content: &mut Content,

			// An index of all sections in this sprite, used to resolve
			// top and bot edges.
			all_sections: &HashMap<String, AnimSectionHandle>,
		) -> Result<((u32, u32), super::SpriteSection)> {
			// Make sure all frames have the same size and add them
			// to the frame vector
			let mut dim = None;
			let mut frames = Vec::new();
			for f in &self.frames {
				let idx = match content.sprite_atlas.path_map.get(f) {
					Some(s) => *s,
					None => {
						bail!("error: file `{}` isn't in the sprite atlas", f.display());
					}
				};
				let img = &content.sprite_atlas.index[idx as usize];

				match dim {
					None => dim = Some(img.true_size),
					Some(e) => {
						if img.true_size != e {
							bail!("failed to load section frames because frames have different sizes.",)
						}
					}
				}

				frames.push(img.idx);
			}
			let dim = dim.unwrap();

			let frame_duration = match self.timing.variant {
				TimingVariant::Duration(d) => d / self.frames.len() as f32,
				TimingVariant::Fps(f) => 1.0 / f,
			};

			if frame_duration <= 0.0 {
				bail!("frame duration must be positive (and therefore nonzero).")
			}

			let edge_top = match &self.top {
				Some(x) => x.resolve_as_edge(all_sections)?,
				None => super::SectionEdge::Stop,
			};

			let edge_bot = match &self.bot {
				Some(x) => x.resolve_as_edge(all_sections)?,
				None => super::SectionEdge::Stop,
			};

			return Ok((
				dim,
				super::SpriteSection {
					frames,
					frame_duration,
					edge_top,
					edge_bot,
				},
			));
		}
	}

	/// A link between two animation sections
	#[derive(Debug, Deserialize)]
	#[serde(transparent)]
	pub struct SectionEdge {
		pub val: String,
	}

	impl SectionEdge {
		pub fn resolve_as_start(
			&self,
			all_sections: &HashMap<String, AnimSectionHandle>,
		) -> Result<super::SpriteStart> {
			let e = self
				.resolve_as_edge(all_sections)
				.with_context(|| format!("while resolving start edge"))?;
			match e {
				super::SectionEdge::Bot { section } => Ok(super::SpriteStart::Bot { section }),
				super::SectionEdge::Top { section } => Ok(super::SpriteStart::Top { section }),
				_ => {
					bail!("bad section start specification `{}`", self.val);
				}
			}
		}

		pub fn resolve_as_edge(
			&self,
			all_sections: &HashMap<String, AnimSectionHandle>,
		) -> Result<super::SectionEdge> {
			if self.val == "stop" {
				return Ok(super::SectionEdge::Stop);
			}

			if self.val == "reverse" {
				return Ok(super::SectionEdge::Reverse);
			}

			if self.val == "restart" {
				return Ok(super::SectionEdge::Restart);
			}

			let (s, p) = match self.val.split_once(":") {
				Some(x) => x,
				None => {
					bail!("bad section edge specification `{}`", self.val);
				}
			};

			let section = match all_sections.get(s) {
				Some(s) => *s,
				None => {
					return Err(anyhow!("bad section edge specification `{}`", self.val))
						.with_context(|| format!("section `{}` doesn't exist", s));
				}
			};

			match p {
				"top" => Ok(super::SectionEdge::Top { section }),
				"bot" => Ok(super::SectionEdge::Bot { section }),
				_ => {
					return Err(anyhow!("bad section edge specification `{}`", self.val))
						.with_context(|| format!("invalid target `{}`", p));
				}
			}
		}
	}
}

// TODO: should be pub crate
/// A handle for an animation section inside a sprite
#[derive(Debug, Copy, Clone)]
pub struct AnimSectionHandle(pub(crate) usize);

/// An edge between two animation sections
#[derive(Debug, Clone)]
pub enum SectionEdge {
	/// Stop at the last frame of this section
	Stop,

	/// Play the given section from the bottm
	Bot {
		/// The section to play
		section: AnimSectionHandle,
	},

	/// Play the given section from the top
	Top {
		/// The section to play
		section: AnimSectionHandle,
	},

	/// Replay this section in the opposite direction
	Reverse,

	/// Restart this section from the opposite end
	Restart,
}

/// Where to start an animation
#[derive(Debug, Clone)]
pub enum SpriteStart {
	/// Play the given section from the bottm
	Bot {
		/// The section to play
		section: AnimSectionHandle,
	},

	/// Play the given section from the top
	Top {
		/// The section to play
		section: AnimSectionHandle,
	},
}

/// Represents a sprite that may be used in the game.
#[derive(Debug, Clone)]
pub struct Sprite {
	/// The name of this sprite
	pub name: String,

	/// This sprite's handle
	pub handle: SpriteHandle,

	/// Where this sprite starts playing
	pub start_at: SpriteStart,

	/// This sprite's animation sections
	sections: Vec<SpriteSection>,

	/// Aspect ratio of this sprite (width / height)
	pub aspect: f32,
}

impl Sprite {
	/// Get an animation section from a handle
	pub fn get_section(&self, section: AnimSectionHandle) -> &SpriteSection {
		&self.sections[section.0]
	}

	/// Get this sprite's first frame
	pub fn get_first_frame(&self) -> u32 {
		match self.start_at {
			SpriteStart::Bot { section } => *self.get_section(section).frames.last().unwrap(),
			SpriteStart::Top { section } => *self.get_section(section).frames.first().unwrap(),
		}
	}

	/// Iterate this sprite's sections
	pub fn iter_sections(&self) -> impl Iterator<Item = &SpriteSection> {
		self.sections.iter()
	}
}

/// A part of a sprite's animation
#[derive(Debug, Clone)]
pub struct SpriteSection {
	/// The texture index of each frame in this animation section.
	/// unanimated sections have one frame.
	pub frames: Vec<u32>,

	/// The speed of this sprite's animation.
	/// This must always be positive (and therefore, nonzero)
	pub frame_duration: f32,

	/// What to do when we reach the top of this section
	pub edge_top: SectionEdge,

	/// What to do when we reach the bottom of this section
	pub edge_bot: SectionEdge,
}

impl crate::Build for Sprite {
	type InputSyntaxType = HashMap<String, syntax::Sprite>;

	fn build(
		sprites: Self::InputSyntaxType,
		build_context: &mut ContentBuildContext,
		content: &mut Content,
	) -> Result<()> {
		for (sprite_name, t) in sprites {
			match t {
				syntax::Sprite::Static(t) => {
					let idx = match content.sprite_atlas.path_map.get(&t.file) {
						Some(s) => *s,
						None => {
							return Err(
								anyhow!("error while processing sprite `{}`", sprite_name,),
							)
							.with_context(|| {
								format!(
									"file `{}` isn't in the sprite atlas, cannot proceed",
									t.file.display()
								)
							});
						}
					};
					let img = &content.sprite_atlas.index[idx as usize];
					let aspect = img.w / img.h;

					let h = SpriteHandle {
						index: content.sprites.len(),
						aspect,
					};

					content.sprite_index.insert(sprite_name.clone(), h);

					content.sprites.push(Self {
						name: sprite_name,
						start_at: SpriteStart::Top {
							section: AnimSectionHandle(0),
						},
						sections: vec![SpriteSection {
							frames: vec![img.idx],
							// We implement unanimated sprites with a very fast framerate
							// and STOP endpoints.
							frame_duration: 0.01,
							edge_top: SectionEdge::Stop,
							edge_bot: SectionEdge::Stop,
						}],
						handle: h,
						aspect,
					});
				}
				syntax::Sprite::OneSection(s) => {
					let mut section_names: HashMap<String, _> = HashMap::new();
					// Name the one section in this sprite "anim"
					section_names.insert("anim".to_owned(), AnimSectionHandle(0));

					let (dim, section) = s
						.add_to(build_context, content, &section_names)
						.with_context(|| format!("while parsing sprite `{}`", sprite_name))?;
					let aspect = dim.0 as f32 / dim.1 as f32;
					let h = SpriteHandle {
						index: content.sprites.len(),
						aspect,
					};

					let mut sections = Vec::new();
					sections.push(section);

					content.sprite_index.insert(sprite_name.clone(), h);
					content.sprites.push(Self {
						name: sprite_name,
						sections,
						start_at: SpriteStart::Bot {
							section: AnimSectionHandle(0),
						},
						handle: h,
						aspect,
					});
				}
				syntax::Sprite::Complete(s) => {
					let mut idx = 0;
					let mut section_names = HashMap::new();
					for (name, _) in &s.section {
						section_names.insert(name.to_owned(), AnimSectionHandle(idx));
						idx += 1;
					}

					let start_at = s
						.start_at
						.resolve_as_start(&section_names)
						.with_context(|| format!("while loading sprite `{}`", sprite_name))?;

					let mut sections = Vec::with_capacity(idx);
					let mut dim = None;

					// Make sure we add sections in order
					let mut names = section_names.iter().collect::<Vec<_>>();
					names.sort_by(|a, b| (a.1).0.cmp(&(b.1).0));

					for (k, _) in names {
						let v = s.section.get(k).unwrap();
						let (d, s) = v
							.add_to(build_context, content, &section_names)
							.with_context(|| format!("while parsing sprite `{}`", sprite_name))
							.with_context(|| format!("while parsing section `{}`", k))?;

						// Make sure all dimensions are the same
						if dim.is_none() {
							dim = Some(d);
						} else if dim.unwrap() != d {
							bail!(
								"could not load sprite `{}`, image sizes in section `{}` are different",
								sprite_name,
								k
							);
						}

						sections.push(s);
					}
					let dim = dim.unwrap();
					let aspect = dim.0 as f32 / dim.1 as f32;

					let h = SpriteHandle {
						index: content.sprites.len(),
						aspect,
					};

					content.sprite_index.insert(sprite_name.clone(), h);
					content.sprites.push(Self {
						name: sprite_name,
						sections,
						start_at,
						handle: h,
						aspect,
					});
				}
			}
		}

		return Ok(());
	}
}